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 Directed Energy Deposition (DED) process is an attractive and versatile process to manufacture these kind of components. In addition to the production of components, DED is used for repair or coating applications. The DED process consists of a multitude of complex thermal mechanisms with high heating and cooling rates of 103 up to 105 K/s. For materials with a high hardness or a 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 an 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 welding tungsten carbide in nickel matrix on S235 steel substrate.
Keywords
- Additive Manufacturing
- Directed Energy Deposition
- Substrate Preheating