Date: Jul 15, 2005 Author: Scott Tillett Source: MDA (
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by Scott Tillett
Putting metal in the microwave usually generates a lot of sparks—and panic—in the kitchen. But M Cubed Technologies, Inc. (MCT; Newark, DE), is using microwaves to make metal-ceramic composites with greater speed and higher quality. A custom-designed cavity rather than a conventional furnace is used to heat reinforcement preforms and infiltrant metal.
Working with Pennsylvania State University researchers, MCT is using its microwave technology to enhance three of its existing composite manufacturing processes: pressure-less metal infiltration, directed metal oxidation, and reaction bonding. Company researchers also say the technology is ideal for producing body armor vest inserts, a market for which MCT already manufactures as many as 20,000 vest inserts each month. In addition to the inserts, researchers say other applications—from heat sinks to high-quality mirrors to machinery used in semiconductor manufacturing—may exist.
MCT was funded by MDA through a Phase II SBIR award to improve processes for materials used in military systems such as the Exoatmospheric Kill Vehicle. Prototype materials emerging from the project are being offered to Raytheon for use in missile defense projects, according to Prashant Karandikar, director of research and development for MCT.
MCT's microwave-assisted processes would compete with traditional resistance-heating methods such as those involving furnaces. When a furnace is used, the core of the material preform reaches an infiltration temperature much later than the areas nearer the surface. But MCT's technology simultaneously affects the entire volume of the preform, reducing process time by 50 to 80 percent, according to Karandikar. Moreover, an added benefit of the process is superior microstructural characteristics of the final product, he said.
"What happens in a micro-wave is volumetric heating, so all the molecules in the work piece can couple with the microwaves," Karandikar said. "So the heating is happening everywhere in the part itself, unlike in the conventional process, where you are heating the furnace element, which then radiates to the part surface, and then the heat has to go from surface to inside of the part."
Karandikar said the micro-wave technology avoids generating the sparks that might occur when subjecting metal sheets or foils to microwaves by using powdered metals or adding susceptors such as silicon-carbide rods. Susceptors heat up and then transfer the heat to the alloy without generating sparks. After the alloy reaches a certain temperature, it starts coupling directly with the microwaves, he said.
Microwave energy has been commonly used for sintering ceramics and powdered metals, but MCT's MDA-funded research for metal-infiltration-based composite manufacturing is a first, according to Karandikar. The company modified a commercial microwave oven for the initial testing, and later built a much larger unit with a 20-inch-diameter cavity, allowing researchers to work with pieces of about 6 x 12 x 14 inches.
The current challenge for MCT is in scaling up the microwave equipment to handle larger pieces. The company also is focused on quantifying benefits of its methods and prototypes, according to Karandikar. "We are building enough experience in terms of making components, so now we can start looking at production rates and energy costs in more detail," he said.
