Hello, friends today we are going to discuss tool wear in which you will learn what is tool wear, types of tool wear as well as their causes and remedies.
Generally, tool wear is the loss of material from the surface.
Wear means that the tool loses its volume and geometric properties.
Tool wear describes the failure of cutting tools due to continuous operation.
If the tool is not giving satisfactory performance then it is an indication of tool failure.
What is Tool Wear?
Tool wear can be defined as the change in the shape of a tool from its original shape during the cutting operation, as a result of the gradual loss of tool material called tool wear.
When a tool is used for some time, wear becomes apparent.
During cutting, the tool must perform satisfactorily. Unsatisfactory performance of the cutting tool indicates tool failure.
Tool wear depends upon the following parameters:
- Tool and workpiece material.
- Tool shape
- Cutting Speed
- Feed and Depth of cut
- Cutting fluid used.
- Machine Tool characteristics, etc.
What happens If Tool Wear Occurred?
The following drawbacks are observed when tool failure occurs.
- Tools stop to produce workpiece as per required dimensions.
- The tools overheated.
- Excessive surface roughness is observed.
- Tool failure increases the cutting forces and hence the power requirement will be higher.
- May cause tools breakdown.
- Decreases accuracy of a tool product and tool life.
Types of Tool Wear
The failure of the cutting tool can be divided into two categories according to the failure mechanism of the cutting tool:
- Slow-Death Mechanism
- Sudden-Death Mechanism
Slow-Death Mechanism
In the slow-death mechanism, Gradual tool wear occurred on the flank of the tool (or) on the rake face of the tool(crater wear) or nose on the tool.
Types of Gradual Tool Wear
Gradual tool wear can be classified into the following types:
- Flank Wear
- Crater Wear
- Nose Wear
- Notch Wear
See in the figure types of tool wear which are described below in detail.
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| Types of Tool Wear |
Flank Wear
Flank wear is a form of wear that appears on the flank face (relief or clearance face) below the cutting edge of the tool.
It is caused by an abrasion between the tool flank and the newly machined workpiece surface.
Flank wear will be greater near the nose of the tool, and it is not uniform along the cutting edge.
It generally results from high temperatures, which affect the tool and workpiece.
This type of wear occurs on all tools when cutting any type of work material.
Reasons for Flank Wear
- Flank wear increases rapidly with increasing cutting speed and increases in feed and depth of cut can also result in larger flank wear.
- Abrasion by hard panicles in the workpiece.
- Shearing of micro welds between tool and workpiece.
- Abrasion by fragments of built-up edge, which strike against the flank face of the tool.
Remedies for Flank Wear
- Reduce cutting speed, feed, and depth of cut.
- Use the hard grade of carbide & prevent the formation of built-up breakers.
Crater Wear
The wear on the rake face of the tool is called crater wear.
In crater wear, chips erode the rake face of the tool.
Chips flow across the rake face develop severe friction between the chip and rake face.
It does not degrade the use of tools until it creates cutting-edge failure.
Crater wear can increase the working rake angle and reduce the cutting force, but it will also weaken the strength of the cutting edge.
This is more common in ductile materials such as steel that produce continuous chips over long periods of time.
It is more common in H.S.S. tools than carbide tools which have higher hot hardness.
Crater depth is the most commonly used parameter in evaluating rake face wear.
It occurs at a height equal to the cutting depth of the material, At high-temperature zones (nearly 700°C) crater wear occurs.
Reasons for Crater Wear
- Severe abrasion between chip-tool interfaces, especially on the rake face.
- High temperature in the tool-chip interface.
- Increase in feed results in rising in the temperature of the tool-chip interface.
- An increase in cutting speed leads to an increase in chip velocity at the rake face, thereby increasing the temperature at the chip-tool interface and hence increasing crater wear.
Remedies for Crater Wear
- Using the proper lubricant can reduce the abrasion process, and therefore reduce crater wear.
- By using proper coolant for rapid heat dissipation from the tool-chip interface.
- Reduced cutting speeds and feed rates.
- Use tougher and hot hardness materials for tools and have a positive rake angle.
Nose Wear
Nose wear occurs as a result of abrasion between the nose and the metal machinability.
It is considered a part of flank wear as there is no specific boundary between them.
It is also called corner wear.
Notch Wear
Notch wear on the trailing edge is largely an oxidation wear mechanism where the cutting edge releases the machined workpiece material in the feed direction.
Notch wear is caused by tool rubbing against the original work surface, which is harder than a machined.
Reasons for Occurred Gradual Tool Wear
These types of tool wear mechanisms are occurred due to the following reasons:
- Abrasion
- Adhesion
- Diffusion
- Chemical interactions
- Oxidation
Abrasion Wear
Abrasion wear occurred when mechanical abrasion between the workpiece material and cutting tool.
In this wear, hard particles on the underside of the chip pass over the tool face.
Adhesion Wear
As part of the friction mechanism, junctions between the chip and tool material are formed.
When these junctions are fractured, small fragments of tool material can be torn out and moved under the chip or to the new workpiece surface.
Diffusion Wear
This type of wear takes place due to the diffusion process where atoms in a metallic crystal lattice move from the region of high atomic concentration to the region of low concentration.
During metal cutting, when the temperature is high at the interface of tool and workpiece, the atoms move from tool material to workpiece materials and thereby weakening the structure of the tool.
Chemical Interaction
This causes due to chemical affinity between the workpiece material and the cutting tool material.
Oxidation
Oxidation is the result of a chemical reaction between the tool face and oxygen.
Sudden-Death Mechanisms
In sudden death mechanism, rapid, usually unpredictable, and often catastrophic failures result from the abrupt and premature death of the tool.
Sudden-death mechanisms are straight forward but less predictable.
These mechanisms are categorised as:
- Plastic Deformation
- Edge Chipping
- Fatigue Fracture
- Brittle Fracture
Plastic Deformation
It is caused by a loss of hardness, generated at the cutting point.
The combined action of cutting force and cutting temperature will cause the tool to deform.
Edge Chipping
This type of tool failure is caused by excessive chip load and also coolant not being able to cover the cutting point constantly.
Fatigue Fracture
Fatigue fracture is caused by the expansion and coalescence of cracks.
When the feed rate increases, the failure mode of the tool is mainly fatigue fracture.
Brittle Fracture
When stress exceeds cohesion, brittle fracture occurs.
This occurs under yield stress. This happens at lower levels of stress.
So here you have to know types of tool wear, factors affecting the tool wear as well as their causes and remedies.
I hope you will learn all aspects related to tool wear if you have any doubt then you are free to ask me by mail or contact us page.
Thank You.
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