Turning plays most important role in Machining and Turning is the form of machining process which uses a single-point cutting tool for material removal,from this slide we can get the importance of turning.
2. Turning
Turning is the form of machining process which uses a single-point cutting tool for material
removal.
The process consists of a machine, workpiece, cutting tool and fixture. The workpiece is held
in the job holding device and attached to the turning center which rotates at high speeds.
The required shape is obtained by feeding the cutting tool into the workpiece, also the
identification of necessary cutting parameter for achieving better cutting performance and
good quality depends on manufacturer handbook, the experience of the operator or trial and
error method.
4. Hard turning
In manufacturing, hard turning has emerged as a potential option operation for finishing
products by eliminating grinding.
Materials with more than 45 HRC machined by robust machining process, but actual hard
turning occurs in the hardness range of 58 HRC to 68 HRC.
In hard turning the surface finish of 0.2 to 0.8 micrometer, the roundness of 1 to 5 micrometer
and diameter tolerance of + 3 to 7 micrometers can easily reach.
Materials such as hardened alloy steel, tool steels, bearing steel, Inconel, case hardened steels,
nitride irons, hard chrome coated steels, metallurgical parts heat-treated by powder and
titanium alloys are used as a hard turning workpiece.
The accuracy level of hard turning depends upon level of machine rigidity.
5. Benefits of hard turning
By hard turning, complex parts made easily.
The shape of the workpiece changes easily and rapidly.
With one set-up, more operations can be carried out.
The rate of material removal is more.
CNC lathe used for hard turning.
Metal chips generated during operations are environment-friendly.
Coolant not required.
Less tool inventory.
6. Limitations of Hard Turning
Compared to grinding tooling cost is more in hard machining.
The ratio of (L/D) Length to Diameter need to be less, i.e., 4:1.
Tool temperature increased by reducing coolant usage.
The wear of tool increased by reducing the coolant usage, hence tool life decreases.
The thickness of the white layer generated during machining gets increases with increase in tool wear.
7. Hard turning applications
Industries that deal with machining Titanium alloy for production of automotive parts, medical
devices, and computer spares.
Aircraft and die mold industries involving machining of more extended Titanium alloy parts.
Valves operate at higher spindle speed.
Hard machining strategy stands useful in case of machining intricate cores, cavity mold machining and for
machining complex aircraft structural components.
Materials machined at high cutting speed, high feed rate, and high removal rate.
9. Assumption in turning
The tool life is governed by the amount of flank wear for which a threshold value is specified,
beyond which tool regrinding has to be made
After regrinding, the tool is assumed to restore its original condition
Any unexpected breakage of the tool is neglected
The criteria used to decide a tool replacement is based solely on the number of times a regrinding is
conducted
Cutting is conducted using sharp edge tools
Effect of each process parameter on the performance parameter should be monotonically increasing
or decreasing.
11. Cutting parameters in turning
Cutting Environment
The purpose of cutting fluid is to remove the heat generated at tooltip which is in
direct contact with the workpiece.
Cutting fluid provide a safe working Environment (non misting, nontoxic,
nonflammable and non smoking)
Cutting fluid account for 15% of the shop production cost
The cost of purchase ,care ,and disposal of the cutting fluids are more than twice as
high as tool costs.
Dry machining, Minimum quantity lubrication and wet machining are used in turning.
13. Cutting speed
The cutting speed in turning is calculated by
v= π DN/1000 m/min
V = Cutting speed m/min
D =Diameter of the workpiece in mm
N= Spindle speed in rpm
Cutting speed depends upon tool material, workpiece material, depth of cut ,feed ,tool
geometry and type of machine tool
Feed
• Feed rate is the parameter related to the cutting tool and defined as advancement tool
rate along the cutting path of an axial direction, and the unit indicated as mm/rev.
Depth of cut
• The depth of removal of the surface layer in a single cut from the work piece is called
the depth of cut. The depth of cut described as the distance between the uncut surface and the
cut surface of the work-piece
16. Insert specification
CNMG 120404 SF 505 F indicates that
C Insert shape (Double-sided 800 rhombic insert)
N Clearance angle
M Tolerance on size
G Insert type
12 Cutting edge length
04 Thickness
04 Nose radius
SF 505 F indicates insert material
17. SELECTION OF Turning INSERTS
The insert shape should be selected relative to the entering angle accessibility required of
the tool. The largest possible nose angle should be selected to provide insert strength and
reliability. However, this has to be balanced against the variation of cuts that need to be
performed.
A large nose angle is strong, but requires more machine power and has a higher tendency for
vibration.
A small nose angle is weaker and has a small cutting edge engagement, both of which can
make it more sensitive to the effects of heat.
