A fundamental investigation on three–dimensional laser material deposition of AISI316L stainless steel

Abstract

Laser material deposition (LMD), a direct laser deposition additive manufacturing technology, has been widely used to build full density metal parts. However, owing to the parallel deposition way which is universal used in LMD process, the staircase effect is presented even the collision occurs during the shape of target part is irregular and relatively complex. In this paper, the appropriate range of z-increment, which can assure the thin-walled part is perfectly fabricated, was verified initially. Based on the effects of defocusing and z-increment on the deposited height, a novel three-dimensional laser material deposition process, which can provide new ways of avoiding the staircase effect and eluding the collision, was proposed. An experimental investigation, which contains the effects of deposition strategies (parallel and three-dimensional deposition way) and slope angle on the microstructures, hardness, and tensile properties of the fabricated slope thin-walled part, was conducted. The results showed that the grain size near the high side of slope thin-walled part increased with the increase of the slope angle regardless of the deposition way due to the increased accumulated heat. The average hardness of the parts with different deposition way were basically the same, but the distributions of harness were quite different. In addition, with the increase of the deposition height, the hardness increased until the distance to the substrate was about 25 mm and then decreased. The UTS and elongation of the LMD part in parallel deposition way were slightly higher than those of the part in three-dimensional deposition way. The UTS and elongation increased firstly and then decreased with the increase of the angle (β) between tensile loading direction and horizontal direction regardless of the deposition way. In the case of parallel and three-dimensional deposition way, the biggest UTS was presented during the β was 45° and 25° respectively because the direction of tensile loading was approximately perpendicular to the sliding surface that ensure the shearing force was smallest and the boundaries of molten pool could suffer from the highest tensile force. The smallest UTS showed when the β was 90°.