Simulation of thermal stress in induction-assisted laser cladding

Abstract

Aim of this work is the prevention of high stresses and cracks which may occur in wear and corrosion protective coatings and three-dimensional structures generated by laser cladding. This may help to overcome the still valid limitations of this technology with respect to very hard coating materials and high feed rates.Thermal stresses which form during laser cladding can be reduced by using tailored temperature fields consisting of a flat base and a steep peak obtained by induction and laser heating, respectively. Optimization of this so called induction assisted laser cladding technology requires a thorough understanding of the mutual interaction of physical phenomena such as heat flow, phase transformations, thermal expansion, and plastic flow, which are responsible for the evolution of stress and distortion. This is best achieved by modeling. On the basis of a semi-analytical description of the laser cladding process a three-dimensional FEM model was developed which enables calculations of the thermally induced stress and strain for single weld beads as well as for coatings consisting of several beads.Since process optimization by parameter studies using that model requires a lot of calculation time, additional simplified models, which are able to reduce significantly the calculation time, were derived and checked by comparison with 3D FEM calculations.Using the mentioned tools the influence of various parameters such as feed rate, bead shape, substrate thickness etc. as well as of the size and the position of the inductors has been studied. Particular attention has been paid to the thermal and mechanical interaction between overlapping weld beads forming coatings or three-dimensional structures.The induction assisted laser cladding technology is not only able to reduce stresses but also to decrease the structural damage caused by plastic strain. The latter seems to be the more important effect in the prevention of cracks for material couples which have strongly different coefficients of thermal expansion and for coating materials with low fracture strain.Aim of this work is the prevention of high stresses and cracks which may occur in wear and corrosion protective coatings and three-dimensional structures generated by laser cladding. This may help to overcome the still valid limitations of this technology with respect to very hard coating materials and high feed rates.Thermal stresses which form during laser cladding can be reduced by using tailored temperature fields consisting of a flat base and a steep peak obtained by induction and laser heating, respectively. Optimization of this so called induction assisted laser cladding technology requires a thorough understanding of the mutual interaction of physical phenomena such as heat flow, phase transformations, thermal expansion, and plastic flow, which are responsible for the evolution of stress and distortion. This is best achieved by modeling. On the basis of a semi-analytical description of the laser cladding process a three-dimensional FEM model was developed which enables calculations of the thermall...