Introduction

A typical feature of a hydraulic press is its hydraulically driven main axes. The main difference between a hydraulic axis and an electrically driven axis is that the hydraulic axis is more compact and generates high forces in a small working area. Further features are:

• Distance or process-controlled traversing of velocity profiles
• Distance, time or process-controlled traversing of pressure profiles

These features make hydraulic presses a universal tool suitable for use in a wide variety of industries. Various types of presses are used for metalworking and processing according to the application:

Solutions for hydraulic presses

Dynamic development is currently taking place in the field of hydraulic presses, combined with an increase in the degree of automation. An example of development is the use of a position control system with servo valves for rapid and accurate positioning of the punch and die cushion.

For reasons of cost, hydraulic axis movements have generally been controlled up to now by open-loop systems using on/off valves and simple proportional valves. Improved technology and a better price/performance ratio of proportional and servo valves are increasing the demand for closed-loop control of hydraulic axes.

A hydraulic press can be used either in an individual machine or as the core component of a production line. In the second case, appropriate handling units are added to the press.

The concepts below show solutions for hydraulic presses with open and closed-loop axis control.

• Single press with open-loop axis control (2 cylinders)
• Single press with open-loop axis control (3 cylinders)
• Single press with closed-loop axis control and mechanization (e.g. electronic transfer)

Функции [PDF]

Функции

The operating principle of various types of presses is described below.

Punching presses

Punching presses use one operating axis: the punch. The punching process is carried out by moving the punch; the press table or die cushion is fixed. The movement starts from the top dead center point (TDC). The punch is moved at the maximum speed (rapid traverse) into the working area. When the plunger surface switches from the rapid traverse area to the machining area, the speed is reduced to the machining rate. When the tool makes contact with the material, the cylinder pressure in increased until the material is pierced. A rapid change in the traversing direction after the bottom dead center (BDC) is reached prevents the tool from penetrating the die. The further the tool penetrates the die, the greater the tool wear. After the tool is returned to the upper dead center of the plunger stroke, a new punching operation begins. Further functions include:

• Bit stop
• Antivibration
• Press force monitoring.

Finish blanking and finish cutting presses

Finish blanking presses use a blankholder in addition to the punch. The blankholder (2 cylinders) or a knife-edged ring secures the workpiece while the punch (1-2 cylinders) carries out the punching operation.

Mechanization: The material is transported by 2 feeder units (infeed, outfeed).

Number of strokes: < 120 H/min (stroke height approx. 20 mm)
Working stroke: 20 mm to 300 mm
Rapid traverse rate: 200 mm/s
Cutting rate: 10 mm/s to 50 mm/s
Blankholder force: 400 kN to 4000 kN

Drawing presses

In terms of drawing press design, we distinguish between single, double or triple-acting presses. In simplified terms, this distinction refers to the number of axes acting on the blank (punch, die cushion, blankholder). The hydromechanical press is a special type of drawing press. In hydromechanical forming, the blank is pressed against the inserted drawing punch by a medium subjected to high pressure (e.g. water emulsion). This process takes place in a controlled chamber and enables high drawing ratios and complex forming in a single machining operation.

Large-part drawing presses

Large-part drawing presses differ from single-acting drawing presses primarily in relation to the number of cylinders per working axis (punch, die cushion).

IHP internal high-pressure forming (without diagram)

IHP technology is based on water and its ability to transmit pressure equally to all sides. A tube inserted in negative format is sealed at both ends and subjected to internal water pressure. It is formed into the defined shape by simultaneous swaging. A regular material flow takes place in the tube wall such that the wall thicknesses of the finished part can be formed to minimum tolerances. This technology can be used to manufacture workpieces with complex geometries with different cross-sections and parts with curvature in the longitudinal axis. Even parts with low extensibility such as alloy plating can be formed well beyond the degree of bending previously attainable.

Powder metal press

Powder metal presses enable the manufacture of complex parts to high precision (e.g. gearwheels). There are three steps in the process used to manufacture workpieces from metal powder:

• Forming of the part to the shape of the installed die (tool) by compacting the metal powder in the powder metal press
• Sintering of the part in an oven at approximately 1000 °C
• Calibration of the workpiece with a calibration press

Powder metal presses have 3 main axes (upper punch, lower plunger for the die movement, and fill shoe), as well as further axes integrated in the tool.