Thixomolding rolls along

The thixomolding process, a way to produce magnesium parts on modified injection molding machines, got its start with small parts like enclosures for electronic gadgets.

As it matured, the process progressed to larger and larger components, culminating with parts as big as the housing for a 36-inch Panasonic television. And now thixomolding stands to make yet another transition, this time into heavy-duty structural parts. "We've started to see a lot of interest in using thixomolding to replace forged, cast, HIP, and extruded aluminum," says Steve LeBeau, vice president of Thixomat Inc., the patent holder for this magnesium molding technology.

In one of the first such applications, an automotive OEM in Asia will soon use the process to make wheels for a luxury car. LeBeau can't yet disclose which OEM, but he does report that the company makes the wheels in a two-step process. First, it turns out a near-net shape preform using the thixomolding process. It then sends these preforms through a warm forging process to densify them. LeBeau notes that thixomolded parts "already start with low porosity"-somewhere around 1 to 2%. The forging process, however, "reduces porosity close to nil," or about one-tenth of a percent, he says.

To support automotive and other structural applications, Thixomat has recently been experimenting with blends of alloys that contain varying amounts of aluminum. A technical paper from the recent TMS Conference details the improved mechanical properties and processing ease of alloys with aluminum content between 6 and 9%. These new blends should help propel thixomolding into more severe structural applications than ever before, according to LeBeau.

New users follow guide. Thixomat has also come out with a new design manual on CD-ROM. LeBeau calls it a "step by step guide for engineers to follow when designing for thixomolding." For those used to working with molded plastic or die-cast parts, the guide does a thorough job describing how to benefit from thixomolding's advantages: dimensional tolerances as good as 0.0005 inch, uniform shrink of 0.005 inch/inch, and low porosity.

"Thixomolded parts lean toward plastic-part design principles, but some of the more limiting rules don't apply," explains Bob Kilbert, a Thixomat representative who authored much of the guide. He cites surface shrink at the juncture of heavy walls and ribs as one example: "We don't have to worry about that with thixomolding," he says. And thanks to their ability to hold tolerances, thixomolded parts can often do away with second-ary machining operations needed with die casting, he adds.

Besides information on the part configurations that make the best use of thixomolding's capabilities, the guide includes sections on prototyping strategies, tooling development, part finishing, joining and fastening, and defect prevention. The manual also includes case histories to reinforce all the design information. E-mail [email protected] for ordering information.

For more information about thixotropic molding technology from Thixomat Inc.: Enter 540