UC Irvine

Laser powder bed fusion (LPBF), as a popular additive manufacturing (AM) technique, has gained a great deal of research attention and industrial application. Its capability of producing complicated shapes and structures enables this technique to be favored for manufacturing critical prototypes and complex parts. Meanwhile, LPBF techniques also have a significant advantage over many other AM processes that is they do not require support structure which allows more interest in producing parts with higher complexity since overhangs and unconnected islands are supported by surrounding unfused powder bed instead. However, in fabrication, the constant melting and cooling of metal powders by layers leads to a large gradient and rapid evolution of temperature, causing considerable residual stress and deformation. Fuel cells are widely regarded as a promising candidate as the next-generation energy device, which electrochemically converts the chemical energy in the injected fuel, such as hydrogen gas, directly to electricity. Fuel cell components are required to be free of distortion to avoid leakage of reactant gases and contaminants and interfacial resistance. In this study, a three-dimensional thermal analysis model is employed to numerically study the residual stress and deformation in the LPBF fabricated inlet/outlet of a fuel cell that connects to its bipolar plate. Inconel 718 and stainless steel SS316L are used as the powder materials, respectively. The results of distortion are validated against both experimental and other modeling data. Additionally, the validated tool is employed to investigate several major parameters in LPBF fabrication and their impacts on distortion, including the laser power, laser speed, and layer thickness. It is found that the laser power and speed have a significant impact on the distortion of the pipe wall, while the scan pattern shows little influence. Additionally, SS316L shows a much less distortion (about 40 µm) than that of In718 which is about 90 µm for the maximum distortion and a nearly 30% smaller average distortion at all measuring locations.