Altan T. Metal Forming Handbook

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reinforcing components (Fig.4.6.24).In the production of complete

assemblies, this reduces lead times and the susceptibility to corrosion

due to the smaller number of welding joints.

By using scrap parts from previous blanking operations, for manu-

facturing tailored blanks it is possible to reduce scrap in the stamping

plant. Costs for input materials can also be reduced by using lower-cost

sheet metal grades for low-stress applications. In addition, tailored

blanks can be configured to special shapes for specific cases of applica-

tion. Such shapes are generally not offered by steel manufacturers.

These benefits have led to the widespread processing of tailored blanks.

Tailored blanks are manufactured on blank welding lines (Fig. 4.6.25).

The blanks produced on a blanking press are loaded in stack form,

aligned, centered and fed to the automatic welding machine. The blanks

are then welded by means of resistance, laser or induction welding

methods (Fig. 4.6.26).

Where resistance welding is used, a control system checks the process,

assuming high output and quality. The welding unit comprises two

loading and centering tables for blank feed, a traversing unit to hold the

311

Shearing lines

Fig. 4.6.24 Passenger car reinforcement formed from a tailored blank

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

overlapping blanks together, and the stationary welding rolls. Alterna-

tively, the blanks can be stationary and the welding rolls may move.

Laser technology using CO

or solid lasers has proven successful as a

new production technology. However, when this method is used the

two sheet metal edges to be welded together must be prepared for the

welding process by laser cutting or by high-precision fine shearing.

Welding itself is performed with the blanks stationary and a mobile laser

focusing device or with moving blanks and a stationary focusing device.

The working speeds are comparable to those of a resistance welding

unit. In the case of coated sheet blanks, it is actually possible to achieve

higher working speeds. The benefit of laser welding is that no weld over-

fill occurs and even coated blanks can be processed without problems.

A third system, which is not yet used on an industrial scale, is

equipped with an induction welding unit. The blanks are pressed togeth-

er at the edges. The welding process itself is carried out at high speed, as

the blanks are joined over the entire length of their edges within about

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Sheet metal forming and blanking

Fig. 4.6.25 Blank welding line with continuous part handling system for the manufacture of

welded side members

(cf. Fig. 4.4.12)

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

2s. The process cannot be executed on a continuous basis, as part trans-

port must be interrupted during welding.

After the welding process, the parts pass through the monitoring station

and the beading and oiling unit. The finished tailored blanks are then

stacked again and made ready for further processing in the forming line.

When deep drawing, depending on the position of the welded seam,

tailored blanks behave differently to conventional parts. If, for example,

the sheet metal thickness differs while the blank holder force remains

constant, wrinkles or tears can occur in the formed part. In these cases,

special blank holders which can be adjusted according to the formed

product, are used in the die set (Fig. 4.6.27).

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Shearing lines

Fig. 4.6.26 Comparison of the principle layouts of resistance, laser and induction welding

systems

laserwelding inductionweldingresistancewelding

blank1 blank2

Fig. 4.6.27 Modified blank holder for deep drawing of tailored blanks

heightdifference

oftheblankholder

die

tailoredblank

segmented

blankholder

clearancefor

weldingseam

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

4.6.6Perforating presses

Perforated sheets are in widespread use in almost every sector of indus-

try: in the form of sieves and filters in the food industry, in mining and

gravel pits, as protective covers in the electrical industry, in building

machinery and machine tools, as partitions and for decorative purpos-

es, in household appliances, office furniture, aircraft and industrial con-

struction.

The number of punch contours and hole patterns is almost infinite.

Steel, NF metals or combinations are among the materials used, and sheet

thicknesses can range anywhere between 0.3 and 30mm. Perforated sheet

metal is manufactured either off the coil or in plate form. Basically, two

main methods are used: Continuous or periodically interrupted hole pat-

terns are manufactured in large series from coil or plate stock on all-across

perforating presses, while strip perforating presses are used for the small-

series production of optional hole patterns from plate material.

Both machine systems can be equipped with units for automatic

sheet metal feed, for removal of finished parts, notching, separating

and splitting, and with quick-action die changing devices, die monitor-

ing systems and sound enclosures.

