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.

Comprehensive Distortion Analysis of a Laser Direct Metal Deposition (DMD)-Manufactured Large Prototype Made of Soft Martensitic Steel 1.4313

“…The prototype was produced on a TruLaser Cell 7020 from Trumpf, Ditzingen, Germany on a flat and steady table by using DMD and laser welding, as described by Dey et al [5]. In order to achieve the required toughness and avoid oxidation, the piston was annealed in a vacuum chamber with the temperature-time profile shown in Figure 2.…”

“…The prototype was built of powder-shaped and hot-forged 1.4313, as described by Dey et al [5]. The powder particles were in the range of 63-150 µm.…”

“…DMD is commonly used in the energy and aerospace industries, where highvalue components are repaired and built. In recent years, complex and large parts, such as impellers [4], propellers [3], or pistons [5], have been built using DMD.…”

“…In a previous study, Dey et al [5] successfully produced a piston for a gas compressor through DMD and laser welding using martensitic steel. The prototype was characterised by a massive outer wall and core interconnected by thin walls.…”

Reducing Oxidation during Direct Metal Deposition Process: Effects on Ti6Al4V Microstructure and Mechanical Properties

“…The focus of research has been on finding process windows and specifying the microstructure and mechanical properties for Fe-and Ni-based alloys [4][5][6][7], but not in creating a nearly oxidation-free process. This is important, however, as Ti alloys and, surprisingly, steels such as the martensitic steel 1.4313 exhibit strong oxidation under uncontrolled conditions [8]. A process window can be found by varying the primary process parameters of laser power, travel speed, mass flow rate and laser spot diameter.…”