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Introduction to Mechanical Engineering Sciences --- KTU

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BE 101-2 -- Introduction to Mechanical Engineering Sciences
Module VI -- Manufacturing Engineering & Materials -- APJ Abdul kalam Technological University --- KTU

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Introduction to Mechanical Engineering Sciences --- KTU

  1. 1. 16-11-2015 1 Manufacturing Engineering & Materials BE 101-2 Introduction to Mechanical Engineering Sciences Module VI Prepared by: Mr. Rejeesh C R, Asst. Professor, Dept. of Mechanical Engineering Federal Institute of Science and Technology Introduction What is Manufacturing? The word manufacture first appeared in English in 1567 and is derived from the Latin manu factus, meaning “made by hand.” The word manufacturing first appeared in 1683, and the word production, which is often used interchangeably with the word manufacturing, first appeared sometime during the 15th century. A manufactured item typically starts with raw materials, which are then subjected to a sequence of processes to make individual products, it has a certain value. 2 History of Manufacturing • Manufacturing dates back to the period 5000-4000 B.C., and thus, it is older than recorded history, the earliest forms of which were invented by the Sumerians around 3500 B.C. • Primitive cave drawings, as well as markings on clay tablets and stone, needed (1) some form of a brush and some sort of “paint,” as in the prehistoric cave paintings in Lascaux, France, estimated to be 16,000 years old; (2) some means of scratching the clay tablets and baking them, as in cuneiform scripts and pictograms of 3000 B.C.; and (3) simple tools for making incisions and carvings on the surfaces of stone, as in the hieroglyphs in ancient Egypt. 3 History of Manufacturing • The manufacture of items for specific uses began with the production of various household artifacts, which were typically made of either wood, stone, or metal. • The materials first used in making utensils and ornamental objects included gold, copper, and iron, followed by silver, lead, tin, bronze (an alloy of copper and tin), and brass (an alloy of copper and zinc). • The processing methods first employed involved mostly casting and hammering, because they were relatively easy to perform. Over the centuries, these simple processes gradually began to be developed into more complex operations, at increasing rates of production and higher levels of product quality. Note, for example, the lathes for cutting screw threads already were available during the period from 1600 to 1700, but it was not until some three centuries later that automatic screw machines were developed. 4 History of Manufacturing  Although iron making began in the Middle East in about 1100 B.C., a major milestone was the production of steel in Asia during the period 600-800 A.D.  A wide variety of materials continually began to be developed. Today, countless metallic and non-metallic materials with unique properties are available, including engineered materials and various advanced materials.  Among the available materials are industrial or high-tech ceramics, reinforced plastics, composite materials, and nano- materials that are now used in an extensive variety of products, ranging from prosthetic devices and computers to supersonic aircraft. 5 History of Manufacturing • Until the Industrial Revolution, which began in England in the 1750s and is also called the First Industrial Revolution, goods had been produced in batches and required much reliance on manual labour in all phases of their production. • The Second Industrial Revolution is regarded by some as having begun in the mid-1900s with the development of solid-state electronic devices and computers. • Mechanization began in England and other countries of Europe, basically with the development of textile machinery and machine tools for cutting metal. This technology soon moved to the United States, where it continued to be further developed. 6
  2. 2. 16-11-2015 2 History of Manufacturing • A major advance in manufacturing occurred in the early 1800s with the design, production, and use of interchangeable parts, conceived by the American manufacturer and inventor Eli Whitney (1765-1825). • Prior to the introduction of interchangeable parts, much hand fitting was necessary because no two parts could be made exactly alike. • By contrast, it is now taken for granted that a broken bolt can easily be replaced with an identical one produced decades after the original. Further developments soon followed, resulting in countless consumer and industrial products that we now cannot imagine being without. 7 History of Manufacturing • Beginning in the early 1940s, several milestones were reached in all aspects of manufacturing. Note particularly the progress that has been made during the 20th century, compared with that achieved during the 40-century period from 4000 B.C. to 1 B.C. • For eg, in the Roman Empire (~500 B.C. to 476 A.D.), factories were available for the mass production of glassware; however, the methods used were generally very slow, and much manpower was involved in handling the parts and operating the machinery. Today, production methods have advanced to such an extent that (a) aluminium beverage cans are made at rates of more than 500 per minute, with each can costing about four cents to make, (b) holes in sheet metal are punched at rates of 800 holes per minute, and (c) incandescent light bulbs are made at rates of more than 2000 bulbs per minute, each costing less than one dollar. 8 9 10 11 Engineering Materials metals, alloys, composites • Based on chemical make up and atomic structure, solid materials have been conveniently grouped into three basic categories: metals, ceramics and polymers. • Most materials fall into one distinct grouping or another, although there are also some intermediates. In addition to these, there are also three other groups of important engineering materials: composites, semiconductors and biomaterials. • There are also advanced materials utilized in high-technology applications. Recently, a group of new and state of the art materials called as smart (or intelligent) materials being developed. Very recently, scientists have developed nano- engineering materials. 12
  3. 3. 16-11-2015 3 Engineering Materials A brief description of the material types and representative characteristics are: 13 Engineering Materials Nanomaterials, shape-memory alloys, superconductors, … Ferrous metals: carbon steels, alloy steels, stainless steels, tool steels and die steels Non-ferrous metals: aluminum, magnesium, copper, nickel, titanium, superalloys, refractory metals, beryllium, zirconium, low-melting alloys, gold, silver, platinum, … Plastics: thermoplastics (acrylic, nylon, polyethylene, ABS,…) thermosets (epoxies, Polymides, Phenolics, …) elastomers (rubbers, silicones, polyurethanes, …) Ceramics: Glasses, Graphite, Diamond, Cubic Boron Nitride Composites: reinforced plastics, metal-, ceramic matrix composites 14 Metals and Alloys • True metals are pure elements, while alloys are blends of two or more metals that have been melted together. • Metallic materials have large number of non localized electrons, i.e. electrons are not bound to particular atoms. Many properties of metals are directly attributable to these electrons. (Conductivity) • All metals are characterized by metallic properties, e.g. lustre, opacity, malleability, ductility and electrical conductivity. • Although metals compose about 3/4th of the known elements but few find service in their pure form. The desired properties for engineering purposes are often found in alloys. • Typical examples of metallic materials are iron, aluminium, copper, zinc, etc. and their alloys. They can be used either in bulk or powder form. 15 Metals and Alloys • Metals are extremely good conductors of electricity and heat are not transparent to visible light; a polished metal surface has a lustrous appearance. Moreover, metals are quite strong, yet deformable, which accounts for their extensive use in structural applications. • Metallic materials are always crystalline in nature. Scientists have developed amorphous (non-crystalline) alloys by very rapid cooling of a melt or by very high-energy mechanical milling. • Recently, scientists have developed materials through rapid solidification called as quasi-crystals. These are neither crystalline nor amorphous, but form an ordered structure somewhere between two known structures. These materials are expected to exhibit far reaching electrical properties. 16 Metals • Ferrous Metals – Cast irons – Steels • Super alloys – Iron-based – Nickel-based – Cobalt-based • Non-ferrous metals – Aluminum and its alloys – Copper and its alloys – Magnesium and its alloys – Nickel and its alloys – Titanium and its alloys – Zinc and its alloys – Lead & Tin – Refractory metals – Precious metals Metals used in manufacturing are usually alloys, which are composed of two or more elements, with at least one being a metallic element. Metals and alloys can be divided into two basic groups: (1) ferrous and (2) nonferrous. 17 Metals • Ferrous metals are based on iron; the group includes steel and cast iron. Pure iron has limited commercial use, but when alloyed with carbon, it has greater commercial value than any other metal. • Alloys of iron and carbon form steel and cast iron. Steel can be defined as an iron–carbon alloy containing 0.02% to 2.11% carbon. It is the most important category within the ferrous metal group. • Its composition often includes other alloying elements as well, such as manganese, chromium, nickel, and molybdenum, to enhance the properties of the metal. • Applications of steel include construction (bridges, I-beams, and nails), transportation (trucks, rails, and rolling stock for railroads), and consumer products (automobiles and appliances). 18
