Understanding why extrusion resistance spot welding is the preferred/required connection method for OEMs is essential to help ensure complete, safe, and high-quality repairs.

Jeff Poole is an I-CAR manager and subject matter expert. He grew up in the automotive field with his father. He has been in the collision industry since the late 1980s and has held various positions at i-car since 1995. Robert Heil is a senior industrial design assistant at I-CAR. He has a lifelong passion for car repairing and has worked in this industry for more than 20 years. He joined i-car in 2019.

Understanding why STRSW is the preferred/required connection method for OEMs is essential to help ensure complete, safe, and high-quality repairs.

Today's vehicles are designed to perform in a certain way during a collision. When you hear the word "influence", what image do you think of? Did the vehicle hit something or was it hit by something? This is the usual thinking of most people. However, this is only part of it.

In a vehicle collision, three effects actually occur:

The challenge for car manufacturers is to make safer cars to better protect the occupants from these three effects. Building a stronger passenger compartment or cab to reduce intrusion is essential, but manufacturers must also ensure that the materials used in vehicle manufacturing minimize the force experienced during the third impact.

Like any good sports team, achieving the goal of occupant safety requires collective effort. No aspect of the vehicle alone can accomplish this task. This is a complete kit designed to work together to ensure the safety of the occupants in a collision.

Airbags and other restraint devices are designed to complement vehicle collision management. This structure not only absorbs as much energy as possible when the components are deformed (energy is required to bend the metal), but also transfers the energy around the cabin, thereby minimizing deformation and intrusion into the occupant space.

Airbag deployment time is a key factor for the normal operation of airbags and seat belt tensioners. If the ability to absorb or transfer energy changes during maintenance, the time to deploy the airbag may also change. Worse, it may result in no deployment at all.

There are reasons why OEM body repair programs are written. It takes a lot of time, energy, and testing to ensure that the repaired vehicle not only looks good and can extend the service life of the vehicle, but also maintains the same standards as the factory when a collision occurs, thereby maintaining the following capabilities: reducing cabin intrusion and Minimize the force of the third impact. Next time you want to deviate from the OEM procedure, please think about it.

When performing welding, STRSW is less prone to incorrect settings and human errors.

When performing collision repair, various connection methods may be identified in the repair procedure. These may vary by OEM or even model, but the two most common methods are plug welding and extrusion resistance spot welding (STRSW). Although some OEMs allow plug welding instead of factory spot welding, the maintenance program may specify that STRSW is the preferred welding method. To help you understand the reason, let's take a look at the difference between plug welding and STRSW.

Plug welding is usually performed using wire-fed GMA (MAG) welding machines. This is a process that requires punching or drilling a hole of a specific diameter within a certain distance, and then each weld must be completed by hand. Due to the nature of the welding method and the nature of the machine used to make it, this can lead to inconsistent and weak welding. Successful plug welding depends to a large extent on the experience of the person setting up the machine and the subsequent experience of performing the welding correctly. There are many variables when creating plug welds-this is enough to make even experienced welders less confident in the results of these welds, especially on unfamiliar materials such as high-strength steel (HSS).

STRSW is performed by a welding machine designed for one thing. However, many spot welders have other accessories that allow additional functions. Although some settings need to be adjusted and sometimes a specific welding tip is required, STRSW is less prone to incorrect settings and human errors when performing welding. Ease of setup and the ability to reduce human error will produce more consistent and predictable welds. In turn, this will increase confidence in the welding result, regardless of the type of steel connected.

Although STSRW is simple, don't mistake it for foolproof.

Many original equipment manufacturers that require or recommend STRSW will approve specific spot welders for their vehicles. This information can usually be found under the general welding information in the vehicle-specific body repair manual (BRM) or in the repair procedure or equipment list. In addition, welding information usually includes information such as current setting, cycle or time, and what technique is used. This is valuable information because the overall purpose of STRSW recommended or required by OEMs is to most accurately replicate factory spot welds removed during repairs.

Although replacing spot welding with spot welding will definitely rebuild the appearance of the repaired factory, the trend of OEMs turning to STRSW instead of plug welding is not only aesthetic. Being able to use a connection method very similar to the OEM method helps maintain vehicle integrity standards. Many reasons for using STRSW are related to vehicle construction.

The materials used in modern vehicles are constantly evolving. We have all witnessed the decline of low-carbon steel and the growth of high-speed steel. Various strength high-speed steels and ultra-high-strength steels (UHSS) are becoming more and more common. Thinner and stronger steel types will continue to be developed and will be used in future vehicles.

As mentioned above, these higher-strength steels play a key role in OEM recommendations or requirements for spot welding for collision repair. The heat-affected zone produced by STRSW is much smaller than plug welding. This is important because many high-strength steels are limited by the amount of heat that can be applied to them.

When spot welding is used during repairs, UHSS may be different from mild steel. It is almost inevitable that welders need different UHSS settings to perform correct welding. Automobile manufacturers may also have requirements for specific spot welders, which may have preset programs for specific applications. Some spot welders may only need to enter the plate thickness and material type, and the welder will make the necessary adjustments.

When executing STRSW, the following points need to be kept in mind:

Although STSRW is simple, don't mistake it for foolproof. Make sure that the welding machine is set up correctly, not only for the vehicle you are repairing, but also for the procedure you are performing. Compared to fewer layers or thinner materials, additional layers or thicker materials often require different welder settings. Again, this should be specified in the BRM.

In addition, original equipment manufacturers usually recommend or require destructive testing of test pieces of the same type and thickness of welding materials. A description or explanation is usually given of what a successful weld looks like after a destructive test. It is important to verify that the destructive testing is performed as specified by the BRM.

Before any welding is carried out on the vehicle, practical spot welding, visual inspection and destructive testing should be carried out to ensure that the welder is set up correctly and working properly. When welding on HSS and UHSS, the solder joints may not tear. When welding low-carbon steel to UHSS or high-strength low-alloy (HSLA) steel to UHSS, the weld nugget of the weaker steel should be torn. If UHSS tears, the heat from STRSW will change the strength of the metal.

When repairing a vehicle, here are a few questions to ask yourself:

Understanding why STRSW has become the preferred or necessary connection method for OEMs is essential to help ensure complete, safe, and high-quality repairs and maintain vehicle integrity to protect occupants from the three effects of collisions.

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