Final Exam Review - Classes期末考试复习班

1、Final Exam ReviewMaterial-Process-Geometry Relationships2FunctionProcessMaterialGeometryRole of Prod EngrRole of Mfg Engr3Materials in Manufacturing lMost engineering materials can be classified into one of four basic categories: lMetalslCeramicslPolymerslComposites4Processing Operations lThree cate

2、gories of processing operations: lShaping operations - alter the geometry of the starting work material lProperty enhancing operations - improve physical properties of the material without changing its shape lSurface processing operations - clean, treat, coat, or deposit material onto the exterior s

3、urface of the work5Shaping Four Main CategorieslSolidification Processes - starting material is a heated liquid that solidifies to form part geometrylDeformation Processes - starting material is a ductile solid that is deformedlMaterial Removal Processes - starting material is a ductile/brittle soli

4、d, from which material is removedlAssembly Processes - two or more separate parts are joined to form a new entity Comparing Processes6Stress-Strain RelationshipsFigure 3.3 Typical engineering stress strain plot in a tensile test of a metal.7True Stress-Strain CurveFigure 3.4 True stress strain curve

5、 for the previous engineering stress strain plot in Figure 3.3.8Strain HardeningFigure 3.5 True stress strain curve plotted on log log scale.9Recrystallization and Grain Growth10Scanning electron micrograph taken using backscattered electrons, of a partly recrystallized Al-Zr alloy. The large defect

6、-free recrystallized grains can be seen consuming the deformed cellular microstructure. -50m-Phase Dispersion speed of quenching11Allotropic Transformation and TemperingFigure 6.4 Phase diagram for iron carbon system, up to about 6% carbon.12Tempered MartensiteAustenizingQuenchingFigure 27.5 Precipi

7、tation hardening: (a) phase diagram of an alloy system consisting of metals A and B that can be precipitation hardened; and (b) heat treatment: (1) solution treatment, (2) quenching, and (3) precipitation treatment.Precipitation Hardening - Al 6022 (Mg-Si)13Machining Relationships14Machine ToolWorkp

8、ieceWorkholding ToolCutting Tool Higher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperatureFigure 21.12 Effect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane

9、area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equationEffect of Higher Shear Plane Angle1516Turning Parameters Illustrated17Machining Calculations: TurninglSpindle Speed - N (rpm)lv = cutting speedlDo = outer diameterlFeed Rate - fr (m

10、m/min -or- in/min)lf = feed per revlDepth of Cut - d (mm -or- in)lDo = outer diameterlDf = final diameterlMachining Time - Tm (min)lL = length of cutlMatl Removal Rate - MRR (mm3/min -or- in3/min)oDvN 2foDDdrmfLTfNfrdfvMRR 18Unit Power in Machining lUseful to convert power into power per unit volume

11、 rate of metal cutlCalled the unit power, Pu or unit horsepower, HPulorlTool sharpness is taken into account multiply by 1.00 1.25 lFeed is taken into account by multiplying by factor in Figure 21.14where MRR = material removal rateMRRPPcuMRRHPHPcuWhat if feed changes?19Unit HorsepowerThe significan

12、ce of HPu is that it can be used: 1) to determine the size of the machine tool required to perform a particular cutting operation; and 2) the size of the cutting force on the workholding and cutting tools.20EMRRCHPEHPHPvMRRCHPvHPFMRRCHPHPfucgfuccfuc000,33000,33HPu hp/in3/minCf correction factorMRR i

13、n3/minFc lbV ft/minE machine tool efficiency33,000 conversion between ft-lb & hpExamplelIn a turning operation on stainless steel with hardness = 200 HB, the cutting speed = 200 m/min, feed = 0.25 mm/rev, and depth of cut = 7.5 mm. How much power will the lathe draw in performing this operation

14、if its mechanical efficiency = 90%.lFrom Table 21.2, U = 2.8 N-m/mm3 = 2.8 J/mm3lSince feed is 0.25 mm/rev, the correction factor is 12122Example: SolutionlMRR = vfd l= (200 m/min)(103 mm/m)(0.25 mm)(7.5 mm) l= 375,000 mm3/min = 6250 mm3/slPc = (6250 mm3/s)(2.8 J/mm3)(1.0) = 17,500 J/s l= 17,500 W =

15、 17.5 kWlAccounting for mechanical efficiency, Pg l= 17.5/0.90 = 19.44 kW23lFlow of Molten Liquid Requires HeatinglHeat Transfer of Liquid in Mold Cavity During and After PouringlSolidification into ComponentCastingCommon process attributes: 24Gating System Channel through which molten metal flows i

16、nto cavity from outside of mold Consists of a downsprue, through which metal enters a runner leading to the main cavity At top of downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue25Pouring CalculationsMinimum mold filling time, MFT MFT =V/QQ:

17、volumetric flow rate, cm3/sV: mold cavity volume, cm3Chvorinovs Rulewhere TST = total solidification time; V = volume of the casting; A = surface area of casting; n = exponent usually taken to have a value = 2; and Cm is mold constantnmAVCTST26Amount and CompositionFigure 6.2 Phase diagram for the c

18、opper nickel alloy system.Shrinkage in Solidification and CoolingFigure 10.8 Shrinkage of a cylindrical casting during solidification and cooling: (0) starting level of molten metal immediately after pouring; (1) reduction in level caused by liquid contraction during cooling (dimensional reductions are exaggerated for clarity).Shrinkage in S