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MANUFACTURING

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Threaded fasteners hardware components with external or internal threads ... without breaking, e.g. the material of pots and pans has to be ductile enough ... – PowerPoint PPT presentation

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Title: MANUFACTURING


1
MANUFACTURING
(Lecture 3)
2
Assembly Processes
  • Mechanical Assembly
  • Threaded fasteners hardware components with
    external or internal threads
  • Screws, bolts, and nuts
  • Screw is externally threaded assembled into a
    blind threaded hole
  • Bolt is also externally threaded inserted
    through holes in the parts and screwed into a
    nut on the opposite side.
  • Nut is internally threaded threads of a nut
    match those on bolts of the same diameter, pitch,
    and thread form

Types of nuts
3
Assembly Processes
  • Mechanical Assembly
  • Washers used with threaded fasteners to ensure
    tightness
  • Common types (a) plain (flat) washer (b)
    spring washers, to dampen vibration or compensate
    for wear and (c) lock washer, to resist
    loosening
  • Washers serve various functions
  • Distribute stresses at the bolt or screw head and
    nut
  • Provide clearance for large holes
  • Protect part surface
  • Seal the joint
  • Resist inadvertent unfastening

Types of washers
4
Assembly Processes
  • Mechanical Assembly
  • Rivets unthreaded, headed pin used for
    achieving a permanent mechanically fastened joint
  • Primary fastening processes in the aircraft and
    aerospace industries
  • Types geometries telling how the rivet will be
    upset to form the second head (a)
    solid, (b) tubular, (c) semi tubular, and (d)
    bifurcated.
  • Other mechanical assembly techniques stitching,
    stapling and sewing

Types of washers
5
Assembly Processes
  • Thermal Assembly
  • Involves the use of heat permanent joining
    process
  • Commonly used processes welding, brazing and
    soldering
  • Welding two or more parts are coalesced by heat
    and /or pressure
  • Usually performed on parts made of the same metal
  • Advantages and disadvantages of the welding are

6
Assembly Processes
  • Thermal Assembly
  • The welding operation most common welding process
    is fusion welding a filler metal is added to
    facilitate the process and provide bulk and
    strength to the welded joint
  • Some types of fusion welding are
  • Arc welding an electric arc is maintained
    between an electrode and the workpiece
    electrode may provide the filler metal
  • Resistance welding an electric current passes
    through two pieces of metal under pressure
    (examples are spot and seam welding)
  • Beam welding supplying heat by bombarding the
    workpiece with a concentrated beam of (a)
    electrons (electron beam welding) or (b)
    high-energy light beam (laser welding)
  • Gas welding a combustible gas (oxyacetylene) is
    burned with air or oxygen to heat the parent
    metal and the filler
  • Types of weld joint butt joint, corner joint
    and lap joint

7
Assembly Processes
  • Thermal Assembly

Arc welding
Spot welding
Seam welding
8
Assembly Processes
  • Thermal Assembly
  • Brazing filler metal is melted and distributed
    between the fusion surfaces of metal parts
  • Melting point of the filler metal is below the
    melting point of the base metal
  • Strength is less than that of a welding
  • Brazing temperature for aluminum alloys 600oC,
    silver alloys 730oC and nickel alloys 1120oC.
  • Advantages (a) dissimilar metals (b) less heat
    and power
  • Soldering similar to brazing, melting point of
    the filler metal does not exceed 450oC
  • Soldering is associated with electronics
    assembly, automobile radiators, food containers
  • Most solders are alloys of tin and lead.

9
Assembly Processes
  • Adhesive bonding is probably the first of the
    permanent joining methods
  • Adhesive is usually a polymer e.g. epoxy, silicon
    and urethane
  • Adhesive bonding a joining process in which a
    filler material is used to hold two (or more)
    closely spaced parts
  • Used for joining similar and dissimilar materials
    such as metals, plastics, ceramics, wood, paper
  • Curing time or setting time is the time required
    to change the physical properties of an adhesive
    from a liquid to a solid state, usually by a
    chemical reaction
  • Major applications automotive, aircraft,
    building products, and packaging industries
    other industries include footwear, furniture,
    bookbinding, electrical, and shipbuilding

