Tool wear: Wear on cutting edges

To understand the advantages and limitations of each material in metal cutting, it is important to have some knowledge of the different wear mechanisms to which cutting tools are subjected.

Flank wear

Abrasive

The most common type of tool wear and the preferred wear type, as it offers predictable and stable tool life. Flank wear occurs due to abrasion, caused by hard constituents in the workpiece material.

Crater wear

Chemical

Crater wear on the cutting tool is localized to the rake side of the insert. It is due to a chemical reaction between the workpiece material and the cutting tool and is amplified by cutting speed. Excessive crater wear weakens the cutting edge and may lead to fracture.

Built-up edge (BUE)

Adhesive

This tool wear type is caused by pressure welding of the chip to the insert. It is most common when machining sticky materials, such as low carbon steel, stainless steel and aluminium. Low cutting speed increases the formation of built-up edge.

Notch wear

Adhesive

Insert wear is characterized by excessive localized damage on both the rake face, and insert flank at the depth of cut line. Caused by adhesion (pressure welding of chips) and a deformation hardened surface. A common wear type when machining stainless steels and HRSA.

Plastic deformation

Thermal

Plastic deformation takes place when the cutting tool material is softened. This occurs when the cutting temperature is too high for a certain grade. In general, harder grades and thicker coatings improve resistance to plastic deformation wear.

Thermal cracks

Thermal

When the temperature at the cutting edge changes rapidly from hot to cold, multiple cracks may appear perpendicular to the cutting edge. Thermal cracks are related to interrupted cuts, common in milling operations, and are aggravated by the use of coolant.

Edge chipping/breakage

Mechanical

Chipping or tool breakage is the result of an overload of mechanical tensile stresses. These stresses can be due to a number of reasons, such as chip hammering, a depth of cut or feed that is too high, sand inclusions in the workpiece material, built-up edge, vibrations or excessive wear on the insert.