1. COMPUTER AIDED PROCESS PLANNING
(CAPP)

2. Introduction
• Process planning is concerned with determining the sequence of individual
manufacturing operations needed to produce a given part or product.
• The resulting operation sequence is documented on a form referred to as
route sheet.
• The route sheet is a listing of the production operations and associated
machine tools for a work part or assembly.
• Computer-aided process planning (CAPP) is the application of the
computer to assist process planners in the planning functions.
• It is considered as the key technology for computer-aided design (CAD) and
computer aided manufacturing (CAM) integration.

4. Roles of CAPP in Manufacturing
• Used to develop a product manufacturing plan based on projected
variables such as cost, lead times, equipment availability, production
volumes, potential material substitution routings and testing
requirements.
• CAPP is a decision-making process, it determines a set of instruction
and machining parameters required to manufacture a part.
• Integrates and optimizes system performance for every
product/component to ensure functionality aspect and design
specifications meet requirements.

5. CAPP Model

6. CAPP Approaches
•The main two CAPP approaches are:
i. Variant (retrieval) approach and
ii. Generative approach

7. Variant (retrieval) Approach
• In variant CAPP system, a process plant for a new part is created by
identifying and retrieving an existing process plan for a part. The
existing process plan in examined, modified to make it compatible to
the new part to adopted it to the new part.
• The variant CAPP system is based on group technology (GT) classified
and coding approach.

8. Variant (retrieval) Approach

9. Advantages of Variant CAPP Approach
• In this system, the process plan are readily available, which can be
retrieved and edited in short time.
• As large database is available, the new process plan can be develop in
short time duration.
• The system reduces manpower requirement.
• Structuring manufacturing knowledge of the process plans to
company’s needs through standardized procedures.

10. Limitation of Variant CAPP Approach
• The quality of process plan depends upon the knowledge and
background of a process planning engineer.
• High initial investment is required in acquiring hardware and
software.
• High level skilled manpower is required to work on the system.
• It is difficult to maintain consistency during editing.
• The quality of the final process plan largely depends on the
knowledge and experience of process planner. The dependency on
process planner is one of the major shortcomings of variant process
planning

11. Generative CAPP Approach
• Generative CAPP system is an automated approach to the process
planning.
• Unlike the variant CAPP system, the generative CAPP system does not
require the assistance from the user to generate the process plan.

12. Major Components of Generative Approach
Geometry description and coding component:
• This defines all geometric features for process related surfaces together with
feature dimensions, locations, tolerances and the surface finish desired on
the features.
• The level of detail is much greater in a generative system than a variant
system.
Process knowledge database & decision making logic:
• The knowledge will be in the form of decision logic.
• It is required to match the part geometry requirement with manufacturing
capability using decision logic and data.
• It includes selection of processes, manufacturing equipment's, work holding
devices, jigs & fixtures and inspection instruments.

13. Generative CAPP Approach

14. Advantages Generative CAPP Approach
• It is fully automated system and up-to-dated process plan is
generated, each time a part is ordered.
• In graphic input format, even it is not required to input data. The
system can be directly interface with the CAD model.
• For operation, system does not require skilled manpower.
• They rely less on group technology code numbers since the process,
usually uses decision tree to categorize parts into families.
• Maintenance and updating of stored process plans are largely
unnecessary.

15. Limitation of Generative CAPP Approach
• High end hardware and software set-up is required by the generative
CAPP system.
• The generative CAPP system requires major revision in design logic, if
new equipment or process capabilities become available.
• In case of generative CAPP, the development of a tailor made system
of specific industry is a formidable task.

16. Conclusion
CAPP is a highly effective technology for discrete manufacturers with a
significant number of products and process steps. Commercially
available software tools currently exist to support both GT and CAPP.
As a result, many companies can achieve the benefits of GT and CAPP
with minimum cost and risks. Effective use of these tools can improve
a manufacturer’s competitive advantage too.