chapter 14 - mechanisation and welding fixtures

14.

Mechanisation

and Welding Fixture

14. Mechanisation and Welding Fixtures 197

2005

As the production costs of the metal-working industry are nowadays mainly determined by

the costs of labour, many

factories are compelled to

rationalise their manufac-

turing methods by partially

and fully mechanised pro-

duction processes. In the

field of welding engineering

where a consistently good

quality with a maximum

productivity is a must,

automation aspects are

conse-quently taken into

account.

The levels of mechanisation in welding are

stipulated in DIN 1910, part 1. Distinctions are

made with regard to the type of torch control

and to filler addition and to the type of process

sequence, as, e.g., the transport of parts to

the welding point. Figure 14.1 explains the

four levels of mechanisation.

Figure 14.2. shows manual welding, in this

case: manual electrode welding. The control

of the electrode and/or the arc is carried out

manually. The filler metal (the consumable

electrode) is also fed manually to the welding

point.

Designationexamples

gas-shielded arc weldingTIG GMAW

movement/ working cycles

manual welding

m

partiallymechanised

weldingt

fully mechanisedwelding

v

automaticwelding

a

mechanically

mechanicallymechanically mechanically

mechanicallymechanically

manually manually

manually

manually

manually

manually

torch-/workpiece

control

workpiecehandling

filler wirefeeding

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Figure 14.1

© ISF 2002br-er14-02e.cdr

Manual Welding(Manual Electrode Welding)

Figure 14.2


2005

In partially mechanised

welding, e.g. gas-shielded

metal-arc welding, the arc

manipulation is carried out

manually, the filler metal

addition, however, is exe-

cuted mechanically by

means of a wire feed mo-

tor, Figure 14.3.

In fully mechanised weld-

ing, Figure 14.4, an auto-

matic equipment

mechanism carries out the welding advance and thus the torch control. Wire feeding is re-

alised by means of wire feed units. The workpieces must be positioned manually in accor-

dance with the direction of the moving machine support.

In automatic welding, be-

sides the process se-

quences described above,

the work-pieces are me-

chanically positioned at

the welding point and,

after welding, auto-

matically trans-ported to

the next working station.

Figure14. 5 shows an ex-

ample of automatic welding

(assembly line in the car

industry).

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Partially Mechanised Welding(Gas-Shielded Metal-Arc Welding)

Figure 14.3

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Fully Mechanised Welding(Gas-Shielded Metal-Arc Welding)

Figure 14.4


2005

Apart from the actual weld-

ing device, that is, the

welding power source, the

filler metal feeding unit and

the simple torch control

units, there is a variety of

auxiliary devices available

which facilitate or make the

welding process at all pos-

sible. Figure 14.6 shows a

survey of the most impor-

tant assisting devices.

Before welding, the parts

are normally aligned and

then tack-welded. Fig-

ure 14.7 depicts a simple

tack-welding jig for pipe

clamping. The lower part of

the device has the shape

of a prism. This allows to

clamp pipes with different

diameters.

Devices, however, may be

significantly more complex.

Figure 14.8 shows an example of an assembly equipment used in car body manufacturing.

This type of device allows to fix complex parts at several points. Thus a defined position of

any weld seam is reproducible.

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Automatic Welding (Assembly Line)

Figure 14.5

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assembly line

welding robot

machine carrier

linear travelling mechanism

track-mounted welding robots

spindle / sliding head turntable

turn-/ tilt table

dollies

assembly devices

Figure 14.6


2005

In apparatus engineering

and tank construction it is

often necessary to rotate

the components, e.g.,

when welding circumferen-

tial seams. The equipment

should be as versatile as

possible and suit several

tank diameters. Figure 14.9

shows three types of turn-

ing rolls which fulfil the

demands. Figure bottom:

the rollers are adjustable;

Figure middle: the rollers

automatically adapt to the

tank diameter; Figure top:

the roller spacing may be

varied by a scissor-like ar-

rangement.

In general, dollies are mo-

tor-driven. This provides

also an effortless move-

ment of heavy compo-

nents, Figure 14.10.

A work piece positioner, e.g. a turn-tilt-table, is part of the standard equipment of a robot

working station. Figure 14.11 shows a diagrammatic representation of a turn-tilt-table. Rota-

tions around the tilting axis of approx. 135° are possible while the turn-table can be turned by

365°. Those types of turn-tables are designed for working parts with weights of just a few

kilograms right up to several hundred tons.

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Simple Tack Welding Jig forWelding Circumferential Welds

Figure 14.7

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1 portal with 2 industrial robots IR 400, equipped with tool change system2 resting transformer welding tongs3 depot of welding tongs4 clamping tool5 copper back-up bar for car roof welding6 transformer welding tongs for car roof welding7 driverless transport system8 component support frame9 swivelled support for component support frames10 resting transformer welding tongs for car boot

Figure 14.8


2005

A turn-tilt-table with hydrau-

lic adjustment of the tilting

and vertical motion as well

as chucking grooves for the

part fixture is depicted in

Figure 14.12.

