1. Tool failure : Defination, 2. Types of Tool Failure, 3. Causes of Tool Failure.

1. ME 405
MANUFACTURING
TECHNOLOGY
TOOL FAILURE AND TOOL LIFE

2. TOOL FAILURE
• A properly designed and ground cutting tool
is expected to perform the metal cutting
operation in an effective and smooth
manner.
manner.
• However if the tool is not giving a
satisfactory performance it is indicative of
Tool Failure.

3. INDICATION OF TOOL FAILURE
• Extreme poor surface finish on the Workpiece.
• Higher consumption of Power.
• Work Dimensions not being produced as
specified.
specified.
• Overheating of Cutting tool.
• Appearance of a burnishing band on the Work
Surface.

4. REASONS OF TOOL FAILURE
• THERMAL CRACKING
CRACKING
Cutting TOOL may fail due to one or more of the
following reasons:
• MECHANICAL CRACKING
• GRADUAL WEAR

5. THERMAL CRACKING AND SOFTENING:
• It is seen that a lot of HEAT is generated during METAL
CUTTING.
• Due to this HEAT, the TOOL Tip and the area closer to the
cutting edge becomes very Hot.
• After certain temperature is reached, the Tool material
starts deforming plastically at the Tip and adjacent to the
cutting edge under the action of the CUTTING PRESSURE
and the HIGH TEMPERATURE.
• Thus the TOOL losses its ability and it is said to have failed
due to SOFTENING or THERMAL CRACKING.

6. TEMPERATURE RANGE OF CUTTING TOOLS
CARBON TOOL
STEELS
200 ° C to 250 ° C
HIGH SPEED
STEELS
560 ° C to 600 ° C
STEELS
CEMENTED
CARBIDE
800 ° C to 1000 ° C

7. • MECHANICAL CHIPPING of the
nose and/ or the Cutting edge of
the Tool are commonly observed
causes of TOOL FAILURE.
MECHANICAL CHIPPING
• The common reasons for such
failure are too high cutting
pressure, mechanical impact,
excessive wear, too high
vibration and chatter, weak tip
and cutting edges, etc.

8. • When a Tool is in use for sometime, it is found
to have lost some weight or mass, i.e. it has
lost some material from it , which is due to
WEAR. The following are the two types of
GRADUAL WEAR
WEAR. The following are the two types of
WEAR found in Cutting Tools:
1. CRATER WEAR
2. FLANK WEAR

9. In CRATER WEAR the principal region where the wear takes
place in a cutting tool is its FACE.
CRATER WEAR generally takes place while machining ductile
materials, like steel and steel alloys, in which continuous
chip is produced.
In this type of WEAR, CRATER is formed at the Tool Face.
CRATER WEAR
In this type of WEAR, CRATER is formed at the Tool Face.

10. Another region where WEAR occurs in the tool is the FLANK below
its cutting edge. This is known as FLANK WEAR.
FLANK WEAR occurs due to abrasion between the TOOL FLANK and
the WORKPIECE and excessive heat is generated.
FLANK wear is more prominent in machining DUCTILE MATERIAL.
FLANK WEAR
The entire area subjected to FLANK WEAR is known as WEAR LAND.
FLANK WEAR mostly occurs on the TOOL NOSE and FRONT and SIDE
RELIEF FACES.

11. • ABRATION: Under this mechanism, hard particles on the underside of the sliding chip,
which are harder than the tool material , plough into the relatively softer material of the
Tool face and removes metal particles by mechanical action. The material of the Tool face
is softened due to the high temperature generated.
• ADHESION: Due to excessive pressure, a lot of friction occurs between the sliding
surface of the Chip and the Tool face. This gives rise to excessive high localized
temperature, causing metallic bond.
MECHANISM /CAUSES OF WEAR
• DIFFUSION: Solid state Diffusion consists of transfer of Atoms in a metal crystal lattice,
which is the cause of Wear. The favorable condition for the diffusion of atoms is provide
by rise in localized temerature in the area of contact between underside of Chip and Tool
Face. Metal Atoms are transferred from Tool Material to Chip material at the points of
contact. This weakens the surfaces and ultimately causes Tool failure.
• CHEMICAL WEAR: This type of wear occurs when a cutting fluid is used in the process
of metal cutting is chemically active to the material of the Tool. This is clearly the result of
the chemical reaction taking place between the cutting fluid and the Tool material,
leading to change in the chemical composition of the surface material of the Tool.