What is a spindle?
Spindles are rotating drive shafts that serve as axes for cutting tools or hold cutting instruments in machine tools . Spindles are essential in machine tools and in manufacturing because they are used to make both parts and the tools that make parts, which in turn strongly influence production rates and parts quality. The design of the spindle and the quality of the components inside the spindle are major factors that contribute to the spindle's durability and longevity. The spindle should be designed in such a manner so that features that keep chips and coolant are kept out of the spindle's bearing system, like in an air purge system and wipers that use positive lubrication pressure to protect the spindle from contaminants.
Spindles: A key to improve manufacturing productivity and machine tool performance There is no doubt about the fact that today the manufacturing industry has become more and more globalized. Manufacturers are constantly looking for various ways and means to improve the productivity of machine tools through improved power densities, higher speeds, greater flexibility, and more multitasking of operations. One important method to achieve this is by continual innovation and improvement of spindles. Spindles play a vital role in the quality of the final product and enhances the overall productivity and efficiency of the machine tool itself. Today's spindle designs offer the manufacturers and machine builders much greater performance and reliability than ever befo re. Users can increase productivity in any industry by properly applying the advanced spindle technologies in specific applications. The powerful, flexible and faster machine tool spindles can reduce the number of cuts and making holes in manufacturing by half.
Performance features To increase productivity and performance of spindles, certain features that are to considered are as follows:
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Desired spindle power both peak and continuous. Maximum spindle load both axial and radial. Minimum size and weight Maximum torque over a broad range of speeds Speed allowed Tooling style Belt driven or integral motor motor-spindle -spindle design
Factors considered for spindles design Besides the above-mentioned performance features, other factors that will affect the ultimate spindle design are as follows: • • • • •
Amount of available space in the head Complexity Purpose and application Cost considerations Market demands
Cost of production plays a significant impact on the final spindle design. A very sophisticated and advanced spindle design may not be acceptable on a low-cost machine tool. As a result, an advanced machine tool design can justify the higher cost of a more complex and advanced spindle package. In fact, a fast, powerful and accurate machine tool will demand a reliable high-speed spindle system.
Benefits of spindles Certain benefits of spindles are as follows: •
Machine tool spindles reduce the number of cuts in manufacturing by half.
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Spindles provide position and transmit power to a tool (as in the case of milling machines).
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They hold a rotating workpiece (as in the case of lathes).
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They hold cutting tools and spin them at high torque and speed.
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Spindles support many key machining tasks.
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Allow flexibility in cutting a variety of materials.
Uses of spindles Spindles are used to perform variety of tasks like as follows: • • • • • •
Grinding Milling Engraving Drilling Boring Turning
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Routing
Applications of spindles Spindles are critical in all kinds of manufacturing and hence used in variety of industrial applications. Spindles are used to support burrs in dental drills and cutters to put together composite materials. They also make parts for pumps and compressors used in the oil and petroleum industry. Spindles are used to make the molds used to make tires for the aircraft sector, the rolls that produce sheet metal for the automotive sector, and parts for the appliance industry. So various applications of spindles are in the following sectors: • • • • • • • •
Automobile Glass Aerospace Machine tool Engine plant units Metal working industry Plastic Construction etc.
Buying tips Certain specifications are to be considered for the bulk purchase of spindles. These are as follows: •
Spindle type: Whether motorized, belt driven or gear driven etc.
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Operating speed
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Cutting Speeds For Common Materials
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Operating power
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Maximum spindle torque
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Spindle features: High frequency drive, linear or compound motion, automatic balancing etc.
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Purpose: Whether drilling, grinding or milling etc.
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Requirement: High Speed, High Stiffness, Radial Loading, Axial Loading, High Accuracy
The power that is required depends on the stock you are cutting. Obviously speed, torque and horsepower are important specifications to evaluate the overall performance of your spindle. The spindle endures a lot of abuse while working on machine tools. The amount of force, wear and tear a spindle must endure implies that the design of the spindle and the quality of the parts used within the spindle are vital to the performance of your spindle and its lifespan. The spindle is indeed the heart of any machining center.
Spindle Major Components
Spindles are rotating shafts installed on machine tools to cut metals. The productivity and performance of any machine tool depends a lot on the spindle attached to the machine. Quality of a machine tool spindle components not only determines longevity of the spindle but also determines how the spindle handles torque, speed and vibration. The following diagram gives us an idea about the various components of a spindle and its lay out. The above figure shows a normal spindle having several components that allow it to achieve high accuracy. Different spindles are used to perform different functions like grinding, milling, drilling etc. and accordingly the parts or components of the spindle also varies. To obtain the desired result, a normal spindle design must take into consideration the following factors: • • • • • •
The required power Torque Tooling system used Speed Accuracy Life
From this design specification, the several components of a spindle can be selected including bearings, motor, lubrication system, shaft design, tooling style, drawbar system, housing and cooling system.
We give below an explanation of the various components of a high-speed spindle design: • • • •
Spindle Spindle Spindle Spindle
Style Bearings Motor Housing Style
Spindle Style
To get a typical style of a spindle, the first thing to decide is whether a belt-driven spindle or integral motor-spindle design is required. This depends upon the requirements of the machine tool which also include the maximum speed, power and stiffness required and also cost. Other options like high frquency driven spindles or gear driven spindles are also very popular.
A basic idea about belt-driven spindle design A belt-driven spindle design consists of the spindle shaft, held with a bearing system and supported by the spindle housing. The entire tooling system, including the tool taper, draw bar mechanism and tool
release system is incorporated in the spindle shaft. An external motor supplies power and rotation to this spindle. The motor is mounted adjacent to the spindle. The torque is transferred to the spindle shaft by using a cogged or V-belt. The power, torque and speed of the spindle hence depend upon the specifications of the driving motor, and the belt ratio used between the motor and the spindle.
Advantages The main advantages of the belt-driven spindle design are as follows: •
Reasonable cost: The spindle is made up of very few basic parts and hence the cost is relatively low.
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Wide variety of spindle characteristics: Another main advantage is that the final specifications or features can be modified for a particular application by using a different motor or belt ratio. This is because the spindle power, speed and torque are dependent upon the driving motor. In some cases, gears are also used in addition to the fixed belt ratio to provide multiple speed ranges.
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High power and torque possible: Since the spindle motor is fixed outside the actual spindle shaft, it is often possible to use a very large motor. A large motor can provide very high torque and high power for spindle use. This is not possible in an integral motor-spindle design because available space is always limited.
Disadvantages However, there are also some disadvantages of a belt-driven spindle design which are as follows: •
Limited maximum speed: A belt-driven spindle has limited maximum rotational speed due to many factors. The mechanical connection which transfers the torque to the spindle shaft, the pulley and the belt system, are limited in maximum operating speed. This depends on the type of belt used. For example, if a poly V-belt system is used, high rotational speeds tend to stretch and disengage the belts which in turn reduces the ability to transmit torque. Cogged belts at higher speeds produce unacceptable levels of vibration. Gears also produce high levels of vibration and heat and are very limited in maximum speed.
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Belts Utilize Bearing Load Capacity: In order to transfer the necessary torque, belt-driven spindles use a belt and pulley connection on the end of the spindle shaft. The required tensioning of these belts leads to a constant force on the rear spindle shaft bearing set. The applied tension and consequent force increases as the power and speed of the spindle increase. This utilizes much of the available radial loading capacity of the bearings. And, adding or substituting additional bearing sets will not be feasible, because they will further reduce the spindle abilities to reach high rotational speeds.
Thus we come to the conclusion that a belt-driven spindle will be limited to certain applications. Typically, belt-driven spindles can operate up to maximum rotational speed of 12,000 - 15, 000 RPM. This also depends on other factors like bearings types, setups, or bearing lubrication.
A basic idea about integral motor-spindle design
While various types of spindles are being developed, integral motor spindle design remains the workhorse for high-speed machining. This design does not depend upon an external motor to provide power and torque. The motor is an integral part inside the spindle shaft and housing assembly, which makes easier for the spindles to rotate at higher speeds as a complete unit, without the additional limitations of gears or belts. Typically, a complete motor-spindle comprises the spindle shaft, including motor element and tooling system. The spindle shaft is held by a set of high precision bearings, which require lubrication like grease or oil. The spindle shaft rotates up to the maximum speed, and display the power characteristics of the motor type that is used. The selection of a particular component depends upon the requirements of the machine tool.
Advantage One of the distinct advantage of the integral-motor design is allowing the spindle to achieve the high speeds required for high-speed machining or high-stock removal applications, and also used in general applications using small diameter tooling. Spindle speeds more than 30,000 rpm are routinely achieved with spindles of integral motor design, while speeds in this range are considered highly impractical or problematic with belt-driven or gear-driven designs.
Disadvantage One of the disadvantage that face the integral-motor spindle design is to provide wider speed ranges for improved applicability and to deliver more torque to achieve higher volume material removal rates.
Spindle Bearings The bearing system is one of the most critical and essential component of any high speed spindle design. The spindle provides high rotational speed, transmits torque and power to the cutting tool, and is worthy of reasonable loading and life. The bearing type used in a spindle must be conform with these demands. Otherwise spindle will not operate or perform to its best. Today, a wide variety of high precision bearings is available from a several manufacturers worldwide. In the bearing system of the spindle, the balls roll between the inner and outer steel raceways.
Types of high speed spindles bearings The type of bearings available for spindles are as follows: •
Angular contact ball bearings: These are the most commonly used bearings today in very high speed spindle designs. Also known as precision ball bearings, they provide the precision, load carrying capacity ( both axial and radial load carrying capacity ) and speed required for metal cutting spindles.
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Roller bearings: The roller bearings, also called cylindrical bearings offer higher load carrying capacity and greater stiffness than angular contact ball bearings. They are applicable in spindles with specific rpm requirements and applications.
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Tapered roller bearings: These bearings are used, because of their higher load capacity and greater stiffness over ball bearings. But they do not allow the high speeds required by many spindles.
Characteristics of spindle bearings • • • •
Axial load supported in one direction only. Necessary of adjustment against a second bearing. Compared to deep groove ball bearings, spindle bearings have extended ball complement. High rigidity and loading capacity.
Spindles bearings : Types of Mounting
Types
Explanation
Referred as "Face-to Face" or "X" configuration,it means bearings are mounted face to face . Here, the outer races are relieved. The Face to Face/DF X relief clearance is removed when the outer races are clamped Configuration Bearing together. This results in the correct pre-load. The bearing pair is Mounting capable of withstanding both axial and radial loading in this type of configuration. Also known as "O", or "DB " mounting, this is the most common Back to Back/DB/O mounting method. In back-to-back configuration, the inner races are Configuration Bearing relieved. The relief clearance is removed, resulting in the correct Mounting pre-load when the inner races are clamped together. This is suitable for most applications and provides good rigidity and accuracy. This is a combination of two or more mounting techniques. This Tandem/DT Configuration mounting does not allow forces in both directions, unless and until Bearing Mounting there is another pair of bearings used on the spindle shaft, facing in the opposite direction.
Bearing Construction: Hybrid ceramic The ball bearings affect vibration levels, temperature and the spindle's life and this is dependent on the materials used in the making of ball bearings. However, the most popularly used ball bearings are hybrid ceramic as they offer distinct advantages over typical steel ball bearings. •
Less mass: The hybrid ceramic balls have 60% less mass than steel balls. This becomes important because as a ball bearings operate, centrifugal forces push the balls to the outer race, and can deform the shape of the ball which leads to rapid wear and bearing deterioration. Ceramic balls because of less mass will not be aff ected even at the same speed. Moreover, the use of ceramic balls allows speed to go up 30% for a given ball bearing size, without sacrificing any bearing life.
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Elimination of cold welding: Ceramic balls eliminate cold welding which is a major cause of bearing failure. They can do this because they do not react with the steel raceways, thereby resulting in longer bearing life.
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Operate at lower temperatures: Because of the nearly perfect round shape of the ceramic balls, hybrid ceramic bearings operate at lower temperatures compared to steel ball bearings, which results in longer life for the bearing lubricant.
