Aluminium butts heads with steel in injection tooling

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No panacea for toolmakers

Aluminium is not suitable for all applications, however. Whilst some aluminium alloys can be used at moulding temperatures up to 180C, non-aluminium alternatives are recommended for moulding at higher temperatures and high pressures. Additionally, certain resins and thermosetting plastics are not suited for use with aluminium moulds, due to processing requirements.

Benefits for those using steel

Aluminium’s properties give it a number of distinct advantages as a mould material. The thermal conductivity of an aluminium mould alloy (~160 W/mK) is about four times higher than that of mould steel (~40 W/mK), which leads to three principal benefits:

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  • Simpler mould design. A less complicated cooling system is required, and issues associated with hotspots in mould design are reduced.
  • Reduced part distortion. Parts made using high strength aluminium and P20 steel moulds were compared. The level of internal residual stress in steel mould-produced parts was higher.
  • Reduced cycle time. Within studies, a high strength aluminium mould extracted more than 1.6 times the thermal energy of a P20 steel mould. This leads to quicker melt solidification, which in turn reduces the moulding cycle time.

Aluminium alloys generally have lower rigidity and lower mechanical strength compared to steels at moulding temperatures. Even though mould wall thicknesses need to be increased by up to 40% to take this into account, an aluminium mould is still less than half the weight of a steel one for the same application. This weight decrease reduces load on process machinery.

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Process modelling software can compare the machinability of steel (P20) with high-strength mould grade aluminium. Aluminium can be machined nine times faster than if there is no limit to the machine capability. When power consumption is a limiting factor, research shows that the same machine can machine aluminium four times faster than steel.