Cold working, Warm Working, Hot Working


Cold working, Warm Working, Hot Working

Cold working process

Plastic deformation of metals below
the recrystallization temperature is known as cold working. It is generally
performed at room temperature. In some cases, slightly elevated temperatures
may be used to provide increased ductility and reduced strength. Cold working
offers a number of distinct advantages, and for this reason various
cold-working processes have become extremely important. Significant advances in
recent years have extended the use of cold forming, and the trend appears
likely to continue.





Cold working process

Cold working process



   In comparison with
hot working, the advantages of cold working are

  •  No heating is required

  •  Bettter surface finish is
    obtained

  •  Better dimensional
    control is achieved; therefore no secondary machining is generally needed.

  •  Products possess better
    reproducibility and interchangeablity.

  • Better strength, fatigue, and
    wear properties of material.

  • Directional properties can be
    imparted.

  •  Contamination problems
    are almost negligible.

    Some
disadvantages associated with cold-working processes are

  • Higher forces are required for
    deformation.

  •  Heavier and more powerful
    equipment is required.

  •  Less ductility is
    available.

  • Metal surfaces must be clean
    and scale-free.

  •  Strain hardening occurs (
    may require intermediate annealing ).

  • Undesirable residual stresses
    may be produced




Cold forming processes, in general,
are better suited to large-scale production of parts because of the cost of the
required equipment and tooling.


Warm Working


Metal deformation carried out at temperatures intermediate to hot and cold
forming is called Warm Forming. 

Compared to cold forming, warm
forming offers several advantages. These include:


  •  Lesser loads on tooling
    and equipment

  • Greater metal ductility

  •  Fewer number of annealing operation (
    because of less strain hardening )



Compared to hot forming, warm
forming offers the following advantages


  • Lesser amount of heat energy
    requirement

  •   Better precision of
    components

  •   Lesser scaling on parts

  •   Lesser decarburization
    of parts

  •   Better dimensional
    control

  •   Better surface finish

  •  Lesser thermal shock on
    tooling

  •  Lesser thermal fatigue to
    tooling, and so greater life of tooling.



Hot Working





Hot working process
Hot working process



         
Plastic deformation of metal carried out at temperature above the
recrystallization temperature, is called hot working. Under the action of heat
and force, when the atoms of metal reach a certain higher energy level, the new
crystals start forming. This is called recrystallization. When this happens, the
old grain structure deformed by previously carried out mechanical working no
longer exist, instead new crystals which are strain-free are formed.


         
In hot working, the temperature at which the working is completed is critical
since any extra heat left in the material after working will promote grain
growth, leading to poor mechanical properties of material.



      In
comparison with cold working, the advantages of hot working are

  • No strain hardening

  • Lesser forces are required for
    deformation

  • Greater ductility of material
    is available, and therefore more deformation is possible.

  • Favorable grain size is
    obtained leading to better mechanical properties of material

  • Equipment of lesser power is
    needed

  • No residual stresses in the
    material.

      Some
disadvantages associated in the hot-working of metals are

  • Heat energy is needed

  • Poor surface finish of material
    due to scaling of surface

  • Poor accuracy and dimensional
    control of parts

  • Poor reproducibility and
    interchangeability of parts

  • Handling and maintaining of hot
    metal is difficult and troublesome

  • Lower life of tooling and
    equipment.


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