Compression molds

Physical and chemical mechanism

Compression molding uses a mold into which a material is pressed under pressure. Unlike injection molding, the material is placed into the closed mold as a preheated mass and compressed so that it fills the cavity and takes its shape. Heat and pressure then cure or solidify the material.

Metallurgical relevance and welding risks

Compression molds are usually made from heat-treatable tool steels that must withstand high contact pressure, elevated temperature, and repeated thermal cycling. Welding on such molds carries a risk of hot cracking in hardened zones, distortion from uneven heat input, and a hardness drop in the heat-affected zone. Repairs therefore demand careful preheating, a matching filler metal, and slow, controlled cooling.

Workshop practice and instructions

When repairing or modifying a compression mold, preheat evenly and keep the heat input low. Use a filler that matches the base material, then cool slowly to avoid cracks and loss of hardness. After welding, re-harden or stress-relieve the mold as required and check the working surfaces for distortion.