It's no great secret that in the quest to decrease vehicle weight, there's been an increase in the use of aluminum for body panels. However, this poses challenges in stamping due to aluminum's lower formability compared to steel. In an effort to overcome this handicap, two researchers at Michigan Technological University (Houghton, MI) are developing a new die technology for deep drawing aluminum. As a part of the Partnership for a New Generation of Vehicles (PNGV), Dr. Klaus Weinman and Dr. Abhijit Chandra have built prototype dies with "active" drawbeads, designed to prevent tearing and wrinkling of the aluminum during stamping.
Traditional dies may use fixed drawbeads to add a consistent frictional resistance to the blank during deformation, thereby controlling the flow of the blank into the die. While the Michigan Tech die does have drawbeads, instead of being fixed, they can be moved via hydraulic actuators. This allows the user to vary the frictional forces created by the drawbeads during deformation. Both practical tests with Michigan Tech's prototypes and finite element analysis testing have shown that by manipulating the drawbeads in this way, it is possible to form aluminum with deeper draws than can be formed with flat tooling or fixed drawbeads.
While Weinman and Chandra have completed this first phase of the project, they are now working on what they see as the ultimate end of this technology: creating a die that can sense problems in the forming process and adjust the drawbeads accordingly. To do this, the die shoulder is equipped with strain gauging sensors that sense the flow of the blank and then automatically adjust the drawbeads in real time. Weinman describes the potential for the die to adjust to conditions that might normally cause a process failure such as material thickness irregularities or variations in the amount of lubricant on the blank.
|Active Drawbead Die: (1) press ram; (2) die table; (3) lower die shoe and tooling; (4) upper die shoe; (5) blankholder stage mounting plate; (6) guide pins; (7) punch tooling; (8) blankholder plate; (9) active drawbeads; (10) drawbead drive cylinder; (11) BHF cylinders; (12) blankholder lift cylinders; (13) die shoulder sensors.|
Given the complaints that some stamping plants have reported with the first-run capabilities of aluminum coil compared to steel, a development like this might be an effective bandage. Unfortunately for those of you hoping for emergency first aid, Weinman reports that it will most likely be several years until you could see a system like this in production. (The Michigan Tech research team has just started working with a $300,000 grant from the Department of Energy and the Aluminum Company of America.) Of course, Weinman is quick to point out that if they had an OEM partner it might make the research go faster (i.e. give them more cash to work with). Speaking of which, although this sort of tooling is likely to be more costly than conventional dies, Weinman hopes that economies of scale might mitigate this drawback. He's hopeful that his further research will produce a marketable "intelligent stamping die" with active drawbeads.
Considering the intensifying necessity to differentiate vehicles through "sheet metal" alone, this technology could be a boon to creative stylists; it would be possible for them to design more distinctive aluminum body panels that would still be manufacturable. Don't laugh, but with the recent trend to retro styling, it might be just a matter of time before we see cars with outlandish fins again—this time, deep drawn from aluminum.