welding technology

ISF Welding Institute RWTH Aachen University

Lecture Notes

Welding Technology 1 Welding and Cutting Technologies

Prof. Dr.Ing. U. Dilthey

Table of ContentsChapter 0. 1. 2. 3. 4. 5. 6. Subject Introduction Gas Welding Manual Metal Arc Welding Submerged Arc Welding TIG Welding and Plasma Arc Welding Gas Shielded Metal Arc Welding Narrow Gap Welding, Electrogas - and Electroslag Welding 7. 8. Pressure Welding Resistance Spot Welding, Resistance Projection Welding and Resistance Seam Welding 9. 10. 11. 12. 13. 14. 15. 16. Electron Beam Welding Laser Beam Welding Surfacing and Shape Welding Thermal Cutting Special Processes Mechanisation and Welding Fixtures Welding Robots Sensors Literature 101 115 129 146 160 175 187 200 208 218 73 85 43 56 Page 1 3 13 26

0. Introduction

2003

0. Introduction

1

Welding fabrication processes are classified in accordance with the German Standards DIN 8580 and DIN 8595 in main group 4 Joining, group 4.6 Joining by Welding, Figure 0.1.

1 Casting

2 Forming

3 Cutting

4 Joining

5 Coating

6Changing of materials properties

4.1 Joining by composition

4.2 Joining by filling

4.3 Joining by pressing

4.4 Joining by casting

4.5 Joining by forming

4.6 Joining by welding

4.7 Joining by soldering

4.8 Joining by adhesive bonding

4.6.1 Pressure weldingbr-er0-01.cdr

4.6.2 Fusion welding

Production Processes acc. to DIN 8580

Figure 0.1

Welding: permanent, positive joining method. The course of the strain lines is almost ideal. Welded joints show therefore higher strength properties than the joint types depicted in Figure 0.2. This is of advantage, especially in the case of dynamic stress, as the notch effects are lower.Adhesive bonding Riveting Screwing

Soldering

Welding

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Connection Types

Figure 0.2

0. Introduction

2

Figures 0.3 and 0.4 show the further subdivision of the different welding methods according to DIN 1910.

Production processes 4 Joining4.6 Joining by welding

4.6.1 Pressure welding


4.6.1.1 Welding by solid bodies

4.6.1.2 Welding by liquids

4.6.1.3 Welding by gas

4.6.1.4 Welding by electrical gas discharge

4.6.1.6 Welding by motion

4.6.1.7 Welding by electric current

Heated tool welding

Flow welding

Gas pressure-/ roll-/ forge-/ diffusion welding

Arc pressure welding

Cold pressure-/ shock-/ friction-/ ultrasonic welding

Resistance pressure welding ISF 2002

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Joining by Welding acc. to DIN 1910 Pressure Welding

Figure 0.3

Production processes 4 Joining4.6 Joining by welding

4.6.1 Pressure welding


4.6.2.2 Welding by liquids

4.6.2.3 Welding by gas

4.6.2.4 Welding by electrical gas discharge

4.6.2.5 Welding by beam

4.6.2.7 Welding by electric current

Cast welding

Gas welding

Arc welding

Beam welding

Resistance welding

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Joining by Welding acc. to DIN 1910 Fusion Welding

Figure 0.4

1. Gas Welding

2003

1. Gas Welding

3 Although the oxy-acetylene process3 4 5 8

has been introduced long time ago it is still applied for its flexibility and mo6

bility. Equipment for oxyacetylene welding consists of just a few elements, the energy necessary for welding can be transported in cylinders, Figure 1.1.

7 12 1 2 3 4 5 6 7 8 9 oxygen cylinder with pressure reducer acetylene cylinder with pressure reducer oxygen hose acetylene hose welding torch welding rod workpiece welding nozzle welding flame 9

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Figure 1.1density in normal state [kg/m ]3

Process energy is obtained from the exothermal chemical reaction between oxygen and a combustible gas, Figure 1.2. Suitable combustible gases are C2H2, lighting gas, H2, C3H8 and natural gas; here C3H8 has the highest calorific value. The highest flame intensity from point of view of calorific value and flame propagation speed is, however, obtained with C2H2.

2.5 2.0 1.5 1.0 0.5 0

2.0 1.29 air 1.17

propane

1.43 oxygen ISF 2002

0.9

ignition temperature [OC] 600 400 200 0flame temperature with O2 flame efficiency with O 2 flame velocity with O2 43 135010.3 8.5 370 330

645

645 oxygen propanenatural gas

air

300

490 335

510

3200 2850 2770 0br-er1-02.cdr

C

KW k

/cm2

cm

/s

Figure 1.2

1. Gas Welding

4 C2H2 is produced in acetylene gas

loading funnel

generators by the exothermal transmaterial lock

formation of calcium carbide with water, Figure 1.3. Carbide is obtained from the reaction of lime and carbon in the arc furnace.

gas exit feed wheel

C2H2 tends to decompose already at a pressure of 0.2 MPa. Nonetheless,grille sludge

commercial quantities can be stored when C2H2 is dissolved in acetone (1 l of acetone dissolves approx. 24 l of C2H2 at 0.1 MPa), Figure 1.4.

to sludge pitbr-er1-03.cdr ISF 2002

Acetylene Generator

Figure 1.3 Acetone disintegrates at a pressure of more than 1.8 MPa, i.e., with a filling pressure of 1.5 MPa the storage of 6m of C2H2 is possible in a standard cylinder (40 l). For gas exchange (storage and drawing of quantities up to 700 l/h) a larger surface is necessary, therefore the gas cylinders are filled with a porous mass (diatomite). Gas consumption during welding can be observed from the weight reduction of the gas cylinder.br-er1-04.cdr

acetone

acetylene

porous mass

N

acetylene cylinderacetone quantity : acetylene quantity : cylinder pressure : ~13 l 6000 l 15 bar

filling quantity : up to 700 l/h

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Storage of Acetylene

Figure 1.4

1. Gas Welding Oxygengaseous cooling nitrogen air bundleoxygen

5 is by profrac-

ducedcylinder

tional distillation of liquid air and stored in cylinders with a filling pressure of up to 20 MPa, Figure 1.5. For higher oxygen

liquid air

oxygen

pipeline liquid

tank car nitrogen vaporized cleaningbr-er1-05.cdr

compressor

separation

supply ISF 2002

consumption, storage in a liquid state and cold gasification is more profitable.

Principle of Oxygen Extraction

Figure 1.5

The standard cylinder (40 l) contains, at a filling pressure of 15 MPa, 6m of O2 (pressureless state), Figure 1.6. Moreover, cylinders with contents of 10 or 20 l (15 MPa) as well as 50 l at 20 MPa are common. Gas consump-

50 l oxygen cylinderprotective cap cylinder valve take-off connection

gaseous

Np = cylinder pressure : 200 bar V = volume of cylinder : 50 l Q = volume of oxygen : 10 000 l content control

tion can be calculated from the pressure difference by means of the general gas equation.manometer foot ring

Q=pV

safety valve

liquidvaporizer

filling connection still liquidbr-er1-06.cdr

user gaseous

Storage of Oxygen

Figure 1.6

1. Gas Welding

6

In order to prevent mistakes, the gas cylinders are colour-coded. Figure 1.7 shows a survey of the present colour code and the future colour code which is in accordance with DIN EN 1089. The cylinder valves are also of show a thread right-hand union nut.actual conditionblue

different designs. Oxygen cylinder connectionsDIN EN 1089white blue (grey)

actual conditiongrey

DIN EN 1089brown grey

Acetylene

cylinderoxygen techn.yellow

heliumbrown red

valves are equipped with screw clamp retentions. Cylinder valves for other

acetylenegrey dark green grey

hydrogengrey vivid green grey

combustible gases have a left-hand

argondarkgreen black darkgreen

argon-carbon-dioxide mixturegrey grey

thread-connectionbr-er1-07.cdr

nitrogen

carbon-dioxide ISF 2002

with a circumferential groove. Figure 1.7

Gas Cylinder-Identification according to DIN EN 1089

Pressure regulators reduce the cylinder pressure to the requested working pressure, Figures 1.8 and 1.9.cylinder pressure working pressure

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Single Pressure Reducing Valve during Gas Discharge Operation

Figure 1.8

1. Gas Welding

7

At a low cylinder pressure (e.g. acetylene cylinder) and low pressure fluctuations, single-stage regulators are applied; at higher cylinder pressures normally two-stage pressure regulators aredischarge pressure locking pressure

used. The requested

pressure is set by the adjusting

screw. If the pressure increases on the low pressure side, valvebr-er1-09.cdr ISF 2002

the

throttle the

closes

increased pressureSingle Pressure Reducing Valve, Shut Down

onto brane.

the

mem-

Figure 1.9

The

injector-typewelding torch injector or blowpipecoupling nut mixer nozzle oxygen valve hose connection for oxygen A6x1/4" right

torch consists of a body with valvesmixer tube

and welding chamber with welding

nozzle, Figure 1.10. By the selection of suitable chambers, welding thewelding torch headbr-er1-10.cdr

injector pressure nozzle suction nozzle welding nozzle fuel gas valve

hose connection for fuel gas A9 x R3/8 left

flame intensity can be adjusted for

torch body ISF 2002

Welding Torch

welding

different Figure 1.10

plate thicknesses.

