Altan T. Metal Forming Handbook

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Depending on the blank geometry, flexible notching systemswork

with transfers or robots.In this case, transport always takes place from

one pallet to the next (Fig. 4.6.17). The standard number of five sta-

tions can be extended at will. As for semi-automatic notching ma-

chines with numerical control, flexible automatic notching lines are

particularly suited for the manufacture of complex blanks: The same

selection criteria apply concerning controllable dies. At a higher level

of automation, automatic notching machines can be individually

adjusted to specific production processes. One such device joins baked

enamel-coated laminationsto create a complete lamination stackof the

type used in electric motors. The stator blanks are individually heated,

inserted in a basket-like device. Pressure is applied onto the complete

stack with each inserted lamination. A measurement device guaran-

tees a consistent stack height. Once the required stack height has been

reached, the basket-like device containing the laminated stack is swiv-

elled out. The pressing process is carried out while the next stack is

being formed. This curing period allows the coating on the lamina-

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Fig. 4.6.15 Complete blanking die for the production of segment blanks

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

tions to harden, fusing the stack together. The stack is then ejected

onto a roller conveyor.

Using a particularly flexible automation method, two individual

notching machines with pallet magazines and pallet storage stations

are linked by means of a pallet handling system. A host computer is

responsible for joint control. This allows both lines to produce stator

and rotor laminations for one size electric motors or for different inde-

pendent sizes.

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Sheet metal forming and blanking

Fig. 4.6.16

Automatic notching line for the production of stator and rotor laminations in two

passes with one notching machine (above) and in a single pass with two notching

machines (below)

position rotor blanks

notching machine:

notch rotor

deposit rotor

laminations

rotor blanks

deposit rotor

destack blanks

destack rotor blanks

orientation

notching machine:

notch stator and

separate

rotor

notching machine:

notch stator and

separate

rotor/notch

rotor

deposit stator blanks

deposit stator blanks/idle station

idle station

punch finish shaft hole

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

In general, large-scale special motors are custom-produced using blanks

which require up to seven different blanking operations (Fig.4.6.11).

The unproductive downtime involved in this type of process can account

for over 50% of the total production time as a result of the resetting

and handling work involved. For this reason, these blanks are most

economically produced using aflexible production cellwhich requires

only a single clamping operation. A central robot is responsible for all

handling functions and also for fully automatic die change. If the

blanks and dies are placed ready for processing during normal working

hours, the production cell is capable of operating unmanned round the

clock.

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Fig. 4.6.17

Flexible automatic notching machine with robot and pallet magazine (nominal press

force 250 kN)

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

Notching machines can be equipped with supplementary attachments

for special applications. These include devices for the production of

–interrupted hole patterns,

–tapered lamination stacks and

–skewed lamination stacks.

Blanking lines with complete blanking dies

Medium-sized batches of electric motors, finished segments, raw seg-

ments and pole blanks are generally produced using complete blanking

dies (Fig.4.6.13). Here, the external contours, holes and notches are

blanked in a single work process, generally using straight-sided presses

(cf. Fig.3.1.1).The press concept used here is similar to that of univer-

sal mechanical presses (cf. Sect. 4.4.1). It is also possible to manufacture

circular blanks, which are frequently used for further processing in

notching machines. The width of the individual blanks, strips or coil

material can be anywhere between 300 and 1,250mm. These presses

are constructed for blanking forces ranging from 1,250 to 5,000 kN. The

stroking rate can be adjusted continuously between 15 and 150 strokes

per minute depending on the size of the machine and the process engi-

neering concept used.

The diesare often constructed in such a way that the punch with the

outside contours is located in the bottom die holder and the female die

is located in the upper die holder. Several parts can be produced simul-

taneously. In some cases, the scrap is punched by the bottom die.

The separate stripper plate in the bottom die strips the scrap web

while the ejector in the upper die ejects the finished part. This requires

a plate or crossbar ejector in the press slide which is active near the top

dead center.

