Welding Processes

Welder TrainingWelding Process

TECHNICAL TRAINING WORKSHOPMANSOR BIN IBRAHIM

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Welding Processes

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WeldingWelding terms

Process that produce coalescence of work pieces by using pressure or without under certain temperature.

BS 499 prt 1 Welding terms

A union between pieces of metal at faces rendered plastic or liquid by heat,pressure or both.

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Welding Processes

ALLIED WELDING PROCESS

FUSION WELDINGSOLID STATE WELDING

RESISTANCE WELDING

BRAZING & SOLDERING

OXY FUEL WELDING

LASER WELDING

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Fusion Welding Factors

The four essential factors for fusion welding

1. Fusion is achieved by melting using a high intensity heat source

2. The welding process must be capable of removing any oxide and contamination from the joint

3. Atmosphere contamination must be avoided

4. The welded joint must possess the mechanical properties required by the specification being adapted

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Manual Metal Arc Process (MMA)

Parent material

Electric Arc

Gas shield (Co2)

Molten weld pool

Solidified slag

Penetration

Build up of weld metal

Electrode covering

Electrode core wire (Rimming

Steel)

SHEILDED METAL ARC WELDING (SMAW)

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Welding Machine Electrode Holder

Work Cable

Return Cable

+

Clamp

Power Source

Work Piece

Earth

Basic MMA Equipment Diagram

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Welding Variables

Arc length

Angle of electrode

Speed of travel

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TYPE OF POLARITY

DIRECT CURRENT (STRAIGHT POLARITY –ve &

REVERSE POLARITY +ve)

ALTERNATING

CURRENT

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Welding Power SourcesDrooping or Constant Current Characteristic

As the welder increases the arc gap, more volts are required for the arc to bridge the increased

arc gap.

Large arc gapRequires more volts

As the welder reduces the arc gap, less volts are required for the arc to bridge the reduced arc gap.

Small arc gapRequires less volts

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Welding Power SourcesDrooping or Constant Current Characteristic

20 8040 60 130 140120100 180160 200

10

60

50

40

30

20

80

70

90

100

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length)

Small amperage change resulting in virtually constant current e.g. + 5A.

Vo

ltag

e

Amperage

O.C.V. Striking voltage (typical) for arc initiation

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Manual Metal Arc (MMA)

The three main electrode covering types used in MMA welding

Rutile - general purpose (E6013)

Basic - low hydrogen (E7018/7016)

Cellulose - deep penetration/fusion (E6010/6011)

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FUNCTION OF FLUX COVERING

ARC STABILIZER – Potassium silicate,

Titanium and Magnesium Oxide

SLAG FORMER – Calcium Flouride,

Iron Oxide and Titanium Oxide

ALLOYING ELEMENT – Ferro

Manganese and Ferro Silicon

ARC IONISER

DEOXIDISER – Ferro Silicon, Ferro

Manganese

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MATERIAL WELDABILITY

SIZE : 4.78 mm MIN through 25 mm

TYPE : Ferrous Metal and Non-Ferrous Metal

CONDITION: Moderate Preparations on Welding Area / Joint from Contaminations

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SELECTION OF ELECTRODES

TYPE OF MATERIAL AWS CLASS

1 . CARBON STEEL E7018, E7016, E6010, E6013

2. STAINLESS STEEL E308L, E316L, E347L

3. ALUMINIUM E1188, E4043,E5356

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M.S.RogersCopyright © 2003 TWI Ltd

E 70 1 8 M G

AWS A5.5 Alloyed Electrodes

Covered Electrode

Tensile Strength (p.s.I)

Welding Position

Flux Covering

Alloy Content

Moisture Control

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CONSUMABLES

SIZE : 2.0mm dia through 6.0mm dia

TYPE : Basic, Rutile, Cellulose, Acid

CONDITION: Basic - Bake 350ºC

- Hold 150ºC

- Store / Quiver 75 - 90ºC.

Rutile – Dry

Cellulose - Dry

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ADVANTAGES

• Cheap Equipment

• Suitable for all weld

position

• Capable of welding

thin material.

