Repairing Auto Aluminum: Not Difficult, Just Different
As aluminum use rises in the auto industry, so does the need for understanding
and applying "best practices" when repairing automotive aluminum components.
A review of both the similaritiesand differencesencountered during
the repair of aluminum panels compared with those of traditional materials shows
that working with aluminum is not difficult; it is merely different.
Some procedures for working with aluminum are easier than with conventional
Most tools for working aluminum are similar to those for working conventional
The skills necessary for working aluminum can be learned as easily as
those required for other materials.
Real repair costs are not very different from those of traditional materials.
Programs in place and others under development offer training for repair
of aluminum panels.
Body Repair Industry
Over the past century, body repair shop practices, tools, and techniques have
been developed to work mainly with automotive steels. As the auto industry looks
to the future, however, it is increasingly turning to aluminum as the material
of choice for use in automotive body structures and closure panels. As a result,
a growing number of repair shops nationwide are acquiring expertise in aluminum
In fact, comprehensive programs are being put in place that address aluminums
different characteristics. The development and implementation of repair instructions
for specific aluminum vehicles has been led by manufacturers. The InterIndustry
Conference on Auto Repair (I-CAR) and others from the auto insurance and repair
equipment supply industries have worked side-by-side with experts from the aluminum
industry to develop training guides for correct repair of aluminum panels. A
nationwide training program began in 1996.
Tools: Adapted or Developed for Aluminum
Tools for working with aluminum are generally similar to those used for working
with steel. However, good practice dictates that the same tools not be used
on both metals because of cross-contamination. This causes problems with welding,
finishing and potential bimetallic corrosion.
Files, sanding discs and associated equipment are as effective when working
with aluminum as with other metals. Cutting and general working of aluminum
is much easier than steel, and the techniques involved are similar to those
used in wood-cutting. Reciprocating saws and band sawsboth with high blade
speedsare normally used.
Use of Heat for Metal Straightening
When an aluminum part is damaged, the deformed area is work-hardened (strengthened).
Pulling on the part to straighten it will deform undamaged areas that have not
been work-hardened before correcting the damaged area. Local heating of the
damaged area will temporarily soften the heated area so the damaged area can
be corrected. The Aluminum Association provides information on the effects of
elevated temperatures on material properties and recommendations for the use
of heat for straightening (visit www.aluminum.org to learn about these publications).
A technique known as heat-shrinking can be used to remove dents from aluminum
skin panels. When the area around a dent is heated with a torch, the stresses
generated by restraining the metal that wants to expand push the dent out.
Another difference between heated aluminum and steel is that aluminum does
not change color, even at its melting point.
Therefore, it is important to use temperature indicators to keep track of the
metal temperature during working. Heat can be used in cases where a technician
needs to disassemble an adhesive-bonded joint. As long as the temperature is
kept within the recommended range, heat will soften the adhesive and enable
the joint to be chiseled open with less mechanical damage and no long-term effects
on material properties.
Conventional Gas Metal Arc Welding (GMAW)
The conventional method for welding common metals is with the GMAW process,
commonly known as metal inert (MIG) gas welding. Aluminum lends itself well
to this type of welding. Virtually all repair shops possess MIG welders. The
more powerful and adaptable pulsed MIG machines required by aluminum are starting
to penetrate the larger repair shops. Lap and fillet welds, butt welds with
a backing added for the repair, and MIG plug welds are all approved for replacing
other joining methods and for repairing original MIG welded joints.
The Bonding Advantage
Aluminum panels have been bonded together with adhesives in the aircraft industry
for decades. This structural bond yields exceptionally strong and reliable joints
that improve the rigidity of the final assembly, particularly for stamped sheet
auto bodies. Automotive engineers designing for precise handling and the quiet,
solid feel of a high-quality car consider high stiffness very important. Using
a suitable surface pretreatment, adhesive-bonded aluminum joints can be repaired
without any sacrifice in strength or stiffness and will outlive a normally protected
steel structure in most situations.
Semi-structural bonding is used widely in steel and aluminum bodies in areas
such as hood hem flanges and roof panel joints. Equivalent bonding products
are available for these applications, and new repair adhesives have been developed
to bond joints spot-welded in the original assembly.
A wide range of coated steel and aluminum stem (pop) rivets are available for
every type of application including high loads and severe corrosion conditions.
A conventional countersunk aluminum rivet may be used for flanges that require
a flush surface on both sides. Precision drills are available for standard rivet
sizes and assembly is straightforward once the parts have been aligned. The
tools required for riveting are inexpensive and simple to use.
Equipment for automated punch riveting is not suitable for repair workshops,
but tools for removing this type of rivet are becoming available. Vehicle manufacturers
will specify a generic or proprietary fastener, which can replace these rivets
and spot welds.
Production spot welds can be neatly removed with a conventional spot weld cutter
by adjusting the drill depth to cut through only the damaged part. Equipment
for spot welding aluminum in production is too large and powerful for the repair
workshop. An alternative joining method is generally recommended.
Aluminum panels are finished the same way as conventional materials, including
the use of body fillers. All major paint suppliers offer aftermarket paint repair
systems, which include products designed and tested for specific materials (aluminum,
steel, galvanized steel, SMC, etc.). Whatever the material, the supplier will
warrantee the quality of the finish, provided the products and procedures for
their complete system are used. Most procedures are standard for all suppliers,
and finish systems are warranted as long as directions are followed.
There are few fundamental differences between the repair of steel and aluminum
panels, and the typical repair shop can be outfitted relatively easily for both.
The difference between the material costs of steel and aluminum are insignificant
in comparison to the cost of replacement parts. For an experienced technician,
the labor time required for aluminum repair is equivalent to that required for
steel. To gain appropriate experience, the first step is training. Such training
is rapidly spreading, and those who complete instruction are more valued assets
to their employers.
As the aluminum content of vehicles increases, more and more repair facilities
will learn to better accommodate aluminum-intensive vehicles. As more aluminum-intensive
vehicles come onto the market, repair shops will reactas they always haveto
economic pressures and equip themselves to handle damage repairs, much like
they did several years ago to adjust to the universal changeover to computer
Comparing the relative ease and costs of repairing aluminum and steel, it is
clear aluminum is not more difficultjust different. Different techniques
are required, as is a clear understanding of the differences between steel and
aluminum alloys and how they affect the repair process. Such understanding is
readily available, as are the necessary specialized tools for proper repair
of aluminum. As for training, I-CAR programs have been in existence for several
years, and manufacturers and suppliers are providing the necessary instructional
materials to assimilate repair of aluminum into everyday shop practices.
As automotive aluminum use continues to climb due to its performance, safety,
and environmental advantages, its repair will become as commonplace and routine
as that of traditional materials.
Body Repair, InterIndustry Conference, Auto Repair, Heat, Metal, GMAW, Gas Metal Arc Welding, Riveting