Hot metal

Automotive engineers at Dana Corporation have succeeded in harnessing the heating power of microwaves to improve the performance of metals.

Automotive engineers at Dana Corporation have succeeded in harnessing the heating power of microwaves to improve the performance of metals and even enable the creation of advanced new materials.

Usually metals undergo heat-treatment processes within conventional furnaces where the high temperature of the atmosphere within the furnace indirectly heats the metal. Microwaves, which heat a material by directly exciting its molecules, represent a potentially far more efficient heating method, but haven’t been used to process metals because metals reflect microwaves. This can cause arcing and damage the microwave source (usually a magnetron).

However, Dana’s engineers discovered that by surrounding metal parts with a microwave-absorbing plasma, they could prevent this reflection taking place, thus preventing damage to the magnetron.

Company spokesman Jeff Gammons explained that during microwave plasma processing (MAP) plasma is confined within a ceramic-walled cavity that is transparent to microwaves. As the plasma absorbs microwaves, its temperature rises and the resulting heat couples rapidly with the metal parts inside the cavity, heating them more efficiently than conventional methods.

A key advantage of the development is the fact that it dispenses with the expensive vacuum equipment traditionally required to create a plasma environment. Instead, by producing and sustaining plasma at atmospheric pressure, equipment costs and cycle time are both significantly reduced. Indeed, Gammons claimed that the technique achieves temperatures of around 1,300 degrees C in seconds.

He added that because the technology confines heat to an insulated cavity, its rapid heating and cooling doesn’t result in thermal stress to the system, eliminating the need for chamber insulation and other replacement parts and reducing the size of the system.

Gammons said that the new method will improve part quality and slash processing times in a variety of metal processing applications including brazing, sintering, carbonising, annealing, tempering, nitriding and coating.

‘Microwave plasma processing delivers superior heating and coating uniformity compared with conventional processes. This is because unlike a conventional furnace, which can develop “hot spots”, MAP forms plasma evenly around materials, yielding consistent temperatures and coating depths,’ he said.

For instance, he claimed that by enabling high-temperature sintering MAP can endow parts with superior performance characteristics. He added that the process can be used to heat a variety of metals (such as steel, aluminum and iron) and to apply a number of hard-material coatings. He also claimed that, unlike induction heating, the technology is easily applied to complex part shapes and sizes and isn’t limited to metals.

While the company is initially targeting the technique at metal processing and coating, Mike Laisure, president of Dana’s Automotive Systems Group, said that it is also exploring applications for the technology in exhaust treatment, surface engineering and hydrogen production.

Dana is in discussions with several companies about commercialising the technology, but Gammon declined to reveal their identity. However, internal production lines deploying the process should be running next year, he said.

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