Development of localised process parameter control for repeatability in metal additive manufacturing

Abstract

Due to the many advantages associated with metal additive manufacturing (AM) processes, research into these technologies has grown significantly over recent years. However, repeatability and reproducibility are critical issues in AM when compared to traditional manufacturing processes.

The overall aim of this project was to comprehensively investigate the sources of this repeatability issue and to develop a means of improving the process repeatability. This was achieved by a thorough literature review with an in-depth focus on the configuration present in the ProX DMP 200.

The causes and impact of repeatability were reviewed at three stages of the AM process: pre-process, para-process and post-process. It was found that the most impactful effect for repeatability is non-uniform energy density in the build area. This was predominantly due to errors associated with the F-Theta lens, plume absorption and the effect of angle of incidence on the powder bed.

A new energy density equation was developed to account for the spatially varying energy density in selective laser melting. This equation was used as a basis for location-dependent control of process parameters. These adapted parameters were tested using samples made of cobalt chrome alloy and 316L stainless steel.

The adapted parameters reduced the range of variation in local mechanical property values by up to 40%, representing a statistically significant reduction in the systematic variation between the centre and edge of the machine?s working envelope.