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Technical

Technical: The Heat is Dropping

Heat is the enemy to a lot of the different metals in vehicles today, which is why many of them require MIG brazing.

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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]

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I have some questions for body shops:

  1. Are you capable of repairing a quarter panel on a 2014 Honda Accord?
  2. Do your people know what it takes to replace this quarter panel?
  3. Do they know where to look for procedures?
  4. Do they know what welding requirements are needed?
  5. Do you have the ability?

Lots of Changes

Car manufacturers have made a lot of changes in the past few years. The drive to make vehicles lighter to meet CAFÉ standards has changed the way we look at damage from collisions. The question no longer is, “What needs to be replaced?” or “What needs to be repaired?” but “How should it be repaired?” Also, “Do I have the right equipment?”

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Direct damage and indirect damage take on serious considerations in the world of stronger steels, aluminum and other materials used in automobile manufacturing. Not only is the damage different and sometimes harder to find, the repair process has changed – in some cases, dramatically. It’s not just what to repair and replace, but how to repair new metals and materials and what to replace and how many welds.

Steels have changed so much that they now require a change in welding. For example, some of the new higher strength steels require lower-heat MIG brazing. This change has been hard to notice what with all the talk about aluminum repair. Honda, GM and Ford, to mention a few, have found MIG brazing to be an excellent procedure.

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Don’t get me wrong, many have been talking about MIG brazing and its applications. But have you been listening? This article is designed to give just a basic understanding of what MIG brazing is and why it’s used.

The Problem

If you’ve been paying attention in I-CAR classes, you’ve learned that heat is a problem to high-strength (HSS) and ultra high-strength steels (UHSS), particularly galvanized steels. There are two basic issues:

Heat affects the strength of steels.

Heat affects the galvanized steel corrosion properties.

This high-heat problem is associated with GMAW. When a shop is using MIG/MAG welding, the high heat required to fuse the metals with the filler materials takes its toll on strength and corrosion. To control some of this damage, stitch or skip welding has been used by technicians to limit this negative side effect. The stitch/skip method prevents the heat from radiating out and damaging the surrounding steel. This welding technique also helps to limit warping of the joint and causing more problems. This is the reason STRSW or spot welding is so appealing to all, as the heat damage and warping effects are somewhat eliminated. But STRSW electrodes can’t reach all the areas requiring welding, so a method to create a strong “bond” with less heat is needed as steels become even more sensitive to heat during repairs.

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MIG Brazing

MIG brazing, or what some call copper-silicon welding, fills the need for a strong bond with less heat. MIG/MAG steel welding uses heat to melt base metals and fuse them with filler wire. This melting creates a large HAZ or Heat Affect Zone, which is where many metals are compromised. The metal being welded melts at around 3,000 degrees Fahrenheit, or 1,650 degrees Celsius. Added to it the use of low-power 110-volt welders, and the radiating heat creates a large heat signature where the HAZ extends away from the weld zone. Although the weld is strong, damage is created further out. This weakening becomes a large problem on UHSS in that a collapse zone could possibly be created where none should be. Also, the corrosion properties would be compromised, leaving a time bomb of a failed repair.

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MIG brazing has a much lower temperature signature or HAZ due to the difference in heat used during brazing. MIG/MAG welding of steels is a fusion process of melting metals. MIG brazing is an adhesion process and uses heat as low as 1,940 degrees Fahrenheit. Brazing does not melt the base metals, only the filler wire. The filler wire flows in the low heat and settles onto the surface or in between metals.This surface area or footprint is quite large in comparison to a weld and gives the brazing process the strength to work. The copper-silicon bronze filler wire flows with heat and has incredible surface tension ability once cooled. Similar to sweating a pipe, but with steroids.

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This lower heat process limits damage to HSS and UHSS steels. MIG brazing allows the bonding of HSS and UHSS where STRSW won’t reach. When reading manufacturers’ requirements on MIG brazing, you’ll see the statement, “Use MIG brazing where STRSW cannot reach.” MIG/MAG plug welds are not an option. Failure to follow these guidelines could be a very costly mistake. Vehicle manufacturers do not state a requirement such as this without serious cause.

MIG brazing has less affect on galvanized steel, allowing steel to maintain much of its corrosion protection properties. This alone is a significant improvement to the longevity of the repair. Add in the technique of brazing, and the negative effects of heat are further reduced as compared to welding.

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Controlling Heat

There are two different types of brazing. One is the use of brazing in place of STRSW welding where STRSW cannot reach, or plug welds. Two is the use of brazing to close gaps in seams. MIG brazing in itself controls heat much better than MIG/MAG steel. The issue is training technicians to correctly use MIG brazing. I-CAR is currently offering a course on this, and I strongly urge all to take it. MIG brazing is not difficult, but doing it incorrectly negates the benefits.

Plug/Fillet Welds

Vehicle manufacturers are specifying methods or techniques to control heat further but allow the filler to flow to create a large footprint for adhesion. Some will use a fillet weld style with a push zigzag pattern. Some will drill two 8mm holes and join them or not, and again a possible push zigzag pattern to heat an area for copper silicon wire to flow and make a large footprint. Looking up vehicle manufacturers’ instructions is critical to making a quality weld.

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Section Joints

When brazing a section joint, once again, certain aspects must be followed. Failure will negate all positives of using this process. Stitch or skip will be used to keep from melting base metals and warping metal.

Using a stitch method to keep heat under control is a must. The bead from brazing will be much different. The bead requires a capillary action to not just flow onto the surface but also flow and form a bead on the backside. Correct root gap is an absolute in MIG brazing, and because of this, controlling the arc at low settings may be a challenge on certain welding machines.

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Learning to keep the heat down is opposite of what so many technicians have been taught for so many years. The use of brazing with a push technique is also a change for technicians who are used to using a drag technique to weld steel. But all of this is necessary to keep the heat in front of the weld to allow the wire to flow.

Equipment

As all this is a practiced skill and can be difficult for many, vehicle manufacturers have started specifying equipment requirements to ensure the process is done correctly to limit possible damage to their vehicles. This has led to an easier learning curve for shops as the new welders compensate and help control heat.

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The 220-volt synergic pulse welders reduce mistakes and allow the technique to be learned much more easily. Pulse welders greatly reduce the heat to the base metals as compared to spool or non-pulse welders. The computer programs in these welders offer a much more stable arc at lower settings. These welders offer a large number of settings for all parameters a shop would need, which nearly eliminates the “dialing in” of a welder by the technician.

Another advantage is that these requirements from vehicle manufacturers cross over into aluminum. MIG brazing and welding aluminum have some similar characteristics. Both are a MIG process using 100 percent argon gas. Both have torch liner recommendations of Teflon. Both have requirements of pulse welder capability. Many of the programs are already in the computers, so if your shop is set, for example, to weld the aluminum F-150, then the brazing settings are ready for you. You just need a separate torch and liner for the brazing operation. The rollers in the machine for aluminum are correct for MIG brazing in the shops that have already started welding aluminum. These considerations must be taken by shops wishing to convert a 220-volt welder to MIG brazing. Keep in mind, however, that some vehicle makers will not accept a conversion.

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Wire

Reference the vehicle manufacturer information on which wire to use on any type of welding or brazing. Just because you have a wire does not make it right. Many will call for CuSi wire, but this is not always true. Not every steel weld requires ER70S-6 wire, either.

Test Welds

Always do test welds prior to repairing a vehicle. The one thing I’ve noticed is that MIG brazing is very comparable in strength to a weld. In I-CAR classes, I find them sometimes harder to break than welds, so do not doubt the strength of a correctly done MIG brazed repair.

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