Editor's note: This originally published in the August, 2021 issue of ABRN. It has been lightly edited since its publication.
It should come as no surprise to anyone in our field that the straightening of today's metals is somewhat different than in days past. Not that long ago, virtually all metal used in vehicle construction was that of mild steel throughout. There was an occasional appearance of aluminum, but the vast majority was mild cold-rolled steel. Those circumstances provided for a relatively short learning curve, as a “one size fits all” approach and technique was common. Today, there are several different types of steel being used and more widespread implementation of aluminum (also in varying grades). We will touch on some of the techniques and rules that are common for straightening metal on today's vehicles. We will focus on cosmetic repairs to outer body panels. The topic of straightening structure is a whole different conversation and frankly has become somewhat of a limited occurrence compared to days past.
If you're reading this and you don't touch the cars, you may wonder why this topic is important. There is no shortage of change coming at a rapid pace lately in our industry, and this subject is no different. One may think that this area would be no different than 50-100 years ago, but guess what? It has changed! We will cover those changes and it's important that everyone in our line of work, regardless of their job description, is aware of what those changes are and more importantly that the proper repairs are being executed. Knowledge is the driving force for that to happen.
The two types of metal most commonly used on today's vehicles are steel and aluminum. Steel is still the more popular choice, but aluminum usage is on the rise. We will begin with steel and cover aluminum topics soon after. Remember, we are covering the straightening of metal so plastic, carbon fiber, SMC and any other material will be a topic covered at another time. We will focus on metals only for now.
Steel has been prevalent since the inception of mass-produced vehicles. It was and mostly and still is a very economical choice for use in vehicle outer body panels. Production efficiency, formability, and repairability are all positive attributes that meet the engineering demands. The early days of automobile design and up to today saw the widespread use of mild steel. Steel usage has changed lately and that is why the repair process or, even the ability to repair it at all, has changed. The first thing one needs to know before considering straightening metal is to identify what type of metal it is and immediately after determine if the manufacturer allows repairs to that type of metal. If repairs are allowed there may be guidelines as to what are acceptable practices. Those questions may be answered in the more general collision repair guidelines or with a repairability matrix the manufacturer has produced for metals used in their vehicles. As mentioned before there is no “one size fits all” anymore. Not that long ago pretty much everything was mild steel and we used the same welders/wire, hand tools, stud pin welders, weld on dent removal equipment, and procedures, no matter what the make of the vehicle was. That logic will not work anymore. I still see it happening day in and day out. I was at a shop not too long ago where a technician was drilling holes in the metal and using a screw-type slide hammer to manipulate the metal. I did not want to cover the history back that far. If you're not familiar with the topic don't fret. It's an old repair method that has been out of practice for some time. I had hoped we were decades past that technique. I keep telling myself that was a fluke and I'll never witness it again, but I do realize too many shops/technicians are not as up-to-date as they should be.
A couple of the early techniques are in use today. The hammer and dolly method may still be a recommended practice by the manufacturer if there is backside access and repairs are acceptable to that particular type of metal whether it is steel or aluminum. Another, newer technique would be that of glue pulling. There are multiple reasons why the glue pulling process may be the best route if feasible. For a more in-depth look at that process refer to my article printed in the April 2020 issue of ABRN. I just went back and reread the article. I was pretty excited to share the process and frankly, I still am. I used it successfully on the shop floor as a technician. There have been incredible advancements in the training and tools used for glue pulling repair as of late. Like any process training and practice go a long way to ensure success!
Some vehicle manufacturers provide guidelines for the straightening of metal. As noted earlier, we are focusing on outer body panels. FCA has a guideline published for Chrysler and associated brands that reads as follows:
FCA US LLC Service Engineering’s position on the use of heat during collision repair is as follows:
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Any damaged body panel or frame component, which is to be repaired, must be repaired using the “cold straightening” method. No heat may be used during the straightening process.
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During rough straightening prior to replacement, damaged panels or frame components may be heated to assist in body/frame realignment. This application of heat, if absolutely necessary, must be constrained to the parts which will be replaced and not allowed to affect any other components.
This “no heat” recommendation is due to the extensive use of high-strength and advanced high-strength steels in FCA US LLC vehicles. High-strength materials can be substantially and negatively affected from heat input which will not be obviously known to the repairer or consumer. Additionally, application of heat will alter or destroy material coatings utilized for corrosion protection and which may not be restore-able.