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Turning Rolls

set of rollers 1 set of rollers 2

Figure 14.9

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Turning Rolls

Figure 14.10

Figure 14.11

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support

tilting axis

table support

gear segmenttable top

rotational axis


2005

Turn-Tilt-Tables


single-column turn-tilt-table orbital turn-tilt-table

table top table top

rotational axisrotational axis

tilting axis tilting axis

support

table support table support

support

Figure 14.13

In robot technology the

types of turn-tilt-tables - as

shown in Figure 14.13 - are

gaining importance. Posi-

tioners with orbital de-

sign have a decisive

advantage because the

component, when turning

around the tilting axis, re-

mains approx. equally dis-

tant to the welding robot.

Other types of workpiece

positioners are shown in

Figure 14.14 – the double

column turn-tilt-table and

the spindle and sliding

holder turn-tilt-table.

Those types of positioners

are used for special com-

ponent geometries and

allow welding of any seam

in the flat and in the hori-

zontal position.

In the field of welding, spe-

cial units are designed for

special tasks. Figure 14.16 shows a pipe-flange-welding machine. This machine allows the

welding of flanges to a pipe. The weld head has to be guided to follow the seam contour.

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Turn-Tilt-Table With Hydraulic Adjustment

Figure 14.12


2005

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Figure 14.16

Figure 14.15 Spindle / Sliding Holder Turntable


bed way

spindle holder

table tops

sliding holder

Double-Column Turn-Tilt-Table


table support

rotational axis

table top

tilting axis

support

Figure 14.14


2005

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Figure 14.17

Plain plates or rounded

tanks are clamped by

means of longitudinal jigs

for the welding of a longi-

tudinal seam, Figure 14.17.

The design and the grip-

ping power are very de-

pendent of the thickness of

the plates to be welded.

A simple example of a

special welding machine is

the tractor travelling car-

riage for submerged-arc

welding, Figure 14.18. This device is de-

signed for the application on-site and pro-

vides, besides the supply of the filler metal,

also the welding speed as well as the feeding

and suction of the welding flux.

For the guidance of a welding head and/or

welding device, machine supports may be

used. Figure 14.19 shows different types of

machine supports for welding and cutting.

Apart from the translatory and rotary principal

axes they are often also equipped with addi-

tional axes to allow precise positioning.

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Tractor for Submerged-Arc Welding

Figure 14.18


2005

To increase levels of

mechanisation of welding

processes robots are fre-

quently applied. Robots are

handling devices which are

equipped with more than

three user-programmable

axes. Figure 14.20 de-

scribes kinematic chains

which can be realised by

different combinations of

translatory and rotary axes.

The most common design

of a track-mounted weld-

ing robot is shown in Fig-

ure 14.21. The robot

depicted here is a hinged-

arm robot with six axes. The

axes are divided into three

principal and three addi-

tional axes or hand axes.

The wire feed unit and the

spool carriers for the wire

electrodes are often fixed on

the robot. This allows a

compact welding design.

br-er14-19e.cdr

boom

pillar

travelling mechanism

a b c

d e

main piloting system case cross pilotingsystem case

auxiliary piloting system case

auxiliary piloting system case

Figure 14.19

Kinematic Chains


designation

arrangement

kinematicschedule

operatingspace

cartesianrobot

cylindercoordinated

robot

sphericalcoordinated

robot

horizontalknuckle arm

robot

verticalknuckle arm

robot

x

y

zz

z

C

C

CC

B

BR R D

A

Figure 14.20


2005

Varying lever lengths permit the design of robots with different operating ranges. Fig-

ure 14.22 shows the operating range of a robot. In the unrestricted operating range the

component may be reached with the torch in

any position. The restricted operating range

allows the torch to reach the component only

certain positions. In the case of a suspended

arrangement the robot fixing device is short-

ened thus allowing a compact design.

For the completion of a robot welding station

workpiece positioners are necessary. Fig-

ure 14.23 shows positioner devices where

also several axes may be combined. These

axes may either turn to certain defined posi-

tions or be guided by the robot control and

moved synchronically with the internal axes.

The complexity and versatility of the axis posi-

tions increases with the number of axes which

participate in the movement.

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Figure 14.22

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Robot Motions

Figure 14.21


2005

Movement by means of a

linear travelling mecha-

nism increases the operat-

ing range of the robot,

Figure 14.24. This may be

done in ease of stationary

as well as suspended ar-

rangement, where there is

a possibility to move to

fixed end positions or to

stay in a synchronised mo-

tion with the other move-

ment axes.

br-er14-24e.cdr

Figure 14.24

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Figure 14.23

chapter 14 - mechanisation and welding fixtures

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