How does a hydraulic press work?

A hydraulic press is a machine that uses liquid static pressure to process metal, plastic, rubber, wood, powder, and other products. It is often used in pressing processes and pressing forming processes, such as forging, stamping, cold extrusion, straightening, bending, flanging, sheet metal drawing, powder metallurgy, pressing, etc. In heavy machinery manufacturing, the aviation industry, the plastic and non-ferrous metal processing industry, etc., hydraulic presses have become important equipment. This article will give a detailed introduction to the structural composition, working principle, characteristics, and other aspects of the hydraulic press.

The hydraulic press consists of two major parts: the main machine and the control mechanism.

1. Main machine: the "output end" of the force
The main machine is the "trunk" of the hydraulic press, the part that directly contacts the workpiece. It includes:

* Body: welded from cast steel or steel plates, like a solid "frame", it withstands the huge reaction force during pressing to ensure that the fuselage does not deform;

* Main cylinder: the "heart" of the hydraulic press, with a piston inside. When high-pressure liquid flows into the bottom of the main cylinder, the piston will be "pushed" to move upward or downward, directly completing the pressing, ejection, and other actions;

* Ejection cylinder: the "helper" of the main cylinder, usually installed at the bottom of the machine body. Its piston can move in the opposite direction to "push" the pressed workpiece out of the mold;

* Filling device: the "accelerator" of the main cylinder. When the main cylinder needs to move down quickly (such as moving without a load), the filling device will add liquid to the main cylinder to reduce the resistance of the piston movement and improve efficiency

2. Control mechanism: "regulator" of force
The control mechanism is the "brain" of the hydraulic press, responsible for converting electrical energy into hydraulic energy and accurately controlling pressure, flow, and direction. It includes:

* Power source (oil tank, high-pressure pump, motor): The motor drives the high-pressure pump to pressurize the hydraulic oil in the oil tank (for example, from 0.5 MPa to 35 MPa) to form a high-pressure oil flow;

* Hydraulic valve group (pressure valve, directional valve): like a "faucet" and a "switch", it controls the flow direction and flow of high-pressure oil. For example, the directional valve determines whether the oil enters the bottom of the master cylinder (pushing the piston downward) or the top (pulling the piston upward); the pressure valve limits the system pressure to prevent overload.

​​* Electrical system​​: Through sensors and controllers (such as PLCs) to monitor parameters such as pressure, temperature, and piston position in real time, the oil valve opening is automatically adjusted to achieve "precise force".

The core principle of the hydraulic press is hidden in the discovery of Pascal, a French scientist, more than 300 years ago: The pressure applied in a closed liquid will be evenly transmitted to every part of the liquid. Simply put, if you press on one end of a closed tube filled with water, the liquid at the other end will instantly "sense" the same force, just like using an "invisible water column" to "relay" the pressure.

The hydraulic press uses this characteristic to convert the "rotational power" of the motor or engine into the "static pressure" of the liquid, and then transmits the pressure to the working parts (such as the main cylinder piston) through the liquid, and finally converts it into a powerful mechanical force. It's like using a "liquid lever" - with a small input force, you can pry a huge output force (the size of the force is proportional to the area of ​​the piston). For example, a small piston with a diameter of 10 cm exerts a force of 1,000 Newtons. If it is transmitted to a large piston (diameter of 1 meter), the force generated can reach 1 million Newtons (equivalent to a weight of about 100 tons)!

According to the working medium used (liquid that transmits pressure), hydraulic presses are mainly divided into hydraulic presses and water presses. Their differences determine the application scenarios:

Hydraulic press: using water (or emulsion) as the medium, usually used in scenarios requiring ultra-large tonnage (such as forging large steel ingots, ship steel plate forming). Water has low compressibility and can transmit higher pressure (up to 100 MPa or more), but it is highly corrosive, and the system maintenance is more complicated.

Hydraulic press: using hydraulic oil as the medium, it is more widely used (such as plastic molding, automobile stamping, powder metallurgy). Oil has good lubricity and is easy to seal, but the upper limit of pressure is low (commonly 6-25 MPa), which is suitable for fine processing with high precision requirements.

The "power" of hydraulic presses is essentially a combination of Pascal's law and precision machinery. From the transmission of liquid pressure, to the collaboration between the main engine and the control mechanism, to the precise control of the working cycle, every step hides the ingenious use of "force" by humans. It can not only easily lift "thousand-ton burdens", but also complete precision molding at micron-level accuracy - this is why hydraulic presses have become the "core equipment" of the manufacturing industry. The next time you see a large forging press roaring, think about it: the seemingly simple "liquid flow" is quietly completing the most shocking industrial power transformation.