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Weld Bonding

Technical

Technical: Weld Bonding – The Best of Two Worlds

Shops that don’t use squeeze-type resistance spot welding in combination with adhesives are missing the big picture and possibly exposing themselves to a negative situation.

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Mitch Becker has been a collision industry trainer for 30 years and an I-CAR instructor for more than 25 years. Contact him at (763) 585-6411 or [email protected]

Weld Bonding

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Today’s transportation is made of stronger steels and construction materials for lighter vehicles, recyclability and corrosion protection. Now add in electronics, cycle time, training, ROI (return on investment), and a shop needs to look at all aspects of repairs. What is the correct repair procedure? How can my shop be economical in this procedure? What is the big picture?

I don’t know how some of you do it. In today’s economy and the ever-changing vehicle, how do you keep up with it all? I got tired just writing that last paragraph.

The Big Picture

Looking at the big picture, change is going to keep coming at us. Adapting is the way of survival. So when a procedure is out there that provides a multi-faceted role in repairs, I like to talk about and explain the big picture to shops and technicians. One of those procedures is weld bonding, the benefits of which many miss out on. Combining squeeze-type resistance spot welding (STRSW) and adhesives offers a great deal of benefits to shops and technicians. Why so many don’t use or follow it is a mystery to me. Yes, it takes some time to learn, but so does using a phone. Once you figure it out, it becomes much easier to use.

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What Is It?

We have seen STRSW for years. It’s the welding preferred by most automakers for many reasons. Now, add adhesives to the mix. We as technicians love adhesives; they’re fast and do so much more than just stick stuff together. When we combine the two processes, the advantages increase greatly. STRSW welding through the adhesives that are applied between the panels first offers some remarkable advantages. Shops not using this procedure where called for in repair procedures are missing the big picture and possibly exposing themselves to a negative situation.

I also want to stress that vehicle manufacturers do give an option in some cases to not use weld bonding even though it was used in the original build process. In these cases, shops need to be sure to look up procedures in ALLDATA, OE websites or I-CAR to see what’s required. Because it’s hard to access certain areas with STRSW electrodes, there are recommended procedures where MIG/MAG plug welds may be acceptable. These alternate repair procedures are based on the availability of the equipment in shops and access to original-build welds. Weld bonding is only to be used when recommended or required by the vehicle manufacturer.

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Before we get too deep in this article, I do need to clarify a statement. An STRSW machine capable of weld bonding is expensive, but I’m sorry to say, it’s a necessity in shops. Unless you won’t be working on any vehicles built after 2007, I think it’s time to really consider one. New steels’ sensitivity to heat may make the old steel plug welds obsolete as STRSW and MIG brazing become increasingly required procedures.

Advantages

The advantages of weld bonding are similar in both the vehicle manufacturers’ industry and auto body repair industry. The advantages can be broken down to some main components:

  • Metal
  • Longevity/fatigue
  • Strength
  • Sound
  • Corrosion
  • Speed
  • Cost

Metals

With steels used today, heat is an issue during repairs. The limitation of a large heat affect zone (HAZ) using STRSW is very appealing. The HAZ created while using traditional steel welders during plug welds creates damage to surrounding steels as well as a corrosion hot spot. The need to dress each weld also consumes time and again creates unwanted heat during grinding. The speed at which STRSW can be done, plus the fact that there is no need to dress the welds, can speed up repair times as compared to plug welds. The grinding of plug welds may also compromise weld integrity if the technician grinds flat or too far.

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Metal fatigue is also a concern on welds and joints. As the vehicle goes through environmental and roadway stress, welds and bonds can be stressed. STRSW welds have great strength but can be susceptible to fatigue in weld areas. Adhesives have great strength and a large footprint to absorb stress but lack the peel strength, in many cases. The combination of the two processes counters the other’s weaknesses.

Longevity and Fatigue

The combination of STRSW and adhesives limits the fatigue in welds and joints, giving the vehicle a much longer life. In the repair industry, this helps shops in making repairs that last. With this higher quality of repair, there is less of a chance of warranty issues or failed repairs.

Strength

Weld bonding gives strength in the build process and repairs without adding significant weight. The combination spreads forces throughout the vehicle, limiting the need for as many welds. This saves energy and creates fewer corrosion hot spots. Also, it leaves the metal integrity intact. This also allows for the use of different materials to be joined with other forms of attachment such as rivets.

Noise Vibration Harshness (NVH)

Weld bonding also gives control of noise and flexing during driving. This sound deadening is a premium option of putting adhesives in the build process and also seals out the elements.

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Corrosion Protection

This leads to my favorite reason why weld bonding is a good choice. All of the above mentioned advantages of sealing and strength also lead to a process that offers fantastic corrosion protection, which adds more to the longevity of the repair and limits the noises or sounds customers always seem to find. As vehicles are designed to last longer and be safer, corrosion is still the No. 1 reason for repair failure. The NVH properties and the sealing of the welds during the repair may rival any weld-through primers and other cavity wax applications. Sealing the welds and any bare metal between welds is a critical factor to corrosion protection.

Weld bonding -- what not to do

This is an example of what NOT to do. This vice grip should be taped or insulated from touching metal, as this will draw power from the weld.

Speed

There is a learning curve to weld bonding. Once a technician is confident doing it, however, the process accelerates repairs. The welding, sealing and corrosion protection are all done at the same time, eliminating extra steps you have to go back to do. There’s no guessing in hard-to-reach areas for wax-based materials. It’s still recommended to use cavity waxes, and you can rest more assured that the repair is solid.

Cost

The process does add cost as adhesives are expensive, but may save time and warranty issues. The cost I like to refer to is the warranty cost. Failure to do a correct repair or properly protect the metal or repair area can be very costly.

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Drawbacks

Multiple layers of weld bonding may be a problem. Check with the vehicle maker for the correct procedure to weld multiple layers, or to add to existing layers. The equipment must have pulse ability, and proper settings as to the amperage of each pulse is a major factor for the success of the weld. Improper settings may cause failed welds or blowouts of the weld zone. In some cases (Honda, for example), the new automated machines may need to be manually set.

Researching new machines could save you thousands. Check with the manufacturers and their reps to view and see possibilities.

Shunt Clamps

Shops must have shunt clamps to properly weld bond. This is a vice grip with four-gauge wire connecting ends and is used for the initial weld. Then, the shunt is removed after the weld is completed, as that completed weld will now shunt for the next weld in succession. If this isn’t done in succession, then the shunt clamp must follow if the welds are more than 18 inches apart. All other clamps must be insulated from touching metal as this will draw power from the weld.

Another Alternative

Not all manufacturers recommend weld bonding. The use of seam sealers during welding is becoming more popular as an option where there is no recommendation. Seam sealers have all the advantages of adhesives, without adding strength to the vehicle or changing the structural integrity. These two procedures, although similar, are vastly different and are not interchangeable. Weld bonding is with adhesives; welding with seam sealers is not the same. Vehicle integrity must be maintained as designed.

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3M has videos on their website on the proper procedures for their products. Fusor and other product manufacturers also have videos of proper procedures. The I-CAR class WCS04 is a great class to learn more. Once technicians realize the advantages of weld bonding, use of it will increase in repairs. It takes time to change to new procedures.

Summary

The list of advantages and disadvantages to welding is longer than what I included in this article, but these are the main reasons recognized.

Changes relating to new products and procedures will always be constant. Keep up as best as you can, and keep in mind that new resources for information such as the I-CAR website will constantly help the repair industry improve.

 

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