Concept of Computer Aided Part Programming

We have seen the manual part programming methods for machining centers and turning centers. The facilities available within them are capable of preparing the part programs practically for any type of job. However, the effort and time needed will start increasing with the complexity of the job. It is possible that it may reach a point where it may be almost impossible to do it manually.

This is the point where computer aided part programming becomes very handy. The use of computer to do a large amount of manual calculations that are needed for writing a part program not only improves the accuracy but also provides a greater amount of reliability to the program. The computer also can help in the proving of the part program without really having to go and carryout an actual dry run on the machine tool. Also the same part programming system can be used for all machine tools, while in the case of manual procedure one has to learn each machine tool programming procedure separately though there is a large amount of commonality between them.

The computer aided part programming systems generally rely on a single programming system to take care of all the varieties of machine tools that are likely to be programmed using the system. How are the differences between the machine tools taken care of in a single programming system? This is done by following a two pass system. In the first pass the input commands of the user are converted into the tool center data or CLDATA, as is generally called, which is based purely on the geometry of the part and can be used to prove the geometrical correctness of the part program. This is the most difficult part and requires sizable complexity in the programming system. The output of this pass is then sent through the second pass termed as postprocessor that will generate the actual part program blocks that directly run on the actual CNC machine tool.

As a result, the postprocessor part of the part programming system will have all the machine tool specific functions taken care of as follows:

1. Converting the CLDATA to the actual CNC control blocks applicable for the particular machine tool.

2. Check for all the machine tool functional limitations such as:

            I. Maximum table or spindle traverses,

           II. Available feeds and speeds, and

          III. Machine tool servo characteristics and other details.

The total system, therefore, should consist of one processor and a number of post processors depending upon the number of different machine tools it has to support. The postprocessor though appears to be different for each of the machine tool, there is going to be large amount of similarity between two similar machines. As a result the postprocessors have been further modified with the concept of a universal postprocessor that can be applied to all the machine tools with a table of parameters to serve as the necessary customization for the individual machine tool. Most of the computer aided programming systems follow this concept.