Lab Session 2: To study the different parts of Lathe machine and to understand the tool/work piece/chip contact in turning operation.
Lathe Machine Lathe machine is a machine tool which rotates the work piece on its axis to perform various operations such as turning, facing, grooving etc. with tools that are applied to the to create an object which has symmetry about an axis of rotation. Lathes are used in wood turning, metal working etc. There are a number of lathes used now a days but major classification of lathe is as under: •
Manually Operated Lathe
•
CNC Lathe
Manually operated lathe is operated manually by a skilled worker and is basically classified into horizontal lathe and vertical lathe and CNC (Computer Numeric Control) lathe is driven by a set of computer instruction called a GM language. Here we will discuss about manually operated Engine Lathe.
a) Parts of Lathe: There are a number of parts in an Engine Lathe but the major/principal components are given as follows and shown in the fig:
Head Stock Tail stock Speed Control Lever Feed Control Lever
Spindle Tool Post Cross Slide Carriage Ways Lead Screws Bed
Now we will discuss these parts in detail.
Head Stock: Head stock is the main part of an Engine lathe. The head stock contains the drive unit to rotate the spindle, which rotates the work piece. The power is given to the spindle from this part of Engine lathe.
Tail Stock: It is on the opposite side of the head stock. A center is mounted in the tail stock to support the other end of work piece.
Speed Control Lever: We rotate the spindle at different rpm (rotations per minute). We can adjust the speed of spindle by this lever.
Feed Control Lever: We can give automatic feed to the tool by adjusting the feed from this lever.
Spindle: We can perform different operations on the work piece by placing it in the spindle.
Tool Post: We can held the cutting tool in the tool post.
Cross Slide: The tool post is fastened to the cross slide which moves vertically into the work piece. How much you move cross slide and tool penetrates in the work piece, this is termed as depth of cut. It is used majorly in Taper turning, Facing, Form turning etc.
Carriage: Cross slide is assembled to the carriage which moves horizontally into the work piece. It moves to feed the tool parallel to the axis of rotation of the work piece. It is used majorly in turning to reduce diameter of the work piece.
Ways: The ways are the tracks on which carriage and tail stock rides, and they are made with great precision to achieve a high degree of parallelism relative to the spindle axis. Ways are built along with bed of the lathe. Ways are mostly triangular in shape.
Bed: Bed is a rigid frame for the whole body of lathe. It support the whole body of lathe.
b) Tool/Work piece/Chip Contact in Turning: There is a single point contact between tool and work piece. Basically there are two surfaces of tool, flank and rake surface.
Here flank surface is shown in two parts, minor and major flank and face is actually the rake surface. Corner is the cutting point, major flank is the flank surface which is closest to the newly generated machined surface. Shank is the part which is clamped in the tool holder.
When we brought the tool (having some feed) near to the work piece (rotating at some cutting speed) and give some depth of cut, tool comes in contact with the work piece and machining starts. The cutting point of the tool cut the surface of the work piece which flow in the form of chips. Chips flow above the rake surface as shown in the fig as shown above.
Lab Session 3: To study the different operations on lathe machine.
Operations on Lathe Basically turning operation can be performed on a lathe machine but there are a number of operations that can be performed on a lathe machine.
Turning Operation: Turning is a machining operation in which a single point cutting tool is used to remove material from a rotating work piece to generate cylindrical surfaces. In a turning operation, the work piece is machined to reduce the diameter of work piece. Cutting tool is fed parallel to the axis of rotation of work piece.
Some other operations related to turning are also performed on lathe machine that are given as follows:
a. Facing: In a facing operation, single point cutting tool is fed radially into the work piece or perpendicular to the axis of rotation of work piece. It is used to generate flat surfaces on one end of the work piece and to reduce its length.
b. Taper Turning: It is type of longitudinal turning in which cutting tool is fed parallel to the axis of rotation of the work piece but at a certain angle.
c. Contour Turning: Instead of feeding the tool along the straight line parallel to the axis of rotation as in turning, the tool follows a contour that is other than straight, thus created a contoured form in the turned part.
