A Closer Look at Thixomolding

Published: 31st March 2011
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The Thixomolding process appears to have taken over the magnesium casting market. The faster, environmentally friendly, and cheaper process spearheaded by Michigan based Thixomat Corporation has become the process used in cresting the magnesium products that are taking the place of steel in the automotive, aviation, and aerospace industries.

The Process
Thixomolding is actually more of an injection molding process than casting. It doesn't use molten metal that the casting process does. The metal alloys are heated to a slurry—a state somewhere between liquid and solid. However, the metal is not in this state when it is introduced to the process. According to Thixomat Corpoaration, the metal is solid granules when fed into the Thixomolding machine. The chamber that the granules are fed into is heated, bringing them to the slurry state. A constantly turning screw inside the chamber shears the metal as it is heated. The semi-solid material it then injected into a mold that is also heated.

Injection molding allows much more of the metal materials to be used. The low heat needed to heat the metal to a point that is much cooler than the melting point requires significantly less energy and resources than casting the molten metal. Thixomolding is more environmentally friendly is its exclusion of gases during the process. Cast magnesium must be covered with sulfur hexafluoride in order to protect it from oxidating and igniting during the casting process. The much cooler alloy used in Thixomolding needs no gas to protect it, as it never reaches the critical temperatures.

The process more closely resembles the methods used for creating plastics from molds. However, the product produced is much stronger than plastic and more resistant to corrosion than other structural metals. An alloy of magnesium, zinc, and aluminum is used to capitalize on the benefits of the process. So in addition to being environmentally friendly, the Thixomolded products have creep resistance, dampening ability and rigidity that is required of a metal that is slated to replace steel in the automobile market in the future.

It helps that the magnesium alloy is as strong as steel, but significantly lighter as well. In fact, the Thixomold process allows the creation of molds with very thin walls that are not structurally compromised. Another trait that makes the injection molded alloy a desired choice for the more fuel efficient vehicles being created today.

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