Comparison of Variant and Generative Process planning methods and their Computer Aided Process Planning Presented By- Pratik Patel. Approaches to Computer Aided Process Planning (CAPP). Variant Process Planning, Advantages and Disadvantages. Generative Process. The next stage of evolution is toward generative CAPP (Stage IV). At this stage, process planning decision rules are built into the system. These decision rules.
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The results of the planning are:. This system can be used to generate process plan for rotational, prismatic and sheet-metal parts. In order to produce such things as NC generaative for CAM equipment, basic decisions regarding equipment to be used,tooling and operation sequence need to be made.
For example, when one changes the design, it must be able to fall back on CAPP module to generate manufacturing process and cost estimates for these design changes.
In the generative Generatuve, process plans are generated by means of decision logic, formulas, technology algorithms and geometry based data to perform uniquely many processing decisions for converting part from raw material to finished state.
A second key to generative process planning is the available data related to the part to drive the planning.
This routing becomes a major input to the manufacturing resource planning system to define operations for production activity control purposes and define required resources for capacity requirements planning purposes.
CAPP integrates and optimizes system performance into the inter-organizational flow. As the design process is supported by many computer-aided tools, computer-aided process planning CAPP has evolved to simplify and improve process planning and achieve more effective use of manufacturing resources. The baseline process plans stored in the computer are manually entered using a super planner concept,that is, developing standardized plans based on the accumulated experience and knowledge of multiple planners and manufacturing engineers Stage III.
Module G:Computer Aided Process Planning
In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved:. The assembly is shown on the screen and as a employee steps through the assembly process with a footswitch, the components to be inserted or assembled are geneative on the CRT henerative along with text instructions and warnings for each step.
This approach would involve a user responding to a series of questions about a part that in essence capture the same information as in a GT or FT code. Computer Aided Process Planning. The variant process planning approach can be realized as a four step process; 1. This suggests a system in which design information is processed by the process planning system to generate manufacturing process details.
Generxtive comapred with manual experience-based process planning, CAPP offers following advantages; Systematic developemnt of accurate and consistent process plans Reduction of cost and lead time of process planning Geneeative skill requirements of process planners Increased productivity of process planners Higher level application progams such as cost and manufacturing lead time estimation and work standards can be interfaced.
Computer-Aided Process Planning
Process cpap is very time-consuming and the results vary based on the person doing the planning. This type of system uses work instruction displays at factory workstations to display process plans graphically and guide employees through assembly step by step.
Sometimes, the process plans are developed for parts representing a fmily of parts called ‘master parts’. Similarly, in case of machine breakdown on the shop floor, CAPP must generate the alternative actions so that most economical solution can be adopted in the given situation. This type of purely generative system in Stage V will involve the use of artificial intelligence type capabilities to produce process plans as well as be fully integrated in a CIM environment.
Development of a standard process plan 4.
This is the function of CAPP. Computer-aided process planning initially evolved as a means to electronically store a process plan once it was created, retrieve it, modify it ca;p a new part and print the plan Stage II.
Finally, this stage of CAPP would directly feed shop floor equipment controllers or, in a less automated environment,display assembly drawings online in conjunction with process plans. There are two major components of generative CAPP; a geometry yenerative coding scheme and process knowledge in form of decision logic data.
Process plans which typically provide more detailed,step-by-step work instructions including dimensions related to individual operations, machining parameters, set-up instructions, and quality assurance checkpoints.
Reduced process planning and production leadtime; faster response to engineering changes Greater process plan consistency; access to up-to-date information in a central database Improved cost estimating procedures and fewer calculation errors More complete and detailed process plans Improved production scheduling and capacity utilization Improved ability to introduce new manufacturing technology and rapidly update process plans to utilize the improved technology SUMMARY CAPP is a highly effective technology for discrete manufacturers with a significant number of products and process steps.
Development of manufacturing knowledge base is backbone of generative CAPP. Since finite scheduling systems are still in their infancy, this additional dimension to production scheduling is still a long way off. Routings which specify operations, operation sequences, work centers, standards, tooling and fixtures.
A typical CAPP frame-work is shown in figure Process planning translates design information into the process steps and instructions to efficiently and effectively manufacture products.
Generative Process Planning
The tools that are widely used in development of this database are flow-charts, decision tables, decision trees, iterative algorithms, concept of unit machined surfaces, pattern recognition techniques and artificial intelligence techniques such as expert system shells. Retrieval and modification of standard process plan A number of variant process planning schemes have been developed and are in use.
The system logic involved in establishing a variant process planning system is relatively straight forward — it is one of matching a code with a pre-established process plan maintained in the system.
Simple forms of generative planning systems may be driven by GT codes. The first key to implementing a generative system is the development of decision rules appropriate for the items to be processed.
Fabrication and assembly drawings to support manufacture as opposed to engineering drawings to define the part. In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved: Further,this graphically-oriented data can then be provided to manufacturing in the form of hardcopy drawings or work instruction displays.
CAD systems generate graphically oriented data and may go so far as graphically identifying metal, etc. The majority of generative CAPP systems implemented to date have focused on process planning for fabrication of sheet metal parts and less complex machined parts. Process knowledge in form of in the form of decision logic and data matches the part geometry requirements with the manufacturing capabilities using knowledge base. The results of the planning are: A number of methods have been developed for part family formation using coding and classification schemes of group technology GTsimiliarity-coefficient based algorithms and mathematical programming models.
When a new part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped. Significant benefits can result from the implementation of CAPP. For example, if a primary work center for an operation s was overloaded, the generative planning process would evaluate work to be released involving that work center,alternate processes and the related routings.