All-across perforating presses

Sheet metal with continuous or periodically repeated hole patterns are

manufactured on all-across perforating presses (Fig.4.6.28).These

presses process both coil and plate stock up to a thickness of around

6mm. The sheet metal runs through the press only in the feed direction

and is normally perforated in a single working stroke over the entire

width. The nominal press force lies between 800 and 5,000kN, the

maximum material width between 1,000 and 1,600mm. Depending on

the press size and feed system, all-across perforating presses operate at

up to 800 strokes per minute.

The press frame is configured as a monobloc (Fig.4.6.29).The slide

runs in clearance-free hardened roller gibs (cf.Fig.3.1.6)via two columns,

and is driven by a DC or threephase control motor via a flywheel, eccen-

tric shaft and two connecting rods. This configuration guarantees a long

die life. Short switching times, short stroke lengths and high resistance to

wear are achieved through the use of a quick-action clutch-brake combi-

nation (cf.Fig.3.2.8).

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

In contrast to conventional perforating presses with a non-adjustable,

rigid sheet metal stripper, in all-across perforating presses the stripper is

driven by an eccentric shaft (Fig.4.6.30).Thus, the stripper and slide

movement are out of phase so that the stripper plate remains at the bot-

tom dead center (Fig. 4.6.31)while the slide travels upwards. The slide

stroke can be increased, so extending the feed phase and increasing the

feed output. Like the slide, the stripper is mounted in clearance-free

hardened roller gibs at two columns, in order to ensure particularly pre-

cise punch guidance.

A major benefit of the moving stripper plate is its additional blank

holder function. The stripper force and stripper stroke can be adjusted to

the sheet metal thickness with the aid of the adjustable stripper linkage or

a variable bed plate. The friction path between the punch and stripper

plate is also reduced, as the downward movement of the plate partially

coincides with that of the punch.

This system helps to reduce wear and the return stroke force at the

punch, increases die service life, and ensures more gentle handling of

the sheet metal. When perforating stainless steel sheets, particularly,

stabilization of the sheet metal by the stripper plays a major role.

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Shearing lines

Fig. 4.6.28

All-across perforating

press (nominal press force

1,000 kN)

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

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Sheet metal forming and blanking

Fig. 4.6.29 Structure of an all-across perforating press

drive shaft

slide connecting rod

camshaft

pressure point

stripper slide

pressure point, slide

column gib

punch control unit

die beams

clamping plate

stripper connecting rod

stripper slide

clamps

gear box

feed drive

Fig. 4.6.30 Section through an all-across perforating press with die holding system and sepa-

rating shear

hydraulic

clamp

bottomdie

hydraulic

clamp

stripper

hydraulic

cropping

shear

outfeed

roller

infeedroller

infeedtable

punchcontrolbeam

movingstripper

pressbed

slide

perforatingpunch

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

The stripper plate is raised during the feed movement sufficiently to

ensure that even corrugated coil stock can be transported through the

open die. After perforation, the corrugated sheet metal can be straight-

ened by the stripper plate.

Before an electrohydraulically powered shear, mounted at the outfeed

roller upright, separates the coil into plates, it can be cut using a supple-

mentary slitting or notching device into various widths. The slitting or

notching device is mounted either at the main slide – the more eco-

nomical solution – or fastened at a slide driven separately by the eccen-

tric shaft. In this case, it must be possible to move the separating shear

out of the way. If the device is mounted at the main slide, it must also be

possible to remove the outfeed system to ensure improved accessibility.

When changing dies, the resetting time required can be reduced by

exchanging the slitting or notching device from the press outfeed side.

The perforating dies can be released by means of hydraulic quick-action

clamping devices and removed complete at the side of the press.

