Manufacturing a prototype with laser direct metal deposition and laser welding made from martensitic steel 1.4313

Abstract

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.