CAM MISSING NOTES BOOK- (M.P Groover)
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OVER VIEW OF AUTOMATION IN INDUSTRY:
Some elements of the firm's production system are likely to be automated, whereas others will be operated manually or clerically. f-or our purposes here, automation can be defined as a technology concerned with the application of mechanical, electronic, and computer-based systems 10 operate and control production. The automated elements of the production system can be separated into two categories: (1) automation of the manufacturing systems in the factory and (2) computerization of the manufacturing support systems. In modern production systems, the two categories overlap to some extent because the automated manufacturing systems operating on the factory floor are themselves often implemented by computer systems and connected to the computerized manufacturing support systems and management information system operating at the plant and enterprise levels. The term computer-integrated manufacturing issued to indicate this extensive use of computers in production systems. The two categories of automation are shown in Figure 1.6 as an overlay on Figure 1.1.
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TYPES OF PRODUCTION: o Job Production:
To produce a variety of jobs within a group in a limited quantity only, by group we mean the type of machinery setup. It uses general purpose machines so that variety of jobs could be made; use of tools, jigs, fixtures is very common. No prior planning is possible. Skilled man power is required to work on different jobs and depend more on skill of workers.
o Batch production:
Batch of an object is processed in a sequence of steps. Each step may possess a single machine or a multiple machine. Garment manufacturers, threading operations, sheet metal jobs, forging, book parts, paints, vegetable oil etc. Most common type of production. A batch of objects (of specified sizes) is produced. Division of labor is possible.
o Mass production:
Computers, mobile phones, automobiles, soft drinks, pharmacy products etc. Specialized (SPM) are used. Involve heavy fixed cost/modern plants. Little material handling. Plant layout is designed well.
o Continuous Production:
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Plant layout/process equipment is different from manufacturing unit. Safety parameters have to be high. Semi-skilled/skilled workers are employed. Material handling is automatic. Via buckets, trolleys, belt conveyers, pipelines etc.
AUTOMATION ACHIEVEMENTS: Automation is the technology by which a process or procedure is accomplished without human assistance. It is implemented using a program of instructions combined with a control system that executes the instructions, to automate a process power is required, both to drive the process itself and to operate the program and control system. Although automation can be applied in a wide variety of areas, it is most closely associated with the manufacturing industries. It was in the context of manufacturing that the term was originally coined by an engineering manager at Ford Motor Company in 1946 to describe the variety of automatic transfer devices and feed mechanisms that had been installed in Ford's production plants (Historical Note 3.1), It is ironic that nearly all modern applications of automation are controlled by computer technologies that were not available in 1946.
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AUTOMATION PRINCIPLES & STRATEGIES: o USA Principle:
The USA Principle is a common sense approach to automation projects. Similar procedures have been suggested in the manufacturing and automation trade literature, but none has a more captivating title than this one. USA stands for' 1. Understand the existing process 2. Simplify the process 3. Automate the process. The article was concerned with implementation of enterprise resource planning (ERP, Section 26.6), but the USA approach is '0 general that it is applicable to nearly any automation project. Going through each step of the procedure for an automation project may in fact reveal that simplifying the process is sufficient and automation is not necessary. Understand the Existing Process. The obvious purpose of the first step in • the USA approach is to comprehend the current process in all of its details. What arc the inputs? What are the outputs? What exactly happens to the work unit between input and output? What is the function of the process? How does it add value to the product? What are the upstream and downstream operations in the production sequence, and can they be combined with the process under consideration? • Simplify the Process. Once the existing process is understood, then the search can begin for ways to simplify. This often involves a checklist of Questions about the existing process. What is the purpose of this step or this transport? Is this step necessary? Can this step be eliminated? Is the most appropriate technology being used in this step? How can this step be simplified? Are there. Unnecessary steps in the process that might be eliminated without detracting from function? Some of the ten strategies at automation and production systems (Section 1.5.2) are applicable to try to simplify the process. Can steps be combined? Can steps be performed simultaneously? Can steps be integrated into a manually operated production line? • Automate the Process. Once the process has been reduced to its simplest form, then automation can be considered. The possible forms of automation include those listed in the ten strategies discussed in the
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following section. An automation migration strategy (Section 1.5.3) might be implemented for a new product that has not yet proven itself.
