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29-*Objectives Use the nomenclature of a cutting-tool pointExplain the purpose of each type of rake and clearance angleIdentify the applications of various types of cutting-tool materialsDescribe the cutting action of different types of machines

CuTTinG tOOLs Preapared by :-JITENDRA JHA Mechanical GEC BHAVNAGAR29-*

29-*Cutting ToolsOne of most important components in machining processPerformance will determine efficiency of operationTwo basic types (excluding abrasives)Single point and multi pointMust have rake and clearance angles ground or formed on them

29-*Cutting-Tool MaterialsLathe toolbits generally made of five materialsHigh-speed steelCast alloys (such as stellite)Cemented carbidesCeramicsCermetsMore exotic finding wide useBorazon and polycrystalline diamond

29-*Lathe Toolbit PropertiesHardWear-resistantCapable of maintaining a red hardness during machining operationRed hardness: ability of cutting tool to maintain sharp cutting edge even when turns red because of high heat during cuttingAble to withstand shock during cuttingShaped so edge can penetrate work

29-*High-Speed Steel ToolbitsMay contain combinations of tungsten, chromium, vanadium, molybdenum, cobaltCan take heavy cuts, withstand shock and maintain sharp cutting edge under red heatGenerally two types (general purpose)Molybdenum-base (Group M)Tungsten-base (Group T)Cobalt added if more red hardness desired

29-*Cemented-Carbide ToolbitsCapable of cutting speeds 3 to 4 times high-speed steel toolbitsLow toughness but high hardness and excellent red-hardnessConsist of tungsten carbide sintered in cobalt matrixStraight tungsten used to machine cast iron and nonferrous materials (crater easily)Different grades for different work

29-*Coated Carbide ToolbitsMade by depositing thin layer of wear-resistant titanium nitride, titanium carbide or aluminum oxide on cutting edge of toolFused layer increases lubricity, improves cutting edge wear resistance by 200%-500%Lowers breakage resistance up to 20%Provides longer life and increased cutting speedsTitanium-coated offer wear resistance at low speeds, ceramic coated for higher speeds

29-*Ceramic ToolbitsPermit higher cutting speeds, increased tool life and better surface finish than carbideWeaker than carbide used in shock-free or low-shock situationCeramicHeat-resistant material produced without metallic bonding agent such as cobaltAluminum oxide most popular additiveTitanium oxide or Titanium carbide can be added

29-*Diamond ToolbitsUsed mainly to machine nonferrous metals and abrasive nonmetallicsSingle-crystal natural diamondsHigh-wear but low shock-resistant factorsPolycrystalline diamondsTiny manufactured diamonds fused together and bonded to suitable carbide substrate

29-*Cutting-Tool NomenclatureCutting edge: leading edge of that does cuttingFace: surface against which chip bears as it is separated from workNose: Tip of cutting tool formed by junction of cutting edge and front faceCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29-*Cutting-Tool NomenclatureNose radius: radius to which nose is groundSize of radius will affect finishRough turning: small nose radius (.015in)Finish cuts: larger radius (.060 to .125 in.)Point: end of tool that has been ground for cutting purposesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29-*Cutting-Tool NomenclatureCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Base: Bottom surface of tool shankFlank: surface of tool adjacent to and below cutting edgeShank: body of toolbit or part held in toolholder

29-*Lathe Toolbit Angles andClearancesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29-*Lathe Cutting-tool AnglesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Positive rake: point of cutting tool and cutting edge contact metal first and chip moves down the face of the toolbitNegative rake: face of cutting tool contacts metal first and chip moves up the face of the toolbit

29-*Positive Rake AngleConsidered best for efficient removal of metalCreates large shear angle at shear zoneReduces friction and heatAllows chip to flow freely along chip-tool interfaceGenerally used for continuous cuts on ductile materials not too hard or abrasive

29-*Factors When Choosing Type and Rake Angle for Cutting ToolHardness of metal to be cutType of cutting operationContinuous or interruptedMaterial and shape of cutting toolStrength of cutting edge

