Numerical investigation into laser-based powder bed fusion of cantilevers produced in 300-grade maraging steel

Laser-based powder bed fusion of 300-grade maraging steel allows the production of parts with a high hardness, which improves the service life and wear resistance of tooling or mould insert produced from this material. The material typically consists of a martensitic matrix material, with retained austenite and nano-precipitation. The transformation from austenite to martensite has been linked to compressive stresses at the surface of parts produced in 300-grade maraging steel. In a cantilever beam-type part, this means that after cutting from the base-plate, the part will bend downwards, which is the opposite direction from the deformation found in most other materials after additive manufacturing. One way to gain insight into processing 300-grade maraging steel, while limiting the number of test samples that need to be printed, is by means of a numerical model. Using previously established models, additive manufacturing of a cantilever part in 300-grade maraging steel is simulated. Inclusion of the transformation from austenite to martensite into a numerical simulation of the laser-based powder bed fusion revealed the origin of the compressive stress at the surface of a simple cantilever beam-type sample. Additionally, changing the effective laser power through the laser absorptivity shows that the behaviour of the post-cutting deformation flips as compared to more conventional materials. Information about the laser absorption coefficient is rare, while it can greatly affect the results of a simulation. It is included in the presented result through the effective laser power, which is the product of the input laser power and laser absorption coefficient. When the effective laser power is changed from 95 W to 47.5 W, the cantilever bends upwards rather than downwards after release from the base plate. The results demonstrate the major influence played by the laser absorption coefficient on the simulation, an aspect to which little attention is paid in literature, but is proven to be one of the main factors to determine the component distortions after the laser-based powder bed fusion process.