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Unit 5 - Turning
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CA1 (35 %) Assignments -15% (review, sketching,
case study)
2 BB Quizzes -10% (turning and milling)
General Performance -10% (attitude,attendance..)
CA2 (40%) Practical (machining tape holder -
individual)
CA3 (25%) Mini Project (machining car chassis and
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Learning Objectives:
List the components of a centre lathe
Discuss the safety rules Discuss the use of tool holding devices Discuss the characteristics of cutting tool
materials and inserts Watch and discuss video VC2495/8
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What is the primary function of a centrelathe?
Can you name the components of a lathe?
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What 2 movements are necessary beforeturning process can take place?
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a) Saddle
b) cross slide
c) compound slide
d) tool post
e) apron
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Knurling toolPartingtool Chamferingtool
Facing andturning tool
Knife
turning tool
toolRadius forming
Undercuttingtool
Facing tool
Boringtool
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Can you give other examples ofturning besides facing and parallel
turning?
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Compare and contrast the differences of a4-way tool-post (above) and quick changetool-post?
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On Centre good finish
Above Centre -not cutting
Below Centre poor finish
= Front Clearance
= Wedge Angle
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Locking screw
Insert
Insert holder
Chip
Breaker
The carbide insert is locked by a lockingscrew or cam. Shape may be triangular(as above) or diamond, square or round.
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2. Define Turning Operation.
3. State the effects of improper tool setting.
4. List 10 safety precautions in the machine shop
and how would you categorised them?5. State the 3 purposes of facing operation.
6. What is the main advantage of quick changetool post?
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Learning Objectives:
Compare and contrast 3-jaw and 4-jaw
chucks Explain the use of work holding support used
in between centres Discuss the use of other work holding
devices like faceplate, mandrels andsteadies.
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Normally used for holding round orhexagonal stock.
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Suitable for round, square, octagonal andodd-shaped workpieces.
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Long Workpiece
Normally used for turning a longworkpiece supported betweenbetween centres. It requires 2centres, a drive plate and a lathe dog.
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Drive Plates
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Compare and contrast live and plaincentres.
Morse standard taper
Plain
Live
Sleeve
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Plain solid mandrel one
size of bore
Gang mandrel manyworkpieces with sameInternal diameter
Expansion mandrel slight difference (up to2mm variation) indiameter
Cone mandrel largevariation in diameterallowed.
Workpiece
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Fixed
Steady
Travelling
Steady
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1. How would you hold a hollow thin wall roundpipe for turning?
2. When is a faceplate used?
3. Explain the reason why the 3-jaw chuck is
self-centred.4. State the advantages of a 4-jaw chuck.
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Learning Objectives:
Distinguish between Orthogonal and obliquecutting.
Discuss the tool geometry of a single-pointedtool.
Discuss the factors that influence metal cuttingoperations.
Discuss the types of chips
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Cutting edge is set at 90 to the direction of movement. Chips in the form of a clock spring or a flat spiral Chips disposal problem & damage to workpiece surface.
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Cutting edge is set at any angle other than 90 to
the direction of tool movement. Chips able to move freely away from workpiece Taking deeper cuts is possible surface finish is better with a nose radius
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Side Rake angle :provides a cutting edgeto allow chips to escapeduring cutting.
Back Rake angle :
promotes smooth chipflow and good finishing
Front Relief angle :prevents tool end fromrubbing
Side Relief angle: allowsthe tool to feed into thework
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Minor cutting edge
Minor cutting edge
angle
Major cutting edge
angle
Major cutting
edge
Nose Radius
Side (Major) cutting edge angle - Mainly responsible for the chipremoval
End (Minor) Cutting edge angle - Mainly responsible for producingthe finished workpiece surface
Nose radius - Influences the surface finish of the workpiece
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Continuous ------------ Discontinuous Chips
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1. Compressive stress cause movement ofmetal.
2. Then, compression increases until plasticflow or rupture (or fracture) occurs.
Ductile material - continuous chip is formed
Brittle materials - rupture takes place withsmall discontinuous fractured chip
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Brittle material, small rake angle, largedepth of cut or feedrate and no cutting fluid
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Ductile materials, large rake angle, smalldepth of cut or feedrate and efficient use ofcutting fluid.
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2. Compare and contrast orthogonal and obliquecutting.
3. With simple sketches, show the tool geometry
of single-pointed cutters.4. List the three types of chip formation.
5. State the conditions for the formation ofcontinuous chip.
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Learning Objectives:
Describe 3 cutting forces acting on the tool Discuss the relationship of cutting forces and the
following:
rake angle
depth of cut
feedrate
cutting speed, and
plan approach angle
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Tangential and Axial Forces
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Besides Tangential and Axial Forces, there isalso a Radial Force.
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Tangential Force (Ft) tangential to thework surface, main power-consuming.
Axial Force (Fa) parallel to the work axisand opposing the lengthwise feed direction.
Radial Force (Fr) present only in oblique
cutting and opposing the crosswise feeddirection.
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Use a Force Dynamometer - calibrate before use. Units - Newton
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A Test pieceFt
Rake angle ()
Dry
With coolant
Uniform thickness
Side Rake angle varies from 0 to 40 in steps of 5 Lower Tangential force when Rake angle is smaller.
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Ft Ft
Fa
Test piece with
stepped-wall
Depth of cut (mm)
Depth of Cut varies from 2 to 10 mm. Bigger Tangential and Axial forces
encountered when Depth of cut increases.
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Test piece with
uniformed wall thickness
Ft Fa
Fa
Ft
Feed rate (mm)
Feedrate varies from 0.1 to 1.0 mm/rev Axial force increases exponentially when Feedrate
increases.
