Session: 02-01-01: 7th Annual Conference-Wide Symposium on Additive Manufacturing: Metals I

Paper Number: 95355

95355 - Modeling Thermal Behavior and Residual Stress for Layer-by-Layer Rotated Scan Direction in Laser Powder Bed Fusion Process 

Laser powder bed fusion (LPBF) is an Additive Manufacturing (AM) process that uses a laser beam to solidify powder particles following a predefined pattern on a powder bed to build up a layer. Then the bed steps down according to the layer thickness and the recoater spreads a new layer of powder for next scanning. This process is repeated to build three-dimensional (3D) parts layer-by-layer. The metal parts built with this technique may contain manufacturing process induced defects such as porosity, low ductility, crack, delamination, deformation/warpage, etc. These defects can be eliminated by improving the powder quality and varying the AM process parameters including laser power, scan speed, scan pattern, hatch spacing, layer thickness, etc. In LPBF process, the moving heat source and the rapid undercooling cause nonuniform variations in temperature along the build part. This transient and moving, heating and cooling process causes uneven expansion and shrinkage of the part that lead to the development of residual stresses inside the part. The residual stresses depend on the thermal history of the part and may eventually lead to part distortion, crack initiation, warpage, etc. The present study focuses on the effect of altering the scan pattern layer by layer on the residual stress. In this paper, we have numerically investigated the thermal history and the resulting residual stresses developed in parts for crisscross zig-jag, regular zig-jag, and spiral scan patterns in the LPBF process. The proposed heat transfer model imitates the layer-by-layer 3D fabrication pattern of the LPBF process and solves for the conduction heat transfer with temperature dependent thermo-physical properties in the computational domain including appropriate flux boundary conditions (i.e., convection, and radiation). To capture the underlying physics of the melt-pool behavior in the LPBF process, an enthalpy method based solid-liquid phase change model is integrated with the conduction heat transfer. While the regular zig-jag scan repeats its pattern and orientation in the successive layers, the crisscross zig-jag pattern rotates the direction of zig-jag by 90° in each successive layer. The spiral scan pattern makes two spiral passes, from boundary to center and center to boundary, within the same layer. This double pass spiral scan pattern is designed to evenly spread the heat across the layer as it visits every section of the layer twice in its forward and backward passes. The residual stress field across the part is numerically determined by using the temperature gradient obtained from the thermal history for each scan pattern. The findings of this study can be helpful in understanding the effects of altering scan directions layer by layer on the temperature gradient and residual stresses. Furthermore, the results of this study can be used to identify a scan strategy that can enhance the usability of the powder bed fusion additive manufacturing technology.

Presenting Author: Nazmul Ahsan Western Carolina University

Presenting Author Biography: Dr. Ahsan is currently an Assistant Professor of Mechanical Engineering and Engineering Technology in the School of Engineering and Technology at Western Carolina University. Dr. Ahsan achieved his Ph.D. degree in Industrial and manufacturing Engineering from North Dakota State University in 2019. Before that he completed his master’s degree in Industrial Engineering and Management from the same university. His teaching and research interests include advanced design and manufacturing, additive Manufacturing/3D printing, AI in additive manufacturing, heterogeneous lightweight porous structure design and manufacturing, and bio-printing. Dr. Ahsan has thus far published over 30 journal papers and conference proceedings. He has received the Outstanding Early-Career Faculty Award 2020-2021 in the College of Engineering and Technology at Western Carolina University. He is a recipient of Chancellor's Gold Medal Award and Prime Minister’s Gold Medal Award for outstanding performance in his bachelor's degree.

Authors:

Md. Saidur Rahman Roney Western Carolina University
Nazmul Ahsan Western Carolina University
Hayri Sezer Georgia Southern University
Joseph Tang Western Carolina University
Sudhir Kaul Western Carolina University
Hossain Ahmed Georgia Southern University