Spot Welding Theoretical and Practical Investigations of the Expulsion Occurrence in Joining Metal for the Automotive Industry

The highly competitive nature of the automotive industry drives demand for improvements and increased precision engineering in resistance spot welding. Currently there are about 4300 weld points on the average steel vehicle. Errors and problems due to tip damage and wear can cause great losses due to production line downtime. Current industrial monitoring systems check the quality of the nugget after processing 15 cars, once every two weeks. The nuggets are examined off line using a destructive process, which takes approximately 10 days to complete causing a long delay in the production process. In addition to this, the force exerted by the tips on the metal is measured by various simulations using SORPAS software, (Simulation and Optimization of Resistance Projection and Spot welding processes). Various data capture devices feed into LabVIEW and SORPAS software to calculate the relevant forces, current, voltage and dynamic resistivity of the materials involved. This paper presents a simulation of the spot welding growth curves, along with a comparison to growth curves performed on an industrial spot welding machine. The correlation of experimental results shows that SORPAS simulations can be used as an off line measurement to reduce factory energy usage. This paper also provides an overview of electrode current selection and its variance over the lifetime of the electrode tip, and describes the proposed analysis system for the selection of welding parameters for the spot welding process, as the electrode tip wears.