PDCPD Mold Design Basics
An engineer's introduction to designing molds for PDCPD reaction injection molding: how the process differs from injection molding, mold materials, shrinkage, gating and clamp force.
What is PDCPD?
PDCPD (polydicyclopentadiene) is a thermoset made by reaction injection molding. Two liquid components, each containing dicyclopentadiene and one half of a catalyst system, are mixed in a high-pressure mix head and injected into a closed mold, where they polymerise within seconds to minutes.
The result is a tough, impact-resistant part. PDCPD is used for large panels and covers such as truck and tractor body panels, agricultural and construction machinery hoods, and housings.
How a PDCPD mold differs from an injection mold
The material enters the mold as a low-viscosity liquid at low pressure, so cavity pressure and clamping force are much lower than for thermoplastic injection molding. A rule of thumb used in the clamp tonnage calculator is 42 tonnes per square metre of projected area.
Lower pressure allows lighter mold construction, and aluminium is widely used for cavities and cores. Steel is used where wear, long production runs or fine detail require it.
Mold temperature and shrinkage
The reaction is temperature-driven, so the mold is heated, typically with the cavity (show side) hotter than the core. The default values in the shrinkage calculator are 75 °C for the cavity and 45 °C for the core.
Resin shrinkage is typically 0.9% to 1.0%. Because the mold also expands at operating temperature, the cavity and core each need a scale factor that combines resin shrinkage with the thermal expansion of the mold metal.
Gating, runners and venting
Flow must stay calm to avoid air entrapment. A common limit is a gate flow velocity of 2 m/s or less for 6–10 mm walls, and 4.5 m/s or less for 3.2–4 mm walls. The molding parameters calculator checks this.
The mold fills from the gate towards the highest point, so vents are placed at the last areas to fill.
Thermal expansion between mold halves
When cavity and core run at different temperatures or are made of different metals, they grow by different amounts. Guide pins and interlocks need per-side clearance to stay free at temperature, which the guide pin clearance calculator estimates.