The document discusses tool specification and chip formation mechanisms. It begins by outlining the American System for specifying tool angles such as rake, relief, and cutting edge angles. It then explains how each angle impacts cutting forces and tool strength. The document also describes the mechanics of chip formation, defining shear angle and relating it to tool rake angle. It outlines factors that influence chip type and discusses tool surfaces and reference planes. Finally, it covers tool wear mechanisms, tool life definitions, and factors that tool life depends on such as cutting speed, depth of cut, and feed rate.

1. 11
Topic – Cutting Tool specification and mechanism of chip formation
by
Mr. Binit kumar
Assistant Prof., ME department
GLBITM, Greater Noida

2. 22
American System of Tool
Specification
αb αs βe βs γe γs r
Back Rake Angle
Side Rake Angle
End Relief/Flank/clearance Angle
Side Relief/Flank/clearance Angle
End Cutting Edge Angle
Side Cutting Edge Angle
Nose Radius

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Importance and selection of angles
Back Rake Angle (αb):
• It is the angle b/w rake face of the tool and line parallel to the base.
• Measured in a plane perpendicular to major (side) cutting edge.
• It is positive when major (side) cutting edge slopes downwards from the
point towards the shank and vice versa.
Side Rake Angle (αs):
• It is the angle b/w face of the tool and line parallel to the base.
• Measured in a plane perpendicular to the base and major (side) cutting
edge.
• It gives slope of the face of the tool from cutting edge.
• It is positive when slope is away from cutting edge and vice versa.
Importance:
• Larger the rake angle, smaller is the cutting angle and low cutting force
and power will be required.
• Decreasing cutting angle will leave less metal at point of tool to support
cutting edge and conduct away the heat reducing the tool strength.

4. 44
End Relief/Flank/clearance Angle (βe):
• Angle b/w portion of end (minor) flank immediately below minor (end)
cutting edge and a line perpendicular to the base of the tool.
• Measured at right angle to minor flank surface.
Side Relief/Flank/clearance Angle (βs):
• Angle b/w portion of side flank immediately below major (side) cutting
edge and a line perpendicular to the base of the tool.
• Measured at right angle to Major (side) flank.
Importance:
• Provided to avoid the rubbing of work piece and the tool during cutting.
• Flank of the tool clears the work piece surface and there is no rubbing
action b/w the two.
• Higher the relief angle, better will be the penetration and cut made by
the tool on work piece thus less cutting force and power required and lower
will be the flank face wear.
• But large rake angles weaken the cutting edge and heat dissipation is also
poor.

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End Cutting Angle (γe):
• Angle b/w minor (end) cutting edge and line normal to tool shank.
Importance:
• Provides clearance or relief to trailing end of the cutting edge to prevent rubbing
b/w machined surface and trailing (non cutting) part of the tool.
Side Cutting Angle or Lead Angle (γs):
• Angle b/w major (side) cutting edge and side of the tool shank.
Importance:
• Provides interface as the tool enters the work material.
• This angle affects tool life and surface finish.
Nose Radius (r):
• For long tool life and surface finish.

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Mechanics of chip formation:
• Wedge shape tool is moved relative to work piece.
• Tool exerts pressure on work piece as it makes contact with the same causing
compression of metal near tool tip.
• Shear type plastic deformation within metal starts.
• Metal starts moving upwards along the top face of the tool.
• Tool advances and material ahead is sheared continuously along shear plane
(Primary shear zone).
• Tool surface along which chip moves upwards is called rake surface.
• Tool surface which is helps in avoiding rubbing with machined surface is called
flank surface.

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Measurement of Shear Angle (Φ)
• Shear Angle Φis defined as the angle made by shear plane with direction of tool
travel.
• Cutting Ratio or Chip thickness ratio or chip compression factor:
• Cutting ratio (r) is defined as the uncut chip thickness (t0) to chip thickness
after metal is cut (tc).
r = t0/tc
• Chip reduction factor (ζ) is the reciprocal of Cutting ratio.
ζ = 1/r = tc/t0
A
B

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9. 99
tanΦ = r*cosα/(1-r*sin α)
Now,
AB = to/sinΦ = tc/cos(Φ-α)
i.e. r = sinΦ / (cosΦcosα + sinΦsinα)
 r*(cosΦcosα + sinΦsinα) = sinΦ
 tanΦ = r*cosα/(1-r*sin α)
• This is a relationship between rake angle and shear angle.