1. Gas Welding

8

The special form of the mixing chamber guarantees highest possible safety against flashback, Figure 1.11. The high outlet speed of the escaping O2 generates a negative pressure in the acetylene gas line, in consequence C2H2 is sucked and drawn-in. C2H2 is therefore available with a very low pressure of 0.02 up to 0.05 MPa compared with O2 (0.2 up to 0.3 MPa).

acetylene oxygen acetylene

welding torch head injector nozzle coupling nut

pressure nozzle

torch body

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Injector-Area of Torch

Figure 1.11 A neutral flame adjustment allows the differentiation of three zones of a chemical reaction, Figure 1.12:

0. dark core: 1. brightly shining centre cone:

escaping gas mixture acetylene decomposition C2H2 -> 2C+H2 1st stage of combustion 2C + H2 + O2 (cylinder) -> 2CO + H2 2nd stage of combustion 4CO + 2H2 + 3O2 (air) -> 4CO2 + 2H2O

2. welding zone:

3. outer flame:

complete reaction:

2C2H2 + 5O2 -> 4CO2 + 2H2O

1. Gas Welding

9

welding flame combustionwelding nozzle centre cone welding zone 2-5 outer flame

3200C

2500C

1800C

1100C

400C

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Figure 1.12welding flame ratio of mixture

By changing the mixture ratio of the volumes O2:C2H2 the weld pool can greatly be influenced, Figure 1.13. At a neutral flame adjustment the mixture ratio is O2:C2H2 = 1:1. By reason of the higher flame temperature, an excess oxygen flame might allow faster welding of steel, however, there is the risk of oxidizing (flame cutting). Area of application: brass

excess of acetylene

normal (neutral)

excess of oxygen

effects in welding of steel sparking foaming spattering reducing oxidizing ISF 2002

The excess acetylene causes the carburising of steel materials. Area of application: cast iron

consequences: carburizing hardeningbr-er1-13.cdr

Effects of the Welding Flame Depending on the Ratio of Mixture

Figure 1.13

1. Gas Welding

10 By changing the gas mixture outlet speed the flame can be adjusted to the heat requirements of the welding job, for example when welding plates (thickness: 2 to 4 mm) with the weldsoft flame

welding flamebalanced (neutral) flame nozzle size: for plate thickness of 2-4 mm discharging velocity and weld heat-input rate: low 2

ing chamber size 3: 2 to 4 mm, Figure 1.14. The gas mixture outlet speed is 100 to 130 m/s when using a medium or normal flame, applied to

discharging velocity and weld heat-input rate: middle 3

moderate flamedischarging velocity and weld head-input rate: high 4

at, for example, a 3 mm plate. Using a soft flame, the gas outlet speed is lower (80 to 100 m/s) for the 2 mm plate, with a hard flame it is higher

hard flamebr-er1-14.cdr

(130 to 160 m/s) for the 4 mm plate. ISF 2002

Effects of the Welding Flame Depending on the Discharge Velocity

Figure 1.14 Depending on the plate thickness are the working methods leftward welding and rightward welding applied, Figure 1.15. A decisive factor for the designation of the working method is the sequence of flame and welding rod as well as the manipulation of flame and welding rod. The welding direction itself is of no importance. In leftward welding the flame is pointed at the open gap and wets the molten pool; the heat input to the molten pool can be well controlled by a slight movebr-er1-15e.cdr

Leftward welding is applied to a plate thickness of up to 3 mm. The weld-rod dips into the molten pool from time to time, but remains calm otherwise. The torch swings a little. Advantages: easy to handle on thin plates

welding-rod

flame

welding bead

Rightward welding ist applied to a plate thickness of 3mm upwards. The wire circles, the torch remains calm. Advantages: - the molten pool and the weld keyhole are easy to observe - good root fusion - the bath and the melting weld-rod are permanently protected from the air - narrow welding seam - low gas consumption

weld-rod

flame ISF 2002

ment of the torch (s = 3 mm).

Flame Welding

Figure 1.15

1. Gas Welding In rightward welding the flame is directed onto the molten pool; a weld keyhole is formed (s = 3 mm). Flanged welds and plain butt welds can be applied to a plate thickness of approx. 1.5 mm without filler material, but this does not apply to any other1,0

11

plate thickness range s [mm] from to1,5

gap preparations~ s+1 ~

denotation

symbol

r=

s

flange weld

1,0 4,0 plain butt weld

plate thickness and weld shape, Figure 1.16.3,0

12,01-2

V - weld

1,0

8,0

1-2

corner weld

By the specific heat input of the different welding methods all welding positions can be carried out using the oxyacetylene welding method, Figures 1.17 and 1.18br-er1-16.cdr

1,0

8,0

lap seam

1,0

8,0

fillet weld

ISF 2002

Gap Shapes for Gas Welding

Figure 1.16butt-welded seams in gravity position

When working in tanks and confined spaces, the welder (and all other persons present!) have to be protected against the welding heat, the gases produced during welding and lack of oxygen ((1.5 % (vol.) O2 per 2 % (vol.) C2H2 are taken out from the ambient atmosphere)), Figure 1.19. The addition of pure oxygen is unsuitable (explosion hazard!).s f

PAgravity fillet welds

PB PF PG PC

horizontal fillet welds vertical fillet and butt welds vertical-upwelding position vertical-down position horizontal on vertical wall

PE

overhead position

PDbr-er1-17.cdr

horizontal overhead position

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Welding Positions I

Figure 1.17

1. Gas Welding

12 A special type of autogene method is flame-straightening, where specific locally applied flame heating allows forPA PB

shape correction of workpieces, Figure 1.20. Much experience is needed to carry out flame straightening processes. The basic principle of flame straighteningPC

PF

depends on locally applied heating in connection with prevention of expansion. This process causes the appearance of aPG

PD PE

heated zone. During cooling, shrinking forces are generated in the heated zone and lead to the desired shape correction.

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Welding Positions II

Figure 1.18

Safety in welding and cutting inside of tanks and narrow rooms

Flame straightening

welded parts

Hazards through gas, fumes, explosive mixtures, electric current protective measures / safety precautions 1. requirement for a permission to enter 2. extraction unit, ventilation 3. second person for safety reasons 4. illumination and electric machines: max 42volt 5. after welding: Removing the equipment from the tank

first warm up both lateral plates, then belt

butt weld 3 to 5 heat sources close to the weld-seam

double fillet weld 1,3 or 5 heat sources

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Gas Welding in Tanks and Narrow Rooms

Flame Straightening

Figure 1.19

Figure 1.20

2. Manual Metal Arc Welding

2003


13 Figure 2.1 describes the burn-off of a covered stick electrode. The stick electrode consists of a core wire with a mineral covering. The welding arc between the electrode and the workpiece melts core wire and covering. Droplets of the liquefied core wire mix with the molten base material forming weld metal while the molten covering is forming slag which, due to its lower density, solidifies on the weld pool. The slag layer and gases which are generated inside the arc protect the metal during transfer and also thec ISF 2002

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weld pool from the detrimental influences of the surrounding atmosphere.

Weld Point

Figure 2.1

Covered stick electrodes have re1. Conductivity of the arc plasma is improved by a) ease of ignition b) increase of arc stability 2. Constitution of slag, to a) influence the transferred metal droplet b) shield the droplet and the weld pool against atmosphere c) form weld bead 3. Constitution of gas shielding atmosphere of a) organic components b) carbides 4. Desoxidation and alloying of the weld metal 5. Additional input of metallic particles

placed the initially applied metal arc and carbon arc The

electrodes.

covering has taken on the functions

which are described in Figure 2.2.br-er2-02.cdr

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Task of Electrode Coating

Figure 2.2


14

The covering of the stick electrode consists of a multitude of components which are mainly mineral, Figure 2.3.coating raw material quartz - SiO2 rutile -TiO2 magnetite - Fe3O4 calcareous spar -CaCO3 fluorspar - CaF2 calcareous- fluorspar K2O Al2O3 6SiO2 ferro-manganese / ferro-silicon cellulose kaolin Al2O3 2SiO2 2H2O potassium water glass K2SiO3 / Na2SiO3br-er2-03.cdr

effect on the welding characteristics to raise current-carrying capacity to increase slag viscosity, good re-striking to refine transfer of droplets through the arc to reduce arc voltage, shielding gas emitter and slag formation to increase slag viscosity of basic electrodes, decrease ionization easy to ionize, to improve arc stability deoxidant shielding gas emitter lubricant bonding agent ISF 2002

Influence of the Coating Constituents on Welding Characteristics

Figure 2.3 For the stick electrode manufacturing mixed ground and screened covering materials are used as protection for the core wire which has been drawn to finished diameter and subsequently cut to size, Figure 2.4.

raw material storage for flux production raw wire storage jaw crusher descaling magnetic separation cone crusher for pulverisation sieving to further treatment like milling, sieving, cleaning and weighing sieving systemdrawing plate

wire drawing machine and cutting system2 3

1

inspection to the pressing plant electrode compound

example of a three-stage wire drawing machine

6 mm

5,5 mm

4 mm

3,25 mm

weighing and mixing inspection

wet mixer

inspection ISF 2002

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Stick Electrode Fabrication 1

Figure 2.4


15

the pressing plant

inspection electrode compound core wire magazine electrodepress compound packing inspection

inspection

TO DELIVERY

nozzleconveying wire wire pressing belt feeder head magazine

drying stove inspection inspection inspectionbr-er10-33e.cdr ISF 2002

Stick Electrode Fabrication 2

Figure 2.5

The core wires are coated with the covering material which contains binding agents in electrode extrusion presses. The defect-free electrodes then pass through a drying oven and are, after a final inspection, automatically packed, Figure 2.5.pressing mass core rod guide pressing cylinder core rod coating pressing nozzle pressing cylinder

Figure 2.6 shows how the moist extruded covering is deposited onto the core wire inside an electrode extrusion press.

