Tool wear describes the gradual failure of cutting tools due to regular operation. It is a term often associated with tipped tools, tool bits, or drill bits that are used with machine tools.

1. TOOL FAILURES
By
Prem kumar soni
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2. Introduction
 Whenever the tool is not performing the machining
operation satisfactorily, then there is a failure of
cutting tool.
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3. 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.
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4. 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 failed.
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5. 2. Forces 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.
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6. 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.
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4. 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.

8. Modes of tools failure:
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Failure through plastic deformation
Failure through mechanical breakage
Failure through mechanical gradual wear

9. 1. Plastic Deformation Failure:
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 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.

10. 2. Mechanical Breakage Failure:
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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

11. 3. Mechanical Gradual wear failure:
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 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 wear

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13. Crater wear:
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 The major tendency for wear is due to the abrasion
between the chip and the face of the tool, a short
distance from the cutting edge.
 The crater (a shallow spherical depression present on
surface) is formed on the surface of the tool by the
nation of chip particles flowing over it because of very
high temperature.
 When Cratering becomes excessive, the cutting edge
may break from the tool.
 Cratering is commonly observed while machining
ductile materials, which produce continuous chips.

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20. Reasons for crater wear:
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 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

21. Flank wear:
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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.

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27. Some General effects of tool wear
include:
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 increased cutting forces
 increased cutting temperatures
 poor surface finish
 decreased accuracy of finished part
 May lead to tool breakage
 Causes change in tool geometry

28. Thank You
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