Altan T. Metal Forming Handbook

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parts (Fig.4.4.4). This type of press is used for example for the produc-

tion of ball and needle bearing sleeves. Depending on the press size

– the rated press force of standard presses ranges from 1,250 to 4,000 kN

– up to 300 strokes per minute can be achieved using a special tri-axis

transfer system. The desired quality and output of the produced parts

place stringent demands on the press configuration, in particular on

the frame, drive system and slide gibs.

The required standard of drive system precision is achieved using an

eccentric shaft mounted in roller bearings. The shaft is driven by a com-

pact drive system with planetary gear. The roller bearings ensure only

minimal play in the power delivery system of the press. A further ben-

efit of the eccentric shaft mounted in roller bearings is that no addi-

tional release devices are required in case of press jamming due to an

operating error. The eccentric shaft drives not only the main slide but

also the transfer system, the draw cushion and a secondary slide. The

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Sheet metal forming lines

Fig. 4.4.3 Components and design of a hydraulic universal press

tie rod

slide

cylinders

slide

drawing die

bed cushion

high-speed

piston

bed cushion

cylinders

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

latter is also mounted in roller bearings and is used to cut the blank

from the coil stock. A zigzag feed device is used to improve material uti-

lization (cf.Fig.4.5.7and 4.5.8). In order to prevent any unwanted

effects of the blanking impact on the drawing operation carried out by

the main slide, the drive of the secondary slide by the eccentric shaft is

performed with a phase shift. A counterbalance mounted eccentrically

in the center of the drive shaft ensures smooth running of the high-per-

formance transfer press. For this reason, simple press installation is pos-

sible by means of damping elements.

Precise slide guidance is provided by four hardened gib columns with

roller cages and gib bushes on the forming level and at the top of the

slide. This system ensures optimum static and dynamic rigidity on the

horizontal plane, so enhancing the service life of dies (cf.Fig.3.1.5). The

rigid press body is a single-part welded structure, ensuring minimal tilt-

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Sheet metal forming and blanking

Fig. 4.4.4 Components and design of a high-performance transfer press

driveofejector

device

clutch-brake

combinationwith

compactdrive

electricmotor

formaindrive

dynamicbalancingunit

eccentricshaft(inrollerbearings)

transferdrive

rollercage

withgibbushes

mainslide

secondary

slide

gearwith

transferdrive

gibcolumn

ejectordevice

damping

element

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

ing of the slide even in the event of eccentric loading. This is an impor-

tant advantage which is particularly important during coining work.

Hybrid presses

Mechanical hydraulic presses, also known as hybrid presses, represent a

new development in the field of press engineering (Fig.4.4.5).This type

of press combines the benefits of mechanical and hydraulic presses. The

hybrid drive system allows gentle impact of the top die on the work-

piece, and also optimum control of the force exerted during the form-

ing process. In contrast to hydraulic presses, hybrid presses offer higher

output due to their mechanical basic drive system. Hybrid presses are

configured for both deep drawing and also complex stamping, blanking

and coining work, combining good flexibility and equipment availabil-

ity with high output.

As in mechanical universal presses, the top slide is driven by the

electric motor via the compact drive system, eccentric shaft and con-

necting rod (pitman aim) with eccentric bushings for adjustable stroke

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Sheet metal forming lines

Fig. 4.4.5 Hybrid press (nominal press force 3,150 kN)

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

(Fig. 4.4.6). The hydraulic bottom slide is used to alter the motion char-

acteristics and for tilt angle compensation. The impact speed on the

workpiece can be reduced by penetration of the bottom slide into the

top slide by up to 200mm/s (Fig. 4.4.7).If the top slide passes through

the bottom dead center (BDC) position, the bottom slide can be moved

up again, for example for coining. During this process, the bottom slide

and top die remain in the BDC position while the top slide is already

moving upwards.

