Weld-bonding can improve strength and stiffness; provide additional fixturing capabilities; allow for fewer welds; improve fatigue and impact resistance as well as cycle time; and increase corrosion protection and noise, vibration and harshness (NVH) control properties. With weld-bonding, vehicles can be repaired to an undetectable factory appearance, while maintaining the original structural integrity.
The popularity of weld-bonding, as an efficient method for joining secondary exterior auto body panels, is rising in response to the increase in complexity of automotive metals. Original equipment manufacturers (OEMs) are progressively utilizing different materials in the construction of automobiles to promote safety, eliminate excessive vehicle weight and enable better styling.
For more than 25 years, the North American automotive collision repair market has used MIG welding (gas metal arc welding) as an accepted industry procedure. Compared to MIG welding, metal adhesives offer collision repair technicians a multitude of advantages such as corrosion protection, NVH reduction, elimination of welding damage, and moisture barrier and workshop efficiencies.
Some metal bonding adhesives stop the rusting process with phosphating agents. Unlike welding that concentrates stress at specific points, certain metal bonding adhesives uniformly distribute stress, which make the repair area stronger and quieter. A substantial benefit of bonding is the reduction of MIG welding damage due to panel warpage, glass burn and interior burns.
While European countries have long utilized STRSW, it has not been widely accepted in the United States because of the high level of voltage required. In North America, a 200-volt/single phase service is typically available to the body shop. In Europe, 400 volts and higher are available, which enables the use of high-powered compression resistance welding equipment. Necessity being the mother of invention, welder manufacturers have made tremendous progress by developing alternative equipment that works well within the North American electrical system. These systems are gradually becoming more popular with the automotive OEMs.
Weld-bonding
Any automotive part (structural and/or non-structural) originally welded or weld-bonded by the manufacturer with adhesives and/or sealers can be repaired using weld-bonding. STRSW welders are often used with advanced steels because there is minimal heat effect damage compared to MIG welding. Since higher strength steels are typically heat-sensitive, technicians use resistance spot-welding to match to the OEM weld appearance without sacrificing integrity to the welded high-strength metals.
There are different types of STRSW equipment that can be used for weld-bonding. The most common are transformer and inverter compression welders. Transformer welders change AC power to DC current to obtain higher amperage, and inverter welders change the wave pattern from a sine wave to a square wave. The inverter welder is usually a better choice because it provides a high-powered weld in a very short time, which minimizes the heat-effect zone on the adhesive and metal and results in nearly undetectable repairs.
Although MIG weld-bonding can be utilized in collision repair, the procedure may seem cumbersome. In a MIG weld-bonding scenario, the technician applies adhesive to the bond locations of the part, but skips areas in which a MIG weld would be placed. Like STRSW weld-bonding, MIG weld-bonding offers corrosion protection in the bond areas and NVH advantages.
However, issues such as the increased heat effect and longer repair times make STRSW weld-bonding a better choice. When choosing between MIG and STRSW for weld-bonding, consider the joint design of the part and the available equipment. Although STRSW has been proven to work well with weld-bonding, not all metal joints allow for STRSW gun access. In addition, the number of shops equipped with the latest in STRSW equipment is still low because the welders are typically pricey and shop electrical upgrades are routinely required.
Before implementing weld-bonding into practice, a shop must consider these factors. First, the shop must be electrically equipped to handle resistance welders. Inverter welders will require more shop power. There must be a dedicated circuit with a minimum of 60 amps, 3 phase and 208/220-volt service to handle most resistance welding equipment. The welder should be UL/CSA-approved and conform to the local electrical code. After obtaining a welder, remember voltage drop can cause welder performance problems.
The future
Weld-bonding has taken the automotive aftermarket to the next level. As more vehicles are built in the factory with weld-bonded joint designs, the collision industry must embrace weld-bonding to repair vehicles in the manner in which they were manufactured. Technicians who are proud to repair damaged vehicles to their pre-accident condition now have the ability to rebuild cars using inverter STRSW welders and OEM-approved structural adhesives.
Editor's note: Ed Staquet, senior technical support manager for LORD Corporation, has worked in the body shop industry for more than 40 years. He managed a body shop before joining LORD in 1992. A member of the I-CAR Hall of Fame, Staquet is a long-time I-CAR trainer and has served two three-year terms on the I-CAR International Board of Directors.
