Computer-Aided Process PlanningAccording to the Tool & Manufacturing Engineers Handbook, process planning is the systematic determination of the methods by which a product is to be manufactured economically and competitively. It essentially involves selection, calculation, and documentation. Processes, machines, tools, operations, and sequences must be selected. Such factors as feeds, speeds, tolerances, dimensions, and costs must be calculated. Finally, documents in the form of illustrated process sheets, operation sheets, and process routes must be prepared. Process planning is an intermediate stage between designing and manufacturing the product. But how well does it bridge design and manufacturing?Most manufacturing engineers would agree that, if ten different planners were asked to develop a process plan for the same part, they would probably come up with ten different plans. Obviously, all these plans cannot reflect the most efficient manufacturing methods, and, in fact, there is no guarantee that any one of them will constitute the optimum method for manufacturing the part.What may be even more disturbing is that a process plan developed for a part during a current manufacturing program may be quite different from the plan developed for the same or similar part during a previous manufacturing program and it may never be used again for the same or similar part. That represents a lot of wasted effort and produces a great many inconsistencies in routing, tooling, labor requirements, costing, and possibly even purchase requirements.Of course, process plans should not necessarily remain static. As lot sizes change and new technology, equipment, and processes become available, the most effective way to manufacture a particular part also changes, and those changes should be reflected in current process plans released to the shop.A planner must manage and retrieve a great deal of data and many documents，including established standards，mach inability data，machine specifications，tooling inventories，stock availability，and existing process plansThis is primarily an informationhandling job，and the computer is an ideal companionThere is another advantage to using computers to help with process planningBecause the task involves many interrelated activities，determining the optimum plan requires many iterations. Since computers can readily perform vast numbers of comparisons，many more alternative plans can be explored than would be possible manuallyA third advantage in the use of computer-aided process planning is uniformity. Several specific benefits Can be expected from the adoption of computer-aided processplanning techniques：1Reduced clerical effort in preparation of instructions2Fewer calculation errors due to human error3. Fewer oversights in logic or instructions because of the prompting capability available with interactive computer programs4Immediate access to uptodate information from a central database5Consistent information，because every planner accesses the same database6. Faster response to changes requested by engineers of other operating departments7Automatic Use of the latest revision of a part drawing8. Moredetailed，moreuniform process-plan statements produced by wordprocessing techniques.9Moreeffective use of inventories of tools，gages，and fixtures and a concomitant reduction in the variety of those items.10. Better communication with shop personnel because plans can be more specifically tailored to a particular task and presented in unambiguous，proven language.11. Better information for production planning, including cutter-life, forecasting, materials-requirements planning, scheduling, and inventory control.Most important for CIM, computer-aided process planning produces machine-readable data instead of handwritten plans. Such data can readily be transferred to other systems within the C1M hierarchy for use in planning.There are basically two approaches to computer-aided process planning: variant and generative.In the variant approach, a set of standard process plans is established for all the parts families that have been identified through group technology. The standard plans are stored in computer memory and retrieved for new parts according to their family identification. Again, GT helps to place the new part in an appropriate family. The standard plan is then edited to suit the specific requirements of a particular job.In the generative approach, an attempt is made to synthesize each individual plan using appropriate algorithms that define the various technological decisions that must be made in the course of manufacturing. In a truly generative process-planning system, the sequence of operations, as well as all the manufacturing-process parameters, would be automatically established without reference to prior plans. In its ultimate realization, such an approach would be universally applicable: present an