Mumbai University > Mechanical Engineering > Sem 7 > Production planning and control

Marks: 5M

Year: May 2016

Computer-aided process planning (CAPP) is the use of computer technology to aid in the process planning of a part or product, in manufacturing. CAPP is the link between CAD and CAM in that it provides for the planning of the process to be used in producing a designed part.

• Computer-aided process planning (CAPP) helps determine the processing steps required to make a part after CAP has been used to define what is to be made.
• CAPP programs develop a process plan or route sheet by following either a variant or a generative approach.
• The variant approach uses a file of standard process plans to retrieve the best plan in the file after reviewing the design. The plan can then be revised manually if it is not totally appropriate.
• The generative approach to CAPP starts with the product design specifications and can generate a detailed process plan complete with machine settings.
• CAPP systems use design algorithms, a file of machine characteristics, and decision logic to build the plans.
• Expert systems are based on decision rules and have been used in some generative CAPP systems.

Retrieval Type Process Planning System or CAPP System

In the retrieval type of CAPP system the various parts to be manufactured are classified, given codes and grouped within certain families.

• Within each part family standard process plan is established, which is stored in the computer. This process plan is also used for the new parts that come under the same family.
• The system developed is such that it is easier to retrieve the process plans for the new work parts. The whole process plan documents the operations as well as the sequence of operations on different machines.
• The retrieval CAPP system offers lots of flexibility as one can do lots of editing and changes as per the requirements.

Generative Process Planning Systems or CAPP Systems

In the generative process planning systems new plan is made automatically from scratch for each part using the computers, without involving human assistance.

• The computer program uses a set of algorithms that enables it to take a number of technical and logical decisions to attain the optimum final manufacturing process plan.
• One has to give certain inputs to the systems like detailed description of the part to be manufactured.
• This CAPP system synthesizes the design of the optimum process sequence based on the analysis of the part geometry, material and other relevant parameters.

Advantages Over Manual Experience-based Process Planning

The uses of computers in process plan have following advantages over manual experience-based process planning:

• It can systematically produce accurate and consistent process plans.
• It leads to the reduction of cost and lead times of process plan.
• Skill requirement of process planer are reduced to develop feasible process plan.
• Interfacing of software for cost, manufacturing lead time estimation, and work standards can easily be done.
• Leads to the increased productivity of process planar.

Steps Involved in CAPP

Now-a-days, rapid progress is being made in the automation of actual production

process and also the product design element. However, the interface between design and production presents the greatest difficulty in accomplishing integration.

CAPP has the potential to achieve this integration. In general, a complete CAPP

system has following steps :

• Design input
• Material selection
• Process selection
• Process sequencing
• Machine and tool selection
• Intermediate surface determination
• Fixture selection
• Machining parameter selection
• Cost/time estimation
• Plan preparation
• Mc tape image generation.