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Relative motion b/w tool & w/p causes material to compress & reach plastic state.
• Formation of chips depends on work material and cutting operations.
• Chip moves upwards along the rake face of the tool.
• Three types of chips are formed.
1. Continuous chip. (Shearing phenomenon.)
2. Continuous chip with built up edge.
(Welding and rupture phenomenon)
3. Discontinuous chip. (High Strain in Brittle materials)
1.
2.
3.
Type of Chips

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Factors Type of chips
Continuous Continuous with BUE Discontinuous
Material Ductile Ductile Brittle
Tool:
Rake Angle Large Small Small
Cutting Edge Sharp Dull ----
Cutting Condition:
Speed High Low Low
Feed Low High High
Friction Low High ---
Cutting Fluid Efficient Poor Effective
Chip Thickness Small Large
Surface Finish: ---- Poor Better

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Tool Surfaces:
•Rake Face (Ay): The surface or surfaces over which the chip flows.
•Chip Breaker: A modification of the face, to control or break the chip.
•Cutting Edge: That edge of the face which is intended to perform cutting.
Major/Side Cutting Edge: Edge which is intended to produce transient surface.
Minor/End Cutting Edge: Edge which is not intended to produce transient surface.
•Flank (Aa): The tool surface or surfaces over which the surface produced on the
work piece passes.
Major /Principal/Side Flank Surface: Flank Surface containing major cutting edge.
Minor/Auxiliary/End Flank Surface: Flank Surface Containing minor cutting edge.
•Corner or nose: The relatively small portion of the cutting edge at the junction of
the major and minor cutting edges

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Reference planes in ASA system of tool designation:
• A plane parallel to ground containing tool shank is taken as
datum and is called base plane.
• Second reference plane is longitudinal plane and is along
longitudinal feed direction and perpendicular to base plane.
• Third reference plane is transverse plane and is
perpendicular to both the above planes.

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Tool Wear And Tool Life:
Wear:
• It is defined as loss of material from surfaces in sliding contact.
• Wear may be due to adhesion, abrasion, erosion, surface fatigue and gross
fracture.
• In metal cutting following three reasons account for tool wear:
1.Adhesion:
• Strong bonds are formed b/w mating surfaces due to welding of surface
asperities.
• If these bonds are stronger than material strength, transfer of particles from
tool surface to material surface during fracture takes place.
• If wear particles are small, process is called attritious wear.
• If wear particles are large, process is called as galling.
2.Abrasion:
• During sliding contact, surface asperities of harder material (tool), plough series
of grooves on softer material (w/p) surface.
• Material removal may be caused by loose hard particles trapped on sliding surface.
• These trapped lose hard particles present on chip tool surface may remove tool
material due to abrasion.

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3. Diffusion:
• During contact atoms from one mating surface may get diffused into the matrix
of other surface as per relative affinity of the atoms.
• It causes wear because of change in physical properties like hardness, toughness
etc.
• Rate of diffusion depends on temperature and thus on sliding speed.
Classification of Tool Wear:
• Flank Wear.
• Crater wear on tool face.
• Tool wear volume.
• Surface finish Value.
• Localized wear like rounding of cutting edge.
• Chipping off of cutting edge.

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Tool Life:
• Total cutting time accumulated before tool failure is called tool life.
• Thus a tool that no longer performs desired function is said to have failed.
• Tool life can be defined on the basis of any of the following criterion:
Cutting time before failure Volume of Material Removed before failure
Cutting length before failure No. of components formed before failure
• Tool life depends on tool failure and tool failure depends on many factors.
• Tool life greatly depends upon cutting speed ‘V’ in m/min (and thus on tool temp.)
• Tool life is inversely associated with cutting speed.
• Experimentally noted that decrease is parabolic in nature.
• Taylor gave following relation by drawing these curves using different cutting
tools at different speeds:
Here,
• V is cutting speed in m/min
• T is time in minute for flank wear
• n is an exponent depending on cutting conditions.
• C is constant
Tool life also depends on depth of cut ‘d’ (mm) and feed rate ‘ f’ (mm/rev)
exponentially. Thus,
V*Tn = C
V*Tn*dm*fx = C