The gib columns generally extend out of the gib bushes when the die

opens. Therefore, they are usually manufactured of steel, while the gib

bushes are made of bronze. The coil guiding elements are combined

with the stripper plate.

As a single-unit welded construction, the press body is configured for

a high degree of rigidity. Considering that high-quality blanking dies

are used, the precision of the slide gib is of particular importance. The

eight-track roller gib system has proven to be an ideal system here

(cf.Fig. 3.1.6).The slide is equipped with a total of 16 roller elements,

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Sheet metal forming and blanking

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

which run, backlash-free, along hardened gib rails. Should the slide

become inadvertently jammed, the press can be quickly released with

the aid of hydraulic oil cushions under the connecting rods.

In earlier systems, presses equipped with complete blanking dies

required frequently manual loading. Now, however, automatedpart trans-

port is increasingly becoming a customary feature. But this is only possi-

ble where machines are equipped with coil lines (cf. Sect. 4.3) or blank-

loaders (cf.Sect.4.4.4) and part discharge devices. The press dimensions

are determined accordingly not only by the width of the coil stock being

processed and the necessary press force and the die dimensions, but also

by the greater space required to accommodate add-on units.

The processing of coil stock using a coil linerequires the use of a decoil-

er and straightening device as well as an efficient feed system at the press.

For small coil stock widths, a dual decoiler is generally used, while wider

coils are processed by a single decoiler with a coil lifting platform. A coil

loading car is also capable of accommodating two or three large coils.

The electronically controlled roller feed system has proven to be

highly popular for material feed.It is driven by a threephase servomotor

with control circuit, which allows the feed phase to be set depending

on the slide stroke and die engineering concept. Today, state of the art

presses are generally equipped only with one feed device at the materi-

al infeed side.

Individual components, such as unfinished segments, are inserted

into the die by a mechanically or electrically driven blankloader. The

roller feed for the coil stock and the blankloadercan be combined with

a vertical adjuster in such a way that one of the two is selected to be in

operation at any one time.

Using a plate-like feed device, the blankloader transfers the blanks

from the stack, which is raised by a lifting platform, to the press. The

electrical device is driven by a threephase servomotor and chain trans-

mission. Output is limited to some 20 blanks per minute. Mechanical

transfer systems driven directly by the eccentric shaft of the press via

cam indexing gears are able to transport up to 40 blanks per minute

depending on the part size.

Removal of the scrap webfrom the tool area is performed by a power-

driven magnetic roller. The scrap web created by the blanking process is

finally chopped by a cropping shear positioned on the outfeed side of

the press.

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

In the case of automatic part discharge, the stroke of the press slide lies

between 150 and 300mm due to the long discharge period. An

adjustable slide stroke offers the advantage that progressive dies with a

small stroke of for example 40 mm can be used to optimum effect (cf.

Fig. 3.2.13).Mechanical discharge devices which are either directly dri-

ven or controlled by the press are generally used.

The parts are ejected when the press is at its top dead center and they

are collected bydischarge plates,which deposit them outside the press on

a magnetic belt, as illustrated in Fig. 4.6.18for a finished segment.

Depending on the part size, this method limits the stroking rate of the

press to between 20 and 60 parts per minute. This requires a slide stroke

of 150 to 300mm. Due to the long slide stroke required, a part discharge

method has been developed in which the punched parts are collected

and pushed out by two raised lugsin the scrap web (Fig. 4.6.19).The dies

can be operated with a substantially smaller slide stroke of 70 mm, so

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Sheet metal forming and blanking

Fig. 4.6.18 Discharge plate and destacking magnetic belt for an unfinished segment

magneticbeltfor

finishedparts

scrapconveyorbelt

rollerfeed

liftingtable

finishedsegmentblank

dischargebelt

forunfinished

segments

dischargeplate

scrapweb

unfinishedsegment

coilstock

scrapchute

completeblankingdie

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

that up to 150 strokes per minute can be achieved depending on the

part size. This is only possible using a special ejector in the slide, which

ejects the part around 10 mm after the bottom dead center and deposits

it on the scrap web. During the subsequent feed movement, the blank

is engaged by the raised lugs and pushed out of the die. Behind the die

is a magnetic belt which takes the part and transports it in an overhead

position. The scrap web is chopped either directly behind the die or

using a separate cropping shear.

