Shape modification of cooling channels obtained by LPBF printing with non-destructive optimization methods

Kurzfassung

The use of laser powder bed fusion (PBF-LB/M – powder bed fusion, laser-based/metal) methods in the aerospace sector can offer significant technological advantages for the production of complex and integrated parts, such as turbine blades or combustion chambers with an internal network of cooling channels [1]. However, the build direction of parts in PBF-LB/M causes sizable differences in the achieved surface qualities. Most critical are the downward-facing areas, the so-called downskin surfaces. These regions are affected by heat-accumulation (overheating) due to the poor heat conductivity of the powder below, which results in fusion defects. Defects and poor surface quality can be especially detrimental for internal cavities that are difficult to access for postoperative processing. Thus, a horizontal orientation of internal cooling channels in a turbine blade that needs to be manufactured in a vertical build direction would be far from optimal. Particularly when the channel diameter approaches the lower limits for PBF-LB/M, a large fraction of the cooling channels commonly end up being clogged with melt conglomerates and attached powder particles. The goal of the study is to optimize the design of the internal channels at the CAD engineering stage in order to achieve the desired netshape with LPBF printing of Inconel 718. Different CAD forms were investigated for a variation of channel orientations (0, 45, 60 and 75 degrees relative to the working platform) and nominal inner diameters (0.6, 0.7 and 0.8 mm). Inconel 718 channel specimens printed on an EOS M300-4 machine were analyzed using non-destructive 3D CT scanning methods. The quantitative and qualitative analysis allowed to fundamentally redesign the channel shapes in CAD design and obtain shapes close to the desired ones after printing.