• Required moderate

welder skill

• Low in maintenance

DISADVANTAGES

• Required Proper

Inter – run cleaning

• Slow weld process

• Required proper

consumable storage

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TYPICAL DEFECTS

• SLAG INCLUSION

• POROSITY

• UNDERCUT

• SPATTERS

• LACK OF SIDEWALL FUSION

• LACK OF ROOT FUSION

• LACK OF ROOT PENETRATION

• ARC BLOW

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QU 1. State the main welding parameters of the MMA welding process

Questions

QU 2. What type of power source characteristic is considered essential for a MMA welding plant?

QU 3. Give three advantages of the MMA welding process when compared to the MAG welding process

QU 4. State the four criteria that will govern the number of weld passes in a MMA welded joint

QU 5. State two types of electrical supply and give the advantages of each

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Tungsten Inert Gas (TIG)

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Tungsten Inert Gas (TIG)

Deposited weld metal

Filler wire

Cap

SwitchHandle

Shielding gas

Molten weld pool

Collet

Switch power cable

Gas inlet& power cable

Non-consumable electrode

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Ceramic shield cup

Gas lens

Torch body

Tungsten electrodes

Spare ceramic shielding cup

Gas diffuser

Split collet

On/Off switch

Fitted ceramic shielding cup

Tungsten housing

TIG Torch Assembly

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Welding Machine

Welding Torch

Work Cable

Work Piece

Return Cable

Shielding Gas + Regulator

Gas Hose

+

Earth

Basic TIG Equipment Diagram

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Tungsten Electrodes

Old types Thoriated: DC -ve electrode - steels and most metals 1% thoriated + tungsten for higher current values 2% thoriated for lower current values

Zirconiated: AC - aluminum alloys and magnesium

New types Cerium: DC -ve elctrode - steels and most metals Lanthanum: AC - Aluminum alloys and magnesium

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Welding Power SourcesDrooping or Constant Current Characteristic

20 8040 60 130 140120100 180160 200

10

60

50

40

30

20

80

70

90

100

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length)

Small amperage change resulting in virtually constant current e.g. + 5A.

Vo

ltag

e

Amperage

O.C.V. Striking voltage (typical) for arc initiation

MBI

Tungsten Inert Gas Welding

1. 2. 3. 4. 5.

1. Pre-flow timer controlAdjusts the time the gas and

water valves are open

2. Start current controlCurrent up slope (slope-in)

3. Output controlWelding current control

4. Crater fill controlCurrent down slope (slope out)

5. Post-flow timer controlAdjusts the time the gas flows after welding

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Argon (Ar) Inert

Suitable for welding carbon steel, stainless steel, aluminium, reactive material and magnesium

23% heavier than air

Forms a tight arc column, high current density, small arc concentration, lower arc voltage,

moderate penetration and moderate thermal conductivity

More suitable for thinner materials and positional welding

Shielding Gases

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Helium (He) Inert

Suitable for welding carbon steel, stainless steel, copper, aluminium and magnesium due to

better puddle fluidity and bead wetting

Second lightest gas – 1/7 as heavy as air

Form a wider arc, lower current density, higher arc voltage, deeper penetration and high

thermal conductivity

Requires higher flow rates

Shielding Gases

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Helium / Helium Argon Mix (He) Inert

Suitable for welding carbon steel, stainless steel, copper, aluminium and magnesium

High cost, high flow rates

More suitable for thicker materials and materials of high thermal conductivity.

Shielding Gases

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How heat produced from welding gasses

The collisions of electrons with atoms and molecules produce thermal ionisation of atoms of shielding gas.

The positively charged gaseous atoms are attracted to the negative electrode , where their kinetic (motion) energy is converted to heat.

Shielding Gases

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MATERIAL WELDABILITY

SIZE :

TYPE : Ferrous Metal and Non-Ferrous Metal

CONDITION: Strictly Clean Preparations on Welding Area / Joint from Contaminations

1.0 mm MIN through 6.0 mm

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CONSUMABLES

SIZE :

TYPE : As per parent metal

CONDITION:

