Influence of thermal ageing on the mechanical properties of an additively manufactured photopolymer used in soft tooling applications

In recent years, direct rapid soft tooling based on inserts manufactured additively by light reactive photopolymer curing has become a solid alternative to classic tooling based on subtractive machining of metals for prototyping and pilot production of polymer parts by injection moulding. Reported numbers of injection-moulded parts per insert are in the low to medium three-digit range. This, however, is based on using additive manufacturing for the production of both mould halves. It was found that combining a soft tooling insert on one mould half and a metal insert on the other half can increase insert lifetime to more than 10 000 parts in acrylonitrile butadiene styrene (ABS) with a negligible influence of insert wear on the dimensional stability of the injection-moulded parts. Photopolymers are known for their very low heat conductivity compared to metals and their sensitivity to elevated temperatures leading to degradation and negative effects on their mechanical properties. Considering heat transfer laws, it can be assumed that most thermal energy brought into the cavity during the plastic injection is conducted away through the steel half of the mould, thus leading to a significant reduction of the thermal ageing of the photopolymer insert. This research supports the quantification of the influence of thermal ageing on insert lifetime by performing experiments with photopolymer samples aged thermally after exposure to different elevated temperature levels for different time spans.