2. Cutting Tools.pdf

Maching tools : metal cutting

1. Cutting Tools
Dr. V.Harinadh
Dept of Mechanical Engineering

2. What is a CuttingTool
⚫Acuttingtoolisanytoolthatisusedtoremovemetalfromthe
workpiecebymeansofsheardeformation.
⚫Itisoneofmostimportantcomponentsinmachiningprocess
⚫Itmustbemadeofamaterialharderthanthematerialwhichis
tobecut,andthetoolmustbeabletowithstandtheheat
generatedinthemetalcuttingprocess.

3. Two basictypes
⚫Singlepoint
⚫Multiplepoint

4. ManufacturingTechnology
Classification of cuttingtools
▪Single-Point Cutting EdgeTools
▪One dominant cuttingedge
▪Point is usually rounded to form a noseradius
▪Turning uses single pointtools
▪Multiple Point Cutting EdgeTools
▪More than one cuttingedge
▪Motion relative to work achieved byrotating
▪Drilling and milling use rotating multiple cutting edgetools

5. ManufacturingTechnology
▪CuttingTools
Figure (a) A single-point tool showing rake face, flank, and tool point; and (b) a helical
milling cutter, representative of tools with multiple cuttingedges.
a. Single-Point CuttingTool b. Multi-Point CuttingTool

6. Single Point CuttingTool

7. Multi Point CuttingTool

8. Cutting-ToolMaterials
⚫Cutting tool bits generallymade
⚫High-speedsteel
⚫Castalloys
⚫Cementedcarbides
⚫Ceramics
⚫Cermets
⚫Cubic BoronNitride
⚫PolycrystallineDiamond

9. Cutting tools & itscharacteristics
Cutting tool is a device, used to remove the unwanted material fromgiven workpiece. For carrying
out the machining process, cutting tool isfundamental and essential requirement. A cuttingtool
must have the followingcharacteristics:
•Hardness:Thetoolmaterialmustbeharderthantheworkpiecematerial.Higherthehardness,
easieritisforthetooltopenetratetheworkmaterial.Cuttingtoolmaterialmustbe1(1/2)times
harderthanthematerialitisbeingusedtomachine.
•Hothardness:HotHardnessistheabilityofthecuttingtoolmusttomaintainitsHardnessand
strengthatelevatedtemperatures.Thispropertyismoreimportantwhenthetoolisusedathigher
cuttingspeeds,forincreasedproductivity.
•Toughness:Inspiteofthetoolbeingtough,itshouldhaveenoughtoughnesstowithstandthe
impactloadsthatcomeinthestartofthecuttoforcefluctuationsduetoimperfectionsinthework
material.Toughnessofcuttingtoolsisneededsothattoolsdon’tchiporfracture,especiallyduring
interruptedcuttingoperationslikemilling.

10. Cutting tools & itscharacteristics
•WearResistance:Thetool-chipandchip-workinterfaceareexposedtosevereconditionsthat
adhesiveandabrasionwearisverycommon.Wearresistancemeanstheattainmentof
acceptabletoollifebeforetoolsneedtobereplaced.
•Lowfriction:Thecoefficientoffrictionbetweenthetoolandchipshouldbelow.Thiswould
lowerwearratesandallowbetterchipflow.
•Thermalcharacteristics:Sincealotofheatisgeneratedatthecuttingzone,thetoolmaterial
shouldhavehigherthermalconductivitytodissipatetheheatinshortestpossibletime,
otherwisethetooltemperaturewouldbecomehigh,reducingitslife.

11. Cutting ToolProperties
●WearResistance
⚫Able to maintain sharpened edge throughout the cutting
operation
⚫Same as abrasiveresistance
●ShockResistance
⚫Able to take the cutting loads andforces
●Shape andConfiguration
⚫Must be available for use in different sizes andshapes.

12. Single Point CuttingTool

14. Nomenclature of Single point
cuttingtool

16. ▪Shank
▪It is the main body of thetool
▪Flank
▪The surface of the tool adjacent to the cuttingedge
▪Face
▪The surface on which the chipslides
▪Nose
▪It is the point where the side cutting edge and end cutting edgeintersect
▪Nose Radius
▪Strengthens finishing point oftool
▪CuttingEdge
▪It is the edge on the face of the tool which removes the material from the workpiece
▪Side cutting edgeangle
Angle between side cutting edge and the side of the toolshank
Tool signature for single
point cuttingtool

17. ▪Endcuttingedgeangle
▪Anglebetweenendcuttingedgeandthelinenormaltothetoolshank
▪SideReliefangle
▪Anglebetweentheportionofthesideflankimmediatelybelowthesidecuttingedge
andalineperpendiculartothebaseofthetool,measuredatrightangletotheside
flank
▪EndReliefangle
▪Anglebetweentheportionoftheendflankimmediatelybelowtheendcuttingedge
andalineperpendiculartothebaseofthetool,measuredatrightangletotheend
flank
Tool signature for single
point cuttingtool

18. ▪SideRakeangle
▪Anglebetweenthetoolfaceandalineparallelto
thebaseofthetoolandmeasured inaplane
perpendiculartothebaseandthesidecutting
edge
▪BackRakeangle
Anglebetweenthetoolfaceandalineparalleltothe
baseofthetoolandmeasuredinaplaneperpendicularto
thesidecuttingedge
Tool signature for
single point cuttingtool

19. CHIPFORMATION

20. Single Point Cutting ToolTerminology-2D
Ƴ

21. Single Point Cutting Tool Terminology –3D

22. Cutting ToolMaterials
❑Carbon steels, High-speedsteels
❑Cast carbides, Cemented carbides, Coatedcarbides
❑Cermets, CeramicTools
❑Polycrystalline Cubic Boron Nitride(PCBN)
❑Polycrystalline Diamond(PCD)
Properties of Cutting ToolMaterials
❑Harder than workpiece.
❑High toughness
❑High thermal shockresistance
❑Low adhesion to work piecematerial
❑Low diffusivity to work piecematerial

