Single point cutting tool geometry and Tool wear

1. Topic – Single point cutting tool geometry and Tool wear
by
Mr. Binit kumar
Assistant Prof., ME department
GLBITM, Greater Noida
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Single Point Cutting Tool:
• A single-point tool is a cutting tool having one cutting part and one shank.
Tool Elements:
Shank: That part of the tool by which it is held.
Tool Axis: An imaginary straight line used for manufacturing and sharpening of the
tool and for holding the tool in use.
Generally, the tool axis is the center line of the tool shank.
Cutting Part or tool point: The functional part of the tool comprised of the chip
producing elements. The cutting edges, face, and flank are therefore elements of
the cutting part.
Base. A flat surface on the tool shank, parallel or perpendicular to the tool
reference plane useful for locating or orienting the tool in its manufacture,
sharpening and measurement. Not all tools have a clearly defined base.
Wedge. The portion of the cutting part enclosed between the face and the flank.
It can be associated with either the major or minor cutting edge.

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American System of Tool Specification

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Oblique Cutting:
• Cutting Edge of tool is inclined at an angle λs
with normal to cutting velocity vector.
• Chip generated flows on rake face of the tool
at angle approx. equal to angle of inclination (λs)
to the normal.
• Cutting edge extends beyond the work piece
width on both sides.
• Cutting forces act along all the three
directions in x, y and z axes.
• Suitable for efficient metal removal.
Oblique vs Orthogonal cutting

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Orthogonal Cutting
Oblique Cutting
V
V

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Cutting edge is perpendicular to direction of cutting velocity (V).
• λs = 0
• Cutting edge extends beyond the work piece width on both sides.
• Chip generated flows on rake face of the tool with chip velocity
perpendicular to cutting edge.
• Cutting forces act along x and z directions only.
• Unsuitable for efficient chip removal.
Orthogonal Cutting:

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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.

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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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Left and Right hand Cutting Tool:
•In a right cut tool side (major or primary) cutting edge is on
the side of the thumb when right hand is placed on the tool
with palm downward and fingers pointing towards the tool
nose.
•Such tool cuts when fed from right to left.
•In a left cut tool side (major or primary) cutting edge is on
the thumb side when left hand is placed on the tool with palm
downward and fingers pointing towards the tool nose.
• Such tool cuts when fed from left to right.

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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