  4. 4. 16-11-2015 4 Metals • Cast iron is an alloy of iron and carbon (2% to 4%) used in casting (primarily sand casting). Silicon is also present in the alloy (in amounts from 0.5% to 3%), and other elements are often added also, to obtain desirable properties in the cast part. • Cast iron is available in several different forms, of which grey cast iron is the most common; its applications include blocks and heads for internal combustion engines. • Nonferrous metals include the other metallic elements and their alloys. In almost all cases, the alloys are more important commercially than the pure metals. • The nonferrous metals include the pure metals and alloys of aluminium, copper, gold, magnesium, nickel, silver, tin, titanium, zinc, and other metals. 19 General Properties and Applications of Ferrous Alloys • Ferrous alloys are useful metals in terms of mechanical, physical and chemical properties. • Alloys contain iron as their base metal. • Carbon steels are least expensive of all metals while stainless steels are costly. 20 Carbon and alloy steels Carbon steels • Classified as low, medium and high: 1. Low-carbon steel or mild steel, < 0.3%C, bolts, nuts and sheet plates. 2. Medium-carbon steel, 0.3% ~ 0.6%C, machinery, automotive and agricultural equipment. 3. High-carbon steel, > 0.60% C, springs, cutlery, cable. Alloy steels • Steels containing significant amounts of alloying elements. • Structural-grade alloy steels used for construction industries due to high strength. • Other alloy steels are used for its strength, hardness, resistance to creep and fatigue, and toughness. • It may heat treated to obtain the desired properties. 21 High-strength low-alloy steels (HSLA) • It is a type of alloy steel that provides better mechanical properties like improved strength-to-weight ratio or greater resistance to corrosion than carbon steel. • HSLA steels vary from other steels in that they are not made to meet a specific chemical composition but rather to specific mechanical properties. • Used in automobile bodies to reduce weight and in agricultural equipment. • Some examples are: 1. Dual-phase steels 2. Micro alloyed steels 3. Nano-alloyed steels 22 Stainless Steels • Characterized by their corrosion resistance, high strength and ductility, and high chromium content. • Stainless as a film of chromium oxide protects the metal from corrosion. 23 Stainless steels • Five types of stainless steels: 1. Austenitic steels 2. Ferritic steels 3. Martensitic steels 4. Precipitation-hardening (PH) steels 5. Duplex-structure steels 24
  5. 5. 16-11-2015 5 Tool and die steels • Tool steel is a type of carbon alloy steel that is well- matched for tool manufacturing, such as hand tools or machine dies. • Hardness and ability to retain shape at increased temperatures are the key properties of this material. Designed for high strength, impact toughness, and wear resistance at a range of temperatures. • The presence of carbides in their matrix plays the dominant role in the qualities of tool steel. The four major alloying elements in tool steel that form carbides are: tungsten, chromium, vanadium and molybdenum. 25 Tool and die steels 26 Aluminium and aluminium alloys • Factors for selecting are: 1. High strength to weight ratio. 2. Resistance to corrosion. 3. High thermal and electrical conductivity. 4. Ease of machinability. 5. Non-magnetic. 27 Magnesium and Magnesium alloys • Magnesium (Mg) is the lightest metal. • Alloys are used in structural and non-structural applications. • Typical uses of magnesium alloys are aircraft and missile components. • Also has good vibration-damping characteristics. 28 Copper and Copper alloys  Copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion.  The best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead.  Copper alloys have electrical and mechanical properties, corrosion resistance, thermal conductivity and wear resistance.  Applications are electronic components, springs and heat exchangers. 29 Nickel and Nickel alloys • Nickel alloys are used extensively because of their corrosion resistance, high temperature strength and their special magnetic and thermal expansion properties. • Used in stainless steels and nickel-base alloys. • Alloys are used for high temperature applications, such as jet- engine components and rockets. 30
  6. 6. 16-11-2015 6 Superalloys • A super-alloy, or high-performance alloy, is an alloy that exhibits several key characteristics like excellent mechanical strength, resistance to thermal deformation, good surface stability and resistance to corrosion or oxidation. • The crystal structure is typically face centered cubic austenitic. Superalloys are high-temperature alloys use in jet engines, gas turbines and reciprocating engines. • Inconel is a family of austenite nickel-chromium based super alloys. • The main alloying ingredient is nickel in hastelloy. Other alloying ingredients added are varying percentages of elements of molybdenum, chromium, iron, manganese, cobalt, copper, titanium, zirconium, aluminium, carbon, and tungsten. 31 Superalloys 32 Titanium and Titanium alloys • Titanium (Ti) is expensive, has high strength-to-weight ratio and corrosion resistance. • Used as components for aircrafts, jet-engines, racing-cars and marine crafts. 33 Other nonferrous metals 1. Beryllium 2. Zirconium 3. Low-melting-point metals: - Lead - Zinc - Tin 4. Precious metals: - Gold - Silver - Platinum 34 Refractory metals • Refractory metals have a high melting point and retain their strength at elevated temperatures. • Applications are electronics, nuclear power and chemical industries. • Molybdenum, columbium, tungsten and tantalum are referred to as refractory metal. 1. Shape-memory alloys (i.e. eyeglass frame, helical spring) 2. Amorphous alloys (Metallic Glass) 3. Nanomaterials 4. Metal foams Special Metals and Alloys 35 Classification of Ceramics • Traditional ceramics – clays: kaolinite – silica: quartz, sandstone – alumina – silicon carbide • New ceramics – oxide ceramics : alumina – carbides : silicon carbide, titanium carbide, etc. – nitrides : silicon nitride, boron nitride, etc. • Glass products – window glass, containers – light bulb glass, laboratory glass – glass fibers – optical glass • Glass ceramics - polycrystalline structure 36
  7. 7. 16-11-2015 7 Classification of Polymers • Thermoplastics - reversible in phase by heating and cooling. Solid phase at room temperature and liquid phase at elevated temperature. • Thermosets - irreversible in phase by heating and cooling. Change to liquid phase when heated, then follow with an irreversible exothermic chemical reaction. Remain in solid phase subsequently. • Elastomers – Rubbers Characteristics of Plastics are:  immune to corrosion  Good insulator  unsuitable for higher temperatures  to improve their properties additives are added. 37 Thermosets • A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 2000C), through a chemical reaction (epoxy, for example).  Amino resins, Epoxies  Phenolics, Polyesters, Polyurethanes  Silicones  Thermosets are usually liquid or malleable prior to curing and designed to be molded in to their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors & integrated circuits.  Once hardened, a thermoset resin cannot be reheated and melted back to a liquid form. 38 Thermoplastics • Thermoplastics, also known as a thermosoftening plastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. • Thermoplastic polymers differ from thermosetting polymers in that they can be remelted and remoulded. – Acetals, Acrylics - PMMA – Acrylonitrile-Butadiene-Styrene - ABS – Cellulosics, Fluoropolymers - PTFE , Teflon – Polyamides (PA) - Nylons, Kevlar – Polysters – PET, Polyethylene (PE) - HDPE, LDPE – Polypropylene (PP), Polystyrene (PS) – Polyvinyl chloride (PVC) 39 Elastomers Characteristics of Rubber are  rough, elastic material  unaffected by water  attacked by oil and steam  Usage: gaskets, flexible couplings, vibration mount  Natural rubber  Different Synthetic rubbers – butadiene rubber, butyl rubber, styrene-butadiene rubber – chloroprene rubber, ethylene-propylene rubber – isoprene rubber, nitrile rubber – Polyurethanes, silicones, thermoplastic elastomers 40 What is a composite Material? 41 Wood is a good example of a natural composite, combination of cellulose fiber and lignin. The cellulose fiber provides strength and the lignin is the "glue" that bonds and stabilizes the fiber. Bamboo is a very efficient wood composite structure. The components are cellulose and lignin, as in all other wood, however bamboo is hollow. This results in a very light yet stiff structure. Composite fishing poles and golf club shafts copy this natural design. The ancient Egyptians manufactured composites!!! Adobe bricks are a good example. The combination of mud and straw forms a composite that is stronger than either the mud or the straw by itself. Composite Material Defined Two or more chemically distinct materials which when combined have improved properties over the individual materials. Composites could be natural or synthetic. ―A composite material is composed of two or more physically distinct phases/materials whose combination produces aggregate properties that are different from those of its constituents‖ Examples: – Cemented carbides (WC with Co binder) – Plastic molding compounds containing fillers – Rubber mixed with carbon black – Wood (a natural composite) 42
