state the main reason of tool failure
Answers
Explanation:
Whenever the tool is not performing the machining operation satisfactorily, then there is a failure of cutting tool.
The following draw backs are observed if the tool failure occurs.
The tool ceases to produce the work-piece according to the required dimensions.
The tool gets overheated.
Excessive surface roughness is observed.
Forces and power consumption increases.
Some times the burnishing brand will appear on the work piece.
Produces vibrations during machining.
The parameters used for measurement of satisfactoriness of machining is
1. Surface finish produced on work piece
At the beginning of machining operation it is found that excellence and mirror like finish is produced on work piece.
After sometimes when the lines are produced on machined surface, it is assumed that surface finish is reduced and tool is failedForces induce during machining:
By connecting dynamo meter to the work table, the forces in machining will be measured online.
Whenever the increase in forces is taking place it is assumed that tool has been failed.
3. Power consumption:
By connecting Ammeter to the input of electrical motor, the current drawn by motor will be measured online.
Whenever the increase in current drawn by motor is greater it is assumed that tool has been failed.Temperature of chip:
The temperature of chip can measured by observing the color of chip formed.
During normal satisfactory machining conditions the color of chip is light Blue or metallic color.
When the machining is done with failure tool, because of higher heat generation the color of chip is turned to black or burnt color.
From the above whenever the color of chip is observed to be black or burnt color, tool is assumed to be failed.
During machining of high carbon work pieces, whenever white colored gases are observed, it is assumed that tool is failed.
Modes of tools failure:
Failure through plastic deformation
Failure through mechanical breakage
Failure through mechanical gradual wear
1. Plastic Deformation Failure:
Whenever the tip of tool is experiencing temperature greater than hot hardness temperature of tool material, it is losing its hardness considerably and the tip of tool is deforming plastically called as plastic deformation failure of the tool.
Reasons for plastic deformation failure:
Wrong selection of tool material.
Wrong selection of process parameters.
2. Mechanical Breakage Failure:
A cutting tool gets broken due to the following factors:
Large cutting force.
By developing fatigue cracks under chatter conditions.
Weak tool materials.
High temperature and high stress.
In this also failure duration is repeatable.
Therefore it is also considered as abnormal failure of tool.
3. Mechanical Gradual wear failure:
During machining operation, the tool is wearing out and slowly and whenever the wear become considerable, it can’t perform the machining satisfactory called as gradual wear failure.
The gradual wear takes place due to
1. Crater wear and
2. Flank wearWrong selection of tool material.
Wrong selection of process parameters.
2. Mechanical Breakage Failure:
A cutting tool gets broken due to the following factors:
Large cutting force.
By developing fatigue cracks under chatter conditions.
Weak tool materials.
High temperature and high stress.
In this also failure duration is repeatable.
Therefore it is also considered as abnormal failure of tool.
3. Mechanical Gradual wear failure:
During machining operation, the tool is wearing out and slowly and whenever the wear become considerable, it can’t perform the machining satisfactory called as gradual wear failure.
The gradual wear takes place due to
1. Crater wear and
2. Flank
wearReasons for crater wear:
Presence of friction between chip – tool interference.
Abrasive action of microchips present at chip – tool interference.
Abrasive action of fragments of built up edge present at chip-tool interface diffusion wear.
Flank wear:
Wear taking place on flank face of tool is called as flank wear.
Reasons for flank wear:
Presence of friction at tool interface.
Abrasion action of microchips present at tool work interface.
Diffusion wear.
FRICTION is the main reason for the tool failure.
Explanation:
Friction is the main reason for the failure of a tool. Friction acts as a two way sword in our daily life. In some function it helps us while in the same function it may obstruct us in some way. For example nothing can be held static under a force in the absence of friction but the friction also opposes in the desired movement of the machine and tools.
For the tools the machining is not possible without friction but the failure of the tool mainly occurs due to friction which results into wear and tear of the tool and the weakening of the tool due to the heat of friction.
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TOPIC: tool failure
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