Page 35 - MetalForming November 2019

strated fas-
tener-welding
challenges and
solutions at Metal-
Forming magazine’s Hot
Stamping Experience and Tech Tour, held this past September in Michigan.
Especially in hot stamping applica- tions, fasteners are extremely soft as compared to the base material, causing the fastener projections to collapse before a good weld is achieved. In addi- tion, hot stamped materials develop
an AlSi coating in the furnace, with the resistive qualities of the coating inconsistent across the hot stamped part. On top of that, the short weld times called for in projection welding bring difficulty in delivering enough
heat to the base material. CD welding stores energy for rapid energy release with large peak currents, which means more energy into weld for- mation and less into heating the sur- rounding material, as well as a smaller heat-affected zone as compared to other welding processes. In metallur- gy-critical hot stamping, these attrib- utes prove advantageous, which is why, despite the above-listed challenges, projection welding of fasteners to hot
stamped parts sees wide use.
Fabrication: Welding Well
Here’s a sample of a fastener welded onto material courtesy of the CD welding process. Note the
clean welds at the base of the nut on the lower left and right.
“Since 2007, we’ve worked with Tier Ones and OEMs producing and pro- cessing hot stamped parts inhouse,” says Kollins. “Typically, materials arrive at a Tier supplier ready to be stamped. Hot stamping, on the other hand, involves inhouse processing, which varies from manufacturer to manufac- turer. Variations exist across the indus- try and even across a part in terms of contact resistance, specifically at the interface where the fastener attaches to the part.”
CD welding technology, Kollins explains, can work with these variations by altering the weld current to match the current needed for resistance at that particular location on the part. Today, Kollins and Agin see a rise in hot stamping usage and applications, and continuously work on developing welding technology, such as a newly released machine and monitoring capa- bility, to account for trends, including the use of thicker material. MF
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