Hydraulic Press

How the hydraulic press works

Since the hydraulic press works on the basis of Pascal's Law, its working is similar to the one of the hydraulic system. A hydraulic press consists of basic components used in a hydraulic system that includes the cylinder, pistons, the hydraulic pipes. The working of this press is very simple. The system comprises of two cylinders, the fluid (usually oil) is poured in the cylinder having a small diameter. This cylinder is known as the slave cylinder.The piston in this cylinder is pushed so that it compresses the fluid in it that flows through a pipe into the larger cylinder. The larger cylinder is known as the master cylinder. The pressure is exerted on the larger cylinder and the piston in the master cylinder pushes the fluid back to the original cylinder.

The force applied on the fluids by the smaller cylinder results in a larger force when pushed in the master cylinder. The hydraulic press is mostly used for industrial purposes where a large pressure is required for compressing metals into thin sheets. An industrial hydraulic press uses the material to be worked upon along with the help of the press plates to crush or punch the 

Parts of hydraulic press

Hydraulic fluid 

Hydraulic fluid is transmitted through various parts of the machine. High pressure is exerted on hydraulic fluid by the hydraulic pump, thus creating highly energized fluid. This fluid then travels to the cylinders (actuators) where it delivers its stock of large amounts of energy to the piston, which operates the bending tools. After delivering the energy, the de-energized hydraulic fluid travels back to the pump to regain its energy and continue the operation of the machine. The hydraulic fluid is usually petroleum oil with various additives. Apart from transferring the energy, the hydraulic fluid also lubricates the various components of the hydraulic press brake and removes the contaminants and metal fittings. The hydraulic fluid should be capable of operating at high temperatures, including a few hundred degrees Celsius, as it gets heated when receives the energy in the hydraulic pump.

Hydraulic pump –

The hydraulic pump actually produces the power that energizes the hydraulic fluid and transmits it through the machine to carry out the pressing operations. If a pump has the rating of say 60bar, it can maintain the flow of liquid against the loads of 60bar or it can apply that much pressure. The power density of hydraulic motors is ten times that of manual hand pump by volume. The hydraulic pump is operated by man power. It is reciprocated pump.

Hydraulic valves

These valves are usually very heavy duty to stand up to high pressures. Some special valves can control the direction of the flow of fluid and act as a control unit for a system.

Classification of hydraulic valves:

Pressure control valves

Flow control valves

Direction control valves

Hydraulic cylinder

Hydraulic cylinders (also called linear hydraulic motors) are mechanical actuators that are used to Maintaining a Hydraulic System give a linear force through a linear stroke. Hydraulic cylinders are able to give pushing and pulling forces of millions of metric tons with only a simple hydraulic system. Very simple hydraulic cylinders are used in presses; here, the cylinder consists of a volume in a piece of iron with a plunger pushed in it and sealed with a cover. By pumping hydraulic fluid in the volume, the plunger is pushed out with a force of plunger-area pressure. More sophisticated cylinders have a body with end cover, a piston rod, and a cylinder head. At one side the bottom is, for instance, connected to a single clevis, whereas at the other side, the piston rod is also foreseen with a single clevis. The cylinder shell normally has hydraulic connections at both sides; that is, a connection at the bottom side and a connection at the cylinder head side. If oil is pushed under the piston, the piston rod is pushed out and oil that was between the piston and the cylinder head is pushed back to the oil tank.

DIES:

V-dies—the most common type of die. The bottom dies can be made with different-sized die openings to handle a variety of materials and bend angles.

90 degree dies—largely used for bottoming operations. The die opening dimension depends on material thickness.

Beading dies—A bead or a "stopped rib" may be a feature that stiffens the resulting part. The punch has a rounded head with flat shoulders on each side of the bead. The bottom die is the inverse of the punch.

Channel-forming dies—A punch can be pressed into a die to form two angles at the bottom of the sheet, forming an angular channel.

Hydraulic circuits

 

 The equivalent circuit schematic.

For the hydraulic fluid to do work, it must flow to the actuator and or motors, then return to a reservoir. The fluid is then filtered and re-pumped. The path taken by hydraulic fluid is called a hydraulic circuit of which there are several types. Open center circuits use pumps which supply a continuous flow. The flow is returned to tank through the control valve's open center; that is, when the control valve is centered, it provides an open return path to tank and the fluid is not pumped to a high pressure. Otherwise, if the control valve is actuated it routes fluid to and from an actuator and tank. The fluid's pressure will rise to meet any resistance, since the pump has a constant output. If the pressure rises too high, fluid returns to tank through a pressure relief valve. Multiple control valves may be stacked in series [1]. This type of circuit can use inexpensive, constant displacement pumps.

Closed center circuits supply full pressure to the control valves, whether any valves are actuated or not. The pumps vary their flow rate, pumping very little hydraulic fluid until the operator actuates a valve. The valve's spool therefore doesn't need an open center return path to tank. Multiple valves can be connected in a parallel arrangement and system pressure is equal for all valves.