Friday, March 14, 2008

CAM and the CAD file

CAD/CAM vendors continue to promote the idea of 'leveraging' the geometric file throughout the process. The unasked question is whether the parametric model can or should be used in the manufacturing process.

Part of the answer depends upon the manufacturing process. Even with additive manufacturing (rapid prototyping) the model is not always used directly but tessellated and sometimes supports are added. This is usually done outside the original CAD software, but is fairly automated.

A properly constructed plastic part can be injection molded using the CAD file, but the mold design is often done with a Mold Design /CAM package other than the original CAD software. The same can be said of other molding processes. Once transferred, the model is seldom parametric and changes must be communicated back to the designer.

CAM vendors have done a lot to integrate with the more popular CAD packages, but often that is just an automated transfer of the static solid model into the CAM software. Certainly the higher end products like Pro-E do integrate CAM into the CAD product. My experience is that the capability of the CNC programmer is more important than the software used.

However, even when the software supports it, is there any true value to the use of the parametric file for Manufacturing? Most CNC programmers feel that they are often better off keeping the manufacturing files separate. This is due to a variety of reasons including the need for geometry changes for intermediate manufacturing steps, errors to the manufacturing process when changes are made to the model, and the administrative overhead required to coordinate a single file. (We’ll discuss PDM at a different time.)

In reality there is a minimal advantage of having a single all encompassing model and there are a minimal number of instances when a single model is truly more efficient. Therefore, I don’t believe that the use of a specific CAD/CAM package from your contract manufacturers should be high on your evaluation criteria. You should care if the vendor has the ability to use your CAD models without conversion, but little else.


No comments: