Page 31 - Metalorming Magazine January/February 2023

Special Section: FABRICATION WELDING FASTENERS
28 MetalForming/January/February 2023 www.metalformingmagazine.com
side equals voltage applied divided by the resistance of the secondary (I = V/R). As resistance increases, current decreases. The inverse also is true—as resistance decreases, current increases.
This makes the CD weld control the perfect tool for welding fasteners to HSBS base material. Fig. 5 shows the current output from a CD welder with an 8-mm fastener at 680 V pro- grammed, and Fig. 6 shows the current output from a CD welder welding through a 1⁄2-in.-thick copper bar— without a fastener—also at 680 V pro- grammed. While this is a somewhat dramatic representation on how the CD weld control works, we only collect this data to benchmark each welding machine before it leaves the shop floor.
Finally, Fig. 7 shows real data from a single machine using an actual appli- cation. Notice the difference between the current and resistance readings— each weld has a different resistance signature and, therefore, a different current output.
Fig. 5
Fig. 7
Fig. 6
Fig. 8
Fig. 5 shows the current output from a CD welder with an 8-mm fastener at 680 V programmed, while Fig. 6 shows the current output from a CD welding machine welding through 1⁄2-in.-thick copper at 680 V pro- grammed without a fastener.
Figs. 7 and 8 show real data from two welds made on the same machine (M8 nut welded to 2-mm- thick HSBS). Notice the difference between the current output and the resistance readings; each weld has a different resistance signature and, thus, a different current output.
Let’s start with the welding-machine frame, which must be rigid with little to no deflection (about 0.002-in. deflec- tion at a weld force of 7500 lb.) Because the average weld force for a HSBS fas- tener weld is approximately 3000 lb., standard fastener-welding machines typically will not suffice. And with esti- mated acceleration rates between 25 to 30 Gs, the last thing we need is a side-loaded force slowing the forward movement of the ram.
In addition, a standard projection- welding machine has a weld time of around 160 msec, enough time to maintain consistent force across the weld interface. However, a CD welder has a much more difficult task as weld time is less than 10 msec and requires much greater force.
Lastly, because heat generation in a CD resistance weld directly relates to contact resistance and not bulk resistance, the rate of acceleration of the projection collapse is much greater than in a traditional weld. This requires appropriate mechanical response, accomplished by properly sizing the welding-machine cylinders, ram and the fast follow-up mechanism for each application. Digging out an old welding machine with a die-cast ram and using roller cams with grease fittings and coil springs for follow-up is not an option for CD welding. MF
The authors credit Kevin Gunning, director of QSS, Amada Weld Tech, for contributing to this article.
Harnessing and Controlling the CD Energy
The last piece of the puzzle—and the most overlooked: the ability of the weld mechanism to harness and con- trol all of the energy supplied by a CD weld control. A properly designed pro- jection welder makes the process easy and trouble-free.