RE: end-life criterion for SL inserts

From: Prof. P. M. Dickens (
Date: Fri Jun 04 1999 - 18:15:05 EEST

There are lots of factors to take into consideration but by far the most
important is - Who is running the injection moulding machine! As the
mechanical properties of SL resin are much lower than aluminium or steel it
is very easy to destroy an SL tool on the first shot.
Try not to use a normal injection moulding machine operator. They will have
a hard time adapting.
I list some of the golden rules:
Build inserts with minimum layer thickness.
Build inserts solid. Using thin shells and backing with resin or low melting
point alloys can cause problems.
You do not have to finish the tools except for aesthetic reasons.
Place a thermocouple in the tool. You must monitor the temperature of the
Run the machine at very low injection speeds.
Use short shots to find out how much material is required to fill.
Use minimum back up pressure possible. Can you live with sink marks on
Open the tool as soon as possible - mainly to let the part cool by
Use proper ejector pins for longer life.
Do not bother with water cooling - not very effective.
Eject the part as soon as possible - long cooling times means higher
ejection forces.
Make sure the tool cools down to a maximum of 50 degrees centigrade before
you put in the next shot.
Use a good release agent.

The tool life also depends on the design of the tool but we have moulded
around some very tall thin cores (5 x 5 mm x 30mm tall) without them

Some tools have run to over 500 parts.

Bye the way, I am not at all convinced that draft angles are needed on these
tools. We are just in the process of seeing how various draft angles effect
the ejection force.

All the work we have done so far has been with Polypropylene but we are
about to work with ABS, Glass Filled Nylon and PEEK!!

Good luck


Prof. P. M. Dickens
Dept. of Mech. & Manuf. Eng.
De Montfort University
The Gateway
England LE1 9BH

Tel: +44 (0)116 257 7689
Fax: +44 (0)116 257 7025
Mobile: +44 (0)468 827039

> -----Original Message-----
> From: []On Behalf
> Of Ricardo B. Gomide
> Sent: 04 June 1999 13:50
> Subject: end-life criterion for SL inserts
> Dear people,
> I'm looking for a end life criterion for stereolithography
> injection moulding inserts. How can I characterize the
> end-life? Any suggestions? Does anyone know something?
> Thanks in advance,
> Ricardo
> ________________________________________________________________
> \\\\\\\\\\\ RICARDO BORGES GOMIDE, Eng.
> CIMJECT - Universidade Federal de Santa Catarina
> Tel: (+55 48) 331-9387 Ramal 221
> Fax: (+55 48) 234-1519
> \\\\\\\\\\\
> ________________________________________________________________
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