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Why does the hydraulic press work slower than the return stroke?

Views: 0 Author: Site Editor Publish Time: 2025-11-26 Origin: Site

The working speed of the hydraulic press is significantly slower than the return speed. This is not because it is technically impossible to achieve high speed, but because it is an active design trade-off based on power balance and molding process requirements. The core logic revolves around the inherent constraints of the hydraulic system 'pressure-flow-power' and is combined with the core demands of its industry application scenarios. The following is a detailed analysis from the four dimensions of principle, difference comparison, design considerations and application adaptation:

1. Core principle: 'Power balance law' of hydraulic system

The operating speed of the hydraulic press is directly determined by the flow of hydraulic oil (the greater the flow, the faster the actuator is pushed), and the core constraint of the system comes from the power limit of the hydraulic pump. The relationship can be expressed intuitively through the formula: pump power (P) = working pressure (p) × flow (Q) (Note: The formula is a simplified model, and the actual system efficiency needs to be considered, but the core logic is consistent)

The rated power of the hydraulic pump is a fixed value (determined by the motor power), so 'pressure' and 'flow' present a complementary relationship: when one of them increases, the other must decrease to ensure that the pump is not overloaded and damaged. This law is the fundamental reason for the difference between the working and return speed of the hydraulic press.

2. The core difference between work and return: load determines pressure, and pressure dominates flow.

In the working cycle of a hydraulic press (work advance + return stroke), the load requirements of the 'working phase' and the 'return phase' are very different, which directly leads to completely different distribution strategies of pressure and flow:

Stage	core task	load situation	work pressure	flow distribution	running speed
Work progress (working stage)	Material forming (stretching, bending, stamping, etc.)	Extremely large (need to overcome material deformation resistance and mold resistance)	Extremely high (usually tens to hundreds of MPa)	Forced reduction (to avoid overloading the pump power)	Slow (low flow drive)
Return trip (reset phase)	Actuator (slider) returns to initial position	Extremely small (only need to overcome its own gravity and sealing resistance)	Extremely low (only 1/5~1/10 of the working pressure)	Can be maximized (power redundancy is fully released)	Fast (high traffic drive)

To put it simply: when there is 'no load and low pressure' during the return trip, the power redundancy of the pump can be all converted into flow, so the speed is fast; when working 'when the load is large and the pressure is high', the power must be controlled by reducing the flow to avoid motor burnout or pump damage, so the speed is slow.

3. Design logic: 'Slow' is to meet core process requirements, not 'restriction'

The core of the design of the hydraulic press is 'forming quality first' rather than simply pursuing speed. The low-speed design in the working stage is a comprehensive optimization of multiple demands:

1. Ensure molding accuracy and quality (adapted to industry application scenarios)

Hydraulic presses are widely used in automobile, aerospace, pipeline and other industries. The core processing objects are high-demand structural parts (such as special-shaped pipe fittings for automobile exhaust systems, engine brackets, body frames, aviation hollow shafts, etc.). Molding of these parts requires:

Sufficient pressure (to overcome the deformation resistance of high-strength materials, such as high-strength steel, aluminum alloy, etc.);
Stable speed (to avoid uneven material deformation, wrinkles, cracks, or loose mold fit due to too fast speed).
For example, the hydroforming of the automobile body frame requires the slider to apply pressure at a slow and even speed to ensure that the pipe fittings are deformed evenly along the axis to meet the accuracy requirements of subsequent assembly (the error needs to be controlled within 0.1~0.5mm). If the working speed is too fast, not only will it not be able to provide sufficient molding pressure, but it will also cause stress concentration inside the material, directly affecting the service life of the parts. This is contrary to the industry's core demands for 'high strength and high precision' for structural parts.

2. Avoid system overload and energy waste

If the working speed is forcibly increased (that is, the flow rate is increased), under the premise of high pressure, the pump power will instantly exceed the rated value, causing the motor to be overloaded and burned, the hydraulic pump to wear and tear, and a large amount of energy consumption to be wasted (the combination of high flow + high pressure will increase energy consumption exponentially). The combination of 'high pressure and low flow' in design is the best solution to take into account equipment life, operational safety and energy efficiency.

3. Adapt to the collaborative needs of complex processes

The hydroforming process often involves multi-step collaboration (such as preforming, main forming, shaping, and pressure holding). Among them, the 'pressure holding stage' requires the slider to remain stationary or run at a very low speed to ensure that the material is fully shaped and internal stress is eliminated. The overall low-speed design of the working stage provides a stable process window for key steps such as pressure maintenance and pressure relief, and avoids poor process connection due to excessive speed.

4. Supplementary explanation: The working speed is not 'unadjustable' and needs to be optimized according to the scene.

Although the working speed of conventional hydraulic presses is slow, it is not absolutely fixed and can be accelerated through technological upgrades, provided that the molding quality and equipment safety are not sacrificed. Common solutions include:

Adopt a variable pump system: automatically adjust the flow rate according to the load, increase the flow rate and speed up when the load is light, and reduce the flow rate and maintain pressure when the load is heavy;
Dual pump/multi-pump linkage: dual pumps supply oil at the same time (high flow) during the return trip, and a single pump supplies oil (high pressure) during operation, taking into account both speed and pressure;
Speed-increasing cylinder design: Through the structural optimization of 'large cavity oil inlet and small cavity oil return', rapid work progress is achieved in the low-pressure stage and automatically switches to low speed during high-pressure molding;
Hydraulic oil cooling and filtration optimization: Reduce the viscosity drop caused by rising oil temperature and ensure flow stability during high-speed operation.

These solutions are usually used in scenarios with special requirements for efficiency (such as mass production of simple stamping parts). However, for the high-precision molding needs of industries such as automobiles and aviation, 'low-speed stable molding' must still be the core to avoid the impact of increased speed on quality.