Study on the Measurement of Stress in the Surface of Selective Laser Melting Forming Parts Based on the Critical Refraction Longitudinal Wave

Measurement and control of stress in the metal forming layer is the basic problem of selective laser melting (SLM) forming parts. The critical refraction longitudinal (LCR) wave method to test stress in metallic materials has been extensively studied. However, when testing of stress in selective laser melting (SLM) forming parts using this method, some deep-seated regularities of this technology are still not clear. In order to reveal the mechanism of the LCR wave method to measure stress in SLM forming parts, specimens made of 316 L stainless steel were manufactured using meander, stripe, and chessboard scanning strategies. Static load tensile test were applied to SLM forming specimens, with the purpose to demonstrate the scanning strategy has important effect on the LCR wave method to test stress in SLM forming parts. The regularity of the LCR wave velocity on stress is obtained in this study. The anisotropic microstructure of SLM forming parts has an unneglectable effect on the LCR wave stress test. The essential principle of anisotropic microstructure effecting the LCR wave velocity in SLM forming parts were revealed in the experiments. The results of the experiment provide a basis for non-destructive and reliable test of stress in SLM forming parts and other inhomogeneous materials.