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 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 shown on the CRT graphically along with text instructions and warnings for each step.
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. 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.
Prior to CAPP, manufacturers attempted to overcome the problems of manual process planning by basic classification of parts into families and developing somewhat standardized process plans for parts families Stage I. A further step in this stage is dynamic, generative CAPP which would consider plant and machine capacities, tooling availability, work center and equipment loads, and equipment status e.
Generative Process Planning
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.
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.
Dynamic, generative CAPP also implies the need for online display of the process plan on a workorder oriented basis to insure that the appropriate process plan was provided to the floor. In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved: The variant process planning approach can be realized as a four step process; 1.
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.
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. 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.
Development of a standard process plan 4. 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.
However, variant CAPP is based on a Group Technology GT coding and classification approach to identify a larger number of part attributes or parameters. The planning begins with engineering drawings, specifications, parts or material lists and a forecast of demand. The similiarities in design attributes and manufacturing methods are exploited for the purpose of formation of part families.
Fabrication and assembly drawings to support manufacture as opposed to engineering drawings to define the part. 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.
Sometimes, the process plans are developed cqpp parts representing a fmily of parts called ‘master parts’. These attributes allow the system to select a baseline process plan for the part family and accomplish about ninety percent of the planning work.
Computer-Aided Process Planning
It includes selection of processes, machine tools, jigs or fixtures, tools, inspection equipments and sequencing operations. The first step is the implementation of GT or FT classification and coding.
Grouping parts into part families 3. While CAPP systems are moving more and more towards being generative, a pure generative system that can produce a complete process plan from part classification and other design data is a goal of the future. Further,this graphically-oriented data can then be provided to manufacturing in the form of hardcopy drawings or work instruction displays.
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.
Manufacturers have been pursuing an evolutionary path to improve and computerize process planning in the following five stages:. The planner will add the remaining ten percent of the effort modifying or fine-tuning the process plan. Computer Aided Process Planning.
Generativve 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. CAPP integrates and optimizes system performance into the inter-organizational flow. The initial challenge is in developing the GT classification and coding structure for the part families and in manually developing a standard baseline process plan for each part family.
Routings which specify operations, operation sequences, work centers, standards, tooling and fixtures. 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.
Significant benefits can result from the implementation of CAPP. The level of detail is much greater in a generative system than a variant system. 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.
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.
The results of the planning are:. 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
In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings benerative achieved:. Simple forms of generative planning systems may be driven by GT codes. In addition, there has been significant recent effort with generative process planning for assembly operations, including PCB assembly.
Process knowledge in form of in the form fapp decision logic and data matches the part geometry requirements with the manufacturing capabilities using knowledge base.
This is the function of CAPP.