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Lower vibration levels: Spindles with ceramic bearings have higher rigidity and higher natural frequencies, which makes them less sensitive to vibration.
Lubrication of bearings For proper functioning of spindles, proper lubrication of bearings is very essential. To keep the bearings properly lubricated, machine tool manufacturers use several systems like oil-mist, oil-air, oil jet, pulsed oil-air etc. Such systems become very necessary if bearing spindle speeds are more than 18,000 rpm. These lubrication systems must be thoroughly monitored so that the ratio and the amount of oil and air and/or mist are correct. Permanent lubricated bearings are the best option for keeping replacement costs lower and maintenance costs down . Lubrication helps to form a microscopic film between the rolling elements and it prevents skidding and abrasion. Besides that lubrication in spindles also protects the surfaces from corrosion, and protects the area from particle contamination.
Bearing life The durability of bearings used in spindles in general is affected by the following factors: • • • • • •
Bearing Loads, Axial and Radial Vibration Levels Quality of Lubrication Quantity of lubrication Maximum Speed Average Bearing Temperature
Spindle Motors
A spindle motor is a small, high-precision, high-reliability electric motor that is used to rotate the shaft or spindle used in machine tools for performing a wide range of tasks like drilling, grinding, milling, high spped routing for woodworking, aluminum cutting or plastic cutting etc. All machine tools consist of motors which provide a mechanical means of transferring motion to the cutting tool and balance control. It is the motor which drives the spindle shafts. All spindles either have an external motor or an internal motor to run. There are some spindles which are driven by an integral motor spindle design and such spindles are known as motorized driven spindles. The motor provides power and torqure to the spindle. It is an integral part of the spindle shaft and housing assembly. It is with the help of the motor that a spindle can rotate at high speeds.
Types of motors used in spindles •
AC motors: Alternating Current motors as the name suggest requires an alternating current. They are usually sized in horsepower. They come with various speed ratings, which are specified as rotations per minute (RPM) at no load condition. As the AC motor is loaded, the speed will slow down. When the AC motor runs at its rated power draw, the speed of the rotating shaft is the full load speed. AC motor are widely used in any applications requiring variable speed and low cost and small size.
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DC motors: Direct current motors as the name suggest requires a direct current to run. These type of motors are electric motors that use electricity and a magnetic field to produce torque, which turns the motor. A simple DC motor requires two magnets of opposite polarity and an electric coil. This serves the purpose as an electromagnet. As the magnets within the motor attract and repel one another, the DC motor turns.
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Universal motors: These motors can use both DC and AC current and they operate at high speed but are not used continuously.
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Brushless DC Motors: They are the preffered motors in spindles because they last longer, more efficient than AC motors and do not produce excessive heat.
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PM DC Motors: They are small motors that produce approximately 50% greater torque than other comparably sized motors.
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Single-phase AC induction motors: This type of motor has a rotating magnetic field to produce the starting torque.
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Three-phase AC induction motors: These are used in high power machine tool applications.
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Single-phase AC synchronous motors: They rotate in a synchronous manner with the main current frequency. They have magnetized rotors and do not need an induced current.
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Spindle Servo motors: They are special types of geared motors, providing more power and have finer controls. They are used in spindles of accurate CNC machine systems. Major types of servo motors are DC and DC.
Favorable features of spindle motors An ideal motor for a spindle should consists of the following features: • • • • • • • • •
Small size Low power consumption High reliability Ability to run many hours Tolerate hundreds of start and stop cycles without failure Minimal wobbling Minimal vibration Low heat output Minimal noise output
Characteristics of spindle motor Some important characteristics of a typical spindle motor are as follows: • • • • • •
Small size Minimal noise output Low power consumption High reliability Minimal wobbling and vibration Low heat output
Calculation of motor speed The speed of a spindle motor is determined by the following formula: Speed (RPM) = (Frequency in Hz x 120) / (number of motor poles). This means that a two pole spindle motor, with top speed of 30,000 RPM, needs a drive with the functionality to provide full motor voltage at an output frequency of 500 Rz. If this motor has four poles then a maximum frequency of 1000 Hz is needed.
Some examples: A diagrammatic representation Example :1 In a bear or a gear driven spindle, there is space for a large motor because the motor can be located outside the spindle as seen in the first part of the diagram below. On the other hand, as seen in the second part, an integral motor can be fitted inside the existing bore.
Example:2 The following diagram shows a spindle with an overhanging motor which places the motor at the back-behind the rear bearing set. This spindle design allows for a larger motor, if the machine design accommodates it.
Buying tips A proper understanding of your requirements will greatly help in choosing what kind of motor is best for the situation. Factors to consider for the purchase of motors to be used in spindles are as folows: • •
Motor type Maximum speed
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Rated power Rated load Rated torque Start up torque Mounting type you require Type of enclosure required Type of shaft output Adequate cooling mechanisms. Durability of major components like brushes, cummutators, windings, which wear out over a certain time.
Spindle Housing
What is a spindle housing ? The housing is a part and parcel of the spindle. The shaft of the spindle and the motor required to run the spindle must be held in a housing , which we refer to as spindle housing. The spindle housing is available in various styles and sizes and and may be an integral part of the machine tool. The spindle housing is connected to the machine tool by using a flange or attaching bracket.
Materials used in making spindle housing • • • • •
Cast Iron Iron Stainless steel Cast aluminum Brass etc.
Functions of spindle housing The primary functions of a spindle housing are as follows: •
To locate the bearings: High precision bearings, which run at dN values, must be located exactly in terms of size, geometry etc.
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To provide the lubrication required by the spindle.
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The housing also provides air seal, cooling water or oil, and other utilities required by the spindle. If the spindle uses oil lubrication, then the spindle housing includes drilled passages to transfer the oil or oil mist to each bearing, and then again transfer the oil out of the bearing to a return line.
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The spindle housing provides a cooling liquid: This helps in removing heat produced by the spindle motor stator, as this heat would affect the spindle performance as a complete unit.
Types of spindle housing There are various types of spindle housing and depending on the different housing, different mounting types are there for spindles. They are as follows:
Cartridge spindle housing This is a popular type of housing used in spindles. This type of housing is the simplest to service, and the tolerances required for high speed are very easy to obtain when the housing of the spindle can be produced as a cylinder. The cylindrical cartridge-style spindle is clamped around the housing with an split-clamp mounting block. Advantages Advantages of this type of mount are as follows: •
The split-clamp mounting allows the use of standard off-the-shelf cartridge spindle designs.
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It permits easy axial and rotational adjustments of the spindle housing inside the mounting bracket.
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Once the mounting block has been located, cartridge-style spindles can be removed and reinstalled without requiring adjustments of positions.
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The spindle is easy to remove from the mount.
Disadvantages •
This type of split-clamp mounting block usually occupies more space than a block-style spindle housing design or flange mount design.
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Increased chances for spindle bearing failure.
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Possible variations in axial location and orientation.
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Additional weight imposed on the machine structure.
Flanged cartridge spindle housing Most spindle builders offer flanged cartridge spindle housings, which allow the spindle to be flange or face mounted. This is usually the preferred method of spindle mounting in a machining center. The flange is a simple, round flange ring having a bolt hole pattern that is permanently attached to the spindle housing. Special designs are possible also with flats or other cut-outs as required to accommodate the machine or tool changer design.
Advantages The advantages of this type of mounting are: •
Lower chances for spindle bearing failure
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Guaranteed repeatability in X, Y, Z locations and squareness when a spindle is re-mounted.
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Very little extra space required.
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Spindle removal is easy.
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The flange design provides additional clearance to the spindle nose if the mounting flange can be located further back on the spindle housing.
Disadvantages • •
Spindle housing can be more expensive than an off-the-shelf cartridge-style spindle. Spindle can only be removed and installed one way .
Block (box) type spindle housing This type of housing is designed to be lifted and transported using either eye bolts or swivel type hoist rings. Spindles are arranged with tapped holes in the top of the spindle housing for accepting eyebolts and such spindles are manufactured to be lifted from the top. Block style housing has jack screw holes both sides and keyway in housing. With this design, the spindle housing has one or more flat sides, which allows the spindle to be mounted directly onto one of the sides. Advantages The advantages of block type mounting are as follows: •
Lower chances for spindle bearing failure caused by mounting problems.
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It is possible to design good repeatability in X, Y, Z locations and squareness in such designs when a spindle is re-mounted.
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Very little extra space required.
Disadvantages •
Some spindle mount design may be special, and the spindle is more expensive than a standard cartridge-style spindle.
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If the machine design does not include accurate location of the block housing, it becomes very necessary to position the spindle every time it is re-installed.
Parameters to consider for spindle housing design For any type of spindle, the housing design parameters include the following:
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Precision dimensions from base to spindle centerline Spindle-bearing condition Spindle operating condition Surrounding conditions like Assembling tolerance Cooling condition Geometric dimension Thermal deformation Air purge housing for virtually contamination-free operation and so on.
Characteristics of Spindles
Spindles are rotating shafts used to cut metals. Spindles play a vital role in enhancing machine tool performance, thereby increasing manufacturing productivity. Today, manufacturers are coming up with wide variety of spindles having advanced technology and additional features for improved performance. Spindles are essential in all kinds of manufacturing. They are used to perform various tasks in a machine tool like grinding, milling, drilling, turning, engraving and routing.
Characteristics There are certain characteristics of spindle, especially a high-speed spindles, that allow it to achieve high accuracy and productivity which we are discussing below: •
Motor power: In most spindles, there is a stock frame less motor mounted directly on the shaft and into the spindle housing. By doing this the bulk required to mount the motor on one side is eliminated. The basic drawback of this configuration is that the motor must able to achieve the maximum spindle speed. However, if the motor was mounted on one side, and a pulley and a belt were used to drive the shaft, the motor could spine at significantly less than the spindle speed. A brushless motor is another option for spindles and it requires more expensive as well as complicated driving circuitry. However, maintenance and reliability of the motor is greatly enhanced because there are no brushes to misalign, replace, wear out, and generate carbon dust.
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Spindle speed: The required speed for the spindle motor is determined by the formula: Spindle Speed [RPM] = Cutting Speed [m/min]/(p * Tool_Diameter [m]). The following table gives an idea about spindle RPM required to achieve various cutting speeds by Tool Diameter. 244 MPM (800 FPM): The minimum cutting speed for copper and aluminum
6.35 mm (0.25 inches)
12,200 RPM
9.525 mm (0.375 inches)
8,150 RPM
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305 MPM (1,000 FPM): The maximum cutting speed for materials except copper and aluminum
6.35 mm (0.25 inches)
15,300 RPM
9.525 mm (0.375 inches)
10,200 RPM
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610 MPM (2,000 FPM): The maximum cutting speed for copper and aluminum
6.35 mm (0.25 inches) 9.525 mm (0.375 inches) •
30,600 RPM 20,400 RPM
Source: pergatory.mit.edu/.../portf/spindle/spindle.
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Spindle torque: Torque is one of the most important characteristic for determining a spindle's cutting performance. Increasing torque in a spindle ultimately affects not only the the design of the machine but also the choice of the spindle. Power is the product of speed and torque. Thus, a high power spindle motor can use high speed with a low amount of torque at that speed. It can also be that the maximum power might not be available at the maximum speed. In both these cases, the amount of torque that can be achieved is proportional to the size of the motor. Specifying torque is very useful to the spindle designers and manufacturers in the machining center, because it is the torque and not the power that determines the size of the motor.
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Spindle Bearing Speeds: Bearings are essential components in spindles. Once the spindle's operating speed is determined, bearings are selected and sized. Bearings are properly lubricated using grease or o il. As the size of the bearing increases, maximum RPM decreases. The reason behind this is that for a given RPM the balls are traveling at a faster velocity due to the larger diameter. The materials used in making balls also affects the maximum speed. Ceramic balls, compared to steel balls allow a higher speed but can cost about 30% more. The maximum speed given by bearing manufacturers are usually for a single bearing. When double bearings are used their maximum speed is further reduced. To achieve a spindle speed of 12,000 RPM, bearings should have a maximum speed between 18,000 and 19,000 RPM.
