Manipulating metal

GETTING TO GRIPS WITH THE LATEST TECHNIQUES IN STRAIGHTENING METAL ON TODAY’S VEHICLES, FOCUSING ON COSMETIC REPAIRS TO OUTER BODY PANELS

It should come as no surprise that the best techniques for straightening today’s high-tensile metals are very different from those used in days past. Not that long ago nearly all vehicle bodies were made of mild steel throughout. You’d see some aluminium, but the vast majority were mild cold-rolled steel so a ‘one-size-fits-all’ approach was common. Today there are several different types of steel being used and widespread implementation of aluminum (also in varying grades), so the topic of straightening structure is a whole different conversation.

Steel is still the more popular choice and has been prevalent since the inception of massproduced vehicles. However, the type of steel used has changed recently and the repair process and even the ability to repair it at all has changed with it. So the first thing to know before considering straightening metal is what type of metal it is and whether it can be safely repaired. If repairs are allowed, there may be guidelines as to what are acceptable practices.

A couple of the early techniques are still in use today. The hammer and dolly method may still be a recommended practice by the manufacturer if there is backside access. Another, newer technique would be that of glue pulling, a technique covered earlier in this magazine. 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: • 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. • 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.

The hammer and dolly method may still be a recommended practice by the manufacturer if there is backside access

One must use common sense when applying these guidelines. I think that they are okay with the use of ‘heat’ when using the glue pulling repair method as the recommended panel temperature of around 26 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. Some manufactures may set 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 backside of the damaged vehicle 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, but the repairability of outer body panels made from material other than mild steel can be lower. 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 elasticity as well as memory, among other factors, may contribute to whether the type of metal in question will return to its original shape.

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. 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 colour as steel does. This note from Ford in the body repair manual for a 2017 F150 explains further why the amount of heat used is critical during repairs:

Typically, an infrared thermometer would be used to most accurately monitor panel temperatures. Alternative methods employ temperatureindicating crayons

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. With the same vehicle listed above, Ford has offered guidelines:

The hammer and dolly method may still be a recommended practice by the manufacturer if there is backside access

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 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. Research is the key to success here. Things to keep in mind when metal working, courtesy of the 3M Collision Repair Academy: • Before starting anything, clean the area with soap and water. Not only will this reduce possible contamination, it will also allow you to better diagnose the damage. • If straightening is allowed, ensure that you follow the OEM recommended straightening method. • Many high-strength steels will be ‘coldstraighten’ only. • You may need heat to straighten aluminum, but only within a specific temperature range. • Choose an abrasive that will remove any coatings without affecting the substrate material. Good examples would include: › Scotch-Brite™ Roloc™+ Clean and Strip XT

Pro Disc › Coarse Scotch-Brite™ Durable Flex Belt › Grade 80+ 3M™ Cubitron™ II Fibre Roloc™ Discs • Do not mix steel straightening tools with aluminum. Working aluminum panels requires dedicated tools for aluminum only. • Once you’ve completed the straightening process, and before applying primer or filler,

check for panel fatigue or microcracks using a penetrating dye. • Determine whether the OEM recommends applying filler to the metal, or if a 2K epoxy primer is required before you start applying body filler. • Use an approved solvent-based cleaner to remove any contaminants from the metal before applying any primer or body filler. • To prevent surface corrosion from developing, make sure to topcoat aluminum, high-strength steel (HSS), ultra-high-strength steel (UHSS), and boron steel in less than 60 minutes.