Ch04 with problems
- 1. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/ePHYSICAL PROPERTIES OF MATERIALSVolumetric and Melting PropertiesThermal PropertiesMass DiffusionElectrical PropertiesElectrochemical Processes
- 2. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/ePhysical Properties DefinedProperties that define the behavior of materials in response to physical forces other than mechanicalInclude: volumetric, thermal, electrical, and electrochemical propertiesComponents in a product must do more than simply withstand mechanical stressesThey must conduct electricity (or prevent conduction), allow heat to transfer (or allow its escape), transmit light (or block transmission), and satisfy many other functions
- 3. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/ePhysical Properties in ManufacturingImportant in manufacturing because they often influence process performanceExamples:In machining, thermal properties of the work material determine the cutting temperature, which affects tool lifeIn microelectronics, electrical properties of silicon and how these properties can be altered by chemical and physical processes is the basis of semiconductor manufacturing
- 4. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eVolumetric and Melting PropertiesProperties related to the volume of solids and how the properties are affected by temperature Includes: DensityThermal expansionMelting point
- 5. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eDensity and Specific Gravity DefinedDensity = weight per unit volume Typical units are g/cm3 (lb/in3) Determined by atomic number and other factors such as atomic radius, and atomic packingSpecific gravity = density of a material relative to density of water and is a ratio with no units
- 6. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eWhy Density is ImportantImportant consideration in material selection for a given application, but it is generally not the only property of interestStrength is also important, and the two properties are often related in a strength‑to‑weight ratio, which is tensile strength divided by densityUseful ratio in comparing materials for structural applications in aircraft, automobiles, and other products where weight and energy are concerns
- 7. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal ExpansionDensity of a material is a function of temperatureIn general, density decreases with increasing temperatureVolume per unit weight increases with increasing temperatureThermal expansion is the name for this effect of temperature on densityMeasured by coefficient of thermal expansion
- 8. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eCoefficient of Thermal ExpansionChange in length per degree of temperature, such as mm/mm/C (in/in/F) Length ratio rather than volume ratio because this is easier to measure and apply Change in length for a given temperature change is: L2 ‑ L1 = L1 (T2 ‑ T1) where = coefficient of thermal expansion; L1 and L2 are lengths corresponding respectively to temperatures T1 and T2
- 9. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal Expansion in ManufacturingThermal expansion is used in shrink fit and expansion fit assembliesPart is heated to increase size or cooled to decrease size to permit insertion into another partWhen part returns to ambient temperature, a tightly‑fitted assembly is obtained Thermal expansion can be a problem in heat treatment and welding due to thermal stresses that develop in material during these processes
- 10. Problem 4.2A bridge built with steel girders is 500 m in length and 50 m in width. Expansion joints are provided to compensate for the change in length in the support girders as the temperature fluctuates. Each expansion joint can compensate for a maximum of 100mm of change in length. From historical records it is estimated that the minimum and maximum temperatures in the region will be -35ºC and 38ºC, respectively. What is the minimum number of expansion joints required?
- 11. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eAssume L1 = 500m at -35ºCCoefficient of Thermal Expansionα = 12 x 10-6/ºC for Steel Table 4.1
- 12. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eUse formula 4.1L2 – L1 = αL1(T2 – T1)L2 - L1 = 12 x 10-6(500)(38-(-35))L2 - L1 = 0.42 m
- 13. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eEach expansion joint will control 100mm = 0.1 m of expansion. 4 joints will provide 0.400 m of expansion. 5 joints will provide 0.500 m of expansion.Therefore a minimum of 5 joints are needed for coverage of the total length.
- 14. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMelting Characteristics for ElementsMelting pointTm of a pure element = temperature at which it transforms from solid to liquid stateThe reverse transformation occurs at the same temperature and is called the freezing pointHeat of fusion = heat energy required at Tm to accomplish transformation from solid to liquid
- 15. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMelting of Metal AlloysUnlike pure metals, most alloys do not have a single melting pointInstead, melting begins at a temperature called the solidus and continues as temperature increases until converting completely to liquid at a temperature called the liquidusBetween the two temperatures, the alloy is a mixture of solid and molten metals Exception: eutectic alloys melt (and freeze) at a single temperature
- 16. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMelting of Alloys: Solidus and LiquidusFigure 6.3 Phase diagram for the tin‑lead alloy system.