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Production of Stick Electrodes

Figure 2.6


16

Stick electrodes are, according to their covering compositions, categorized into four different types, Figure 2.7. with concern to burn-off characteristics and achievable weld metal toughness these types show fundamental differences.

cellulosic type cellulose 40 rutile TiO2 20 quartz SiO2 25 Fe - Mn 15 potassium water glass almost no slag droplet transfer : medium- sized droplets toughness value: goodbr-er2-07.cdr

acid type magnetite Fe3O4 50 SiO2 20 quartz CaCO3 10 calcite Fe - Mn 20 potassium water glass slag solidification time: long droplet transfer : fine droplets to sprinkle toughness value: normal

rutile type rutile TiO2 45 magnetite Fe3O4 10 SiO2 quartz 20 CaCO3 10 calcite Fe - Mn 15 potassium water glass slag solidification time: medium droplet transfer : medium- sized to fine droplets toughness value: good

basic typ fluorspar CaF2 45 CaCO3 40 calcite SiO2 10 quartz 5 Fe - Mn potassium water glass slag solidification time: short droplet transfer : medium- sized to big droplets toughness value: very good ISF 2002

Characteristic Features of Different Coating Types

Figure 2.7

The melting characteristics of the different coverings and the slag properties result in further properties; these determine the areas of application, Figure 2.8.

coating type symbol current type/polarity gap bridging ability welding positions sensitivity of cold cracking weld appearance slag detachability characteristic featuresbr-er2-08.cdr

cellulosic type C ~/+ very good PG,(PA,PB, PC,PE,PF) low moderate good spatter, little slag, intensive fume formation

acid type A ~/+ moderate PA,PB,PC, PE,PF,PG high good very good

rutile type R ~/+ good PA,PB,PC, PE,PF,(PG) low good very good

basic type B =/+ good PA,PB,PC, PE,PF,PG very low moderate moderate low burn-out losses hygroscopic predrying!! ISF 2002

high burn-out losses

universal application

Characteristics of Different Coating Types

Figure 2.8


17

The dependence on temperature of the slags electrical conductivity determines the reignition behaviour of a stick electrode, Figure 2.9. The electrical conductivity for a rutile stick electrode lies, also atconductivityslag taining tile-con high ru r nducto semico

room temperature, above the threshreignition threshold

old value which is necessary for reignition. rutile Therefore, electrodes

h ac co igh id s n d - te l a uc mp g to e r r a tu re hig bas h- ic s co tem lag nd pe uc ra to tur r e

are given prefertemperaturebr-er2-09.cdr ISF 2002

ence

in

the

Conductivity of Slags

production of tack welds where reig-

Figure 2.9 The complete designation for fillerDIN EN 499 - E 46 3 1Ni B 5 4 H5

nition occurs frequently.

materials, following European dardisation, cludes Stanin-

details

partly as encoded abbreviation

hydrogen content < 5 cm /100 g welding deposit butt weld: gravity position fillet weld: gravity position suitable for direct and alternating current recovery between 125% and 160% basic thick-coated electrode chemical composition 1,4% Mn and approx. 1% Ni o minimum impact 47 J in -30 C 2 minimum weld metal deposit yield strength: 460 N/mm distinguishing letter for manual electrode stick welding

3

which are relevant for welding, Figure

The mandatory part of the standard designation is: EN 499 - E 46 3 1Ni B

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2.10. The identification letter for the Figure 2.10

Designation Example for Stick Electrodes

welding process is first: E T S -

manual electrode welding flux cored arc welding submerged arc welding

G W

-

gas metal arc welding

- tungsten inert gas welding


18

The identification numbers give information about yield point, tensile strength and elongation of the weld metal where the tenfold of the identification number is the minimum yield point in N/mm, Figure 2.11.

key number

minimum yield strength N/mm2 355 380 420 460 500

tensile strength N/mm2 440-570 470-600 500-640 530-680 560-720

minimum elongation*) % 22 20 20 20 18

35 38 42 46 50 *) L0 = 5 D0

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Characteristic Key Numbers of Yield Strength, Tensile Strength and Elongation

Figure 2.11

The identification figures for the minimum impact energy value of 47 J a parameter for the weld metal toughness are shown in Figure 2.12.

characteristic figure Z A 0 2 3 4 5 6 7 8

minimum impact energy 47 J [ C] no demands +20 0 -20 -30 -40 -50 -60 -70 -80

0

The minimum value of the impact energy allocated to the characteristic figures is the average value of three ISO-V-Specimen, the lowest value of whitch amounts to 32 Joule.br-er2-12.cdr

Characteristic Key Numbers for Impact Energy

Figure 2.12

2. Manual Metal Arc Welding The

19 chemical of

composition

the weld metal is shown by the alloy symbol, 2.13. Figure

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Alloy Symbols for Weld Metals Minimum Yield Strength up to 500 N/mm2

Figure 2.13

The properties of a stick electrode are characterised by the covering thickness and the covering type. Both details are determined by the identification letter for the electrode covering, Figure 2.14.A B C R RR RA RB RC acid coating basic coating cellulose coating rutile coated (medium thick) rutile coated (thick) rutile acid coating rutile basic coating rutile cellulose coating key letter type of coating

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Figure 2.14

2. Manual Metal Arc Welding Figure 2.15 ex-

20

plains the additional identification figure for electrode recovery and applicable type The of current.

subsequent

identification figure determines the application ties for possibilidifferent Figure 2.15 12345all positions all positions, except vertical down position flat position butt weld, flat position fillet weld, horizontal-, vertical up position flat position butt and fillet weld as 3; and recommended for vertical down positionbr-er2-15.cdr ISF 2002

welding positions:

Additional Characteristic Numbers for Deposition Efficiency and Current Type

The last detail of the European Standard designation determines the maximum hydrogen content of the weld metal in cm per 100 g weld metal. Welding amperage current and

core wire diameter of the stick

electrode are determined thickness workpiece by of to the the be

welded. Fixed stick electrodebr-er2-16.cdr ISF 2002

lengths to

are each

assigned

Size and Welding Current of Stick Electrodes

diameter,

Figure 2.16

Figure 2.16.

2. Manual Metal Arc Welding Figure 2.17 showselectrode holder

21

the process principle of manual- (+) power source = or ~ + (-) arc stick electrode

metal arc welding. Polarity and type of current depend on the trode known applied types. elecAll

powerwork piecebr-er2-17.cdr ISF 2002

sources with a descending characteristic curve can be used. Figure 2.17

Principle Set-up of MMAW Process

Since in manual metal arc welding the arc length cannot always be kept constant, a steeply descending powerpower source characteristic UA2 A1

source is used. Different arc lengths lead therefore to just minimally altered weld current intensities, Figure 2.18. Penetration remains basically unal-

2 1

A2

tered.

A1

21 characteristic of the arcbr-er2-18.cdr

I

ISF 2002

Figure 2.18


22 Simple welding transformers arearc welding converter

used for a.c. welding. For d.c. welding mainly converters, rectifiers and series regulator transistorised power sources (inverters) are applied. Con-

transformer

verters are specifically suitable for site welding and are mains-

independent when an internal combustion engine is used. The advanrectifier

tages of inverters are their small size and low weight, however, a more complicated electronic design is necinverter type

essary, Figure 2.19.

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Figure 2.1945 RA73

Figure 2.20 shows the standard welding parameters of different stick electrode diameters and stick electrodemedium weld voltage

V 40 RR73

types.

35

The rate of deposition of a stick electrode is, besides the used current intensity, dependent on the so-called electrode recovery, Figure 2.21. This describes the mass of deposited weld metal / mass of core wire ratio in percent. Electrode recovery can reach values of up to 220% with metal

30

RR12 RA12 B53

25= = = =

B153,25 4 5 6

20

100

200

300

A

400

medium weld currentbr-er2-20.cdr ISF 2002

covering components in high-efficiency electrodes. Figure 2.20


23

A survey of the material spectrum which is suitable for manual metal arc welding is given in Figure 2.22. The survey comprises almost all metals known for technical applications and also explains the wide application range of the method.7eff ic ien cy

kg/h 6de po s it ion

steel:

c

burn-off rate at 100% duty cycle

5

4

de po s it io n

ef fic

X

b

3

th

ed at co ick

16 0%

a

constructional steels shipbuilding steels high-strength constructional steels boiler and pressure vessel steels austenitic steels creep resistant steels austenitic-ferritic steels (duplex) scale resistant steels wear resistant steels hydrogen resistant steels high-speed steels cast steels combinations of materials (ferritic/ austenitic) cast iron with lamella graphite cast iron with globular graphite pure nickel Ni-Cu-alloys Ni-Cr-Fe-alloys Ni-Cr-Mo-alloys electrical grade copper (ETP copper) bronzes (CuSn, CuAl) gunmetal (CuSnZnPb) Cu-Ni-alloys pure aluminium AlMg-alloys AlSi -alloys ISF 2002

22 0%

ien

cy

2th in-

ed at co

cast iron: nickel:

1X=

= RR12 - 5 mm RR73 - 5 mm 400 A 500

copper:

0

0

100

200 300 welding amperage

a = A- and R- coated electrodes, recovery 105% b = basic-coated electrodes, recovery 2CO2 in the workpiece proximity) intensifies

wire elektrodes

this effect when CO2 is used. In argon, the current-carrying arc core is wider and envelops the wire electrode end, Figure 5.13. This generates electromagnetic forces whichargon carbon dioxide

current-carrying arc core

bring about the detachment of the liquid electrode material. This socalled pinch effect causes a metal transfer in small drops, Figure 5.14.

