Combining material extrusion of metals and copper infiltration for manufacture of tailored injection moulding tool inserts

Material Extrusion of Metals (MEX/M) combines high geometry and design freedom of additive manufacturing with materials-flexibility of powder metallurgy. As a sinter-based method, however, MEX/M suffers from high susceptibility to cracking of large-scale parts during sintering due to high shrinkage rates. In this work, we aim to reduce the risk of sinter defects by combining MEX/M with spontaneous copper infiltration of AISI H11 (1.2343) tool steel preforms, whose sintering involves lower shrinkage rates. Moreover, the H11/Cu composite material exhibits improved thermal conductivity compared to bulk H11 steel. The impact of the printing parameters (filament feed rate and extrusion temperature) on the density and surface roughness of the green part as well as thermal conductivity and Vickers hardness of the H11/Cu composite material were studied. The particular phase structure obtained by MEX/M caused significant anisotropy with 18 % higher thermal conductivity in X and Y direction compared to Z. Dilatometer measurements revealed that sintering of preforms for infiltration yielded three times lower shrinkage rates compared to sintering of regular MEX/M parts. Associated with the lower shrinkage rates is the good process stability that allowed successful manufacture of a large-scale (∼1.4 kg) tool insert. Placing the tool insert on stilts for infiltration prevented infiltration of channels without compromising the infiltration of the preform itself. The H11/Cu composite material exhibited compression strengths of up to 1900 MPa, good bonding quality between the steel and copper phase and no intermetallic phases. This suggests that the developed process is promising for manufacturing material-tailored tool inserts.