Altan T. Metal Forming Handbook

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Consequently, extremely precise pressed parts can be produced. Cen-

tral offset, in particular, is considerably lower than when using conven-

tional gib systems. As a result, additional measures such as lateral punch

adjustments or column gibs can be eliminated.

In warm and hot forming applications, this concept is supplemented

by highly efficient cooling systems which substantially reduce the over-

all heat generation in the dies.

Horizontal multiple-station presses for manufacture of pressed parts

made of wire

The major benefit of horizontal multiple-station presses is that wire,

suitably pre-treated for cold forming, can be used. Thus, the manufac-

ture of (largely cold pressed) contoured parts is possible without addi-

511

Presses used for solid forming

Fig. 6.8.5 Warm forming line comprising a multiple-station press with eccentric drive

(nominal press force 20,000 kN, induction furnace, transfer feed and die change

support)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

tional chemical or thermal treatment. The wire is drawn and straight-

ened by a wire feed device. An integrated shearing system with closed

shearing dies is used to produce volumetrically precise slugs. The spe-

cial gripper transfer system transfers the parts from one station to the

next (cf. Sect. 6.6).

The main design feature of the press line illustrated in Fig. 6.8.6is the

laterally positioned die mounting area which is accessible from the

operator’s side. This concept permits an ergonomically favorable tool

setting and convenient tool change. Other important design features

include the highly robust slide gib against off-center loading, the cast

monobloc frame structure (cf.Fig.3.1.1)and individually adjustable

gripper and ejection systems for each press station.

The production stroking rates for this type of press are substantially

higher than that found in comparable vertical multiple-station presses.

Thus, the use of these presses is highly economical for large-scale pro-

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Solid forming (Forging)

Fig. 6.8.6 Horizontal multi-station press suitable for fasteners and form parts manufactured

from wire (nominal press force 1,300 kN, five stations, quick tool change system,

wire diameter max 18 mm)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

duction despite the high initial investment costs involved. By using

semi-automatic and automatic die resetting and die change systems, set-

up times can be substantially reduced, meaning that even medium

batch sizes of 20,000 to 40,000 parts can be economically manufactured

(cf.Fig.3.4.5).The presses are used at nominal press forces of between

1,000 and 6,300 kN for wire diameters ranging from 10 to 36 mm.

Horizontal presses – single-station with knuckle-joint drive

These press systems are used mainly for the production of extruded

parts made of aluminium and aluminium alloys (Fig.6.8.7): These

machines are also ideally suited for pre-forming steel slugs. The presses

are fully automated and make use of simple, cam-controlled pushers for

part feed. The horizontal design, simple part feed and discharge and the

superior forming characteristics of aluminium permit high stroking

rages of up to 300/min. Compared with vertical presses, substantially

higher stroking rates also result when forming steel. Nominal press

forces range between 1,500 and 12,000 kN.

513

Presses used for solid forming

Fig. 6.8.7 Single-station horizontal press with knuckle-joint drive

(nominal press forces 1,500 to 12,000 kN)

punch

slide

connectingrod

eccentricdrive

fixedlinkpoint

driveshaft

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Horizontal presses with modified knuckle-joint

If longer forming strokes are necessary, a modified knuckle-joint drive

system can be used as a special variation of the standard knuckle-joint

power unit. The force-stroke curve and the slide velocity correspond to

the vertical press shown in Fig. 6.8.3.

6.8.3Hydraulic presses

Hydraulic presses are also designed in vertical and horizontal layouts.

They enjoy extremely universal application in solid forming both on a

single-station and multiple-station basis, either with manual operation

for small batch sizes or fully automatically for production rates of up to

1.8 million pressed parts per year. They are frequently used as presses

for long shafts and shaft-type parts, or for large parts with weights of up

to approx.15 kg.

As in mechanical presses, the selection of the necessary press size is

made on the basis of part geometry, workpiece material and of the

required manufacturing process. The basic principles are described in

Sects. 3.3 and 6.5.

Vertical design

The hydraulic components and oil tanks are generally accommodated

in the press crown (Fig.6.8.8).A service platform offers convenient

maintenance of the easily accessible units. The uprights are generally

configured in the form of a welded monobloc or panel structure (cf.

Fig. 3.1.1).

In special cases (for example in the event of space problems or to

reduce noise), the pumps and motors can also be mounted in the foun-

dation or in a separate room. Vertical hydraulic presses are generally

used for cold forming. However, it is not unusual for them to also be

used for hot forming under certain circumstances (cf. Sect. 6.8.5). Par-

ticularly where large parts are involved (weights above 5 kg), hydraulic

presses are frequently used for hot forging. The usual press forces lie

between 1,600 and 36,000 kN, and presses with slide strokes of up to

1.5 m have already been manufactured.

514

Solid forming (Forging)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Horizontal design

Long tubular parts such as shock absorber sleeves are drawn from

flat blanks or backward cup extrusions made from circular blanks (cf.

Fig.6.1.1).A subsequent ironing process over several stages then

reduces the wall thickness (cf. Fig. 6.1.2).The workpiece is held by a

punch, which draws it through one or more ironing rings. The bottom

thickness remains unchanged. For this process, extremely long forming

strokes are required. Therefore, in such applications hydraulic presses

are most frequently used.

A horizontal press layout has a number of benefits to offer here:

–set-up on floor level,

–simple gravity feed,

–simple discharge by means of synchronized conveyor belts,

–simple interlinking, for example with automatic edge trimming de-

vices.

