Laser Direct Metal Deposition (DMD) has been developed as a manufacturing process to deposit coatings on existing materials and proves advantageous in Additive Manufacturing (AM) of complex and precise components. However, it is necessary to carefully determine the proper process parameter combinations to make this method economically viable for industries. The intent of this study is to address enhancement in productivity of laser DMD of stainless steel EN X3CrNiMo13-4. Accordingly, the effects of the main laser process parameters of laser power P, scan speed v, powder flow rate $$\dot{\mathrm{m}}$$ m ˙ , and spot diameter s on track geometries and build-up rate are discussed. The regression analysis is conducted to derive correlations between the combined set of main parameters and deposition rate. The results show a good linear regression correlation of R2 >0.9 for the geometrical characteristic of aspect ratio, dilution, and deposition rate. The constructed processing map, using linear regression equations, presents proper process parameters selection in connection with deposition rate, aspect ratio, and dilution rate.

Burckhardt Compression Holding AG, based in Winterthur, is an internationally active manufacturer of reciprocating compressors who uses three-piece pistons in its Laby® reciprocating compressors. Due to their design for casting, the pistons have a high weight, which limits the size of the piston, particularly for the large diameters. For this reason, solutions are being looked for to produce pistons in lightweight design using metal additive manufacturing processes to counteract these challenges. One of the innovative techniques for weight reduction that has been applied in various fields of science and industry is laser direct metal deposition (DMD). Therefore, a project was started with Burckhardt Compression to reduce the mass enabling higher operating speeds. This study presents a workflow to manufacture a lightweight piston from martensitic steel 1.4313 by direct metal deposition (DMD) with a diameter of approximately 342 mm and a height of 140 mm. The piston is characterized by different segments, which are conventionally and additively manufactured to overcome machine limitations. The piston crown was joined to the additive manufactured part and sealed by CO2 laser welding. Reducing the laser power in DMD reduced the temperature, and hence, oxidation of manganese and silicium and reducing the carrier gas flow improved the buildup rate and reduced the turbulence induced oxidation. Alternating the feed direction per layer improved the geometrical accuracy and avoided material accumulation at sharp corners. A method was found to indicate quantitatively the geometrical accuracy of a radius in buildup direction. The welding types and seams for laser welding were selected to enable a good force flow; however, a clamping device was necessary. A double weld strategy was considered in order to reduce a notch effect at the hidden T-joints. The design enabled a 40% weight reduction resulting in a weight of 24 kg compared to the cast piston with a weight of 40 kg. Metallographic analysis and 3D scans were performed in order to evaluate the material quality and geometrical accuracy. The study shows the limitations and challenges of DMD and how to overcome machine limitations by part segmentation.

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