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Hydraulic pressFrom Wikipedia, the free encyclopedia

Hydraulic force increase

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Ahydraulic press is a machine (see machine press) using a hydraulic cylinderto generate a compressive

force. It uses the hydraulic equivalent of a mechanical lever, and was also known as a Bramah press after the

inventor, Joseph Bramah, of England. He invented and was issued a patent on this press in 1795. As Bramah

(who is also known for his development of the flush toilet) installed toilets, he studied the existing literature on

the motion of fluids and put this knowledge into the development of the press. [1]

Contents

[hide]

1 Principle

2 See also

3

References

4 External links

[edit]Principle

The hydraulic press depends on Pascal's principle: the pressure throughout a closed system is constant. One

part of the system is a pistonacting as a pump, with a modest mechanical force acting on a small cross-

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sectional area; the other part is a piston with a larger area which generates a correspondingly large mechanical

force. Only small-diametertubing (which more easily resists pressure) is needed if the pump is separated from

the press cylinder.

Pascal's law: Pressure on a confined fluid is transmitted undiminished and acts with equal force on equal areas

and at 90 degrees to the container wall.

A fluid, such as oil, is displaced when either piston is pushed inward. The small piston, for a given distance of

movement, displaces a smaller amount ofvolume than the large piston, which is proportional to the ratio of

areas of the heads of the pistons. Therefore, the small piston must be moved a large distance to get the large

piston to move significantly. The distance the large piston will move is the distance that the small piston is

moved divided by the ratio of the areas of the heads of the pistons. This is how energy, in the form ofwork in

this case, is conserved and the Law of Conservation of Energy is satisfied. Work is force times distance, and

since the force is increased on the larger piston, the distance the force is applied over must be decreased.

The pressurized fluid used, if not generated locally by a hand or mechanically-powered pump, can be obtained

by opening a valve which is connected to a hydraulic accumulatoror a continuously-running pump whose

pressure is regulated by a relief valve. When it is desired to generate more force than the available pressure

would allow, or use smaller, higher-pressure cylinders to save size and weight, a hydraulic intensifiercan be

used to increase the pressure acting on the press cylinder.

When the pressure on the press cylinder is released (the fluid returning to a reservoir), the force created in the

press is reduced to a low value (which depends on the friction of the cylinder's seals. The main piston does not

retract to its original position unless an additional mechanism is employed.

Hydraulic Press in a machine shop. This press is commonly used forhydroforming.

[edit]See also

Simple machine

[edit]References

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1. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p. 266. John Wiley & Sons, Inc.,

New Jersey. ISBN 0471244104.

[edit]External links

Wikimedia Commons has

media related to:Hydraulic

presses

Stamping

Introduction

The operations associated with stamping are blanking,piercing,forming, anddrawing.

These operations are done with dedicated tooling also known as hard tooling. This type oftooling is used to make high volume parts of one configuration of part design. (Bycontrast,soft tooling is used in processes such as CNC turret presses, laser profilers andpress brakes). All these operations can be done either at a single die station or multiple diestations performing a progression of operations, known as aprogressive die.

Equipment Types

The equipments of stamping can be categorized to two types: mechanical presses andhydraulic presses.

Mechanical Presses: Mechanical presses has a mechanical flywheel to store the energy,transfer it to the punch and to the workpiece. They range in size from 20 tons up to 6000tons. Strokes range from 5 to 500 mm (0.2 to 20 in) and speeds from 20 to 1500 strokesper minute. Mechanical presses are well suited for high-speedblanking, shallow drawing andfor making precision parts.

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Hydraulic Presses: Hydraulic Presses use hydraulics to deliver a controlled force. Tonnagecan vary from 20 tons to a 10,000 tons. Strokes can vary from 10 mm to 800 mm (0.4 to

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32 in). Hydraulic presses can deliver the full power at any point in the stroke; variabletonnage with overload protection; and adjustable stroke and speed. Hydraulic presses aresuitable for deep-drawing, compound die action as in blanking with forming or coining, lowspeed high tonnage blanking, and force type of forming rather than displacement type offorming.

Top of Page

Tooling Considerations

Optimum clearance (total = per side 2) should be from 20 to 25% of the stockthickness. This can be increased to 30% to increase die life.

Punch life can be extended by sharpening whenever the punch edge becomes 0.125mm (0.005 in) radius. Frequent sharpening extends the life of the tool, cuts down onthe punch force required. Sharpening is done by removing only 0.025 to 0.05 mm(0.001 to 0.002 in) of the material in one pass with a surface grinder. This is repeateduntil the tool is sharp. If it is done frequently enough, only 0.125 to 0.25 mm (0.005 to

0.010 in) of the punch material is removed. Grinding is to be done with the proper wheel for the tool steel in question. Consult with

the abrasive manufacturer for proper choice of abrasive material, feeds and speeds,and coolant.

After sharpening the edge is to be lightly stoned to remove grinding burrs and end upwith a 0.025 to 0.05 mm (0.001 to 0.002 in) radius. This will reduce the chance ofchipping.

Punching Force: Punching can be done without shear or with shear.

- Punching without shear. This is the case where the entire punch surface strikes thematerial square, and the complete shear is done along the entire cutting edge of thepunch at the same time. Punching Force = Punch Perimeter Stock thickness Material Shear Strength.

e.g.,Punch Diameter = 25 mm (1 in),Circumference = 78.54 mm (3.092 in)Thickness = 1.5 mm, (0.060 in)Material Shear Strength (Steel) = 0.345 kN/mm2 (25 tons/in2)Punching Force = 78.54 1.5 0.345 (3.09 0.060 25)

= 40.65 kN (4.64 tons)= 4.14 Metric Tons (4.64 US Tons)

- Punching with shear. This is the case where the punch surface penetrates thematerial in the middle, or at the corners, first, and as the punch descends the rest of

the cutting edges contact the material and shear the material. The distance betweenthe first contact of the punch with the material, to when the whole punch startscutting, is the Shear Depth. Since the material is cut gradually (not all at the sametime initially), the tonnage requirement is reduced considerably.

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- The Punching Force calculated above is multiplied by a shear factor, which ranges in

value form 0.5 to 0.9 depending on the material, thickness, and shear depth. Forshear depths of 1.5 mm (0.060 in) the shear factor ranges from 0.5 (for 1.2 mm /0.047 in stock) to 0.9 (for 6.25 mm / 0.25 in stock). For shear depth of 3 mm (0.120in) the shear factor is 0.5.Punching Force = Punch Perimeter Stock thickness Material Shear Strength Shear Factor.Since shear factor is about 0.5, the Punching Force is reduced by about 50%.

For the same example above,Punching Force = 78.54 1.5 0.345 (3.09 0.060 25) 0.5 (Shear Factor)

= 40.65 kN (4.64 tons) 0.5= 2.07 Metric Tons (2.32 US Tons)