Researchers Developing New Material for Die-casting Molds

Automotive manufacturers may soon benefit from a new breed of metals – known as functionally gradient materials – that can withstand the high temperatures of die casting without cracking under pressure, according to a researcher at the University of Missouri-Rolla.

UMR researchers, led by Dr. Frank Liou, director of the manufacturing engineering program and professor of mechanical and aerospace engineering, hope to build better die-casting molds by developing materials that are both durable and heat resistant.

Traditional die-casting molds, made from hardened steel and used to make engine blocks and other components, can cost about $500,000 each, are fairly large and take a long time to build. One of the greatest challenges for car manufacturers has been finding a die-cast metal that can take the heat while maintaining its durability. Now, thanks to Liou’s work, manufacturers are one step closer to having the best of both worlds.

“It is now possible to gradually transition from one material to another,” says Liou. “Potentially this can have a lot of applications. You can basically create a material that gradually transitions from being totally titanium to being totally copper.” These metals are known as functionally gradient materials.

Spartan Light Metal Products, an Illinois-based company that uses die-cast molds to create engine parts, has asked Liou and his research team to investigate whether functionally gradient materials could be used in its manufacturing process. The company produces engine blocks for major automotive companies, including Ford, General Motors, Honda and Toyota.

If the molds were properly created using functionally gradient materials, the cracking could be eliminated, extending the lifespan of these expensive components. “The mold is under a lot of thermal stress,” says Liou. “If it were composed of copper and tool steel, the copper could transfer the heat out, preventing the mold from cracking.”

Thermal barrier coatings, another class of functionally gradient materials, would be able to impede heat transfer where necessary, such as in turbine blades. “Having a smooth transition between the two metals is critical,” says Liou. “Without the gradual change, the mold would still break under the stress.”

The research team is developing gears and a variety of other prototypes using functionally gradient materials. “They are trying to make gears where the outside would be made of Carbide (hardened material) while the inside would be steel,” says Liou, “so the gear would have much stronger properties on the outside.”

Applications for functionally gradient materials are as diverse as the manufacturing field itself. For example, the Navy is interested in using the technology to embed sensors in components, allowing for early detection of a failing part, such as a submarine propeller. “It would be important to detect any problems so they could be fixed before returning to the sea,” says Liou. “In order to place a sensor there, you would need to use functionally gradient materials because the propeller may break away under the strong forces.”

Even researchers in UMR’s own High Pressure Waterjet Laboratory have asked Liou and his team to investigate whether the process could be used to combine diamond powder with steel. “The original steel nozzle for their waterjet lasted about one hour, then had to be thrown away,” says Liou. “Now what they are using is a diamond nozzle, which is very expensive. They would like us to develop a functionally gradient material so that the inside, which is in contact with the water, is made of diamond and the outside is steel.”