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 majority of generative CAPP systems implemented to date have focused on process planning for fabrication of sheet metal parts and less complex machined parts. A second key to generative process planning is the available data related to the part to drive the 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.
The planner will add the remaining ten percent of the effort modifying or fine-tuning the process plan. Manufacturers have been pursuing an evolutionary path to improve and computerize process planning in the following five stages:.
However, variant CAPP is based on a Group Technology GT coding and classification approach to identify a larger number 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.
Process planning translates design information into the process steps and instructions fenerative efficiently and effectively manufacture products. While CAPP systems are moving more and more towards being generative, a pure generative system cqpp can produce a complete process plan from fenerative classification and other design data is a goal of the future.
Rapid strides are being made to develop generative planning capabilities and incorporate CAPP into a computer-integrated manufacturing architecture. 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.
Definition of coding scheme 2. Tight integration with a manufacturing resource planning system is needed to track shop floor status and load data and assess alternate cwpp vis-a-vis the schedule. 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.
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 generrative highly capl technology for discrete manufacturers with a significant number of products and process steps.
CAPP integrates and optimizes system performance into the inter-organizational flow.
Generative Process Planning
The decision rules would result in process plans that would reduce the overloading on the primary work center by using an alternate routing that would have the least cost impact.
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.
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 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.
When a caapp part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped. 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. 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 cappp family.
In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved:. The baseline process plans stored in the computer are manually genfrative 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. At this stage, process planning decision rules are built into the gneerative.
Dynamic, generative CAPP geneartive 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. While this improved productivity, it did not improve the quality of the planning of processes geneartive it did not easily take into account the differences between parts in a family nor improvements in production processes. The first key to implementing a generative system is the development geenerative decision rules appropriate for the items to be processed.
Sometimes, the process plans are developed for parts representing a fmily of parts called ‘master parts’.
Simple forms of generative planning systems may be generativr by GT codes. CAPP is a highly effective technology for discrete manufacturers with a significant number of products and process steps. 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. The nature of genefative parts will affect the complexity of the decision rules for generative planning and ultimately the degree of success in implementing the generative CAPP system.
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. Process planning is very time-consuming and the results vary based on the person doing the planning. 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 generativee more effective use of manufacturing resources.
The system logic involved in establishing a variant process planning system gemerative relatively straight forward — it is one of matching a code with a pre-established process plan maintained in the system.
Computer-Aided Process Planning
Retrieval and modification of standard process plan A number of variant process planning schemes have been developed and are in use. 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. This is the function of CAPP. Development of a standard process plan 4. Development of manufacturing knowledge base is backbone of generative CAPP.
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 and print the plan Stage II. 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.
Further,this graphically-oriented data can then be provided to manufacturing in the form of hardcopy drawings or work instruction displays. Significant benefits can result from the implementation of CAPP. Other capabilities of this stage are table-driven cost and standard estimating systems.
The level of detail is much greater in a generative system than a variant system. The results of the planning are:. 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.
Module G:Computer Aided Process Planning
This system can be used to generate process plan for rotational, prismatic and sheet-metal parts. Similarly, in case of machine breakdown on the shop floor, CAPP must generate the alternative actions gnerative that most economical solution can be adopted in the given situation. The results of the planning are: