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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Process planning encompasses the activities and functions to prepare a detailed set of plans and instructions to produce a part.
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 system can be used to generate process plan for rotational, prismatic and sheet-metal parts. Definition of coding genetative 2. This suggests a system in which design information is processed by the process planning system to generate manufacturing process details.
Computer-Aided Process Planning
Fabrication and assembly drawings to support manufacture as opposed to engineering drawings to define the part. The results of the planning are: However, variant CAPP is based on a Group Technology GT coding and classification approach to identify a larger generativw of part attributes or parameters.
This type of system uses work instruction displays at factory workstations to display process plans graphically and guide employees through assembly step by step.
Since finite scheduling systems are still in their infancy, this additional dimension to production scheduling is still a long way off. CAD systems generate graphically oriented data and may go so far as graphically identifying metal, etc.
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. 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.
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.
The first step is the implementation of GT or FT classification and coding. 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. 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.
Retrieval and modification of standard process plan A number of variant cap planning schemes have been developed and are in use. This is the function of CAPP.
When a new part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped. 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.
CAPP is a highly effective technology for discrete manufacturers with a significant number of products and process steps. Routings which specify operations, operation sequences, work centers, standards, tooling and fixtures.
At this stage, process planning decision rules are built into the system. A typical CAPP frame-work is shown in figure Significant benefits can result from the implementation of CAPP. 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.
In addition, there has been significant recent effort with generative process planning for assembly operations, including PCB assembly. 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.
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.
Computer-Aided 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.
Process planning translates design information ccapp the process steps and instructions to efficiently and effectively manufacture products. Process planning is very time-consuming and the results vary based on the person doing the planning.
Process plans which typically provide more detailed,step-by-step work instructions including dimensions related gennerative individual operations, machining parameters, set-up instructions, and quality assurance checkpoints.
A second key to generative process planning is the available data related to the part to drive the 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.
The similiarities in design attributes and manufacturing methods are exploited for the purpose of formation of part families. Sometimes, the process plans are developed for parts representing generrative fmily of parts called ‘master parts’. The majority of generative CAPP systems implemented to date have focused on process geberative for fabrication of sheet metal parts and less complex machined parts.