Characteristic of high speed spindles compared to conventional spindles High speed spindles are designed with the spindle motor flanged to the spindle shaft. While conventional or normal spindles are mostly gear or belt driven. The maximum rotational speed of conventional spindles are limited to about 12000 to 15000 RPM. The greater the speed, the greater the chances of vibrations, which usually result in poor surface finish. That is the reason why most high speed spindles use a directly flanged motor.
Two types of high speed spindles. •
Spindles running in an open loop: This spindle is not always controlled. The speed of this spindle may drop as a matter of load. It is usually used for graphite machining, small cavities in hardened steel or finishing operations.
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Vector controlled spindles: They run in a closed loop and their exact angular position and speed are always controlled. Vector control spindles are today considered as the underlying technology of high-performance motorized spindles.
Future characteristics With proper research work and advancement of technology, most spindle designers are of opinion that the ultimate spindle will have the following characteristics: • • • • •
Unlimited Speed High Power Long Life Self-Balancing Self-Diagnostic
This might seem unattainable but they will definitely be fulfilled in the future.
Spindle Uses
Spindles have become increasingly popular as a part and parcel of any machine tool used in various applications. A wide range of manufacturing industries worldwide are reaping substantial savings in labor costs and equipment by introducing flexible manufacturing lines and cutting cycle time by using innovative spindles. Spindles today appear to break new grounds in machine tool performance. Spindles are rotating shafts that hold cutting instruments in machine tools and they are highly essential in manufacturing because they strongly influence production rates and parts quality. Conventional and high-speed spindles can provide the dynamic performance and torque-speed characteristics required to make a machine tool perform efficiently and sufficiently.
Benefits •
According to a recent study, new, fast, advanced and flexible spindles can raise productivity of any manufacturing unit.
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A proper high speed spindle can save machining time by half.
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Benefits of spindles are not only small machine tools but can also extend to aircraft, electronics, appliance, oil, and other sectors.
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A spindle can provide high-speed milling of steel parts at a high metal-removal rate.
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A spindle can meet flexible and varying machining requirements.
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A spindle can work for simultaneous multiple-hole production in automobile transmissions and engines etc.
Uses of spindles Spindles are used to perform several machining tasks, like turning an axle to cut it smoothly, drilling holes, milling a cylinder head's surface to make it flat, reaming or enlarging the opening of a hole. Bearings in spindles help to hold the spindle steadily and prevent vibration or wobbling. The
production rates of any machine tool are strongly influenced by the precision, power, and speed of the spindle. Let us now explain in details the various uses of spindles: • • • • •
Grinding Drilling Milling Turning Boring
Spindles used in Grinding
Spindle as a machine tool is used for grinding. There are different spindles for performing different types of grinding. Grinding is considered to be a finishing process or finishing operation having many different applications in the machine tool industry. Grinding covers a wide range of finishing and machining tasks like as follows • • • • • • •
Abrade hard materials Improve surface finish Tighten the tolerance on cylindrical or flat surfaces by removing a small amount of material Resharpening cutting tools Surface grinding of mold sections Surface grinding of work fixtures Internal diameter and outer diameter grinding of valve bodies, and many other useful applications.
Grinding process For material removal, the method used in grinding is called abrasion. In other words, in grinding, an abrasive material rubs against the metal part and clears or removes tiny pieces of material. The process implies that instead of cutting like a lathe bit, the material is slowly and steadily worn away. This is because compared to the material being ground, the abrasive is harder. The grinding wheel actually acts like many hundreds of very small lathe bit, each cutting off some metal. The abrasive must be strong enough to bear any kind of forces acting upon it while grinding. Usually some sort of impact shock occurs when the abrasive comes in contact with the material. Grinding abrades material in a way similar to sanding. The grinding operation is performed on a several machines like the lathe and the mill, with the appropriate add-on accessories, the most important of which is the spindle.
Why grinding is necessary? Grinding is necessary for the following reasons: •
The material is too hard to be machined economically.
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If the surface is adequately supported, grinding can produce flatness tolerances of less than ±0.0001 in. (±0.0025 mm) on a 5 x 5 in. (127 x 127 mm) steel surface.
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Machining removes excessive material.
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Grinding should be used when size tolerance specifications are beyond the capability of turning.
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It is also applied if the requirements of surface finish is too tight for hard turning.
Types of grinding Grinding can be of various types, like as follows: • • • •
Surface grinding Centered grinding Centerless grinding Contour grinding
Surface grinding: This is perhaps the most fundamental of operations. Surface grinding is the process of providing precision ground surfaces either to a critical size or for the surface finish. In other words, it accurately processes or grounds a surface. Parts require surface grinding for various reasons like: • • • •
Produce a flat surface. For specifying accurate tolerance thickness. A very smooth surface roughness is required. For sharpening of cutting tool.
Centered grinding: In this type of grinding, the grinding is performed at the center. There are two types of centered grinding-OD grinding and ID grinding. In Outside Diameter (OD) grinding , the work piece has center drilled ends, accommodating center points and surface is removed by rotating the grinder's face plate. With OD grinding the work piece and the grinding wheel moves or rotates in clockwise directions. Inside Diameter (ID) grinding is performed on tubular parts that are generally held in a chuck or collet. The grinding wheel turns at very high speed to maintain the proper surface speed but it moves anticlockwise. Contour grinding: In case of contour grinding, the chopping function is used to grind the side face of a workpiece.
Spindles used in Drilling
Spindles are widely used in drilling. Drilling is one of the most common and easy machining process. About 75% of all metal
or wood cutting material removed comes from drilling operations.
Drilling process The process of drilling leads to the creation of holes that are right circular cylinders. This is done most by using a twist drill. A twist drill is a tool having a rotating drill bit which is used for drilling holes in various materials. With the help of a chuck, the drill bit is gripped at one end of the drill and is pressed or forced against the target material and then rotated. The tip of the drill bit perform the work of cutting into the target material like grinding off small particles as in oil drilling or slicing off thin shavings as in twist drills or auger bits.
Diagrammatic representation In the figure given below, we depict a a cross section of a hole being cut using a common twist drill. The tools have flutes at the outside, specially made for the exit of the chips.
Types of drilling Drilling is of various types depending on the mode of operation. The various types are as follows: • • • •
Drills Drills Drills Drills
powered by hand. powered by using electricity. powered by compressed air. with a percussive action etc.
Characteristics of drilling There are certain characteristics of drilling that sets it apart from other powered metal cutting operations: •
The chips while drilling exit out of the hole created by the cutting.
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Certain problems can arose with chips exit when chips are large and/or continuous.
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The drill tool can wander upon entrance and for deep holes.
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In large workpieces for deep holes, coolant is delivered through the drill shaft to the cutting front.
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Of the several powered metal cutting processes, drilling is considered to be the most easily used by someone who is not a machinist.
Work Area of drill press
We give below a diagrammatic view of the metal-cutting area of a drill press. By using a C clamp, the workpiece is held in place. The cutting forces can be at times very large. So it is advisable not to hold a workpiece by hand during drilling. Wood is often used underneath the part to be cut so that the drill bit can overshoot without destroying the table. The cutting table also has holes for drill overshoot as well as weight reduction. As seen in the figure, the spindle is just at the top to hold the machine tool for drilling.
Spindles used in Milling
An important function of spindle is milling. Milling is an important metal cutting process like drilling. However, because there are many degrees of freedom in milling set up, milling is usually less accurate than turning or grinding unless and until rigid fixturing is implemented. Hence milling is considered versatile for a basic machining process. In manual machining, milling fabricates any object that is not
axially symmetric.
Milling Machine process at the cutting area: A diagrammatic representation The process of cutting away material by inserting a workpiece past a rotating multiple tooth cutter is known as milling. The action of cutting by many teeth around the milling cutter leads to a fast method of machining. The machined surface takes various shapes like flat, angular, or curved,including any combination of shapes. The milling machine is the one which holds the workpiece, rotating the cutter, and feeding it.
Methods of milling There are two methods of milling. They are as follows: Up Milling: Also known as conventional milling, the cutter rotation's direction is opposite to that of the feed motion. For example, if the cutter rotates clockwise, in up milling, the workpiece is fed to the right.
Down Milling: This is also known as climb milling. Here, the cutter's direction is same as the feed motion. For example, if the cutter rotates counterclockwise ,in down milling, the workpiece is fed to the right.
Types of milling There are different types of milling and accordingly different spindles are used. We describe some types of milling below: Peripheral Milling Also known as slab milling, in peripheral milling, the milled surface is generated by teeth. These teeth are located on the area of the cutter body. The axis of cutter rotation is usually in a plane which is parallel to the surface of the workpiece to be machined.
Face Milling In this type of milling, the cutter is mounted on a spindle whose rotation axis is perpendicular to the workpiece surface. The milled surface is attained from the task of cutting edges located on the face and periphery of the cutter.
End Milling In end milling, the cutter rotates on an axis vertical to the workpiece, which can also be tilted to
machine tapered surfaces. Cutting teeth are fixed on both the end face of the cutter and inside the cutter body.
Spindles used in Turning
A very important function of spindles is turning. Like drilling, milling, grinding, turning is another important basic machining processes. Turning as a machining process produces cylind rical parts. Turning produces cylindrical components in a lathe and this is done manually or by using a CNC (computer numerical control) machine. The manual turning is done on conventional machines or lathes which are not computerized, requiring constant supervision. Turning can also be done using automatic lathes operated by skilled fitters and turners. With advance technology, modern turning is moving towards the use of CNC controls.
Turing process Turning process produces solids of revolution which can be adjusted because of the specialized nature of the operation. This machining is done on a machine called a lathe in which the tool is stationary and the part is rotated. When turning, a cylindrical piece of material, made of wood of wood,, metal metal,, etc. is rotated. The cutting tool moves along two axes of motion, thereby producing precise depths and diameters. Turning is done either on the inside of the cylinder or outside to produce tubular components to various measurements. Diagrammatic representation:The representation:The cutting is done as shown below
Features of turning Turning is the machining of an external surface with the following features: •
Turning with the workpiece rotating.
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Turning with a single-point cutting tool.
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Turning with the cutting tool feeding parallel to the workpiece's axis and at a distance that will remove the work's outer surface.
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There is a type of turning known as taper turning where the cutter path is at an angle to the work axis.
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Contour turning is another type of turning where the distance of the cutter from the work axis is changed to produce the desired shape.
Adjustable cutting factors available in turning There are three primary factors in any turning operation. They are as follows:
Speed This factor generally refers to the spindle and the workpiece. It tells their rotating speed in revolutions per minute(rpm). The most important figure for a particular turning operation is the surface speed. This is the speed where the work piece material moves past the cutting tool. This is measured by multiplying the rotating speed with the circumference of the workpiece before the cut is started and this is expressed as sfpm (surface feet per minute). Every workpiece with different diameter will have a different cutting speed, even though the rotating speed is the same. Depending on the spindle used, the speed varies.
Feed This is the cutting tool, and here the rate is that at which the tool advances along its cutting path. On many lathes, the feed rate is directly related to the spindle speed and is expressed in ipr (inches per revolution).
Depth of Cut
This refers to the thickness of the layer being cut from the workpiece or the length of the uncut surface of the workpiece to the cut surface, expressed in inches. The important fact out here is that the diameter of the workpiece is reduced by two times the depth of cut. The reason behind this is that this layer is being removed from both sides of the work.
Spindles used in Boring
Another important function performed by spindles is boring. Boring is an important machining process like grinding, drilling, mining etc. The basic purpose of boring in machining is enlarging or expanding a hole that has already been drilled. This is achieved by using a single-point cutting tool. tool. Boring helps in achieving greater accuracy of the diameter of a hole. This machining process is also used to cut a tapered hole. In simple language, boring can be defined as a machining process for drilling a hole, especially a large hole like tunnels and wells in the earth.