515

Presses used for solid forming

Fig. 6.8.8 Hydraulic multiple-station press (nominal press force 20,000 kN,

four stations, loading system, transfer feed and die change support)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Figure 6.8.9illustrates the layout of a particularly economical press sys-

tem for ironing. The slide is driven on two sides by plunger pistons. The

die sets are located on both sides with loading chambers positioned in

front. The right and left-hand punches are guided immediately in

front of the workpiece loading chamber using an additional punch sup-

port. With each stroke, alternatively forming and stripping of the

formed part take place on either side. Each new workpiece pushes the

previously stripped part through the workpiece holder out of the press.

With the same forming process taking place in the left and right-hand

die sets, it is possible to almost double the output compared to a con-

ventional vertical press design. Alternatively, the part produced in one

of the die sets can be further processed in the other die set following

intermediate treatment. In the case of thick-walled blanks, an upstream

deep-drawing process can be integrated as an initial operation. Precise

slide guidance on the press bed and precisely adjustable punch guid-

ance permit to obtain extremely narrow tolerances concerning the con-

centricity of dimensions.

516

Solid forming (Forging)

Fig. 6.8.9 Horizontal hydraulic press with one slide and two press beds

punch guide

loading chamber

punch supportironing ring

stripper

slide die chamber

slide stroke

die holder die holder

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

6.8.4Supplementary equipment

A large number of special measures and equipment are available to ad-

dress ever more stringent demands for maximum possible production

outputs, low set-up times and the minimum achievable manufacturing

costs. The most important elements here are systems for the automatic

loading and transfer of parts through various die stations.

Loading systems for blanks and pre-formed workpieces

Where parts weighing less than 150 g are produced, presses are general-

ly loaded using vibration feeding devices which are filled using inclined

conveyors. Heavier parts are generally fed using inclined conveyors

with rotating steel belts or – in particular where pre-formed parts are

being fed – by means of pushing conveyors. The outfeed area of these

systems is equipped with devices for part orientation to ensure that the

parts are correctly aligned when they enter the in-feed channel and the

loading station (Fig. 6.8.10).

517

Presses used for solid forming

Fig. 6.8.10 Loading device for cold extrusion press lines

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Feed systems

A number of different feed systems can be used to transfer the parts

through the press and into the dies. The so-called transfer feed system

is the dominating method for vertical multiple-step presses. Feed sys-

tems come in a dual-axis version, or with an additional lifting stroke for

long parts, in the form of a tri-axis transfer. The control cams are driven

in mechanical presses by direct coupling with the press drive system. In

the case of hydraulic presses, the various units are actuated by servo dri-

ve systems(Fig. 6.8.11).

Hydraulically driven swivel-mounted grippers are used to transport

heavy pressed parts with weights over 5 kg (Fig. 6.8.12). The controlled

grippers are configured for a substantially higher clamping force than is

possible using transfer feed systems. The swivel-mounted grippers gen-

erally execute a lifting movement. A loading arm (swivel or linear move-

ment) is used to transfer the parts from the loading station into the first

pressing station, and one gripper arm is allocated to each die station.

518

Solid forming (Forging)

Fig. 6.8.11

Two-axis transfer feed

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

In addition to these systems, a number of other feed devices is used

including the freely programmable handling robot. In horizontal mul-

tiple-station presses, gripper arms powered individually by cams or ser-

vo drive systems are used.

Weight control

When billets are prepared, weight differences are unavoidable. These

are the result not only of length tolerances occurring during the billet

separation, but also (sometimes to a far greater extent) of diameter tol-

erances in the starting material. Particularly when using closed

(trapped) die systems, exceeding the admissible blank weight may

cause die failure.

When transporting the container filled with billets to the intermedi-

ate treatment processes and to the press, it is also possible for parts to

be accidentally placed in the wrong containers. This can naturally lead

to die damage when pressing. In order to eliminate the risk of feeding

incorrect parts, automated press lines are frequently equipped with a

519

Presses used for solid forming

Fig. 6.8.12 Swivel arm feed for pressed parts with piece weights up to 15 kg

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

device which checks part weight. The devices used here are electroni-

cally controlled automatic scales, which are mounted between the

loading system and the feeding station. Parts which are too heavy or

too light are automatically ejected. The weighing accuracy is below

0.2% of workpiece weight. These devices are able to weigh automati-

cally up to 80 parts per minute.

Die change

Fast die change can be a decisive factor when it comes to the economic

viability of a press, in particular when working with small batch sizes.

Both die set and individual die changing systems are used (cf. Fig. 3.4.5).

The basic die change principle used in presses for sheet metal forming

and solid forming are very similar. A more detailed description is pro-

vided in Sect. 3.4. However, die change is only one aspect which deter-

mines short set-up times in automatic press lines. Fast resetting of the

loading and feed systems is equally important here.

6.8.5Special features of hot and warm forming lines

The special supplementary equipment described in Sect. 6.8.4 is also

used for hot forming. An additional and essential requirement of hot

forming systems is an effective cooling and lubrication system.

Depending on the degree of forming difficulty, basically two different

systems are used:

Flooding

Dies are cooled and lubricated by continuous flooding using special

lubricants, some of which are mixed with water at a ratio of between

1 : 2 and 1 : 4. The lubricant and water mixture is fed towards the die

through boreholes and spray rings, and drains away via generously

dimensioned channels. The lubricant is supplied from a central reservoir

with a capacity of between 400 and 1,000l by means of medium pres-

sure pumps (working at a pressure level of 10 to 20 bar) (cf. Sect. 3.2.11).

Used lubricating emulsion is collected, purified and returned to the

reservoir, which is equipped with a re-cooling system. Filters in the

return and pressure circuits take care of the necessary purification. The

lubricant is mixed with bactericides in order to prevent bacterial infes-

520

Solid forming (Forging)

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998