普通液压机基本原理是油泵把液压油输送到集成插装阀块，通过各个单向阀和溢流阀把液压油分配到油缸的上腔或者下腔，在高压油的作用下，使油缸进行运动.液压机是 利用液体来传递压力的设备。液体在密闭的容器中传递压力时是遵循帕斯卡定律。四柱液压机的液压传动系统由动力机构、控制机构、执行机构、辅助机构和工作介质组成。动力机构通常采用油泵作为动力机构，一般为积式油泵。为了满足执行机构运动速度的要求， 选用一个油泵或多个油泵。
The principle of ordinary hydraulic press is that it is made of Pascal's law and driven by liquid pressure. There are many kinds of machines. Of course, there are various uses according to the needs. The hydraulic press is not only used for forging, but also for straightening, pressing, packing, pressing block and pressing plate.
The basic principle of the common hydraulic press is that the oil pump transmits the hydraulic oil to the integrated cartridge valve block, distributes the hydraulic oil to the upper or lower cavity of the oil cylinder through each check valve and overflow valve, and makes the oil cylinder move under the action of the high pressure oil. The hydraulic press is a device that uses the liquid to transmit the pressure. When liquid transfers pressure in a closed container, it follows Pascal's law. The hydraulic transmission system of four column hydraulic press consists of power mechanism, control mechanism, actuator, auxiliary mechanism and working medium. The power mechanism usually uses the oil pump as the power mechanism, generally the integral oil pump. In order to meet the requirements of the moving speed of the actuator, one or more oil pumps are selected.
The servo motor drive of hydraulic press is to replace the common motor of driving press with servo motor, that is, servo hydraulic press, also known as servo press and servo press. The movement curve of the slider of the servo hydraulic press can be set according to the stamping process, and the stroke can be adjusted. This kind of press is mainly for the high-precision forming of difficult to form materials and complex shape parts. It greatly improves the processing accuracy and stamping efficiency of the press, and also cancels the flywheel, clutch and other parts, reduces the production cost of the enterprise and saves energy.
The development of servo hydraulic press is seriously affected by servo motor. At present, the hydraulic press driven by servo motor is mainly some small tonnage presses. In order to break through the limitation of servo motor, the hybrid driving mode is a developing direction of press at present. The structure of the hybrid drive press adopts differential wheel to realize the hybrid input of common motor and servo motor, and adopts two degree of freedom rod system to realize the hybrid closed two-point press.
Because of its servo function, the moving curve of the slider is not only a sine curve, but also an arbitrary curve that can be optimized according to the technological requirements. Because the linear grating ruler is used to detect the position of the slider, the slider has high motion control accuracy throughout the whole working process of the press, especially near the bottom dead point, which can ensure that the accuracy of the slider changes within ± 0.01mm, thus ensuring the accuracy stability of the closing height of the press in the production process, inhibiting the occurrence of product burrs, and preventing the production of bad products. Because of the advantages of the crank press, the productivity of the servo hydraulic press is much higher than that of the hydraulic press, which embodies "the processing quality of the hydraulic press and the production efficiency of the mechanical press". Moreover, the crank press driven by the servo motor can adjust the stroke of the slider according to the different workpieces. In a working cycle, it does not need to complete 360 degree rotation, but only carries out a certain angle swing to complete the stamping work, which further shortens the cycle time. Minimize the unnecessary travel and greatly improve the productivity.
The main difference between servo hydraulic press and common hydraulic press is the difference of power source. One is to use the hydraulic oil cylinder in the hydraulic system to generate pressure, the other is to use compressed air as the power source and use the air cylinder to implement the device, which is their essential difference.