Zinc-coated steel materials are often used to form various structures, including automobile frames and bodies. Creating such structures typically requires using one or more types of welding. While zinc provides excellent corrosion resistance to steel, it can also cause difficulties during welding. During fusion welding, for example, explosive zinc vapor can form and cause undesirable spattering of the weld metal, as well as extensive porosity in the weld after solidification. The issue of porosity is more significant in certain types of welds, such as lap welds, which are a preferred welding method for automotive body fabrication. Thus, the scrap rate in this type of welding process is typically higher, forcing manufacturers to incur material losses to maintain certain quality standards. As such, manufacturers that weld zinc-coated steel materials would benefit from improved welding techniques and in-process quality control methods.
Researchers at the University of Michigan have developed a laser welding approach to overcome some of the current limitations. The method includes applying a thin layer of an alloying agent on at least one of the metal members, and melting the protective metal coating and the alloying agent to form an alloy that is disposed between the overlapping members with zero gap. The overlapping metal members can be welded and the amount of the alloying agent can be controlled to ensure that extended solid solubility of the alloying agent in the weld is not exceeded. In addition, the researchers have developed an optical sensor to monitor the welding process by examining the spectra of zinc and iron in the plasma generated during a welding process. The monitoring system can monitor multiple parameters, including spectral line intensity, electron temperature, and ratio of zinc and iron composition in the plasma. The results can then be used individually or in combination to predict resulting weld quality and generate appropriate feedback control signals.
Applications and Advantages
- Welding of zinc-coated steel
- Monitoring of welding process
- US Patent 6,479,168
- Canadian Patent ZL 01823231.0
- 2 Pending US applications
- Robust, reliable and efficient methods for lap-nl-welding of zinc-coated steel for commercial-nl-production
- In-process quality control and prediction of-nl-resulting weld quality