exercises in welding process and equipment ---part 1 ......exercises in welding process and...

1

Exercises in Welding Process and Equipment --- Part 1: Introduction to Welding Processes---

Takayoshi OHJI

Professor Emeritus, Osaka University

Dr. of Engineering

VIRTUAL WELD CO.,LTD

[email protected]

JICA_JICA_JICA_JICA_OHJI

© OK 0912

Classification of metal joining methodsClassification of metal joining methodsClassification of metal joining methodsClassification of metal joining methods JWES_JWES_JWES_JWES_OHJI

Shielded metal arc welding

TIG welding

Plasma arc welding

MIG/MAG welding

Self-shielded arc welding

Submerged arc welding

Electrogas welding

Arc stud welding

Electron beam welding

Laser welding

Spot welding

Projection welding

Seam welding

Upset welding

Flash welding

Gas welding

Arc welding

Electroslag welding

Forge welding

Electricresistance welding

Friction welding (inc. FSW)

Explosion welding

Pressure gas welding

Ultrasonic welding

Cold welding

Brazing

Soldering

Fusion

welding

Pressure

welding

Brazing and

Soldering

Adhesive bonding

Weld bond method

Deposition method

Riveting and bolting

Folding and roll-in fastening

Screwing and key joining

Shrinkage fitting

Metallurgi-

cal joining

(welding)

Chemicaljoining(adhesivebonding)

Mechanicaljoining

Joining

Diffusion welding

High energy beam welding

Thermite welding

2

Ex. MAG welding

The figure shows schematically MAG arc welding process.

Complete the figure with the appropriate words in the list.

feed rolls

gas nozzle

arc

weld metal

welding direction

List of words：

ａ．contact tip ｂ．cable ｃ．molten pool

ｄ．molten drop e ．plasma gas ｆ．shielding gas

ｇ．wire electrode ｈ．filler wire ｉ．tungsten electrode

ｊ．base metal

JWES_JWES_JWES_JWES_OHJI

Ex. Ex. Ex. Ex. GMA weldingGMA weldingGMA weldingGMA welding

The figure below shows the equipment for GMA welding. Fill in the following parentheses with the appropriate words in the list, and complete the figure.

GMA welding

List of words

ａ．gas supply ｂ．power source ｃ．carriage

ｄ．regulator and flow meter e．workpiece ｆ．wire feed unit

ｇ．welding torch ｈ．wire electrode


3

Apparatus for Shielded Metal Arc Welding


Power inputPower inputPower inputPower inputPower inputPower inputPower inputPower input

GroundGroundGroundGroundGroundGroundGroundGround

SwitchSwitchSwitchSwitchSwitchSwitchSwitchSwitch

Current control handleCurrent control handleCurrent control handleCurrent control handleCurrent control handleCurrent control handleCurrent control handleCurrent control handle

Welding Power SourceWelding Power SourceWelding Power SourceWelding Power SourceWelding Power SourceWelding Power SourceWelding Power SourceWelding Power Source

Cable jointCable jointCable jointCable jointCable jointCable jointCable jointCable joint

Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )Power line (AC single phase )

Welding cableWelding cableWelding cableWelding cableWelding cableWelding cableWelding cableWelding cable

Electrode holderElectrode holderElectrode holderElectrode holderElectrode holderElectrode holderElectrode holderElectrode holder

Covered electrode Covered electrode Covered electrode Covered electrode Covered electrode Covered electrode Covered electrode Covered electrode

WorkpieceWorkpieceWorkpieceWorkpieceWorkpieceWorkpieceWorkpieceWorkpiece

Earth cramp Earth cramp Earth cramp Earth cramp Earth cramp Earth cramp Earth cramp Earth cramp

© OK 0806

Flux (covering)

Core wire

Metal droplet

ArcMolten slag

Slag

Weld-beadMolten pool

Workpiece

Shielded metal arc welding with a flux-coated

electrode is the most widely used welding

process in the world, where the arc supplies the

heat for fusion while the flux, decomposed by

arc heat, makes it possible to shield the arc and

metal from air-contamination.

The shielded metal arc welding, commonly

called as “manual” welding, is characterized by

its flexible application and relative simplicity in

the equipment.

The welding process is widely used in

shipbuilding and structural and general

engineering, because it can be used in all

position with various types of steel and other

metals such as some copper and nickel base

alloy.

Shielded Metal Arc Welding （SMAW）

© OK 0806


Covered electrode

Welding direction

4

If we use a core wire without flux as an electrode in SMAW, we have a “weld bead”

with many defects. The arc with the core wire is not easy to strike and sustain even in

D.C., and very difficult in A.C., and the “weld” is poor in penetration, porous, contains

oxides due to the air contamination. As a result, the weld is brittle and of low-strength.

