Residual Stress in Laser Melting Process: Analysis and Prevention(1/2)

Laser melting process is commonly seen in laser-based machining, including laser cutting, laser welding,laser surface modification, and the newly developed laser additive manufacturing. In a laser meltingprocess, heated affected zones are rapidly heated and cooled as the high-energy laser beam passes through theplanned path. Consequently, large temperature gradients and thermal stresses are generated in theworkpiece because of a mismatch in volume expansion and contraction. The thermal-mismatch inducedstresses are eventually, to a certain extent, left as residual stresses which could reduce the structural strengthand degrade the quality and reliability of the workpiece. If the variations of temperature and thermal stresscan be predicted in a laser melting process, it is possible to adjust the process parameters to minimize theresidual stresses in the workpiece. In this way, quality and reliability of the workpiece can be improved soas to broaden the applications of laser melting process. It is thus necessary to develop an effective modeland relevant prevention technique for prediction and prevention of residual stress in a laser melting process.For this reason, the aim of this two-year study is, through finite element method (FEM) modeling, to developan effective modeling technique for predicting the variations of temperature and thermal stress in a lasermelting process by systematically characterizing the process parameters that govern the residual stressdistribution. FEM models for laser melting process are to be developed in the following sequence: heatsource of a fixed-point laser beam, heat source of a moving laser beam, one-dimensional laser additivemanufacturing, two-dimensional laser additive manufacturing, optimization of laser process parameters forminimizing residual stress, three-dimensional additive manufacturing, and evaluation of a residual stressprevention technique using multiple laser beams. Counterpart experiments are also to be conducted tovalidate the FEM models developed. It is hoped that results of this study could provide useful informationfor laser additive manufacturing developers and makers to prevent distortion and/or early failure ofworkpiece made by laser melting process.