Additive Manufacturing of Mould Inserts with Mirror-like Surfaces

Selective laser melting (SLM) is often applied in the production of steel moulds with high wear resistance and conformal cooling channels for advanced thermal management. The surface finishing of such moulds is crucial, especially if it is intended for the moulding of plastic parts with aesthetic functionality.

The surface quality of such metal 3D printed moulds is typically refined by means of subsequent material removal processes, but this is often hindered by residual porosity and inhomogeneity in the metal structure of the 3D-printed part. In this paper an indirect tooling process chain for production of mould inserts is proposed.

The process chain aims at exploiting the good replication capability of electroformed nickel, to copy mirror-like substrates. The bulky part of the insert is produced by means of SLM that shows a considerably higher material deposition rate. The thermal input is controlled throughout the process chain to prevent deleterious grains growth in the nickel layer.

The roughness of the nickel surface is measured after the selective etching of the substrate and compared with the substrate roughness before the nickel deposition, showing good replication of the master surface. The proposed process chain overcomes the problems related to the deposition of thick electroformed coatings by coupling electroforming with higher output additive processes such as SLM - that furthermore allows the introduction of cooling channels in close contact with the mould surface.