Comparison of Theoretical and Practical Studies of Energy Input in Laser Additive Manufacturing (LAM) Using Stainless Steel
A. Stepanov, H. Piili, M. Islam, A. Salminen and O. Nyrhilä
Laser additive manufacturing (LAM), known also as laser sintering, is an additive manufacturing process where powder material is molten with laser beam layer by layer. From simple to very complex three-dimensional (3-D) geometries can be manufactured to solid components from metallic, ceramic, composite or polymer powder. Methods to control the process have started to gain an essential role in laser additive manufacturing processes. The objective of this study was to investigate laser additive manufacturing monitoring methods and find suitable method for detection and calculation of thermal features. The LAM process was monitored in situ simultaneously with pyrometer and active illumination system. Energy input and volumetric energy density were compared for energy evaluation. In the study it was noticed that an increase in energy input to the range of 250 to 2000 J/m results in ball formation. Homogenous and non porous evenly distributed surface was achieved with energy input of 2500 J/m. Energy input of 5000 J/m showed interesting phenomena; layer formed is the most uniform of all results. However, some unevenly distributed porosity is noticed. It can be concluded that with energy input the heat penetration start decreasing to this semi molten surface of the stainless steel powder. At the same time, a denser surface with less balling phenomena was obtained. Collapse of surface was observed with energy input of 10000 J/m. Such behaviour with this energy input on stainless steel suggests lower heating impact what might be caused by lower absorption.
Keywords: Laser additive manufacturing (LAM), additive manufacturing (AM), stainless steel, energy, heat affected zone (HAZ)