Geometry of Single Point Cutting Tool

DEEPAK KUMARAssistant Professor,

Department of Mechanical Engineering,Dr. B. C. Roy Engineering College, Durgapur

Introduction• Production, Manufacturing and Machining

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MACHINING

PRODUCTION Manufacturing

Joining

FormingPowder

Metallurgy

Casting Turning Milling

Grinding Drilling

Introduction• What is Manufacturing?

•Primary manufacturing processes convert raw material or scrap to a basic primary shaped and sized product.

•Secondary manufacturing processes further improve the properties, surface quality, dimensional accuracy, tolerance, etc.

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Value AdditionProcesses

Raw materials Finished Product

Introduction• Machining

• One of the secondary manufacturing processes.• Excess material is removed (by shearing) from the preformed blank in the form of chips.• Uses a wedge shaped cutting tool in order to get product having desired shape, size and

tolerance.

• Machining to high accuracy and finish essentially enables a product to• Fulfill its functional requirements• Improve its performance• Prolong its service

• Tools necessary for machining• Machine Tools• Cutting Tools

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Cutting Tools• Both material and geometry of the cutting tools play very important roles on

their performances in achieving effectiveness, efficiency and overall economyof machining.

• Classified according to the number of major cutting edges (points) involved in cutting:

• Single point: only one cutting tip is available.e.g., turning tools, shaping, planning and slotting tools andboring tools

• Multipoint: more than one tip is available.e.g., drills, milling cutters, broaching tools, hobs,gear shaping cutters etc.

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Salient features of cutting tool point1. Nose2. Rake surface3. Principal Flank4. Auxiliary Flank5. Principal Cutting Edge6. Auxiliary Cutting Edge

6Tool-in-Hand System

Systems of description of tool geometry • Tool-in-Hand System – Only the salient features of the cutting tool point are

identified or visualized such as• Nose (Cutting Tip)• Rake surface, Principal Flank, Auxiliary Flank• Principal Cutting Edge, Auxiliary Cutting Edge.

• There is no quantitative information, i.e., value of the angles. • Machine Reference System – ASA system • Tool Reference Systems

• Orthogonal Rake System – ORS • Normal Rake System – NRS

• Work Reference System – WRS

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Systems of description of tool geometry

8Top view of Lathe Machine

Reference planes and Axes in ASA system

ASA and ORS systems

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Reference planes and Axes in ASA system Reference planes and Axes in ORS system

ORS and NRS systems

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Reference planes and Axes in ORS system Reference planes and Axes in NRS system

Machine Reference System – ASA system • The planes of reference and the coordinates used in ASA system for tool geometry are :

• =Reference plane; plane perpendicular to the velocity vector, • =Machine longitudinal plane; plane perpendicular to and taken in the direction of assumed

longitudinal feed.• =Machine Transverse plane; plane perpendicular to both and , in the direction of assumed

cross feed.

• The axes are:• =in the direction of longitudinal feed, • =in the direction of cross feed.• =in the direction of cutting velocity (vector).

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Tool Signature of SPTT in ASA system

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Tool Signature of SPTT in ASA system

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Tool Signature of SPTT in ASA systemAngle Made by With Measured

onBack Rake angle,γY

rake surface reference plane

πY

Side Rake angle,γX

rake surface reference plane

πX

Back Clearance,αY

principal flank

VC (or Zm) πY

Side clearance,αX

principal flank

VC (or Zm) πX

End Cutting Edge

angle,φe

end cutting edge

πX πR

Approach angle,φs

Side cutting edge

πY πR14

Tool Reference Systems- ORS System• The planes of reference and the co-ordinate axes used for expressing the tool

angles in ORS are: πR – πC – πO and X0 – Y0 – Z0• πR = Reference plane perpendicular to the cutting velocity vector,

πC = cutting plane; plane perpendicular to πR and taken along the principal cutting edgeπO = Orthogonal plane; plane perpendicular to both πR and πC and the axes;Xo = along the line of intersection of πR and πOYo = along the line of intersection of πR and πCZo = along the velocity vector, i.e., normal to both Xo and Yo axes

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Tool Signature of SPTT in ORS system

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Tool Signature of SPTT in ORS systemAngle Made by With Measured

onInclination

angle, λrake

surfaceprincipal

cutting edgeπC

Orthogonal rake angle,γ0

rake surface

reference plane

πo

Orthogonal clearance,αo

principal flank

πC πo

Auxiliary orthogonal

clearance αo’

Auxiliary flank

πC’ πo’

φ1= φe end cutting edge

πX πR

φ=90- φs Side cutting edge

πX πR17

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Auxiliary orthogonal clearance angle

Summery of SPTT geometry• ASA system-convenience of inspection• ORS system- for analysis and research

in machining and tool performance

• ORS does not reveal the true picture of the tool geometry when λ≠0.

• sharpening or resharpening of the tool by grinding in ORS requires some additional calculations for correction of angles.

• In NRS, rake and clearance angles are visualized in the normal plane, πN.