d. Form Turning: Also called as forming in which a tool has a shape that is imparted to the work by plunging the tool radially into the work.
e. Chamfering: The cutting edge of the tool is used to cut an angle on the corner of the cylinder, forming what is called chamfer. It is used to safe the corners of the work and to reduce the stress consideration which is maximum at the boundary due to the corner edges of work.
f. Cutoff/Parting off: The tool is fed radially into the rotating work at some location along its length to cut off the end of the part i.e. it is used to separate the work piece into two parts.
g. Grooving: The tool is fed radially into the rotating work at some location along its length to give some impression not to cut off the work.
h. Threading: A pointed tool is fed linearly across the outside surface of the rotating work part in a direction parallel to the axis of rotation at a large effective feed rate, thus creating threads in the cylinder. Threads are used as temporary fastening.
i. Boring: Tool is fed linearly into work piece, parallel to the axis of rotation of work piece, on inside diameter of work piece of an existing hole in the work. It is basically used to enhance the size of the existing hole.
j. Drilling: Drilling can be performed on a lathe by feeding the drill (fastened in the tail stock) into the rotating work along its axis. Reaming can be performed in a similar way.
k. Knurling: This is not a machining operation because it does not involve cutting of material. Instead, it is a metal forming operation used to produce a regular cross hatched pattern in the work surface.
Lab Session 4: To study about drill machine and to discuss the different operations performed on it.
Drill Machine It is a machine tool which is used to generate round holes in a surface. Drilling is performed on custom designed machines called drill press. The cutting tool used in drilling is termed as drill bit. It is used to generate round holes where diameter of the hole is approximately equal to the diameter of the drill bit.
There are number of drilling machines but here we will discuss about:
Pillar Type Drilling Machine: It is a type of vertical drilling machine in which the drill bit generate a hole vertically in the work piece. Its name pillar type indicates that its vertical column is just like a pillar.
a) Parts: Main parts of the Pillar type drilling machine are given as under and shown in fig:
Head Stock Head Stock Control Lever Gear Box Speed/RPM Control Lever Electric Motor Supplying Shaft Spindle Drill Chuck Spindle Control Lever Electric Panel Spindle Feed Control Lever Disk Lever Sprocket and Chain Mechanism Vertical Column Table Base
Now the description of these parts is as follows.
Head Stock: It is the main component of this machine. All the functions of this machine are controlled from here.
Head Stock Lever: It is a lever for controlling the movements of head stock. To penetrate the drill bit in the work piece, we have to move head stock up and down in the work.
Gear Box: The gear mechanism of pillar drill mechanism is present here. The power is given to the head stock from here.
Speed/RPM Control Lever: It is a lever used to control the speed of the rotating spindle.
Electric Motor: When we switch on the main supply, electricity is passed to the machine which operates the electric motor and electric motor gives drives the gear mechanism.
Supplying Shaft: It is a shaft that connects gear box and head stock. It transmits the power from gear box to the head stock.
Spindle: The power from head stock is given to the spindle that rotates in clock wise or anti clock wise direction.
Drill Chuck: The spindle holds the drill chuck which holds the drill bit of any type according to the size of the drill chuck.
Spindle Control Lever: The speed of the spindle is controlled from this lever.
Electric Panel: To give drive to the spindle from the head stock, electric panel is used. Electric panel comprises three buttons; one for the spindle to rotate it in clock wise direction, second one is to rotate it in anti-clock wise direction and the third one is to stop the spindle.
Spindle Feed Control Lever: This lever is used when we want to feed the drill bit automatically. This lever is used along with a disc lever.
Disc Lever: This lever is used with spindle feed control lever. When the disc lever engage, then we apply automatic feed to the drill bit.
Sprocket and Chain Mechanism: There is a sprocket and chain mechanism to operate this drill machine.
Vertical Column: It is basically the support for the machine. Sprocket and chain mechanism lies here.
Table: Table is for holding the work piece. There is vise or any other work holding device lies on the table. It is basically used for adjusting the work piece with respect to the drill bit.
