Thermal Finite Element Analysis and Optimization of Carbon Steel Stud Arc Weld

Abstract

In this work an investigation to the temperature distribution during the stud arc welding process by building a thermal finite element (FE) model with the aid of Comsol- program was conducted. Also, an optimization to the ultimate applied torque of the welded stud and the total input heat during welding process by individual and composite desirability was intended.  A stud of carbon steel-B7 is welded to a plate of carbon steel-grade-C. The welding machine parameters are; current, welding time and plunge. Three levels for each parameter, mentioned above, are used to optimize the resistance torque and the total heat flux using the design of experiments according to Taguchi method. The finite element model is built upon the input heat source, convection and radiation heat transfer during stud welding process. The tests include the torsional test and actual heat transfer depending on the record of temperatures at different locations. The suggested FE model gave good agreement with the experimental temperature record with an approximate error of 5%. The results indicated that the torsional resistance increases with the increasing of weld time at small welding current of 400 A. At higher welding current (I = 800 A) the torsional resistance decreases with the increasing of the plunge welding value. The maximum temperature region lies at the center of the FE welded model and reduced gradually away from it with a symmetrical distribution. A sufficient welding heat input can make the torsional resistance of the weld line more than those of the stud. Due to the higher temperature gradient during the welding process, the microstructure of the welded joint exhibits three regions; nugget zone (NZ), thermo-mechanical affected zone (TMAZ) and the heat affected zone (HAZ). The first region consists of Martensite and ferrite phase with a higher plastic deformation, in which, the peak value of temperature was observed numerically. A coarse grain size with higher dislocations was found in the second stage. While, the