Enabling Electropolishing of Complex Selective Laser Melting Structures

In the last years the industrial application of selective laser melting (SLM) has been increased. Main advantages of SLM are the reduction of production time for small batches and the freedom to generate complex designs. However, the rough surface quality of SLM parts currently limits their use and hinders the application in several industry sectors such as the hygienic and food industry. Due to the high complexity of SLM parts, the application of conventional processes is limited. Electropolishing (EP) is a promising process for reducing the roughness of simple SLM parts. However, it has not yet been explored intensively on complex SLM parts. Additionally, design constraints for the design of SLM parts to enable post processing are not yet existent. This experimental study investigates the resulting roughness of EP on different SLM design elements. Three types of EP were investigated, direct current, pulse/pulse reverse current and pulsed current EP. Additionally, the current density and processing time were varied. The SLM test sample (316L) contains internal pipe surfaces with different diameters in different orientations, overhangs and a lattice structure. To analyze the surface roughness, the arithmetic mean height of the roughness (Sa) was measured. At the end of the paper the findings on the process and the design constraints for SLM parts are summarized. The results show a significant improvement of the roughness on the external surfaces of the test sample for all parameter sets. The orientation of the surfaces with respect to the build direction influences the reduction of Sa. Increasing the pipe diameter leads to an increasing effect of internal EP. Finally, the DC parameter set showed a significantly better improvement of the Sa value on the internal lattice structure.