How to Cast Resin for Vacuum Forming Tooling

Casting resin is a quick, cost effective tooling method solution that gives you great results.

We recommend using epoxy resins because they are more hard-wearing than polyurethane resins and can be screwed down to baseboards. Epoxy resins usually take at least 12 hours to cure.  When casting epoxy resin, you’ll want to follow this general procedure:

• • Vacuum Forming – Vacuum form over your master pattern or tool and turn your vacuum forming upside down ready for casting.
  • Support – Support the formings on the underside to stop deformation caused by the weight of the resin when poured into the forming.
  • Release agent – Apply a wax release agent either by brush or spray can to the inside of the vacuum forming. Once this has dried, polish the surface with a cloth or duster.
  • Foam blocks – Position foam blocks and wooden strips within forming to reduce the amount of resin used. The foam is covered with packaging tape and your release agent.
  • Pour the resin – Always pour into the lowest part the vacuum forming first and start with a thin coating of mixed resin. Brush the resin all over the surface and leave for 15 minutes until any bubbles have risen to the surface (slow cure epoxy resin only). A stipple action with the brush will help to eliminate air bubbles.
  • Position blocks – Position the Polyurethane foam blocks and apply weights. Power the remainder of the resin to the correct level and top up as required. Leave the resin to harden for the correct time. Epoxy resins can take up to 24 hours before they can be demolded. P.U. resins can often be demolded after 1 hour.

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• Break out – Break out the foam inserts and cast resin tool from the vacuum forming to give you your production tool.
• First post cure – Cure the resin tool for the first period of 4 hours at 40C (epoxy resin).
• Sanding and drilling – Drill the vacuum holes as required, which is typically 1mm – 1.5mm diameter after the first curing session. This is so the resin is not too soft so that it clogs the drill and not too hard so that it blunts the drill. Use either 1mm or 1.5mm long reach drill bits.
• Second and third post cure – Cure the resin tool 3 hours at 60C and then 2 hours at 80C (epoxy resin). Sand down the resin tools until they are smooth.

For more detailed instructions and a visual guide on how to cast resin for vacuum forming, read Formech’s article here.