RE: scale and warpage of sls

From: denis bonnenfant (denis.bonnenfant@diderot.org)
Date: Mon Apr 02 2001 - 14:21:36 EEST


Neil,

We are using a sinterstation 2000 with duraform in our CADCAM Lab for
prototyping student's projects, and this RP process is a very good way to
validate plastic parts design : mosts of the defects observed on SLS parts
were reproduced when the part is really injected.

Duraform SLS parts are very similar in its mechanical and thermal properties
with injected PA parts.

The problem is to keep shrinkage as uniform as possible, avoiding
temperature gradients during sintering and cooling

Design rules (very very basically)

- constant thickness walls
- avoid large plane surfaces (or put lots of ribs to stiffen it), but a
rounded shape will be better
- shell designs are always better than U-style parts
- of course, you don't have to take care of undercuts....

or get some advices from a plastic parts designer... It's very easy to find
in any company

I never succeed in building accurate parts more than 15-20 mm thick.
So if your parts have to be massive (for weight, vibrations, or any other
reasons), the best way is to build a thin shell ( 1 - 3 mm) and fill it with
epoxy-glass or Al filler (and you are saving powder ! ).

my placement rules :

- 5 x y rotation,
- circular shapes nearly horizontal,
- same orientation for all the parts of an assembly
- 1.04 x 1.04 y 1.01 z (duraform)
- 168.5 C / 13% laser
- .2 x 0.2 y offset

I hope it can help you,

Regards

Denis

For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/



This archive was generated by hypermail 2.1.2 : Fri Jan 04 2002 - 09:57:02 EET