The pointed shape of the arc attachbr-er5-14e.cdr ISF 2002

ment in carbon dioxide produces a reverse-direction force component,

i.e., the molten metal is pushed up Figure 5.14

until gravity has overcome that force component and material transfer in the form of very coarse drops appear.

acceleration due to gravity electromagnetic force FL (pinch effect) wire electrode

Besides the pinch effect, the inertia and the gravitational force, othersurface tension S viscosity droplets necking down

forces, shown in Figure 5.15, are active inside the arc space; however these forces are of less importance.

inertia electrostatic forces

backlash forces fr of the evaporating material suction forces, plasma flow induced

work piecebr-er5-15e.cdr ISF 2002

Forces in Arc Space

Figure 5.15

5. Gas-Shielded Metal Arc Welding

63

If the welding voltage and the wire feed speed are further increased, a rotating arc occurs after an undefined transition zone, Figure 5.16. High-efficiency MAG welding has been applied since the beginning of the nineties; the deposition rate, when this process is used, is twice the size as, in comparison, to spray arc welding. Apart from a multicomponent gas with a helium proportion,

also a high-rating power source and a precisely controlled wire feed system for high wire feed

speeds are necessary.br-er5-16e.cdr ISF 2002

Rotating Arc

Figure 5.16

Figure 5.17 depicts the deposition rates over the wire feed speed, as achievable with modern high-efficiency MAG welding processes.

During25kg/h 1,2 mm

the

transi-

tion from the shorthigh performance GMA welding 1,0 mm

to the spray arc the drop frequency rate increases erratically

deposition rate

20 15 10 5 0 0 5 10conventional GMA

0,8 mm

while the drop volume the decreases same at

degree.

15

20

25

30

35

40

45 m/min

With an increasing CO2-content, this current

wire feed speedbr-er5-17e.cdr ISF 2002

criticalDeposition Rate

range moves up to higher power ranges

Figure 5.17


64

and is, with inert gas constituents of lower than 80%, hardly achievable thereafter. This effect facilitates the pulsed-arc welding technique, Figure 5.18.300 number of droplets 1/s 200 critical current range 100 100 300 35 10 cm 200-4 3

UEff

V arc voltage 25 20 15 10 5 Um

drop volume

0 0 tP 200 400 A 600

0

500 A 400 welding current 350 300 250 200 150 100 50 0 0 ISF 2002 br-er5-19e.cdr

Setting parameters: - background current IG - pulse voltage UP - impulse time tP - background time tG or frequency f with f = 1 / ( tG + tP), resp. - wire feed speed vD

IEff Im

time

Ikrit

tG

IG

Im

5

10

15 time

20

ms

30 ISF 2002

br-er5-18e.cdr

Pulsed Arc

Figure 5.18

Figure 5.19

In pulsed-arc welding, a change-over occurs between a low, subcritical background current and a high, supercritical pulsed current. During the background phase which corresponds with thewelding currentpulsed current intensity Non-short-circuiting metal tranfer range

short arc range, the arc length is ionised and wire electrode

backround current intensity

and work surface are preheated. During thetime

pulsed material

phase is

the

molten

and, as in spray arc welding,br-er5-20e.cdr isf 2002

superseded magnetic

byPulsed Metal Transfer

the

forces. Figure 5.20. Figure 5.20


65

Figure 5.19 shows an example of pulsed arc real current path and voltage time curve. The formula for mean current is:

Im =

1T idt T 01T 2 i dt T 0

for energy per unit length of weld is:

Ieff =

50 working range welding current / arc voltage 45 40 35 voltage [v] 30 transition arc 25 short arc 20 15 10 50 75 100 125 150 175 200 225 250 welding current 275 300 325 350 375 400 shielding gas: 82%Ar, 18%CO2 wire diameter: 1,2 mm wire type: SG 2 optimal setting lower limit upper limit spray arc

By a sensible selection of welding parameters, GMA the

welding

technique allows a selection of different arc types which are by distinguished their metal

br-er5-21e.cdr

ISF 2002

transfer way. Figure 5.21 shows the setting range for a good welding

Parameter Setting Range in GMA Welding

Figure 5.21filler metal: SG2 -1,2 mm shielding gas: Ar/He/CO2/O2-65/26,5/8/0,5

process in the field50 V 30high-efficiency spray arc transition zones spray arc rotating arc

of

conventional

GMA welding.

voltage

Figure 5.22 shows the extended setting range for the high-efficiency MAGM100br-er5-22e.cdr

20high-efficiency short arc

10

short arc

welding with a

200

300 welding current

400

AQuelle: Linde, ISF2002

600

process

Setting Range or Welding Parameters in Dependence on Arc Type

rotating arc.

Figure 5.22


66 Some typical ap-

arc typesspray arc welding methods MAGC MAGM MIG aluminium copper steel unalloyed, lowalloy, high-alloy long arc short arc aluminium (s < 1,5 mm) pulsed arc aluminium copper

plications of the different arc types are depicted in Figure 5.23. The

steel unalloyed, low-alloy steel unalloyed, low-alloy fillet welds or inner passes and cover passes of butt welds at medium-thick or thick components in position PA, PB

steel unalloyed, low-alloy, steel low-alloy, high-alloy high-alloy steel unalloyed, low-alloy

applications

fillet welds or inner passes and cover passes of butt welds at medium-thick or thick components in position PA, PB welding of root layers in position PA

-

seam type, positions workpiece thickness

fillet welds or butt welds fillet welds or inner at thin sheets, all positions passes and cover passes of thin and root layers of butt welds medium-thick at medium-thick or thick components, all components, all positions positions inner passes and cover passes of fillet or butt welds in position PC, PD, PE, PF, PG (out-of-position) root layer welds only conditionally possible

rotating arc, (not mentioned in the figure), is applied in just the same way as the spray

br-er5-23e.cdr

ISF 2002

Applications of Different Arc Types

arc, however, it is not used for the

Figure 5.23

welding of copper and aluminium.

The arc length within the working range is linearly dependent on the set welding voltage, Figure 5.24. The weld seam shape is considerably influenced by the arc length. A long arc produces a wide flat weld seam and, in the case of fillet welds, generally undercuts. A short arc produces a narrow, banked weld bead.operating point: wire feed speed: arc length: welding current: deposition efficiency: AL low long low low AM medium medium medium medium vD, I AL AM AK U arc length: long medium short

AK high short high high

On the other hand, the arc length is inversely proportional to the wire feed speed, Figure 5.25. This has influence on the current over the internal adjustment with a slightly dropping power source characteristic. This

weld appearance:

br-er5-24e.cdr

ISF 2002

Wire Feed Speed

again is of considerable importance for the deposition rate, i.e., a low wire feed speed leads to a low deposition Figure 5.24


67 rate, the result is flat penetration and

U AL AM AK

arc length: long medium short

low base metal fusion. At a constant weld speed and a high wire feed speed a deep penetration can be obtained.

vD, I

operating point: welding voltage: arc length:

AL high long

AM medium medium

AK low short

At equal arc lengths, the current intensity is dependent on the contact tube distance, Figure 5.26. With a

weld appearance butt weld

large contact tube distance, the wire stickout is longer and is therefore characterised by a higher ohmic resis-

weld appearance fillet weld

tance which leads to a decreased current intensity. For the adjustment of

br-er5-25e.cdr

ISF 2002

the contact tube distance, as a thumb rule, ten to twelve times the size of

Welding Voltage

Figure 5.25 the wire diameter should be considered.lk1 lk2 lk3

The torch position has considerablecontact tube-to-work distance lk

influence on weld formation and welding process, Figure 5.27. When welding with the torch pointed in forward direction of the weld, a part of the weld pool is moved in front of the arc. This results in process instability. However, it ha s the advantage of a

30 mm 20

3

2

operating rule: lk = 10 to 12 dD1

10

0 200

250

300 A

350 1,2 mm diameter 82% Ar + 18% CO2 29 V 8,8 m/min 58 cm/min ISF 2002

currentwire electrode: shielding gas: arc voltage: wire feed speed: welding speed:br-er5-26e.cdr

flat smooth weld surface with good gap bridging. When welding with the torch pointed in reversing direction of the weld, the weld process is more stable and the penetration deeper, as

Contact Tube-to-Work Distance

Figure 5.26


68 base metal fusion by the arc is better,

advance direction

although the weld bead surface is irregular and banked.

Figure 5.28 shows a selection of different application areas for the GMA technique and the appropriate shieldpenetration: gap bridging: arc stability: shallow average deep

ing gases.

good bad

average average average average average

bad

The welding current may be producedgood low

by different welding power sources. In d.c. welding the transformer must be

spatter formation: strong weld width: wide

narrow

equipped with downstream rectifierweld appearance: smooth rippled

assemblies, Figure 5.29. An additional ripple-filter choke suppresses the residual ripple of the rectified current and has also a process-stabilising

br-er5-27e.cdr

ISF 2002

Torch Position

Figure 5.27 With the develop-

effect.83% Ar + 15% He + 2% CO2 90% Ar + 5% O2 + 5% CO2 80% Ar + 5% O2 + 15% CO2 92% Ar + 8% O2 92% Ar + 8% CO2 forming gas (N2-H2-mixture)