  8. 8. 16-11-2015 8 Why Composites are Important  Composites can be very strong and stiff, yet very light in weight, so strength-to-weight ratio and stiffness-to-weight ratio are several times greater than steel or aluminum.  Fatigue properties are generally better than for common engineering metals.  Toughness is often greater too  Composites can be designed that do not corrode like steel  Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone. 43 Components of composite materials 44 Composites are combinations of two materials in which one of the material is called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other material called the matrix phase. Typically, reinforcing materials are strong with low densities while the matrix is a ductile/tough material. When a composite designed and fabricated correctly, it combines the strength of reinforcement with the toughness of matrix to achieve a combination of desirable properties not available in a single conventional material. Reinforcement: fibers Carbon, Boron, Organic, Glass, Ceramic, Metallic Matrix materials Polymers, Metals, Ceramics Interface Bonding surface The Reinforcing Phase  Function is to reinforce the matrix phase  Imbedded phase is most commonly one of the following shapes:  Fibers  Particles  Flakes  In addition, the secondary phase can take the form of an infiltrated phase in a skeletal or porous matrix  Example: a powder metallurgy part infiltrated with polymer 45 Fig: Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, (c) flake Composite Structures  Laminar composite structure – conventional  Sandwich structure  Honeycomb sandwich structure 46 Consists of a relatively thick core of low density foam bonded on both faces to thin sheets of a different material. Fig: Laminar composite structures: (b) sandwich structure using foam core 47 Sandwich Structure – Foam Core  An alternative to foam core  Either foam or honeycomb achieves high strength -to - weight and stiffness - to - weight ratios Fig: Laminar composite structures: (c) sandwich structure using honeycomb core 48 Sandwich Structure – Honeycomb Core
  9. 9. 16-11-2015 9 Classification Scheme for Composites 1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals, such as cemented carbides and other cermets 2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with fibers to improve properties, especially in high temperature applications – The least common composite matrix 3. Polymer Matrix Composites (PMCs) - thermosetting resins are widely used in PMCs – Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders 49 Advantages of Composites 50 Higher Specific Strength (strength-to-weight ratio) Composites have a higher specific strength than many other materials. A distinct advantage of composites over other materials is the ability to use many combinations of resins and reinforcements, and therefore custom tailor the mechanical and physical properties of a structure. Corrosion Resistance Composites products provide long-term resistance to severe chemical and temperature environments. Composites are the material of choice for outdoor exposure, chemical handling applications, and severe environment service. Advantages of Composites 51 Design flexibility Composites have an advantage over other materials because they can be molded into complex shapes at relatively low cost. This gives designers the freedom to create any shape or configuration. Boats are a good example of the success of composites. Low Relative Investment One reason the composites industry has been successful is because of the low relative investment in setting-up a composites manufacturing facility. This has resulted in many creative and innovative companies in the field. Advantages of Composites 52 Durability Composite products and structures have an exceedingly long life span. Coupled with low maintenance requirements, the longevity of composites is a benefit in critical applications. In a half-century of composites development, well-designed composite structures have yet to wear out. In 1947 the U.S. Coast Guard built a series of forty-foot patrol boats, using polyester resin and glass fiber. These boats were used until the early 1970’s when they were decommissioned because the design was outdated. Extensive testing was done on the laminates after decommissioning, and it was found that only 2-3% of the original strength was lost after twenty-five years of hard service. Disadvantages of Composites 53  Composites are heterogeneous Properties in composites vary from point to point in the material. Most engineering structural materials are homogeneous.  Many of the polymer based composites are subject to attack by chemicals or solvents, just as the polymers themselves are susceptible to attack.  Composite materials are generally expensive.  Manufacturing methods for shaping composite materials are often slow and costly. Disadvantages of Composites 54  Composites are highly anisotropic The strength in composites vary as the direction along which we measure changes (most engineering structural materials are isotropic). As a result, all other properties such as, stiffness, thermal expansion, thermal and electrical conductivity and creep resistance are also anisotropic. The relationship between stress and strain (force and deformation) is much more complicated than in isotropic materials. The experience and intuition gained over the years about the behavior of metallic materials does not apply to composite materials.
  10. 10. 16-11-2015 10 Disadvantages of Composites 55  Composites materials are difficult to inspect with conventional ultrasonic, eddy current and visual NDI methods such as radiography. American Airlines Flight 587, broke apart over New York on Nov. 12, 2001 (265 people died). Airbus A300’s 27-foot-high tail fin tore off. Much of the tail fin, including the so-called tongues that fit in grooves on the fuselage and connect the tail to the jet, were made of a graphite composite. The plane crashed because of damage at the base of the tail that had gone undetected despite routine nondestructive testing and visual inspections. The Crystal Structure of Metals  When metals solidify from a molten state, the atoms arrange themselves into various orderly configurations, called crystals; this atomic arrangement is called crystal structure or crystalline structure.  The smallest group of atoms showing the characteristic lattice structure of a particular metal is known as a unit cell. It is the building block of a crystal, and a single crystal can have many unit cells. 56 The Crystal Structure of Metals The following are the four basic atomic arrangements in metals: l. Simple cubic (SC); examples: alpha - polonium 2. Body-centered cubic (bcc); examples: alpha iron, chromium, molybdenum, tantalum, tungsten, and vanadium. 3. Face-centered cubic (fcc); examples: gamma iron, aluminium, copper, nickel, lead, silver, gold, and platinum. 4. Hexagonal close-packed (hcp); examples: beryllium, cadmium, cobalt, magnesium, alpha titanium, zinc, and zirconium. • These structures when represented in illustrations; each sphere represents an atom. The distance between the atoms in these crystal structures is on the order of 0.1 nm. 57 Simple Cubic Fig The Simple cubic (sc) crystal structure: (a) hard-ball model; (b) unit cell; • Each layer is stacked on the previous layer perfectly. • There are 8 eighths (one in each corner) for a total of ONE atom in the unit cell. 58 Coordination Number • CN, the coordination number, which is the number of closest neighbours to which an atom is bonded. 59 5 Atomic Packing Factor (No. of atoms/unit cell) X volume of each atom Volume of unit cell APF = In crystallography, atomic packing factor (APF), packing efficiency is the fraction of volume in a crystal structure that is occupied by constituent particles. It is dimensionless and always less than unity. 60
  11. 11. 16-11-2015 11 4 • Rare due to poor packing (only Po has this structure) • Close-packed directions are cube edges. • Coordination # = 6 (# nearest neighbors) Simple Cubic Structure (SC) APF for a simple cubic structure = 0.52 61 Body-Centered Cubic Crystal Structure Fig The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; • Each layer is offset from the layer before. Arrangements duplicate themselves every other layer. • There are 8 eights (one in each corner) and one full atom in the centre for a total of Two atoms in the unit cell. 62 a R 9 • APF for a body-centered cubic structure = 0.68 Unit cell contains: 1 + 8 x 1/8 = 2 atoms/unit cell Atomic Packing Factor: BCC • Coordination # = 8 63 Face-Centered Cubic Crystal Structure Fig: The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; • Each layer is offset from the layer before. Arrangements duplicate themselves every third layer. • There are 8 eighths (one in each corner), and 6 halves (one on each face of the cube) for a total of Four atoms in the unit cell. 64 Unit cell contains: 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell a 7 • APF for a body-centered cubic structure = 0.74 Atomic Packing Factor: FCC Coordination # = 12 65 Hexagonal Close Packed Crystal Structure Fig: The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells. 66
