Numerical Study on Effect of the Building Height and Material Properties on Thermal Distortion of Large Cylinders Manufactured through Laser Powder Bed Fusion

Abstract

The laser powder bed fusion technique involves depositing layers by selectively melting a material. This leads to rapid melting and solidification, followed by repeated reheating and remelting. The complex thermal hysteresis and resultant thermal gradient inevitably cause thermal stress and distortion in additively manufactured products. The thermal stress and distortion lead to dimensional inaccuracies, defects such as delamination and cracking, and finally, adverse effects on the product life. In this study, a thermomechanical analysis of a large cylinder (hollow shape, with a height of 750 mm, an outer diameter of 500 mm, and a thickness of 20 mm) was performed using the finite element method to investigate the effects of building height and material properties on thermal distortion. Specifically, the evolution of thermal distortion was systematically interpreted with the thermal hysteresis. Depending on the building height of the cylinder, the thermal hysteresis was influenced by the bed plate and the thermal effect of the predeposited and postdeposited layers. In addition, the thermal distortion tendencies of Ti-6Al-4V and Inconel 718 metal powders were examined based on the material properties, particularly thermal diffusivity. The maximum thermal distortion occurred at approximately 100 mm below the top surface of the cylinder for both materials. Moreover, the thermal distortion of the Ti-6Al-4V was more significant than that of Inconel 718 because of the lower thermal diffusivity of the former. Key words: Powder bed fusion, Thermo-mechanical analysis, Thermal distortion, Thermal hysteresis, Material properties, Metal powders