Selection of inserts is based on accuracy, quantity, workpiece material, availability of
machine tools and tool material.
The knowledge of workpiece materials, geometries, and limitations of the cutting tool are
also essential.
The cost of cutting tool cost is about 3 percent of the total component cost. Further
classification of tools can be done based on the cutting edge material, method of clamping
and geometry
18. Turning heat resistant super alloys (HRSA)
A super alloy has excellent mechanical strength and resistance to creep (the tendency
for solids to slowly move or deform under stress) at high temperatures. It also offers
good corrosion/oxidation resistance. HRSA can be divided into four material groups:
Nickel-based (for example Inconel)
Iron-based
Cobalt-based
Titanium alloys (titanium can be pure or with alpha and beta structures)
The machinability of both HRSA and titanium is poor, especially in aged conditions,
requiring particular demands on the cutting tools. It is important to use sharp edges to
prevent the formation of so-called white layers with different hardness and residual
stress.
HRSA material: PVD and ceramic grades are commonly used when turning HRSA
materials. It is recommended to use geometries optimized for HRSA.
Titanium alloys: Mainly use uncoated and PVD grades. It is recommended to use
geometries optimized for HRSA.
19. Characteristics of the TURNING insert
High penetration hardness at elevated temperatures to resist abrasive wear.
Resistance to deformation and prevents the edge from deforming during chip formation.
High fracture toughness to resist edge chipping and breakage, especially interrupted cutting.
Resist to diffusion, chemical reaction, and oxidation wear.
The tool edge temperature reduced due to high thermal conductivity.
High fatigue and shock resistance
More stiffness to sustain accuracy.
Provides lubricity to the work material for preventing built-up edge.
20. Work piece parameters
Workpiece material
The choice of material depends on the desired shape and size ,the dimensional
tolerance ,the surface finish ,and the required quantity.
In addition it depends on economy and environmental considerations
Mechanical properties
Properties
Tensile strength
Yield strength
Elongation in 5D
Reduction of area
Density
Modulus of Elasticity in tension
Transformation temperature
Hardness
21. SELECTION OF MACHINE FOR
TURNING
High static stiffness of machine elements such as spindles, joints, and structure
Acceptable level of vibration
Adequate damping capacity
High feed rates and speeds
The low rate of wear in sliding parts
Low thermal distortion of machine elements.
Part difficulty and complexity
23. Specification of CNC turning Centre
Model DX 200 5A
Swing over the bed (mm)
Standard turning diameter (mm)
Max. turning diameter (mm)
Max. turning length (mm)
500
250
365
500
X-Axis travel (Cross) (mm)
Z-Axis Travel (Longitudinal) (mm)
Rapid feed (x and z-axis) m/min
200
500
24
Power of spindle motor (kW) 7.5
The range of spindle speed (rpm) 50-4000
Positional accuracy (mm) 0.007
Repeatability (mm) 0.005
24. Machining time
It is the time for which the machine works on the component, i.e. from the time when the tool
touches the work piece to when the tool leaves the component after completion of operation.
Material removal rate
Metal removal rate (MRR) in metal cutting is a volume of chips removed in 1 minute, and it is
measured in a three-dimensional quantity.
Cutting power
The amount of power required to cut that material.
25. Symbol Designation/ definition
Unit, metric
(imperial)
fn Feed per revolution mm/r (inch/r)
ap Cutting depth mm (inch)
vc Cutting speed m/min (feet/min)
n Spindle speed rpm
Pc Net power kW (HP)
Q Metal removal rate cm3/min (inch3/min)
Tc Period of engagement min
lm Machined length mm (inch)
kc Specific cutting force N/mm2 (N/inch2)
Abbreviation
26. Trouble shooting in Turning
Vibration
High radial cutting
forces due to
vibrations or
chatter marks
which are caused
by the tooling or
the tool mounting.
Typical for
internal machining
with boring bars.
• Unsuitable
entering angle
•Select a larger
entering angle
(lead angle).
KAPR = 90°
(PSIR = 0°)
• Nose radius is
too large
•Select a smaller
nose radius
• Unsuitable
edge rounding,
or negative
chamfer
•Select a grade
with a thin
coating, or an
uncoated grade
• Excessive flank
wear on the
cutting edge
•Select a more
wear resistant
grade or reduce
speed
Parameter Problem Solution
27. Flank wear
Preferable wear type in every application. Offers
predictable and stable tool life.
•Cutting
speed too
high
•Too
tough
grade
•Insufficie
nt wear
resistance
•Hard
inclusions
in
workpiece
material
•Reduce
cutting speed
•Select a
more
suitable
grade
depending
on toughness
demand or
wear
resistance
28. References
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