  12. 12. 16-11-2015 12 10 • Coordination # = 12 Number of atoms per unit cell : 12 (corner atoms) x 1/6 + 3 (interior atoms) + 2 (face atoms) x 1/2= 6 atoms / unit cell • APF = 0.74 Hexagonal Close-packed Structure (HCP) 67 Definition of Heat Treatment Heat treatment is an operation or combination of operations involving heating at a specific rate, soaking at a temperature for a period of time and cooling at some specified rate. The aim is to obtain a desired microstructure to achieve certain predetermined properties (physical, mechanical, magnetic or electrical). 68 Objectives of Heat Treatment Processes The major objectives are • to increase strength, hardness and wear resistance (hardening) • to increase ductility, toughness and softness (tempering, annealing) • to obtain fine grain size (annealing, normalising) • to remove internal stresses induced by differential deformation by cold working, non-uniform cooling from high temperature during casting and welding (stress relief annealing) 69 • to improve machinability (annealing and normalizing) • to improve cutting properties of tool steels (hardening and tempering) • to improve surface properties (surface hardening, corrosion resistance-stabilizing treatment and surface treatment) • to improve electrical properties (recrystallization, tempering, age hardening) • to improve magnetic properties (hardening, phase transformation) 70 Objectives of Heat Treatment Processes Annealing • It alters the physical and chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. • It involves heating of material above recrystallization temperature, maintaining it for some time and then cooling. • In the cases of copper, steel, silver and brass, this process is performed by heating the material (until glowing) for a while and then slowly cooling to room temperature in still air. • Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. • In this fashion, the metal is softened and prepared for further work -- such as shaping, stamping, or forming. 71 Hardening • Hardening is used to increase the hardness of a metal. A harder metal will have a higher resistance to plastic deformation than a less hard metal. • Hardening is a form of heat treatment in which a metal part is heated and then quenched. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part. • Martensitic transformation, is a hardening mechanism specific for steel. The steel must be heated to a temperature where the iron phase changes from ferrite into austenite, i.e. changes crystal structure from BCC to FCC. • In austenitic form, steel can dissolve more carbon. Once the carbon has been dissolved, the material is then quenched with a high cooling rate so that the carbon does not have time to form precipitates of carbides. When the temperature is low enough, the steel tries to return to the low temperature crystal structure BCC. This change is very quick and is called a martensitic transformation. This phase is called martensite, and is extremely hard. 72
  13. 13. 16-11-2015 13 Quenching • Quenching is the rapid cooling of a work piece to obtain favourable material properties… For instance, it can reduce crystallinity and thereby increase the hardness of both alloys and plastics. • It is commonly used to harden steel by introducing martensite, in which case the steel must be rapidly cooled, the temperature at which austenite becomes unstable. • Extremely rapid cooling can prevent the formation of crystal structure, resulting in amorphous metal or "metallic glass". • If the percentage of carbon is less than 0.4 %, quenching is not possible. 73 Tempering • Tempering is used to increase the toughness of iron- based alloys. • Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. • The exact temperature determines the amount of hardness removed, and depends on both the composition of the alloy and on the desired properties in the finished product. • For instance, very hard tools are often tempered at low temperatures, while springs are tempered to much higher temperatures. 74 Normalizing • Normalizing is for making the material softer but does not produce the uniform material properties of annealing. • A material can be normalized by heating it to a specific temperature and then letting the material cool to room temperature outside of the oven. • Normalising refines the grain size, improves the uniformity of microstructure and properties of hot rolled steel. • Normalizing is used in some plate mills, in the production of large forgings such as railroad wheels and axles, some bar products. This process is less expensive than annealing. 75 Carburizing • In carburization iron or steel absorbs carbon, when the metal is heated in the presence of carbon bearing materials like charcoal or carbon monoxide, with the intent of making the metal harder. • Depending on the amount of time and temperature, the affected area can vary in carbon content. Longer carburizing times and higher temperatures typically increase the depth of carbon diffusion. • When the iron or steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard via the transformation from austenite to martensite, while the core remains soft and tough as a ferritic and/or pearlite microstructure. 76 Carburizing • This manufacturing process can be characterized by the following key points:  It is applied to low-carbon work pieces;  work pieces are in contact with a high-carbon gas, liquid or solid;  it produces a hard work piece surface;  work piece cores largely retain their toughness and ductility;  it produces case hardness depths of up to 0.25 inches (6.4 mm). • In some cases it serves as a remedy for undesired decarburization that happened earlier in a manufacturing process. 77 Properties of materials Mechanical properties of materials Strength, Toughness, Hardness, Ductility, Elasticity, Fatigue and Creep Chemical properties Oxidation, Corrosion, Flammability, Toxicity, … Physical properties Density, Specific heat, Melting and boiling point, Thermal expansion and conductivity, Electrical and magnetic properties 78
  14. 14. 16-11-2015 14 Mechanical Properties • Subgroup of physical properties. • response to force or stress – force – a push or pull – stress – force causing a deformation or distortion (force per unit area) Stress is the applied force or system of forces that tends to deform a body. From the perspective of what is happening within a material, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. 79 80 Types of Stresses Tension Compression TorsionShear Mechanical Properties Examples • Workability – malleability – can be flattened – ductility – can be drawn into wire (stretched), bent, or extruded • Brittleness - breaks instead of deforming when stress is applied 81 • elasticity – ability to return to original shape after being deformed by stress – rubber ball or piece of elastic • plasticity – retains new shape after being deformed by stress – wet clay ball or piece of saran wrap Mechanical Properties Examples 82 • hardness – resistance to denting or scratching – Brinell Hardness, Vickers hardness and Rockwell test are used to measure hardness. Mechanical Properties Examples 83 Mechanical Properties Examples • Strength is the ability of a material to resist deformation. The strength of a component is usually considered based on the maximum load that can be borne before failure. • Toughness is the ability of a material to absorb energy and plastically deform without fracturing. Impact strength is the ability to withstand sudden impact without fracture. • Impact strength/Toughness –- Charpy test, IZOD test. • Universal testing machine is used to find compressive strength, tensile strength and bending strength. 84
  15. 15. 16-11-2015 15 Mechanical Properties Examples • Fatigue is the phenomenon of sudden fracture of a component after a period of cyclic loading in the elastic regime. Failure is the end result of a process involving initiation and growth of a crack, usually at the site of stress concentration on the surface. Eventually after reaching a critical size, the crack will propagate suddenly, and the structure will fracture. • Creep (cold flow) is the tendency of a material to deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. A yield strength of a material is defined as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. 85 Methods of Manufacturing 1. Shaping processes Casting, forging, rolling etc.. 2. Machining processes Turning, Milling, drilling, grinding etc.. 3. Joining processes Welding, soldering, riveting etc.. 86 Moulding Mould A mould is a cavity or void made in a compact sand mass, which when filled molten metal, will produce a casting of the desired shape. The mould made in the sand is known as sand mould. The process of producing a mould or cavity in the sand is called moulding. A casting can be defined as a molten material that has been poured into a prepared cavity and allowed to solidify. Casting Sand Casting Making of castings in moulds of sand or similar material. The principal metals used are cast irons and steel, brass and other copper alloys, aluminium and magnesium alloys. The softer alloys of lead, tin etc. are usually cast in steel moulds or dies. The principal raw material used in moulding. The sand in moulding is silica, the oxide of silica. The factors to be controlled in the preparation of sand for making moulds are clay content, moisture content, grain size permeability, and strength of the sand. Moulding Sand 89 Green sand It is moist sand containing about 5% moisture. Moulds and cores may be made from green sand.  Both moulds and cores may be baked to drive out the moisture.  However, the most commonly used moulds are of that is not dried. They are called green sand moulds. The moisture content and permeability may be closely controlled to prevent the trapping of gases which could cause voids in the casting. Green sand moulds are those sand moulds, in which moisture is present in the sand at the time of pouring the molten metal. 90