29-*Shape of ChipAltered in number of ways to improve cutting action and reduce amount of power requiredContinuous straight ribbon chip can be changed to continuous curled ribbonChanging angle of the keenessIncluded angle produced by grinding side rakeGrinding chip breaker behind cutting edge of toolbit

29-*Tool LifeCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.When flank wear is .015 to .030 in. need to be reground

29-*Factors Affecting the Life of a Cutting ToolType of material being cutMicrostructure of materialHardness of materialType of surface on metal (smooth or scaly)Material of cutting toolProfile of cutting toolType of machining operation being performedSpeed, feed, and depth of cut

29-*TurningCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Assume cutting machine steel: If rake and relief clearance angles correct and proper speed and feed used, a continuous chip should be formed.

29-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Nomenclature of a Plain Milling Cutter

29-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Nomenclature of an End Mill

29-*Nomenclature of an End MillCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Characteristics of a Drill PointCutting-point angles for standard drill

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.PowerPoint to accompanyKrar Gill SmidTechnology of Machine Tools6th Edition

Operating Conditions and Tool Life Unit 30

30-*Objectives Describe the effect of cutting conditions on cutting-tool lifeExplain the effect of cutting conditions on metal-removal ratesState the advantages of new cutting-tool materialsCalculate the economic performance and cost analysis for a machining operation

30-*Operating ConditionsThree operating variables influence metal-removal rate and tool lifeCutting speedFeed rateDepth of cut

30-*Reduction in Tool LifeOperating ConditionsCUTTINGSPEED + 50%FEEDRATE + 50%DEPTH OFCUT + 50%90%60%15%

30-*General Operating Condition RulesProper cutting speed most critical factor to consider establishing optimum conditionsToo slow: Fewer parts produced, built-up edgeToo fast: Tool breaks down quicklyOptimum cutting speed should balance metal-removal rate and cutting-tool lifeChoose heaviest depth of cut and feed rate possible


Carbide Cutting Tools Unit 31

31-*Objectives Identify and state the purpose of the two main types of carbide gradesSelect the proper grade of carbide for various workpiece materialsSelect the proper speeds and feeds for carbidetools

31-*Carbide Cutting ToolsFirst used in Germany during WW II as substitute for diamondsVarious types of cemented (sintered) carbides developed to suit different materials and machining operationsGood wear resistanceOperate at speeds ranging 150 to 1200 sf/minCan machine metals at speeds that cause cutting edge to become red hot without loosing harness

31-*BlendingFive types of powdersTungsten carbide, titanium carbide, cobalt, tantalum carbide, niobium carbideOne or combination blended in different proportions depending on grade desiredPowder mixed in alcohol (24 to 190 h)Alcohol drained offParaffin added to simplify pressing operation

31-*CompactionCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Must be molded to shape and sizeFive different methods to compact powderExtrusion processHot pressIsostatic pressIngot pressPill pressGreen (pressed) compacts soft, must be presintered to dissolve paraffin

31-*PresinteringGreen compacts heated to about 1500 F in furnace under protective atmosphere of hydrogenCarbide blanks have consistency of chalkMay be machined to required shape40% oversize to allow for shrinkage that occurs during final sintering

31-*SinteringLast step in processConverts presintered machine blanks into cemented carbideCarried out in either hydrogen atmosphere or vacuumTemperatures between 2550 and 2730 FBinder (cobalt) unites and cements carbide powders into dense structure of extremely hard carbide crystals

31-*Cemented-Carbide ApplicationsUsed extensively in manufacture of metal-cutting toolsExtreme hardness and good wear-resistanceFirst used in machining operations as lathe cutting toolsMajority are single-point cutting tools used on lathes and milling machines

31-*Types of Carbide Lathe Cutting ToolsBrazed-tip typeCemented-carbide tips brazed to steel shanksWide variety of styles and sizesIndexable insert typeThrowaway insertsWide variety of shapes: triangular, square, diamond, and roundTriangular: has three cutting edgesInserts held mechanically in special holder

