Machining ProcessCast, formed and shaped products may need further machining operations to give them the desired final shape, after removal of extra material in the form of chips.

Machining processes remove material from a work piece byCUTTING ( As in case of machine tools like lathe, shaper etc)ABRASIVE ( As in case of a grinding wheel)NON TRADITIONAL ( Processes such as EDM, ECM Etc.)

*Metal Cutting Processes

*TurningHigh proportion of work machined in shop turned on latheTurning tool set to given depth of cut, fed parallel to axis of work (reduces diameter of work)Chip forms and slides along cutting tool's upper surface created by side rake

*Planing or ShapingWorkpiece moved back and forth under cutting toolFed sideways a set amount at end of each table reversal

*Plain MillingMulti-tooth tool having several equally spaced cutting edges around peripheryEach tooth considered single-point cutting tool (must have proper rake and clearance angles)Workpiece held in vise or fastened to tableFed into horizontal revolving cutterEach tooth makes successive cutsProduces smooth, flat, or profiled surface depending on shape of cutter

*Inserted Blade Face MillConsists of body that holds several equally spaced insertsCutting action occurs at lower corner of insertCorners chamfered to give strength

*End MillingMulti-fluted cutters held vertically in vertical milling machine spindle or attachmentUsed primarily for cutting slots or groovesWorkpiece held in vise and fed into revolving cutterEnd millingCutting done by periphery of teeth

*DrillingMulti-edge cutting tool that cuts on the point

Drill's cutting edges (lips) provided with lip clearance to permit point to penetrate work piece as drill revolves

*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 carbidesCeramicsCermetsCubic 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.

*Side RakeLarge as possible to allow chips to escapeAmount determined Type and grade of cutting toolType of material being cutFeed per revolutionAngle of keennessFormed by side rake and side clearance

*Back RakeAngle formed between top face of tool and top of tool shankPositiveTop face slopes downward away from pointNegativeTop face slopes upward away from pointNeutral

Rake AnglesSmall to medium rake angles cause: high compressionhigh tool forceshigh frictionresult = Thickhighly deformedhot chips

Negative Rake ToolsTypical tool materials which utilize negative rakes are: CarbideDiamondsCeramicsThese materials tend to be much more brittle than HSS but they hold superior hardness at high temperatures. The negative rake angles transfer the cutting forces to the tool which help to provide added support to the cutting edge.

*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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