Moldflow

Adviser requirements for STL files

Requirement 1

The STL file should be complete and incorrupt.

An ASCII .stl file must start with the lower case keyword solid and end with endsolid.

For example:

solid

...

facet normal 0.00 0.00 1.00

outer loop

vertex 2.00 2.00 0.00

vertex -1.00 1.00 0.00

vertex 0.00 -1.00 0.00

endloop

endfacet

...

endsolid

Requirement 2

The STL file can be in either ASCII or binary format. It is important to use the correct format with FTP. For example, if you have a binary STL file, you must set the FTP file type to "binary" before transferring.

Requirement 3

Only one solid should be present.

Requirement 4

The mesh triangles should be defined clockwise, with the normal indicating the "out" direction:

Requirement 5

The orientation of the triangle normals should be aligned.

Requirement 6

The triangles should share common corner node positions (the "vertex to vertex" rule), there should be no gaps or free edges in the mesh of triangles:

Requirement 7

There should be no intersections between the triangles' surfaces (naturally, edges should overlap).

Requirement 8

There should be no triangle overlaps.

Requirement 9

As a guide (not a requirement), there should be no more than 100,000 triangles in one model. If a model has more triangles than this, some fillets and other minor details are probably facetted too precisely.

If you can, use the STL settings in your CAD system to base the resolution of the tessellations on the chord height calculation below. You can thus reduce the number of triangles.

where:

·         c = chord height

·         p = part surface

·         t = tesselated surface

·         m = model size (the distance between opposite diagonals of the bounding box of the part)

·         q = part quality (recommended 0.3, limits 0.1 to 1.0)

Requirement 10

If your STL model has triangles with very high aspect ratio, the mesh will be distorted, and the analysis results will be less accurate.

For a mesh triangle, the aspect ratio is the ratio of the length of the longest side (a), to the height perpendicular to that side (b). As a general rule, this ratio should be less than 6:1.

The Adviser can accept some triangles with very high aspect ratios (hundreds or even thousands). However, try to keep the average aspect ratio below 6.