Base: It is basically the support to the whole body of the machine. It is made fix in the ground.
b) Operations: Operations other than drilling that can be performed on Pillar type drilling machine are given as follows: Reaming Taping Counter Boring Counter Sinking Centering Spot Facing Now their details are as under:
i.
Reaming:
It is used to slightly enlarge a hole, to provide a better tolerance on its diameter, and to improve its surface finish. Tool is called as reamer, and it usually has straight flutes. Reamer is in Hexagonal shape having 6 edges but its edges are straight.
ii.
Taping: This operation is performed by a tap and is used to provide internal screw threads on an existing hole.
iii.
Counter Boring: It provides a stepped hole, in which a larger diameter follows a smaller diameter partially into the hole. A counter bore hole is used to seat bolt heads into a hole so the heads do not protrude above the surface. Bore Tool=Bolt Head Diameter
iv.
Counter Sinking: This is similar to counter boring, except that the step in the hole is cone-shaped for flat head screws and bolts.
v.
Centering: Also called center drilling, this operation drills a starting hole to accurately establish its location for subsequent drilling. The tool is called center drill.
vi.
Spot Facing: Spot facing is similar to milling. It is used to provide a flat machined surface on the work part in a localized area or to remove irregularity on surface of drilled area.
Lab Session 5: To study the different parts and operations of milling machine.
Milling Machine Milling operation is performed on a milling machine and is defined as follows:
“It is a machining operation in which work piece is fed past to a rotating cylindrical cutting tool which has multiple cutting edges.” The tool is called as Milling Cutter and its cutting edges are basically the Teeth of the cutting tool. It is a multiple point cutting tool. The tool is not continuously in contact with the work piece. Cutting tool’s teeth enter and exit into the work piece during each revolution.
Types of Milling Machine: Basically milling machine is divided into two types according to the arrangement of tool and work piece. These two types are given as follows: 1) Peripheral/Horizontal Milling Machine 2) Face/Vertical Milling Machine Now their details are under:
Horizontal Milling Machine In Horizontal milling, also called plain milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by cutting edges on the outside periphery of the cutter.
a) Parts:
Some main parts of the horizontal milling machine are as following: Over Arm Vertical Head Collet Collet Chuck Table Vice Cross Slide Knee Table Control Lever Cross Slide Control Lever Knee Control Lever Automatic Lever Feed Change Lever Electric Panel Coolant Drum Speed Control Lever Now their details are given as follows:
Over Arm: It is a support to the vertical head. It start from the vertical column and ends at vertical head.
Vertical Head: Vertical head receives power from gear box and gives it to the spindle.
Collet: Collet is used to grip the milling cutter very firmly.
Table: Table gives the place for vice. The milling cutter moves on the work piece by the movement of the table in left and right direction, i.e. Table moves longitudinally across the work piece.
Vice: Vice is present on the table which holds the work piece so that in cutting the work piece does not displace from its position.
Saddle: Saddle is another part of the machine which moves forward and backward. It moves vertical to the work piece, i.e. inward and outward to the work piece.
Knee: Knee is the part of the machine that moves in upward and downward direction which utilizes in giving the depth of cut to the work piece by the cutter.
Table Control Lever: Movement of the table to the left or right is controlled from this lever.
Saddle Control Lever: Movement of the saddle in inward or outward direction is controlled from this lever.
Knee Control Lever: Movement of the knee in upward or downward direction is controlled from this lever.
Automatic Lever: This lever is when we want to give automatic movement to table, cross slide and knee but only one at a time. This is used in combination with other lever.
Feed Control Lever: This is used when we give feed to the milling cutter.
Electric Panel: When we switch on the main supply of the machine, it does not operate. To give power to the cutter, table etc. electric panel is used to give power to these parts. There are some buttons in the electric panel.
Coolant Drum: There is a coolant drum in the base of the milling machine.
Speed Control Lever: Also called rpm control lever, is used to give variable speed to the milling cutter.
Cutters: The cutter mostly used in horizontal milling machine is end mill cutter which is straight in shape and used in simple machining. To generate T-shape slots, T-slot cutter is used.
b) Operations: Operations that can be performed on this horizontal milling machine are given as follows: Slab Milling Slot Milling Saw Milling Side Milling Straddle Milling Now their description is as follows:
i.
