Re: CAD problems and Swiss Cheese

From: lblasch@opw-fc.com
Date: Thu Oct 01 1998 - 13:54:41 EEST


     Chris,
     
     First, how much RAM and SWAP space do you have?
     
     I experimented with hollow lattice structures like "Swiss Cheese" as a
     way of reducing the mass of large objects 7 or 8 years ago. I also ran
     into the problem of processing these large datasets and abandoned the
     idea after limited success.
     
     I did, however, work out a way of processing large data files with
     limited RAM and CPU resources both on UG and in SLA.
     
     By dividing the CAD model into smaller pieces you can minimize the
     problem you are having. Just cut both the object and the sphere-set
     with the same planes and do your Boolean intersect, the resulting
     parts should match up just fine when you build them together.
     
     If the STL data is too complex to process, then you can keep the STL
     objects separate and build them one at a time. Back in the early days
     of SLA, the disk drives were too small to hold the massive build files
     I needed to work with so I actually built them as one "slab" on top of
     another in successive builds. You may or may not be able to do that on
     your SLS machine, I've never tried.
     
     With SLA, the process worked like this:
     
     1.) Add registration objects (tall, thin cylinders) at the extreme
        limits of machine build envelope in CAD model. They must match the
        height of the object. (This will keep the successive builds aligned
        properly)
     
     2.) Position part, orient, and cut entire model and registration
        cylinders into reasonable thickness slabs. (You may have to
        experiment to determine what "reasonable" is.)
     
     3.) Prepare each "slab" as a separate build but add a pause (no drain)
        command to the end of the each build.
     
     4.) Build slab #1 which will pause at the end of the last layer, build
        "slab" #2 on top by instructing it to start on the first layer of
        that "slab" which will then adhere to the previous slab.
     
     5.) Repeat until entire model is completed.
     
     I also use Unigraphics, and I would love to see this model data
     myself.
     
     Sincerely,
     
     Larry Blasch
     System Administrator for Engineering Services
     
     OPW Fueling Components Voice: (513) 870-3356
     P.O. Box 405003 Fax: (513) 870-3338
     Cincinnati, OH 45240-5003 USA
     *********************************************************************
     * "When all else fails, Manipulate the data... Albert Einstein" *
     *********************************************************************
     
     
     ______________________________ Reply Separator
     _________________________________
     Subject: CAD problems and Swiss Cheese
     Author: "Chris Sutcliffe" <c.j.sutcliffe@liverpool.ac.uk> at internet
     Date: 10/1/98 6:03 AM
     
     Can anyone help
     
     
     We are doing some research at Liverpool which involves the generation
     of = a plastic structure made up from small interlinked balls. We
     have a CAD = solid model of the geometry but we need to turn the
     geometry into the = inverse of Swiss Cheese!!!! and subsequently
     manufacture it on out SLS = machine. The route I have used so far is
     as follows
     
1. Create the geometry on UG
2. Create an array of interlinked spheres
3. Intersect the two solid models
     
Unfortunately because there are so many balls my machine (SG octane) =
keeps killing the application which is unfair to say the least. Can =
anyone help,does anyone know of a structure like Quick Cast for example =
which does not have the outer skin and can be automatically generated?
     
Thanks
     
Dr. Chris. Sutcliffe
Product Innovation and Development Centre
Department of Engineering
3 Brownlow St.
Liverpool L69 3GL
     
(0151) 794 8022 Direct
(0151) 794 8021 Secretary
01893 209 556 Bleeper
EMail c.j.sutcliffe@liv.ac.uk
     
     
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