Transcript IN THE NAME OF ALLAH, THE MOST MERCIFUL, THE MOST BENEFICIENT. Engr. Abid Hussain Lecturer MED U.E.T.

IN THE NAME OF
ALLAH,
THE MOST MERCIFUL,
THE MOST
BENEFICIENT.
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Engr. Abid Hussain
Lecturer MED
U.E.T. Taxila
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First cutting-tool inserts on market in 1956
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Inconsistent: improper use and lack of knowledge
Uniformity and quality greatly improved
Widely accepted by industry
Used in machining of hard ferrous materials
and cast iron
Gain: lower costs, increased productivity
Operate 3 to 4 times speed of carbide toolbits
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Most economical
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Especially if tool shape must be altered from
standard shape
Bonded to steel shank with epoxy glue
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Eliminates strains caused by clamping inserts
in mechanical holders
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Retain their strength and hardness at high
machining temperatures [in excess of
2000°F]
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Withstand abrasion of sand inclusions
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Better surface finish
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Heat-treated materials as hard as
Rockwell c 66 can be readily machined
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Brittle and therefore tend to chip easily
Satisfactory for interrupted cuts only under
ideal conditions
Initial cost of ceramics higher than carbides.
Require more rigid machine than is necessary
for other cutting tools
Considerably more power and higher cutting
speeds required for ceramics to cut efficiently
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Material to be machined
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Operation performed
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Condition of machine
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Rigidity of work setup
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Rigidity of toolholding device
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Use highest cutting speed possible that
gives reasonable tool life
Two to ten times higher than other cutting
tools
Less heat generated due to lower
coefficient of friction between chip, work,
and tool surface
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Most of heat generated escapes with chip
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Great wear resistance (permit higher cutting
speeds than carbide tools)
Edge buildup and cratering minimal
High hot-hardness qualities
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Greater than carbide but less than ceramic
Lower thermal conductivity than carbide
because heat goes into chip
Fracture toughness greater for ceramic but
less for carbide tools
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Two distinct types
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Polycrystalline cubic boron nitride
Polycrystalline diamond
Manufacture of blanks basically same
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Layer of polycrystalline diamond or cubic
boron nitride (.020 in. thick) fused on cementedcarbide substrate by high temperature (3275ºF),
high pressure (1 million psi)
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Created from substrate composed of tiny
grains of tungsten carbide cemented
tightly together
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Cobalt binder
High-heat, high-pressure conditions
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Cobalt liquefies, flows up and sweeps around
diamond or cubic boron nitride abrasive
Serves as catalyst that promotes intergrowth
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Structure of cubic boron nitride feature
nondirectional, consistent properties
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Resist chipping and cracking
Provide uniform hardness
Abrasion resistance in all directions
Qualities built into turning and milling
butting-tool blanks and inserts
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Can operate at higher cutting speeds, and take
deeper cuts
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Hardness
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Impact resistance, high strength, hardness in all
directions (random orientation of tiny CBN
crystals)
Highest Hot Hardness of all tools
Abrasion Resistance
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Maintain sharp cutting edges much longer
Second only to Diamond
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Compressive Strength
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Maximum stress in compression material will
take before ruptures
Thermal Conductivity
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Allow greater heat dissipation or transfer
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High Material-Removal Rates
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Cutting speeds (250 to 900 ft/min) and feed
rates (.010 to .020 in.) result in removal rates
three time carbide tools with less tool wear
Cutting Hard, Tough Materials
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Capable of machining all ferrous materials
with Rockwell C hardness of 45 and above
Also used to machine cobalt-base and nickelbase high temperature alloys (Rockwell c 35)
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Polycrystalline diamond (PCD) layer fused
to cemented-carbide substrate
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.020 in. thick
Highly efficient cutting tool
Increased production when machining
abrasive nonmetallic, nonferrous materials
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Catalyst-bonded PCD available in three
microstructure series
Coarse PCD blanks
 Medium-fine PCD blanks
 Fine PCD blanks
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Basic difference between types is size of
diamond particle used to manufacture
blank
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Composite materials found in base provide
mechanical properties
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High thermal conductivity and low coefficient of
thermal expansion
Diamond layer
Hardness, abrasion resistance, compressive
strength, and thermal conductivity
 Compressive strength highest of any tool
 Thermal conductivity highest of any tool
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Offset their higher initial cost
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Long tool life
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Cuts tough, abrasive material
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High quality parts
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Fine surface finishes
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Reduced machine downtime
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Increased productivity
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Nonferrous metals
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Typically soft but have hard particles dispersed
Silicon-aluminum alloys
Copper alloys
Tungsten carbide
Advanced composites
Ceramics
Wood composites
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Carbon Solubility Potential
Their higher initial cost
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Early 1980s brought new process of
chemical vapor deposition (CVD)
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Produce diamond coating few microns thick
Process
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Elemental hydrogen dissolved in hydrocarbon
gas around 1330º
Mixture contacts cooler metal, carbon precipitates
in pure crystalline form and coats metal with
diamond film (slow 1-5 microns/hr)
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