JSN ImageShow - Joomla 1.5 extension (component, module) by JoomlaShine.com
|
|
A guide to shunting the current when spot welding |
|
|
Tuesday, 05 June 2007 |
|
Page 2 of 2
Shunting with weld bonding
Weld bonding is resistance spot welds made through adhesive on the same flange. The process requires removing all coatings from the mating flanges, including the zinc coating, but the recommended repair adhesive is not conductive so shunting is required. The bond line is thin, but thicker than E-coat so a clamp specially designed for shunting is usually recommended. This specialty clamp has a thick, stranded copper wire connected to copper pads for a much better conductive path than regular locking pliers. In fact, using this dedicated shunting clamp is a good idea when doing any shunting. With locking pliers, there’s a good chance some of the current will be lost at the pivoting rivet.
Shunting alternative
Of course a shunt is not needed for any of these conditions if the E-coat on the mating surfaces is removed, or if the adhesive is left off the part of the flange where the first spot weld can be made. The concern at that spot is corrosion protection, but seam sealers and paint coatings will help keep the moisture out. The zinc coating can be left on the spot without adhesive when weld bonding. The uncoated spot doesn’t have to be at the beginning of the flange, but you wouldn’t want it at a location such as the bottom of the B-pillar where road splash may be an issue.
Using the first spot weld as the shunt is the preferred method when weld bonding three or more panels, such as when attaching an outer panel to a two-piece inner. Another recommendation that will ensure conductivity between the panels in this worst-case scenario. The recommendation is to make an initial spot weld on the two inner panels. Leave the adhesive off that spot on the outer panel, and when the outer panel is attached, make another spot weld on top of the first spot weld.
Conclusion
With the STRSW process, shunting of the current is required for the first weld when there is a nonconductive coating or adhesive on the mating flanges. Other clamps used for fit-up should be insulated to prevent any unwanted current shunting. When weld bonding, a dedicated shunting clamp should be used for the best weld performance.
More on the current shunting process is discussed in the newly updated I-CAR Live program Squeeze-Type Resistance Spot Welding (WCS04). Watch for it in your area later this Spring.
For comments or suggestions on the Advantage Online, please contact I-CAR Senior Instructional Designer Bob Jansen at
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
.
This article first appeared in the I-CAR Advantage Online, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free publication, visit http://www.i-car.com.
<< Start < Prev 1 2 Next > End >>
|
|
|