Slab Milling: It is the basic form of peripheral milling in which the cutter width extends beyond the work piece on both sides.
ii.
Slot Milling: Also called as slotting, in which the width of the cutter is less than the width of the work piece, creating a slot in the work.
iii.
Saw Milling: When the cutter is very thin, this operation can be used to mill narrow slots or cut a work part in two parts, called saw milling.
iv.
Side Milling: In this type of milling the cutter machines the side of the work piece. Machining takes place on one side at one time.
v.
Straddle Milling: It is same as that of side milling, only cutting takes place on both sides of the work at a time.
Now second form of milling is:
Face Milling In face milling, the axis of the cutter is perpendicular to the surface being machined, and machining is performed by cutting edges on both the end and outside periphery of the cutter.
a) Parts: There is not a great difference in horizontal and face milling. Some parts of face milling machine that differ from horizontal milling machine are as following: Vertical Column Over Arm Arbor Dividing Header Now description is as follows:
Vertical Column: It is support to the machine. Gear box, spindle etc. is present in it.
Over Arm: It is a support to the arbor. It start from the vertical column and ends at vertical head.
Arbor: Arbor is like a cylinder in which a milling cutter is fixed.
Dividing Header: It is a separator that separates one cutter from other and divide the work piece.
Form Cutters: There are two form cutters, concave and convex.
b) Operations: Operations that can be performed on this face milling machine are given as follows: Conventional Face Milling Partial Face Milling End Milling Profile Milling Pocket Milling Surface Contouring Now their description is as follows:
i. Conventional Face Milling: In this type of milling, the diameter of the cutter is greater than the work part width, so the cutter over hangs the work on both sides.
ii. Partial Face Milling: In this milling, the cutter over hangs the work on only one side of the work.
iii. End Milling: The diameter of the cutter is less than the work piece width, so a slot is cut into the work.
iv. Profile Milling: It is a form of end milling in which the outside periphery of a flat part is cut.
v. Pocket Milling: It is another form of end milling used to mill shallow pockets into flat parts.
vi. Flat Contouring: It is a type of face milling, in which a ball-nose cutter (rather than square-end cutter) is fed back and forth across the work along a curvilinear path at close intervals to create a three dimensional form.
Lab Session 6: To study the different parts and operations of shaper machine
SHAPER MACHINE “A shaper is a type of machine tool that uses linear relative motion between the work piece and a single-point cutting tool to machine a linear tool path’’ Its cut is analogous to that of a lathe, except that it is (archetypally) linear instead of helical. (Adding axes of motion can yield helical tool paths, as also done in helical planning.) A shaper is analogous to a planner, but smaller, and with the cutter riding a ram that moves above a stationary work piece, rather than the entire work piece moving beneath the cutter. The ram is moved back and forth typically by a crank inside the column; hydraulically actuated shapers also exist.
Purpose and importance of working with shaping machines Shaping machines are machine tools which by way of chip removal give work pieces the desired shape, dimension and surface finish. They produce mainly flat surfaces, shoulders, grooves and similar shapes. It is, however, also possible to make circularly arched surfaces. The cutting is effected with single-edged tools in the interrupted cut with a working stroke and a return stroke. Since shaping can be understood as turning of work pieces with infinitely large diameter, there are many similar aspects between shaping and turning and shaping and turning tools. The main purpose of shaping is in most cases to remove relatively big amounts of material in the form of chips. Shaping is applied, for example, to remove cast-iron scale and to get fiat and aligned surfaces or to cut long or heavy parts (for machining plate edges among other things).
a) Parts: Some main parts of the horizontal milling machine are as following:
Ram Tool head Tool holder Vice Table Clutch Ram lock lever Automatic feed lever for table Manual handle for movement of table Position adjusting lever Length adjusting lever Levers for ram speed
Tools for shaping Knowing the tools, their shapes, kinds and application is necessary for an economic working. The kind of tool to be applied in each case is determined by the shape of the work pieces to be machined. If much material has to be removed, start working with the straight tool. If the demands stipulated for the surface quality are high, use the finishing tool. So for each job the corresponding tool must be used. The following tools can be used: (1) Straight Tool (2) Bent Tool (3) Swan-necked Tool (4) Offset Tool
b) Setting and Operations: Clamping of the work piece: Clamp the work piece according to its shape safely and firmly and secure it against distortion and deformation.
