Tools to cut and scrape goback at least 150 000 yrsback at least 150,000 yrsMachiningMachining2.810 Fall 2008T. GutowskiT. Gutowskigo to website below http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTraining/machineshop/mill/intro.htmlReadingsReadings1Kl kji Ch21271.Kalpakjian Ch 21-272“Simplified Time Estimation Booklet for2.Simplified Time Estimation Booklet for Basic Machining Operations” 3. Design for Machining handoutOutlineOutline1Bi1.Basics2Machine Configurations2.Machine Configurations3. Production Configurationsg4. Processing Planning5. EnvironmentBasic Machining ProcessesBasic Machining Processes–Single point machiningSingle point machining• Turning, boring, trepanning, planing–Multiple point machiningMultiple point machining• Drilling, milling, reaming, sawing, broaching, grindinggrindingMachining processesMachining processesTurning*GrindinggGrindingwheelDGrainsVMillingWorkpiecevCutterArborSpindleSpindleEnd millShankMilling*ArborHorizontal Slab milling Face milling End milling* Source: Kalpakjian, “Manufacturing Engineering and Technology”Machine ToolsHorizontal-spindle surface grinderMachine Tools*Spindlespeed selectorHeadstockSpindleCross slideWaysCarriage*Feed change gearboxCarriageCenterTailstock quillTailstockColumnHeadTable*Compound rest and slides (swivels)ApronBedLead screwFeed rodColumnSaddleKneeFeed rodBasic LatheBaseVertical-Spindle Mill* Source: Kalpakjian, “Manufacturing Engineering and Technology”Basic Mechanics IssuesBasic Mechanics Issues– Power, Forces– Heat, Tool materials, Rate limitsTemperature–Temperature– surface finishSee Video on Plastic DeformationSee Video on Plastic DeformationBasic Machining MechanismBasic Machining Mechanismworkd(work)PowerVF===•tcChipuenergyspecificworkworkdt Power VFS=====⋅•TlVα+-Rakeangleu 80%) to(65 u uuenergy specific volfriction workplasticSS+=∫•t0φShear planeShear angleTool)42(61 u4 2 d upp−×≅≅≤≤≅=∫HτγγτγεσApproximationuH(Hardness)Shear planeWorkpiece6pus~ H(Hardness)Specific energy uSSpecific energy, uSBasic Machining MechanismHence we have the approximation;Basic Machining MechanismPower ≈ usX MRRMRR is the Material Removal Rate or d(Vol)/dtSi P iSince Power isP = F * Vand MRR can be written as,d(Vol)/dt=A*Vd(Vol)/dt A VWhere A is the cross-sectional area of the undeformed chip, we can get an estimate for the cutting force as,F ≈ us×ANote that this approximation is the cutting force in the cutting direction.Cutting Force Directions in MillingCutting Force Directions in MillingFcnFcFpFpFcnFcFFcnFpFFc~ H × AcFpFcFcnFc(Tangential Cutting Force ~ Chip Cross-section × Hardness)Feed per Tooth and MRRFeed per Tooth and MRRΩ = rotational rate (rpm)v (m/s)Top view of face millingWith 4 tooth cutterf = feed per tooth (m)w = width of cut (m)Side viewConsider the workpiece moving into the cutter at rate “v”. In travel time t’ the feed is v t’. The time for one rotation is t’ = 1/Ω. The travel for one tooth is 1/4Ω Hence the feed per tooth isf=v/4Ω. In general, a cutter may have“N”1/4Ω. Hence the feed per tooth is f v/4Ω. In general, a cutter may have N teeth, so the feed per toothisf = v / NΩThe material removal rate (MRR) is,MRR = v w dwhere “d” is the depth