Modeling of Resistance Spot Welding Using FEM

Abstract

The resistance spot welding process is significant for joining materials in the automotive industry because it offers high speed and can be easily automated. Recently, there has been a demand in the automotive industry to reduce vehicle weight to improve fuel efficiency. Aluminium alloys are considered a viable alternative for auto-body materials to meet this requirement. It not only helps enhance fuel efficiency but also addresses the issue of vehicle corrosion. However, joining aluminium through resistance spot welding presents serious challenges compared to steel. One significant difficulty arises from the faster deterioration of electrodes. Aluminium alloys possess high electrical and thermal conductivity, significant shrinkage during solidification, and a natural oxide coating. These features make the spot welding process for aluminium alloys notably distinct. When exposed to high temperatures, aluminium undergoes a chemical reaction with the copper alloy found in the electrode material. This results in the unpredictable removal of material from the electrode surfaces, causing wear and significantly reducing the lifespan of the electrode during spot welding of aluminium alloys. This decrease in electrode tip longevity poses a significant drawback in weldability, as the durability of the electrode tip significantly affects its suitability for automotive applications. Due to the rapid nature of the process, obtaining crucial information, such as the transient distribution of current density and temperature through experimental methods, becomes challenging. Therefore, this study aims to develop an integrated computer simulation model using the finite element method to analyze the resistance spot welding process of aluminium alloys. Multiple calculations were performed considering different welding currents, weld times, electrode forces, and various surface conditions of the aluminium sheets. The simulation considers the nonlinear, temperature-dependent, thermo-physical properties of the materials. Interestingly, it was observed that in most cases, the nugget diameter is formed within a short time frame of 0.02 to 0.04 seconds, and further application of welding current primarily increases the heating of the electrode face. Moreover, the aluminium sheets’ initial surface condition significantly influences the nugget’s formation. Several other conclusions have been drawn as a result of this study.