[wg11] Fwd: RE: Step Standards for Additive Manufacturing

[Martin Hardwick]

All,

Here is the paper that raised questions about the ability of traditional 
CAD systems to model very large structures for applications such as 
additive manufacturing.

This does not mean that they cannot be used for such modeling but it 
does imply that new infrastructure is required to enable such modeling 
and in my opinion the best hope for a near term solution is Part 21 
Edition 3 combined with AP242, and the STEP-NC models for additive and 
subtractive machining.

Key advantages include:
1. Interfaces to read and write the geometry to and from nearly all the 
CAD systems
2. Very efficient format for modeling facets
3. Information models both additive and subtractive manufacturing
4. International Standard

What we need to do is create an infrastructure for processing this data 
in very large volumes so that we can support applications like additive 
manufacturing, 3D circuit design, very large buildings construction and 
very large defense platforms.

I would see this mostly as imposing an organization onto the division of 
an AP242 file into billions of linked P21 e3 segments. Seemingly trivial 
until you start to think about all the different ways that applications 
will want to find and access the data.

Here is the problem statement that I received from a well known CAD/CAM 
vendor
(1) Simple calculations. Suppose you have an object with a volume of 1 
cubic meter, and the
cells in the lattice have a volume of 1 cubic millimeter. Then there 
will be 10^9 cells.
If you use a curvy b-rep, there might only be 2 or 3 faces per cell; 
with a facetted b-rep,
maybe 10 or 20 facets per cell. But, either way, that's a huge number of 
faces. If the cells are
all identical, you can represent them using a repeated pattern technique 
some of the time,
but, for some operations, you will actually need explicit 
representations of all those faces.
No modeler (as far as I know) can handle that many faces, and no 
graphics card can handle
10^9 triangles. Not even close.
(2) These folks ... (in the attached paper)
found that ACIS ground to a halt when they tried to model a lattice with
around 2400 simple cells (see pages 9-10). This was 10 years ago, and 
computers are
bigger/faster nowadays, but I don't see that this will allow us to make 
the leap from
2400 cells to 10^9. I'd love to be proven wrong. If plain old b-reps 
could be made to
work, that would certainly make life easier for us.
Martin Hardwick
President STEP Tools, Inc.
Professor of Computer Science, RPI
Team Leader ISO STEP-Manufacturing

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.steptools.com/pipermail/wg11/attachments/20140826/6479f043/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: A Hybrid Geometric Modeling Method for Large Scale Conformal Cellular Structures.pdf
Type: application/pdf
Size: 407125 bytes
Desc: not available
URL: <http://lists.steptools.com/pipermail/wg11/attachments/20140826/6479f043/attachment.pdf>