23. Orthogonal and oblique cutting
•Instructional Objectives
•At the end of this lesson, the student would be able to
•(i) define and distinguish, with illustrations, between orthogonal cutting and oblique cutting
•(ii) identify the causes of oblique cutting and chip flow deviation
•(iii) determine angle of chip flow deviation.
•(iv) illustrate and deduce effective rake angle
•(v) state the effects of oblique cutting

24. ▪Metalcuttingormachiningistheprocessofproducingaworkpiecebyremovingunwanted
materialfromablockofmetal,intheformofchips.
▪Thisprocessismostimportantsincealmostalltheproductsgettheirfinalshapeandsizeby
metalremoval,eitherdirectlyorindirectly.
Figure (a) A cross-sectional view of the machiningprocess,
(b) tool with negative rake angle; compare with positive rake angle in(a).
TheoryofMetalCutting

25. ◼Orthogonalcutting
❑The cutting edge of the tool is straight and perpendicular to the direction of motion. (surfacefinish)
◼Obliquecutting
❑Thecuttingedgeofthetoolissetatanangletothedirectionofmotion.(depth ofcut)
Orthogonal and obliquecutting

26. The Mechanism ofCutting
◼Cuttingactioninvolvessheardeformationofworkmaterialtoformachip.Aschipisremoved,new
surfaceisexposed
◼OrthogonalCutting-assumesthatthecuttingedgeofthetoolissetinapositionthatisperpendicularto
thedirectionofrelativeworkortoolmotion.Thisallowsustodealwithforcesthatactonlyinoneplane.
(a) A cross-sectional view of the machining process, (b) tool with negative rake angle;
compare with positive rake angle in(a).

27. Mechanics of OrthogonalCutting
OrthogonalCutting
▪IdealOrthogonalCuttingis when the cutting edge of the tool is straight and perpendicular to the
direction ofmotion.
▪During machining, the material is removed in form of chips, whicharegenerated by shear deformation
along a plane called the shearplane.
◼The surface the chip flows across is called the face or rakeface.
◼The surface that forms the other boundary of the wedge is called theflank.
◼The rake angle is the angle between the tool face and a line perpendicular to the cutting point of the
work piecesurface.

28. ◼The relief or clearance angle is the angle between the tool flank andthe newly formed
surface of the work pieceangle.
Mechanics of OrthogonalCutting

29. Mechanics of OrthogonalCutting
Orthogonal cuttingmodel:
◼t
1 = un deformed chipthickness
◼t
2 = deformed chip thickness (usually t
2 >t
1)
◼α = rakeangle
◼If we are using a lathe, t
1 is the feed perrevolution.

30. The Mechanism ofCutting
◼In turning, w = depth of cut and t
1=feed

31. The Mechanism ofCutting
Cutting force (Fc) is tangential and Thrust force is axial(Ft)
Cutting forces in a turningoperation

32. Mechanics of OrthogonalCutting
Chip thickness ratio (or) cuttingratio
where
▪r = chip thickness ratio or cuttingratio;
▪t
1 = thickness of the chip prior to chipformation;
▪t
2= chip thickness afterseparation
Which one is morecorrect?
◼r ≥1
◼r≤1
◼Chip thickness after cut always greater than before, so chip ratioalways less than1.0
Cutting ratio=r=
t
1
t
2

33. Mechanics of OrthogonalCutting
Shear PlaneAngle
▪Based on the geometric parameters of the orthogonal model, theshearplane angle ө can be
determinedas:
where
▪r = chip thickness ratio or cuttingratio;
▪= Rakeangle
▪ө= Shearangle
tan=
r cos 
1−rsin

34. Mechanics of OrthogonalCutting
Shear Plane AngleProof

35. Mechanics of OrthogonalCutting
Shear Strain in chipformation
(a) chip formation depicted as a series of parallel plates sliding relative to each other, (b) one ofthe
plates isolated to show shear strain, and (c) shear strain triangle used to derive strainequation.
θ
θ
θ-α

36. Mechanics of OrthogonalCutting
Shear StrainProof
◼From the shear strain triangle (image c –slide35)
▪= AC/DB=(AD+DC)/DB
▪= AD/DB +DC/DB
▪AD/DB = Cotθ
▪DC/DB = tan (θ -)
▪Therefore = Cot θ + tan (θ -)
❑= tan(θ -) + cotθ

37. Mechanics of OrthogonalCutting
Shear Strain in chipformation
◼Shear strain in machining can be computed from the following equation, based on the
preceding parallel platemodel:
❑= tan(θ -) + cotθ
where
❑= shearstrain
❑θ = shearangle
❑= rake angle of cuttingtool

38. Cutting ToolMaterials

39. Zones of HeatGeneration

40. HeatDissipation
80% Energy is
converted toheat
18% of Energy
is converted toheat
Work
2% of energy
converted toheat

41. ▪Mechanics of metal cutting is greatly depend on the shape and sizeofthe chipsformed.
More realistic view of chip formation, showing shear zone rather than shear plane. Also shown is the secondary
shear zone resulting from tool-chipfriction.
Chipformation

42. Selection of cutting speed and feed
•The selection of cutting speed and feed is based on the following parameters:
•Workpiecematerial
•ToolMaterial
•Tool geometry anddimensions
•Size of chipcross-section
•Types of finishdesired
•Rigidity of themachine
•Types of coolantused

43. Selection of cutting speed and feed