Ar/He-mixture Ar + 5% H2 or 7,5% H2

99% Ar + 1% O2 or 97% Ar + 3% O2 97,5% Ar + 2,5% CO2

ment

of

efficientshielding gasesArgon 4.8 Helium 4.6 Argon 4.6

transistors the design of transistorindustrial sections

88% Ar + 12% O2 82% Ar + 18% CO2

application examplesautoclaves, vessels, mixers, cylinders panelling, window frames, gates, grids stainless steel pipes, flanges, bends spherical holders, bridges, vehicles, dump bodies reactors, fuel rods, control devices rocket, launch platforms, satellites valves, sliders, control systems stator packages, transformer boxes passenger cars, trucks radiators, shock absorbers, exhausts cranes, conveyor roads, excavators (crawlers) shelves (chains), switch boxes braces, railings, stock boxes mud guards, side parts, tops, engine bonnets attachments to flame nozzles, blast pipes, rollers vessels, tanks, containers, pipe lines stanchions, stands, frames, cages beams, bracings, craneways harvester-threshers, tractors, narrows, ploughs waggons, locomotives, lorries

analogue sources possible,

power became Figure

5.29. The operating principle of a transistor analoguebr-er5-28e.cdr

ISF 2002

power source follows the principle of an audio frequency amplifier which amFigure 5.28

Fields of Application of Different Shielding Gases

plifies a low-level to a high level input signal, possibly distortion-free. The transistor power source is, as conventional power sources, also equipped with a three-phase


69

transformer, with generally only one secondary tap. The secondary voltage is rectified by silicon diodes into full wave operation, smoothed by capacitors and fed to the arc through a transistor cascade. The welding voltage is steplessly adjustable until no-load voltage is reached. The difference between source voltage and welding voltage reduces at the transistor cascade and produces a comparatively high stray power which, in general, makes water-cooling necessary. The efficiency factor is between 50 and 75%. This disadvantage is, however, accepted as those power sources are characterised by very short reaction times (30 to 50 s). Along with the development of transistor analogue power sources, the consequent separation of the power section (transformer and rectifier) and electronic control took place. The analogue or digital control sets the reference values and also controls the welding process. The power section operates exclusively as an amplifier for the signals coming from the control.

The output stage may also be carried out by clocked cycle. A secondary clocked transistor power source features just as the analogue power sources, a transformer and a rectifier, Figure 5.30. The transistor unit functions as an on-off switch. By varying the on-off period, i.e., of the pulse duty factor, the average voltage at the output of the transistor stage may be varied. The arc voltage achieves small ripples, which are of a limited amplitude, in the switching frequency of, in general, 20 kHz; whereas the welding current shows to be strongly smoothed during the high pulse frequencies caused by inductivities. As the transistor unit has only a switching function, the stray power is lower than thatthree-phase transformer mains supply fully-controlled three-phase bridge rectifier energy store transistor power section welding current

of

analogue

sources. The efficiency factor is approx. 75 95%. The reaction timesuist

ofcurrent pickup

these

clocked

u1 . . un

iist

units are within of 300 500 s

reference input values

signal processor (analog-to-digital)

clearly longer thanbr-er5-29e.cdr isf 2002

GMA Welding Power Source, Electronically Controlled, Analogue

those of analogue power sources.

Figure 5.29


70

Series regulator power sources, the so-called inverter power sources, differ widely from the afore-mentioned welding machines, Figure 5.31. The alternating voltage coming from the mains (50 Hz) is initially rectified, smoothed and converted into a medium frequency alternating voltage (approx. 25-50 kHz) with the help of controllable transistor and thyristor switches. The alternating voltage is then transformer reduced to welding voltage levels and fed into the welding process through a secondary rectifier, where the alternating voltage also shows switching frequency related ripples. The advantage of inverter power sources is their low weight. A transformer that voltage transforms with fre3-phase transformermains supply

quency of 20 kHz, has, compared with a 50 Hz trans-

3-phase bridge rectifier

energy store

transistor switch

protective reactor welding current

former,

consideraUist U1 . . Un Iist

bly lower magnetic losses, that is to say, its size may accordingly smaller and bebr-er5-30e.cdr



current pickup

ISF 2002

its

weight is just 10% of that of a 50 Hz transformer. Figure 5.30

GMA Welding Power Source, Electronically Controlled, Secondary Chopped

Reaction time and efficiency factormains supply

filter

3-phase bridge rectifier

energy storage

transistor inverter

medium frequency transformer

rectifier welding current

are comparable to the corresponding

values of switchingtype power sources.Uist U1 . . Un Iist



current pickup

br-er5-31e.cdr

ISF 2002

GMA Welding Power Source, Electronically Controlled, Primary Chopped, Inverter

Figure 5.31


71

All welding power sources are fitted with a rating plate, Figure 5.32. Here the performance capability and the properties of the power source are listed. The S in capital letter (former K) inmanufacturer rotary current welding rectifierinsulations class

F

cooling type

the middle showsF

~type welding MIG/MAG

_

VDE 0542production number

protective IP21 system switchgear number

DIN 40 050

thatpower range power capacity in dependence of current flow power supply

the

power

source is suitable for welding operations ardous under haz-

U0 15 - 38 V input 3~50Hz 6,6 kVA (DB) cosj 0,72

SU1 220 V U1 380 V U1 U1 V V

35A/13V - 220A/25V X 60% ED 100% ED 170 A I2 220 A 23 V U2 25 V I1 26 A I1 I1 I1 15 A A A 17 A 10 A A A

situations,

i.e., the secondary no-load voltage is lower than 48 Volt ISF 2002

min. and max. no-load voltagebr-er5-32e.cdr

and therefore notRating Plate

dangerous to the welder.

Figure 5.32

Besides the familiar solid wires also filler wires are used for gas-shielded

metal arc welding. They consist of aa b c

metallic tube and a flux core filling.

seamless flux-cored wire electrode

form-enclosed flux-cored wire electrode

Figure 5.33 depicts common cross ISF 2002

br-er5-33e.cdr

Cross-Sections of Flux-Cored Wire Electrodes

sectional shapes.

Figure 5.33


72

Filler wires contain arc stabilisators, slag-forming and also alloying elements which support a stable welding process, help to protect the solidifying weld from the atmosphere and, more often than not, guarantee very good mechanical properties. An important distinctive criteria is the type of the filling. The influence of the filling issymbol R P B M V W Y S slag characteristics rutile base, slowly soldifying slag rutile base, rapidly soldifying slag basic filling: metal powder rutile- or fluoride-basic fluoride basic, slowly soldifying slag fluoride basic, slowly soldifying slag other types customary application* S and M S and M S and M S and M S S and M S and M

very similar to thatshielding gas ** C and M2 C and M2 C and M2 C and M2 without without without

of

the

electrode

covering in manual electrode (see welding 2).

chapter

Figure 5.34 shows a list of the different types of filler wire.

*) S: single pass welding - M: multi pass welding **) C: CO2 - M2: mixed gas M2 according to DIN EN 439br-er5-34e.cdr ISF 2002

Type Symbols of Flux-Cored Wire Electrodes According to DIN EN 12535

Figure 5.34

6. Narrow Gap Welding, Electrogas - and Electroslag Welding

2003

6. Narrow Gap Welding, Electrogas- and Electroslag Welding

73

Up to this day, there is no universal agreement about the definition of the term Narrow Gap Welding although the term is actually self-explanatory. In the international technical literature, the process characteristics mentioned in the upper part of Figure 6.1 are frequently connected with the definition for narrow gap welding. In spite of theseProcess characteristics: - narrow, almost parallel weld edges. The small preparation angle has the function to compensate the distortion of the joining members - multipass technique where the weld build-up is a constant 1 or 2 beads per pass - usually very small heat affected zone (HAZ) caused by low energy input

definition all about

difficulties questions the valid

universally advantages

Advantages: - profitable through low consumption quantities of filler material, gas and/ or powder due to the narrow gaps - excellent quality values of the weld metal and the HAZ due to low heat input - decreased tendency to shrink

Disadvantages - higher apparatus expenditure, espacially for the control of the weld head and the wire feed device - increased risk of imperfections at large wall thicknesses due to more difficult accessibility during process control - repair possibilities more difficult

and disadvantages of the narrow gap welding method

can be clearly answered.

br-er6-01e.cdr

ISF 2002

Narrow Gap Welding

Figure 6.1 The numerous variations of narrow gap welding are, in general, a further development of the conventional welding technologies. Figure 6.2 shows a classification with emphasis on several important process characteristics. Narrow gap TIG welding with cold or hot wire addition is mainly applied as an orbital process method or for the joiningsubmerged arc electroslag narrow narrow gap welding gap welding process with straightened wire electrode (1R/L, 2R/L, 3R/L) process with oscillating wire electrode (1R/L) process with twin electrode (1R/L, 2R/L) process with lengthwise positioned strip electrode (2R/L) flat positionbr-er6-02e.cdr

of

high-

gas-shielded metal arc narrow gap welding

tungsten innert gas-shielded narrow gap welding

alloy as well as non-ferrous met-

process with linearly oscillating filler wire

electrogas process with linearly oscillating wire electrode electrogas process with bent, longitudinally positioned strip electrode

process with hot wire addition (1R/L, 2R/L) MIG/MAGprocesses (1R/L,2R/L,3R/L) process with cold wire addition (1R/L, 2R/L)

als. This method is, however, hardly applied in the practice. The other are widely and are detail

process with stripshaped filler and fusing feed

processes more

vertical up position

all welding positions

spread

explainedinSurvey of Narrow Gap Welding Techniques Based on Conventional Technologies

in the following.

Figure 6.2


74

In Figure 6.3, a systematic subdivisionGMA narrow gap welding no wire-deformation long-wire method (1 B/P, 2 B/P) thick-wire method (1 B/P, 2 B/P) twin-wire method (1 B/P) tandem-wire method (1 B/P, 2 B/P, 3 B/P) twisted wire method (1 B/P) rotation method (1 B/P) coiled-wire method (1 B/P) corrugated wire method with mechanical oscillator (1 B/P) corrugated wire method with oscillating rollers (1 B/P) corrugated wire method with contour roll (1 R/L) zigzag wire method (1 B/P) wire loop method (1 B/P)explanation: B/ P: Bead/ Passbr-er6-03e.cdr

GMA narrow gap welding wire-deformation

of the various GMA narrow gap technologies is shown. In accorA

dance with this, the fundamental distinguishing feature of the methods is whether the process is carried out

D

B

with or without wire deformation. Overlaps in the structure result from the application of methods where a single or several additional wires are

C

used. While most methods are suitable for single layer per pass welding, other methods require a weld build-up with at least two layers per pass. A

A: method without forced arc movement B: method with rotating arc movement C: method with oscillating arc movement D: method with two or more filler wires ISF 2002

further subdivision is made in accordance with the different types of arc movement.

