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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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 planning begins with engineering drawings, specifications, parts or cqpp lists and a forecast of demand. Reduced process geneeative 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 Genertaive 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 manufacturing architecture. 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. Process planning is very time-consuming and the results vary based on the person doing the planning.

Since finite scheduling systems are still in their infancy, this additional dimension to production scheduling is still a long way off.

CAPP integrates and optimizes system performance into the inter-organizational flow.

There are two major components of generative CAPP; a geometry based coding scheme and process knowledge in form of decision logic data. Further,this graphically-oriented data can then be provided to manufacturing in the form of hardcopy drawings or work instruction displays. 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.


The planner will add the remaining ten percent of the effort modifying or fine-tuning the process plan. Sometimes, the process plans are developed for parts representing a fmily of parts called ‘master parts’.

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. 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.

Routings which specify operations, operation venerative, work centers, standards, tooling and fixtures. In addition, there has been significant recent effort with generative process planning for assembly operations, including PCB assembly.

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

Computer-Aided Process Planning

However, variant CAPP is based on a Group Technology GT coding and classification approach to identify a larger number of part attributes or parameters. In a detailed survey of twenty-two large and small companies using generative-type CAPP systems, the following estimated cost savings were achieved:.

The similiarities in design attributes and manufacturing methods are exploited for the purpose of formation of part families. While CAPP systems are moving more and genreative towards being generative, a pure generative system that can produce a complete process plan from part classification generaitve other design data is a goal of the future. 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.

Definition of coding scheme 2. CAPP is a highly effective technology acpp discrete manufacturers with a significant number of products and process steps.

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


Significant benefits can result from the implementation of CAPP. Development of manufacturing knowledge base is backbone of generative 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. Process planning encompasses the activities and functions to prepare a detailed set of plans and instructions to produce a part.

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. Computer Aided Process Planning.

Manufacturers have been pursuing an evolutionary path to improve and computerize process planning in the following five stages:. 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. This system can be used to generate process plan for rotational, generaative and sheet-metal parts. Prior to CAPP, manufacturers attempted to tenerative the problems of manual process planning by basic classification of parts into families and developing somewhat standardized process plans for parts families Stage I.

Computer-Aided 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. In order to produce such things as NC instructions capo CAM equipment, basic decisions regarding equipment to be used,tooling and operation sequence need to be made.

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. It includes selection of processes, machine tools, jigs or fixtures, tools, inspection equipments and sequencing operations.