Boring as a machining process An important attribute of bored holes is concentricity. The work usually is held on a face plate or in a chuck when boring is done in a lathe lathe.. Holes formed by boring may be bored straight, tapered, or to irregular contours. Boring is essentially internal turning while feeding the drill or machine tool parallel to the axis of the rotation of the workpiece.
Boring on a mini-lathe or a small lathe In a mini lathe, the idea of boring is simply the art of taking a small hole and making it bigger. A spindle is installed on the mini lathe and it helps in boring. For example, a tube is to be made with inner diameter of perhaps 1 inch and there is no 1 inch wide drill bit. To make such a shape on a minilathe, the method known as boring is used. The following picture shows a mini-lathe setup for a boring job.
Uses of boring Earth boring is very popular and used to do one of the following things: •
Return rock samples through which the machine tool passes.
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Rocks from which material is extracted can be extracted.
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Earth boring can be used to access rocks which can then be measured.
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Boring can also provide access to rock for the purpose of providing engineering support.
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Boring helps in enlarging an existing hole which may have been the result of a drill or made by a core in a casting.
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Another important purpose of boring is to make the hole concentric with the rotational axis of the workpiece. This helps in correcting any eccentricity that may result from the drill's having drifted off the center line.
Application fields Boring is used for a wide variety of applications like as follows: • • • • • • • • • • •
Agriculture Geology Hydrology Civil engineering Oil and natural gas industries Shipyards and Repairers Offshore Heavy Industrial Sectors Petrochemical Earthmoving Equipment Power Generation etc.
Functions and Requirements of Spindles
The spindle of a machine tool is so designed so as perform the following important funtions: •
Centering the workpiece as in lathes, turrets, boring machines etc. Or the cutting tool as in drilling , grinding, milling machines
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Clamping the workpiece or cutting tool such that the workpiece or the cutting tool is reliably held in position during the machining operation.
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Imparting rotary motion, e.g. as in lathes.
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Imparting translatory motion (as in drilling machines) to the cutting tool or workpiece. On the basis of the above fuctions, a spindle is capable of performing wide range of funtions like
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Drilling
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Milling
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Cutting
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Grinding
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Routing
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Engraving
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Boring etc.
The operational capabilities of machine tools in terms of productivity, accuracy, finish machine parts largely depend upon the extent to ehich the above functions are qualitatively satisfied. They also determine the important design requirements to spindle units which aregiven below:
Requirements •
The spindle should rotate with high degree of accuracy. The accuracy of rotation is determined by the axial and radial run out of the spindle nose and these must not exceed certain permissible values which are specified depending upon the required machining accuracy. The rotational accuracy is influenced at the most by the stillness and accuracy of the spindle bearings, particularly the one located at the front end.
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The spindle unit must have high static stiffness. The stiffness of the unit is made up of the stiffness of the spindle unit proper and the spindle bearings. Machining accuracy is influenced on bending, axial as well as torsional stiffness.
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The spindle unit must have high dynamic stiffness and damping. Poor dynamic stability of the spindle unit adversely affects the dynamic behavior of the machine tool as a whole.
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All spindles consider to be of the highest quality after having passed inspection, testing and run-off procedures prior to shipment, done by the manufacturer
Applications of Spindles
Today in this fast age of technology, the machining centers are not lagging behind. Modern machine tools have become more flexible capable of performing a range of programmed tasks. An essential component in all machine tools is the spindle which is used to perform a range of cutting and finishing operations. A spindle is a motor driven shaft that helps in both positioning and transmiting power to a tool or holding a work-piece. Spindles play a vital role in determining the quality of the final product produced and in turn the total productivity and efficiency of the machine tool itself. Spindles have a direct impact on efficiency, accuracy and overall productivity.
Types of spindles Depending on the purposes to be served or the drives that are used to make the spindle run or on the applications, there is a wide variety of spindles. For example:
Spindles on the basis of bearings used •
• •
Spindles in machining centers
Air bearing spindle· Air driven
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spindle
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Hydrostatic spindle Hydrodynamic spindle
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CNC spindle Lathe spindle High speed spindle
Spindles on the basis of drives used Spindles for machines • • • •
Spindles for grinding ferrite core Spindles for grinding optical lenses Spindles on dynamo testing machines in
• • •
High frequency driven spindle Gear driven spindle Belt driven spindle Motorized spindle
automobile industries Application of High Speed Spindles • •
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Spindles for tool and cutter grinding
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machines
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Spindles for CNC Grinding machines Spindles for CNC Lathes
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Grinding spindle· Milling spindle Turning spindle Boring spindle· Routing spindle Drilling spindle
• •
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Spindles for CNC Milling machines Spindles fo Hobbing Machine
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Engraving spindle
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Dressing Spindle
Spindles for Drilling and Boring machine
High Speed Spindles Application On the basis of the above classification, we can easily say that spindles are used to perform a wide range of tasks. Spindles are used to give the final shape and specification of any product in a machining center. Spindles are used in the following applications:
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Turning Cutting Drilling Counter-sinking Tapping Reaming
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Grinding
• • • • •
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Milling Dressing Polishing Finishing Assembly Balancing
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Winding
• • • • •
Spindles are used for processing • • • • •
Metal Composite Glass Wood Process Equipment
Spindles are used in different industries • • • • • • • • • •
Aerospace Automotive Medical Construction Metal cutting Micromachining & Fine Milling Fine Drilling Soft and Hard-Material Dicing Wafer testing Printing industry
Some examples: Aerospace and automotive: Major application areas of spindles include automotive and aerospace industries. Many automotive parts have certain geometries that lend themselves to vertical grinding. They are the most common applications for vertical grinders.
Micromachining & Fine Milling: This requires spindle with high speed with features of low vibration and high stiffness under high load so as to get the highest quality surface finishing. Fine Drilling: It is an evident fact that quick and accurate drilling of tiny holes requires spindles with high-speed rotation, low run out and compact design. Soft and Hard-Material Dicing: For dicing Silicon wafers, GaAs, Fiber Glass Epoxy, PZT, Alumina, Ceremic BGA, Plastic or Sapphire, Glass, Titanium Carbide, and Tantalum, a spindle with high stiffness, low run out and high-speed rotation is required to achieve an exact cutting matrix. Spindles used for such purpose should have the ability to reverse directions for left and right rotation and to work in a wet environment. Wafer testing: A spindle with quick acceleration and deceleration, high speed, and low vibration is always required in automatic wafer testing industry, where a laser scans a rotating wafer for contamination or defects. Spinners: A spindle with high speed, low vibration, and an integrated encoder and with quick acceleration and deceleration is required in Optical or Drum Spinners that use a laser to etch plates for printing. Optical Components: Spindles are required for dicing, cutting or polishing optical components to assure the highest quality surface finishing.
Factors affecting Spindle Performance
It is evident that it is not always easy to replace existing spindle equipment, but it is extremely important for any manufacturer to keep up with today's production requirements. That is why proper care and maintenance should be taken to continuously upgrade spindle performance and service, depending on the applications in which they are used. Spindles are rotating shafts used to cut or hold cutting tools in machine tools used in grinding, milling, boring etc. Any kind of problem associated with spindles must be taken care of to avoid any kind of loss in manufacturing. For proper working of spindles, certain things are to be avoided.
Factors affecting the performance of spindle: Common Spindle Problems The major factors affecting the performance of the spindle are as follows: •
Heat & Temperature: A factor that leads to spindle problem is the temperature. All spindles are made of metal. Metals like steel expands when heated and as such there is every chance of the non-performance of a spindle when it is operated for a long time and heat is generated. Under such circumstances, manufacturers should explain what measures have been taken to protect the spindle from head growth-which usually leads to Y and Z axis changes.
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Contaminants: The contaminants usually get inside the spindl e because of the easy opening or loosening of the the spindle seal. Under such circumstances, the buyer must find out what design features are taken by the machine tool manufacturer to keep the seal tight.
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Bearing failure: It is necessary to find out the design features that protect the spindle. It has been found out that the most common factor causing the failure of spindle is the bearing failure. The bearing failure is due to contamination from chip damage, coolant ingress, condensation etc.
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Tooling used: Another factor contributing to spindle performance is the tooling used. Using worn tools, unbalanced tools or long tools can affect the longevity of your spindle.
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Wrong Spindle for the Job: It so happens at times that a spindle is used in an application for which it was never intended by the manufacturer.
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RPM: All spindles are manufactured with a rated maximum operating speed stamped on the spindle body. It is essential to know that when rebuilding a spindle, if there is a deviation from that RPM, there should be proper bearing preloads optimum to the application. Running a spindle very slow or very fast will always result in poor performance.
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Outside Influences: In many cases, the spindle is usually the first component of a machine or machine tool to be blamed when things go wrong. But it so happens that the actual cause of the trouble is elsewhere.
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Drive Motors and Idlers: Bad bearings or out-of-balance will transmit through the spindle into the machining process and in turn will eventually damage the spindle.
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Tool holding equipment: All tool holding attachments to the spindle should perfectly fit to the pilot surfaces of the spindle face. Various problems like bad taper, bent or out-of-round, rusted, holding devices can result in severe vibration or misalignment of the tool or wheel to the work piece.
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Belt Tension: One of the severe cause of spindle failure is due to loosening of belts. The belt for the belt driven spindle should be just tight enough to avoid slippage. Excessive tightening creates problems of shaft deflection and makes the rear bearings out of alignment, thereby leading to poor performance, friction and vibration problems, heat and early failure.
Example of a spindle to remove contamination and control temperature Spindle with coolant ring having adjustable nozzles To remove the problem of contamination and to control the fluctuating temperature, some spindles are manufactured with a coolant ring having adjustable nozzles. This following picture shows a coolant ring having eight adjustable nozzles to remove chips and keep the temperature of the machine tool and the workpiece cool. Coolant Through the Spindle (CTS) This is important to give protection to expensive and custom tools. This type of spindle is recommended when machining at 12,000 rpm or more. Conclusion For any machining center, the spindle is the workhorse. It is very essential for all buyers to find out whether the manufacturer has taken spindle design seriously and given importance to quality components that will help increase the longevity and performance of your machining center's spindle.
Spindle Market
The machine-tool spindle industry is a vital sector of manufacturing. Machine tools, which are used to cut and form metal, are very essential for reproducing the technologies required in an industrial economy. A weak domestic machine-tool industry of any country means that the manufacturers risk losing access to the latest manufacturing technologies. The machine tool industry helps foster innovation in manufacturing processes. However, the growth of the machine tool industry is dependent upon various factors. One significant factor is the development of the machine tool spindle market.
Importance of spindles in machine tool industry Machine tool spindles are engineered and manufactured for machine tools used in CNC machines, machining centers in addition to grinding, turning, tapping, boring and drilling applications. The regular trends in the machine tool industry are traced by increasing globalization, standardization of systems and components , and greater i nternational collaboration. The continuous need and drive to improve machine tool productivity is viewed in higher speeds, improved power densities, more flexibility and more multi-tasking of operations. A key factor to achieve this is the continual innovation and improvement of spindles. Spindles are essential for any machine tool industry because they are the ones which largely determine the quality of the final product produced and the overall productivity, performance, and efficiency of the machine tool itself. There are many parameters indicating a machine tool's functioning. One important parameter which shows the advances over the last 200 years is the increase in spindle speed. During the 19th century, spindle speeds of 100 to 750 revolutions per minute were very common. Today, spindles can rotate at much higher speeds. Spindles are important in the machine tool industry for many reasons: •
Powerful spindles boost machine
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Tool performance
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New, fast, flexible spindles could raise productivity and spindle market share of any country.
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In the US, it has been reported that one perfect spindle design could save the auto industry more than 100,000 hours in annual machining time for a single part.
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Benefits of spindles could extend to appliance , aircraft, electronics, oil, and other sectors as well.
Top 10 machine tool markets 2001-2002
Major factors affecting the growth of spindle market worldwide •
Not enough large firms and little cooperation among small companies in most countries.
