Hot working and Cold working

The deformation of metal according to the temperature of the material is 

1. Hot working
2. Cold working

Hot working 

Mechanical working processes which are done above recrystallization temperature of the metal are known as hot working processes.
Some metals, such as lead and tin, have a low recrystallization temperature and can be hot-worked even at room temperature

 The advantages of hot working are -

• No strain hardening
• Greater ductility of material is available, and therefore more deformation is possible.
• Favorable grain size is obtained leading to better mechanical properties of the material
• lesser power is required to deform the material
• No residual stresses in the material
• No heat treatment required

 Disadvantages of the hot-working of metals are:-

• High tooling cost.
• The poor surface finish of material due to the scaling of surface
• Poor tolerance accuracy 
• Poor reproducibility and interchangeability of parts
• Handling and maintaining of hot metal is difficult
• Lower life of tooling and equipment

type of hot working-

1. Hot Rolling
2. Hot Forging
3. Hot extrusion
4. Hot drawing

Cold working -

Deformation of metals below the recrystallization temperature is known as cold working.

 The advantages of cold working are:-

• Better surface finish is obtained
• Better dimensional tolerance is achieved.
• Improved strength obtained
• Products possess better reproducibility and interchangeability.
• Better strength, fatigue, and wear properties of a material.
• Directional properties can be imparted.
• Contamination problems are almost negligible.

Disadvantages of 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.
• Undesirable residual stresses may be produced.
• May required extra heat treatment.

Type of cold working process-

1. cold Rolling
2. cold forging
3. cold Extrusion
4. cold drawing