Ceramic cutting insert of polycrystalline tungsten carbide

Abstract

A polycrystalline tungsten carbide ceramnic cutting insert with chip control is disclosed for high speed machining.

Description

[0001] This invention relates to the field of ceramics and particularly to dense polycrystalline tungsten carbide inserts with chip control.[0002] In the machining process, it is important for the cutting tool to work effectively at high speeds and to have a long tool life. In order for the cutting tool to be effective, it must be made of a material which results in the tool having a high heat hardness and a high transverse rupture strength and fracture toughness, and it must also have a design sufficient to control the flow of chips which are formed in the machining process and to reduce the cutting forces.[0003] Chip control is an important element of the machining process, in order to break up the length of undesirably long chips which may be formed in the machining process. In high speed machining, if the strip taken off from the workpiece by the cutting insert is not broken up, the strip can interfere with the machining process in a variety of ways. For example, an undesirably ...

AI Technical Summary

Benefits of technology

0020] Tungsten carbide (WC) ceramics of the present invention can be tailored for use in particular applications by an appropriate choice of starting WC powder size and by controlling densification conditions control grain growth.

0021] Desirable starting powder sizes fall within a range of from greater than 0.001 .mu.m up to 20 .mu.m. The range, depending on application, is preferably from about 0.001 .mu.m to about 10 .mu.m, more preferably from about 0.001 to about 4 .mu.m. In one embodiment, the tungsten carbide powder size is about 1.0 .mu.m. Starting powder sizes of less than 20 .mu.m should provide densified bodies having excellent properties.

0022] Tungsten carbide powders having an average particle size of less than or equal to 10 .mu.m are commercially available. One such powder, Teledyne type IV, has a nominal average particle size of 8 .mu.m and includes a small amount of vanadium carbide as a grain growth inhibitor. Attriting such a powder simultaneously reduces the average particle size, reduces grain size distribution, and more uniforrnly disperses the grain growth inhibitor. Even in the absence of a grain growth inhibitor, attrition provides the benefits of smaller average particle size and a narrower particle size distribution. As an alternative, the WC powder may have these characteristics as synthesized. As a further alternative, powders with even larger average particle sizes may be used provided they are milled or attrited under conditions sufficient to reduce the average particle size to less than or equal to 0.2 .mu.m. These powders necessarily require longer size reduction procedures and may, as a consequence, pick up additional quantities of impurities from media used t

Problems solved by technology

In high speed machining, if the strip taken off from the workpiece by the cutting insert is not broken up, the strip can interfere with the machining process in a variety of ways.

For example, an undesirably long chip can be re-cut and welded onto a portion of the workpiece, thereby causing poor surface conditions on the workpiece.

An undesirably long chip, if not broken under chip control, can also cause breakage of the machining tool itself.

Additionally, undesirably long chips can feed into the tool holder or other portions of the machine and cause difficulties, e.g., damaging parts of the tool holder or obstructing visibility of the working area.

Further, long ribbons are difficult to handle and can represent a safety hazard to the machine operator.

Early work with WC focused upon densifying WC by heating to a temperature of, for example, 2,000 C.degree.. The densified material was judged unsu

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