  16. 16. 16-11-2015 16 Main Constituents of Mould Sand • Silica sand Binder • Additives Water Binder impart sufficient strength and cohesiveness to the moulding sand so as to retain its shape after the mould has been rammed and the pattern withdrawn. Additives are added to the moulding sand to improve upon some of its existing properties or to impart new properties to it. Water content is mainly responsible for enabling the clay to impart the desired strength to the sand. 91 Green-Sand Moulding The sand is mixed with water and suitable proportions of bonding agents, as this mixture, in wet (or “green”) state, is used for making the moulds.  The mould is prepared in the usual manner. Molten metal is poured into the mould through the runner. There is no need of baking the mould before pouring. Most of the small and medium sized castings, particularly non-ferrous ones, are made by green-sand moulding. 92 Advantages of Casting Complicated shapes can be obtained in quantities at low cost. Within certain limits the units are identical in size and properties. Replacement can be quickly obtained, provided the pattern is kept safe. Certain castings, being solid integral units, are more rigid than built up units. Cast metals and alloys, in general, resist creep under high temperature conditions better than the wrought product. Steps in making a Casting • The making of a pattern, which may be in exactly the same form as the finished product • The actual making of the mould in sand. • The pouring into the mould of molten metal, which is allowed to solidify. • The removal of casting from the sand, and its cleaning by removing all superfluous adherent metal a process called dressing or fettling. 94 Properties of Moulding Sands  Permeability  Cohesiveness  Adhesiveness  Plasticity  Refractoriness 95 Making a Sand Mould 96
  17. 17. 16-11-2015 17 Core and Core Prints • Castings are often required to have holes, recesses, etc. of various sizes and shapes. These impressions can be obtained by using cores. • So where core is required, provision should be made to support the core inside the mold cavity. Core prints are used to serve this purpose. • The core print is an added projection on the pattern and it forms a seat in the mold on which the sand core rests during pouring of the mold. • The core print must be of adequate size and shape so that it can support the weight of the core during the casting operation. • Depending upon the requirement a core can be placed horizontal, vertical and can be hanged inside the mold cavity. 97 Pattern having core prints. 98 Pattern Making:  A Pattern is a model or the replica of the object to be cast.  Except for the various allowances a pattern exactly resembles the casting to be made.  A pattern is required even if one object has to be cast. 99 Pattern Allowances: A pattern is larger in size as compared to the final casting, because it carries certain allowances due to metallurgical and mechanical reasons for example, shrinkage allowance is the result of metallurgical phenomenon where as machining, draft, distortion, shake and other allowances are provided on the patterns because of mechanical reasons. 100 Types of Pattern Allowances: The various pattern allowances are: 1. shrinkage or contraction allowance. 2. Machining or finish allowance. 3. Draft or tapper allowances. 4. Distortion or camber allowance. 5. Shake or rapping allowance. 101 1. Shrinkage Allowance: All most all cast metals shrink or contract volumetrically on cooling. The metal shrinkage is of two types: 1. Liquid Shrinkage: It refers to the reduction in volume when the metal changes from liquid state to solid state at the solidus temperature. To account for this shrinkage; riser, which feed the liquid metal to the casting, are provided in the mold. 2. Solid Shrinkage: It refers to the reduction in volume caused when metal loses temperature in solid state. To account for this, shrinkage allowance is provided on the patterns. 102
  18. 18. 16-11-2015 18  Almost all cast metals shrink or contract volumetrically after solidification and therefore the pattern to obtain a particular sized casting is made oversize by an amount equal to that of shrinkage or contraction.  Different metals shrink at different rates because shrinkage is the property of the cast metal/alloy.  The metal shrinkage depends upon: 1. The cast metal or alloy. 2. Pouring temp. of the metal/alloy. 3. Casted dimensions(size). 4. Casting design aspects. 5. Molding conditions(i.e., mould materials and molding methods employed) 103 Rate of Contraction of Various Metals : Material Dimension Shrinkage allowance (inch/ft) Grey Cast Iron Up to 2 feet 2 feet to 4 feet over 4 feet 0.125 0.105 0.083 Cast Steel Up to 2 feet 2 feet to 6 feet over 6 feet 0.251 0.191 0.155 Aluminum Up to 4 feet 4 feet to 6 feet over 6 feet 0.155 0.143 0.125 Magnesium Up to 4 feet Over 4 feet 0.173 0.155 104 2. Machining Allowance: A Casting is given an allowance for machining, because: i. Castings get oxidized in the mold and during heat treatment; scales etc., thus formed need to be removed. ii. It is the intended to remove surface roughness and other imperfections from the castings. iii. It is required to achieve exact casting dimensions. iv. Surface finish is required on the casting. How much extra metal or how much machining allowance should be provided, depends on the factors listed below: i. Nature of metals. ii. Size and shape of casting. iii. The type of machining operations to be employed for cleaning the casting. iv. Casting conditions. v. Molding process employed 105 Machining Allowances of Various Metals: Metal Dimension (inch) Allowance (inch) Cast iron Up to 12 12 to 20 20 to 40 0.12 0.20 0.25 Cast steel Up to 6 6 to 20 20 to 40 0.12 0.25 0.30 Non ferrous Up to 8 8 to 12 12 to 40 0.09 0.12 0.16 106 3. Draft or Taper Allowance:  It is given to all surfaces perpendicular to parting line.  Draft allowance is given so that the pattern can be easily removed from the molding material tightly packed around it with out damaging the mould cavity.  The amount of taper depends upon: i. Shape and size of pattern in the depth direction in contact with the mould cavity. ii. Moulding methods. iii. Mould materials. iv. Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces. 107 108
  19. 19. 16-11-2015 19 Fig: Taper in design 109 Table 2 : Draft Allowances of Various Materials: Pattern material Height of the given surface (inch) Draft angle (External surface) Draft angle (Internal surface) Wood 1 1 to 2 2 to 4 4 to 8 8 to 32 3.00 1.50 1.00 0.75 0.50 3.00 2.50 1.50 1.00 1.00 Metal and plastic 1 1 to 2 2 to 4 4 to 8 8 to 32 1.50 1.00 0.75 0.50 0.50 3.00 2.00 1.00 1.00 0.75 110 4. Distortion or Camber allowance: A casting will distort or wrap if: i. It is of irregular shape, ii. All it parts do not shrink uniformly i.e., some parts shrinks while others are restricted from during so, iii. It is u or v-shape, iv. The arms possess unequal thickness, v. It has long, rangy arms as those of propeller strut for the ship, vi. It is a long flat casting, vii. One portion of the casting cools at a faster rate as compared to the other. 111 112 5. Shake Allowance:  A pattern is shaken or rapped by striking the same with a wooden piece from side to side. This is done so that the pattern a little is loosened in the mold cavity and can be easily removed.  In turn, therefore, rapping enlarges the mould cavity which results in a bigger sized casting.  Hence, a –ve allowance is provided on the pattern i.e., the pattern dimensions are kept smaller in order to compensate the enlargement of mould cavity due to rapping.  The magnitude of shake allowance can be reduced by increasing the taper. 113 Die Casting 114
  20. 20. 16-11-2015 20 Die Casting 115 116 Casting Defects Blowholes:  Blowholes/Pinholes: These defects can appear in any region of a casting. They are caused when gas is trapped in the metal during solidification.  Caused due to excess moisture content in moulding sand or low permeability/venting. Scab  It is caused when sand erodes from mould due to uneven ramming and the recess is filled with metal. Scar and blister  Due to improper permeability or venting. A scar is a shallow blow. It generally occurs on flat surf; whereas a blow occurs on a convex casting surface. A blister is a shallow blow like a scar with thin layer of metal covering it. 117 Casting Defects Wash  They appear as rough spots or areas of excess metal, and are caused by erosion of moulding sand by the flowing metal.  This is due to loose ramming of moulding sand, and not having enough strength and if the molten metal flowing at high velocity.  The former can be taken care of by proper choice of moulding sand and the latter can be overcome by the proper design of the gating system. Misrun  A mis-run is caused when the metal is unable to fill the mould cavity completely and thus leaves unfilled cavities.  A mis-run results when the metal is too cold to flow to the extremities of the mould cavity before freezing.  Long, thin sections are subject to this defect and should be avoided in casting design. 118 Casting Defects Cold shut • A cold shut is caused when two streams while meeting in the mould cavity, do not fuse together properly thus forming a discontinuity in the casting. • When the molten metal is poured into the mould cavity through more- than-one gate, multiple liquid fronts will have to flow together and become one solid. • If the flowing metal fronts are too cool, they may not flow together, but will leave a seam in the part and is called a cold shut, and can be prevented by superheat in the poured metal and sufficiently thick walls in the casting design. • The mis-run and cold shut defects are caused either by a lower fluidity of the mould or when the section thickness of the casting is very small. Fluidity can be improved by changing the composition of the metal and by increasing the pouring temperature of the metal. 119 Casting Defects Hot Tear Hot tears are cracks which appear when the solidifying melt does not have sufficient strength to resist tensile forces produced during solidification. They may be due to  excessively high temperature of casting metal,  increased metal contraction,  incorrect design of the gating system or casting,  poor deformability of the cores, and  non-uniform cooling which gives rise to internal stresses. This defect can be avoided by improving the design of the casting and by having a mould of low hot strength and large hot deformation. 120