- 17. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMelting of Noncrystalline MaterialsIn noncrystalline materials (glasses), a gradual transition from solid to liquid states occursThe solid material gradually softens as temperature increases, finally becoming liquid at the melting pointDuring softening, the material has a consistency of increasing plasticity (increasingly like a fluid) as it gets closer to the melting point
- 18. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eVolume-to-Weight ChangesFigure 4.1 Changes in volume per unit weight (1/density) as a function of temperature for a hypothetical pure metal, alloy, and glass.
- 19. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eImportance of Melting in ManufacturingMetal casting - the metal is melted and then poured into a mold cavityMetals with lower melting points are generally easier to cast Plastic molding - melting characteristics of polymers are important in nearly all polymer shaping processesSintering of powdered metals - sintering does not melt the material, but temperatures must approach the melting point in order to achieve the required bonding of powders
- 20. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal PropertiesThermal expansion, melting, and heat of fusion are thermal properties because temperature determines the thermal energy level of the atoms, leading to the changes in materialsAdditional thermal properties:Specific heatThermal conductivityThese properties relate to the storage and flow of heat within a substance
- 21. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eSpecific Heat The quantity of heat energy required to increase the temperature of a unit mass of material by one degreeTo determine the energy to heat a certain weight of metal to a given temperature: H = C W (T2 ‑ T1) where H = amount of heat energy; C = specific heat of the material; W = its weight; and (T2 ‑ T1) = change in temperature
- 22. Problem 4.5With reference to Table 4.2, determine the quantity of heat required to increase the temperature of an aluminum block that is 10 cm x 10 cm x 10 cm from room temperature (21ºC) to 300ºC.
- 23. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eUse formula 4.2H = CW(T2 – T1)The Specific Heat of aluminum from Table 4.2 is C = 0.21Cal/gºC
- 24. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThe weight of aluminum is equal to the Volume x DensityW = (10 cm3)(2.70 g/cm3)
- 25. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eHeat = (0.21cal/gºC)(103 cm3)(2.70 g/cm3)(300ºC - 21ºC)Heat = 158,193 calConversion: 1.0 cal = 4.184 J, so Heat = 661,879 J
- 26. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eWhy convert from cal to J?
- 27. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eWhy convert from cal to J?Calories is a unit of work; Joules is a unit of heat energy.
- 28. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eVolumetric Specific Heat The quantity of heat energy required to raise the temperature of a unit volume of material by one degreeDensity multiplied by specific heat CVolumetric specific heat = C
- 29. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal ConductivityThermal conductivity of a material = capability to transfer heat through itself by the physical mechanism of thermal conductionThermal conduction = transfer of thermal energy within a material from molecule to molecule by purely thermal motions; no transfer of mass Measure= coefficient ofthermal conductivityk. Units: J/s mm C (Btu/in hr F) Coefficient of thermal conductivity is generally high in metals, low in ceramics and plastics
- 30. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal DiffusivityThe ratio of thermal conductivity to volumetric specific heat is frequently encountered in heat transfer analysis
- 31. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eThermal Properties in ManufacturingImportant in manufacturing because heat generation is common in so many processes In some cases, heat is the energy that accomplishes the process Examples: heat treating, sintering of powder metals and ceramicsIn other cases, heat is generated as a result of the processExamples: cold forming and machining of metals
- 32. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMass DiffusionMovement of atoms or molecules within a material or across a boundary between two materials in contactBecause of thermal agitation of the atoms in a material (solid, liquid, or gas), atoms are continuously moving about In liquids and gases, where the level of thermal agitation is high, it is a free‑roaming movement In metals, atomic motion is facilitated by vacancies and other imperfections in the crystal structure
- 33. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMass DiffusionFigure 4.2 Mass diffusion: (a) model of atoms in two solid blocks in contact: (1) when two pieces are first brought together, each has its own compositions; (2) after time, an exchange of atoms occurs; and (3) eventually, a uniform concentration occurs. The concentration gradient dc/dx for metal A is plotted in (b).
