Neutral file format 1

[grunt58]

Not really a SW question more of a general CAD question.

What is the best neutral CAD format across all MCAD software? We are in the process of starting to upload our files to our website for customers to design with. We'd prefer to offer one format as it just makes things easier.

I have suggested parasolid which I know works best with SW. Does it play as nice with other CAD software inventor, unigraphics, pro-e etc.? Which type of parasolid .x_t, .x_b? Maybe .step is a better neutral format?

Thanks

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[MessersmithS82]

I'm not sure that CATIA can bring in parasolid files so you may be better using a step format rather then parasolid.

 

[kellnerp]

STEP is considered better because the STEP standard requires any program reading it to produce identical geometry. IGES is probably read by more programs, BUT, IGES is flavored by whatever program writes it and so is not necessarily compatible with another piece of software. In other words the IGES standard does not guarantee that another piece of software can reproduce the geometry it contains, even though the IGES standard is met.



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[KevinDeSmet]

I'm going to have to go with STEP as well. Mind you there are still, maybe flavours. SolidWorks will export AP203 and AP214 and then not to mention the options therein, but SolidWorks doesn't really allow you to tinker with them very much. I would advise STEP 203.

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[kellnerp]

Here is an in depth discussion of STEP/ISO10303.The key statement is

"STEP shall be based on one single, complete, implementation-independent Product Information Model, which shall be the Master Record of the integrated topical and application information models".

which is itself a quote from ISO TC184 / SC4 resolution 33, Tokyo - December 1988 TC184.


It is not known whether the SolidWorks API has any PDM related hooks when it comes to reading or writing document control information in and out of STEP files.

Here is an in depth discussion of IGES. Note that the US DoD requires submissions in IGES format, not STEP. In SolidWorks IGES files are perhaps the most flexible in that they can carry sketch information in them which is extremely helpful when determining intent from free form customer data. SolidWorks will import IGES drawings as parts which means you can see the drawing, but it will not be to scale and will be extremely difficult to work with. IGES is frequently used in advance surfacing and in import repair to store temporary or scratch faces.

SolidWorks cannot read or write either STEP or IGES drawing files as drawings.

VDAFS is the unsung hero of SW file formats in the US. VDAF does extensive geometry correction and can be used effectively to help heal defective models or as a check of a current model. Because it does a lot of checking, it is slow.

One of the biggest issues that SW users run into when using neutral formats is that of the order of the polynomials used to represent complex curvy geometry. Many of the high end CAD packages use higher order polynomials for complex surfaces. SW on the other hand uses 3rd order AFAIK which means it has to approximate a higher order definition of a surface when importing. This is one reason why SW users historically have had trouble with fillets in Pro/E IGES files. SW users will find that imported sufaces from higher end packages and even from round trips through SW may see the number of surface faces change due to the approximation algorithm. (this is speculative)

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[KevinDeSmet]

DoD requires IGES? That's pretty insane, I guess they have many legacy systems that don't play well with STEP, if at all. Otherwise I see no reason to pick an old outdated standard like IGES.

STEP is far from perfect too. If it tries to be such a complete format, why does it break it up into all those application protocols? Not good. Just not good. ISO at its finest people! breaking 'er all up!

You're right about the polynomial thing, it is an issue, but honestly you gotta pick. To me degree 3 nurbs geometry is the way to go, but some applications work best with bezier math and then you need higher degrees unless you want a dozen surfaces to define a model. By all accounts, degree 3 nurbs geometry is the more modern of the two. IMO

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[rstupplebeen]

It really depends on the geometry and what the part was made in and will be opened with. For SolidWorks to Abaqus SAT works best. Because of this I would just create a macro that saves out a variety of file parts and host them all. I would use (x_t, step, igs, sat). The next question is what versions of each. I would go with SWx defaults and hope for the best. I hope this helps.

Rob Stupplebeen

https://sites.google.com/site/robertkstupplebeen/

 

[grunt58]

We have been sending files for awhile now as step AP214 with no complaints. We chose AP214 as it retains colors. Kind of a moot point but it keeps the parts all pretty for the customer. Just in the last few months have been able to post them on our site, again no one has complained or asked for other files. I'd say most of our customers have mid range CAD software inventor, pro-e or SW so I think step is just fine.

Was just wondering others opinions.

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[TheTick]

Besides choosing the right format, take time to look at the export options in your software.

Unless you really don't care about the integrity of your design, don't make the mistake of loosening tolerances simply for the sake of reducing file size.

 

[KevinDeSmet]

Tick,

OMG - that is the worst idea I've read in a while

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