The technicalities and techniques of weld bonding

by Douglas Craig, Technical Application Engineer & Collision Industry Liaison, Structural Adhesives Tech Service, LORD Corporation

Although weld bonding is not a new technology, knowing how and when to use weld bonding in the repair process can help technicians become more productive, and ultimately lead to higher customer satisfaction metrics for the repair body shop.

Douglas-Craig-edited photo

Douglas Craig

The weld bonding process uses adhesive bonding and resistance spot welding to deliver a sealed joint that is stronger than either of these procedures used individually. After the adhesive is applied and the parts are assembled, spot welding is done through the adhesive. The adhesive is then cured to complete the assembly.

Repair weld bonding not only duplicates the original OEM manufacturing construction but also reduces the Heat Affect Zone (HAZ). HAZ refers to the portion of metal surrounding a weld that has not been welded (melted), but has had its properties altered during the welding process. It is crucial to keep the HAZ as small as possible in order to not weaken the original properties of the parent material.

However, weld bonding is more than just “putting adhesive on a part” – liability issues can develop if the repair job is not properly executed. Furthermore, if a repair technician is not using the appropriate repair products and the approved procedures, a vehicle will not be restored to its pre-loss condition, and the customer will not be satisfied.

In the weld bonding process, squeeze-type resistance spot welding (STRSW or RSW) is used as opposed to metal inert gas (MIG) or metal active gas (MAG) welding techniques. STRSW forms a welded attachment similar to the original assembly. With STRSW, the weld joint is not impacted by the zinc coatings present in the substrate steel metals.

Along with STRSW, the weld bonding process uses a structural metal adhesive in the middle of a joint or assembly. The STRSW can weld right through the adhesive to provide a complete, bonded interface for replacing structural or non-structural auto body panels. The adhesive significantly increases the strength of the joint.

So how does a repair technician know when to use weld bonding, or MIG or MAG welding, to repair a damaged vehicle? And which are the correct adhesives and bonding sealants to use? Presently, there are no industry standards that can help with these determinations. It is necessary, therefore, to rely on each individual car manufacturer’s recommendations for repair techniques and products. There are courses offered that teach weld bonding, and collision shop owners should also confer with their product suppliers for “how-to” information.

By law, all auto OEMs must provide servicing and repair information to the general public. Most auto manufacturers’ websites feature some level of information that relates to collision repair and auto body rebuilding instructions. While it is easy to access an auto OEM site, it can be confusing to navigate each site to find the repair information.

To make it easier to find specific auto model repair instructions, the National Automotive Service Task Force (NASTF), at www.nastf.org, provides access to auto OEM websites. NASTF’s site, oem1stop.com, has direct links to over 60 auto manufacturers and their OEM Electric/Hybrid Vehicle Handling Guidelines.

Welding training and certification courses are offered from the Inter-Industry Conference on Auto Collision Repair I-CAR (www.i-car.com). I-CAR not only offers courses on STRSW and other welding techniques, it can also perform a comprehensive evaluation of your collision repair facility and equipment to ensure that it is equipped to perform safe and proper welds.

Suppliers of weld bonding adhesives are another good source for training information. Many suppliers host in-house training courses or feature training videos on their websites with details on how to use weld bonding adhesives for repairing damaged auto panels. Speak to your supplier about how you can access these programs to help educate collision repair technicians.

Crash-durable, structural metal-bonding adhesives are designed to replace all OEM one-component crash durable adhesives, returning vehicles to pre-accident condition. They are ideal for weld bonding of replacement structural and non-structural autobody panels. Crash durable adhesives offer higher impact strength performance, excellent corrosion protection, and are immediately weldable after application.

Proper application of the weld bonding adhesive is also crucial to achieving a successful repair. Carefully follow both the vehicle manufacturer’s guidelines for replacement panel fastening and the removal of any metal coatings, and the supplier’s instructions for applying the weld bonding adhesive. When the proper metal preparation, product preparation and application procedures are followed, the weld bonding adhesive will provide an excellent bond with corrosion-protection properties. Once the adhesive is cured, it can be painted.

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