Types Of Tool Wear Zones-Crater wear,Flank wear,Corner wear

Introduction
The life of a cutting tool can be terminated by a number of means, although they fall broadly into two main categories:

• gradual wearing of certain regions of the face and flank of the cutting tool, and
• abrupt tool failure.

Considering the more desirable the life of a cutting tool is therefore determined by the
amount of wear that has occurred on the tool profile and which reduces the efficiency of cutting to an unacceptable level, or eventually causes tool failure

When the tool wear reaches an initially accepted amount, there are two options,

1. to resharpen the tool on a tool grinder, or
2. to replace the tool with a new one. This second possibility applies in two cases,

Wear zones
Gradual wear occurs at three principal location on a cutting tool. Accordingly, three main types of tool
wear can be distinguished,

• crater wear
• flank wear
• corner wear

These three wear types are illustrated in the figure:

Crater wear:  consists of a concave section on the tool face formed by the action of the chip sliding on the surface. Crater wear affects the mechanics of the process increasing the actual rake angle of the cutting tool and consequently, making cutting easier. At the same time, the crater wear weakens the tool wedge and increases the possibility for tool breakage. In general, crater wear is of a relatively small concern.
The crater is predominant in high-speed cutting.

Flank wear: occurs on the tool flank as a result of friction between the machined surface of the workpiece and the tool flank. Flank wear appears in the form of so-called wear land and is measured by the width of this wear land, VB, Flank wear affects to the great extend the mechanics of cutting. Cutting forces increase significantly with flank wear. If the amount of flank wear exceeds some critical value (VB > 0.5~0.6 mm), the excessive cutting force may cause tool failure.
Flank wear is predominant in low-speed cutting.

Corner wear: occurs on the tool corner. Can be considered as a part of the wear land and respectively flank wear since there is no distinguished boundary between the corner wear and flank wear land. We consider corner wear as a separate wear type because of its importance for the precision of machining. Corner wear actually shortens the cutting tool thus increasing gradually the dimension of machined surface and introducing a significant dimensional error in machining, which can reach values of about 0.03~0.05 mm.