  21. 21. 16-11-2015 21 Extrusion is defined as the process of shaping material, by forcing it to flow through a shaped opening in a die. Extruded material emerges as an elongated piece with the same profile as the die opening. Drawing is defined as the process of shaping material, by pulling the material through a shaped opening in a die (draw die). This process of drawing is not to be confused with the drawing process related to the forming of sheet metals Extrusion and Drawing 121 Extruded items  Railings for sliding doors  Window frames  Tubing having various cross-sections  Aluminum ladders  Numerous structural and architectural shapes  Rods and wires Including:  Rods for shafts  Machine and structural components  Electrical wiring  Tension-loaded structural members  Welding Electrodes  Springs, Cables & Paper clips  Spokes for bicycle wheels  Stringed musical instruments Drawing Products 122 Extrusion • Metal is compressed and forced to flow through a shaped die to form a product with a constant cross section • A ram advances from one end of the die and causes the metal to flow plastically through the die Figure Direct extrusion schematic showing the various equipment components. (Courtesy of Danieli Wean United, Cranberry Township, PA.) 123 Extrusion • Definition: – Process of forcing a billet through a die above its elastic limit, taking shape of the opening. • Purpose: – To reduce its cross-section or to produce a solid or hollow cross section. • Analogy: “Like squeezing toothpaste out of a tube”. 124 Extrusion  Extruded products always have a constant cross-section.  It can be a semi-continuous or a batch process.  Extrusions can be cut into lengths to become discrete parts like gears, brackets, etc.  A billet can also extruded individually in a chamber, and produces discrete parts.  Typical products: railings, tubing, structural shapes, etc. 125 Typical Extruded Products (Left) Aluminum products. (Right) Steel products. Figure Typical shapes produced by extrusion. (Courtesy of Aluminum Company of America, Pittsburgh, PA.). (Courtesy of Allegheny Ludlum Steel Corporation, Pittsburgh, PA.) 126
  22. 22. 16-11-2015 22 Extrusion • Can be performed at elevated temperatures or room temperatures, depending on material ductility. • Commonly extruded materials include aluminum, magnesium (low yield strength materials), copper, and lead. • Steels and nickel based alloys are far more difficult to extrude (high yield strength materials). • Lubricants are essential to extrude high strength alloys to avoid tendency of material to weld to die walls. 127 Advantages of Extrusion • Many shapes can be produced that are not possible with rolling • No draft is required • Amount of reduction in a single step is only limited by the equipment, not the material or the design • Dies are relatively inexpensive • Small quantities of a desired shape can be produced economically 128 Extrusion Methods Methods of extrusion: Hot extrusion is usually done by either the direct or indirect methods. – Direct extrusion  Solid ram drives the entire billet to and through a stationary die.  Must provide additional power to overcome friction between billet surface and die walls. – Indirect extrusion  A hollow ram pushes the die back through a stationary, billet.  No relative motion and no friction between billet and die walls.  Lower forces required, can extrude longer billets.  More complex process, more expensive equipment required. 129 Extrusion Methods Fig. Direct and Indirect extrusion. In direct extrusion, the ram and billet both move and friction between the billet and the chamber opposes forward motion. For indirect extrusion, the billet is stationary. There is no billet- chamber friction, since there is no relative motion. 130 Extrusion of Hollow Shapes • Mandrels may be used to produce hollow shapes or shapes with multiple longitudinal cavities. Fig. Two methods of extruding hollow shapes using internal mandrels. (a) the mandrel & ram have independent motions; (b) they move as a single unit. 131 Cold Extrusion Fig. (Right) Steps in the forming of a bolt by cold extrusion, cold heading and thread rolling. Fig. (a) Reverse (b) forward (c) combined forms of cold extrusion. 132
  23. 23. 16-11-2015 23 Drawing • Cross section of a round rod / wire is reduced by pulling it through a die. • Work has to be done to overcome friction. Force increases with increasing friction. • Cannot increase force too much, or material will reach yield stress. • Maximum reduction in cross-sectional area per pass = 63%. • To produce a desired size or shape, multiple draws may be required through a series of progressively smaller dies. • Intermediate annealing may also be required to restore ductility and enable further deformation. 133 Deep Drawing Blanking Deep Drawing Redrawing Ironing Doming Necking Seaming 134 135 Examples of Deep Drawing 136 Tube and Wire Drawing • Tube sinking does not use a mandrel – Internal diameter precision is sacrificed for cost and a floating plug is used Fig. Tube drawing with a floating plug. Fig. Schematic of wire drawing with a rotating draw block. The rotating motor on the draw block provides a continuous pull on the incoming wire. 137 Examples of Sheet metal parts 138
  24. 24. 16-11-2015 24 Bending • Beyond yield strength but below the ultimate tensile strength • Placed on die and bent using a simple punch. 139 Bending Mechanism 140 What is Spinning? • Spinning is the process of forming sheet metals or tubing into contoured and hollow circular shapes. 141 Conventional Spinning- Mandrel 142 Forging Forging is defined as the controlled plastic deformation of metal at elevated temperatures into a predetermined size or shape by operations like hammering, bending and pressing etc. These operations can be carried out by hand hammers, power hammers, drop hammers or by forging machines. Forging is generally employed for those components which require high strength and resistance to shock or vibration and uniform properties. Forging Tools • Smith’s forge or hearth • Swage block • Tongs • Punches and drafts • Swages • Flatter • Anvil • Sledge hammers • Chisels • Fullers • Set hammer • Beck iron 144
  25. 25. 16-11-2015 25 Forging Operations • Upsetting • Drawing • Setting down • Cutting • Bending • Welding • Punching • Rotary swaging • Cold heading • Riveting and stacking • Hobbing • Coining • Embossing 145 Forging Operations Upset forging Upsetting FINISHED PART Bending (on Anvil)Setting down Punching 146 Forging Operations Cold heading Riveting CoiningHobbing Embossing Stamping 147 Rolling •Rolling is a process of compressing and squeezing a metal piece between two rolls rotating in opposite directions. •It is the method of forming metal into desired shapes by plastic deformation as the metal passes between the rolls. •Rolling is used to produce structural shapes like channels, I-beams, rail-road rails, bars of circular or hexagonal cross-section and sheets, plates etc. Types of Rolls • Grooved Roll produce structural shapes, like channels, angles etc. • Plain Roll produce sheets, plates, strips etc. 149 Methods of Rolling • Hot Rolling • Cold Rolling 150
  26. 26. 16-11-2015 26 Rolling Mills • Two-high reversing mill • Three-high mill 151 Rolling 152 Welding Welding is the process of joining two pieces of metal by application of heat.  Soldering and brazing are adhesive bonds, whereas welding is a cohesive bond. Arc Welding Arc welding is used in fusion processes for joining metals and alloys. The heat required is developed by striking an arc between a metal rod and the parts to be joined. By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts. Energy for the arc is provided by AC transformed from the mains supply to 50-100V, 10-300A. DC may be used at 40-60V. Arc Welding Prepared joints for Arc Welding
  27. 27. 16-11-2015 27 Welding Operation Before welding, earthing connections should be checked, voltage and amperage has to be adjusted. welding rod is selected to suit the nature and thickness of the metal to be joined. 157 158 Gas Welding In gas welding, combustion is obtained by mixing oxygen with a fuel to support combustion at high temperature. The most common fuel is acetylene. The fuel gas could also be hydrogen, natural or producers gas. Oxy-Acetylene Welding CaC2 + 2H2O = C2H2 + Ca(OH)2 Calcium Carbide Water Acetylene Hydrated lime Types of Flames • Carburizing flame - excess of acetylene • Neutral flame - aprox. equal volume of O2 and C2H2 • Oxidizing flame 161 Machining (a) Purpose of Machining • Most of the engineering components such as gears, bearings, clutches, tools, screws and nuts etc. need dimensional and form accuracy and good surface finish for serving their purposes. • Preforming like casting, forging etc. generally cannot provide the desired accuracy and finish. • Such preformed parts are called blanks, and need semi-finishing or finishing and is done by machining and grinding. Grinding is also basically a machining process. • Machining to high accuracy and finish enables a product to: • fulfill its functional requirements • improve its performance • prolong its service 162
