SUPER PLASTIC FORMING AND EXPLOSIVE FORMING
DEFINITIONShaping metal parts in dies by using an explosive charge to generate forming pressure. ORThe shaping or modifying of metals by means of explosions.
VARIOUS TECHNIQUESExplosive Forming Operations can be divided into two groups, depending on the position of the explosive charge relative to the work piece.Stand Off Method2. Contact Method
STAND OFF MATHOD
In this method metal plate is placed over a die, with the intervening space evacuated by a vacuum pump, then whole assembly is placed underwater and explosive material is placed at an appropriate height above the plate. For complicated shapes, a segmented die can be used.
intervene: become involved
In this method, the explosive charge is held in direct contact with the work piece while the detonation is initiated. The detonation produces interface pressures on the surface of the metal up to several million psi.
PROCESSThe rapid change in explosive in to gas produce a shock wave. The pressure of this shock wave is sufficient to form metal sheet.The peak pressure , p , due to explosion, generated in water, is given by expression
p = k(((w)^1/2)/R)^a
Where P is in psi. K is the constant depends on the type of explosive. W is the weight of Explosive in pounds. R is the distance of explosive from the work piece and a is the constant.
OTHER EXAMPLESRocket engine nozzleSpace shuttle skin
ADVANTAGES It can simulate a variety of other conventional metal forming techniques such as stamp- or press-forming and spin-forming in a single operation.Explosive hydro-forming can efficiently form large parts up to 4 square or 10 in diameter. It is particularly suitable for short production runs of a large parts such as occurs in aerospace applications. It Maintains precise tolerances and Eliminates costly welds.
DISADVANTAGES1.Low tooling costs, but high labor cost. 2. Suitable for low-quantity production.3. Due to shock waves and spillage of water it is not suitable to carry out indoor.4. It should be done in open air.
COMPARISONEXPLOSIVE FORMING In Explosive forming an explosive charge is used instead of a punch or press. It can be use for large size of metal sheets. No preheating required before the explosive forming Less production cost. Any product size, shape and sheet thickness is possible.
SUPERPLASTIC FORMINGIn super plastic forming punch or press is used to form metal sheet forming. It can be only used for limited die design.High production cost. It can be used for definite shape, size and sheet thickness .