New Math Method Adds To Likelihood Of Super-Reliable Metal Parts

A technology called "superfinish hard machining" promises to make such a feat possible, while saving time and money and reducing pollution. Now, researchers at Purdue University have developed a mathematical method that may speed the emergence of hard machining. Details about the work will be released Tuesday (8/24) at a scientific conference in Switzerland.

Presently, parts that carry critical loads in everything from cars and appliances to jet engines are produced in many steps, including time-consuming and costly grinding and polishing operations. The parts are first machined out of metal that is relatively soft. Then, they are hardened by being subjected to high heat and quickly cooled in water, or "quenched." After those steps, they still require precision finishing processes to make their surfaces ultrasmooth to reduce friction and wear.

In superfinish hard machining, the metal is hardened first and then machined in a single-step process that yields smoother surfaces, reduces waste and eliminates the need for polluting oils now essential for cutting and grinding, says C. Richard Liu, a Purdue professor of industrial engineering who has been a pioneer in hard machining research.

Purdue is helping industry pursue ways to perfect hard machining and reap its potentially dramatic benefits. For example, it might be used one day to increase the service life of hardened metal parts by 20 to 50 times. Essentially, parts such as bearings and jet engine components that might ordinarily require replacement several times during the lifetime of a piece of equipment would never have to be replaced, Liu says.

One obstacle to the widespread use of hard machining is that, as the cutting tools that are used to machine hardened steel begin to wear, they cause thermal damage that weakens the metal being machined. The tools, which come in a variety of shapes, are small, sharpened bits like those used on a lathe to machine metal. Before superfinish hard-machining can be perfected, engineers need better methods to analyze precisely how heat is conducted between the cutting tool and the metal surface. They also need to take into account how much heat is released as it is carried away by metal shavings, or chips, removed from the metal during machining.

"It's a very complex heat-transfer system," Liu says.

To attack that problem, he has developed a new mathematical method to predict the precise temperature distribution at the interface of the cutting tool and the metal surface. A major benefit of the new model is that it can be used to predict which specific cutting tools will cause the least heat damage. Liu will present a paper detailing the work on Aug. 24, during the annual meeting in Switzerland of the International Institution for Production Engineering Research.

Purdue researchers have used the method to enhance a patented process for machining hardened components, which up until now have been extremely difficult to machine without causing thermal damage. During the process, the metal's surface is "prestressed," which means it is formed to counteract the stresses it will encounter in everyday use.

The research is funded by the National Science Foundation.