I feel your pain. Unfortunately, I have not found a very efficient way to only design the model once in CAD to import into other software like Molflow. Same applies to other programs like ANYSIS for example. SolidWorks has a couple problems when exporting in STL. First it doesn’t have enough precision compared to Molflow so facets that share vertices wind up having different values. This can cause small leaks. Depending on what you are modeling this may be significant or not. It just depends on many times a particle has to bounce around near the leak before it is absorbed on a pumping facet. Second, if your CAD model has smooth curved surfaces, it can be random where the STL export decides to put vertices. So vertices from one body may not line up with vertices on other bodies, creating gaps and hence leaks in your model.
So, I just use the CAD model as a template for making the model within Molfow. It’s a major pain in the butt because you have to redo it every time they make a change in the CAD model. I usually wait until the changes have are significant enough to redo it.
The first thing I do is get rid of non-vacuum surfaces and all non-vacuum hardware (bolts, screws and etc for example). If you can hide non-vacuum parts in the CAD model before exporting, less to delete later. I also use smart select ALOT in Molflow to quickly select large sections of facets. Keeping below 90 degrees you can easily delete the non-vacuum surfaces since typically those facets will have a 90 degree bend difference between the internal and external surfaces. You can experiment with the setting because it’s not always the case. To use smart select you have to collapse the vertices first.
How I create the model varies, but as a general rule 1) I always collapse vertices before creating new parts. This is because many times I want to be able to move created parts that share a vertex separately. If you collapse later then those parts are now tied together. Sometimes there are just too many lines and it hard to tell things apart from each other. So I just move some of the parts temporarily out of the way. I can’t do this if it is tied to a part I don’t want to move without screwing up the non-moving part. 2) I always try to build new facets in either one of the X,Y or Z planes. 3) Create the new parts away from the original, so I can just do a simple move command to see that they overlap as they should if I created it correctly. Also, keep in mind there is not one single way to create a new part, there are usually a few different ways to accomplish the same task. So in more detail…
The imported CAD model facets are all triangles, so they will ALWAYS be planer. But even if a group of them forms a “flat” plane, it will not because of the lack of precision. So if you built a simplified facet out of a bunch in one of the planes it’s easy to set the vertices to the same plane value to make sure it is really flat. You can also do projections onto plane function too. I’ve developed a spreadsheet that calculates how parts need to be rotated based on copying selected vertices in the display box and pasting them into Excel. I have others that don’t calculate rotations, but from 3 vertices on a “circle” can calculate the center, diameter, and normal. I then use that to create a new circle in Molflow. I use this a lot to make round ports onto a vessel (Create circle, Extrude, and Build Intersection). For circles I also usually stick to number of sides that give vertices at every 45 degrees. You can have more in-between obviously. More sides for big diameters and less for smaller.
Sometimes I’ll take slices on the part, so the points are all in the same plane, before copying and moving vertices that then may get rotated or combined in some other way to create a new chamber.