General Motors Overlap Sectioning Joint

Until recently, General Motors has generally specified butt joints with backings when sectioning parts of a uniside. However, an overlap joint is now being required for some uniside sectioning joints. This is being done to reduce the transfer of heat from GMA welding into heat-sensitive high- and ultra-high-strength steel reinforcements. The concern with a butt joint with backing is that the backing piece does not extend to the pinchweld flange, and leaves the reinforcement exposed. As a result, a GMA weld is made on the pinchweld flange area of the reinforcement (see Figure 1).

Overlap Joint
The overlap joint specified in some new General Motors repair procedures is made by cutting the replacement part to overlap the original part on the vehicle 25 mm (1"). The overlap allows the original panel to serve as a backing for the seam weld, even on the pinchweld flanges, better protecting the reinforcement from the heat of the weld (see Figure 2). This is also a less complicated process compared to a butt joint with backing, and reduces the chance for cutting the replacement part too short.

Figure 2 - The original panel serves as a backing, and protects the reinforcement from welding heat.

The overlap joint was first specified for the outer rocker panel on the 2010 Chevrolet Camaro, and is mentioned in a previous I-CAR Advantage Online article, "Collision Repair For The 2010 Chevrolet Camaro." Since then, an overlap joint has been specified for various sectioning joints on the 2011 Chevrolet Volt, 2011 Buick Regal, and 2012 Chevrolet Sonic. Common procedures this type of joint is used for include replacement of the outer A-pillar, rocker panel, B-pillar, and quarter panel.

Welding
The overlap joint is welded using a fillet weld. Plug welds may be required as well, but this recommendation varies according to the procedure. The fillet weld should be made using a skip or stitch technique to minimize the chance for heat distortion. This is done by making 25 mm (1") welds along the seam with 25 mm (1") gaps between each weld, and then going back to fill in the gaps (See Figure 3).

Conclusion
Figure 3 - The first set of seam welds should leave a 25 mm (1") gap between each weld. The second set of seam welds fill in the gaps.A butt joint with backing is not always specified for sectioning procedures on General Motors vehicles anymore. It is becoming more common for sectioning procedures to specify an overlap joint when sectioning parts of a uniside. This is why it is so important to always refer to the vehicle maker procedures to ensure the correct joint is being used. Collision repair procedures for General Motors vehicles can be accessed at acdelcotds.com.

This article first appeared in the May 31, 2012 edition of the I-CAR Advantage Online.

For additional links to GM, check out the following pages:
Chevrolet OEM Information
GMC OEM Information
Buick OEM Information
Cadillac OEM Information

Additional I-CAR Collision Repair News you may find helpful:

• Collision Information Website Access: General Motors
• Step-By-Step: Accessing General Motors Repair Information

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