o Ten Automation Strategies:
Following the USA Principle is a good first step in any automation project. As suggested previously, it may turn out that automation of the process is unnecessary or cannot be cost justified after it has been simplified. If automation seems a feasible solution to improving productivity, quality, or other measure of performance, then the following ten strategies provide a road map to search for these improvements. 1. Speciattzauon of operations , The first strategy involves the use of special-purpose equipment designed to perform one operation with the greatest possible efficiency. This is analogous to the concept of labor specialization, which is employed to improve labor productivity. 2. Combined operations. Production occurs as a sequence of operations. Complex parts may require dozens, or even hundreds, of processing steps. The strategy of combined operations involves .reducing the number of distinct production machines or workstations through which the part must be routed. This is accomplished by performing more than one operation at a given machine, thereby reducing the number of separate machines needed. Since each machine typically involves a setup, setup time can usually be saved as a consequence of this strategy. Material handling effort and non-operation time are also reduced. Manufacturing lead time is reduced for better customer service. 3. Simultaneous operations. A logical extension of the combined operations strategy is to simultaneously perform the operations that are combined at one workstation. In effect, two or more processing (or assembly) operations are being performed simultaneously on the same work part. Thus, reducing total processing time. 4. Integration of operations. Another strategy is to link several workstations together into a single integrated mechanism, using automated work handling devices to transfer parts between stations. In effect, this reduces the number of separate machines through which the product must be scheduled. With more than one workstation. Several parts can be processed simultaneously, thereby increasing the overall output of the system. 5. Increased flexibility . This strategy attempts to achieve maximum utilization of equipment for job shop and medium-volume situations by using the same equipment for a variety of parts or products, It involves the use of the flexible automation concepts (Section 1.3.1). Prime objectives are to reduce setup time and programming time for the production machine. This normally translates into lower manufacturing lead time and less work-in-process. 6. Improved material handling and storage. A great opportunity for reducing non-productive time exists in the use of automated material handling and storage systems. Typical benefits include reduced work-inprocess and shorter manufacturing lead times.
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7. On-line inspection , Inspection for quality of work is traditionally performed after the process is completed. This means that any poorquality product has already been produced by the time it is inspected. Incorporating inspection into the manufacturing process permits corrections to the process as the product is being made. This reduces scrap and brings the overall quality of the product closer to the nominal specifications intended by the designer. 8. Process control and optimization. This includes a wide range of control schemes intended to operate the individual processes and associated equipment more efficiently. By this strategy, the individual process times can be reduced and product quality improved. 9. Plant operations control . Whereas the previous strategy was concerned with the control of the individual manufacturing process, this strategy is concerned with control at the plant level. It attempts to manage and coordinate the aggregate operations in the plant more efficiently. Its implementation usually involves a high level of computer networking within the factory. 10. Computer-integrated manufacturing (CIM). Taking the previous strategy one level higher. We have the integration of factory operations with engineering design and the business functions of the firm; CIM involves extensive use of computer applications, computer data bases, and computer networking throughout the enterprise.
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CAD/CAM IN DIFFERENT AREAS OF OPERATION: CAD/CAM is concerned with the engineering functions in both design and manufacturing. Product design, engineering analysis, and documentation of the design (e.g. drafting) represent engineering activities in design. Process planning, NC part programming, and other activities associated with CAM represent engineering activities in manufacturing. The CAD/CAM systems developed during the 1970s and early 1980s were designed primarily to address these types of engineering problems. In addition, CAM has evolved to include many other functions in manufacturing, such as material requirements planning, production scheduling, computer production monitoring, and computer process control. It should also be noted that CAD/CAM denotes an integration of design and manufacturing activities by means of computer systems. The method of manufacturing a product is a direct function of its design. With conventional procedures practiced for so many years in industry, engineering drawings were prepared by design draftsmen and later used by manufacturing engineers to develop the process plan. The activities involved in designing the product were separated from the activities associated with process planning. Essentially, two-step procedure was employed. This was time-consuming and involved duplication of effort by design and manufacturing personnel. Using CAD/CAM technology, it is possible to establish a direct link between product design and manufacturing engineering. In effect, CAD/CAM is one of the enabling technologies for concurrent engineering. It is the goal of CAD/CAM not only to automate certain phases of design and certain phases of manufacturing, but also to automate the transition from design to manufacturing. In the ideal CAD/CAM system, it is possible to take the design specification of the product as it resides in the CAD
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data base and convert it into a process plan for making the product, this conversion. being done automatically by the CAD/CAM system. A large portion of the processing might be accomplished on a numerically controlled machine tool. As part of the process plan, the NC part program is generated automatically by CAD/CAM; The CAD/CAM system downloads the NC program directly to the machine tool by means of a telecommunications network. Hence, under this arrangement, product design, NC programming, and physical production are all implemented by computer.