In comparison with conventional discharge systems, this method

permits the output to be doubled, so ensuring the economical applica-

tion of complete blanking dies. However, this method can only be used

when only one finished part is produced at a time and where the out-

side shape of the part permits discharge using raised lugs in the scrap

web.

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Fig. 4.6.19 Discharge of finished parts by lugs stamped into the sheet metal strip

magneticbeltfor

finishedparts

scrapconveyorbelt

rollerfeed

liftingtable

magneticroller

croppingshear

finishedpart

scrapweb

finishedblank

withshafthole

coilstock

completeblankingdie

scrapchuteforshafthole

scrapchute

transportluginthe

scrapweb

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

High-speed blanking lines with progressive blanking dies

Large series of rotor, stator and magnetic laminations are produced

using progressive blanking dies on high-speed blanking lines, in which

coil stock feed, part discharge and frequently also die changes are all

automatic (cf. Sect.4.6.3). In progressive blanking dies, piercing and cut-

out are executed first for the rotor and then for the stator (Fig. 4.6.20). At

feed rates of up to 100m/min over 1,000 parts per minute can be

punched. Where small feed distances are involved, output is limited by

the press stroking rate, while in the case of larger feed steps the output is

limited by the feed system.

Small blanks are frequently discharged using stacking channels.

Often, considerable time – up to three hours – is required for changeover

of the stacking channels in magnetic lamination production. Therefore,

automatic die change systems have been developed which permit lines

to be automatically reset in less than 10min. As a rule, these systems

comprise a die change cart capable of accommodating two dies, actua-

tors and positioning devices for the axes to be traversed, and a dialogue-

oriented, programmable logic controller. The dies are exchanged com-

plete with mounted and filled stacking channels (Fig. 4.6.21).After spec-

ifying the relevant die set, the complete die changing and resetting

process runs fully automatically.

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Sheet metal forming and blanking

Fig. 4.6.20

Progressive blanking die set for rotor and

stator blanks

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

Larger rotor and stator laminations, in contrast, are still arranged in

accordance with their notching pattern in the die, stacked on mandrels

or in magazines up to a preselected stack height and conveyed out of

the press by means of transport systems. A sequence of stacks of vary-

ing heights, for example for ventilated motors, can also be pro-

grammed.

Another method for the ordered unloading of electric laminations is

by punch-bundling (Fig. 4.6.22).For this purpose, additional punches

are located in the die set and they punch for example lugs, cams or neps

into the laminations. During the cut-out process, these raised areas

press the laminations into the corresponding recess in the previously

punched part (Fig.4.6.23).Once the required stack height has been

reached, the following lamination is pierced where the raised area is

prior to bundling by means of a piercing hole punch. This ensures that

the pierced lamination is not able to link up with the previous lamina-

tion and becomes the first lamination of the new stack.

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Fig. 4.6.21 Automatic die change using a die changeover cart

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

4.6.5 Production and processing of tailored blanks

Welded blanks comprising different materials, thicknesses or coatings

are known as tailored blanks. The most important benefits offered by

tailored blanks are weight savings and also reduction of the number of

parts required to form assemblies, for example in the case of car body

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Sheet metal forming and blanking

Fig. 4.6.22 Punch-bundled rotor and stator lamination stacks

Fig. 4.6.23 Joining laminations by means of punch-bundling

punch

blank

female

die

punched part

with cams

punched

part without

cams

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