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Difficulty obtaining capital.
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Lack of supply of skills and disincentives to invest in training.
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Poor performance in converting technological research into market advantage.
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Unsophisticated domestic demand.
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Weak export capacity and infrastructure.
Government Policies Required for the growth of the spindle market •
Provision of development of local cooperative networks among machine-tool makers, suppliers, users to improve the adoption of new technology.
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Providing more investment in the manufacturing infrastructure.
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Help machine-tool makers compete internationally.
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Streamlining export licensing procedures, giving support to international sales efforts.
Machine tool spindle matket includes • • • • • •
Machine Tool Manufacturers Metal-Cutting & Metal-Forming CNC & Conventional Machine Tools Powertrain Machinery Manufacturers and End Users Special Machine Tool Builders & Integrators Industrial End Users etc.
Global spindle market The global machine tool spindle market is estimated to be over $1 billion, according to a recent report. However, more than half of this corresponds to spindle maintenance and refurbishment. As there is high demand of higher speeds, improved power density and more multi-tasking in the machine tool industry, there are obviously greater needs for innovative spindle solutions. The largest market for machine tool spindles worldwide are US and Germany. Taiwan and China play a significant role in the manufacturing and exporting of spindles. In recent years, however China has not only overtaken the US and Germany to become the largest machine tool/spindle market in the world but also China's skilled labor force and low cost base makes it a solid base for sourcing or manufacturing.
Spindle Selection Guide
How to select your machine tool spindle to perform various tasks like drilling, milling, grinding, turning etc.? There are many specifications to consider before buying spindles. We give below a selection guide to make the right choice. To buy any type of spindle, you need to know and specify certain things. These are as follows: •
What operation needs to be performed by the spindle?
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What are the operating parameters in terms of Speed o o Accuracy-Runout Power Requirements-at work or tool o Tool or Work Holding Method o
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What is the type of Spindle Body? Whether Base Mounted o Block Style o o Flange Cartridge Cartridge o o Special Configuration
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What type of Lubrication is required? Whether Oil/Air o Grease o Recirculating Oil o
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What is the basic sizing of the spindle? Basic sizing for boring spindles front bearing diameter which is usually equal or larger o than the bore being machined. o
Basic sizing for Face Milling Spindle, the face mill is somewhere around 1.5-2 times the front bearing diameter.
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Largest spindle that meets RPM and Quill Size requirements.
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Internal Grinding
Determine operating speed and wheel size Know the type of wheel holding Taper Shank Quill Straight Shank Quill Wheel Mount (For larger bores)
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External Grinding
Know the wheel size and operating speed. What wheel mount is required based on wheel size? Select spindle on the basis of top of taper of wheel mount.
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What type of drive is required? Whether Belt Driven o Direct Motorized o Coupled Motor o Gear Driven o
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What are the different factors to determine the type of spindle for any one given application? The various factors to consider are like Speed o Rigidity o Size constraints o Lubrication o Special Accuracy Requirements o Motorized vs. Non-Motorized etc. o
Any buyer interested in buying spindle can fill up the questionnaire given above and accordingly buy the spindle of his choice. The above questionnaire provides ample help to make the right choice.
Machine Tool Spindle Specification
Spindles used in machine tools are rotating components used to hold and drive cutting tools or workpieces on milling machines, lathes and other machine tools. For all spindles used in machine tools, the specifications that are to be considered as follows:
Performance Specifications The following factors are to be considered for performance specifications of spindles: •
Operating Speed: This is the rotational speed up to maximum under load.
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Spindle Power: This is the maximum rotational power that a spindle can operate and provide operate within specifications.
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Maximum Torque: This is the maximum continuous torque transmission, excluding peak ratings.
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Input Voltage (if required)
Spindle Drive Spindles are activated by the following: •
Gear Drive: Driven by gears allowing high or low-speed spindle rotation.
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Belt Drive: This type of spindle drive has has pulley for drive with the help of a belt.
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Motorized: This is driven by a motor integrally built into the spindle.
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Direct / Shaft Drive: It is driven on spindle axis and the drive end has shaft for coupling or joining to drive motor.
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Pneumatic: Driven with pressurized air.
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Hydraulic: Hydrostatic or hydraulic spindle power.
Configuration Spindles configurations are of following types: •
Cartridge : The spindle assembly can be inserted into a stationary housing.
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Block: This is a square or rectangular or a type of box housing.
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Spindle Speeder/Head: For any purposes of milling, drilling, turning or for any machine tools, the spindle can be mounted into the head.
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Foot Mounted: In such types, the housing is bolted down with the help of flanges or feet at the bottom of the housing.
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Multiple Spindle Head: These kind of spindle heads mount directly onto a machine tool and allow for milling, drilling, tapping, etc. simultaneously with multiple tool spindles. These help in speed machining operations and for repetitive precision work.
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Angle Head: Machine head mounted spindles have right-angle or adjustable angle tool rotation.
Spindle Application The applications of spindles are wide and varied. •
Drilling: Used in drilling operations, with good thrust capacity and radial load rating.
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Boring: Used in boring, that is enlarging a hole of an already drilled hole or the machining of an internal diameter in the workpiece.
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Grinding: Used in grinding for precision size and surface finishing.
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Milling: Used with milling cutters, including a variety of machining operations and tools.
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Turning: Used in vertical or horizontal lathes and turning centers.
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Hobbing: Used to cut gear tooth profiles.
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Test Systems: Spindles contain design features which are just ideal for test setups and systems, like computer drive testing, semiconductor testing, bearing spinning and friction tests, dynamic balancing, etc.
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Tapping: Designed specifically to be used with taps to create internal threads.
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Wheel Dressing: Spindles are used in dressing, contouring, and re-profiling abrasive grinding wheels.
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Specialty Industry: Used in specialty or non-machine tools for jewelry manufacturing, optical lens processing, and many others.
Tool Mounting •
Unit designation: Unit designation for O.D., I.D., etc. can be either English as inches or fractions of an inch or Metric as millimeters or centimeters.
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Spindle interface size: This refers to the cutting tool's diameter or the grinding wheel's bore that can be mounted to the spindle.
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Tool / Workholder Mounting: This refers to mounting interface on spindle end, including mounting options for cutting tools, workpieces, grinding wheels, etc. The various options are: Arbor / Shaft: Driven end here is a straight shaft for tool or wheel mounting. o o
Standard Bore: The bore is straight or standard for tool mounting.
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Collet: Coming in standard tooling sizes and tapers, tool mounts into a collet, which is tightened properly to secure the tool for operation.
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Threaded Hole: The shaft consists a threaded hole for screw or stud mounting, typically used in grinding wheels.
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External Taper: The shaft has external taper, used for mounting or grinding, polishing, or buffing wheel.
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Internal Taper: Accept standard machine tool collets.
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Wheel Collet: They have external tapered nose designed to accept grinding wheel mounting.
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Flanged Bore: Here, the tool end has a bore for location, with flange mounting attribute around the bore.
Spindle Options The various options are as follows: •
Automatic Balancing spindle: This spindle with dynamic balancing system can prevent tool or wheel unbalance without using any extensive operator interaction.
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Air Purge spindle: This has an automatic blow-off of contamination, chips, dust, etc., at or near spindle bearings.
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High Frequency Drive: This allows a spindle to operate at very high speeds.
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Coolant Feed: This allows for direct application of coolant to the grinding or cutting operation.
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Linear / Compound Motion: In addition to its rotation, spindle can also move axially. Very common in drilling and other machining operations.
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Liquid Cooled: This leads to high heat dissipation capacity and can translate into higher speed ratings.
Spindles Repair Services
It is very important for all manufacturers and buyers to upgrade spindle performance, keep your spindle equipment up and running at peak performance, and to help minimizing their downtime. When we talk about spindle repair services, it implies the rebuilding, repair or replacement of spindle and its associated accessories. It is also necessary that any kind of spindle or spindle repair service should meet International Standards Organization (ISO) requirements or OEM certifications or specific automotive specifications.
How to select spindle repair services? It requires a complete understanding of spindle technologies to select any kind of spindle repair services. For example, bearings are used to provide clearance and permit rotary motion without eliminating wear and friction and physical contact, thereby facilitating high speeds. Bearings are of various types. Again there are spindles mount in a block or cartridge-style housing or bolted in place with the use of flanges or feet. Spindles with angled head configuration allow adjustable tool or right angle rotation. Spindles that perform the tasks of milling, turning , drilling fit the heads of different machines include gearing to multiply the spindle speed and so on.
Certifications and quality requirements There are various certifications and quality requirements for spindle repair services. The various certifications are •
ISO 9001: This provide requirements for organizations whose business involves design and development, production, installation, servicing.
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ISO 9002: This provide requirements for organizations whose business involves production, installation, servicing, but not design and development.
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QS 9000: Based on the 1994 edition of ISO 9001 with additional requirements particular to the automotive industry, this is the must have quality standard for suppliers of Ford Motor Company and General Motors Corporation etc.
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OEM specifications: Another quality certification available on spindles is by original equipment manufacturers (OEM) to repair spindles according to specified tolerance and conditions.
Classifications of spindles repair services For any manufacturer or supplier of spindles, it becomes very necessary to provide the following services as spindles repair services for i ts customers: •
Inspection of disassembled spindle: This service includes determining possible spindle crash, overheating, improper bearing fits, improper tooling, use of spindle after initial failure, lack of lube or overloading.
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Condition of bearings: This service is performed under laboratory conditions to determine over speeding, spindle crash, lack of lubrication, overloading, loss of pre load, contamination or overheating.
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Engineering recommendations of spindle repair: This service includes various suggestions of spindle design changes or improvements to spindle longevity and performance.
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On-site training and preventative maintenance: This service is a must for all spindle suppliers to give proper guidance on spindle care and installation, appropriate alarm levels and predicting imminent failures.
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Repair, rebuilding of spindles: Repair or rebuilding of spindles become very necessary in spindles used in lathes, milling machines, grinding machines and various other machine tools.
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Component evaluation and replacement.
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Clean room assembly.
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Inspection and quality control.
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Failure analysis.
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Dynamic testing.
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Vibration analysis.
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Spindle speed range upgrades etc.
Additional services Spindle repair services also provide some other services, in addition to above. Of course, this depends a lot on customer's recommendations. For example: •
Some manufacturers use computer aided design or drafting (CAD) to design products quickly and accurately and computer aided manufacturing (CAM) is used to fabricate spindles from these CAD outputs. Such companies that provide design assistance can also help the customers in providing o Concepts Manufacturing costs o Manufacturing techniques o o Material considerations for various types of spindles
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There are certain repair services that can rebuild machine tools or provide refurbished spindles or provide on-site support or warranty repaired products.
How to Improve Spindle Performance
To improve the performance of a machining tool spindle, there are a lot of things that can be done. We give below some suggestions to improve the performance of a spindle:
The spindle should be constantly monitored: Installing SMRU It is not a very easy task to properly maintain spindles because they are manufactured in such a way so that they can work in a certain temperature range for a certain period in time. Different temperature range has different effects on the spindle. Some experts have suggested the installing of a spindle monitoring and recording unit (SMRU). This unit provides an easy way to keep track of critical maintenance issues. For example, when operated at 15°C above normal, installing of SMRU will give an indication that grease life decreases by a factor of 2. SMRUs are used to record temperature, running hours and speed. Another version of SMRU is that the information is stored in a histogram form which helps in providing the maintenance engineer with information to find out how long the spindle has been running and also to predict the remaining grease life. This unit can be installed as a part of the spindle or bolted to it. Usually software is available for configuration of the SMRUs displays and settings.
