Defect guide · Filling
How to solve short shots in PDCPD-RIM molding
A short shot, where resin does not fill the whole cavity, means scrap and weak parts. PDCPD is a low-viscosity reacting liquid, so the causes are usually air and reaction timing, not injection pressure.
1. Seal the mold
- Air aspiration is the most overlooked cause. Resin flowing through the runner into the cavity creates a venturi effect. Damaged or badly seated O-rings near the runner or gate let outside air into the cavity.
- Result: air displaces resin and leaves voids that look like a lack of material.
- Fix: make the parting line and the mix-head connection fully airtight.
2. Set the cavity temperature correctly
- Typical setting: 80–90 °C on the female mold to trigger a complete, even exothermic reaction.
- Too cold: slow or incomplete polymerization, soft spots, resin retreating from edges.
- Too hot too early: the material gels before reaching the far end of the part.
3. Vent the last-to-fill areas and add overflow wells
- Air collects in sharp corners and at the end of fill.
- Put 0.1 mm vents and overflow wells at these points. The air and the bubbly leading edge of the resin leave the cavity, and the part stays dense and complete.
4. Guide the flow
- Some geometries create dead zones where resin bypasses a region or slows down.
- If one area keeps filling short, add internal ribs or flow channels to the part. They act as paths that lead resin into hard-to-reach corners before the reaction reaches the no-flow point.
Seeing this defect on your parts? Send photos and the 3D data. We will tell you whether the fix is in the process, the part design or the mold. Contact us.