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What is Hard Turning?
Answer: Hard turning is a term given to
machining Hardened steel with CBN (Cubic Boron Nitride)
tools for replacing conventional method of finishing by
What is the advantage
of hard turning as compared to grinding?
Answer: Reduction in Machine & man
power cost by reduction in cycle time, improved accuracy,
flexibility to do intricate shapes and environmentally friendly
as chips produced can be recycled as compared to Grinding
Sludge & used coolant which is hazardous.
What are usual
work materials finished by Hard Turning?
Answer: Carbon steel, Chromium Molybdenum
Steels, chromium steels etc. In existing customers hard
turning is being done on 70% in Case Hardened Steels, 20%
to induction Hardened steels & 10% others..
What are usual
parts machined by Hard Turning?
Answer: Transmission gears, Differential
Bevel Gears, Shafts, Bearings, Diesel Pump parts etc. in
Automotive. Construction, Machine parts, Oil Pressure parts
etc. in Engineering.
What are the ideal
shapes to be finished by Hard Turning?
Answer: Components with Concave or convex
shape, with many surface to be turned like boring, Grooving
External diameter & face turning in single chucking,
Components with small bores, Components where linear/axial
dimension controlling is difficult in grinding Esc are good
examples of Hard Turning.
For what Hardness
range Hard Turning can be applied?
Answer: Hard turning can be applied to
Steel having Hardness from 45 to 68 HRc.
Can we apply Hard
Turning on interrupted components?
Answer: Yes Hard Turning can be applied
to any degree of interruption & for That Sumitomo has
suitable grades. The components like Splined shaft or bore,
Bore with keyway, holes on the face or bore etc. can be
Hard turned with Sumitomo Grades BN 250 or BN 300.
What surface Tolerance
and Surface Finish is achievable by Hard Turning?
Answer: Generally H7 or 7 class Tolerance
& Surface Finish of Rmax 3.2 (Ra0.8m) is achievable
by Hard Turning. With a rigid set up customers are achieving
6 class (H6) Tolerance & up to Rmax 2.0( Ra 0.5m). With
the latest developed wiper edge inserts finish can be achieved
even finer than above.
What is the difference
in the quality of surface turned by hard Turning as compared
with that of Grinding?
Answer: Grinding being a operation in which
the cutting takes place by abrasion the heat produced is
much higher. This heat when goes to the component surface
it leads for the problems like surface cracks, Re-hardened
& tempered layers, which are no good for the life of
the component. Hard Turning being single point turning &
CBN being an excellent thermal conductive material negligible
heat is transmitted to the component surface. So many a
times Hard Turning is preferred to solve the surface Integrity
Problems faced in Grinding.
Is my machine
capable of doing Hard turning?
Answer: Any NC Machine can do the Hard
turning which has min. surface speed for the job to be turned
about 100Mtr/min. There is no extra power required in the
machine to do Hard turning only force as mentioned before
higher in case of Hard turning is Trust/radial outward force.
To counter that the job chucking & in case of boring
carbide shank boring bar is recommended if the overhang
of the bar is more than 3.
What cutting speed
is recommended for Hard Turning?
Answer: Usually 80 to 180 m/min is used
in Hard Turning depending on other machining conditions
like rigidity, chucking, overhang etc. We also have grades
for high efficiency machining on continuous turning where
the cutting speed can be as high as 250m/min.
How are the cutting
forces while doing Hard turning as compared to soft machining
& how to counter those?
Answer: In Hard Turning only thrust/radial
outward force is higher as compared to soft machining. Rest
of the forces i.e. Principal force (downward on tool) &
Feed force (axial force pushing tool in opposite direction
of feed) remain unchanged. Thrust force affects the dimension
in deep boring application (L/D of boring Bar more than
3), to counter this we recommend to use Carbide shank boring
bar. Sumitomo has introduced a special series of Boring
bars, for Hard Turning, made of 100% carbide. By these boring
bars the finish, accuracy & life of the tools can be
expected better than the conventional carbide boring bar
being marketed. For further details write to us or contact
our regional sales team.
How does the variation/tolerance
in Hardness affect the accuracy in Hard turning & how
the same should be countered?
Answer: The Thrust force, which is responsible
for the dimension, increases with increase in Hardness after
45 HRc. The variation in hardness by more than 5HRc can
result in variation of dimension produced. To counter this
variation in Hardness more than 5HRc should be avoided.
How does hard
turning surface roughness profile different from surface profile
generated by grinding operation?
Answer: Grinding is multipoint cutting
operation where N number of abrasive particles produce the
ground surface by rubbing. This action creates irregular
peak and valleys so the surface graph is irregular. In contrast
Hard Turning is a process of single point turning which
will give regular feed marks and periodic surface profile.
Is coolant needed
for Hard Turning?
Answer: Generally Hard Turning is recommended
in dry condition. Interrupted machining must be used only
in dry condition. Some conditions where use of coolant can
be helpful are Die Steels, applications where thermal distortion
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