Figure 6.3 In the following, some of the GMA narrow gap technologies are explained: Using the turning tube method, Figure 6.4, side wall fusion is achieved by the turning of the contact tube; the contact tip angles are set in degrees of between 3 and 15 towards the torch axis. With an electronic stepper motor control, arbitrary transversearc oscillating mocorrugated wire method with mech. oscillator

tions with defined dwell periods of oscillation and oscillation frequencies can be realised - independent of the filler wire properties. In contrast, when the corrugated method with wire me1 - wire reel 2 - drive rollers 3 - wire mechanism for wire guidance 4 - inert gas shroud 5 - wire guide tube and shielding gas tube 6 - contact tipbr-er 6-04e.cdr

1

1

2 3 4 5 6

2 3 4 5 6

12 - 14

1 - wire reel 2 - mechanical oscillator for wire deformation 3 - drive rollers 4 - inert gas shroud 5 - wire feed nozzle and shielding gas tube 6 - contact tip

chanical oscillator is Figure 6.4

Principle of GMA Narrow Gap Welding

8 - 10


75

applied, arc oscillation is produced by the plastic, wavy deformation of theplate thickness: gap preparation: 300 mm square-butt joint, 9 mm flame cut 1.2 mm elctrode diameter: amperage: 260 A pulse frequency: 120 HZ arc voltage: 30 V welding speed: 22 cm/min -1 wire oscillation: 80 min oscillation width: 4 mm shielding gas: 80% Ar/ 20% Co2 primery gas flow: 25 l/min secondary gas flow: 50 l/min number of passes: approx. 70

wire electrode. The deformation is obtained by a continuously swinging oscillator which is fixed above the wire feed rollers. Amplitude and frequency of the wave motion can be varied over the total amplitude of oscillation and the speed of the mechanical oscillator or, also, over the wire feed speed. As the contact tube remains stationary, very narrow gaps with widths from 9 to 12 mm with plate thicknesses of up to 300 mm can be welded.

br-er6-05e.cdr

ISF 2002

Figure 6.5 Figure 6.5 shows the macro section of a GMA narrow gap welded joint with plates (thickness: 300 mm) which has been produced by the mechanical oscillator method in approx. 70 passes. A highly regular weld build-up and an almost straight fusion line with an extremely narrow heat affected zone can be noticed. Thanks to the correct setting of the oscillation parameters and the precise, centred torch manipulation no2 3 4 5 rotation method 1 spiral wire method 1

2 3 4

sidewall fusion defects occurred, in

6

5

13 - 14

sidewall penetration depth. A further advantage of the tech-

1 - wire reel 2 - drive rollers 3 - mechanism for nozzle rotation 4 - inert gas shroud 5 - shielding gas nozzle 6 - wire guiding tubebr-er 6-06e.cdr

1 - wire reel 2 - wire mechanism for wire deformation 3 - drive rollers 4 - wire feed nozzle and shielding gas supply 5 - contact piece

weave-bead


Figure 6.6

9 - 12

spite

of

the

low


76

nique is the high crystal restructuring rate in the weld metal and in the basemetal adjacent to the fusion line an advantage that gains good toughness properties.

Two narrow-gap welding variations with a rotating arc movement are shown in Figure 6.6. When the rotation method is applied, the arc movement is produced by an eccentrically protruding wire electrode (1.2 mm) from a contact tube nozzle which is rotating with frequencies between 100 and 150 Hz. When the wave wire method is used, the 1.2 mm solid wire is being spiralwise deformed. This happens before it enters the rotating 3 roll wire feed device. With a turning speed of 120 to 150 revs per minute the welding wire is deformed. The effect of this is such that after leaving the contact piece the deformed wire creates a spiral diameter of 2.5 to 3.0 mm in the gap adequate enough to weld plates with thicknesses of up to 200 mm at gap widths between 9 and 12 mm with a good sidewall fusion.

Figure 6.7 explains two GMA narrow gap welding methods which are operated without forced arc movement, where a reliable sidewall fusion is obtained either by the wire deflection through constant deformation (tandem wire method) or by forced wire deflection with the contact tip (twin-wire method). In both cases, two wire electrodes with thicknesses between 0.8 and 1.2 mm are used. When the tandem technique is applied, these electrodes are transported to the two weld heads which are arranged inside the gap in tandem and which are indeFigure pendently selectable.

Whentandem method 1350

the

twin-

twin-wire method 1

wire method is applied, two parallel switched elec-

2 3 4 5 6 2 3 4 5

trodes are transported by a common wire feed unit,

1 - wire reel 2 - deflection rollers 3 - drive rollers 4 - inert gas shroud 5 - shielding gas nozzle 6 - wire feed nozzle and contact tipbr-er 6-07e.cdr

9 - 12

1 - wire reel 2 - drive rollers 3 - inert gas shroud 4 - wire feed nozzle and shielding gas supply 5 - contact tips

15 - 18

and, subsequently, adjusted common in a

sword-


type torch at an incline towards the

Figure 6.7


77

strip electrodeSO stick out s

weld edges at small spaces behind each other (approx. 8 mm) and mol-

s a x h w

gap width electrode deflection distance of strip tip to flank twisting angle bead hight bead width

ten.

sox

a

In place of the SA narrow gap welding methods, mentioned in Figure 6.2, the method with a lengthwise po-

h

f

w

twin-wire electrode

sitioned strip electrode as well as the twin-wire method are explained in

vw

s

vw a H z s h w p

weld speed electrode deflection stick out distance torch - flank gap width bead height bead width penetration depth

more detail, Figure 6.8. SA narrow gap welding with strip electrode is carried out in the multipass layer technique, where the strip electrode is deflected at an angle of approx. 5

Hz

a h

pbr-er6-08e.cdr

w

towards the edge in order to avoidSubmerged Arc Narrow Gap Welding

collisions. After completing the first

Figure 6.810 7

fillet weld and slag removal the oppo8

site fillet is made. Solid wire as well as8 s

cored-strip electrodes with widths between 10 and 25 mm are used. The gap width is, depending on the number of passes per layer, between 20 and 25 mm. SA twin-wire welding is, in general, carried out using two elec6 double-U butt weld SA-DU weld preparation (8UP DIN 8551) 8

16

square-edge butt weld SA-SE weld preparation (3UP DIN 8551) 10

trodes (1.2 to 1.6 mm) where one electrode is deflected towards one weld edge and the other towards the bottom of the groove or towards the opposite weld edge. Either a single pass layer or a two pass layer technique are applied. Dependent on the electrode di-

3

s

double-U butt weld GMA-DU weld preparation (Indexno. 2.7.7 DIN EN 29692)br-er6-09e.cdr

3

narrow gap weld GMA-NG weld preparation (not standardised)

Comparison of the Weld Groove Shape

Figure 6.9

s

s


78

ameter and also on the type of welding powder, is the gap width between 12 and 13 mm.

Figure 6.9 shows a comparison of groove shapes in relation to plate thickness for SA welding (DIN 8551 part 4) with those for GMA welding (EN 29692) and the unstandardised, mainly used, narrow gap welding. Depending on the plate thickness, significant differences in the weld crosssectional dimensions occur which may lead to substantial saving of mabr-er6-10e_sw.cdr ISF 2002

terial and energy during welding. For example, when welding thicknesses of 120 mm to 200 mm with the narrow

Figure 6.10 gap welding technique, 66% up to 75% of the weld metal weight are saved, compared to the SA square edge weld.electrode shielding gas arc +

workpiece

wire guide

The practical application of SA narrow gap welding for the production of a flanged calotte joint for a reactor pressure vessel cover is depicted in Figure 6.10. The inner diameter of the pressure vessel is more than

weld pool Cu-shoe weld advance weld metal water

5,000 mm with wall thicknesses of 400 mm and with a height weight of is

designation: gas-shielded metal arc welding (GMAW acc. DIN 1910 T.4) position: vertical (width deviations of up to 45) plate thickness: 6 - 30 mm square-butt joint or V weld seam 30 mm double-V weld seam materials: unalloyed, lowalloy and highalloy steels gap width: 8 - 20 mm electrodes: only 1 (flux-cored wire, for slag formation between copper shoe and weld surface) 1.6 - 3.2 mm amperage: 350 - 650 A voltage: 28 - 45 V weld speed: 2 - 12 m/h shielding gas: unalloyed and lowalloy steels CO2 or mixed gas (Ar 60% and 40% Co ) 2 highalloy steels: argon or heliumbr-er6-11e.cdr

40,000 mm.

The

total

3,000 tons. The weld depth at the joint was 670 mm, so it had been necesFigure 6.11

Electrogas Welding


79

sary to select a gap width of at least 35 mm and to work in the three pass layer technique.

Electrogas welding (EG) is characterised by a vertical groove which is bound by two water-cooled copper shoes. In the groove, a filler wire electrode which is fed through a copper nozzle, is melted by a shielded arc, Figure 6.11. During this process, are groove edges fused. In relation with the ascending rate of the weld pool volume, the welding nozzle and the copper shoes are pulled upwards. In order to avoid poor fusion at the beginning of the welding, the process has to be started on a run-up plate which closes the bottom end of the groove. The shrinkholes forming at the weld end are transferred onto the run-off plate. If possible, any interruptions of the welding process should be avoided. Suitable power sources are rectifiers with a slightly dropping static characteristic. The electrode has a positive polarity.

