Basically
metal forming is the process of getting permanent changes in the shape of the
body under plastic deformation by the use of external forces on the metal
component.
Purpose
Of Metal Forming
In
order to get the desired shape of components from ingot and thereby cut down
the further machining cost, materials & time to make it economical.
It
can improve the mechanical properties of metal by refinement of grain structure
which is achieved by directional control of flow lines.
Reducing
any kind of blowhole, voids as well as cavities.
To
equally distribute the impurities in the metals if at all exist.
And
this process of deformation can be carried out under two conditions:
- Hot working
- Cold working
1)
Hot Working Of Metals
Hot
working can be explained simply as the plastic deformation of metals and alloys
under such conditions of temperature where recovery and re-crystallization
takes place simultaneously during the deformation.
And
hot working of the materials is carried out under 0.7 to 0.9 times the melting
point of the metals to obtain a refined grain structure.
Advantages
Of Hot Working
- By hot working the physical or mechanical properties of the metals like strength, ductility or toughness can be improved further.
- Also the metal density or the component density can be improved by removing the present voids or cavities.
- Here the deformation can be done by application of low pressure in order to get the possible desired shape.
- The present impurities can be divided uniformly all over the metal so that its effect can be reduced.
- The grain structure of metals can be refined.
- It can even cut down the machining cost to make the component economical.
- The atoms of the metals are arranged uni-directionally to achieve their maximum strength.
Disadvantages
Of Hot Working
Although
we have a lot of benefits due to hot working but still there are a few things
that can’t be overcome.
- Due to oxidation at high temperature better surface finish is rather not possible.
- As the metals after forming needs to be cooled hence accurate size and shape of component is not possible incase if close tolerances are needed.
- Since the process are carried out at high temperature so the tool life reduces.
- The handling costs are comparatively high.
Principal
Methods Of Hot Working
- Hot rolling
- Hot forging
- Hot drawing
- Hot extrusion
- Hot spinning
- Hot piercing
2)
Cold Working Of Metals
Cold
working can be explained simply as the plastic deformation of metals and alloys
under such conditions of temperature such that work hardening or strain
hardening is not relieved.
Basically
in cold working the temperature is below the re-crystallization temperature. However
cold working is usually carried out at room temperature.
Advantages
Of Cold Working
- Cold working usually improves the physical properties of metals like strength, hardness.
- Since here there is no oxidation issue so we can get better surface finish.
- Also better accuracy can be obtained as there is no change in operating temperature.
- As heating of metal is not needed so the cost and time both reduces automatically.
Disadvantages
Of Cold Working
- Though it increases the strength and hardness but decreases ductility on the other hand making it difficult to work on it.
- Need of external force is quite high compared to hot working to get desired shape.
- Cold working produces internal stresses & residual stresses which is not ggod for the components life.
- It automatically decreases the ability of component to resist corrosion.
- Distortion takes place in metals in its atomic structure.
- On metals undergoing cold working annealing is done on it for the second time which increases its cost.
Principal
Methods For Cold Working
- Cold rolling
- Cold drawing
- Cold extrusion
- Cold spinning
- Other methods include squeezing, bending & hobbing etc
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