The existing problems of weld defects in welding zinc coated steels in a overlap situation are present in the automotive industry. Overlap joints are the most common type of joint geometry used in the automotive industry. In this case there are 2 layer of zinc coatings in between the two steel sheets. The boiling point of Zinc is at 906C and the melting point of steel at 1536C. The different boiling and melting points causes Zn outgassing. Welding with a technically zero gap creates weld defects by material ejection. The consequences are reduced strength of the weld, requirement of additional sealer and additional maintenance of the equipment. The technical work around are designed gaps between the sheet to allow controlled outgassing Extensive research has been taken on with highspeed cameras to evaluate the root cause. Continue reading →