The effect of variable tool path in directed energy deposition method on the material properties

Additive manufacturing (AM) is preferred in many industries due to the design flexibility it provides, providing mechanical properties close to parts obtained by traditional methods and shortening lead times. Direct energy deposition (DED) is a variant of additive manufacturing and laser metal deposition (LMD) is considered a sub-branch of the DED process. It uses laser energy to melt and deposit powder material fed from a nozzle. This thesis presents parameter optimization by producing "S" shaped samples using PH -13-8 Mo stainless steel powder and then tool path optimization studies by producing block samples using 17-4 PH powder. The effect of the concept of energy density on the obtained sample geometry was made by producing S-shaped single-row samples by determining the process parameters that directly affect the energy density. As a result, using parameters with low energy density, it is clear that S-shaped walls are not in the desired structure and are inappropriate. With parameters with high energy density, samples with a more suitable structure and larger in volume can be obtained. However, the geometry of the samples does not remain constant during deposition due to thermal deposition and has a variable structure. Such geometric defects can be seen in samples obtained at any energy density. Such defects occur when sufficient heat energy cannot be obtained from a moving nozzle to melt the powder. The level of this defect varies according to the energy density. After the first experiment was completed, the effect of the toolpath strategy on the hardness and porosity of the material cross-section, 17-4 PH stainless steel material with a composition used similar to the PH-13-8 Mo stainless steel material, block samples were produced by applying 2 different toolpath strategies. The samples produced with the variable tool path strategy had more porosity across the section and provided better results in terms of hardness. The samples produced with the fixed tool path strategy had lower porosity and lower hardness than the samples produced with the variable tool path strategy. Porosity reduces the mechanical strength of the parts because of volume ratio of porosity and size of the porosity and makes it difficult to meet the part requirements. Therefore, minimal porosity formation is expected for samples produced by additive manufacturing. Otherwise, it is necessary to reduce the porosities with additional processes that require heat treatment under pressure, such as "HIP", and this creates high costs.