The ultrasonic burnishing of cobalt-chrome and stainless steel surface made by additive manufacturing

The purpose of this paper is to investigate the post-processing of Co-Cr and 316L stainless steel components made by additive manufacturing (AM) using ultrasonic burnishing. AM is able to produce functional parts for medical and industrial applications; however, the parts require support removal and post-processing to achieve the technical requirements. To this end, ultrasonic burnishing is a formative method used to improve surface quality and increase surface hardness. The aim of this work is to characterize the effect of process variable (e.g. machine and workpiece relative displacements and spring compression) in the surface quality of AM burnished materials. Two separate design of experiments were performed to find optimal values for the process parameters. The analysis of the experimental result was performed using “Minitab 16” statistical software. To this end, an analysis of variance (ANOVA) was performed to study the effect and interactions of process parameter on the final surface quality. The results showed that surface roughness (Ra) was decreased to 0.18 µm for as-built Co-Cr and 0.55 µm for as-built 316L stainless steel. In addition, the relative increase in average hardness from as-built Co-Cr was 47.4% (i.e. 551.07 Hv) and 70.7% from as-built 316L stainless steel (i.e. 338.17 Hv). The optimal process parameters for post-processing Co-Cr material are around 0.05 mm/r for the feed and 1.5 mm for the spring compression, whereas post-processing of 316L requires 1000 mm/min for the feed speed, 0.025 mm for the side shift and 1 mm for spring compression, when taking also productivity into consideration. The results of this experiment show that the subtractive methods and labour-intensive post-processing of AM metal parts can be replaced by burnishing methods, thus reducing the cost barriers of additive technology and drive its adoption in industry.