Individual or multiple rows of perforating punches in the die can be

moved into place, depending on the specifications of the program,

using a electrohydraulically actuated sliding beam. Even at maximum

317

Shearing lines

Fig. 4.6.31 Stroking curves of the slide and stripper plate with a sheet metal thickness of 2 mm

slidestroke[mm]

stripper stroke [mm]

start feed phase

120°

slide

stripper

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

stroking rates, the control system is able to move the punch in and out

of position without the need to stop the press. The feed devices arranged

directly in front of and behind the tool mounting area can also be pro-

grammed. The upper and lower rollers of the feed units are connected by

means of clearance-free mechanical intermediate gear drives. Both rollers

are supported in several points, and the upper rollers are hydraulically

pressed downward above the support in the area of the rollers. The rollers

are lifted manually or by means of program control. The infeed device is

removable, the outfeed device either removable or stationary.

To ensure a perfectly perforated pattern, a photoelectric camera mon-

itoring system is used (cf.Fig.4.9.7).While the all-across perforating

press is in the set-up mode, the device is programmed using the teach-

in mode. If the actual hole pattern deviates from the programmed pat-

tern during production, the press is automatically switched off.

Strip perforating presses

While perforated sheets are produced in medium and large-series on

all-across perforating presses, strip perforating presses are used for the

production of individual plates, particularly where large or thick sheet

metal materials are used or where individual hole patterns are required

(Fig.4.6.32). Strip perforating presses are available with nominal press

forces ranging from 500 to 2,500kN for sheet metal plates between

1,500 33,000mm and 2,000 36,000 mm with a maximum thickness

of 30 mm. Depending on the sheet metal thickness and feed step, it is

possible to achieve between 40 and 400 strokes per minute.

The strip perforating press control system permits simple program-

ming on screen and storage of complex hole patterns. The stored data

records can be simply accessed if a particular production run has to be

repeated.

The sheet metal plates are fastened on a clamping plate which can be

moved horizontally in two axes. Electrical servo drive systems with

clearance-free intermediate gear drives are used to power the feed sys-

tem. These permit perforation to take place during forward and reverse

movement of the material. As is the case with all-across perforating

presses, here too a separately moved stripper plate with stripping func-

tion can be used (Fig. 4.6.33).

Stationary single punches or small punch assemblies perforate the

sheet metal plates. Where complicated hole patterns are involved, the

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

punches can be driven using two additional programmable axes. Par-

ticularly complex geometrical shapes can also be programmed record

by record or using the teach-in mode, whereby the patterns being pro-

grammed can be displayed on screen. Temporary deactivation of the

slide movement irrespective of the clamping plate feed movement can

be used to create optionally interrupted patterns.

319

Shearing lines

Fig. 4.6.32 Examples of hole patterns produced on a strip perforating press

Fig. 4.6.33 Die with separately controlled stripper plate

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

The clamping plate is equipped with electrohydraulically actuated

clamping dogs which are retracted in the area of a perforation close to

the material edge, so eliminating the need to reclamp the sheet metal

plate. Support rails equipped with rollers which can be moved as

required on the clamping plate are positioned in front of and behind the

die to prevent unwanted sagging of the sheet metal plate. This system

allows to reduce the mass of inertia to a quarter of that of the old-style

solid construction clamping plates. Used in conjunction with modern

optimized high-performance actuators, extremely short traversing peri-

ods of for example 0.2 s with a feed length of 80 mm can be achieved.

4.6.7Control systems for blanking presses

The concept of production cells and team work is being introduced in

production and assembly plants in order to improve flexibility, quality

and also productivity. This involves extending the responsibility of

each group or single workplace to include planning, inspection and

maintenance activities. As a result, structures will become increasingly

decentralized in the future. The greater degree of automation resulting

from this development will inevitably lead to machines and production

lines of ever greater complexity. At the same time, optimum operating

and maintenance capability as well as high equipment availability must

be achieved. This means that decentralized units must take increasing

responsibility for the provision and updating of production and equip-

ment-related data and information at the point of its generation. A vari-

ety of technical aids must be made available to enable the machine

operator to avoid or quickly remedy any machine standstill.

Information technology

It is necessary to have an operating and information system, integrated in

the machine control, that must fulfil the following criteria (Fig. 4.6.34):

–a simple, easily understood system of operator support when setting

the operating parameters for start-up and resuming operation fol-

lowing a die change or machine failure,

–a tool data management system that has an overview of existing dies

and related features as well as machine parameters and that permits

simple access and editing,

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