Development of a laser preheating concept for directed energy deposition

In today’s manufacturing, additive manufacturing processes enable the production of complicated three-dimensional structures that are hard to be manufactured with traditional manufacturing processes. Due to its high build rate, the laser-based directed energy deposition (DED-LB) process is an attractive and versatile process to manufacture these kinds of components. In addition to the production of components, DED-LB is used for repair or coating applications. The DED-LB process consists of a multitude of complex thermal mechanisms with high heating and cooling rates of 5 × 102 up to 5 × 105 K/s. For materials with high hardness or low thermal conductivity like tool steels, cast iron, or tungsten carbide, these high cooling rates can lead to defects in the microstructure like cracks, pores, or delamination between the substrate and the deposited structures. By preheating the substrate, the cooling rates can be reduced and defects can be eliminated. In this paper, a preheating cycle was developed, which uses the laser of a DMG MORI LT 65 DED hybrid machine as a moving heat source for the substrate preheating. For this cycle, process parameters, a tool path strategy, and a temperature control system were developed. The impact of the elaborated concept was shown by depositing tungsten carbide in a nickel matrix on an S235 steel substrate.