Tool wear

In machining, tool wear is the gradual failure of cutting tools due to regular operation. Tools affected include tipped tools, tool bits, and drill bits that are used with machine tools.

Types of wear include:

• flank wear in which the portion of the tool in contact with the finished part erodes. Can be described using the Tool Life Expectancy equation.
• crater wear in which contact with chips erodes the rake face. This is somewhat normal for tool wear, and does not seriously degrade the use of a tool until it becomes serious enough to cause a cutting edge failure. Can be caused by spindle speed that is too low or a feed rate that is too high. In orthogonal cutting this typically occurs where the tool temperature is highest. Crater wear occurs approximately at a height equalling the cutting depth of the material. Crater wear depth (t₀) = cutting depth
• Notch wear which happens on both the insert rake and flank face along the depth of cut line causing localised damage to it primarily due to pressure welding of the chips. The chips literally get welded to the insert.

• built-up edge in which material being machined builds up on the cutting edge. Some materials (notably aluminium and copper) have a tendency to anneal themselves to the cutting edge of a tool. It occurs most frequently on softer metals, with a lower melting point. It can be prevented by increasing cutting speeds and using lubricant. When drilling it can be noticed as alternating dark and shiny rings.
• glazing occurs on grinding wheels, and occurs when the exposed abrasive becomes dulled. It is noticeable as a shine while the wheel is in motion.
• edge wear, in drills, refers to wear to the outer edge of a drill bit around the cutting face caused by excessive cutting speed. It extends down the drill flutes, and requires a large volume of material to be removed from the drill bit before it can be corrected.

• Edge Rounding, Edge rounding refers to the radius increase of cutting edge of the tool due to material removal. Edge rounding combines wear contribution from both flank face and rake face. Edge rounding is mostly found in machining of composite, i.e. Carbon Fiber Reinforced Plastics (CFRP), hybrid composite, metal-CFRP stack like CFRP-Ti stack. Edge rounding is reported for both hard ceramic-coated, and uncoated cutting tool. ^{[1] [2]}