special forming process

7/27/2019 Special Forming Process

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Sheet metal operations not performed on presses

No of sheet metal operations not performed on conventional

stamping press they are

1. stretch forming

2. Spinning3. High energy rate forming

a) explosive forming

b) electro hydraulic forming

c) electro magnetic forming


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Stretch forming process

Stretch forming is a sheet metal deforming process in which the

sheet metal is intentionally stretched and simultaneously bent in

order to achieve shape change. this process is illustrated in fig for a

relatively simple and gradual bend. The work part is gripped by one or

more jaws on each end and then stretched and bent over a positivedie containing the desired form. The metal is stressed in tension to a

level above its yield point. When the tension load is released , the

metal has been plastically deformed. This combination of stretching

and bending results in relatively a little spring back in the part.

An estimate of force required in stretch forming can be obtained by

multiplying the cross sectional area of the sheet in the direction of

pulling by the flow of the stress of the metal


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Stretch forming process


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Explosive forming


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Explosive forming

Explosive forming involves use of explosive charge to form sheet

metal into a die cavity. one method of implementing the process

is illustrated in figure . The work part is clamped and sealed over the

die and a vacuum is created in the cavity beneath . The apparatus is

then placed in a large vessel of water. An explosive charge placed in

the water at a certain distance above the work. Detonation of a

charge results in a Shock wave whose energy is transmitted

By the water to cause rapid forming of the part into the cavity. The

size of the explosive charge and the distance at which it is placedabove the part largely a matter of art and experience.

Explosive forming reserved for large parts typical of the aerospaceindustry.


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Electro hydraulic forming


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Electro hydraulic forming

Electro hydraulic forming is a HERF process in which a shock

wave to deform the work into a die cavity is generated by the

discharge of electrical energy between two electrodes is

submerged in a transmission fluid (water).owing to its principle

of operation, this process is also called electric discharge

forming. The set up for the process is illustrated in the figure.

Electrical energy is accumulated in large capacitors and then

released to the electrodes .electro hydraulic forming is similar to

explosive forming . The difference is in the method of generation the

energy and the smaller amounts of energy that are released. This

limits electro hydraulic forming to much smaller part sizes.


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Electro magnetic forming


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Electro magnetic forming

Electro magnetic forming also called magnetic pulse

forming , is a process in which sheet metal is deformed by

the mechanical force of an electro magnetic field induced

in the work part by an energized coil . The coil is energized

by a capacitor, produces a magnetic field . This generates

eddy currents in the work that produce their own magnetic

field. The induced field opposes the primary field,

producing a mechanical force that deforms the part into the

surrounding cavity. Developed in the 1960s electro magnetic

forming is the most widely used HERF process . It is typically

used to form tubular parts, as illustrated in figure

special forming process

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