Analysis of Internal High Pressure Stretching in Sheet Metal Forming

One of the aims of the sheet metal processing industry is the minimization of the costs and the optimization of its product concerning weight, strength characteristics and rigidity. In conventional deep drawing process, the mechanical force of the punch imparts non-uniform strain distribution and the cost of tooling, (i.e., the cost involved in the die and punch) is also too high while drawing complex shapes. Another drawback of the conventional process is that, it cannot be used for forming of tubes. Internal high pressure stretching, otherwise called as hydro forming uses directly the hydrostatic pressure of the fluid media to form the sheet metal. The detailed studies on the existing development have shown that this technique can be used for forming complex parts with increased strength-to-weight ratio due to work hardening and help reducing the cost involved by part consolidation and no punch is required. In this paper an attempt has been made to find the pressure required for drawing sheet metal to the required shape, size and depth by stretching it using high pressure oil and consolidates the parameters available. It is found that internal high pressure forming of sheet results in a much larger draw depth compared to forming using mechanical punch obtained through empirical relation.