  28. 28. 16-11-2015 28 (b) Principle of Machining • The basic principle of machining is illustrated in Figure. • A metal rod of irregular shape, size and surface is converted into a finished rod of desired dimension and surface by machining by proper relative motions of the tool-work pair. 163 Definition of Machining: • Machining is an essential process of finishing by which jobs are produced to the desired dimensions and surface finish by gradually removing the excess material from the preformed blank in the form of chips with the help of cutting tool(s) moved past the work surface(s). 164 Machining Requirements The essential requirements for machining work are schematically illustrated as The blank and the cutting tool are properly mounted (in fixtures) and moved in a powerful device called machine tool enabling gradual removal of material from the work surface resulting in its desired dimensions and surface finish. Additionally environment like cutting fluid is generally used to ease machining by cooling and lubrication. 165 Basic functions of Machine Tools • Machine Tools basically produce geometrical surfaces like flat, cylindrical or any contour on the preformed blanks by machining work with the help of cutting tools. • The physical functions of a Machine Tool in machining are:  firmly holding the blank and the tool.  transmit motions to the tool and the blank.  provide power to the tool-work pair for the machining action.  control of the machining parameters, i.e., speed, feed and depth of cut. 166 Machine Tool - definition • A machine tool is a non-portable power operated and reasonably valued device or system of devices in which energy is expended to produce jobs of desired size, shape and surface finish by removing excess material from the preformed blanks in the form of chips with the help of cutting tools moved past the work surface(s). 167 Lathe The main function of a lathe is to remove the metal from the piece of work to give it the required shape & size. 168
  29. 29. 16-11-2015 29  This is accomplished by holding the work securely & rigidly on the machine & then turning it against a cutting tool, which will remove metal from the work in the form of chips.  If the tool is moved parallel to the axis of rotation of the work then a cylindrical surface is produced as shown.  If the tool is moved perpendicular to the axis of rotation of the work, then a flat surface is produced as shown. 169 Working Principle of a lathe 170 Diagram of a Lathe 171 Schematic Diagram of a Lathe 172 Diagram of a Lathe 173 Specification of a lathe 174
  30. 30. 16-11-2015 30 Principal parts of a Lathe  Bed: - the body structure supported at both ends. The head stock, tail stock, carriage etc. are mounted on it. The bed provides required strength and rigidity to the machine.  Head stock:-the head stock is mounted on the bed at the left end permanently. It has got a gear box for getting different speeds for the spindle and work piece.  Tail stock: - this is mounted on the right hand end of the bed which can however clamp at any position. Tail stock supports one end of work piece and used for holding the tool for drilling and reaming operations. 175 Lathe Bed 176  Carriage: -the carriage consists of so many parts that serve to support the cutting tool and control the action of the cutting tool. It can be moved along the bed ways provided at the top of the bed.  Lathe centers: -these are tapered components fit in to spindles provided in the tail stock and head stock. The center fitted to the tail stock is called dead center which supports the work piece and that connected to the head stock is called live center since it will rotate along with the spindle.  Tool post: -tool post is mounted on the carriage to hold the cutting tool and enable the cutting tool to be adjusted to a convenient position.  Lead screw: -this is a long threaded shaft used for cutting threads and to give automatic movements to carriage and cross slide to achieve the tool movements in the longitudinal and lateral directions with respect to the bed. Principal parts of a Lathe 177 Compound Rest & Tool Post 178 Chucks 179 Holding & Turning job 180
  31. 31. 16-11-2015 31 Various operations performed on lathe Facing  facing is the operation of producing flat end surface that is normal to the axis of rotation.  While facing cutting tool is moved right angles to the axis of rotation and the cutting edge must be set at the same height at the centre of the work. 181 TURNING 182 Drilling:  Drilling is a process used extensively by which through or blind holes are originated or enlarged in a work piece.  This process involves feeding of a cutting tool (drill) into a rotating work piece fixed on a chuck. 183 Boring  It is the operation of enlarging the previously drilled hole with the aid of single point cutting tool called boring tool.  The feed is given parallel to the axis of revolution. 184 REAMING The process of making a hole smoothly and accurately, holes may be reamed by a straight shank or taper shank reamer. 185 Thread Cutting (Internal & External) 186
  32. 32. 16-11-2015 32 Knurling The process of indentation of various forms on cylindrical work surfaces, a knurl tool is held in tool post and pressed against the rotating work piece with a cross slide and then it is fed for required length with the carriage. 187 Chamfering  It is the beveling or turning at the end of the work piece.  This operation is done to remove burrs from the end of work piece. 188 Drilling Machine 189 190 Shaper It is reciprocating type of machine tool used for producing flat surfaces. Surfaces may be horizontal, vertical or inclined. 191 Working Principle of a Shaper 192
  33. 33. 16-11-2015 33 Machining vertical surfaces: Machining horizontal surfaces: 193 Milling Operations  Milling is the removal of metal by feeding the work past a rotating multi toothed cutter.  In this operation the material removal rate (MRR) is enhanced as the cutter rotates at a high cutting speed.  The surface quality is also improved due to the multi cutting edges of the milling cutter. 194 195 Milling Cutters  The action of the milling cutter is totally different from that of a drill or a turning tool.  In turning and drilling, the tools are kept continuously in contact with the material to be cut.  whereas milling is an intermittent process, as each tooth produces a chip of variable thickness. 196 UP MILLING DOWN MILLING 197 1.Face milling 2. Side milling 3.End milling 4.T-slot milling 5.Angular milling 6.Form milling 7.Gear cutting 198
  34. 34. 16-11-2015 34 Grinding Machine  The process of metal removal by a rotating abrasive wheel is called grinding.  The wheels are made of abrasive materials called silica, bauxite, mixed with the bonding material and casting in the form of wheels of different diameters and shapes.  The feed is given to the work while the wheel rotates. 199 200 Surface Grinding Machine work 201 202 Computer Integrated Manufacturing • Computer-integrated manufacturing (CIM), integrates the software and hardware needed for computer graphics, computer-aided modelling and computer-aided design and manufacturing activities, from initial product concept through its production and distribution in the marketplace. • This comprehensive and integrated approach began in the 1970s and has been particularly effective because of its capability of making possible the following tasks:  Responsiveness to rapid changes in product design modifications and to varying market demands.  Better use of materials, machinery, and personnel.  Reduction in inventory.  Better control of production and management of the total manufacturing operation. 203 Computer Integrated Manufacturing 204
