Weld bonding: Understanding the technicalities and the techniques

July 10, 2015
Knowing how and when to use welding bonding in the repair process can help technicians become more productive and ultimately lead to higher customer satisfaction metrics for the repair body shop.

Weld bonding is a procedure that has been commonplace in most collision repair shops for the past 15 years. However, though weld bonding is not really a “new” technology, repair shop technicians have much to learn. Knowing how and when to use welding bonding in the repair process can help technicians become more productive and ultimately lead to higher customer satisfaction metrics for the repair body shop.

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.

It sounds like a simple procedure, and, in reality, it actually is – but using the proper adhesive and equipment, and knowing how to use them properly, can make all the difference between a successful repair and one that fails. It’s 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.

The Weld Bonding Process
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.

Zinc coatings can affect MIG or MAG welding by creating porosity in the weldments. These welding techniques also impart excessive heat into the steels which adversely affects the surrounding material and can lead to joint corrosion. Consequently, MIG or MAG welding is unsuitable for weld bonding.

Do not confuse the zinc coatings with other “coatings,” such as the paint or e-coat that is applied to a part. The zinc galvanized coating is applied to steel materials for corrosion protection. Structural metal epoxy adhesives are not affected by the zinc coatings on steel, as with acrylic adhesives.

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 autobody panels. The adhesive significantly increases the strength of the joint.

In the weld bonding process, squeeze-type resistance spot welding (STRSW) forms a welded attachment that replicates the original assembly.

Crash durable adhesives provide higher impact strength performance and excellent corrosion protection, and can be welded immediately after application.

Picking the Right Repair Solution
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 autobody 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. The NASTF is a cooperative effort among the automotive service industry, the equipment and tool industry, and automotive manufacturers to facilitate the accessibility of automotive service information, training, and diagnostic tools and equipment for automotive service professionals. NASTF’s site, oem1stop.com, has direct links to over 60 auto manufacturers and their OEM Electric/Hybrid Vehicle Handling Guidelines.

Getting Educated
Welding training and certification courses are offered from the Inter-Industry Conference on Auto Collision Repair I-CAR (www.i-car.com), an international not-for-profit organization dedicated to providing the information, knowledge and skills required to perform complete, safe and quality repairs. According to I-CAR, “when a poor or improper weld is performed during a structural collision repair, it can compromise the vehicle’s structural integrity. The result may be a “repaired” vehicle that is dangerously unsafe to drive.”

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. All I-CAR training courses are based on auto OEM-approved procedures and recommendations.

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 Adhesives
A significant advancement in structural adhesives has been the development of crash-durable formulations. 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.

The inherent strength of crash durable adhesives is what makes them different from other bonding/structural adhesives. All bonding/structural adhesives are strong, but crash durable adhesives take strength “to another level.” The enhanced toughness allows any crash durable adhesive to handle excessive stress over its lifetime, resulting in a repair that is not only as good as the original construction, but at times, even better.

Crash durable adhesives offer higher impact strength performance, excellent corrosion protection, and are immediately weldable after application. It is important for the collision repair technician to follow auto OEM instructions and supplier directions for using crash durable adhesives in weld bonding.

Nevertheless, weld bonding can be used as a repair technique on most auto parts – bumper-to-bumper (depending on the auto OEM manufacturer) – and is employed for steel-to-steel applications. As with any other in-shop repair procedure, make sure to use the proper personal protective equipment (PPE) when using STRSW equipment.

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.  

Collison repair shops only get paid once to do a repair job. If the weld is not done properly, the result is not only liability and safety issues, but a job that must be done over at a cost disadvantage.

Weld bonding is an efficient method to repair damaged vehicles and to return them to pre-accident condition. Knowing how to weld properly and how to select and use the correct adhesives is essential to achieving a successful repair job. Crash durable structural adhesives offer the versatility and ease-of-use necessary to attain a strong, corrosion-resistant weld. With the proper training, equipment and adhesives, weld bonding can be a valuable tool for remaining competitive in the collision repair business.

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