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QUIZ• Select the correct answer from the given four options : 1. Back rake of a turning tool is measured on its (a) machine longitudinal plane (b) machine transverse plane (c) orthogonal plane (d) normal plane

2. Normal rake and orthogonal rake of a turning tool will be same when its

(a) φ = 0 (b) φ1 = 0 (c) λ = 0 (d) φ1 = 90o

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QUIZ3. Normal plane of a turning tool is always perpendicular to its

(a) πX plane (b) πY plane (c) πC plane (d) none of them

4. Principal cutting edge angle of any turning tool is measured on its

(a) πR(b) πY(c) πX(d) πo

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QUIZ

5. A cutting tool can never have its (a) rake angle – positive (b) rake angle – negative (c) clearance angle – positive (d) clearance angle – negative

6. Orthogonal clearance and side clearance of a turning tool will be same if its perpendicular cutting edge angle is

(a) φ = 30o (b) φ = 45o (c) φ = 60o (d) φ = 90o 22

QUIZ7. Inclination angle of a turning tool is measured on its (a) reference plane (b) cutting plane (c) orthogonal plane (d) normal plane

8. Normal rake and side rake of a turning tool will be same if its

(a) φ = 0o and λ = 0o (b) φ = 90o and λ = 0o (c) φ = 90o and λ = 90o (d) φ = 0o and λ = 9

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Conversion of tool angles• Purposes of conversion of tool angles from one system to another

• To understand the actual tool geometry in any system of choice or convenience from the geometry of a tool expressed in any other systems.

• To derive the benefits of the various systems of tool designation as and when required

• Communication of the same tool geometry between people following different tool designation systems.

• Methods of conversion of tool angles from one system to another• Analytical (geometrical) method: simple but tedious• Graphical method – Master line principle: simple, quick and popular• Transformation matrix method: suitable for complex tool geometry• Vector method: very easy and quick but needs concept of vectors

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Conversion of tool angles

• From ASA to ORS

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• From ORS to NRS

QUIZ1. If the approach angle of a turning tool be 30o, the value of its principal cutting edge angle will be

(a) O deg.

(b) 30o deg.

(c) 60o deg.

(d) 90o deg.

2. The values of orthogonal clearance and normal clearance of a turning tool will be same if,

(a) φ=0

(b) αX = αY

(c) λ = 0

(d) none of the above

3. Determine the values of normal rake of the turning tool whose

geometry is designated as : 10o, - 10o, 8o, 6o, 15o, 30o, 0 (inch)?

4. Determine the value of side clearance of the turning tool whose

geometry is specified as 0o, - 10o, 8o, 6o, 20o, 60o, 0 (mm) ? 26

Effect of tool Geometry on machining• Back Rake angle

• Guides the direction of the chip flow.• The size of the angle depends upon the material to be machined

Softer the material greater the positive rake angle.• Rake angle (Al) > Rake angle (C.I.)• With increase in back rake angle, the strength, forces and power consumption of tool will decrease and tool life will be increased.

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• Positive rakes are used when cutting low tensile strength and non-ferrous materials

• Zero back rake is used during machining of brass work pieces and also during thread cutting operations.

• The negative rake angles are used with tools which are weak in tension. (Carbide cutting tools)

Effect of tool Geometry on machining• Back Rake angle

• Higher value of rake angle weakens the cutting edge of tool.

• the maximum value of positive rake angle is 45◦.

• Cutting tools with negative rake angle are stronger and are used to cut high strength alloys.

• the uses of an increased negative rake angle leads to increase cutting force during machining.

• maximum negative back rake angle used = 10°

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• Side Rake angle (5°-15°)• guides the direction of the chip away from the job.• With increase in side rake angle, the amount of chip bend in width direction decreases.• Larger side rake angle produces smooth surface finish.• As it increases, strength decreases, forces decreases, Power consumption decreases

and Tool life increases.

• Clearance Angles• If this angle is very large, the cutting edge of the tool will be unsupported and will break.• If this angle is very small, the tool will rub on the job, cutting will not proper and poor

finish will be obtained on the job.• Its values varies from 5 to 15°.

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• End cutting edge angle:• It acts as a relief angle that it allows only small section of the end cutting edge to contact with the

machine surface and prevents chatter and vibration.• Normally it varies from 8 to 20°.

• Approach angle:• Avoids the formation of built up edge, controls the direction of chip flow and distributes the cutting

force and heat produce over larger cutting edge.• Normally Cs = 0 to 90°

• The cutting edge angles are mainly influencing surface finish produced on the work piece.

Let Rt = Maximum peak to valley height (mm)• If the value of s increases then Rt decreases. Thus better surface finish will be

obtained.

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Quiz• For cutting of brass with single‐point cutting tool on a lathe, tool should have

• Negative rake angle • Positive rake angle • Zero rake angle • Zero side relief angle

• The following tool signature is specified for a single point cutting tool in American system:10, 12, 8, 6, 15, 20, 3. What does the angle 12 represent?

• Side cutting‐edge angle • Side rake angle • Back rake angle • Side clearance angle

• Normal rake and side rake of a turning tool will be same if its Principal cutting edge angle and inclination angle respectively are (in degree)

• 0,0• 90,0 • 90,90 • 0,90

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Thank you

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