INTRODUCTION Super plastic Forming is a metalworking process for forming sheet metal. It works upon the theory of super plasticity, which means that ” capability that some materials have to undergo large uniform elongation prior to necking and fracture tension”. Super plastic forming (SPF) of sheet metal has been used to produce very complex shapes and integrated structures that are often lighter and stronger than the assemblies they have to replace. Titanium alloys and alloys of zinc-aluminum; when heated , they can elongate to many times their original length.
Some other materials which shows “superplasticity” are:1. Titanium alloys2. Aluminum alloys3. Bismuth-tin alloys4. Zinc-aluminum alloys5. Stainless steel6. Aluminum-lithium alloys
• PROCESS• The process typically conducted at high temperature and under controlled strain rate, can give a ten-fold increase in elongation compared to conventional room temperature processes. Components are formed by applying gas pressure between one or more sheets and a die surface, causing the sheets to stretch and fill the die cavity. Specific alloys of titanium, stainless steel, and aluminum are commercially available with the fine-grained microstructure and strain rate sensitivity of flow stress that are necessary for Super plastic deformation.• SPF can produce parts that are impossible to form using conventional techniques. During the SPF process, the material is heated to the SPF temperature within a sealed die. Inert gas pressure is then applied, at a controlled rate forcing the material to take the shape of the die pattern. Super plastic alloys can be stretched at higher temperatures by several times of their initial length without breaking.
EXAMPLES Construction of fuel Tanks Muddy Guards of MotorcarsADVANTAGES• The finished product has excellent precision and a fine surface finish.• Products can also be made larger to eliminate assemblies or reduce weight, which is critical in aerospace applications.• Lower strength required and less tooling costs.
LIMITATIONS• The biggest disadvantage is its slow forming rate.• Materials must not be superplastic at Lower temperatures.• It is usually used on lower volume products.
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DEFINITION “Shaping metal parts in dies by using an explosive charge to generate forming pressure.” OR “The shaping or modifying of metals by means of explosions.”
VARIOUS TECHNIQUES Explosive Forming Operations can be divided into two groups, depending on the position of the explosive charge relative to the work piece.1. 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
CONTACT MATHOD 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.
PROCESS The 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)^aWhere 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 nozzle Space shuttle skin
ADVANTAGESo It can simulate a variety of other conventional metal forming techniques such as stamp- or press-forming and spin-forming in a single operation.o Explosive hydro-forming can efficiently form large parts – up to 4’ square or 10’ in diameter.o It is particularly suitable for short production runs of a large parts such as occurs in aerospace applications.o 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 SUPERPLASTIC FORMING• In Explosive forming an • In super plastic forming explosive charge is used punch or press is used to instead of a punch or press. form metal sheet forming.• It can be use for large size of • It can be only used for metal sheets. limited die design.• No preheating required before the explosive forming • High production cost.• Less production cost. • It can be used for definite• Any product size, shape and shape, size and sheet sheet thickness is possible. thickness .