Clamping of the tool: Clamp the tool short and firmly.
Setting of cutting values: Set the number of strokes per minute, stroke length, feed, cutting depth taking into consideration the tables available and graphical symbols. Switch only when machine is at rest!
Operation of the shaping machine (sequence of operations): The work piece mounts on a rigid, box-shaped table in front of the machine. The height of the table can be adjusted to suit this work piece, and the table can traverse sideways underneath the reciprocating tool, which is mounted on the ram. Table motion may be controlled manually, but is usually advanced by an automatic feed mechanism acting on the feed screw. The ram slides back and forth above the work. At the front end of the ram is a vertical tool slide that may be adjusted to either side of the vertical plane along the stroke axis. This tool-slide holds the clapper box and tool post, from which the tool can be positioned to cut a straight, flat surface on the top of the work piece. The tool-slide permits feeding the tool downwards to deepen a cut. This adjustability, coupled with the use of specialized cutters and tool holders, enable the operator to cut internal and external gear tooth profiles, splines, dovetails, and keyways. The ram is adjustable for stroke and, due to the geometry of the linkage, it moves faster on the return (non-cutting) stroke than on the forward, cutting stroke. This action is via a slotted link or Whitworth link.
Safety Precautions
Never stand in front of the machine, but always beside the machine on the side of the control elements (splashing chips, danger of getting injured). Make inspections of the work piece or tool, on principle, only when the machine is at a standstill.
Lab Session 7: To study the different parts and operations of surface grinding machine
Surface Grinding Machine “It is machine used to produce a smooth finish on flat surfaces.” It is a widely used abrasive machining process in which a spinning wheel covered in rough particles (grinding wheel) cuts chips of metallic or nonmetallic substance from a work piece, making a face of it flat or smooth.
Numerical control (NC): It is the automation of machine tools that are operated by precisely programmed commands encoded on a storage medium, as opposed to controlled manually via hand wheels or levers, or mechanically automated via cams alone.
a) Parts: Some parts of surface grinding machine are as given below:
Vertical column: To give z-axis movement.
Grinding head: Equipped with coolant supply and have grinding wheel assembly.
Grinding wheel: Made of abrasive material and removes material from work piece in microns.
Magnetic chuck: Unlike other chucks it is magnetized to hold the work piece during machining.
Table: Magnetic chuck is fixed on table.
Cross slide: It gives the y-axis movement to table.
Stopper and sensor: These are used to reduce the time for machining by making x-axis and y-axis motion limited.
Dressing tool: It is a tool to dress the surface of a grinding wheel. Grinding dressers are used for making different profile on grinding wheel. The dressing of a wheel in order to return the wheel to its original shape
DRO unit Automatic/speed control lever Manual handle for table
Lab Session 8: To study the different parts and operations of CNC Machining Centre
CNC Machining Centre “A machining center is a highly automated machine tool capable of performing multiple machining operations under CNC control in one setup with minimum human attention.” Typical operations are those that use a rotating cutting tool such as milling and drilling.
a) Parts: Some important parts of CNC machining center are given below:
Vertical head Base Table Spindle Chuck Fixtures Tool drum Automatic tool changer Coolant Control panel MPG Compressor Sump AVR (Automatic voltage regulator) Pendant controller (with half keypad) Tool drum
b) Operations: Following operations can be performed on these machine tools
Milling Drilling Turning Grinding Welding Inspection operations etc.
Automatic tool changing, pallet shuttles and automatic work part positioning are the features that make a machining center such a productive machine tool.
Experiment no 9: To study the operation of cutting fluid in CNC machining centre and different cooling methods used in CNC machining centre
Cutting Fluids Cutting fluids play a significant role in machining operations, tool life and quality of work. There is a wide variety of cutting fluids available today. Many new coolants have been developed to meet the needs of new materials, new cutting tools, and new coatings on cutting tools. The goal of machining operations must be to improve productivity and reduce costs.