The application of electrogas welding for low-alloyed steels is more often than not limited, as the toughness of the heat affected zone with the complex coarse grain formation does not meet sophisticated demands. Long-time exposure to temperatures of more than 1500C and low crystallisation rates are responsible for this. The same applies to the weld metal. For a more wide-spread application of electrogas welding, the High-Speed Electrogas Welding6. copper shoe 7. water cooling 8. weld seam 9. Run-up plate 1 2 3 4 5 6 7 8 9 1. base metal 2. welding boom 3. filler metal 4. slag pool 5. metal pool

Method has been developed in the ISF. In this process, the gap crosssection is reduced and additional metal powder is added to increase the deposition rate. By the increase of the welding speed, the dwell times of weld-adjacent regions above critical temperatures and thus the brittleness effects are significantly reduced. Figure 6.12designation: position: plate thickness: gap width: materials: electrodes:

resistance fusion welding vertical (and deviation of up to 45) 30 mm (up to 2,000 mm) 24 - 28 mm unalloyed, lowalloy and highalloy steels 1 or more solid or cored wires 2.0 - 3.2 mm plate thickness range per electrode: fixed 30 - 50 mm oscillated: up to 150 mm amperage: 550 - 800 A per electrode voltage: 35 - 52 V welding speed: 0.5 - 2 m/h slag hight: 30 - 50 mmbr-er6-12e.cdr

Electroslag Welding


80

Figure 6.12 shows the process principle of Electroslag Welding. Heating and melting of the groove faces occurs in a slag bath. The temperature of the slag bath must always exceed the melting temperature of the metal. The Joule effect, produced when the current is transferred through the conducting bath, keeps the slag bath temperature constant. The welding current is fed over one or more endless wire electrodes which melt in the highly heated slag bath. Molten pool and slag bath which both form the weld pool are, sideways retained by the groove faces and, in general, by water-cooled copper shoes which are, with the complete welding unit, and in relation with the welding speed, moved progressively upwards. To avoid the inevitable welding defects at the~powder

beginning

of

the welding process (insufficientslag

penetration, incluignition with arc powder fusion

sion of unmolten powder) and at the end of the welding (shrinkholes, slag

slag molten pool weld metal

start of weldingbr-er6-13e.cdr

welding

end of welding ISF 2002

inclusions), run-up and run-off plates are used.

Process Phases During ES Welding

Figure 6.13 The electroslag welding process can be divided into four process phases, Figure 6.13. At the beginning of the welding process, in the so-called ignition phase, the arc is ignited for a short period and liquefies the non-conductive welding flux powder into conductive slag. The arc is extinguished as the electrical conductivity of the arc length exceeds that of the conductive slag. When the desired slag bath level is reached, the lower ignition parameters (current and voltage) are, during the so-called Data-Increase-Phase, raised to the values of the stationary welding process. This occurs on the run-up plate. The subsequent actual welding process starts, the process phase. At the end of the weld, the switch-off phase is initiated in the run-off plate. The solidifying slag bath is located on the run-off plate which is subsequently removed.


81

The electroslag welding with consumable feed wire (channel-slot welding) proved to be very useful for shorter welds.

The copper sliding shoes are replaced by fixed Cu cooling bars and the welding nozzle by a steel tube, Figure 6.14. The length of the sheathed steel tube, in general, corresponds with the weld seam length (mainly shorter than 2.500 mm) and the steel tube melts during welding in the ascending slag bath. Dependent on the plate thickness, welding can be carried out with one single or with several wire and strip electrodes. A feature of this process variation is the handiness of the welding device and the easier weldingdrive motor welding cable run-off plate workpiece = ~ workpiece wire or strip electrode

Electroslag fusing nozzle process (channel welding) position: vertical plate thickness: 15 mm materials: unalloyed, lowalloy and highalloy steels welding consumables: wire electrodes: 2.5 - 4 mm strip electrodes: 60 x 0.5 mm plate electrodes: 80 x60 up to 10 x 120 mm fusing feed nozzle: 10 - 15 mm welding powder: slag formation with high electrical conductivity

area

preparation.

Also curved seams can be welded with a bent consumable electrode. As the groove width can be significantly when with

fusing feed nozzle workpiece cable workpiece run-up plate copper shoes workpiece

reduced comparing

copper shoesbr-er 6-14e.cdr

Electroslag Welding with Fusing Wire Feed Nozzle

conventional processes, and a strip shaped filler material with a consumable guide

Figure 6.14

technological measurespost weld heat treatment decrease of peak temperature and dwell times at high temperatures increase of welding speed reduction of energy per unit length continuous normalisation furnace normalisation increase of deposit rate application of several wire electrodes, metal powder addition decrease of groove volume V, double-V butt joints, multi-pass technique

metallurgical measuresincrease of purity application of suitable base and filler metals

piece is used, this welding process is rightly placed under the group of narrow gap weld-

addition of suitable alloy and micro-alloy elements (nucleus formation)

reduction of S-, P-, H2-, N2 and O2 - contents and other unfavourable trace elements

C-content limits Mn, Si, Mo, Cr, Ni, Cu, Nb, V, Zr, Ti

ing techniques.

Likewise in electrogas welding, the electroslag welding

br-er 6-15e.cdr

Possibilities to Improve Weld Seam Properties

Figure 6.15


82

process is also characterised by a large molten pool with a simultaneously - low heating and cooling rate. Due to the low cooling rate good degassing and thus almost porefree hardening of the slag bath is possible. Disadvantageous, however, is the formation of a coarse-grain structure. There are, however, possibilities to improve the weld properties, Figure 6.15.

To avoid postweld heat treatment the electroslag welding process with local continuous normalisation has been developed for plate thicknesses of up to approx. 60 mm, Figure 6.16. The welding temperature in the weld region drops below the Ar1temperature and is subsequently heated to the normalising temperature (>Ac3). The specially designed torches follow thetemperature C1. filler wire 2. copper shoes 3. slag pool 4. metal pool 5. water cooling 6. slag layer 7. weld seam 8. distance plate 9. postheating torch 10. side plate 11. heat treated zone

copper1 2 3 4 5 6 7 8 9 10

shoes the weld

2 2000 1500 7 8 9 11 900 500 10 950

along

seam. By reason of the residual heat in the workpiece the necessary perature can tembe

reached in a shortbr-er 6-16e.cdr

ES Welding with Local Continuous Normalisation

time.

Figure 6.16

In order to circumvent an expensive postheat weld treatment which is often unrealistic for use on-site, the electroslag high-speed welding process with multilayer technique has been developed. Similar to electrogas welding, the weld cross-section is reduced and, by application of a twin-wire electrode in tandem arrangement and addition of metal powder, the weld speed is increased, as in contrast to the conventional technique. In the heat affected zones toughness values are determined which correspond with those of the unaffected base metal. The slag bath and the molten pool of the first layer are retained by a sliding shoe, Figure 6.17. The weld preparation is a double-V butt weld with a gap of approx. 15 mm, so the carried along sliding shoe seals the slag and the metal bath. Plate preparation is, as in conventional elec-


83

troslag welding, exclusively done by flame cutting. Thus, the advantage of easier weld preparation can be main1 2 3 4 9 5 6 7 8 41 magnetic screening 2 metal powder addition 3 tandem electrode 4 water cooling 5 copper shoe (water cooled) 6 slag pool 7 molten pool 8 solidified slag 9 welding powder addition 10 weld seam

tained.

For larger plate thicknesses (70 to 100 mm), the three passes layer technique has been developed.

When welding the first pass with a double-V-groove preparation (root

width: 20 to 30 mm; gap width: approx. 15 mm) two sliding shoes which are adjusted to the weld groove are used. The first layer is welded using the conventional technique, with one wire electrode without metal powder addition.

10

br-er6-17e.cdr

ES-welding in 2 passes with sliding shoe

ISF 2002

Figure 6.1712

When welding the outer passes flat Cu shoes are again used, Figure 6.18. Three wire electrodes, arranged in a triangular formation, are used. Thus, one electrode is positioned close to the root and on the plate outer sides two electrodes in parallel arrangement are fed into the bath. The single as well as the parallel wire electrodes are fed with different metal powder quantities which as outcome permit a welding speed 5 times higher than the

11

1 2 3 4 9 5 6 7 8 41 magnetic screening 2 metal powder supply 3 three-wire electrode 4 water cooling 5 copper shoe (water cooled) 6 slag pool 7 molten pool 8 solidified slag 9 welding powder supply 10 weld seam 11 first pass 12 second pass ISF 2002

10

speed of the single layer conventional technique and also leads to strong increase of toughness in all zones of the welded joint. Figure 6.18br-er6-18e.cdr

ES-welding of the outer passes


84

If wall thicknesses of more than 100 mm are to be welded, several twin-wire electrodes with metal powder addition have to be used to reach deposition rates of approx. 200 kg/h. The electroslag welding process is limited by the possible crack formation in the centre of the weld metal. Reasons for this are the concentration of elements such as sulphur and phosphor in the weld centre as well as too fast a cooling of the molten pool in the proximity of the weld seam edges.

