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U.S. Defense Logistics Agency Allots Copper Industry $1 Million for New Casting Technology
(continued) Think outside the box for a second. CDA's motor rotor is not just a way to replace aluminum squirrel cages with copper. What CDA actually developed, says Cowie, is "a new way (using ordinary pressure die casting) to make a whole lot of things from copper and copper alloys that didn't exist before." "Taking that one step further," he continues, "and applying the key technical elements of the motor rotor's success (using superalloy casting dies and operating them at elevated temperatures), to products other than motors, you find an answer that might help solve DLA's supply problem. It's a process known as semi-solid casting." Semi-solid casting is nothing new. Among other things, this offshoot of pressure die-casting technology is used to make products such as "mag" automotive wheels, which are actually aluminum. Like die casting, the process is fast, economical (for large-volume production) and capable of producing near-net-shape products with good mechanical properties and excellent surface finishes. As its name implies, the semi-solid process involves the pressure casting of metal while it is in a partly liquid/partly solid state at temperatures between the liquidus and solidus for the alloy in question. Cowie says the metallurgical key to success is that the alloys' freezing ranges must be fairly wide. A number of copper alloys meet that criterion. Just as was the case with aluminum squirrel cage rotors, the roadblock to copper-based semi-solid castings was limited die life. Therefore, the know-how CDA gained while developing the die-cast copper motor rotor is precisely the information needed to make semi-solid casting work with copper alloys. MORE >> |
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