Laser Surface Hardening of Industrial Parts via Predictive Modeling

Surface hardening is an important manufacturing operation for components that require a hardened case such as bearing races, gears, pistons, cylinder liners, and valve seats. Laser hardening is a surface enhancement process, similar to traditional hardening techniques, but with a few distinct advantages. A high level of laser energy can be very precisely delivered to a small area of the workpiece. Since the heated region is so small, the bulk of the part acts as a heat sink, causing rapid quenching. In this way, the heat affected zone will become almost fully martensitic, producing a surface that can better withstand wear and corrosive environments while minimizing distortion. The phase transformation will also produce high compressive stresses within the hardened region, giving the workpiece better fatigue strength as well. If an area of a part can be seen optically, it can be laser hardened. A predictive model for laser hardening of complex geometric features has been developed and experimentally verified. A transient three-dimensional thermal model is combined with a three-dimensional steel phase transformation kinetic model to be solved simultaneously into one model in order to predict the temperature history and solid phase history of the workpiece, the results of which are then sequentially coupled to a three-dimensional stress model to predict residual stresses. The phase transformation strains are added to the thermal strains at each time step during the heating and cooling cycles to obtain the resultant residual stresses in the workpiece. Accuracy of the predicted results is validated by experiments. Finally, the laser hardening of two industrial workpieces is simulated using two different industrial laser systems in order to verify the hardening model: the laser hardening of a groove on the side of a crankshaft journal and both faces of a mechanical spline.