Functions of the Flux in SMAW

© OK 0910


Specific functions of the flux (electrode coating) in SMAW

① To strike and sustain the arc easily under D.C. or A.C. conditions.

② To provide a gas stream to shield the arc and the molten pool from air-contamination.

③ To supply deoxidizers and fluxing agents to clean the weld.

④ To provide a slag to protect the weld and to control cooling rate and weld shape.

＋＋＋＋－－－－

In MAG (Metal Active Gas) welding, the arc is formed between the tip of a consumable welding wire and the

workpiece and the arc and weld-zone are shielded by an active gas．Some of the important features of the process

are summarized below：

（ⅰ） high deposition rate；（ⅱ）low heat input（compared with SMAW and SAW）；（ⅲ）no heavy slag;；

The process is widely used for joining steel in the following applications：automobile bodies，storage tanks，bridges, pipelines, marine structures, etc.

Torch

Shielding gas

ArcPower source

Wire feed unitContact tip

Bead

Work piece

Molten pool

Metal Active Gas (MAG) welding

© OK 0806


5

Ex. TIG arc welding

The figure shows TIG arc welding schematically.


List of words

ａ．molten pool ｂ．filler wire ｃ．electrode wireｄ．tungsten ｅ．flux ｆ．contact tipｇ．high frequency unit

powersource

shielding gas

nozzle

welding direction

weld metal

arc

（）

（）

（）

（）


Nozzle

Filler wire

W-electrode

Arc

Shielding gas

Workpiece

Molten pool

TIG arc welding

Bead

In TIG welding process, the arc is maintained between

the work-piece and a non-consumable tungsten electrode

in an inert gas to protect the weld pool and the electrode

from atmospheric contamination.

The process is characterized as follows,

（ⅰ）joint quality is usually high；the process is under achemically inert atmosphere；

（ⅱ）the process is very controllable；（ⅲ）welding speeds and deposition rates are low；

The process is applied to the welding of a wide

range of engineering materials including stainless

steel, aluminum alloys and titanium．

Tungsten Inert Gas (TIG) welding

© OK 0806


6

Ex. Plasma arc weldingEx. Plasma arc weldingEx. Plasma arc weldingEx. Plasma arc welding

The figure shows schematically the plasma arc welding method with a keyhole.


（b）

List of words：

ａ．plasma jet ｂ．plasma arc ｃ．plasma gas ｄ．shielding gas

ｅ．active gas ｆ．tungsten electrode ｇ．constricting nozzle

ｈ．contact tip ｉ．wire electrode ｊ．keyhole

PowerSource

P.S.for

pilot arcH.F.unit

（）

（）

（）

pilot arc

（）

（）

（a）

welding direction

（）

（）

molten pool


Plasma arc torch

Electrode

Shielding

nozzle

Plasma gas

Constricting

nozzle

Arc

Work-piece

Plasma Arc Welding

Plasma arc may be considered as a development of

the TIG arc. In the plasma arc torch, the arc is

constricted by being forced through a relatively

small nozzle, i.e. the arc is thermally pinched by the

nozzle.

There are two types, the transferred and the non-

transferred arc. Because of the high energy density

of the plasma arc, the transferred arc is useful for

welding as well as cutting.

Plasma arc welding is used often as a substitute for

TIG arc welding. In some cases, it offers greater

welding speed and better weld quality.

Shielding gas

© OK 0806


7

Ex. Ex. Ex. Ex. SAW : Submerged Arc WeldingSAW : Submerged Arc WeldingSAW : Submerged Arc WeldingSAW : Submerged Arc Welding

The following figure shows Submerged Arc Welding schematically. Fill in the following

parentheses with the appropriate words in the list, and complete the figure.

List of words

ａ．molten pool ｂ．filler wire ｃ．electrode wire

ｄ．tungsten ｅ．flux ｆ．contact tip

ｇ．high frequency unit

（）

SAW

arc

slag

weld metal

（）

welding current

feed rolls

（）

（）


Flux

Wire

Slag

Bead

Workpiece

Molten slag

ArcWelding direction

Submerged Arc Welding （（（（SAW））））

Submerged arc welding is an automatic flux-

shielded process with consumable electrode,

where the weld pool is protected from the air

contamination by the molten slag and the gas，ｇenerated by the decomposition of a granular

flux．In the process, the arc is submerged in the flux,

a high welding current can be used without

spatter or the air-entrainment.

The high current （200～2000A） gives deep penetration and high deposition rate.

