SHAPE DEFORMATION OF A PISTON-RING GROOVE BY LASER-SURFACE HARDENING

With laser beam heating it is possible to obtain a precisely controlle d hardening area, in which the process parameters and material propert ies are important for the hardened area and deformed surface shape. In this study, the transient heat flow, thermal stress and deformed shap e during laser surface hardening of the piston ring groove of a ship's engine were analysed by a finite element method. Using a modified two -dimensional finite element model, the heat-affected zone (HAZ) sizes and the deformed shapes in laser surface hardening were successively c alculated. The effects of the process parameters and material properti es on the deformed shape of the hardened part were investigated by usi ng 2(n-1) fractional factorial design. The simulation results revealed that the process parameters such as laser power and traverse speed ha d a greater influence on the deformed shape of the surface-hardened pa rt than the physical properties of the base metal. The displacement of the hardened surface was determined mainly by the bending and bulging phenomena which were due to the temperature gradient and martensitic phase transformation; the bending effect played a more important role than the bulging effect. Tensile residual stress occurred in the harde ned area, while the maximum compressive residual stress occurred under the boundary of the hardened zone.