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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CAD systems generate graphically oriented data and may go so far as graphically identifying metal, etc.
Fabrication and assembly drawings to support manufacture as opposed to engineering drawings to define the part. The variant process planning approach can be realized as a four step process; 1.
It includes selection of processes, machine tools, jigs or fixtures, tools, inspection equipments and sequencing operations.
Computer-Aided Process Planning
Similarly, in case of machine breakdown generstive the shop floor, CAPP must generate the alternative actions so that most economical solution can be adopted in the given situation.
The first key to implementing a generative system is the development of decision rules appropriate for the items to be processed. 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.
Finally, this stage of CAPP would directly ccapp shop floor equipment controllers or, in a less automated environment,display assembly drawings online in conjunction with process plans.
The results of the planning are: Grouping parts into part families 3. Simple forms of generative planning systems may be driven by GT codes. CAPP integrates and optimizes system performance into the inter-organizational flow. However, variant CAPP is based on a Group Technology GT coding and classification calp to identify a larger number of part attributes or parameters.
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. 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 nature of the parts will affect the complexity of the decision rules for generative planning and ultimately the degree of success in implementing the generative CAPP system. Rapid strides are being made to develop generative planning capabilities and incorporate CAPP into a computer-integrated manufacturing architecture.
Process planning encompasses the activities and functions to prepare a detailed set of plans and instructions to produce a part. 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.
Development of manufacturing knowledge base is backbone of generative CAPP. This is the function of CAPP.
Computer-Aided Process Planning
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.
The geometry based coding scheme defines all geometric features for process related surfaces together with feature dimensions, locations, tolerances and the surface finish desired on the features. Since finite scheduling systems are still in their infancy, this additional dimension to production scheduling is still a long way off. 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.
CAPP is a highly effective technology for discrete manufacturers with a significant number of products and process steps.
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. Dynamic, generative CAPP also implies the need generatiive online display of the process plan on a workorder oriented basis to insure that the appropriate process plan was provided to the floor.
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 henerative the related routings. When a new part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped.
A second key to generative process planning is the available data related to the part to drive the planning. 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 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.
The baseline process plans stored in the computer generativf 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. This type of system uses work instruction displays at factory workstations to display process plans graphically and guide employees through assembly step by step.