Ceramics are better For a much better performance of spindles, try to replace a spindle's bearings with hybrid ceramic bearings. For example, in a grinding spindles, 25 percent higher rpm can be achieved by using hybrid ceramic bearings and synthetic grease lubricant in place of steel ball bearings using oil or air-mist running at 10,000 to 15,000 rpm. Grinders with ceramic bearings can run 4000 hours without problems, when compared to 3000 hours with steel bearings. There are hybrid bearings running up to 5000 hours at speeds more than 2.0 million ndm before degradation of parts occurs. Ndm is defined as the bearing pitch diameter in mm multiplied by rpm). On the other hand, a steel bearing can quit after 700 hours. Hybrid ceramic bearings also have the benefit of lowering temperature almost 50 percent and are more durable than steel bearings. In any machining tool center, the use of hybrid ceramics bearings has been shown to drop bearing temperature from 60°C to 36°C at 12000 rpm.
Sophisticated belt drives Another factor that can be considered to improve the performance of spindles is to use sophisticated belt drives rather than conventional belt-driven spindles. A normal belt drive uses a angular contact bearings pair at the belt-drive end and studies have shown that such belt drive face many problems with spindle deflection and premature failures. At very high speeds, the bearings are loaded radially with the belt pull and it also restricts the axial movement of the bearings which compensates the thermal growth of the spindle system.
Shielded ball bearings To remove the need for air purge or spot oil lubrication, it is necessary to upgrading the shielded ball bearings. This can improve the spi ndle's performance because it can reduce contamination and helps to increase spindle speed. A standard or a normal shielded bearings have the same ball diameter, speed rating, internal geometry, load ratings, matching criteria, preload classes, and contact angles as the bearings they replace. On the other hand shielded bearings are dependent only on the pre-packed lubricant of the bearing. A double-shielded design has smaller diameter rolling elements and the rings have open conformities for high speed performance. As such it has higher speed capability but lower
load ratings compared to the same size of the standard bearing.
Use of air seals Air seals contain usually an air distribution ring and a rotating metal cased elastic sealing which have the advantages of contact seals and air purge. Air seals are provided by few manufacturers in spindles. The elastic sealing move up from the contact surface as the rotation of the spindle increases the centrifugal force. The metal case cast away any kind of contaminants coming into the spindle. There is uniform airflow from the air-distribution ring. This helps the seal to move on a thin film of air while rotating. The air also pushes contaminants and dust away from the spindle while moving. In a static condition also, the elastic seal provides a positive contact by keeping away contaminants from entering into the spindle.
Some Do's and Dont's Since the spindle is the heart of the machine, it must always be handled with care and maintained regularly for best performance. The following list provides few easy checks you can make to reduce your spindle repair cost and improve the spindle's performance. •
If the spindle is kept in a storage without using it for some time, then rotate the shaft 3 or more turns quarterly top to bottom to circulate grease and lubricate internal components.
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Store the spindle in a dry heated area and in an area away from traffic to avoid damage.
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Keep the spindle covered covered so as to avoid dust and other foreign matter if not in use.
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Do not bump or stand on pulley ends while handling or installation.
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Check the spindle mounting surfaces for flatness and remove all dirt.
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Change filters before connecting them to the spindle.
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Flush out lubrication and air purge supply lines.
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Check housing for leaks and tears.
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Check for a clean lubricant supply.
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Check for a correct operating pressure.
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Check the air purge operating pressure and flow.
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Check pulley and belt for operating and do not tighten the belt very heavily.
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Check spindle rotation direction and speed.
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Use balanced tooling assemblies and cutting tools.
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Check the tool clamping pressure.
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Do not blow air or coolant at the face of spindle or spindle seals.
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If your spindle needs repair service, then always ship all spindle components, keys, pulleys so they can be checked for proper balance.
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Clean the spindle's exterior before shipping it to the repair house etc.
Spindle Error Motions
In the world of spindle metrology, there are six different motions that are available in spindles. These six motions are as follows: • •
Pure rotation around the spindle axis which is the Z axis. Motion in any of the other five directions o X axis Y axis o o Z axis Tilt along the X axis o Tilt along the Y axis o
Of all these motions, the first one is the desired motion while the other five are considered as spindle error motions. Tilt measurements help in calculating the error at some distance projected beyond the point at which another measurement is taken. Spindle errors are classified for the sole prupose of distinguishing the root cause of the error or its effect on part quality.
Drift This is a type of slow change that occurs over time due to some external influence, like temperature, that makes a change in the tool position.
Shift This is an abrupt change in an operating parameter due to some change in the system, like airpressure change or speed change on an air-bearing spindle. Since high-speed machining involves a considerable level of centrifugal fo rce on spindle components, speed changes can cause bearing elements which in turn affect tool position to be repositioned.
Synchronous error motions Error motions that are "synchronized" with the rotational speed is known as synchronous error motion. Thse kind of motions repeat every revolution of the spindle. A plot of these errors displays lobes that can occur once, twice or at some multiple of times per revolution. This type of motion is also known as out-of roundness motion and it can predict the ability to bore a round hole or to turn a round part. The tool will cut a part with the same number of lobes as viewed in the synchronous error motion plot. Manufacturers can measure the synchronous error motions of spindles to find out which spindles they should use for critical jobs. Also, it helps in determining the effects of a crash on a spindle's precision. Spindles run true until they operate at a resonant speed that leads to excessive vibration. Synchronous error motion plots, viewed at various spindle speeds, can make resonant speeds apparent to allow operators to avoid them.
Asynchronous error motions These motions are not synchronized with spindle rotation. In other words, error motions that are not "synchronized" with the rotational speed of the spindle is known as asynchronous error motions. Bearing "defect" frequencies usually cause asynchronous error motion. They do not repeat on successive spindle rotations. These error motions are depicted by the "fuzziness" of a polar plot, and
are related to surface finish. Asynchronous error motions develop due to the interaction of spindlebearing elements that are rotating at different speeds,like rolling elements, bearing races, rolling element retainers or cages. The errors can also develop from a machine tool's non-structural elements like as in hydraulic pumps or coolant pumps. They can develop from external factors as well like a forklift driving past the machine.
Spindle error analyzer Spindle Error Analyzer is used for analyzing, measuring and monitoring machine tool spindle health and performance. Virtually all types of spindles in any machines and machine tools can be evaluated. It can also be used with precision spindles in disk drives and precision, high-speed drills. The analyzer enables manufacturers to predict and prevent part errors like as follow: • • •
Hole location Surface finish Roundness
by measuring and tracking error motions that indicates: • • • • • • •
Out of round bearing components Bearing wear Misaligned bearing seats Structural vibration Inadequate stiffness Improper preload Resonant machine frequencies etc.
The Spindle Error Analyzer performs tests by complying with some certifications standards like as follows: •
ANSI/ASME Standard B5.54-2005: "Methods for Performance Evaluation of CNC Machining Centers"
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ANSI/ASME B89.3.4: "Axes of Rotation, Methods for Specifying and Testing"
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ANSI/ASME B5.57-1998: "Methods for Performance Evaluation of CNC Turning Centers"
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ISO230-7: Test Code for Machine Tools Part 7, "Geometric Accuracy of Axes of Rotation "
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ISO230-3: Test Code for Machine Tools Part 3, "Determination of Thermal Effects
Chiller/Cooling Units
Introduction The constant loads and continuous functioning of the spindle leads to a generation of a lot of heat. For proper functioning and durability of the spindle, it is very essential to remove this excess heat and this is done through a separate chiller or a cooing unit. Chillers keep the spindle cool and control spindle growth and head growth. Chillers are very essential component of spindles as they add life to the spindle and they are typically used in long cycles or high duty cycles.
What is a chiller? The chiller is a cooling system that removes heat from one element, say water and transfers it into another element, say water or ambient air. It is a compressor based cooling system. It is similar to an air conditioner. The only difference is that it cools and controls the temperature of a liquid instead of air. The chiller also consists of a temperature controller, a reservoir and a recirculating pump.
Operation and setup of a chiller This is very simple. The reservoir is filled with fluid to be recirculated, maybe water or an ethylene glycol or water mix. Plumbing is installed between the chiller and the application and power is provided to the chiller. The controller regulates the functions of the chiller. Once the chiller has been programmed by a user for individual needs, it will provide a stable temperature, flow and pressure. Harmful particles are kept out by an internal strainer.
Types of chiller •
Portable chiller: This is a liquid cooling system on casters or wheels that can be relocated from one application to another with great ease and can be used to cool one or more heat generating devices.
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Air-cooled chiller: This type absorbs heat from process water which is transferred to the surrounding air. It is used in applications where the additional heat that is discharged is not a factor. It requires less maintenance compared to water-cooled chillers. Air colled chiller eliminates the need for a condense water pump and a cooling tower. It however consumes approximately 10% more power than a water-cooled unit because a wet surface transfers heat much better than a dry surface.
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Water-cooled chiller: This type of chiller absorbs heat from process water which is then transferred to a separate water source like a cooling tower, pond, river etc. It is used large capacity applications, especially when the heat generated by an air-cooled chiller creates a problem. It requires condenser water treatment to remove mineral buildup.
Selection guide: Properties of air and water cooled chillers
Water cooled chiller
Air cooled chiller
Adequate water supply available.
Adequate water supply not available.
Water supply is of good quality.
Water supply is not of good quality.
Plant ambient temperatures consistently exceed 95º F.
Plant ambient temperatures will not consistently exceed 95º F.
Ambient air is polluted with large dust and dirt particles.
Ambient air is not polluted with large dust and dirt particles.
Heat recovery is not practical or unimportant. Heat recovery is practical and important. Source: http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=coolschool.htm&ID=85
Applications of chillers Chillers are used in many industrial applications such as follows: •
Plastics: In this industry chillers are used to cool the equipment used in the manufacturing process and for cooling the hot plastic that is injected, blown extruded or stamped.
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Laser: Chillers are used to cool down the lasers as well the power supplies needed to power them.
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Printing: Chillers are used to remove the heat generated by the printing rollers. They also cool down the paper when it comes out of the ink drying ovens.
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EDM: During the cutting process, chillers keep machinery at ambient temperature.
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MRI and PET Scans: Chillers are used here to cool the high powered electronics used in the machines and diagnostic tools.
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Machine Tooling: Chillers are very essential to cool the spindle of the machine as it produces or holds the part. They also cool the liquid being sprayed on part itself as it is being turned on the spindle.
Need for chiller in a spindle The speed and accuracy of production in a machining center will increase when there is a constant maintainence and a proper cooling temperature in the equipment. A chiller is very essential in a spindle because it is the only method to remove escees heat that is generated while the spindle is in operation. The chiller will reduce the number of rejected parts while at the same time increasing the number of parts produced per hour.
An example
The above picture depicts a spindle designed with a coolant ring which has adjustable nozzles. The picture shows a coolant ring having eight adjustable nozzles which help in blasting away chips and also keep the temperature of the tool and the workpiece cool.
Spindle Collet
What is a collet? Collet is an essential component of a spindle because it is the collet which helds the spindle in a machine tool. Collet is a cone shaped sleeve generally used for holding circular or rod like pieces in so many machines typically in lathe. It has usually a cylindrical inside and a conical outside and has kerf edges along its length to permit it to expand and contract. The collets are so designed that either they can be pulled or pushed into a matching conical socket to attain the clamping. When it is inserted into the socket, it contracts and grip the surface of the inner cylinder. Collet is an adjustable metal part that is used to tightly grip a tool or any workpiece. Collets expand spindle applications.
Materials used in making collets • •
Steel Brass
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Nylon etc.
Types of collets There are two main types of collets: Half-grip collets: They are identified by slits running from the bottom which is the mouth of the collet to the top for about 80% of the collet length. They are the simpler of the two collet types, and are ideal to be used with shorter shank tools where the shank cannot fill the entire collet length. Full-grip collets: They have slits running up from the bottom and down from the top, for about 80% of the length of the collet. They can grip the over the entire length and have more flexibility, which results in or "ranged" collet sizes. In other words, a specific collet size can hold a tool sizes
tool evenly "universal" range of
Collet Maintenance For any machine performance, tool geometry, cutting material, and machine feeds and speeds are all important factors to consider. Tooling maintenance is very essential for any machine tool performance. Collet affects the cut quality and durability of the spindle and hence it should be properly maintained. A clean collet allows for a firm grip of the spindle, preventing tool run out which occurs when the tool and spindle do not share the same center of rotation. It is highly recommended that the collet, router bit, tool holder and spindle taper be cleaned each and every time a tool is changed. When the machine is running, debris, dust, chips collect in all crevices of the spindle which will eventually accumulate around the mouth of the collet. Because of this accumulation, the tool may not be properly gripped. Proper cleaning and maintenance of the collet easily solves this problem. Besides this, proper maintenance should be taken to extend cleaning of the spindle as well for optimal performance.
