CNC tool wear is one of the basic problems in cutting. Understanding the forms and causes of tool wear can help us prolong tool life and avoid machining abnormalities in CNC machining.
1) Different Mechanisms of Tool Wear
In metal cutting, the heat and friction generated by chips sliding along the tool rake face at high speed make the tool in a challenging machining environment. The mechanism of tool wear is mainly the following:
1) Mechanical force: Mechanical pressure on the cutting edge of the insert causes fracture.
2) Heat: On the cutting edge of the insert, temperature changes cause cracks and heat causes plastic deformation.
3) Chemical reaction: The chemical reaction between the cemented carbide and the workpiece material causes wear.
4) Grinding: In cast iron, SiC inclusions will wear down the insert cutting edge.
5) Adhesion: For sticky materials, buildup/buildup buildup.
2) Nine forms of tool wear and countermeasures
1) flank wear
Flank wear is one of the common types of wear that occurs on the flank of the insert (knife).
Cause: During cutting, friction with the surface of the workpiece material causes loss of tool material on the flank. Wear usually starts at the edge line and progresses down the line.
Response: Reducing cutting speed, while increasing feed, will extend tool life at the expense of productivity.
2) Crater wear
Reason: The contact between chips and the rake face of the insert (tool) leads to crater wear, which is a chemical reaction.
Countermeasures: Reducing the cutting speed and selecting inserts (tools) with the correct geometry and coating will prolong tool life.
3) Plastic deformation
cutting edge collapse
cutting edge depression
Plastic deformation means that the shape of the cutting edge does not change, and the cutting edge deforms inward (cutting edge depression) or downward (cutting edge collapses).
Cause: The cutting edge is under stress at high cutting forces and high temperatures, exceeding the yield strength and temperature of the tool material.
Countermeasures: Using materials with higher thermal hardness can solve the problem of plastic deformation. The coating improves the resistance of the insert (knife) to plastic deformation.
4) Coating peeling off
Coating spalling usually occurs when processing materials with bonding properties.
Reason: Adhesive loads develop gradually and the cutting edge is subjected to tensile stress. This causes the coating to detach, exposing the underlying layer or substrate.
Countermeasures: Increasing the cutting speed and selecting an insert with a thinner coating will reduce the coating spalling of the tool.
5) Crack
Cracks are narrow openings that rupture to form new boundary surfaces. Some cracks are in the coating and some cracks propagate down to the substrate. Comb cracks are roughly perpendicular to the edge line and are usually thermal cracks.
Cause: Comb cracks are formed due to temperature fluctuations.
Countermeasures: In order to prevent this situation, high toughness blade material can be used, and coolant should be used in large quantities or not.
6) Chipping
Chipping consists of minor damage to the edge line. The difference between chipping and breaking is that the blade can still be used after chipping.
Cause: There are many combinations of wear states that can lead to edge chipping. However, the most common ones are thermo-mechanical and adhesive.
Countermeasures: Different preventive measures can be taken to minimize chipping, depending on the state of wear causing it to occur.
7) Groove wear
Notch wear is characterized by excessive localized damage at greater depths of cut, but this can also occur on the secondary cutting edge.
Reason: It depends on whether the chemical wear is dominant in the groove wear, compared with the irregular growth of adhesive wear or thermal wear, the development of chemical wear is regular, as shown in the figure. For adhesive or thermal wear cases, work hardening and burr formation are important contributors to notch wear.
Countermeasures: For work-hardened materials, choose a smaller entering angle and change the depth of cut.
8) Break
Fracture means that most of the cutting edge is broken and the insert can no longer be used.
Cause: The cutting edge is carrying more load than it can bear. This may be due to the fact that the wear was allowed to develop too quickly, resulting in increased cutting forces. Incorrect cutting data or setup stability issues can also lead to premature fracture.
What to do: Identify the first signs of this type of wear and prevent its progression by selecting the correct cutting data and checking setup stability.
9) Built-up edge (adhesion)
Built-up edge (BUE) is the buildup of material on the rake face.
Cause: Chip material may form on top of the cutting edge, separating the cutting edge from the material. This increases cutting forces, which can lead to overall failure or built-up edge shedding, which often removes the coating or even parts of the substrate.
Countermeasures: Increasing cutting speed can prevent the formation of built-up edge. When processing softer, more viscous materials, it is best to use a sharper cutting edge.
Post time: Jun-06-2022
