UL Lafayette MCHE 365 - Machining Processes Used to Produce Round Shapes

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Slide 1Various Cutting OperationsCutting OperationsTool GeometryTurning ParametersComponents of a LatheLathes and Lathe OperationsLathe SpecificationsRight Hand Cutting ToolWorkholding DevicesMandrelsSlide 12Turret LathesComputer Numerically Controlled LathesTurning Process CapabilitiesDesign Considerations for Turning OperationsGuidelines for Turning OperationsHigh-Speed Machining, Ultraprecision Machining, and Hard TurningCutting Screw ThreadsSlide 20Slide 21Types of Screw threadsBoringDrilling And DrillsSlide 25Slide 26Drill point GeometriesReaming And ReamersGun DrillingTrepanningDrilling MachinesCNC Milling MachineReamersTapping And TapsTapping and TapsTHE ENDChapter 22Machining Processes Used to Produce Round ShapesVarious Cutting Operations•Turing – produces straight, conical, curved, or grooved workpieces•Facing – produces a flat surface at the end of the part•Boring – to enlarge a hole•Drilling - to produce a hole•Cutting off – to cut off a workpeiece•Threading – to produce threads•Knurling – produces a regularly shaped roughnessCutting OperationsFig : Various cutting operations that can be performed on a late. Not that all parts have circular symmetryTool Geometry–Rake angle•controls direction of chip flow•Strength of the tool•Side rake angle – •Bake rake angle – controls direction of chip flow–Cutting edges – affects surface finish and tool-tip strength–Nose radius – affects surface finish•Material Removal Rate – (MRR) is the volume of material removed per unit timeTurning Parameters•Forces in turning –Cutting force: acts downward on the tool tip–Thrust force: acts in the longitudinal direction–Radial force: acts in the radial direction•Roughing and Finishing Cuts–Rough cut: high speed cut with little regard for dimensional tolerance–Finishing cut: lower feed rate and depth of cut•Tool Materials, Feeds, and Cutting Speeds–See table 22.4•Cutting Fluids–See table 22.5Components of a LatheFig : Components of LatheLathes and Lathe Operations•Lathes are the oldest machine tools•Lathe Components–Bed: supports all major components–Carriage: slides along the ways and consists of the cross-slide, tool post, apron–Headstock – Holds the jaws for the work piece, supplies power to the jaws and has various drive speeds•Tailstock – supports the other end of the workpiece•Feed Rod and Lead Screw – Feed rod is powered by a set of gears from the headstockLathe Specifications•A lathe is specified by its –Swing – maximum diameter of the workpiece–Distance from headstock and tailstock centers–Length of the bed•Lathes are available in a variety of styles and types of construction power•Types of lathes–Bench lathe: •Placed on a bench•Low power•Hand feed operated–Toolroom lathes: High precision–Engine lathes•Available in a wide variety of sizes•Used for a variety of turning operationsRight Hand Cutting ToolFig : (a) Designations and symbols for a right-hand cutting tool; solid high-speed-steel tools have a similar designation. Right-hand means that the tool travels from right to left.Tool SignatureDimensions Abbreviation8 Back Rake Angle BR14 Side Rake Angle SR6 End Relief Angle ER12 End Clearance Angle …….6 Side Relief Angle SRF12 Side Clearance Angle ……20 End Cutting-Edge Angle ECEA15 Side Cutting-edge angle SCEA3/4 Nose radius NRWorkholding DevicesChucksusually equipped with 3 or 4 jaws3 jaw chucks generally are self centering. Used for round work pieces. Can be centered within .025mm independently. 4 jaw chucks are for square, rectangular, or odd-shaped workpieces–Can be power actuatedFig : (a) and (b) Schematic illustrations of a draw-in-type collets. The workpiece is placed in the collet hole, and the conical surfaces of the collet are forced inward by pulling it with a draw bar into the sleeve. (c) A push-out type collet. (d) Workholding of a part on a face plate.MandrelsFig : Various types of mandrels to hold workpieces for turning. These mandrels are usually mounted between centers on a lathe. Note that in (a) both the cylindrical and the end faces of the workpiece can be machined, whereas in (b) and (c) only the cylindrical surfaces can be machined.Tracer Lathes•Machine tools with attachments•Capable of turning parts with various contours•A tracer finger follows the template and guides the cutting toolAutomatic Lathes•Increasingly being automated •Automatic Lathes are suitable for medium to high volume productionAutomatic Bar Machines•Formerly called automatic screw machines•Designed for high-production-rate machining of screws and other threaded parts•All operations are preformed automatically•Equipped with single or multiple spindlesTurret LathesCapable of performing multiple cutting operations on the same workpiece–Turning–Boring–Drilling–Thread cutting–FacingTurret lathes are very versatileTypes of turret lathes–Ram-type: ram slides in a separate base on the saddle–Saddle type: •more heavily constructed•Used to machine large workpeicecesComputer Numerically Controlled Lathes•Computer Numerical Controls (CNC)•Equipped with one or more turrets•Each turret is equipped with a variety of tools•Performs several operations on different surfaces of the workpieceFig : A computer numerical control lathe. Note the two turrets on this machine.Turning Process Capabilities•Production rates–See Table 22.8•Surface finish and dimensional accuracyFig : The range of dimensional tolerances obtained in various machining processes as a function of workpiece size. Note that there is an order of magnitude difference between small and large workpieces.Design Considerations for Turning Operations•Parts should be designed so that can be fixtured and clamped in the work holding devices•Dimensional accuracy and surface finish specified should be as wide as possible•Avoid sharp corners, tapers, and major dimensional variations in the part•Use near-net-shape forming•Cutting tools should be able to travel across workpiece without obstruction•Standard cutting tools, inserts, and toolholders should be used•Materials should be selected for their machineabilityGuidelines for Turning Operations•Minimize tool overhang•Support workpiece rigidly•Use machine tools with high stiffness and high damping capacity•When tools begin to vibrate and chatter, modify one or more of the process parameters, such as tool


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