Collet fixture in a milling machine Standard collet fixture: The configuration of a standard endmill fixtured in a milling machine using a collet is illustrated below:
Horizontal Collet Fixture: This type of collet is fixed horizontally and on a cylindrical part the configuration allows flats to be cut at specified angles.
Applications of Collets • • • • • •
Widely used in precision grinders. Also used in milling machines, and wood routers. Used in mechanical labs in institutions. Used in automotive and aerospace industry. Used in machines as lathe chuck. Also used with hydraulic or pneumatic actuators.
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Can also be used as original equipment in lathes, grinding machines. They are also used in the manufacture of medical and electronic components.
Spindle Pulleys
What is a pulley? Pulley is a simple machine used in a number of machinery work or machine parts to reduce the amount of force required to do a work. Usually a pulley consists of a wheel with a grooved rim in which a rope or chain is run. What pulleys actually do is that they change the direction of force applied on the load to do the required work. Pulleys work in a similar way like gears but they are not directly joined but linked by tubular springs, elastic bands or some flexible but strong material which is referred to as a belt pulley.
Advantages & disadvantages of pulleys over gears The main advantage of pulley over gear is that it is simple to make and can be used at a distance from each other whereas gear needs to touch to work. The disadvantage of the pulley is that it works by friction and can slip.
Uses of pulleys Pulleys are used in belt driven spindles. They are used as single or in combination to transmit energy and motion. In belt driven spindles, they are attached to the shafts at their axes. The power is transferred between the shafts by means o f endless belts running over these pulleys. Pulleys are used to change the spindle speed and feed rate.
Materials used in making pulleys • • • • •
Fiberglass Plastic Polyester Steel Cast iron etc.
Styles of pulley There are two pulley styles: •
Solid: They use belts that have a uniform thickness along the radius.
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Spoke, Thin or ribbed: They are designed for applications that require a reduction in pulley weight.
Types of pulleys in belt driven spindles • •
V-belt spindle pulley Flat belt spindle pulley
V-belt pulleys V belt pulleys are attached with drive belts in several power transmission applications. They are efficient and cost-effective. These type of pulleys have a triangular or trapezoidal cross-section. They are available in both single groove and multiple groove devices. They differ in terms of pulley size, belt width, belt angle, shaft mounting, operating temperature, and pulley web style. There are different types of V belt pulleys. •
Standard V belt pulleys: They have one or more grooves and are used for general-purpose applications.
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Variable speed pulleys: They have faces or flanges which can adjust axially to vary pitch diameter.
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Idler pulleys: They are used as belt tensioners and contain bearings allowing free rotation.
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Companion pulleys: This type has ribbed webs for high strength-to-weight ratios.
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Multiple-size pulleys: They use step-down or cone configurations.
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Poly-V pulleys: They are the most common belts used in spindles and used with mating belts for high-speed power transmission.
Flat belt pulleys These type of pulleys are used in transmission systems that are driven by flat belts, typically used in high-speed , low-power applications. Flat belts are smaller than V belts because they are thinner by 25% or more. They require flat pulleys and flat pulley idlers and not necessarily grooved flat belt pulleys. They apply motive power to the belt.
Bearing lubricants
Lubrication is a very important factor for the proper functioning of any machine tools and spindle bearing is no exception. Lubrication is necessary to protect the different parts from wear and tear. Different types of materials are used for lubricating the bearings. To enhance the service of bearings, you must choose the right type of lubricants.
Types of Lubricants: • • •
Oils Greases Dry lubricants
Function of Lubricants Despite having different types of lubricants for spindle bearings, their function is almost same. All lubricants provide some common services. •
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Lubricants apply a thin elasto hydrodynamic layer that reduces contact between the rolling parts. They protect certain spindle bearing components from oxidation. They help in minimizing the effect of contamination. They enable spindles to run faster, cooler and longer. They allow a significant increment in the operating speed of the spindles. They enable the spindles to run at the same speed and help in reducing the operating temperature.
Oil Lubrication Different types of oils are used for bearing lubrication. In industrial applications, petroleum based oils are the most common in use. A general misconception about oil lubrication is that more is better. Too much oil isn't good for the health of bearings. To produce the perfect elasto hydrodynamic (EHD) film between the layers of rolling elements of bearing, an adequate amount of oil is required at the specific temperature and operating speed. Any excess amount of oil will be responsible for increased bearing temperature.
Lubrication Systems Lubricating the spindle bearings require certain oil introducing mechanism. Here are given three basic ways of it: •
Air-oil mist: This method is very simple, inexpensive and reliable. A fog of oil droplets is created in an air stream delivered to the bearing. It features adjustable air pressure and oil delivery rate.
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Air-oil injection: This method delivers a controlled microscopic oil stream to the bearing, featuring adjustable oil and air delivery rate. They demand slightly increased cost set up. They provide a longer bearing life.
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Oil-injection: This method needs high cost for set up, but they ensure maximum bearing life. In it high pressure oil is directly fed to the bearings. But generally it is not used in machine tools.
Grease Lubrication Grease lubrication in bearings is very common and simpler. It is a permanent greasing solution and require minimal maintenance and is inexpensive. The grease is injected between the balls and races. Grease is actually oil mixed with a thickener. Thickener is an inert substance added just to hold the oil like sponge.
Limitation of Greasing However there are certain limitations on grease limitation. Almost all greases are rated to operate up to the temperature of 300°F. Those grease which can tolerate high speeds have ester oil base and barium complex as thickener. •
The spindles packed with grease are unable to run above dN values of 850,000 for continuous operation.
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When the operating speed increases the operating temperature increases too and it started to break down the grease.
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Excess of grease application is not good for bearings because it can create heat due to churning which can cause grease to deterio rate.
Buying tips Selection of proper lubricants should be made by following certain parameters such as:
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The viscosity of the lubricant at all relevant temperatures. The operating speed of the bearings.
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Compatibility of the lubricant to all components and potential contaminants
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Belt Driven Spindle
Belt driven spindles are one of the major categories of spindle based on the driving medium. Belt driven spindles cover almost all categories of the application spindles. Though it is the traditional technique in use from a long time and many new variations have come up in the market like the motorized or the high frequency spindles, still belt driven spindles are popular and used in a large number of industrial applications. These spindles find its use in grinding, drilling, milling, turning and many other machining tasks. The spindles operate with a tangential belt drive system. They are best accommodated to the places where there is suffi ciency of space because the belts require certain space. Now-a-days these spindles are available in variety of sizes and models in compact designs.
How does a belt driven spindle operates? Power and rotation are provided to this spindle with the help of external motor. The motor is usually mounted adjacent to the spindle, the torque is transferred to the shaft of the spindle by using a cogged or V-belt. The speed, power, torque of the spindle depend upon the performance features of the driving motor, and the belt ratio used between the spindles and the motor.
Features of belt driven spindles •
The belt driven spindles are available in block, cartridge, and flange cartridge styles.
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Belt-driven spindles are of different types based on bearing construction and overall spindle configuration.
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They are available in a variety of sizes and models and with many optional features.
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To optimize the performance of the belt driven spindles for specific applications, a number of specific machines like bearings are used. Certain bearings like tapered roller bearings, angular
contact ball bearings and tapered bore roller bearings are used to maximize the performance of belt-driven spindles. •
High speed belt driven spindles require special lubrication.
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Belt driven spindles are sensitive to vibration.
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They are also sensitive to run-out generated by the drive motor.
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Belt-driven spindles are offered in grinding head, boring head, milling head which helps in grinding, boring, milling and so on.
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With a belt-driven spindle, the belt is easy to maintain and easily accessible.
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The type of belt affects the noise level of the spindle.
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High radial and axial stiffness.
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Minimized excessive temperature rise and minimized shaft elongation in action in some spindles.
Other Belt Driven Spindles • •
Belt Driven Grinding Spindles Belt Driven Milling Spindles
Uses of Belt Driven Spindles Belt driven spindles are highly popular because of the following reasons: •
Belt driven spindles are used for all grinding purposes.
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Belt driven spindles are used in all types of milling and drilling applications.
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They provide a low cost simple design just suitable for a wide range of applications.
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The flexibility of a belt driven spindle design makes it easy to customize.
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They meet a wide variety of load, size and speed requirements.
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They are required for high-speed machining. These spindles are used especially where a l arge number of different bores have to be ground with high precision, which is not possible in a normal spindle.
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Belt driven spindles are considered less expensive as power is passed from the motor to the spindle by simple toothed or "V" type rubber belts or poly-V belts.
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They are capable of attaining higher spindle speeds than geared spindles.
Applications of Belt Driven Spindles Belt driven spindles find their greatest applications in • • • • • • • • • • • •
Light machining of steels and non ferrous metals. Light internal grinding Heavy internal grinding Light external grinding Heavy external grinding Grinding deep holes Grinding in high speed Milling Drilling Boring Routing Engraving etc.
Buying tips Specifications to consider are as follows: • • • • • • • • • •
Spindle speed Spindle power Bearing types Spindle lubrication Type of belt Durability Clamping tool Rotation direction Applications The proper bearings and shafts are to be selected for the speed and load conditions for the specific applications of the belt driven spindle etc.
Motorized Spindle
What is a motorized spindle? Motorized machine tool spindles are a popular category of spindles used in various industrial applications. Motorized spindles are becoming more common on new machining centers. The motorized spindle unit is generally the preferred design option for high-speed, high-power systems and medium and high performance machine tools. These high-speed motorized spindles have the drive motor integral to the spindle. The motor is built directly into the spindle, which eliminates the need for a belt or gears for power transmission. These spindles are available in a variety of sizes and models in a compact design. Such spindles are highly recommended for high productivity where there is limited space for the spindle, and high flexibility in terms of service and improved dynamic behavior. Speeds beyond 100,000 rpm can be achieved by machining center spindles using motorized design-a
speed level that would be impractical or problematic using a belt driven approach. Motorized spindles are used in all types of machine tool applications, including grinding, drilling, milling, turning and boring.
How does a motorized spindle operate? A motorized spindle either has an internal motor installed into the system or an external motor outside the system to provide torque and power. The motor in the spindle is the integral part of the spindle shaft and housing assembly. It is the motor which allows the spindle to rotate at very high speeds as a complete unit, without facing the conventional drawbacks of belts or gears. In general, a complete motorized-spindle comprises the following • • •
The spindle shaft The motor element and The tooling system.
The shaft is held in position by using high precision bearings, which rotates up to the maximum speed and display the power characteristics of the motor type that is used.
Features of motorized spindles Different models of motorized spindles have different features. Some notable features of motorized spindles are as follows: •
Available in different sizes, the motorized spindles offer a robust combination of speed and power to support machining needs. These motorized spindles are available with a wide range of horsepower and speed combinations.
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The drive of the spindle unit is implemented by a DC or an AC motor, characterized by greater output, better tolerances, lower heat rises and longer bearing life.
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Motorized spindle units also incorporate asynchronous or synchronous motor technology that will push spindle speeds.
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The unique motor drive system used in spindles offer high-resolution position encoder with high power over a wide speed range, full torque and highly accurate spindle orientation.
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Most of the motorized spindles are ruggedly designed and built to offer long trouble-free service as they operate at very high speeds.
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There are different models of motorized spindles and each model has a design suitable for grinding, boring, milling applications.
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Some spindles have bracket mount design, while others are foot mounted.
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These motorized spindles are available in block, cartridge, and flange styles.
