ISR research accomplishments

A Method of Fabricating Oxide Ceramic Articles
US Patent 5,507,962    April 16, 1996

Research team

Guangming Zhang (ME/ISR)
Said Jahanmir (NIST)

Accomplishment

The need for the method. Structural ceramics typically have many properties that make them attractive materials for many high performance applications. Some of these are high strength at elevated temperatures, excellent resistance to chemical degradation and wear, and low density. High fabrication costs and uncertain reliability, however, create considerable barriers to using these materials.

Both the cost and performance of ceramic materials are strongly influenced by machining operations. Machining costs make up a large component of the cost of structural ceramics, sometimes constituting as much as 90 percent of the total fabrication cost. In addition, the performance and reliability of ceramic articles are strongly influenced by the presence of machining-induced damage.

Machining ceramic materials places stringent demands on the performance of cutting tools and cutting fluids, which are customarily used to provide cooling and lubrication during machining operations. Because of their hardness, ceramic materials are generally more difficult to machine than metals. Their machining usually requires a normal (feed) cutting force that is higher than that required for metals. Additionally, while metals are ductile, ceramic materials are typically quite brittle. As a result of these factors, the machining of ceramic materials is likely to produce machining-induced damage in the finished ceramic article and lead to increased cutting tool wear rates (in comparison to metals).

For ceramic materials to compete directly with metals in many high performance applications, significant advances in machining techniques to permit their rapid, economical fabrication must occur.

Oxide ceramic materials, which typically are somewhat easier to machine, offer more promise as potential workpieces for rapid machining methods. For ceramic articles to be routinely fabricated, cutting methods which avoid excessive machining-induced damage to the workpiece and achieve acceptable tool wear rates must be available.

In the cutting of a ceramic workpiece, cutting conditions that increase the removal rate, while at the same time minimizing the level of machining-induced damage, are to be desired.

Cutting fluids may have a substantial effect on cutting efficiency and tool wear, as well as on the surface finish and the surface and subsurface damage of the finished ceramic article. In addition to reducing contact forces, which may be accomplished by using additives in the cutting fluid that reduce the coefficient of friction, the cutting process may also be improved by controlling the temperature during the cutting operation.

What does the method accomplish? This patent is a method of fabricating an oxide ceramic article which includes cutting an oxide ceramic workpiece in a cutting zone and applying a cutting fluid to the cutting zone. The cutting fluid includes an aqueous solution which contains a sufficient amount of a boron compound to effectively provide lubrication.

It provides a method of fabricating a steel article which includes cutting a steel workpiece with at least one oxide ceramic cutting point. The method of this embodiment includes cutting the steel workpiece in a cutting zone with the oxide ceramic cutting point and applying a cutting fluid, which includes an aqueous solution which contains a sufficient amount of a boron compound to provide effective lubrication, to the cutting zone.

It also provides a method of fabricating an oxide ceramic article including cutting an oxide ceramic workpiece with at least one cutting point; and applying a cutting fluid to the cutting point and the workpiece.

This patented invention provides a safe, cost-effective, environmentally acceptable, water-based cutting fluid for use in cutting oxide ceramic workpieces.

Using this cutting fluid reduces the tangential cutting force while maintaining or increasing the normal (feed) cutting force. This combination of effects gives rise to a resultant cutting force which enhances the cutting effect. The increase in the normal component also leads to an attenuation of tool vibration and improves the retention of the cutting point in the cutting zone. Moreover, decreasing the tangential component of the cutting force reduces power consumption during cutting.

The lubricating and cooling properties of the cutting fluid provide a means of maintaining the cutting point and ceramic workpiece at lower temperatures during cutting. The combination of these factors permits oxide ceramic articles to be cut with a reduction in the machining-induced damage in the surface of the ceramic, i.e., with a reduction in the number and size of microcracks in the machined surface and in the amount of debris redeposited on the surface. This allows oxide ceramics to be cut to higher tolerances and to an improved surface finish (as evidenced by a lower surface roughness).

The lubricating and heat removal properties of the cutting fluid also permit increased cutting rates and prolonged life of the cutting tool. When coupled with the reduction in power requirements and the relatively low cost of the components of the cutting fluid, this patented invention may lead to a major reduction in the total fabrication costs of a ceramic article.

For more information

View this patent at Delphion.