The important features of the process are as

follows,

（ⅰ）high deposition rates；（ⅱ）no visible arc radiation；（ⅲ）beｔｔｅｒ for thicknesses above 6 mm；（ⅳ）welding position is limited／downward

or horizontal．

Submerged arc welding

The main applications of submerged arc welding are on thick mild and low-alloy steels and

it is widely used for butt and fillet welds in offshore structures and shipbuilding, pressure vessel,

power generation plant，heavy structural steelwork. © OK 0806


8

Self-shielded (Flux Cored) Arc WeldingJWES_JWES_JWES_JWES_OHJI

Flux cored wireFlux cored wire

DropDrop

ArcArc SlagSlag

Weld beadWeld beadMolten poolMolten poolBase metalBase metal

Contact tipContact tip

Power sourcePower source

Feed rollsFeed rolls

Wire feed motorWire feed motorTubular metal Flux

Flux cored wire

Molten slagMolten slag

In this process, the flux vaporizes at the wire tip to shield the arc and pool and makes it possible to

complete the weld bead without any shielding gas. The process is suitable for site work in the

construction and shipbuilding industries because high deposition rates are obtained and the shielding

is less-affected by winds.© OK 0902

Ex.Ex.Ex.Ex. ElectroElectroElectroElectro----slag weldingslag weldingslag weldingslag welding

（）

（）

base metal

weld metal

（）

molten pool

（）

（）

feed roller

base metal

The figure shows the electro-slag welding with three electrodes.


List of words：

ａ．wire electrode ｂ．weld metal c．molten slag

ｄ．nozzle (guide tube) ｅ．water-cooled shoes


9

Electro-Slag Welding

Electroslag welding is not an arc welding, while an arc is used to start it. The process starts by striking an

arc on the bottom of the joint. Powdered flux set on the joint is melted by the arc heat into a molten slag.

Once a suitable molten slag is formed, the arc is

stopped and the wire （electrode) current flows through the molten slag. And the process

continues with the Joule’s heat generated by the

current.

As shown in the figure, the molten slag and weld

metal are supported by water-cooled copper shoes

on the joint faces, They moves up vertically along

the welding line.

The process is for joining thick steel plates in one

pass. Two or three electrodes may be used to

speed up the process.

Wire

Wire guide

Moltenslag

Weld pool

Water-cooledcopper shoe

Weld metalBase metal

Convection in molten slag pool

Schematic of electroslag welding process[Japan Welding Society, Advanced Welding & Joining Technology, Sanpo-pub. 2005]

© OK 0806


Electro-gas Welding

Weld poolWire guide nozzle

(welding torch)

Wire feed rollers

Welding wire

CO gas2

Weld metal

Base metal

Arc

CO gas2

Cooling water

Copper shoe

Cooling water

Weld bead

Electro-gas welding (EGW) is a highly efficient gas-shielded arc welding process in the vertical

position. In the process, molding shoes (copper shoes) are used to support the weld pool as shown

in the figure. The electrodes is either flux-cored or solid and carbon dioxide gas is generally used

as a shielding gas.

This welding process is characterized as follows,

① High welding efficiency with high currents ／high deposition rate

② Less angular distortion due to a small number of welding passes

③ The heat-affected zone can be softened and embrittled caused by the high welding heat input.

④ The application is limited to vertical up welding of thick plates.


10

Two Electrodes Electro-gas Welding

Courtesy of Mitsubishi Heavy Industries, Ltd.

Electron beam welding

CathodeCathode

(filament)(filament)

GridGrid

AnodeAnode

Focusing Focusing

coilcoil

Deflection Deflection

coilcoil

Electron Electron

beambeamVacuum Vacuum

chamberchamber

WorkWork--piecepiece

HighHigh

voltagevoltage

power power

sourcesource

Exhaust Exhaust

gasgas

In electron beam welding (EBW), electrons emitted from

the hot cathode are accelerated by a high voltage and are

converged into a high energy density beam by a magnetic

coil. The high energy density beam makes it possible to get

the weld with a deep penetration.


Examples of weld penetration by a

high voltage electron beam. M. Tomie and N. Abe, Transaction

of Heat Source Research Center in

JWRI, No.11, 10, 1995.