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Ft
Breakage point of cutter
Cutting speeds (m/min)
Cutting Speed varies from 30 to 80 of allowablespeed value
No change in tangential force before tool break-up.
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Plan Approach Angle varies from 45 to 90. Axial force equals to Radial force at 45. Radial force equals to zero at 90 and
tangential force is at maximum.
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2. Describe the forces acting on the cutterduring orthogonal and oblique cutting.
3. Sketch the graph and explain test resultswhen the rake angle was varied.
4. Explain the effects of depth of cut andfeedrate on the following:
Chip thickness
Cutting force
5. Explain the effects of the cutting forceswhen plan approach angle is set at 45.
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Learning Objectives: Discuss the differences of cutting speed, spindle
speed and feedrate. Calculate the machining time, cutting power,
feed power and specific metal removal rate. Discuss the different types of cutting tool
materials. Describe the effects of positive and negative
back rake angle Explain the functions of cutting fluid.
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WORKPIECE
MATERIALS
FEED (mm/rev) CUTTING
SPEED (m/min)
Aluminium 0.2 1.0 70 100
Brass (Alpha,Ductile)
0.2 1.0 50 80
Brass (free-cutting) 0.2 1.5 70 100
Bronze (phosphor) 0.2 1.0 35 70
Cast iron (grey) 0.15 1.0 25 40
Copper 0.2 1.0 35 - 70
Steel (mild) 0.2 1.0 35 - 70
Steel (medium
carbon)0.15 0.7 30 - 35
Steel (alloy, high-tensile)
0.08 0.3 5 10
Thermo-settingplastic
0.2 1.0 35 - 50
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0
sec
1
min
1 rev = d
The rate at which a point in the circumference of the worktravels past the cutting tool (V=m/min).
Depends on work material, tool material, type of operation,machine condition, coolant type, type of cuts.
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The spindle speed is the number orrevolutions turned in one min.
N = 1000V (rev/min) d
The Spindle Speed, N depends on:
3. the cutting speed, V and4. the diameter, d of the workpiece.
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Feedrate is the distance the tool bit advances alongthe work for each revolution of the spindle(F=mm/rev)
Depends on work material, tool material, type ofcut, cutting speed.
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Calculate the spindle speed, to the nearest rev/min,for turning a 50 mm diameter bar at a cutting speedof 40 m/min.
1000 * V where, N = spindle speed
N = ---------------- V = 40 m/min D D = 50 mm1000 * 40
= ------------------ = 255 (rev / min)
3.142 * 50
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Calculate the time taken to turn a brass component 65mm diameter by 95 mm long, if the cutting speed is45 m/min and the feed is 0.6 mm/rev. Only one cut isto be taken.
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Use Ft
Work done = force * dist moved
= force * Circumference * N
= F * 2 r N= F * d NPower is the rate of doing work
= work done time taken
= F * d N Nm or watts 1000*60 sec
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D NWORKDONE = Ft (Newtons) x ---------- (Nm/min) or (Joules /
min)
1000
D N 1CUTTING POWER (watts) = Ft x ------------- x ------ (Nm / sec)
1000 60
Where, Ft = tangential force; = 3.142D = diameter of workpiece (mm);N = rotational speed in rpm
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Feed x NWORKDONE = Fa (Newtons) x --------- (Joules / min)
1000
Fa x Feed x NFEED POWER = ------------------------ (Joules / s or Watts)
1000 x 60
Where, Fa = Axial force;Feed = mm / rev;
N = spindle speed in rpm
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During turning on the lathe, the workpiece has adiameter of 75 mm & the spindle speed was set at 200rpm. If the feed rate was 0.33 mm / rev & the
dynamometer readings for the tangential force and theaxial force were 1,600 N & 900 N respectively, find thecutting & feed power.
3.142 x 75 mm x 200 rpm
Cutting power = 1600 N x ---------------------------------------1000 x 60
= 1,257 watts
900 N x 0.33 mm / rev x 200 rpmFeed power = ----------------------------------------------
1000 x 60
= 0.99 Watts
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V=25m/min
D=3mmF=1.5mm/rev
The volume of metal removed perminute is
= V * D * F
= 25000 * 3 * 1.5
= 112500 mm3/min = 112.5 cm3/min
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= Volume removed per min
Power consumed
= (mm/min)/watt
N.B. Power consumed is the sum of the
power at the cutting tool and including thepower to drive the mechanical systems.
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High Carbon steel HSS
Cemented carbide(contains 90% carbidepowder and 10% cobalt as binder) Cemented ceramic(contains 95% Al2O3)
Diamond
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Ability to: Retain hardness at high temperature
Resist Shock i.e. toughness Resist Wear Reasonably cheap
Acceptable mechanical properties
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Good abrasion resistance Slow rate of wear Hot Hardness properties
Vibration and chatter must be avoided Very brittle Unable to withstand shock and bending
loads
Used it as a throwaway tip or insert.
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Normal force, N,on unsupportedpart
Tendency to break
Lower cutting
forces
positive rake
Cutting tool
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Normal force, N, onsupported part
Less likely to break
Operate at higherspeed Higher compressive
forces
Nnegative rake
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Functions: Cooling and lubrication Better surface finish and accuracy Flushing away chips Longer Tool life Preventing chip welding, corrosion
Permits higher speed and feedrate
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1. Explain the difference between cuttingspeed and spindle speed.
2. What are the factors that determinecutting speed?
3. What is SMRR used for?
4. Explain the toughness of cutting toolmaterial.
5. Compare and contrast positive andnegative back rake angle.
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