An additive manufacturing assisted electric discharge machining technique to produce complex, thin-walled, injection mould cavities in 316 L stainless steel

Abstract

This study takes a unique approach using an additively manufactured (AM) copper electric discharge machining (EDM) electrode to surface finish a 316 L Stainless Steel AM injection mould cavity. The research has a dual focus: first, to comprehend the achievable accuracy and surface finishing capabilities of a complex geometry electrode, manufactured using atomic diffusion additive manufacturing (ADAM). Second, reduce the volume of material used to manufacture electrodes and workpieces by printing the cavity geometry net shape, thereby reducing the number of electrodes and EDM process steps required to form the desired cavity geometry and surface finish. The study reveals that the ADAM electrode was subject to variable shrinkage, leading to varied results on the cavity surface finish and geometric accuracy after the EDM process. This method resulted in an average surface roughness (Ra) improvement of 56.3 %, with some surfaces seeing up to a 77 % reduction in their Ra compared to the as printed roughness. This study achieved a mean cavity accuracy of 0.07 mm, standard deviation 0.204 mm and median accuracy was 0.081. However, the maximum and minimum workpiece accuracy was + 0.442 mm / −0.24 mm. These findings indicate that an AM assisted EDM post-processing method, using a net shape AM cavity and an ADAM EDM electrode, can significantly reduce the number of electrodes in EDM post-processing from 10 to 1. Further opportunity exists to improve the accuracy obtained in this study by optimising the ADAM and EDM process parameters to better control the electrode geometry or apply alternative AM technologies for similar workflows.