The Planning Function
Every part or product that has to be manufactured in the machine shop of the manufacturing company has to undergo through a series of machining operations in a proper sequence. The manufacturing process planning involves determining proper sequence of manufacturing operations to be carried out so that part can be produced in the least possible time making the optimum use of the available resources. To make the proper sequence the operations are documented on a form known as the route sheet. In the route sheet there is a list of the production operations and the machine tools that can carry out these operations on the part or the assembly.
Apart from process planning the manufacturing supervisor has to determine the appropriate cutting conditions for the machining operations, ensuring that there is least wastage of the material. Then the supervisor also sets the appropriate time for each machining operations so that the part can be manufactured within the stipulated time ensuring the optimum productivity.
Traditional Manufacturing Process Planning
All the three tasks: process planning, determining cutting conditions, and setting the time standards are routine ones for the production engineer and it mostly involves the clerical content. Among the different companies and the industries there are lots of variations in the format of the route sheet and the details found on it.
The whole process of planning is done in different way in different companies. In some companies the machinists are merely given the drawing and asked to complete the job. In some cases the manufacturing engineering gives detailed list of the steps of the machining operations and also mentioning the work center on which the operation has to be carried out.
It is the duty of the manufacturing engineer within the company to write the process plans for the new part designs to be manufactured in the machine shop. The process planning task is usually too much dependent on the experience and the judgment of the engineer working in the production shop since years.
Until recently, the whole process planning tasks were being done manually. However, the individual engineers have their own opinions about what constitutes the best routing for the manufacture of a job. Due to this there are differences in the sequence of the machining operations developed by different planners. But now the computers are being used for manufacturing planning tasks. The use of computers for process planning enables removing a number of problems associated with the manual process planning.
Computer Aided Process Planning
The use of computers for process planning is called as Computer Aided Process Planning or simply CAPP. With CAPP the routine clerical tasks of the manufacturing engineers are reduced, so they can invest their time in more productive tasks. Further, with computers it becomes easier to generate production routings that are rational, and consistent without depending on the experience or the judgment of the individuals.
There are two approaches for computer aided planning process: retrieval type CAPP systems and generative CAPP systems. Both these systems have been described below.
- 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.
Benefits of CAPP
Whether one is using the retrieval system or the generative system, there are number of benefits of CAPP as described below:
1) Process rationalization: In CAPP the same software carries out the process planning and its procedure remains the same whoever uses it. Thus the process planning becomes logical, consistent and rationalized as it does not depends on the individualistic experience or judgment.
2) Higher productivity of the process planners: With CAPP the amount of the clerical work is greatly reduced for the process engineers and there are fewer chances of errors. The planners can invest their time on more skilled jobs and also attain the better process plan that is eventually translated into their higher productivity.
3) Faster planning: With CAPP system the engineers can make the routing sheets for the jobs faster resulting in lesser lead times for the manufacturing process.
4) Good visibility: The documents made from the computer are neat, clean and clear, which makes reading the routing sheets easier.
5) Operate with other software: The CAPP software can be easily integrated with the other software like designing and manufacturing software. This makes the whole process of designing, planning and manufacturing an integrated process.
- Book: CAD/CAM: Computer-Aided Design and Manufacturing by Mikell P. Groover and Emory W. Zimmers, Jr. Published by Prentice-Hall of India Pvt. Ltd.