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Besides the standard models, a motorized spindle can be custom designed to meet application needs. Whatever the requirement like housing style, special bearing arrangement, tool interface or spindle configuration, a motorized spindle can be built to customer's specifications.
Other Motorized Spindles • •
Motorized Grinding Spindles Motorized Milling Spindles
Uses of Motorized Spindles Motorized machine tool spindles are highly recommended in various applications because of the following reasons: •
The motorized spindle is considered to be the ultimate in reliability and precision machining of today's machine tools.
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They operate at very high speed.
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They are intended for applications at small CNC milling, routing, engraving, drilling machines for machining various materials.
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They are also suitable for applications like internal grinding of bearing races, internal thread grinding, and other precision bore grinding applications.
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Motorized spindles allow extremely good cutting capacities.
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They also provide good surface finishes of the workpiece. They deliver smoother operation with lower operating vibration, which in turn leads to improved surface finish.
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They are suitable for internal grinding, external grinding, face grinding and surface grinding.
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Motorized spindles are the ideal option for a precision machine application requiring a low profile, close-center distance, and compact design.
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For general-purpose applications that require flexibility and automatic spindle change, motorized spindles are the norm etc.
Applications of motorized spindles Applications of motorized spindles include • • • • • • • • • • •
Machining centers Tool machine manufacturing Milling machine tools for aerospace, automotive use Grinding machine tools Pick-up lathes High performance lathes Surface grinding applications Planers Lathes Vertical boring mills Vertical turret lathes etc.
Buying tips Technical specifications to consider are as foll ows: • • • • • • • •
Speed Motor Type Voltage Current Maximum Power Maximum Torque Radial Tolerance Axial Tolerance
Other specifications are as follows: • • • • • •
Tool clamping system: Manual, automatic, collet, pneumatic Cooling system Spindles bearings: Bearing type Spindles lubrication: Oil, mist, grease Housing diameter Model: Standard or customized etc.
The best motorized spindle will be that which provide the best combination of speed, power, stiffness and load capacity.
Grinding Spindles
What are grinding spindles? An important category of machine tool
spindles are grinding machine spindles. As the name suggests these spindles are specially designed to grind. They are of various types and available in various configurations. For any kind of grinding whether on a large scale or a small scale, the grinding spindles play a vital role. Grinding spindles are used in any machine tools with grinding wheels for precision, size and surface finishing. Most of these spindles are designed in such a way so as to be fully interchangeable with each other and with existing systems. They are made of hard, durable steel alloys which helps to prevent premature damage on the surface as well seizing during machine assembly. The grinding spindles' housing diameters are available in various lengths depending on the size of the machine tool in which it will be fitted while some are available in standard, industry dimensions. Coolant and oil connections meet the most common worldwide standards.
Grinding : Meaning The process of removing metal by using abrasives bonded to form a rotating wheel is known as grinding. When the moving abrasive particles come in contact with the workpiece, they act as tiny cutting tools, thereby cutting a tiny chip from the workpiece. Though many people believe that grinding abrasive wheels remove material by the method of a rubbing action, the process is the same as a cutting action as drilling, milling, and lathe turning.
Grinding spindles: Characteristics Some important characteristics common to many grinding spindles are as follows: •
In most grinding spindles, there is an oil/air mist lubrication system with an effective heat dissipation method which helps in simplifying the spindle configuration.
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There is the standard spindle range for vertical grinding and horizontal grinding which is developed to enable vertical applications and horizontal applications.
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There is also spindle range for internal grinding and motorized main spindle ranges.
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Grinding spindles include special solutions to prevent or avoid dirt collection inside.
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The spindle design also considers the different vibration behavior of a rotating shaft from vertical and horizontal positions etc.
Grinding spindles: Uses The grinding efficiency is measured in terms of material removal rate which is attained by employing ultra high wheel speeds. For any ultra high speed grinding machine tool, the spindle is a key component. The various uses of grinding spindles are given below: •
The grinding spindle is used for roughing and finishing flat, cylindrical and conical surfaces.
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The grinding spindle is used for finishing internal cylinders or bores.
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It helps in forming and sharpening cutting tools.
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It also helps in snagging or removing rough projections from castings and stampings.
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Another important task of grinding spindles is to cleaning, polishing and buffing surfaces.
New innovations Many grinding spindles are now combining cutting and grinding into a single platform. The benefits of performing multi tasks lead to improved work flow, fewer machines and operators, reduced setups, and higher and better parts resulting from performing all operations in one setup.
Types of grinding machine spindles All spindles are usually classified into three main categories-high frequency, belt driven or motorized. Other popular types of grinding spindles are: •
Internal grinding spindles: Internal grinding is considered to be the most challenging of all grinding applications. Internal grinding means the precision grinding of the inside surface of the hole in a work piece, enlarging or finishing of the cylindrical opening or inside diameter in a workpiece.
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External grinding spindles: External grinding, which is also important to many manufacturing organizations, refers to grinding of the outer surface of a workpiece.
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Horizontal grinding spindles: Horizontal grinding spindles are designed to grind advanced materials, including wafer backside grinding operations, achieving a high degree of flatness while at the same time optimizing surface finishes. They are so called because the grind ing process takes place in a horizontal way. On machines with horizontal spindle the motor-driven spindles are horizontal. In such machines the parts are guided through the grinding wheels vertically.
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Vertical grinding spindles: Vertical grinding , as the name suggests, fixes the workpiece on a rotary chuck in the machine base , similar to the orientation of the workpiece on a vertical lathe. The vertical grinding spindle travels up and down and side to side and at times may also swivel from above the workpiece. On machines with vertical spindle, the motor-driven spindles are vertical and the parts are guided through the grinding wheels horizontally.
All these spindles can either be belt driven or motorized or high frequency spindles. Let us now explain in details the various types of grinding spindles on the basis of the above classifications: • • • •
High Frequency Grinding Belt Driven Grinding Motorized Grinding Surface Grinding
Buying tips Certain specifications to be considered for the purchase of grinding spindles are as follows: •
Spindle drive: Whether belt driven, high frequency or motorized.
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Spindle applications: In which area of application the grinding spindle should be used.
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Spindle speed: Spindle rpm capabilities.
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Spindle performance: High Speed Capability, Smooth Running - Low Vibration, High Accuracy - Runout Tolerances, High Rigidity, Low Speed - High Torque Operation
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Environment: Medium Chip or Dust (regularly removed), Light Chip or Dust (frequently removed), Open, allowing coolant and chips to flow away, Heavy Chip or Dust (build-up around spindle) etc. These options differ in different grinding spindles and the manufacturer should give proper guide as to whether it is recommended or acceptable or better or best in different options available.
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Type of lubrication required.
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Machine specifications: For instance, rigid wheel head spindles, rigid bearings, feed increments.
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Types of grinding heads in spindles: Whether air turbine grinding heads or electric grinding heads.
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Durability: Warranty period.
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Spindle repair services offered by the manufacturer etc.
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General: Cost, quick delivery, choice of accessories, compact design, availability of customization etc.
High Frequency Spindle
What is a high frequency spindle? High-frequency spindles form a very important category of spindles designed for precision, high speed and productivity. These spindles are suitable for milling and drilling of metallic and non-metallic materials at highest speed and continuous power. They are available with different power and speed ranges and cartridge, flange cartridge, block body, base mount styles. High frequency spindles are helpful in getting better surface finish and high productivity. They have integrated motor design which eliminates gears and pulleys, and thus making it very compact. They are so called because they require separate external frequency converter.
Features of hi-frequency spindles •
Aggressive motors
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Excellent bearing rigidity
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High rotational accuracy
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Vibration-free operation
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Extreme precision
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Maximum efficiency
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High rigidity
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High-performance spindles feature various external diameters range and various tensioning systems.
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They come in a wide variety of horsepower, rpm levels and body styles.
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They are engineered for optimal reliability and long-life.
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Body styles of hi-frequency spindles can be cartridge, flange cartridge, base mounted and block style.
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In some spindles, the components feature case hardening, tempering treatments, isothermal annealing to prevent wear and loss of precision.
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High precision ball bearings to optimize the speed/bearing diameter ratio.
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Forced motor cooling
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All rotating parts in the spindle are balanced carefully before and after assembly.
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Lubrication systems are designed and optimized to obtain maximum speed in such spindles.
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Usually automatic tool change.
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Assembly in such spindles is designed to allow for easy maintenance.
Accessories for High frequency spindles •
Frequency Converter: Suitable frequency converter to assure optimum compatibility with and best performance of the hf spindles.
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Lubricating Systems, Cooling Units: Very essential in order to protect the life and performance of the spindle.
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Tool Clamping Systems: Either automatic or manual.
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Screw-in mandrels, Flanges, Collets, Arbors etc.
Other High Frequency spindles
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High Frequency Grinding Spindles High Frequency Milling Spindles
Uses of high-frequency spindles High frequency spindles are recommended for those applications where high speed and high accuracy is required. These spindles relate to a technology that permits on average the highest level of performance.
Applications of high frequency spindles Hi-frequency spindles are suitable to perform various machining tasks like • • • •
Grinding Milling Drilling Engraving
They are used in applications like internal grinding of bearing races, internal thread grinding, and other bore grinding applications. They satisfy very precise milling requirements. They are used in drymachining and high-speed-cutting applications as well.
Buying tips Certain specifications to consider are as follows: • • • • • • • • • •
Spindle speed Spindle power Frequency Rotation direction Lubrication Bearing type Radial and axial tolerances Spindles accessories Cooling system Tool clamping
High Speed Spindles
What is a high speed spindle? High speed spindles have today emerged as the most important component of any kind of high machining process. For all kind of machining tasks, whether in the CNC, tool, machining center and other process components, the use of high speed spindles always optimizes productivity. For all manufacturers in this fast growing world, using high speed spindles has become a "rule" in keeping ahead of competitors. High speed spindles are considered to be the most critical elements of high speed machine tools and usually very expensive.
Major components of a high speed spindle All spindles are not necessarily high speed spindles. Certain specific points are to be taken into consideration for the design of a high speed spindle because the performance of a high speed spindle is different and better than a conventional spindle. The major components that are to be considered for a high speed spindle design include: •
Spindle Drive: This can be either belt driven or motor driven. While the belt driven spindle is run by a tangential belt system, the motorized spindle is driven by an external or internal motor installed in to the system. This is determined by evaluating the requirements of the machine tool, considering the requirement of the the maximum speed, power and stiffness.
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Spindle Bearings: This includes the evaluation of the type, quantity, mounting, and lubrication method used in the bearings.
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Spindle Motor: Belt-Type, Motor-Spindle, Capacity and Size
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Spindle Shaft: This includes tool retention drawbar and tooling system used
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Spindle Housing: Evaluate the size, mounting style and capacity of the housing.
Functions of high speed spindles Numerous industries use high speed spindles to • • • • •
Deliver high speed Maximize application performance Deliver high power Shorter through time Better accuracy
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Reliability for high performance machine tools Used for all applications like Micro machining o Engraving o Drilling o o Milling Grinding o o Boring
Difference between a high speed spindle and a conventional machine tool spindle High speed spindles are more or less designed with the motor directly flanged to the spindle shaft. On the other hand conventional spindles are mostly gear or belt driven. While the maximum rotational speed of belt or gear driven spindles is some where about 12000 to 15000 RPM and at speed higher than this the spindle tends to induce vibrations, which usually result in poor surface finish. For this reason, machine tool spindle spindles mostly use a directly flanged motor and thereby achieving more higher speed, torque and power compared to a standard spindle.
Types of retro fit high speed spindles Some advantages of high speed spindles can be attained in high speed machining by retrofitting a high speed spindle to an existing machine. The high speed spindle can be chosen according to the needs of the application. The various options are as follows: Replacement spindle: The existing machine tool spindle is replaced by a high speed spindle .
Fixed Centerline Spindle :An independently powered machine tool spindle mounts in the original spindle. At times, the high speed spindle can be removed allowing the original spindle take slower, heavier cuts.