Study of Resistance Spot Welding Heat Input Method and Effect to Weldability

摘要

Using Resistance Spot Welding to join Aluminum-coated Boron steels has been shown to be problematic under certain circumstances. This study compares square (SQ) and pulse waveforms (PW) to identify benefits to the manufacturing process while maintaining or improving metallurgical and mechanical properties. SQ is a fixed weld current applied for a specific duration while PW is tailored to a specific stack or type of stack that uses short bursts of current with cooling time. SQ was found to give inconsistent results across multiple weld lobe tests. Tensile shear strength (TSS) reduction was observed when not welding at the ideal current and several samples within the weld lobe exhibited undersize nuggets. Conversely, PW showed a robust window for welding due to larger and consistent weld nuggets as well as reduced spattering. Both weld conditions failed by TSS fatigue at similar cycles at a given load. There were no large variations between the two welding methods in terms of fatigue life-or failure mode. Both weld conditions produced a similar hardness pattern and similar hardness levels in the nugget. Both parameters maintain acceptable levels of strength and thin side nugget diameter. In terms of manufacturability, the welding tips used for the PW pattern had less aluminum buildup, which is directly linked to improved welding conditions and fewer tip dressing interruptions. The PW pattern yielded a larger acceptable Weld Lobe when compared to SQ. Weld Lobe size has a strong correlation to manufacturing robustness due to protection from process variation.