Q. Describe the advantages and disadvantages of hot working and cold working processes. Explain the extrusion process.

Ans. Advantages of hot working process

         (i)Due to refinements of grains, mechanical properties such as toughness, ductility, elongation and reduction in area are improved.

(ii) Great latitude in shape and size of farm is possible to reduction of elastic limit.

(iii) The power required to finish the part from ingot is less.

(iv) Directional property resulting from a fiber structure is obtained.

(v) The strength and hardness decreases at elevated temperature.

Disadvantages of hot working process

(i) The life of the tools used is less.

(ii) Tooling and handling costs are high.

(iii) Close tolerances cannot be maintained, oxide films are surface characteristics.

Advantages of cold working process

(i) Surface finish is improved and close tolerance can be maintained.

(ii) Distortion or fragmentations of the grain structure is created.

(iii) Accurate dimensions of parts can be maintained.

(iv) Strength and hardness of the metal are increased but ductility is decreased.

(v) Resistance to corrosion is decreased while ultimate tensile strength, yield point and hardness are increased.

(vi) Loss of metal due to oxidation is prevented.

Disadvantages of cold working process

(i) The grain structure is not refined and residual stress have harmful effects on certain properties of metals.

(ii) Tooling costs are high and as such it is used when large quantities of similar components are required.

(iii) Only small size components can be easily cold worked as greater forces are required for large section.

Extrusion process : The process of extrusion consists of compression a metal inside a chamber to force it out through a small opening called die.

The extrusion process can be classified as :

(i) Direct or Indirect extrusion 

(ii) Forward or backward extrusion