Re: Improved Accuracy Tools

Date: Thu Apr 22 1999 - 19:22:22 EEST

>Are there any "automatic" and easy ways to compensate and make a new STL
>file when you have got your first 3-D file and the first cast tool, which
>will because of metal shrinkage be smaller than your first 3D model?
> What programs and services are available to make this second 3D model
>easily? The model has to be exactly as much oversized as the shrinkage of
>the first tool?

I have just read the response by Bert VandenBerg.

We at the University of Utah did something quite similar for a different

We were producing a mold from soft polystyrene foam and then using it in a
room temperature vaccuum bagging process to produce fiberglas composites.

We created the CAD model using spline points (even if this wasn't
convenient or necessary for the part gometry). Then we created an FEM
model with nodes positioned at the spline points. We applied loads to the
FEM model, found the nodal displacements, calculated the vector difference
between the displaced nodes and the desired position for that node/spline
point, subtracted this error from the spline points, and regenerated the
CAD model. The result is a CAD model that does not have the desired shape
until it is loaded.

In our case, we worked from the FEM model and never created the actual part
until several iterations of the process had reduced the error below a
desired threshold. All the displacement measurement, vector subtraction,
etc. was automated using a custom program created by one of my students.



Charles L. Thomas
Assistant Professor
Department of Mechanical Engineering
University of Utah
50 South Central Campus Drive
Salt Lake City, Utah 84112
FAX (801) 585-9826

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