Chapter 26 -

Chapter 26 Hydraulic presses

CHEN ZEZHONG MSE, USST

1

Materials Forming Processes and Machines

Chapter 26 -

Contents

• 26.1 Hydraulic press drives

• 26.2 Example

• 26.3 Advantages of hydraulic presses

• 26.4 Practical application of hydraulic presses

• 26.5 Exercise on Chapter 26

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Chapter 26 -

• The frames of hydraulic presses

– welded steel O-frames (straight-side frames)

(Figure 26.1).

– In smaller presses

• the frame is built in one piece

– in larger presses

• in three pieces.

• The three main elements

» bottom platen,

» side columns

» head

– are held together with tie rods.

3

Chapter 26 - 4

Figure 26.1 Three-part

hydraulic press.

1 head, 2 pump, 3 side

column, 4 press cylinder, 5

ram, 6 guide, 7 cross-

section of side column,

8 tie rod, 9 bottom platen

(Illustration from LASCO

Umformtechnik works,

Coburg, Germany)

Chapter 26 -

26.1 Hydraulic press drives

• The ram movement (Figure 26.2)

– is produced by a differential piston.

• the required amount of compressed oil

– In small presses,

• is provided by means of constant feed pumps (gear or screw

pumps)

– in larger presses

• by adjustable axial or radial piston pumps.

• The operating pressure for hydraulic presses

– is between 200 and 300 bar.

– Too low a pressure

• would require an oversized piston

– too high a pressure

• would mean leakage would be hard to control.

5

Chapter 26 - 6

Figure 26.2 Highly simplified drive layout of a

hydraulic press

Chapter 26 - 7

The most important technical data can be determined

as follows:

Chapter 26 - 8

Chapter 26 - 9

Chapter 26 - 10

Chapter 26 -

26.2 Example

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Chapter 26 - 12

Chapter 26 -

26.3 Advantages of hydraulic

presses • The advantages of hydraulic presses are:

– a) constant power all through the stroke,

– b) force can be finely regulated (so no extra

load-limiting safety device required),

– c) work capacity unlimited until Wmax = Fmax ·

smax.

• One disadvantage

– is the lower operating speed

• compared with crank presses,

• which results in lower output (parts per time unit).

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Chapter 26 -

26.4 Practical application of

hydraulic presses • 26.4.1 Drawing presses

• Generally wherever constant power along

a long stroke depth is required:

– forward extrusion of long parts,

– ironing,

– embossing and coining (here, there is

enough time for material to flow),

– deep drawing.

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Chapter 26 -

Triple-action drawing press

• triple-action presses

– For deep drawing,

– are sometimes used (Figure 26.4).

• The press shown here

– consists of two main elements:

• the press frame

• and the blank holder,

• as well as an ejector or a die cushion in the

bottom platen (Figure 26.4a).

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Chapter 26 - 16

Figure 26.4 Cross-section

of a triple action hydraulic

drawing press

(Illustration from Schuler,

SMG GmbH & Co. KG,

Waghausel, Germany)

Chapter 26 - 17

Figure 26.4a Layout of blank

holder, drawing ram and

ejector on the drawing press

(Illustration: Schuler, SMG

GmbH & Co. KG,

Waghausel, Germany)

Chapter 26 -

26.4.2 Deep drawing percussion

presses • Deep drawing percussion presses

– are also double- or triple-action drawing presses

– which can work

• both as normal drawing presses

• and also as drop hammers.

• In the double-action hydraulic deep drawing percussion

press

– shown in Figure 26.5,

– a drawing press is combined with a hammer.

– The die cushion to operate the blank holder

• is built into the lower part of this press, under the platen.

• It is driven separately,

– so the drawing ram and the die cushion can be controlled

completely independently of one another.

• The die cushion can also act as an ejector.

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Chapter 26 - 19

Figure 26.5 Electric/oil

hydraulic deep drawing

percussion press

1 axial piston pump, 2 press

piston, 3 ram 4 ram guide, 5

press frame, 6 bottom platen, 7

deep drawing die cushion

(Illustration from LASCO

Umformtechnik works, Coburg,

Germany)

Chapter 26 -

26.4.3 Hydraulic extrusion presses

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Figure 26.6 Hydraulic

double-sided extrusion

press

(Photograph: Dunkes

GmbH works, Kirchheim

unter Teck, Germany)

Chapter 26 -

• Hydraulic extrusion presses

– are used for manufacturing larger

workpieces

• using a cold forward extrusion method.

• This kind of workpiece

– requires constant force

– across a long distance.

• This is provided with a hydraulic extrusion

press,

– as the available deformation force does not

depend upon the deformation distance.

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Chapter 26 -

Homework: 2, 3, 4, 5

• 26.5 Exercise on Chapter 26

– 1. Explain the drive layout of a hydraulic press.

– 2. How is the ram speed raised on the return

stroke?

– 3. Why is high speed on the return stroke

desirable?

– 4. What is the difference between a double-

action and a single-action press?

– 5. What kind of operations are double-action or

triple-action presses needed for?

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