© OK 0902

11

Laser beam welding ①①①①

YAG laserYAG laser／／／／／／／／optical pumpingoptical pumping

〔〔〔〔〔〔〔〔Wave length: 1.06Wave length: 1.06μμμμμμμμm/ m/ 11..0808μμμμμμμμmm 〕〕〕〕〕〕〕〕

＋＋＋＋＋＋＋＋

－－－－－－－－

Rear mirrorRear mirror

YAG laser rodNd-YAG (yttrium-aluminum garnet)

Power Power sourcesource

LampLamp

LampLamp

Output mirrorOutput mirror

LensLens

Cooling Cooling waterwater



© OK 0902


LensLens

MirrorMirrorCOCO22＋＋＋＋＋＋＋＋NN22＋＋＋＋＋＋＋＋HeHe

WindowWindow

TransmissiveTransmissive reflectorreflectorDischarge circuitDischarge circuitTotal reflector Total reflector

(resonator)(resonator)

(40(40--120 120 TorrTorr))

Gas inGas in Heat exchangerHeat exchanger PumpPump Gas out Gas out

(partially)(partially)

In order to apply the laser beam to

materials processing such as

welding and cutting, a high power

is necessary, and hence CO2 and

YAG lasers are used for these

industrial applications.

COCO22 laserlaser／／／／／／／／electrical pumpingelectrical pumping

〔〔〔〔〔〔〔〔Wave length: 10.6Wave length: 10.6μμμμμμμμmm 〕〕〕〕〕〕〕〕

Laser beam welding ②②②②JWES_JWES_JWES_JWES_OHJI

In the laser system, atoms (or molecules) in the medium are pumped to an excited energy level first,

and then, a laser beam is produced by stimulated emission, if a large number of atoms are in a

particular high energy level. The laser beam, caused by the stimulated emission, is characterized by

the “coherence”, i.e. the light waves are in phase temporally and spatially.

Consequently, the laser beam, a coherent light beam, is easily converged into a high energy density

beam by using a lens and/or mirror and is irradiated on the work-piece, and the beam heat and melt it

to join.

The advantages and disadvantages of LBW are described in the following.

[Advantages]

① Deep penetration with narrow HAZ (Heat Affected Zone) as well as EBW.

② Low heat Input and less welding distortion as well as EBW.

③ Compared with the case of EBW, LBW is possible under the atmospheric condition (without an

vacuum chamber) and insensitive to magnetic field. .

④ Possible to transfer the laser light by using mirrors or fibers and to weld in several places by time-

sharing

⑤ Possible to weld a wide variety of materials, including metals with dissimilar physical properties.

[Disadvantages]

① The absorptivity of laser beam energy is low in metals, e.g. 2% for pure-Aluminum for CO2 laser,

8% for YAG laser, and it depends on the surface conditions such as roughness and oxidation.

② The equipment is expensive as well as EBW.

③ Necessary to machine and assemble the welding grooves with high accuracy

④ The plasma plume and metal vapor disturb the LBW process.

⑤ Necessary to take safety-measures against the laser light

© OK 0902

12

Ex.Ex.Ex.Ex. Resistance spot weldingResistance spot weldingResistance spot weldingResistance spot welding

The figure shows schematically the resistance spot welding.


electrode clamping force

（）

（）

（）

（）

ｉ2

ｉ1

（）

N1N2

List of words：

ａ．electrode（tip）ｂ．workpiece ｃ．primary current

ｄ．secondary current ｅ．nugget


Resistance spot welding machine

Courtesy of DAIHEN Corporation.

Air cylinder

Upper arm

Lower arm

（fixed）

Electrodes

Secondary loopTimer

Power source

Foot switchResistance spot welding robot


13

Application of resistance spot welding

Automotive robotic resistance welding line

Courtesy of TOYOTA MOTOR COPORATION


Resistance Seam Welding

Pressure

Welding transformer

Nugget

Wheel electrode

Base metal

Current

Rotatingdirection

Moving direction

Cooling water

Resistance seam welding process

The figure shows the resistance seam welding, where the work-pieces are clamped between the

rotating wheel electrodes and the overlapping sheets are locally melted and joined by Joule’s

heat of the welding current.

In resistance seam welding (RSEW), the welding current is supplied intermittently as shown in

the figure, while the current is supplied continuously at a high speed welding.

This welding process is widely applied for mild steel, stainless steel and aluminum alloy.

© OK 0806

Welding current

Time

ON ON ONOFF OFF

Intermittent welding current


14

Ex. Classification of welding and joining methodsThe welding process is classified into three types, i.e. the fusion welding, the pressure

welding and the brazing. Select the fusion welding out of the processes in the list and

encircle their numbered symbol.

(1) Soldering, (2) Laser welding, (3) Ultrasonic joining, (4) Electron beam welding,

(5) Submerged arc welding, (6) Plasma welding, (7) MAG welding, (8) Friction stir

welding (FSW), (9) Electro-slag welding, (10) Diffusion bonding.

