It is also called as shot peening. The free forming obtain where the steam of small steel balls are forced together again the metal surface, when the metal forming process restricted to fulfillment of fairly specialized function. The peen forming is used to form of various irregular shapes on the aluminium sheet plate. That requires large plate and small control in the process.
The peen forming process not requires any die and forming press. The part to be made by the sheet metal placed on block or it suspended from support and it has blasting together with shot, small steel balls. During the operation blanks are clamped over simple form blocks. The ball forced by compressed air or rotating blade. The ball is having high velocity directly imping the sheet metal to the form of block. There is repeated force by sheet metal get the require form block shape.
The numerous small balls is having diameter of 2.5 mm size cast- steel ball blast again the metal surface. The ball discharged from the rotating wheel or by air blast from nozzle.
The balls travelling speed of 60 m/s. The residual stress are induced to the compressive surface which improve the fatigue strength of sheet metal.
Advantages of peen forming:
- Tooling cost will be low
- Require no maintenance cost of tooling
- The compound curvatures are easily produced
- It is a die less forming, So that require minimum lead time
- That process permit rework and design changes for improve the fitness of sheet metal
- Formed product improve the fatigue strength and stress corrosion resistance
Disadvantage of peen forming process:
- Exhibited increase the resistance to flexural bending fatigue
- The surface of metal compressed together, that prevent stress corrosion cracking.
Application of peen forming:
- Provide smoothing and complex curvature of aircraft wings
- From of large tubular shapes
- military air craft