31-*Grades of Cemented CarbidesTwo main groups of carbidesStraight tungsten carbideContains only tungsten carbide and cobaltStrongest and most wear-resistantUsed for machining cast iron and nonmetalsCrater-resistant Contain titanium carbide and tantalum carbide in addition to tungsten carbide and cobaltUsed for machining most steels

31-*Tool GeometryCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.SIDE RELIEFSIDE CLEARANCETerms adopted by ASME

31-*Cutting-Tool TermsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Front, End, Relief (Clearance)Allows end of cutting tool to enter workSide Relief (Side)Permits side of tool to advance into work

31-*Cutting Speeds and FeedsImportant factors that influence speeds, feeds, and depth of cutType and hardness of work materialGrade and shape of cutting toolRigidity of cutting toolRigidity of work and machinePower rating of machine


Cutting FluidsTypes andApplications Unit 34

34-*Objectives State the importance and function of cutting fluidsIdentify three types of cutting fluids and state the purpose of eachApply cutting fluids efficiently for a variety of machining operations

34-*Cutting FluidsEssential in metal-cutting operations to reduce heat and frictionCenturies ago, water used on grindstones100 years ago, tallow used (did not cool)Lard oils came later but turned rancidEarly 20th century saw soap added to waterSoluble oils came in 1936Chemical cutting fluids introduced in 1944

34-*Economic Advantages to Using Cutting FluidsReduction of tool costsReduce tool wear, tools last longerIncreased speed of productionReduce heat and friction so higher cutting speedsReduction of labor costsTools last longer and require less regrinding, less downtime, reducing cost per partReduction of power costsFriction reduced so less power required by machining

34-*Heat Generated During MachiningHeat find its way into one of three placesWorkpiece, tool, chipsCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Too much, work will expandToo much, cutting edge will break down rapidly, reducing tool lifeAct as disposable heat sink

34-*Heat Dissipation Ideally most heat taken off in chipsIndicated by change in chip color as heat causes chips to oxidizeCutting fluids assist taking away heatCan dissipate at least 50% of heat created during machining

34-*Characteristics of a Good Cutting FluidGood cooling capacityGood lubricating qualitiesResistance to rancidityRelatively low viscosityStability (long life)Rust resistanceNontoxicTransparentNonflammable

34-*Types of Cutting FluidsMost commonly used cutting fluidsEither aqueous based solutions or cutting oilsFall into three categoriesCutting oilsEmulsifiable oilsChemical (synthetic) cutting fluids

34-*Oil CategoriesSulfurized mineral oilsContain .5% to .8% sulfurLight-colored and transparentStains copper and alloysSulfochlorinated mineral oils3% sulfur and 1% chlorinePrevent excessive built-up edges from formingSulfochlorinated fatty oil blendsContain more sulfur than other types

34-*Inactive Cutting OilsOils will not darken copper strip immersed in them for 3 hours at 212FContained sulfur is naturalTermed inactive because sulfur so firmly attached to oil very little releasedFour general categoriesStraight mineral oils, fatty oils, fatty and mineral oil blends, sulfurized fatty-mineral oil blend

34-*Emulsifiable (Soluble) OilsMineral oils containing soaplike material that makes them soluble in water and causes them to adhere to workpieceEmulsifiers break oil into minute particles and keep them separated in waterSupplied in concentrated form (1-5 /100 water)Good cooling and lubricating qualitiesUsed at high cutting speeds, low cutting pressures

34-*Functions of a Cutting FluidPrime functionsProvide coolingProvide lubricationOther functionsProlong cutting-tool lifeProvide rust controlResist rancidity

34-*Functions of a Cutting Fluid: CoolingHeat has definite bearing on cutting-tool wearSmall reduction will greatly extend tool lifeTwo sources of heat during cutting actionPlastic deformation of metalOccurs immediately ahead of cutting toolAccounts for 2/3 to 3/4 of heatFriction from chip sliding along cutting-tool faceWater most effective for reducing heat (rust)

