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Magnesium die casting advances aid application.

With density about two-thirds that of aluminum, magnesium is valued for its light weight. Unfortunately, many magnesium alloys have been relative lightweights in terms of mechanical properties and processability as well.

Now, however, process improvements are resulting in expanding use of magnesium die castings in applications ranging from automotive structural components to micro-sized parts for electronics and consumer products.

Spartan Aluminum Products Inc, a Sparta, IL, producer of magnesium and aluminum die castings, undertook a program to optimize die casting of AM60, a common alloy containing 6% aluminum and 0.13% manganese. Vice president of engineering Mike Dierks says Spartan started with the assumption that published mechanical property data for magnesium diecasting alloys did not reflect optimal processing conditions. "We've always felt the accepted published data, which were developed by the metal producers, were inherently conservative," he says.

Accordingly, the company obtained the die used to cast mechanical test specimens that resulted in the published information. Spartan engineers cast their own specimens using the die, and mechanical tests at an independent laboratory duplicated the published properties.

Then Spartan designed a new die incorporating its knowledge of tool design and gating for magnesium diecasting. Using vacuum processing and computerized process monitoring equipment coupled with a design of experiments approach to process optimization, Spartan achieved significant property improvements: a 20% increase in tensile strength, an 80% increase in yield strength, a 400% increase in impact strength, and elongation of 22.5%--nearly three times the published standard.

The improved properties--particularly increased ductility--are resulting in magnesium die castings for automotive applications that have the strength and ductility to pass crash tests where conventional magnesium die castings fail.

"We've actually adapted what we've learned (in the development process) to several prototype components, and it has made the difference between failing and passing," Mr Dierks tells T&P. "This is without making any structural changes to the component, only adapting what we've learned."

As an example, he cites a diecast magnesium steering wheel frame. Frames currently are either a steel or aluminum tube ring and steel or aluminum spokes that are joined with small, individual aluminum die castings. A solid-frame, one-piece magnesium die casting is not only much less complex than the composite frame assembly, but weighs only one-third to one-half as much.

Other applications being explored by Spartan include seat and steering column brackets and instrument panel components. The company plans to use the same development approach it took with AM60 alloy in an effort to expand applications of other magnesium materials and will provide test bars and data to interested potential users.

In another diecasting process development, Dynacast Inc, Yorktown Heights, NY, has developed a proprietary process it says opens the way for production of small, complex magnesium components for automotive, electronics, and consumer applications and makes magnesium die castings cost-competitive with machined, stamped, and formed components.

In the four-slide diecasting process, the sections of a limited-cavity die can move vertically and horizontally, resulting in processing up to five times faster than conventional machines using multi-cavity dies.

Dynacast managing director Keith Thompson says the four-slide process allows economical production of parts with difficult configurations, such as very thin walls or cast-in-place threads and gears. Other advantages, according to Mr Thompson, include more uniform part-to-part quality and longer die life.
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Manufacturing Update
Publication:Tooling & Production
Date:May 1, 1993
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