  35. 35. 16-11-2015 35 Elements in CIM 1. Computer numerical control (CNC). First implemented in the early 1950s, this is a method of controlling the movements of machine components by the direct insertion of coded instructions in the form of numerical data. 2. Adaptive control (AC). The processing parameters in an operation are automatically adjusted to optimize the production rate and product quality and to minimize manufacturing cost. For example, machining forces, temperature, surface finish, and the dimensions of the part can be constantly monitored; if they move outside the specified range, the system adjusts the appropriate variables until the parameters are within the specified range. 205 Elements in CIM 3. Industrial robots. Introduced in the early 1960s, industrial robots have rapidly been replacing humans, especially in operations that are repetitive, dangerous, and boring. As a result, variability in product quality is decreased and productivity improved. Robots are particularly effective in assembly operations, and some (intelligent robots) have been developed with sensory perception capabilities and movements that simulate those of humans. 4. Automated materials handling. Computers have made possible highly efficient handling of materials and components in various stages of completion (work in progress), as in moving a part from one machine to another, and then to points of inspection, to inventory, and finally, to shipment. 206 Elements in CIM 5. Automated assembly systems. These systems continue to be developed to replace assembly by human operators, although humans still have to perform some operations. Assembly costs can be high, depending on the type of product; consequently, products are now being designed so that they can be assembled more easily, and faster by automated machinery, thus reducing the total manufacturing cost. 6. Computer-aided process planning (CAPP). By optimizing process planning, this system is capable of improving productivity, product quality, and consistency and hence reducing costs. Functions such as cost estimating and monitoring world standards (time required to perform a certain operation) are also incorporated into the system. 207 Elements in CIM 7. Just-in-time production (JIT). The principle behind JIT is that (1)supplies of raw materials and parts are delivered to the manufacturer just in time to be used, (2)parts and components are produced just in time to be made into subassemblies, and (3)products are assembled and finished just in time to be delivered to the customer. As a result, inventory carrying costs are low, defects in components are detected right away, productivity is increased, and high-quality products are made at low cost. 208 Elements in CIM 8. Group technology (GT). The concept behind group technology is that parts can be grouped and produced by classifying them into families according to similarities in design and the manufacturing processes employed to produce them. In this way, part designs and process plans can be standardized and new parts (based on similar parts made previously) can be produced efficiently and economically. 9. Cellular manufacturing (CM). This system utilizes workstations that consist of a number of manufacturing cells, each containing various production machines controlled by a central robot, with each machine performing a different operation on the part, including inspection. 209 Elements in CIM 10. Flexible manufacturing systems (FMS). These systems integrate manufacturing cells into a large production facility, with all of the cells interfaced with a central computer. Although very costly, flexible manufacturing systems are capable of producing parts efficiently, but in relatively small quantities, and of quickly changing manufacturing sequences required for different parts. Flexibility enables these systems to meet rapid changes in market demand for all types of products. 11. Expert systems (ES). Consisting basically of complex computer programs, these systems have the capability of performing various tasks and solving difficult real-life problems, much as human experts would, including expediting the traditional iterative process in design optimization. 210
  36. 36. 16-11-2015 36 Elements in CIM 12. Artificial intelligence (AI). Computer-controlled systems are now capable of learning from experience and of making decisions that optimize operations and minimize costs, ultimately replacing human intelligence. 13. Artificial neural networks (ANN). These networks are designed to simulate the thought processes of the human brain, with such capabilities as modelling and simulating production facilities, monitoring and controlling manufacturing processes, diagnosing problems in machine performance, and conducting financial planning and managing a company’s manufacturing strategy. 211 Lean Production Lean production is a methodology that involves a thorough assessment of each activity of a company, with the basic purpose of minimizing waste at all levels and calling for the elimination of unnecessary operations that do not provide any added value to the product being made. This approach, also called lean manufacturing, identifies all of a manufacturer’s activities from the viewpoint of the customer and optimizes the processes used in order to maximize added value. 212 Lean Production • Lean production focuses on (a) The efficiency and effectiveness of each and every manufacturing operation, (b) The efficiency of the machinery and equipment used, and (c) The activities of the personnel involved in each operation. This methodology also includes a comprehensive analysis of the costs incurred in each activity and those for productive and for non productive labour. 213 Lean Production • The lean production strategy requires a fundamental change in corporate culture, as well as an understanding of the importance of cooperation and teamwork among the company’s workforce and management. • Lean production does not necessarily require cutting back on a company’s physical or human resources; rather, it aims at continually improving efficiency and profitability by removing all waste in the company’s operations and dealing with any problems as soon as they arise. 214 Agile Manufacturing • The principle behind agile manufacturing is ensuring agility and hence flexibility-in the manufacturing enterprise, so that it can respond rapidly and effectively to changes in product demand and the needs of the customer. • Flexibility can be achieved through people, equipment, computer hardware and software, and advanced communications systems. • As an example of this approach, it has been predicted that the automotive industry could configure and build a car in 3 days and that, eventually, the traditional assembly line will be replaced by a system in which a nearly custom made car will be produced by combining several individual modules. 215 Agile Manufacturing • The methodologies of both lean and agile production require that a manufacturer benchmark its operations. • Benchmarking involves assessing the competitive position of other manufacturers with respect to one’s own position (including product quality, production time, and manufacturing cost) and setting realistic goals for the future. • Benchmarking thus becomes a reference point from which various measurements can be made and to which they can be compared. 216
  37. 37. 16-11-2015 37 Environmentally Conscious Manufacturing • An inherent feature of virtually all manufacturing processes is waste. The most obvious examples are material removal processes, in which chips are removed from a starting work piece to create the desired part geometry. Waste in one form or another is a by-product of nearly all production operations. • Another unavoidable aspect of manufacturing is that power is required to accomplish any given process. Generating that power requires fossil fuels, the burning of which results in pollution of the environment. • At the end of the manufacturing sequence, a product is created that is sold to a customer. Ultimately, the product wears out and is disposed of, perhaps in some landfill, with the associated environmental degradation. 217 Environmentally Conscious Manufacturing • More and more attention is being paid by society to the environmental impact of human activities throughout the world and how modern civilization is using our natural resources at an unsustainable rate. • Global warming is presently a major concern. The manufacturing industries contribute to these problems. • Environmentally conscious manufacturing refers to programs that seek to determine the most efficient use of materials and natural resources in production, and minimize the negative consequences on the environment. 218 Environmentally Conscious Manufacturing • Other associated terms for these programs include green manufacturing, cleaner production, and sustainable manufacturing. • They all boil down to two basic approaches: (1) design products that minimize their environmental impact, (2) design processes that are environmentally friendly. • Product design is the logical starting point in environmentally conscious manufacturing. 219 Design For Environment (DFE) • The term design for environment (DFE) is sometimes used for the techniques that attempt to consider environmental impact during product design prior to production. • Considerations in DFE include the following: (1) select materials that require minimum energy to produce, (2) select processes that minimize waste of materials and energy, (3) design parts that can be recycled or reused, (4) design products that can be readily disassembled to recover the parts, (5) design products that minimize the use of hazardous and toxic materials, (6) give attention on how the product will be disposed at the end of its useful life. • To a great degree, decisions made during design dictate the materials and processes that are used to make the product. These decisions limit the options available to the manufacturing departments to achieve sustainability. 220 Design For Environment (DFE) • However, various approaches can be applied to make plant operations more environmentally friendly. They include the following: (1) adopt good housekeeping practices—keep the factory clean, (2) prevent pollutants from escaping into the environment (rivers and atmosphere), (3) minimize waste of materials in unit operations, (4) recycle rather than discard waste materials, (5) use net shape processes, (6) use renewable energy sources when feasible, (7) provide maintenance to production equipment so that it operates at maximum efficiency, (8) invest in equipment that minimizes power requirements. 221 Organization for Manufacture 222
  38. 38. 16-11-2015 38 Organization for Manufacture 223 Organization for Manufacture 224 Organization for Manufacture 225 Organization for Manufacture 226 THE END 227

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