Cold working process explained

COLD WORKING
Cold working is the process of strengthening material by changing its shapes without the use of heat. In this process, the material is deformed below the recrystallization temperature. The recrystallization temperature generally varies between one third to half the melting point of most of the metals. The major cold working process is rolling, bending and drawing etc.

Cold rolling is widely used for strengthening the metal, in which work is compressed between two rollers due to this grain size decreases so strength and hardness increases And Ductility decrease.
During cold working, the microstructure is permanently deformed with the grains being elongated in the direction of the applied forming stress.

EFFECTs ON GRAIN SIZE : –

Since in cold working material is pressed by roller so due to compressive force materials get compressed and the grains of the material comes close to each other and small gains which are known as Fine-grain. After the cold working process material becomes brittle in the structure and hardness of material increases.

Cold working is a metal forming process it is generally done for materials which have high recrystallisation or melting point temperature. It’s also called work hardening process or work strengthening process because it increases strength and hardness.
In this process strain hardening is take place so the materials obtained from cold working can not go for further deformation or in other words after the strain hardening, the maximum amount of deformation that can be given is limited.
Cold worked items suffer from a phenomenon known as spring back, or elastic spring back. After the deforming force is removed from the workpiece, the workpiece springs back slightly. The amount of material springs back is equal to the yield strain.

The most common application of this process is steel, aluminium, nickel, titanium and copper etc. 
 
TYPES OR EXAMPLES OF COLD WORKING PROCESS : –  
  • Squeezing: – Rolling, extrusion, forging, sizing etc
  • Bending: –  angle bending, roll bending, roll forming, draw and compression etc.
  • Shearing: – sheet metal shear cutting, blanking, piercing, lancing etc.
  • Drawing:- wire drawing, tube drawing, metal spinning etc.
ADVANTAGES OF COLD WORKING PROCESS  : – 
  • Strength and hardness of material increases due to strain hardening.
  • No heating required.
  • Better reproducibility and interchangeability
  • Superior dimension control
  • Contamination problems are minimised.
  • Since working is done in a cold state, no oxide would form in the surface and consequently, good surface finish is obtained.
  • Better dimensional accuracy is achieved.
  • It is easier to handle the cold part
  • Less costly as compared to hot working.
  • Reduce the waste of material.
  • Grain flow during deformation can cause desirable directional properties in the product.
DISADVANTAGES OF COLD WORKING PROCESS : – 
  • Since material gate strain hardened, the maximum amount of deformation that can be given is limited.
  • Less malleable and ductile.
  • May leave undesirable anisotropy in the final shape.
  • Some brittle materials cannot be cold worked.
  • Equipment of higher focus and power required.
  • Ductility decrease.
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