Shrinkage analysis of forged ultra-high molecular weight polyethylene parts

Some engineering thermoplastics cannot be easily processed by injection molding because of their high viscosity. This is the case for Ultra‐High Molecular Weight Polyethylene (UHMWPE). Parts are either compression molded or machined from extruded shapes. Over the years, forging has been increasingly used to produce more or less complicated parts. Forging is a process in which a preform is subjected to bulk deformation in constraining dies, by applying heat and pressure, but with the polymer remaining in the solid (semi‐crystalline) phase. To fabricate acceptable mechanical components such as gears and sprockets, a close control of the operating conditions and a good prediction of shrinkage are necessary, For a better understanding, a study has been conducted on forged UHMWPE disks and gears. Parameters such as material and mold temperatures, dwell time, speed of forging and dwell pressure were investigated. Results show that material and mold temperatures are the most important parameters. For gears, optimization of processing conditions led to a shrinkage of ∼0.2 percent, measured on pitch diameter. The effect of post‐annealing at various temperatures is also reported.