The effect of process parameters and mechanical properties of direct energy deposited stainless steel 316

Process parameters in Direct Energy Deposition (DED) Additive Manufacturing are playing an important role in order to fabricate desired parts. In this research, we studied the effect of 3 process parameters, namely laser power, scan speed and powder feed rate. Based on variation of these parameters, we examined macrostructure and mechanical properties of stainless steel 316 fabricated parts, employing an orthogonal L9 array using the Taguchi technique. The results showed laser power to be the most effective factor whereas scan speed and powder feed rate were respectively less effective. In addition, effect of height of deposition was also considered. The results indicated change in macrostructure with increasing height. Finally, validation of a previously defined energy density equation for the DED process was studied. The results clearly showed the current energy density equation cannot fully represent a relation between input energy and output geometry, macrostructure, and mechanical properties. Introduction Additive Manufacturing (AM) is a relatively new method of fabrication that is being implemented widely in automotive, medical, aerospace industries [1]. Metal-based AM is increasing at a particularly high rate, focusing on direct manufacture of complex geometry metal parts. Control of process parameters in order to achieve desired mechanical property, macrostructure, microstructure, and dimensional accuracy has been always a challenge on Direct Energy Deposition metal AM processes in particular [2]. Laser Engineered Net Shaping (LENS) is a typical process of Direct Energy Deposition and the subject of this research. In this specific process, there are up to four nozzles that deposit powders and a laser which melts this powder to create a melt pool in order to fabricate or repair a metallic part on a substrate [3]. To address these problems, firstly it is necessary to have an understanding of the effect of parameters on part properties. In order to reach that goal, Kobryn et al studied the effect of laser power, scan speed, and substrate thickness on porosity for Ti-6Al-4V (Ti6-4) deposits. They found porosity declines with increasing laser power [4]. Krishna et al fabricated several cylindrical titanium samples with different dimensions, and different values of open and close pores with random process parameters such as laser power, scan speed, powder feed rate and hatch distance. They reported compressive strength changes by changing the mentioned process parameters [5]. With the same methodology, Bandyopadhyay et al deposited several samples with different materials such as pure Ti and TiNi alloy and then compared compressive stiffness of samples that have similar porosity[6]. They showed compressive stiffness for NiTi samples are much lower. The main drawback of these studies is that all process parameters were chosen randomly. Two further studies, one using pure titanium and one using Ti6-4, were carried out on the effect of porosity distribution on mechanical properties. The result clearly indicated pore distribution is very important on mechanical property for both materials [7, 8]. 1058 Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference Reviewed Paper