Cutting Fluid Purpose: Cutting fluids are mainly use for two purposes
Cooling Lubrication
Now their description is as follows:
Cooling: Machining operations create heat. This heat must be removed from the process. The chip helps carry away heat from the tool and work piece. Coolant takes heat from the chips tool, and work piece. To be effective the fluid must be able to transfer heat very rapidly. The fluid absorbs the heat and carries it away.
Lubrication: In a typical machining operation, two-thirds of the heat is created by the resistance of the work piece atoms to being sheared. The friction of the chip sliding over the cutting tool face creates the other one-third of the heat. Cutting fluid with good lubrication qualities can reduce the friction of the chip sliding over the tool face. The lubrication actually changes the shear angle, which reduces the shear path and produces a thinner chip. Good lubrication also reduces internal friction and heat through less molecular disturbance
Cutting fluid in CNC: Cutting fluid is used in CNC machines which is controlled using G and M codes
M08 code is used to start cutting fluid M09 code is used to end the cutting fluid
Different types of cooling used in CNC: Cryogenic Cooling: Cryogenic cooling using liquefied gases is one of the techniques used by many researchers to improve the machinability of different materials including titanium by reducing the cutting temperature and modifying the material properties of the workpiece and cutting tool. However despite the introduction of an industrial cryogenic milling system, in the context of machining of titanium, most cryogenic scientific studies are limited to turning operations. . These experiments showed that cryogenic cooling has resulted in 11% and 59% reduction in the surface roughness of the machined parts as compared to dry and wet conditions respectively whilst no major impact on the power consumption as a result of cryogenic cooling was recorded. In addition, the study of the cutting tools indicated that cryogenic cooling has significant potential to slow down the growth of tool wear resulting in longer tool life in comparison with conventional machining environments.
Minimum Quantity Lubrication (MQL): Minimum quantity lubrication has found its way into the area of metal cutting machining, and in many areas, has been established as an alternative to conventional wet processing. In contrast to flood lubrication MQL usesonly a few drops of lubrication (approx. 5ml to 50 ml per hour) in machining. Minimum quantity lubrication is a total-loss lubrication method rather than the circulated lubrication method used with emulsions. This means using new, clean lubricants that are fatty-alcohol or ester based. Costs generated by conventional flood lubrication (e.g. maintenance, inspection, preparation and disposal of metalworking fluids) are no longer an issue with minimum quantity lubrication.
Use of MQL: •
Reduction of metalworking fluid quantities in use
•
Decrease in the work required for monitoring and metalworking fluid maintenance
•
No need to prepare and dispose of used metalworking fluids
•
Decrease in the work required for cleaning the processed pieces
•
Easy recycling of the nearly dry chips due to less oil soiling.
Air Jet Assisted Turning: Air jet assisted turning presents an innovative method of lubricating and/or cooling the cutting zone during machining. Additional to cooling effect, air jet assisted turning is able to control friction conditions between cutting tool rake face and chip back side. This further offers control of chip breakability through forming a physical hydraulic effect between cutting tool rake face and chip back side, leading into improved machining performances . Advantages of assisted turning are: decreasing the cutting tool-chip contact length, resulting in lower cutting forces and longer tool-life drastic improvement of chip breakability extension of machining parameters operational ranges, resulting in increased process productivity through higher MRR.
High pressure cooling: Adding high pressure coolant to your machine tool is an easy way to increase production and cut manufacturing costs. The addition of high pressure coolant can increase productivity by allowing for increased feeds and speeds, it can improve workpiece quality by providing better surface finish and it can reduce manufacturing costs with longer insert and tool life. High pressure coolant can be very beneficial for almost any job on your CNC, some much more than others. The benefits of the high pressure coolant usually outweigh the initial cost when it comes to tooling savings, cycle time and finish. Tooling will last longer, speeds will be increased especially when drilling or boring. High pressure coolant will keep the part from heating up by transferring the heat into the coolant, away from the tool and part. Therefore, holding tighter tolerances, keeping your chips consistent and heat free.
