Experimental and Numerical Study of Heat Transfer in Thin-Walled Structures Built by Direct Metal Deposition and Geometry Improvement via Laser Power Modulation

Direct metal deposition (DMD) is a method of additive manufacturing in which parts are manufactured layer by layer by melting powder particles, carried in a stream of gas to the working area by using a laser beam. Due to the layer wise nature of the process, heat eventually builds up inside a part, leading to increased temperatures and melt pool volumes in the working area. This effect is especially prominent in thin single-pass wall structures, which leads to a deformation of geometry or, in extreme cases, to a complete failure of a build. In this paper, a numerical simulation of the thermal behavior of thin-walled structures made from 316L stainless steel by direct metal deposition method with variable and constant laser power was performed. The work is carried out to study the effect of the number of deposited metal layers and their radius of curvature on thermal fields distribution in the workpiece and the resulting geometry of the part. Dependencies of the molten pool volume on the number of layers and a radius of curvature of thin walls have been established. To stabilize the wall thickness of parts, polynomial equations relating laser power input and radius of curvature to layer number are obtained. By modulating the laser power, it is possible to maintain the same volume of the molten pool in each layer, and at different radiuses of curvature, which favorably affects the uniformity of the thickness of thin walls. An analysis of the geometry of obtained samples is carried out, results of which are consistent with the simulation results. It has been established that the use of a variable power of laser radiation when growing thin walls makes it possible to reduce the roughness of their lateral surface by more than 2 times.