1. Dr. Laila Guessous (ME), Dr. Sayed Nassar (ME), Dr. Meir Shillor (Math), Suresh Putta (M.S. Student) Development and Numerical Simulation of Spot Welding Model The goal of this collaborative project is to develop and numerically simulate a model to describe the process of resistance spot welding (RSW). Of particular interest are the differences in weld nugget formation and quality when AC or DC power is applied. Of further future interest is the quantification of residual stresses in welded joints. Resistance spot welding is a common industrial process used for the manufacturing of a host of products ranging from automobiles to the assembly of small parts. Its use in the automotive industry is of great importance, since every car includes approximately 5000 welds in its assembly process. Spot welding involves the joining of two or more metal parts together in a localized area by the application of heat and pressure. The heat is generated within the material being joined by the resistance to the passage of a high current through the metal parts, which are held under a pre- set pressure. The electrical current induces the melting of some of the plates’ material to form a molten nugget. When the current is disconnected, the plates cool down and the nugget solidifies, forming a material bond between the two plates. Weld quality has been shown to depend on various factors such as contact resistance, electrode shape, welding current, squeeze pressure and time schedules. A need is recognized to base these schedules on a scientific basis instead of trial and error together with experimental verification. We are in the process of developing 1-D and 2-D numerical models for spot welding. The model uses the enthalpy formulation to describe the melting process and a charge conservation equation for the evolution of electrical potential. Temperature dependence is allowed for density, electrical resistance, specific heat, electrical and thermal conductivity. 1.Objective: 2. Motivation: 3. Approach: 4. Preliminary Results A nugget function is introduced which keeps track of the molten part and,therefore determines the size of the molten nugget. The model and its numerical implementation will allow for simulation of the welding of dissimilar material properties and dissimilar material thicknesses. A finite difference based 2-D code is currently under development. Preliminary tests have been conducted to evaluate the ability of the model and the code to predict and track the development of the nugget and mushy (solid/liquid mixture) zone as a function of time. Sample plots from these tests for the joining of two similar plates are shown below (note that somewhat arbitrary temperatures were used for the testing). The model is able to capture both melting and solidification, as well as the constant temperature that accompanies the phase change process. Temperature dependent properties have been incorporated into the program and model. representative property plots can be seen below. Except for the electrical conductivity, all show the variation of solid and liquid Aluminum properties.