Magnetically Impelled Arc Butt (MIAB) welding is a forge welding technique which generates uniform heating at the joint through rapid rotation of an arc. This rotation results from forces imposed on the arc by an external magnetic field. MIAB welding is used extensively in Europe, but seldom utilized in the United States. The MIAB equipment is robust and relatively simple in design, and requires low upset pressures compared to processes like Friction welding.
In the automotive industry, tubular construction offers many advantages due to the rigidity, light weight, and materials savings that tubes provide. In the case of automotive suspension components, tubes may be chromium-plated on the ID to reduce the erosive effects of a special damping fluid. Welding these tubes using the MIAB welding process offers unique technical challenges, but with potential for significant cost reduction vs. other welding options such as Friction welding. Based on published literature, this research project represented the first attempt to MIAB weld chromium-plated steel tubes, and to utilize voltage monitoring techniques to assess weld quality.
Optical and SEM microscopy, tensile testing, and an ID bend test technique were all used to assess the integrity of the MIAB weldments. This analysis revealed the potential for chromium-enriched regions, most likely chromium oxides, to become trapped at the weld interface resulting in severe degradation of mechanical properties. Voltage plots generated during the arc monitoring were analyzed and correlated with Design of Experiment (DOE) statistical results and high speed video images.
The DOE results revealed the individual and interactive importance of arc heating (referred to as level II) time, expulsion (referred to as level III) current, and arc gap on weld quality. Correlations were established between specific features of the arc voltage plots and weld quality. Based on arc physics theory, it was proposed that these three variables affected arc pressure, which contributed to improved expulsion and a reduction in chromium entrapment in the joint. As a result, feasibility for MIAB welding chrome-plated suspension components was established, and voltage monitoring methodology was identified as a potential quality control technique for producing this joint.