Coexisting with Pro/ENGINEER

Pro/Engineer has become a very popular CAD software, so we must coexist in an environment that includes OSDM and Pro/E. There are two forms of geometry that can be passed between solid modelers: solids or surfaces. When we sent IGES wireframe or IGES surfaces in the past, sometimes translation problems could be neglected because most of the geometry passed through the process. Pure solid modelers cannot do anything useful with most of the geometry; it's all or nothing (*1).

I.e. AutoCAD R13 and R14 are ACIS solid modelers, and OSDM can export an ACIS file. Pro/E, however, uses a proprietary solids kernel. There are two possible ways to transfer geometry between OSDM and Pro/E: IGES surfaces or STEP B-Rep solids. Degenerating a solid to IGES surfaces and rebuilding it in other software is not a reliable process. STEP is considerably more robust. But any Pro/E user has IGES, and few spend the $5K or $6K to purchase a STEP translator. Importing Pro/E IGES files into OSDM will be more reliable if they are exported correctly from Pro/E. You can find IGES settings recommended by a Pro/E user group.

STEP should provide very reliable transfer of geometry from OSDM to Pro/E. But STEP alone cannot make the transfer of geometry from Pro/E to OSDM reliable. STEP can give an accurate description of inaccuracte geometry, but it cannot make the geometry more accurate. It can precisely describe the mismatch between surfaces, but it cannot make them match.

Pro/Engineer Accuracy

Pro/E provides two methods to define accuracy: relative and absolute. The default method is relative accuracy, and the default magnitude is 0.0012. That means the precision of a 100 mm part is 0.12 mm! OSDM uses only absolute accuracy, and the coarsest accuracy it allows is 0.01 mm. If a Pro/E user utilizes the default settings, you should not depend upon OSDM being able to create a solid with the geometry.

OSDM can use accuracy from E-6 to E-2 mm. CoCreate recommends an order of magnitude overlap in accuracy (E-3, or 0.001 mm). When you pay a supplier to create geometry in Pro/E, to be imported into OSDM, the contract should specify geometry that we can use: 0.001 mm absolute accuracy. The Pro/E manual says, "Use the default accuracy until you have a reason not to do so." (The bold print is theirs.) We should give them a reason not to do so.

Many Pro/E users do not know how to use absolute accuracy. (They may not know it is possible. It wasn't until Release 17.) A default installation of Pro/E does not even allow absolute accuracy!

What if the part has already been created in Pro/E without the necessary accuracy? It is theoretically possible to modify the accuracy. Page 10-52 of Release 17 Part Modeling User's Guide describes how. But there is a serious catch: modifying the part accuracy causes the entire part to regenerate. There are two reasons a vendor should be reluctant to do that without financial incentives.

  1. The better the accuracy, the more computer time it takes to regenerate the part.
  2. The better the accuracy, the more likely the part will become corrupt in regeneration. Removing corruption takes human time.

(*1)    ... all or nothing - or fixing models inaccuracies which sometimes becomes a very difficult and time consuming task.