7. Pressure Welding

2003

7. Pressure Welding

85

Figure 7.1 shows a survey of the pressure welding processes for joining of metals in accordance withwelding

DIN 1910.

pressure welding

fusion welding

Infriction welding

gas

pressure

welding a distincgas pressure welding resistance pressure welding

tion is made between square open and square pressure Fig-

induction pressure welding

conductive pressure welding

resistance spot weldingbr-er7-01e.cdr

projection welding

roll seam welding

pressure butt welding

flash butt welding

closed gas welding,

Classification of Welding Processes acc. to DIN 1910

ure 7.2.

Figure 7.1 Both methods use efficient gas torches to bring the workpiece ends up to the welding temperature. When the welding temperature is reached, both joining members are butt-welded by the application of axial force when a flash edge forms. The long preheating time leads to the formation of a coarse-grained structure in the joining area, therefore the welds are of low toughness values. As the process is operated mainsindependently andinitial state: gap closed initial state: gap opened(for special cases)

the process equipment weight is low in also

gas flame torch in the open gap stationary mobile

and

easy to handle, theworkpiece closed gap ring-shaped burner (sectional view) pressure

main

application

1. heating 2. torch positioning 3. welding by rapid pressing

areas of gas pressure welding are the welding of reinforcement steels

completed weld seam working cycles: 1. heating 2. welding by pressingbr-er7-02e.cdr

Open Square and Closed Square Gas Pressure Welding

and of pipes in the building trade.

Figure 7.2

7. Pressure Welding

86

In pressure butt welding, the input of the necessary welding heat is produced by resistance heating. The necessary axial force is applied by copper clamping jaws which also receive the current supply, Figure 7.3. The current circuit is closed over the abutting surfaces of the two joining members where, by the increased interface resistance, the highest heat generation is obtained. After the welding temperature which is lower than the melting temperature of the weld metal is reached, upset pressure is applied and the current circuit is opened. This produces a thick flash-free upset seam which is typical for this method. In order to guarantee the uniform heating of the abuttingbefore upset force has been applied upset force

faces, they must be conformable in their cross-sectional sizes and shapes with each other and they must have

water-cooled clamping chucks (Cu electrodes)

parallel faces.

bulging at the end of the weld

_ ~

As no molten metalbr-er7-03e.cdr

develops

during

pressure upset butt welding, the joining surfaces must be free from contaminations and from Figure 7.3

Process Principle of Pressure Butt Welding

fixed clamping chuck

a+b b 2 a

mobile clamping chuck clamping force steel chuck

oxides. Suitable for welding are unalloyed and low-alloy steels. The welding of aluminium and copper material is, because of the tendency towards oxidation and good Figure 7.4primary side secondary side

copper shoe

welding transformerbr-er7-04e.cdr

a = flashing length b = upset loss

Schematic Structure of a Flash Butt Welding Equipment

conductivity, possi-

7. Pressure Welding

87

ble only up to a point. For the most part, smaller cross-sections with surfaces of up to 100 mm are welded. Areas of applications are chain manufacturing and also extensions of wires in a wire drawing shop.

A flash butt welding equipment is, in its principal structure, similar to the pressure butt welding device, Figure 7.4.

While in pressure upset butt welding the joining members are alwaysbr-er7-05e.cdr ISF 2002

strongly pressed together, in flash butt welding only fusing contact is made during the heating phase. During the welding process, the workpiece ends

Figure 7.5

are progressively advanced towards each other until they make contact at several points and the current circuit is over these contact bridges closed. As the local current density at these points is high, the heating also develops very fast. The metal is liquified and, partly, evaporated. The metal vapour pressure causes the liquified metal to be thrown out of the gap. At the same time, the metal vapour is generating a shielding gas atmosphere; that is to say, with the exception of pipe welds, welding can be carried out without the use of shielding gas. The constant creation and destruction of the contact bridges causes the abutting faces to burn, starting from the contact points, with heavy spray-type ejection. Along with the occurrence of material loss, the parts are progressively advanced towards each other again. New contact bridges are created again and again. When the entire abutting face is uniformly fused, the two workpiece ends are, through a high axial force, abruptly pressed together and the welding current is switched off. This way, a narrow, sharp and, in contrast to friction welding, irregular weld edge is produced during the upsetting progress, which, if necessary, can be easy mechanically removed while the weld is still warm, Figure 7.5.

7. Pressure Welding

88

In flash butt welding, a fundamental distinction is made between two different working techniques. During hot flash butt welding a preheating operation precedes the actual flashing process, Figure 7.6. The preceding resistance heating is carried out by reversing, i.e., by the changing short-circuiting and pressing of the joining surfaces and by the mechanical separation in the reversed motion. When the joint ends are sufficiently heated, is the flashing process is initialised automatically and the following process is similar to cold flash butt welding. In contrast to cold flash butt welding, the advantage of hot flash butt welding is that, on one hand, sections of 20 times the size can be welded with the same machine efficiency and, on the other hand, a smaller temperature drop and with that a lower cooling rate in the workpiece can be obtained. This is of importance, especially with steels which because of their chemical composition have a tendency to harden. The cooling rate may also be reduced by conductive reheating inside the machine. A smooth and clean surface is not necessary with hot flash butt welding. If the abutting faces differ greatly from the desiredupset force upset travel flashing travel

plane-parallelism, an additional flashing process (a short flashing period with

preheating

flashing

flashing

amperage

time

time

low speed and highbr-er7-06e.cdr

hot flash welding

cold flash welding

energy) may be carried out first. Figure 7.6

Flashing Travel, Upset Travel, Upset Force and Welding Current in Timely Order

The welding area of the structure of a flash butt weld shows a zone which is reduced in carbon and other alloying elements, Figure 7.7. Moreover, all flash butt welded joints have a pronounced coarse grain zone, whereby the toughness properties of the welded joint are lower than of the base metal. By the impact normalizing effect in the machine successive to the actual welding process, can the toughness properties be considerably increased. By one or several current impulses the weld

7. Pressure Welding

89

temperatures are increased by up to approximately 50 over the austeniting temperature of the metal. Steels, aluminium, nickel and copper alloys can be welded economically with the flash butt welding process. Supportedheat affected zone

by the axial force, shrinkage in flash butt welding is so insignificant that0,1 mm

10 mm

material: C60 E

only very low residual stresses occur. It is, therefore, posweld coarse grain zone fine grain zone soft-annealing zone base metal

sible to weld alsobr-er7-07e.cdr

steels with a higher carbon content. Figure 7.7

Secondary Structure Along a Flash Butt Weld

Profiles of all kind are butt welded with this method. The method is usedn

for large-scale manufacture and with components of equal dimensions. The weldable cross-sections may reach dimensions of up to 120,000 mm. Areas of application are the welding ofnF1 friction force

rails, the manufacture of car axles, wheel rims and shafts, the welding of chain links and also the manufacture of tools and endless strips for pipeF2 upset force

production. Friction welding is a pressure welding method where the necessary heat

br-er7-08e.cdr

ISF 2002

for joining is produced by mechanical friction. The friction is, as a rule, generated by a relative motion between a

Figure 7.8

7. Pressure Welding

90

rotating and a stationary workpiece while axial force is being applied at the same time, Figure 7.8.

After the joint surfaces are adequately heated, the relative motion is discontinued and the friction force is increased to upsetting force. An even, lip-shaped bead is produced which may be removed in the welding machine by an additional accessory unit. The bead is often considered as the first quality criterion.

br-er7-09e_sw.cdr

Figure 7.9 shows all phases of thePhases of Friction Welding Process

friction welding process. In most cases this method is used for rota-

Figure 7.9 tion-symmetrical parts. It is, nowabrake clamping tool workpiece clamping tool pressure element for axial pressure

days, also possible to accurately join rectangular sections. and polygonal cross-

clutch

The most common variant of friction welding is friction welding with a continuous drive and friction welding with a flywheel drive, Figure 7.10. In friction welding with continuous drive, the clamped-on part to be joined is kept at a constant nominal speed by a drive, while the workpiece in the sliding chuck is pressed with a defined friction force. The nominal speed is maintained until the demanded temFigure 7.10br-er7-10e.cdr

conventional friction weldingdriving motor

flywheel

clamping tool

clamping tool workpiece

pressure element for axial pressure

flywheel friction welding

ISF 2002

7. Pressure Welding

91

perature profile has been achieved. Then the motor is declutched and the relative motion is neutralised by external braking. In general, the friction force is raised to upsetting force after the rotation movement has been discontinued. During flywheel friction welding, the inertia mass is raised to nominal speed, the drive motor is declutched and the stationary workpiece is, with a defined axial force, pressed against the rotating workpiece. Welding is finished when the total kinetic energy - stored in the flywheel has been consumed by the friction processes. This is the so-called self-breaking effect of the system. The method is used when, based on metallurgical processes, extremely short welding times may be realised. Further process variants are radial friction welding, orbital friction welding, oscillation friction welding and friction However, process surfacing. these variantsnumber of revolutionsfriction welding time 1...100s braking 0,1...0,5s friction welding time 0,125...2s

1800... 5400 min-1

900... 5400min-1

are until today still in the experimental stage. Recently,axial pressure20...100 Nmm

time

40...280-2

40...280 Nmm-2

Nmm

-2

new developments in the field of friction stud welding torque

studs on plates have duced. been intro-

conventional friction weldingbr-er7-11e.cdr

flywheel friction welding

Comparison of the Welding Processes for Conventional and Flywheel Friction Welding

Figure 7.11

Figure 7.11 depicts the variation in time of the most important process parameters in friction welding with continuous drive and flywheel friction welding. The occuring moments maxima may be interpreted as follows: The first maximum, at the start of the frictional contact, is explained by the formation of local fusion zones and their shearing off in the lower temperature range. The torque decreases as a result of the risen temperature - which again is a consequence of the increased plasticity - and of the lowered deformation resistance. The second maximum is generated du

welding technology

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