In order to compensate for the lateral offset between the top and

bottom die, in particular when dies are used without guide posts or

gibs, an automatic centering device has been developed. This type of

device is commonly used, for example, in the cutlery industry. The bed

plate position is detected by position sensing systems and corrected

by comparison with the workpiece geometry. Correction is performed

by six horizontally arranged hydraulic cylinders, which are able to dis-

place and rotate the ball bearing-mounted clamping plate on the hori-

zontal plane within a range of hundredths of a millimeter to 1.5mm

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Sheet metal forming and blanking

Fig. 4.4.6 Components and design of a hybrid press

feed drive

slide

counter-

balance

hydraulic

cylinder

bed plate

shift device

bed plate

hydraulic

draw cushion

clamp set for stroke adjustment

eccentric shaft

clutch-brake

combination with

compact drive

hydraulic accumulator

for bottom slide

compressed air

accumulator for

slide counterbalance

mechanically actuated

top slide

hydraulically actuated

bottom slide

position sensing system

for the slide

scrap chute

damping element

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

(Fig.4.4.8). Once correction is completed, the bed plate is precisely

clamped in its new position by releasing the hydraulics.

Universal presses with modified top drive system

If an operating sequence involves a wide variety of work processes such

as drawing, blanking, bending, stamping or reducing, it is rarely possi-

ble to achieve ideal working conditions for the respective forming

process when using conventional press drive systems.

The modified knuckle-joint system used in mechanical presses offers

considerable benefits (Fig. 4.4.9)when it is necessary to satisfy the wide-

lydiffering demands made on the optimum forming velocity for uni-

versal operating sequences. By actuating the press drive and slide in this

special way, it is possible to alter the movement and velocity profile of

the slide (Fig. 4.4.10). A velocity reduction is achieved over a relatively

large slide stroke in the working area, while the idle strokes for forward

and return travel are conducted at increased speed (compared to eccen-

tric and knuckle-joint drive system) (cf. Fig. 3.2.3).

This drive system provides power transmission from the drive to the

slide, allowing to achieve high press forces and nominal force-displace-

ment curves with a relatively small drive torque. As a result, the gearbox

with clutch and brake can be produced in a compact and cost effective

way.

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Sheet metal forming lines

400

300

200

100

– 100

– 200

– 300

– 400

200

150

100

0 90 180 270 360

crank angle [°]

TDC TDC

slide velocity V

[mm/s]

slide velocity V

slide displacement h [mm]

BDC

slide displacement h

Fig. 4.4.7

Slide displacement and

velocity versus crank angle

of a hybrid press

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

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Sheet metal forming and blanking

Fig. 4.4.8 Clamping and release device for an adjustable bed plate

shift ball bearings

hydraulic piston

press bed

cup springs

clamping plate

bed clamping plate

Fig. 4.4.9

Universal press with modified top drive

(nominal press force 8,000 kN)

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

The two links are located at the outsides of the slide and allow for

good compensation of the eccentric forces that may occur. Direct appli-

cation of force in the upright area of the press crown helps to reduce

deflection and bending and makes a major contribution to high system

rigidity. The lateral forces, caused as a result of the force exerted by con-

necting rod, are absorbed by a crossbar, so that they cannot adversely

affect the slide gibs. This system permits extremely precise slide guid-

ance under load.

The reduced forming speed permits a higher stroking rate during

drawing and reducing processes, protects the dies and reduces noise

development. In addition, the added rigidity offers a number of bene-

fits during stamping due to precise, plane-parallel forming. A reduction

of dynamic deflection effects and blanking shock, as well as lower

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Sheet metal forming lines

Fig. 4.4.10

Structure of a

modified top drive

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

impact speeds allow to extend service life considerably. Through this

optimization of working and forming conditions improved part quali-

ty and increased tool life are achieved while increasing stroking rates.

The variety of parts which can be produced on these lines include

evaporator plates, bearing elements, hinges, hardware fittings and oth-

er components supplied to the automotive industry as well as parts for

refrigerators, lock elements and clutch disks.

4.4.2Production lines for the manufacture

of flat radiator plates

The combined forming and coining of large-panel press parts, such as

those needed to make the plates for flat radiators, calls for a press sys-

tem with extreme system robustness together with a generously dimen-

sioned die space. In view of the wide variety of radiator designs, a uni-

versally applicable die technology concept is required.