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MOTION CONTROL SYSTEMS: o
Some NC processes are performed at discrete locations on the work part (e.g., drilling and spot welding). Others are carried out while the work head is moving (e.g., turning and continuous arc welding). If the work head is moving, it may be required to follow a straight line path or a circular or other curvilinear path. These different types of movement are accomplished by the motion control system, whose features are explained below. Point-to-Point versus Continuous Path Control. Motion control systems for NC can be divided into two types: (1) pointto-point and (2) continuous path. Point-to point systems , also called positioning systems, move the worktable to a programmed location without regard for the path taken to get to that location. Once the move has been completed, some processing action is accomplished by the work head at the location. Such as dril ling or punching a hole. Thus, the program consists of a series of point locations at which operations are performed, as depicted in Figure 6.3.
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Continuous path systems generally refer to systems that are capable of continuous simultaneous control of two or more axes. This provides control of the tool trajectory relative to the work part. In this case, the tool performs the process while the worktable is moving, thus enabling the system to generate angular surfaces, two-dimensional curves, or three-dimensional contours in the work part. This control mode is required in many milling and turning operations. A simple twodimensional profile milling operation is shown in Figure 6.4 to illustrate continuous path control. When continuous path control is utilized to move the tool parallel to only one of the major axes of the machine tool worktable, this is called straight-cut NC. When continuous path control is used for simultaneous control of two or more axes in machining operations, the term contouring is used.
APPLICATIONS OF NC IN METAL CUTTING: o
Machining is a manufacturing process in which the geometry of the work is produced
by removing excess material. By controlling the relative motion between a cutting tool and the work piece, the desired geometry is created. Machining is considered one of the most versatile processes because it can be used to create a wide variety of shapes and surface finishes. It can be performed at relatively hi gh production rates to yield highly accurate parts at relatively low cost. There are four common types of machining operations: (a) turning, (b) drilling, (c) milling, and (d) grinding. Use of NC is widely in the below four metal cutting processes.
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APPLICATIONS OF NC IN NON-METAL CUTTING: o
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Electrical wire, wrap machines. These machines, pioneered by Gardner Denver Corporation, have been used to wrap and string wires on the back pins of electrical wiring boards to establish connections between components on the front of the board. The program of coordinate positions that define the back panel connections is determined from design data and fed to the wire wrap machine. This type of equipment has been used by computer firms and other companies in the electronics industry. Component insertion machines. This equipment is used to position and insert components on an x-y plane, usually a flat hoard or panel. The program specifics the x and y-axis positions in the plane where the components are to be located. Component insertion machines find extensive applications for inserting electronic components into printed circuit boards. Machines are available for either. Throughhole or surfaces mount applications as well as similar Insertion-type mechanical assembly operations. Drafting machine. Automated drafting machines serve as one of the output devices for a CAD/CAM [computer-aided design/computer-aided manufacturing) system. The design of a product and its components are developed on the CAD/CAM system. Design iterations arc developed on the graphics monitor rather than on a mechanical drafting board. When the design is sufficiently finalized for presentation, the output is plotted on the drafting machine, basically a high speed x-y plotter.
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Coordinate measuring machine. A coordinate measuring machine (CMM) is an inspection machine used for measuring or checking dimensions of a part. The CMM has a probe that can be manipulated in three axes and Identifies when contact IS made against a pan surface. The location of the probe tip is determined by the CMM control unit. Thereby indicating some dimension on the part. Many coordinate measuring machines are programmed to perform automated inspections under NC. Tape laying machines for polymer composites. The work head of this machine is a
dispenser of uncured polymer matrix composite tape. The machine is programmed to lay the tape onto the surface of a contoured mold, following a back-and-forth and crisscross pattern to build up a required thickness. The result is a multilayered panel of the same shape as the mold. o
Filament winding machines for polymer composites. This is similar to the preceding
except that a filament is dipped in uncured polymer and wrapped around a rotating pattern of roughly cylindrical shape. UNIT-3 -
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PREPARATORY G-CODES, MISCELLANOUS M-FUNC CODES, COMMON WORD PREFIXES.
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