Printed moulds for injection moulding

I have a Form2 and a Travin TP2 desktop injection moulding machine.
I had plans to print moulds and use them in the Travin.
I have achieved the first part. Printing 2 and 3 part moulds in HT resin with appropriate gates/keys and locators etc.
The second phase has me beat at the moment.
I am finding the HT resiin too brittle. The two mating faces of the mould have ended up slightly “warped” after cleaning and UV curing. They crack when I place them in the holding vice, even if I am really careful with the pressure. Any slight variation or deformation seems to offer the mould any opportunity to crack, eventually. 4 squirts has been my record so far.
I tried putting a very thin bit of cushioning between the vice faces and the mould in the vain hope that would help but after a couple of squeezes that cracked as well.

Am i living in a fools hope or am i missing a trick somewhere.

I tried the moulds in previous incarnations printed in SLS nylon and the “technical” ABS from Stratsys (i think) both worked in tests at Travin on the same machine… although the Nylon did melt quite quickly!!

Did you try standard resin as well? I’ve seen some molds here on the forum with grey resin.

Did you check warpage before UV curing? I recently found parts getting warped in the direction of the UV light source.

You may need to have an aluminum frame to keep the printed part from crushing/cracking.

If you’re running a low melt temp material like Polypropylene you may be able to lightly clamp the print and inject plastic. ABS will likely require a frame (and high temp resin).

Formlabs has a white paper and a video of their webinar for mold making.

All my moulds so far have been HT. I will need the temperature resistance when I move on to moulding with Nylon!

I am just printing off a mould in Standard; as a test., It might cope with the low temp of my testing plastic ( Capa polyester).

Formlabs have just come back and suggest pringing the mould parts aligned vertical flat on the printing platform, no supports. Unusual but they have had some success with this method.

I am hoping to avoid any kind of aluminium frame, it would kind of defeat the object of low cost.
So far the failures have not been pressure/temp related, they have all been brittle breaks when clamping or handling.

I am slowly chipping away at the challenges. I am finding that design of the mould is playing a large part in its survival.
All my outside edges are filleted. My gates are now up to 4mmdia. Main injection entry is as large and extended as I can get it… I have a tongue and groove going around 90% of the inside as a secondary “fire wall”.
I put plywood between the mould and the vice plates.
I have moved from silicone lubricant to liquid vaseline as my mould release.
After squirting I put the injected mould into the freezer for 9mins to solidify the plastic.
My latest HT mould is up to a record 5 squirts and still looking good.

My feeling at the moment is to concentrate on the design and avoid any areas that could act as a weekness and form a stress fracture.

If you don’t want to use a frame try adding dowel pins to the mold halves. The pins could limit how much you can crush the mold and keep it from breaking from clamping.

Printing flat only works if you’re willing to have a thick base. The first 5mm or so is over compressed and fairly useless for accurate parts.

My first response to the pins was - how can I get them to be the exact size I need. But having thought about it I could make the mould to a standard bolt size depth and then design the pin holes to take bolts… M3 or 4 to thelength i need. Although no doubt that well know auction site would sell metal pins somewhere.
Unless the pins would stop the mould getting just that touch of compression it needs to give a good seal??
More tests are required.