Re: Beefy SLA part warpage question.

From: Joe Allison (
Date: Mon Jan 10 2000 - 18:20:30 EET

This is definitely sounds like curl.

The name curl is used because it best describes the shape of the distortions
where the extremities curl upwards. It is similar to the bi-metallic strip
affect where you have two thin layers laminated together with different
thermal coefficients of expansion. As the temperature changes, the two
layers will expand or contract at different rates. The difference in
Stereolithography is that the contraction is occurring on the top layer due
to a density change during cross-linking - and it is cumulating every time
you add another layer.

The cumulative forces seem to reach a critical mass at about a 1/4" wall
thickness and are capable of bending a stainless steel platform if the
supports hold on. I have seen this first hand.

The reason the bottom shows more curl than the top is the forces are
cumulating a layer at a time. Therefor the distortions are increasing with
time and are developing in and out of the vat. As distortions occur in the
vat, the recoating process will slowly bring the top surface back to flat.
This is because both the doctor blade and gravity promote flatness. After
the part comes out of the vat and is released from the restraining supports,
it will usually move a lot more. The built in stresses will then cause the
part to creep for days.

3D Systems has developed some draw styles to minimize these distortions
(e.g. STAR Weave and ACES), but as long as SLA resins shrink (or contract)
during cross-linking, I don't think there is any way to completely eliminate

Joe Allison
Solid Concepts Inc.
28231 Avenue Crocker Bdg 10
Valencia, CA 91355
Tel: 661-257-9300
Fax: 661-257-9311
----- Original Message -----
From: Luper, Harold <>
To: <>
Sent: Thursday, January 06, 2000 2:13 PM
Subject: RE: Beefy SLA part warpage question.

> I have had this problem building "beefy" ACES parts as well, with all
> machines and resins we've had over the years; an SLA 250 running 5170, SLA
> 3500 running 5190, and our current machine, an SLA 5000 running 5195. I've
> tried different orientations in the PCA (like face down with blocks under
> the corners) to no avail. I haven't tried curing the part on the platform.
> I have even seen parts where there was less "curl" in the top of the part
> than there was on the bottom (the part was actually thicker in the
> especially off of the SLA 250.
> Could this be caused by the effect of the resin being cured from the top
> every layer, and/or that the shrinkage occurring in each layer is
> in the build? In other words, if layer #1 shrinks, then layer #2 attaches
> and shrinks, layer #3..... and so on, wouldn't that pull up the edges?
> Thanks,
> Harold Luper
> Prototyping Specialist email:
> Solidiform Incorporated Phone: (817)-831-2626
> 3928 Lawnwood Fax: (817)-831-8258
> Fort Worth, Texas
> -----Original Message-----
> From: Bill Cannon-WM []
> Sent: Thursday, January 06, 2000 3:14 PM
> To:
> Cc:
> Subject: Beefy SLA part warpage question.
> I too have had this same problem. The diameter of my part was
> 16
> inches and the thickness was roughly .75. The next time I built the part
> cured it with the platform, supports and all. This worked. I have an SLA
> 5000
> and use 7120 resin. Did I just get lucky the second time?
> Bill Cannon
> ---------------------- Forwarded by Bill Cannon-WM/PGI on 01/06/2000 04:08
> PM
> ---------------------------
> Internet Mail Message
> Received from host:
> []
> Envelope Sender:
> From: Tim Bush <> on 01/06/2000 03:13 PM
> To:
> cc: (bcc: Bill Cannon-WM/PGI)
> Subject: Beefy SLA part warpage question.
> Dear SLA Users,
> Recently, we built 14
> For more information about the rp-ml, see

For more information about the rp-ml, see

This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 23:02:34 EEST