- 34. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMass Diffusion in ManufacturingSurface hardening treatments based on diffusion include carburizing and nitridingDiffusion welding - used to join two components by pressing them together and allowing diffusion to occur across boundary to create a permanent bond Diffusion is also used in electronics manufacturing to alter the surface chemistry of a semiconductor chip in very localized regions to create circuit details
- 35. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrical PropertiesEngineering materials exhibit a great variation in their capability to conduct electricityFlow of electrical current involves movement of charge carriers ‑ infinitesimally small particles possessing an electrical charge In solids, these charge carriers are electrons In a liquid solution, charge carriers are positive and negative ions
- 36. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrical PropertiesMovement of charge carriers is driven by the presence of electric voltageAnd resisted by the inherent characteristics of the material, such as atomic structure and bonding between atoms and molecules Ohm's law: I = where I = current, A, E = voltage, V, and R = electrical resistance,
- 37. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrical ResistanceResistance in a uniform section of material (e.g., a wire) depends on its length L, cross‑sectional area A, and resistivity of the material r or where resistivity r has units of ‑m2/m or ‑m (‑in.)
- 38. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eResistivity Property that defines a material's capability to resist current flow Resistivity is not a constant; it varies, as do so many other properties, with temperature For metals, resistivity increases with temperature
- 39. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eConductivityOften more convenient to consider a material as conducting electrical current rather than resisting its flowConductivity of a material is simply the reciprocal of resistivity: Electrical conductivity = where conductivity has units of (‑m)‑1 or (‑in)‑1
- 40. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eMaterials and Electrical PropertiesMetals are the best conductors of electricity, because of their metallic bondingMost ceramics and polymers, whose electrons are tightly bound by covalent and/or ionic bonding, are poor conductors Many of these materials are used as insulators because they possess high resistivities
- 41. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eSemiconductors A material whose resistivity lies between insulators and conductorsMost common semiconductor material is silicon, largely because of its abundance in nature, relative low cost, and ease of processingWhat makes semiconductors unique is the capacity to significantly alter conductivities in their surface chemistries in very localized areas to fabricate integrated circuits
- 42. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrical Properties in ManufacturingElectric discharge machining - uses electrical energy in the form of sparks to remove material from metals The important welding processes, such as arc welding and resistance spot welding, use electrical energy to melt the joint metalCapacity to alter electrical properties of semiconductor materials is the basis for microelectronics manufacturing
- 43. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrochemistryField of science concerned with the relationship between electricity and chemical changes, and the conversion of electrical and chemical energyIn a water solution, molecules of an acid, base, or salt are dissociated into positively and negatively charged ionsIons are the charge carriers in the solution They allow electric current to be conducted, playing the same role that electrons play in metallic conduction
- 44. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eTerms in Electrochemical ProcessesElectrolyte - the ionized solutionElectrodes – where current enters and leaves the solution in electrolytic conductionAnode - positive electrodeCathode - negative electrode The whole arrangement is called an electrolytic cell
- 45. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrolysisThe name given to these chemical changes occurring in the solutionAt each electrode, chemical reaction occurs, such as: Deposition or dissolution of materialDecomposition of gas from the solution
- 46. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrolysis ExampleFigure 4.3 Example of electrolysis: decomposition of water; electrolyte = dilute sulfuric acid (H2SO4); electrodes = platinum and carbon (both chemically inert).
- 47. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eChemical Reactions in the Decomposition of WaterThe electrolyte dissociates into the ions H+ and SO4=H+ ions are attracted to negatively charged cathode; upon reaching it they acquire an electron and combine into molecules of hydrogen gas 2H+ + 2e H2 (gas)
- 48. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eChemical Reactions in the Decomposition of WaterThe SO4= ions are attracted to the anode, transferring electrons to it to form additional sulfuric acid and liberate oxygen 2SO4= ‑ 4e + 2 H2O 2H2SO4 + O2 The product H2SO4 is dissociated into ions of and SO4= again and so the process continues
- 49. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/eElectrolysis in Manufacturing ProcessesElectroplating ‑ an operation that adds a thin coating of one metal (e.g., chromium) to the surface of a second metal (e.g., steel) for decorative or other purposesElectrochemical machining ‑ a process in which material is removed from the surface of a metal part Production of hydrogen and oxygen gases