Researcher Uses Casting Method to Improve Molds Used in Auto Parts

Newswise — A good wax mold lies behind every fast car. And a University of Missouri-Rolla researcher's efforts to improve wax investment casting -- a technique with roots dating back to ancient Egypt and China -- should make fast cars even more efficient by improving the quality and strength of the mold shells used to create engine parts. "A lot of high-performance engines use investment casting because manufacturers can make them with low-alloy steel in a very complex shape and actually save weight over using a previously stamped and formed component," says Dr. Von L. Richards II, the Robert V. Wolf Professor of Metallurgical Engineering at UMR. Investment casting in its early stage of development dates back to the era of the Great Pyramids in Egypt. Ancient Egyptians and Chinese used this process to create jewelry and statues. The process has evolved since that time with advances in areas such as surface chemistry, robotics and fracture mechanics. The ancient methods were more of a "can" mold type of process, which hobbyists and artists still use, says Richards. In today's wax investment casting, a ceramic material -- a "slurry" or paste made up of fine grains and a bonding agent -- surrounds and coats the wax mold. Then the product is heated, and the extremely high temperatures melt the wax from the mold, often causing the mold shell to crack, says Richards. After the wax melts from the mold shell, it bakes at a high temperature and molten metal replaces the wax, creating the part or component. Richards found that the quality of the wax affects the reliability of the mold shells. By studying the physics of wax, Richards has developed a method to test the wax. When the wax melts from the mold shell it undergoes "crystallinity," a chemical change that causes patterns of crystals to form. The more crystallinity found in the wax, the more pressure the ceramic shell comes under -- and the more likely it is to crack, says Richards. "The real savings from this it is the less metal you have to throw back into the furnace because you have a cracked shell, the more energy you save in the melting operation," says Richards. "In a foundry the big energy consumption occurs during the melting operation." Completed in June, Richards' research project, "Thermal Expansion of Investment Casting Pattern Wax," received $100,000 from the Department of Energy through the Cast Metals Coalition, and another $100,000 from five foundries over the course of three-and-a-half years. In the future Richards plans to focus on the micro-structure of the shell and how it can be made stronger. Those most interested in using Richards' research results include the automotive, high-temperature ceramics, food processing, defense and marine-engine industries, he says.