Ford made headlines when it gutted body shops at two pickup truck plants to build the new 2015 F-150 with an aluminum body instead of heavier steel, convinced the cost and risk were worth it for a lighter and better truck. General Motors is equally committed to reducing the weight of future vehicles but has taken a different approach. It quietly pursued ways to use existing body shops, tools, and equipment to spot weld future vehicles with a mix of materials, including aluminum — a strategy deemed less costly and disruptive.
After years of development and testing, engineers at GM are on the verge of putting a couple parts for the Cadillac CT6 sedan into production that are notable because they require welding steel to aluminum. GM is only months away from assembling seat backs and hood reinforcements using spot welding to join the two metals.
It is potentially a game-changer for an industry seeking the fastest and cheapest way to make lighter, more fuel-efficient vehicles. Others have expressed interest in GM’s technology. Ford’s strategy, so far, is not being emulated by others.
It might not sound sexy but making cars and trucks comes down to mating metal. When you think of an auto plant, the image that comes to mind is robots and sparks flying as they spot weld steel parts to form the body and frame of a new automobile. The growth of aluminum in vehicles posed manufacturing challenges on the plant floor.
GM tested the water when it put an aluminum liftgate on a Tahoe hybrid in 2008 and tested its ability to do aluminum-to-aluminum spot welding. Today it is a manufacturing staple at GM, but it took eight years for these spot welds to become mainstream, said Blair Carlson, Lightweight Material Processing Lab Group Manager.
Next up: applying spot welding — which is quicker and cheaper, and plants are already set up to do it — to the joining of steel and aluminum. GM will start with parts on the CT6 and Carlson is optimistic it won’t take another eight years for this latest advance to become mainstream practice at GM. The challenge was that at 655 degrees Celsius aluminum is molten whereas steel is just starting to warm up — it needs 1,538 degrees to melt. And where the two layers of hot metal meet, a glassy layer forms that is brittle.
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