This paper first summarizes the application fields, working principles, classification and characteristics of hydraulic presses for forging and pressing machine tools. Then it reviews the current technical status of hydraulic presses at home and abroad. Finally, the future development trends of hydraulic press technology are prospected.

1 Overview

As one of the most widely used equipment in product forming manufacturing, hydraulic presses have developed rapidly since their emergence in the 19th century and have become indispensable in industrial production. Due to their wide adaptability in operation, hydraulic presses have been extensively applied in various sectors of the national economy, such as sheet metal forming; extrusion of pipes, wires and profiles; powder metallurgy, plastic and rubber product molding; plywood pressing and baling; production of synthetic diamonds, refractory bricks and carbon electrode pressing; wheel and axle press-fitting, straightening, and so on. The rapid development of various types of hydraulic presses has effectively promoted the progress of various industries.

Since the 1980s, with the development and popularization of microelectronic technology and hydraulic technology, hydraulic presses have achieved further advancement. At present, the maximum nominal pressure of hydraulic presses has reached 750 MN [1], which is used for die forging of metals. Many models adopt CNC or industrial PC control, which greatly improves processing quality and productivity.

With the improvement of living standards, the demand for metal pressed and drawn products has increased year by year, and the demand for product varieties has also grown. Meanwhile, production batches are becoming smaller. To adapt to small and medium-batch production, processing equipment with quick adjustment capability is required, making hydraulic presses ideal forming equipment.

Especially after hydraulic systems realize independent adjustment of pressure, stroke and speed, they can not only process complex and asymmetric workpieces but also achieve an extremely low scrap rate. This processing mode is also suitable for long-stroke, difficult-to-form and high-strength materials. Flexible power combinations, short processing cycles, and easy adjustment of pressure and stroke according to workpiece length give hydraulic presses obvious advantages over mechanical processing systems.

2 Characteristics and Classification of Hydraulic Presses

As a general non-cutting forming machine, a hydraulic press transmits energy through liquid pressure to complete various pressure processing operations.

Its main characteristics are:First, it adopts flexible transmission, avoiding the complex transmission structures of mechanical processing equipment and providing inherent overload protection.Second, the drawing process produces only a single linear driving force without angular forces, resulting in longer service life and higher workpiece yield.

Hydraulic presses have three basic operating modes: single-action, double-action, and triple-action.

In single-action presses, the ram or slide moves in one direction to complete pressing without a blank holder. They are mainly used for thin workpiece forming with coil and strip materials.

Double-action presses have two moving parts: the slide (punch) and the die cushion. The punch performs drawing, while the cushion acts as a blank holder and ejector. The pressure of the cushion can be adjusted based on material and workpiece parameters.

Triple-action presses include a deep-drawing slide, a blank-holding slide, and a lower cushion. They can perform complex deep drawing and also operate as double-action presses.

According to frame structure, hydraulic presses can be divided into column-type, assembled frame-type, integrated frame-type, single-arm (C-frame) type, etc.According to function and application, they are classified into manual hydraulic presses, forging hydraulic presses, stamping hydraulic presses, general-purpose hydraulic presses, straightening and press-fitting presses, laminating presses, extrusion presses, compression presses, baling presses, special hydraulic presses, and others.

3 Development of Hydraulic Press Technology at Home and Abroad

As the hydraulic system and overall structure of hydraulic presses have become relatively mature, the development of hydraulic presses worldwide is mainly reflected in control systems. The rapid advancement of microelectronics has made it possible to improve performance, stability and efficiency.

In general, although domestic hydraulic presses cover a complete range of models, their technical content is relatively low, and high-end models are insufficient, which is inconsistent with the trend of mechatronics and flexible small-and-medium batch production.

Hydraulic presses can be divided into three categories based on control systems:

Traditional presses dominated by relay control

Presses controlled by programmable logic controllers (PLC)

High-performance presses using advanced microprocessors or industrial PCs

Their functions and applications differ, but the overall trend is toward higher speed and intelligence.

(1) Relay Control

Relay control is a traditional method used for decades. It features simple circuits, low technical requirements and low cost, but limited functions and poor flexibility. It is suitable for single machines and mass production with low precision requirements (e.g., tableware, kitchenware). Due to circuit limitations, stability and flexibility are insufficient.

At present, many domestic manufacturers still produce such machines, mainly for small workshops or low-precision civil products. Foreign manufacturers generally only retain production capacity and focus on the two more advanced types.

(2) PLC Control

PLC-controlled hydraulic presses represent the mainstream of modern presses. They offer stable performance, strong anti-interference ability, low failure rate, and flexible programming. They adapt well to multi-variety, small and medium-batch production and can form automated production lines.

(3) Advanced Microprocessor / Industrial PC Control

This type represents the highest technical level of hydraulic presses. Based on high-performance microprocessors or industrial computers, it achieves closed-loop precise control of pressure, stroke, speed, temperature and other parameters. It supports data collection, process storage, fault diagnosis, remote monitoring and intelligent adjustment.

Equipped with CNC systems, these presses achieve high precision and efficiency for complex workpieces and high-strength materials. Foreign leading enterprises have realized mass production, while domestic manufacturers are accelerating research to break the monopoly in the high-end market.

4 Development Trend of Hydraulic Press Technology

Driven by Industry 4.0, intelligent manufacturing and green manufacturing, hydraulic press technology is developing toward:

Ultra-large and micro-scale polarization

High precision and intelligence

Energy saving and environmental protection

Modularity and flexibility

Future hydraulic presses will become intelligent terminal units integrated into the smart manufacturing system, with capabilities such as remote monitoring, predictive maintenance, self-adjustment and process optimization.

The domestic hydraulic press industry will continue to focus on breakthroughs in core components, high-end hydraulic systems and intelligent control systems, narrowing the gap with advanced international levels, and promoting the transformation from large-scale production to high-quality, high-end equipment, providing strong support for the high-quality development of China’s manufacturing industry.