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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 dapp 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 suggests a system in which design information is processed by the process planning system to generate manufacturing process details. Definition of coding scheme 2. 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. Process planning translates design information into the process steps and instructions to efficiently and effectively manufacture products.

The planner will add the remaining ten percent of the effort modifying or fine-tuning the process plan. CAPP is a highly effective technology for discrete manufacturers with a significant number of products and process steps. Rapid strides are being made to develop generative planning capabilities and incorporate CAPP into a computer-integrated genrative architecture.

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.

In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved: At this stage, process planning decision rules are built into the system.

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 first step is the implementation of GT or FT classification and coding. Manufacturers have been pursuing an evolutionary path to improve and computerize process planning in the following five stages:.

CAD systems generate graphically oriented data and may go so far as graphically identifying metal, etc. Computer Aided Process Planning. Sometimes, the process plans are developed for parts representing a fmily of parts called ‘master parts’. In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved:.

Computer-Aided Process Planning

Process planning is very time-consuming and the results vary based on the person doing 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 nature of the parts will affect the complexity of the decision rules generattive generative planning and ultimately the degree of success in implementing the generative CAPP system.


Simple forms of generative planning systems may be driven by GT codes. 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 cpap.

Process planning encompasses the activities and functions to prepare a detailed set of plans and instructions to produce a part. Fabrication and assembly drawings to support manufacture as opposed to engineering genegative to define the generaitve. Significant benefits can result from the implementation of CAPP. 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.

In the generative CAPP, process plans are generated by means of decision logic, formulas, technology algorithms gejerative geometry based data to perform generativw many processing decisions henerative converting part from raw material to finished state.

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

The results of the planning are:. 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. This type of system uses work instruction displays at factory workstations to display process plans graphically and guide employees through assembly step by step.

Retrieval and modification of standard process plan A number of variant process planning schemes have been developed and are in use. This approach would involve a user cappp to a series of questions about a part that in essence capture the same information as in a GT or FT code.

Module G:Computer Aided Process Planning

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. 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.

There are two major components of generative CAPP; a geometry based coding scheme and process knowledge in form of decision logic data. A second key to generative process planning is the available data related to the part to drive the planning. 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.


Development of a standard process plan 4. The first key to implementing a generative system is the development of decision rules appropriate for the items to be processed. 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. This is the function of CAPP. 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.

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.

When a new part was introduced, the process plan for that family would be manually retrieved, marked-up and retyped.

Development of manufacturing knowledge base is backbone of generative CAPP. The variant process planning approach can be realized as a four step process; 1. The decision rules would result in process plans that fenerative reduce the overloading on the primary work center by using an alternate routing that would have the least cost impact. In addition, there has been significant recent effort with generative process planning for assembly operations, including PCB assembly.

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.

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. 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. 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.

A typical Generatife frame-work is shown generativw figure A further step in this gneerative is dynamic, generative CAPP which would consider plant and machine capacities, tooling availability, work center and equipment loads, and equipment status e.