34-*Functions of a Cutting Fluid: LubricationReduces friction between chip and tool faceShear plane becomes shorterArea where plastic deformation occurs correspondingly smallerExtreme-pressure lubricants reduce amount of heat-producing frictionEP chemicals of synthetic fluids combine chemically with sheared metal of chip to form solid compounds (allow chip to slide)

34-*Cutting-Tool LifeHeat and friction prime causes of cutting-tool breakdownReduce temperature by as little as 50F, life of cutting tool increases fivefoldBuilt-up edgePieces of metal weld themselves to tool faceBecomes large and flat along tool face, effective rake angle of cutting tool decreased

34-*Application of Cutting FluidsCutting-tool life and machining operations influenced by way cutting fluid appliedCopious stream under low pressure so work and tool well coveredInside diameter of supply nozzle width of cutting toolApplied to where chip being formed

34-*MillingFace millingRing-type distributor recommended to flood cutter completelyKeeps each tooth of cutter immersed in cutting fluid at all timesSlab millingFluid directing to both sides of cutter by fan-shaped nozzles width of cutter

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*********The side cutting edge angle is the angle the cutting edge forms with the side of the tool shank (Fig.29-4). Side cutting angles for a general-purpose lathe cutting tool may vary from 10 to 20, depending on the material cut. If this angle is too large (over 30), the tool will tend to chatter.The end cutting edge angle is the angle formed by the end cutting edge and a line at right angles to the centerline of the toolbit (Fig.29-4). This angle may vary from 5 to 30, depending on the type of cut and finish desired. An angle of 5 to 15 is satisfactory for roughing cuts; angles between 15 and 30 are used for general-purpose turning tools. The larger angle permits the cutting tool to be swiveled to the left for taking light cuts close to the dog or chuck, or when turning to a shoulder.The side relief (clearance) angle is the angle ground on the flank of the tool below the cutting edge (Figs.29-4 and 29-5). This angle is generally 6 to 10. The side clearance on a toolbit permits the cutting tool to advance lengthwise into the rotating work and prevents the flank from rubbing against the workpiece.The end relief (clearance) angle is the angle ground below the nose of the toolbit, which permits the cutting tool to be fed into the work. It is generally 10 to 15 for general-purpose tools (Figs.29-4 and 29-5). This angle must be measured when the toolbit is held in the toolholder. The end relief angle varies with the hardness and type of material and the type of cut. The end relief angle is smaller for harder materials, providing support under the cutting edge.The side rake angle is the angle at which the face is ground away from the cutting edge. For general-purpose toolbits, the side rake is generally 14 (Figs.29-4 and 29-5). Side rake creates a keener cutting edge and allows the chips to flow away quickly. For softer materials, the side rake angle is generally increased. Side rake may be either positive or negative, depending on the material being cut.The angle of keenness is the included angle produced by grinding side rake and side clearance on a toolbit (Fig.29-4). This angle may be altered, depending on the type of material machined, and will be greater (closer to 90) for harder materials.The back (top) rake angle is the backward slope of the tool face away from the nose. The back rake angle is generally about 20 and is provided for in the toolholder (Fig.29-5). Back rake permits the chips to flow away from the point of the cutting tool. Two types of back or top rake angles are provided on cutting tools and are always found on the top of the toolbit:>Positive rake (Fig.29-6a), where the point of the cutting tool and the cutting edge contact metal first and the chip moves down the face of the toolbit>Negative rake (Fig.29-6b), where the face of the cutting tool contacts the metal first and the chip is forced up the face of the toolbit**

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***********Indexable Inserts**AATool GeometryThe geometry of cutting tools refers to the various angles and clearances machined or ground on the tool faces. Although the terms and definitions relating to single-point cutting tools vary greatly, those adopted by the American Society of Mechanical Engineers (ASME) and currently in general use are illustrated in Fig.31-6.

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