High production output levels are only achievable using fully auto-

mated production lines which permit set-up within a short period for

the production of different parts. Special press systems, with a nominal

press force of between 4,000 and 10,000 kN (Fig.4.4.11), have been

developed for the manufacture of flat radiator plates.

In order to achieve the largest possible system robustness, a bottom

knuckle-joint drive system was selected (cf. Fig.3.2.3). This principle is

distinguished by the highly compact, low-deflection construction of

the knuckle-joint bearing and the press bed. As blanks with large sur-

face area require large bed surfaces, a double knuckle-joint system is

provided to improve press bed support. This design corresponds in

principle to the single knuckle-joint system illustrated in Fig.3.2.5.

The widely spaced link joints of the double knuckle-joint ensure tilt-

resistant drive of the press frame. The height position of the upper die

is adjusted by two wide power driven wedges which cover the entire die

width. Due to the reduction in forming speed and the optimized weight

of the slide frame construction, the knuckle-joint drive system ensures

a high stroking rate in conjunction with smooth, quiet press operation.

An optimized welded design of the press frame allows even wider

machines, with a frame width of up to around 2m, to be run at high

speeds. A press with a nominal press force of 7,100 kN, a frame width of

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Sheet metal forming and blanking

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

1,860mm and a working stroke of 80mm can produce 80 strokes per

minute in continuous operation.

The machine is based on a modular design and can be equipped, as

required, with or without a hydraulic draw cushion in the press bed and

slide (cf.Sect.3.1.4). The wedge adjustment of the slide ensures the

high degree of rigidity required for drawing and coining work.

The modified knuckle-joint geometry and the connecting rod link-

age prevent the knuckle-joint system from being fully extended at the

bottom dead center. The bottom dead center has already been reached

when the knuckle-joint system is still located some 2 to 3mm before

the maximum extended position. This design feature eliminates any

possibility of press jamming, and the need to use a hydraulic overload

safety system. The press force monitoring can take place exclusively

with electronic measurement systems.

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Sheet metal forming lines

Fig. 4.4.11

Bottom drive knuckle-joint press

for the manufacture of flat

radiator plates(nominal press

force 6,300 kN)

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

The slide gib is mounted at six points in spherical ball joints (cf.

Fig. 3.1.5). The necking action of the press frame which occurs under

load is compensated by a supplementary internal slide gib in the bed.

Pneumatic slide weight compensation is performed by maintenance-

free bellow cylinders (cf. Fig. 3.2.11). The die mounting area is designed

to permit the use of all feasible die systems:

–single-action dies for individual radiator plates,

–double-action dies which can be used to stamp two adjacent plates

from wide coil stock,

–sandwich dies in which two blanks are fed one above the other and

two plates, i.e. top and bottom plates are pressed at the same time.

The sheet material is fed by an electrical roll feed system located on the

back of the press, above the drive system. Special frame seals prevent

the die lubricating emulsion from penetrating into the driving unit.

Surplus emulsion is collected in a peripheral groove at the press bed or

press frame and returned to the system to perform further greasing or

lubrication work.

The line is controlled by a PLC control system with operator guid-

ance and program pre-selection for different radiator types. The num-

ber of parts necessary for corresponding lengths can be put into the

controller by specifying the appropriate radiator plate type.

The complete line is supplemented by a decoiler and a die change

cart or a die change system with quick-action die clamping on the slide

or bed plate (cf. Sect. 3.4). Scrap disposal takes place under the die by

means of a scrap chute directly into a scrap container. All the drive

units are accessible from the floor.

4.4.3Lines for side member manufacture

Production methods

The production of chassis side members for the truck industry is carried

out in two steps: First, a blank is cut out and perforated. Next, the blank

is bent to a U-shape to form a side member, while simultaneously web

necks and where applicable also offsets are formed (Fig. 4.4.12). Left-

and right-hand members, for instance, must be configured in mirror

image to each other and have reduced rib heights in the area of the dri-

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Sheet metal forming and blanking

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