You wrote:
Since 2 weeks ago, we started getting parts out from the SLA500 with
undesirable results unseen before.
>From the look of the part, it sure looks like after certain height of
building, there was a shift of about 2mm in the X direction & this off-set
position remained over the next 5mm build before it returned back to the
original position. It remained so for a certain height before the same thing
happened again with the literally same off-set & duration. This would self
repeat over & over again throughout.
The platform is well secured down & even if it's not, surely a mechanical
shift if any would unlikely yield such a consistent pattern of steps on the
part. It can't be the blade sweeping action along the Y axis either as the
shift is along the X.
I wonder has anyone out there observed this rather strange phenomenon & the
solution??
Alvin Cheong
Thomson mutimedia
cheonga@thmulti.com.sg <mailto:cheonga@thmulti.com.sg>
Yes, we have a SLA-5000 and we have had parts shift in the vat. We have
found that part of the problem is in the generation of the supports. If a
part is not supported with enough supports it will tend to move around until
another feature in the geometry can lock the moving part down. Let me give
you an example of this.
We had a part design that was essentially a flat part with a boss in the
center of it. The parts were about .050 in thick and 6.5 in square. The
boss in the center was around 3 inches square protruding about .500 inches
perpendicular to the flat edges. We decided to turn them on end and build
them 6.5 inches in Z to have a better layering definition on the part as
well as cut down on the supports. As we found out, the parts built great
but had a shift in them just as they reached the boss area. When it reached
the boss, the first layer bonded to the supports and was locked down thus
pulling the part back to center. This was a shift of about .020 at 1.45
height. We concluded that the line support holding the edge in place when
the parts were starting out was not enough to stop the movement of the part
when the wiper blade passed over the top. Understand that the movement was
very slight on each layer up until the 1.450 layer. When the 1.455 layer
solidified to the boss support the 1.460 layer started building on what
could now be call a stable part position. By redefining our supports we
were able to correct the problem. I must mention that we have had shifts in
some of our builds that we could not solve or determine why they happened.
I presume that many factors contribute to this condition.
This example may not be the answer to the problem you are having but maybe
it will help.
Good Luck.
Paul Hanna
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:47:20 EEST