The Finite Element Simulation Research on Stress-Strain Field of Laser Cladding

Abstract

The tensile plastic strains and the residual tensile stresses caused by heat input during the laser cladding process are the main reasons for the cracking. In this paper, the laser cladding process on a type 1045 steel plate with Ni60 powder feeding was investigated and simulated by finite element method to analyze the temperature field and stress-strain field of the laser cladding process. In the temperature field model, the main considerations were given to the heat source data and the thermal boundary conditions. The interactions of laser, powders and base metal were mainly considered in the application of the heat source data. The relationship between the heat convection coefficient of work piece surface and the temperature variation was mainly considered in the application of thermal boundary conditions. In the stress-strain field model, the main consideration was given to the elastic-plastic characteristics of the materials, and the materials were assumed to be linear strain-strengthened. Moreover, the thermal stresses could be solved through the temperature field and were subsequently applied directly to the stress-strain field model as loads. Besides the temperature variations, the stress variations and the strain variations of some critical points (including the crest point of the cladded layer and intersection point of cladded layer and plate) were also obtained through the finite calculation. The temperature variations show that the heating curve is approximately a straight line while the cooling curve is like an arm of a hyperbola. The strain variations show that the thermal strain has a variation trend similar to the temperature variations. The elastic strain of each point is very low when compared to the plastic strain. The calculated results show that the tensile plastic strain of the crest point on the coating is the greatest in the cladding direction and the tensile stress in this direction of this point is great too. As a result, transverse crack can be easily initiated at the crest of the coating. While the tensile plastic strain at the intersection point of the base metal and coating is the greatest in the direction vertical to the plate thickness, the stress at this point (in the same direction) is compressive. Therefore, the intersection points tend to form a limited toe crack which can not grow.

Lasers Based Manufacturing

“…Sequential thermomechanical analysis of laser cladding process in ANSYS ® has been performed to obtain temperature profile for both planar and curved mesh of clad profile (Chen and Xue 2010;Deus and Mazumder 2006;Zhang et al 2008Zhang et al , 2011Plati et al 2006). The temperature values obtained from transient thermal analysis are used as input for obtaining longitudinal and shear residual stresses for the thermomechanical analysis (Chen and Xue 2010;Deus and Mazumder 2006;Zhang et al 2008Zhang et al , 2011Plati et al 2006) As noted previously, most of the laser cladding work reported is for non-powder metallurgical materials which are not very applicable for die repairs.…”