*What is a Cutting ToolA cutting tool is any tool that is used to remove metal from the work piece by means of shear deformation.It is one of most important components in machining processIt must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal cutting process. Two basic typesSingle pointMultiple point

Single Point Cutting Tool

Multi Point Cutting Tool

*Cutting-Tool MaterialsCutting tool bits generally madeHigh-speed steelCast alloysCemented carbidesCeramicsCubic Boron NitridePolycrystalline Diamond

*Cutting Tool PropertiesHardnessCutting tool material must be 1 1/2 times harder than the material it is being used to machine.

Capable of maintaining a red hardness during machining operationRed hardness: ability of cutting tool to maintain sharp cutting edge at elevated temp.It is also sometimes referred to as hot hardness or hot strength

*Cutting Tool PropertiesWear ResistanceAble to maintain sharpened edge throughout the cutting operationSame as abrasive resistance

Shock ResistanceAble to take the cutting loads and forces

Shape and ConfigurationMust be available for use in different sizes and shapes.

*High-Speed SteelMay 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

*Cast AlloyUsually contain 25% to 35% chromium, 4% to 25% tungsten and 1% to 3% carbonRemainder cobaltQualitiesHigh hardnessHigh resistance to wearExcellent red-hardnessOperate 2 times speed of high-speed steelWeaker and more brittle than high-speed steel

*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

Single Point Cutting Tool*

*Single Point Cutting Tool

Know the Single Point Cutting ToolShank: Main body of tool, it is part of tool which is gripped in tool holderFace: Top surface of tool b/w shankand point of tool. Chips flow along this surfaceFlank: Portion tool which faces the work. It is surface adjacent to & below the cutting edge when tool lies in a horizontal position.Point: Wedge shaped portion where face & flank of tool meet.Base: Bearing surface of tool on which it is held in a tool holder.Nose radius: Cutting tip, which carries a sharp cutting point. Nose provided with radius to enable greater strength, increase tool life & surface life. Typical Value : 0.4 mm 1.6 mm

*SPC Tool GeometrySIDE RELIEFSIDE CLEARANCE

*The most significant terms in the geometry of a cutting tool angles are:Relief or clearance angleSide reliefEnd reliefRake angleBack Rake angleSide Rake angleCutting edge angleSide Cutting edge angleEnd Cutting edge anglNose Radius

Nomenclature of Single Point Lathe Tool

*Cutting-Tool TermsRelief or Clearance angle:Ground on the end and side faces of a tool to prevent it from rubbing on the work piece.To enable only the cutting edge to touch the work piece.

Side Relief angle:Angle ground directly below the cutting edge on the flank of the toolEnd Relief angle:Angle ground from the nose of the tool

*Cutting-Tool TermsCutting edge angleGround on a tool so that it can be mounted in the correct position for various machining operations.

Side Cutting edge angleAllows flank of the tool to approach the work piece firstSpreads the material over a greater distance on the cutting edge, thereby thinning out the chip.Approximately 150 End Cutting edge angleAllows the cutting tool to machine close to the work piece during turning operationsUsually 20 300

*Rake angle:Ground on a tool to provide a smooth flow of the chip over the tool so as to move it away from the work pieceCutting-Tool TermsBack Rake angleGround on the face of the toolInfluences the angle at which chip leaves the nose of the toolGenerally 8 - 100Side Rake angleGround on the tool face away from the cutting edgeInfluences the angle at which the chip leaves the work pieceA lathe tool has 140 side rake.

*Cutting-Tool TermsFunctions:Strengthens finishing point of tool Improves surface finish on workShould be twice amount of feed per revolutionToo large chatter; too small weakens pointNose Radius:Rounded tip on the point of the tool

Tool Angle ApplicationFactors to consider for tool anglesThe hardness of the metalType of cutting operationMaterial and shape of the cutting toolThe strength of the cutting edge

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*****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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