Abstract
A laser powder bed fusion (LPBF) strategy was developed for manufacturing small channels with high dimensional accuracy in Inconel 718 structures. Particular attention was paid to surface characteristics such as equivalent diameter and shape factor. The inherent surface quality of external surfaces was optimized by a systematic variation of the LPBF contour parameters as well as the channel cross-section. The mean arithmetic roughness Sa was analysed for upskin, vertical and downskin surfaces with respect to the build platform. Simultaneously, the effect of the build direction on the quality of internal free-shaped surfaces was investigated on channels with diameters from 500 to 1000 µm and build orientations from the horizontal (0°) to vertical (90°). A significant improvement in dimensional accuracy was achieved by using an optimized droplet-shaped cross-section that is scaled as a function with the build inclination. An angular analysis of the surface roughness in different regions of the channels confirms that this modified cross-section reduces the fraction of channel regions that show a particularly high surface roughness due to inward melting. In combination with an optimized contour processing strategy, the modified channel resulted in the best properties for inclinations below 45°. The shape factor increased from 0.4 to almost 0.9, i.e., close to the ideally round shape.
Highlights
Laser powder bed fusion (LPBF) is one of the preferred additive manufacturing (AM) technologies for creating highly complex metallic components directly from digital models by melting metal powders layer-by-layer [1,2,3]
The goal of the present study is to investigate the effects of the processing strategy and the build direction on the quality of small internal channels in Inconel 718 structures produced by LPBF and to improve their geometrical accuracy by a combination of manufacturing parameters, scan strategy and geometrical shape optimization
The importance of the contour parameters for external roughness has been discussed in many works, but the systematic optimization approach for the contour parameters chosen here, ‘‘laser power - scan speed” and ‘‘scan speed - energy density”, has not yet been reported for the surface manufacturing of parts produced by LPBF
Summary
Laser powder bed fusion (LPBF) is one of the preferred additive manufacturing (AM) technologies for creating highly complex metallic components directly from digital models by melting metal powders layer-by-layer [1,2,3]. Inconel 718 is characterized by a high strength, good fatigue properties as well as oxidation and corrosion resistance at elevated temperatures of up to 700 °C [9,10]. For these reasons, conventionally manufactured IN718 is widely used for high temperature applications in aerospace industry, gas turbines, turbocharger rotors, nuclear reactors, highly-loaded rotating parts, and a variety of other applications [11,12,13]. IN718 is of interest for use in aircraft engine components such as combustion chambers with a modern cooling system consisting of multiple thin internal channels [14,15,16,17,18]. Along with the powder deposits on the walls, the roughness adversely affects the functionality of the cooling systems and leads to a decrease in the flow rate due to high friction, possible turbulence, loss of pressure and loose particles that could damage other equipment
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