Prostep | Newsletter

PMI alone does not make a model-based enterprise

A Comment by Michael Wendenburg

Extending 3D models to include dimensions, tolerances and other manufacturing information is a necessary, but not in itself sufficient, condition for their end-to-end use in manufacturing and quality assurance processes. The users and IT systems in Manufacturing and Quality Assurance must also be able to process the PMI (product manufacturing information).

There is a lot of talk of model-based definition (MDB) and model-based enterprise (MBE) in PROSTEP's latest newsletter. My own personal impression is that, when it comes to these topics, far too much emphasis is still being placed on product development, even though the amount of time saved by adding dimensions to 3D models compared to creating conventional drawings is negligible. The true benefits of PMI are not reaped until this information can be evaluated automatically for use in downstream processes, as Continental is doing in its Testing department with annotated CAD models, for example. This, however, tends to be the exception rather than the rule.

At this year's AMB in Stuttgart, the international exhibition for metal working, Geometric, the manufacturer of the CAM software CAMworks, presented a first, namely tolerance-based processing on the basis of PMI evaluation. However, it only works in conjunction with the CAD system SolidWorks. Other CAM vendors have invested a lot of time and effort in developing proprietary interfaces to specific CAD systems so that manufacturing features can be read directly from the systems, or they use color coding in the CAD models to assign hole types, surface qualities, etc. The latter, however, is most likely to be found in CATIA environments.

In other words, there many different approaches for exchanging manufacturing information between CAD and CAD. PMI is just one approach and by no means the most common. Much to my surprise, the term "PMI" means very little to most of the CAM vendors I spoke to in Stuttgart, which suggests that the topic of MBD has not yet reached the shop floor. The divide between CAD and CAM vendors appears to be just a deep as the one between Development and Manufacturing at some of their customers.

Digitalization of the process chains will, however, only succeed if the users and departments that ultimately have to make real components from the digital model data are involved in the discussions to a greater extent. Being able to read tolerances in the future as PMI in the 3D model offers no real benefit to employees in Work Preparation if they still have to enter the tolerances in their CAM system manually. On the contrary, in case of doubt, they will favor the 2D drawing because that is what they have been accustomed to using for decades. From the point of view of manufacturing, communicating manufacturing information in 3D only makes sense if conditioning the annotated models for processing involves less manual intervention than before.

There are still huge gaps in the digital process chains between Engineering and Manufacturing and between Engineering and Quality Assurance, and they cannot be closed by merely attaching the dimensions and tolerances to the 3D model. The question of formats, standards and interfaces is not really that important, as it is in particular an organizational integration task.

I know from numerous reports just how much time and effort the staff involved in work preparation and NC programming often put into conditioning the CAD models they get from Engineering to reflect production requirements merely because the design engineers are incapable of or unwilling to specify tolerances correctly prior to export. In some cases, highly complex components are re-modeled in the CAM system based on the drawings because it is faster than entering the tolerances in the imported models. Aside from the question of whether this even complies with regulations when it comes to ensuring traceability, there is the fact that there is enormous potential for rationalization that could be exploited without first having to intelligently network entire factories. All this requires is better networking between users in Engineering and Manufacturing and above all between their bosses.