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The continuing process for reducing the weight of automobiles as a means to improve fuel economy is leading to the greater use of lightweight materials such as aluminum and advanced highstrength steel alloys. Though stronger than conventional metals, one of the challenges lies in the fact that advanced high-strength steels and aluminum alloys have lower formability compared to conventional mild steels. This challenge has led to the need for better metalforming techniques.
One such process being utilized is known as tube hydroforming. Michael Worswick, professor of mechanical engineering at the University of Waterloo in Ontario, Canada, says, "Tube hydroforming involves placing a tube within a female die and then filling the inside of the tube with hydraulic fluid or water. Fluid pressure is then applied to expand the tube into the desired shape."
In contrast to conventional stamping, hydroforming uses fluid pressure in place of a punch. Fluid pressures can reach 30,000 pounds per square inch during hydroforming. Worswick adds, "The hydraulic fluid is usually water formulated with a rust preventative package and lubricity additives."
Hydroforming has been used fairly recently in the manufacture of automotive parts. Worswick says, "The technique is at least 50 years old and was originally used to fabricate copper "t" junctions utilized as plumbing fixtures."
The auto industry has found that tube hydroforming provides a number of benefits compared to conventional metalforming such as a reduction in the number of parts needed and the weight of the vehicle, increased strength and stiffness, improved precision and, as a consequence, lower manufacturing cost. Many of the parts made by hydroforming are complex parts with irregular shapes. Examples used in an automobile are the roof header, radiator support...