Effect of projection height on projection collapse and nugget formation : A finite element study

Projection welding is a variation of resistance welding in which current flow is concentrated at the point of contact with a local geometric extension of one (or both) of the parts being welded. These projections are used to concentrate heat generation at the point of contact, and, therefore, to generate a weld nugget faster and at a lower current level compared to conventional spot welding. Many factors affect the heat generation and projection collapse of the projection welding process. The effects of some of these factors, such as welding current, electrode force, and sheet material properties, have been studied using the coupled finite element simulation procedures in an earlier study by the author (Ref. 1). This paper is a sequel to the previous effort, It investigates the effect of projection height on projection collapse and nugget formation. Three projection designs with different projection heights were selected for 0.059-in., cold-rolled, low-carbon steel according to Ref. 2. The corresponding heat generation processes using one set of welding parameters were simulated using an incrementally coupled, thermal-electrical-mechanical modeling procedure (Refs. 1, 3). The predicted heating patterns were compared with the weld cross sections obtained from an earlier experimental approach using high-speed motion photography (up to 6000 frames/s). The study offers fundamental understanding of the process physics for different projection designs and demonstrates again the effectiveness of an incrementally coupled modeling procedure.