1. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e PHYSICAL PROPERTIES OF MATERIALS Volumetric and Melting Properties Thermal Properties Mass Diffusion Electrical Properties Electrochemical Processes

2. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Physical Properties Defined Properties that define the behavior of materials in response to physical forces other than mechanical Include: volumetric, thermal, electrical, and electrochemical properties Components in a product must do more than simply withstand mechanical stresses They 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/e Physical Properties in Manufacturing Important in manufacturing because they often influence process performance Examples: In machining, thermal properties of the work material determine the cutting temperature, which affects tool life In 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/e Volumetric and Melting Properties Properties related to the volume of solids and how the properties are affected by temperature Includes: Density Thermal expansion Melting point

5. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Density and Specific Gravity Defined Density = weight per unit volume Typical units are g/cm3 (lb/in3) Determined by atomic number and other factors such as atomic radius, and atomic packing Specific 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/e Why Density is Important Important consideration in material selection for a given application, but it is generally not the only property of interest Strength is also important, and the two properties are often related in a strength‑to‑weight ratio, which is tensile strength divided by density Useful 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/e Thermal Expansion Density of a material is a function of temperature In general, density decreases with increasing temperature Volume per unit weight increases with increasing temperature Thermal expansion is the name for this effect of temperature on density Measured by coefficient of thermal expansion 

8. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Coefficient of Thermal Expansion Change 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/e Thermal Expansion in Manufacturing Thermal expansion is used in shrink fit and expansion fit assemblies Part is heated to increase size or cooled to decrease size to permit insertion into another part When 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 4.2 A 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/e Assume L1 = 500m at -35ºC Coefficient of Thermal Expansion α = 12 x 10-6/ºC for Steel Table 4.1

12. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Use formula 4.1 L2 – 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/e Each 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/e Melting Characteristics for Elements Melting pointTm of a pure element = temperature at which it transforms from solid to liquid state The reverse transformation occurs at the same temperature and is called the freezing point Heat 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/e Melting of Metal Alloys Unlike pure metals, most alloys do not have a single melting point Instead, melting begins at a temperature called the solidus and continues as temperature increases until converting completely to liquid at a temperature called the liquidus Between 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/e Melting of Alloys: Solidus and Liquidus Figure 6.3 Phase diagram for the tin‑lead alloy system.

17. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Melting of Noncrystalline Materials In noncrystalline materials (glasses), a gradual transition from solid to liquid states occurs The solid material gradually softens as temperature increases, finally becoming liquid at the melting point During 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/e Volume-to-Weight Changes Figure 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/e Importance of Melting in Manufacturing Metal casting - the metal is melted and then poured into a mold cavity Metals with lower melting points are generally easier to cast Plastic molding - melting characteristics of polymers are important in nearly all polymer shaping processes Sintering 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/e Thermal Properties Thermal expansion, melting, and heat of fusion are thermal properties because temperature determines the thermal energy level of the atoms, leading to the changes in materials Additional thermal properties: Specific heat Thermal conductivity These 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/e Specific Heat The quantity of heat energy required to increase the temperature of a unit mass of material by one degree To 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 4.5 With 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/e Use formula 4.2 H = 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/e The weight of aluminum is equal to the Volume x Density W = (10 cm3)(2.70 g/cm3)

25. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Heat = (0.21cal/gºC)(103 cm3)(2.70 g/cm3)(300ºC - 21ºC) Heat = 158,193 cal Conversion: 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/e Why convert from cal to J?

27. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Why 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/e Volumetric Specific Heat The quantity of heat energy required to raise the temperature of a unit volume of material by one degree Density multiplied by specific heat C Volumetric specific heat = C

29. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Thermal Conductivity Thermal conductivity of a material = capability to transfer heat through itself by the physical mechanism of thermal conduction Thermal 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/e Thermal Diffusivity The 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/e Thermal Properties in Manufacturing Important 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 ceramics In other cases, heat is generated as a result of the process Examples: cold forming and machining of metals

32. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Mass Diffusion Movement of atoms or molecules within a material or across a boundary between two materials in contact Because 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/e Mass Diffusion Figure 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/e Mass Diffusion in Manufacturing Surface hardening treatments based on diffusion include carburizing and nitriding Diffusion 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/e Electrical Properties Engineering materials exhibit a great variation in their capability to conduct electricity Flow 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/e Electrical Properties Movement of charge carriers is driven by the presence of electric voltage And 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/e Electrical Resistance Resistance 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/e Resistivity 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/e Conductivity Often more convenient to consider a material as conducting electrical current rather than resisting its flow Conductivity 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/e Materials and Electrical Properties Metals are the best conductors of electricity, because of their metallic bonding Most 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/e Semiconductors A material whose resistivity lies between insulators and conductors Most common semiconductor material is silicon, largely because of its abundance in nature, relative low cost, and ease of processing What 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/e Electrical Properties in Manufacturing Electric 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 metal Capacity 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/e Electrochemistry Field of science concerned with the relationship between electricity and chemical changes, and the conversion of electrical and chemical energy In a water solution, molecules of an acid, base, or salt are dissociated into positively and negatively charged ions Ions 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/e Terms in Electrochemical Processes Electrolyte - the ionized solution Electrodes – where current enters and leaves the solution in electrolytic conduction Anode - positive electrode Cathode - negative electrode The whole arrangement is called an electrolytic cell

45. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Electrolysis The name given to these chemical changes occurring in the solution At each electrode, chemical reaction occurs, such as: Deposition or dissolution of material Decomposition of gas from the solution

46. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Electrolysis Example Figure 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/e Chemical Reactions in the Decomposition of Water The 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/e Chemical Reactions in the Decomposition of Water The 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/e Electrolysis in Manufacturing Processes Electroplating ‑ 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 purposes Electrochemical machining ‑ a process in which material is removed from the surface of a metal part Production of hydrogen and oxygen gases