The process of hydroforming in some ways resembles the hot dogs that plump when you cook them. But instead of heat, parts makers use pressurized water to make it all happen.
The process begins with a metal tube. Suppliers have been working with a wide variety of steel types, including stainless and high-strength steels. Some have also been experimenting with hydroforming aluminum.
In many cases, the tube is bent by a computer-controlled bending machine so that it will fit into the die.
The tube is then loaded into the bottom half of the die. The ends are capped and the tube is filled with water as the top half of the die is lowered into place.
When the die is secured, the water in the tube is pressured between 7,000 and 60,000 pounds per square inch. That presses the tube into the shape of the die cavity. Then the pressure is released, the tube uncapped and the hydroformed part removed from the die.
The whole process takes about 30 seconds. On smaller parts, such as exhaust manifolds and roof rails, two pieces can be formed end to end on the same tube, or 'stick' as it's known in manufacturing circles, and then cut apart to increase output from the press.