Ignoring these recommendations may lead to serious compromises in the ability to protect occupants in a future collision event, reduce the engineered qualities and attributes, or decrease the durability and reliability of the vehicle.
This statement supersedes any previously released information by FCA US LLC.
Release Date: August 11, 2010
For more information, log on to www.MoparRepairConnection.com.
One must use common sense when applying these guidelines. I would have to think that they are OK with the use of “heat” when using the glue-pulling repair method, as the recommended panel temperature is around 80 degrees is the generally accepted temperature. The use of a heat gun to bring a panel to that temperature would be acceptable. Obviously, panel temperature can reach well above those ranges in various climates around the world.
When using a repair manual for a specific model, it is important to check for general guidelines as it relates to straightening metal. Some manufacturers may set forth an outline for making repairs to outer sheet metal using a welded washer or welded stud pin method such as this example taken from a 2018 Honda Accord repair manual provider listed under “body shop basics:”
This repair method is used to repair recessed areas where the back side of the damaged cannot be easily accessed such as a door panel, pillar, side sill, or rear wheel arch.
Because the heat generated while welding washers will damage the paint or anti-rust coating inside the panel, it is necessary to treat the area with anti-corrosion materials after the repair.
A related repair method uses welded on studs instead of washers, but the processes are similar.
If backside access is available, the traditional hammer and dolly method would be recommended. As the use increases of materials besides mild steel, the repair-ability of outer body panels may decrease. The elasticity, as well as memory, among other factors, may contribute to whether the type of metal in question will return to its original shape using traditional hammer and dolly methods. In a more basic explanation, newer steels may not react the same as mild steel does when using traditional methods such as hammer/dolly or pushing with body picks/PDR rods. The use of body picks for pushing the metal back in shape is also a longstanding technique when there may be limited backside access. More recently, rods used for PDR repair have been adopted by collision repair technicians for a similar technique that body picks served. Both are somewhat similar, although there are a lot more choices of style with the PDR tools. Those variances range from a small wire type form up to a very large rod diameter. Length and shape vary widely as well.
Straightening aluminum has several similar traits as steel. Heat is typically used in conjunction with several of the techniques/tools used. As with steel, it is VERY important to know first if heat is allowed, how much heat can be applied, and for how long. It is critical to monitor the heat being used in any repair regardless of the type of metal. Typically, an infrared thermometer would be used to most accurately monitor panel temperatures. Alternative methods employ temperature-indicating crayons. The panel is marked with the crayon and when a certain temperature is reached the mark will melt. It's a method that can keep you from overheating a panel provided the mark is made using a lower temperature threshold. If all the finish material has been removed and you are left with bare aluminum there is no way to visually indicate the heat being applied as aluminum will not change color as steel does. This note from Ford within the body repair manual for a 2017 F150 explains further why the amount of heat used is critical during repairs:
Use of heat on body panels
Aluminum body panels are highly receptive to heat transfer. With the extensive use of structural adhesives and non-structural sealers used in vehicle construction, the potential of heat transfer could impact adhesives and sealers in non-associated panels during the repair process.
Many repair areas that utilize structural adhesive may be separated after rivet removal by using a panel chisel along the joint/flange. Using heat (not exceeding 425°F (218.333°C)) to loosen a rivet bonded panel should only be done when all panels in the joint will be replaced or separated and new adhesive applied.
Another consideration when repairing steel and/or aluminum body panels is that of keeping the tools used for each type of metal separate. The same is true for most any type of work to be performed. Galvanic corrosion can be formed due to the transfer of dissimilar metals from the tools. Within the same vehicle listed above, Ford has offered guidelines as such:
Hand tools
Hand tools, such as hammers and dollies, must be dedicated and labeled for each substrate worked on. Metal hand tools used in aluminum repairs must consist of polished surfaces and should be stored in a dedicated toolbox when not in use. When possible, the use of rubber or wooden mallets is recommended providing these are also dedicated to aluminum repairs only.
Hammers and dollies used in steel component repair may create the concern of embedding steel particles in aluminum if used for both systems. Also, tools used for steel repair may have a rougher than required surface created through regular use which may also result in cross-contamination. Tools with serrated faces should never be used in aluminum repairs.
To sum it up, there is no longer a “one-size-fits-all” approach to straightening today's metals. One must first determine if the vehicle manufacturer allows repairs to that type of metal, and if they do, what guidelines they might have. Indeed, methods of days past may still apply. It's also true that there may be new and different circumstances as we move forward. Research is the key to success here. I hope I've “straightened” out some of these oftentimes misunderstood topics!
