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Mechanical working of metals

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					Mechanical working of metals
                        By
                  Anil Kumar S
                  Asst professor
                   Mechanical
Definition :-

• The Mechanical working of metal is defined
  as the plastic deformation of metals under
  action of externally applied forces.
Plastic deformation :-
 Introduction :-
• It reduces internal voids & cavities, this
  makes metal dense.

• Impurities present in the metal also get
  elongated with the grains.

• Improves the mechanical strength.
.The metal is subjected to mechanical working
  for the following purpose:-

• To reduce the original block or ingot into
  desired shape.
• To refine grain size
 Hot working & cold working :-

• Mechanical working of metals is described
  into.
• As hot working and cold working
• Depending upon whether the metal is
  worked above or below the recrystallisation
  temp.
Recrystallisation :-

• Under the action of heat & force the atoms
  reach a certainly high energy level, the new
  structure starts forming which is termed a
  recrystallisation.
  Hot working :-

• Process carried above recrystallisation
  temperature.
• For lead & tin recrystallisation temp is
  below room temp.
• Heated to plastic state& then pressure is
  applied.
• Pressure applied is different in different
  process.
HOT WORKING PROCESSES ARE:-
• Hot rolling
• Hot extrusion
• Hot forging
              Hot forging




Hot rolling
Hot Extrusion :-
Advantages :-
•   The porosity of metal is eliminated.
•   Grain structure is refined.
•   Hot work require much less force.
•   Giving rise to better mechanical properties
 Limitations :-

• some metals cannot be hot worked
  because of their brittleness.
• It produces poor surface finish, due to
  rapid oxidation on the metal surface.
• Due to the poor surface finish, close
  tolerances cannot be maintained.
• The correct temp. range for working is
  difficult to maintain
    Cold working :-

• The working of metals below their
  recrystallisation temperature is known as cold
  working.

• Most of cold working process are performed at
  room temperature
.
  Advantages :-
• Cold working produces a good surface finish, close
  dimensional tolerance.

• Does not result in weight loss during working.

• It produces considerable increase in strength and
  hardness, and reduces ductility.

• By repeatedly cycling a material through stages of
  annealing and cold working, a very strong material can
  be produced.
Limitations :-
• The stresses are set up in the metal which
  remain in the metal, unless they are removed by
  subsequent heat treatment .

• Some materials which are brittle cannot be cold
  worked.

• Since the material has higher yield strength
  at lower temperature.
               Cold forging




Cold rolling
Cold extrusion
Press working :-
• Press working may be defined as chip less
  manufacturing process

• By which various components are made from
  sheet metal.

• These process are generally carried out at room
  temperature
Classification of press operations :-

• Cutting operation

• Forming operation
Stamping :-
    Various press working operations :-

•    BLANKING

•    PIERCING

•    NIBBLING

•    BENDING

•    COINING

•    DRAWING
Blanking :-
Piercing :-
Nibbling :-


        Sheet metal
  Bending :-

Complex parts such as U-sections channel sections
of different profiles can be produced by doing
multiple bends.
Following types of bending :-
Coining :-
   used to produce coins, medallions
 Drawing :-
automotive bodies and fuel tanks, cans, cups, kitchen sinks, and pots and pans.
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posted:10/4/2012
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