of the tool into the workpiece.Ex) Face milling of Al AlloyEx) Face milling of Al AlloyvN = 4 (number of teeth)dφ=DvwD = 2” (cutter diameter)Let w = 1” (width of cut), d=0.1” (depth of cut)f = 0.007” (feed per tooth), f/ ( f d d dwdφ=Dvs= 2500 ft/min (surface speed; depends on cutting tool material; here, we must have a coated tool such as TiN or PCD) The rotational rate for the spindle isΩ = vs/ πD = 4775 rpmNow, we can calculate vw, workpiece velocity,f=v/NΩ=> v= 134 [in/min]f = vw/ N Ω=> vw= 134 [in/min]Material removal rate, MRR = vw*w*d = 13.4 [in3/min] Power requirement, P = us*MRR = 5.36 [hp]Cutting force / tooth, F ~ us*d*f = 111 [lbf]usfrom Table 21.2 (20.2 ed 4); Note 1 [hp min/in3] = 3.96*105[psi]Ex) Turning a stainless steel barEx) Turning a stainless steel barRecommended feed = 0.006” (Table 23.4 (22.4))fD=1”Recommended surface speed = 1000 ft/minΩ = 1000 ft/min = 3820 rpmπ∗1”∗1ft/12”dToolπ∗1 ∗1ft/12Let d = 0.1”Material removal rate, MRR = 0.1∗0.006∗(π∗1∗3820) = 7.2 [in3/min] Power requirement, P = us*MRR = 1.9*7.2 = 13.7 [hp]Ci f / h*d*f ( 9*3 96* 05)*(0 *0 006)Cutting force / tooth, F ~ us*d*f = (1.9*3.96*105)*(0.1*0.006) = 450 [lbf]f T bl 21 2 (20 2 d 4) N t 1 [h i /i3] 3 96*105[i]usfrom Table 21.2 (20.2 ed 4); Note 1 [hp min/in3] = 3.96*105[psi]Temperature Rise in CuttingTemperature Rise in Cutting*Adiabatic Temperature Rise: ρ cpΔT = uSNote : uS~ H, HardnessΔTadiabatic> ½ Tmelt(Al & Steel)Interface Temperature: ΔT = 0.4 (H / ρ cp)(v f / α)0.33Typical temperature distribution in the cutting zonev = cutting speedf = feedα = thermal diffusivity of workpiecef//dNote v f / α = Pe = convection/conduction* Source: Kalpakjian, and Schmidt 5thed* Reference: N. Cook, “Material Removal Processes”Cutting tool materials & process conditionsCutting tool materials & process conditionsardness (HRA)HRCfe (min)HaTool lifTemperature (°F))min)Cutting Speed (ft/min)utting speed (ft/minm/minMachining time (Feed (in/rev)CuYear* Source: Kalpakjian, “Manufacturing Engineering and Technology”Limits to MRR in MachiningLimits to MRR in Machining1. Spindle Power –for rigid, well supported partspg, pp p2. Cutting Force – may distort part, break delicate tools3. Vibration and Chatter – lack of sufficient rigidity in the machine, workpiece and cutting tool may result in self-excited vibration4Heat–heat build-up may produce“welding”poor4.Heat –heat build-up may produce welding, poor surface finish, excessive work hardening; can be reduced with cutting fluidSee Video on Rate Limits In MachiningTypical Material Removal RateTypical Material Removal Rate10-410-310-210-1110102[cm3/sec]1010101011010EBM1EDM1,2Machining[cm/sec]Grinding3gCreep Feed2Grinding25A, 6um RMS1Rough milling of Al > 35hpLASER3Chem Milling2Chem. Milling21m X 1m areaNote: 1cm3/sec = 3.67 in3/min* References: 1. Advanced Methods of Machining, J.A.McGeough, Chapman and Hall, 19882. Manufacturing Engineering and Technology, S. Kalpakjian, Addison-Wesley, 19923. Laser Machining, G. Chryssolouris, Springer-Verlag, 1991High speed Machining and AssemblyHigh speed Machining and Assembly• High Speed Machined aluminum parts are
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