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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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. Simple forms of generative planning systems may be driven by GT codes. While CAPP systems are moving more and more towards being generative, a pure generative system that can produce a complete czpp plan from part classification and other design data is a goal of the future.

The results of the planning are:. 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 czpp manufacturing resources. Process planning encompasses the activities and functions to prepare a detailed set of plans and instructions to produce a part.

Retrieval and modification of standard process plan A number of variant process planning schemes have been cap and are in use.

There are two major components of generative CAPP; a geometry based coding scheme and process knowledge in form of decision logic data. In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved:.

The planning begins with engineering drawings, specifications, parts or material lists and a forecast of demand. This system can be used to generate process plan for rotational, yenerative and sheet-metal parts.

Module G:Computer Aided Process Planning

The process plan developed with a CAPP system at Stage V would vary over time depending on the resources and workload in the factory.

A typical CAPP frame-work is shown in figure Finally, this stage of CAPP would directly feed shop floor equipment controllers or, czpp a less automated environment,display assembly drawings online in conjunction with process plans.


Computer Aided Process Planning. Development of manufacturing knowledge base is backbone of generative CAPP. The tools that are widely used in development of this database are flow-charts, decision tables, decision trees, iterative algorithms, concept generatlve unit machined surfaces, pattern recognition techniques and artificial intelligence techniques such as expert system shells.

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. While this improved productivity, it did not improve the quality of the planning of processes and it did not easily take into account the differences between parts in a family nor improvements in production processes. When 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 Reduced 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.

However, variant CAPP is based on a Group Technology GT coding and classification approach to identify a larger number of part attributes or parameters. Since finite scheduling systems are still in their infancy, this additional dimension to production scheduling is still a long way off. Grouping parts into part families 3.

Computer-Aided Process Planning

Routings which specify operations, operation sequences, work centers, standards, tooling and fixtures. At this stage, process planning decision rules are built into the system. Development of a standard process plan 4. Further,this graphically-oriented data can then be provided to manufacturing in the form of hardcopy drawings or work instruction displays. Rapid strides are being made to develop generative planning capabilities and incorporate CAPP into a computer-integrated manufacturing architecture.

For example, details such as rough and finished states of the parts and process capability of machine tools to transform these parts to the desired states are provided. In the generative CAPP, 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.


Generative Process Planning

These attributes allow the system to select a baseline process plan for the part family and accomplish about ninety percent of the planning work. 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 similiarities in design attributes and manufacturing methods are exploited for the purpose of formation of part families. The results of the planning are: Tight integration with a manufacturing resource planning system is needed to track shop floor status and load data and assess alternate routings vis-a-vis the schedule.

Significant benefits can result from the implementation of CAPP. Process planning translates design information into the process steps and instructions to efficiently and effectively manufacture products.

Computer-aided process planning initially evolved as a means to electronically store a process plan once it was created, retrieve it, modify it for a new part generatiev print the plan Stage II.

This suggests a system in which design information is cappp by the process planning system to generate manufacturing process details. This approach would involve a user responding to a series of questions about a part that czpp essence capture the same information as in a GT or FT code. The nature of the parts will affect the complexity generativd the decision rules for generative planning and ultimately the degree of success in implementing the generative CAPP system.

The first step is the implementation of GT or FT classification and coding. Process plans which typically provide more detailed,step-by-step work instructions including dimensions related generativ individual operations, machining parameters, set-up instructions, and quality assurance checkpoints.

In order to produce such things as NC instructions for CAM equipment, basic decisions regarding equipment to be used,tooling and operation sequence need to be made. When a new part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped. This is the function of CAPP. It includes selection of processes, machine tools, jigs or fixtures, tools, inspection equipments and sequencing operations.