© OK 0806

OPTION

Ex. How does FSW work?


Joining direction

Joining tool

Joining pin

Workpiece

Backing metal

Schematic of friction stir welding process[Koga, J. of Japan Weld. Soc., Vol.69, No.3,18, 2000]

Friction Sir Welding

Friction stir welding (FSW) is a new process developed by The Welding Institute (TWI)

in the early 1990s.

The principles of this welding process are shown in the figure.

The joining pin is plunged into the work-pieces to be welded and is forced to rotated,

and the frictional heat due to the rotation, causes a plastic metal flow in the work-pieces.

The joining tool, by traveling along the welding line, makes it possible to produce a

continuous weld.

© OK 0806


15

Friction Sir Welding

© OK 0806

Courtesy of Kawasaki Heavy Industries, LTD.


Appendix

① Arc stud welding

② Thermite welding


Ex. Briefly explain the following welding methods.

16

Stud

Chuck

Ferrule

Macrostructure of an arc stud weld

(a) Positioning of stud

Arc

(b) Arcing

Lift up Press down

(c) Joining (d) Removal of ferrule

Arc stud welding

In arc stud welding, the end of stud is joined to the work-piece, where the stud and work-piece are

heated by a DC arc, as shown in the figure. A stud welding gun is used to control the process and

a ceramic cap (ferrule) is applied to shield the arc. The processing time is very short, usually in

less than one second / one stud.

Arc stud welding process

Courtesy of DAIHEN STUD Corporation.

Thermite welding ／Alminothermic welding

Thermite welding is based on the chemical reaction between metal oxide and aluminum that produces

superheated molten metal and a slag of aluminum oxide. The molten metal in a crucible is poured into

the parts to be joined by striking the tapping pin. Thermit welding is widely used for joining rails.

Thermite(e.g. Fe2O3 +Al）

Crucible lining

Slag sealHeat resistant disc

ThimbleTapping pin

Crucible shell

Fe2O3 + 2Al = 2Fe + Al2O3 (+ 850kJ)

3Fe3O4 + 8Al = 9Fe + 4Al2O3 (+ 3,350kJ)

Crucible and chemical reaction in Thermite welding


© OK 0812

17

Thermite welding of long rails on site JWES_JWES_JWES_JWES_OHJI

Courtesy of Kintetsu Track Engineering.

Ex. Comparison between SAW and SMAW

Give three advantages and three disadvantages of SAW (Submerged Arc Welding),

compared with SMAW (Shielded Metal Arc Welding).

.

© OK 0806


18

[Group A]

Electron beam welding （）

MAG welding （）

TIG welding （）

Electro-slag welding （）

Self-shielded arc welding （）

Gas welding （）

Resistance welding （）

Laser welding （）

[Group B]

(a) Arc welding with flux cored wire and without shielding gas

(b) Tungsten electrode and inert gas shielding

(c) Deep penetration in vacuum chamber

(d) Spot and seam welding for metal sheets

(e) Arc welding robot

(f) Photon energy of high power density

(g) Vertical fusion welding of thick plates

(h) Low power density and shallow penetration

Ex. Welding processes ①①①①

Choose one phrase in the group B, which is most deeply related to the welding process

in group A.


Ex. Welding processes ②②②②

Complete the following sentences with the words in the list.

○ In the ( ) process, the material to be joined is clamped between two electrodes and a high current

(typically 10,000A) is applied and pressure is applied to the electrodes.

○ In the ( ) process, the arc is maintained between the work-piece and a non-consumable tungsten

electrode.

○ The ( ) process is also known as manual metal arc welding and the shielding is provided by gases

generated by the decomposition of the electrode coating materials.

○ In the ( ) process, the arc is formed between the tip of a consumable wire and the work-piece and

the arc space is shielded by the active gases.

○ In the ( ) process, welding currents from 200 to 2000A are commonly used, and very high melting

and deposition rates are achieved.

List of words

① SMAW (Shielded Metal Arc Welding), ② ESW (Electro-Slag Welding), ③ MAG welding,

④ SAW, ⑤ TIG welding, ⑥ Resistance welding, ⑦ Electron beam welding.


19

© OK 0806

Ex. Heat sources for weldingSelect the welding process where the arc is not used as a heat source from following welding

processes, and encircle their numbered symbol.

(1) MIG welding, (2) Electro-gas welding, (3) Resistance seam welding, (4) MAG welding,

(5) Thermit welding, (6) TIG welding, (7) Resistance spot welding, (8) Laser welding,

(9) Plasma welding, (10) Friction welding.


exercises in welding process and equipment ---part 1 ......exercises in welding process and...

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