HOW A BROACH CUTTING TOOL WEARS
There is no known tool material that can completely withstand contact and rubbing at high temperatures and pressures over
a period of time without some changes from its original contour. It becomes necessary, therefore, to think of the effect of the controlling factors not only upon the cutting process, but upon the performance of the broach cutting tool, which itself affects the cutting process. For the sake of recognition and understanding of the fundamentals of metal cutting, the effects of changes in the controlling factors have been described without regard to their influence upon such criteria as tool wear and tool life.

CLIP FORMATION WHEN BROACHING STEEL

TOOL FAILURE

Failure of the broach cutting tool has occurred when it is no longer capable of producing parts within the required specifications. The point of failure, together with the amount of wear that determines this failure, is a function of the broaching objective. Surface quality, dimensional stability, cutting forces, and production rates may alone, or in combination, be used as criteria for tool failure.

It may, for instance, take very little wear to affect surface quality, although the tool itself could continue to remove metal with little, if any, loss of efficiency. In contrast, only a few thousandths of an inch of wear on a wide tooth form might cause such a large increase in the pulling force required that it would result in a loss of dimensional stability, or worse yet, a broken broach.
 

TOOL WEAR

Tool failure is usually associated with some form of breakdown of the cutting edge. Under proper operating conditions, this breakdown takes place gradually over a period of time. In the absence of rigidity, or because of improper tool geometry that gives inadequate support to the cutting edge, the tool may fail by mechanical fractures or chipping under the load of the cutting forces. This is not truly a wear phenomenon for it can be eliminated or at least minimized by proper design and application.

As a direct result of contact with the work material, there are two major regions on the tool where wear can take place: (1) the face, or front of the tooth, and (2) the land, or top of the tooth.