MANUFACTURING

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MANUFACTURING
(Lecture 3)
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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
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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
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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
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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

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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

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Assembly Processes

• Thermal Assembly

Arc welding
Spot welding
Seam welding
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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.

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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

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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

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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

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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

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Properties of Materials

• Mechanical Properties

Four types of mechanical forces
Toughness test of a car
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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
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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

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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.