10
Conditioning Processes
  • Conditioning processes change internal properties
    of a material magnetizing a piece of steel
  • Classification mechanical, chemical and thermal
    conditioning
  • Mechanical conditioning is a process in which we
    use a mechanical force
  • Example hammering a piece of metal makes it
    harder and its crystal structure changes, getting
    longer and thinner
  • Chemical conditioning is a process in which a
    chemical reaction takes place to change the
    internal proprieties and structure of a material
  • Example mixing plaster and water, heat is given
    off and the plaster hardens
  • Thermal conditioning is the other name of heat
    treatment in which we change the internal
    characteristics through controlled heating and
    cooling of metals to alter their physical and
    mechanical properties without changing the
    product shape

11
Conditioning Processes
  • Thermal conditioning is often associated with
    increasing the strength, obtaining different
    hardness/softness levels
  • Example raise the temperature of a piece of
    steel to red-hot, in a furnace and then
  • Keep the piece in there for a long time after
    switching off the furnace, the metal to gain the
    most uniform crystal structure and become quite
    soft annealing
  • Cool the piece in water, it becomes harder
    hardening
  • Heat the piece again, not quite as hot, and cool
    it quickly, the steel becomes less brittle
    tempering
  • Allow the piece to cool very quickly, for example
    in ice-cold water, the crystals have no time to
    gain a proper structure and the material becomes
    most brittle quenching
  • Other common examples of conditioning may be

12
Properties of Materials
  • Materials are chosen for their characteristics or
    properties
  • Examples glass for windows, plastic for dishes,
    copper for electrical wires
  • Common properties strength, hardness,
    appearance, ability to conduct electricity, and
    resistance to corrosion etc.
  • Mechanical Properties
  • Mechanical properties determine the behavior of a
    material when subjected to mechanical forces
  • Strength is the ability of a material to keep its
    own shape when a force is applied
  • There are four kinds of forces
  • Tension is a force that pulls on a piece of
    material, e.g. pulling a spring
  • Compression is a force that pushes on or squeezes
    a material, e.g. squeezing s sponge
  • Torque or torsion is the twisting force, e.g.
    using a wrench to turn a bolt
  • Shear force acts on a material like a pair of
    scissors. One part of the material slides in one
    direction and the other part slides in the
    opposite direction
  • Toughness is the ability of a material to absorb
    energy without breaking, e.g. leather is tough

13
Properties of Materials
  • Mechanical Properties

Four types of mechanical forces
Toughness test of a car
14
Properties of Materials
  • Mechanical Properties
  • Hardness is the ability of a material to
    withstand penetration forces, e.g. the teeth of a
    circular saw blades are often made of tungsten
    carbide
  • Malleability is the ability of a material through
    which it can be shaped or extended, e.g. thin
    wires are drawn from rods
  • Ductility is the ability of a material through
    which it can be bent without breaking, e.g. the
    material of pots and pans has to be ductile
    enough
  • Elasticity is the stiffness of a material
  • Elastic materials are those that come back to its
    original shape and size after bending, e.g. a
    rubber band
  • Plastic materials stay bent after bending, e.g.
    modeling clay is a plastic material
  • Yield strength marks the transition of a material
    from elastic to plastic state

Response of a material upon bending forces
15
Properties of Materials
  • Electrical Properties
  • Materials that offer very little resistance to
    the flow of electricity are conductors, e.g.
    silver and copper
  • Materials that resist the flow of electricity
    most strongly are insulators, e.g. plastic and
    rubber
  • Materials that can be attracted by a magnet are
    called magnetic materials, e.g. iron, nickel etc
  • Electromagnet a piece of iron becomes a magnet
    when current flows in a wire around it
  • Thermal Properties
  • Properties related to the ability of a material
    to conduct heat thermostat and thermos bottle
    thermometer
  • Copper and aluminum are the two best conductors
    of heat
  • Insulation is a layer of material used to prevent
    the movement of heat

16
Properties of Materials
  • Optical Properties
  • These properties refer to a materials ability to
    transmit or reflect light, e.g. window
  • Plastic is used making contact lenses
  • Other scientific applications of these properties
    are fiber optics, telescopes, microscopes,
    headlights and flashlights etc.
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