Multi-purpose parameter development for high productivity in Laser Powder Bed Fusion of IN718

Examensarbete för masterexamen
Panahi, Negar
Laser-Powder Bed Fusion (L-PBF) is one of the main metal Additive Manufacturing (AM) technologies that has seen major developments in terms of materials development, applications, design and quality assurance, etc. One of the main limitations of L-PBF process is the high cost of machine time dedicated to the production of the parts. It is therefore desirable to speed up the process, making wide application of the process more economically viable. In this thesis, we aim to increase the productivity of L-PBF processing of IN718 by using a layer thickness (80 μm) which is at least two times larger than the state-of-art (20 - 40 μm). An increase in the layer thickness essentially decreases the amount of energy input by the laser beam to the material per unit volume. Consequently, other process parameters including but not limited to laser power, hatch distance, scanning speed, etc., shall be adjusted accordingly to enable full densification of the part. Additionally, other aspects of the product qualities should be considered during the optimization process, which includes surface finish, geometrical compliance, and microstructure. This thesis employs statistical Design of Experiments (DoE) and regression analysis for the optimization of key L-PBF processing parameters. In the meantime, two separate experimental campaigns were conducted using similar DOE matrix (central composite design) but different sample geometries. In the first experimental campaign, a simple cubic specimen was used, a processing window with optimized combination of laser power, scan speed, hatch distance was determined using regression analysis based on the measurements of relative densities from cross-sections. In the second experimental campaign, more complex designs (staircase geometry) were used to characterize the influence of heat accumulation effects at thin wall structures on relative density and surface roughness. The applicabilities of volumetric energy density (VED) and its normalised form for evaluation of process stability are discussed.
Additive manufacturing, Laser powder bed fusion, Porosity, Powder layer thickness, IN718, Scanning speed, Laser power, Hatch distance, Image analysis, Surface roughness
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