Look around your shop, and you’ll likely see an old, transformer-based spot, MIG or MAG welder. Every facility has at least one, and many of these welders have been in service for years, if not decades. If it has lasted this long, there’s no rush to replace an old welder, right?
Car and truck body design is evolving rapidly, driving advancements in welding technology. Welders that have limited, all-manual inputs and no feedback for the operator are now facing competition from automatic setting transformer welder as vehicle manufacturers increase their use of advanced high-strength steels and aluminum. These metals react very differently than traditional steel when welded. To repair the vehicles of today and the future, you will have to continually maintain your welding training to ensure you can properly work with modern materials and those to come.
Understanding advanced high-strength steel and aluminum
OEMs are using a variety of strategies to boost the fuel efficiency of their vehicles. One way to limit fuel consumption is by making the vehicle body lighter through the use of two groups of metals: advanced high-strength steels and aluminum alloys.
Advanced high-strength steels include a variety of steels with tensile strengths ranging from 550 MegaPascals (MPa) to 2,000 MPa. These are significantly stronger than traditional “mild” steels, enabling OEMs to design thinner, lighter structural pieces and panels. Automakers also save weight by replacing steel components with aluminum ones. Today’s aluminum alloys have tensile strengths similar to mild steel, but weigh up to 40 percent less.
According to a Ducker Worldwide study, North American vehicle manufacturers nearly doubled their use of advanced high-strength steels between 2005 and 2009, and are expected to more than double it again by 2025. A separate Ducker study predicts that North American OEM demand for aluminum will grow from less than 200 million pounds in 2012 to nearly 4 billion pounds in 2025.
As the vehicle body becomes lighter in the coming decades, it will also become more diverse. That’s because automakers can pick and choose from an array of advanced high-strength steels and aluminum alloys, each with its own strength and weight characteristics. Some of these metals are ideal for crumple zones or structural pieces, while others are more suited for body panels and closures.
Modern spot welders continually detect metal composition, thickness and impedance, and automatically adjust current levels, clamp pressure and weld time on the fly to ensure perfect welds no matter what type of steel is being welded.
What advanced high-strength steel means for your spot welder
The next vehicle that comes into your shop could include a variety of advanced high-strength steels in its body, but all of these metals will look the same once the paint is removed. There are no labels to tell you which metal is being used where, and a manual spot welder will have no idea what kind of steel it is welding. It will be up to the technician to not only identify the metal he or she is going to weld, but to also properly set up the welder.
So why not let the technician fire up a manual spot welder and see if he or she can figure out which settings will work? You only get one chance to weld a piece of advanced high-strength steel. If too much heat is added, you’ll create a large heat effect zone that will significantly weaken the part. If you add heat too fast, the metal will rapidly melt and become brittle upon cooling.
That’s why automatic spot welders are becoming more common in collision repair shops. These welders continually detect metal composition and material thickness through impedance — electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (AC) circuit — and automatically adjust current levels, clamp pressure and weld time on the fly. There’s no need to worry about heat control or ruined parts, because the welder adapts to each change in metal as you work.
Aluminum MIG welding
Spot welders lack the power needed to work with aluminum, since the metal conducts heat away from the weld at a much higher rate than steel. That leaves MIG welding as the preferred method for welding an aluminum-bodied vehicle. Tungston Inert Gas (TIG) would affect and damage electrical components in the vehicle due to the high frequency.
So what happens when you try to weld aluminum with a non-automatic MIG welder? At a recent training event, a participant with plenty of welding experience found out. This welder laid what looked to be a good weld to join two pieces of aluminum. After the weld cooled, the instructor picked up the two pieces and promptly snapped them apart, to the surprise of many in attendance. While the weld appeared visually to be sound and strong, the bead never sufficiently penetrated the metal.
The inability to visually tell a good aluminum weld from a bad weld is one reason OEMs now recommend that aluminum be welded with a modern inverter pulsed MIG welder. These welders are designed specifically to penetrate aluminum, and they come with preset programs that ensure proper voltage and current, making the process easier. The technician does have to enter the type of wire before beginning to weld, and also adjust settings for arch length, pulse correction, two step/four step, wire size and amp and volt adjustments based on the welder’s speed.
OEMs also require inverter pulsed MIG welders because the aluminum wire required for most vehicles today is incompatible with old welders. Since the wire is so soft, it can easily be tangled if loaded in a welder that uses a single feeder to push the wire all the way from the roll to the gun. An ideal inverter pulsed MIG welder will come with a push-pull torch that maintains constant, uniform tension on the wire, minimizing breakage or tangling.
Inverter pulsed MIG welders are not just for aluminum. They can also be used for brazing, a low-current soldering-like bonding method for advanced high-strength steel. Since brazing requires little heat, there’s less chance that the advanced high-strength steel piece will be damaged.
Ease of use
New automatic spot, MIG and MAG welders save time during setup, since little input is needed from the technician. They also will assist in help the technician produce the best possible weld the first time, so there’s less chance of needing to go back to correct insufficient work. But please keep in mind that travel time/speed, gun angle, gun position, gas pressure and technician steadiness can all affect the weld quality, and this is why test welds are paramount prior to welding on the vehicle.
Technicians may prefer working with new welders for several other reasons. Inverter pulsed MIG welders with double pulsed technology repeatedly cycle current from high to low during the welding process, which allows the aluminum weld droplets to slightly cool as soon as they are created. Since technicians often have to weld above their heads or on a vertical surface, this slight cooling prevents excess droplets from falling on their masks or on the floor.
When it comes to spot welders, today’s versions have longer cables than their old counterparts, making it easier to reach confined areas of the vehicle and reducing the need to frequently move the welder base. Some modern spot welders also detect which electrodes and arms are in use, reducing the risk of operator error while also eliminating the need to stop and program the welder every time the technician changes tips.