1.0 mm dia through 2.4 mm dia

Place in the original container & dry

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SELECTION FILLER METAL

MATERIAL TYPE

1. CARBON STEEL ER70 S-G,

AWS CLASS

2. STAINLESS STEEL ER 308L, ER316L, ER347L

3. ALUMINIUM ER1188, ER4043, ER5356

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HEAT DISTRIBUTION AND CURRENT POLARITY TABLE

DC EP DC EN AC

GRAPH

CURRENT FLOW + -

+ + - -

+ + - -

- +

- - + +

- - + +

- +

- +

- +

PENETRATION

MATERIAL CARBON STEEL, STAINLESS STEEL,

ALUMINIUM, MANGANESE

CARBON STEEL, STAINLESS STEEL,

ALUMINIUM, MANGANESE

ALUMINIUM, MAGNESIUM

ALLOY

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ADVANTAGES DISADVANTAGES

• Expensive equipment

• Required high skill

weld technique.

• Very slow weld

process.

• High in maintenance.

• Virtually no

spatters produced

• High quality welds

• Capable to weld thin

material

• Capable to weld any

type of material.

• Capable to be used

in all weld position.MBI

TYPICAL DEFECTS

• TUNGSTEN INCLUSION

• POROSITY

• LACK OF SIDEWALL FUSION

• LACK OF ROOT FUSION

• LACK OF ROOT PENETRATION

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QU 1. Give three reasons for the occurrence of tungsten inclusions

Questions

QU 2. What type of power source characteristic is considered essential for a MMA welding plant?

QU 3. Give three advantages of the MMA welding process when compared to the MAG welding process

QU 4. State the four criteria that will govern the number of weld passes in a MMA welded joint

QU 5. State two types of electrical supply and give the advantages of each

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Metal Active/Inert Gas (MAG/MIG)

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Metal Active/Inert Gas (MAG/MIG)

Parent material

Electric Arc

Gas shield

Penetration

Build up of weld metal

Current conductor

Contact tip and electrode wire guild

Gas nozzle

Molten weld pool

Shielding gas in

Wire electrode

Wire feedrolls

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Metal Active/Inert Gas (MAG/MIG)

Contact Tube/tip

Filler Extension

Nozzle to work distance

Contact Tube to Work Distance

Gas Nozzle

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Torch body

Contact tips

Spot welding spacer

Gas diffuser

Nozzles or shrouds

Torch head assembly (Less nozzle)

On/Off switch

Hose port

MAG/MIG Torch Head Assembly

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Plain top roller

Half grooved bottom roller

Wire guide

15 Kg Filler Wire Spool

MAG/MIG Internal Wire Drive

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MAG/MIG Wire SpoolMBI

Metal Transfer Modes for MAG/MIG Short Circuit / Dip Transfer:

Uses small wire diameter, thin (all position) and thick (vertical & o/head) material low deposition rate and filling large gaps.

Voltage ~ < 21 Amperage ~ < 200

Spray Transfer:

Uses larger wire diameter, high deposition rates, t >2.4mm, restricted to

flat & horizontal position.

Voltage ~ > 27 Amperage ~ > 250 Globular Transfer: Deposits at high rates & capable

producing high quality welds and for flat & horizontal position.

Between Dip & Spray Transfer Modes.

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Flat or constant voltage characteristic

4 mm

Correct arc gap

3 mm2 mm

Arc gap to small, requires the current to be increased to allow the wire to burn back to the correct arc gap

Arc gap to large, requires the current to be reduced to slow down the burn off rate to allow the correct arc gap to be maintained

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Welding Power SourcesFlat or Constant Voltage Characteristic

100 200 300

33

32

31

Flat or Constant Voltage Characteristic Used With MIG/MAG, ESW & SAW < 1000 amps

O.C.V. Arc Voltage Virtually no Change.

Large Current Change

Small Voltage Change. Voltage

Amperage

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< Filler Extension

> Filler Extension

Shorter filler extension produces burn-through at welding area

Longer filler extension

produces lack of fusion (cold lap), spatter. The wire tends to melt before reaching the weld puddle.

Filler Wire Extension

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Shielding Gases

Carbon Dioxide (CO2) Active

Compound of 27% Carbon and 72% oxygen

11/2 times heavier than air

At elevated temperature , it will disintegrates to oxygen and carbon monoxide

Suitable for ferrous metal welding

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Shielding gases

Example gases and applications for MIG/MAG welding

Pure argonAluminium, copper, 9% nickel steel

Argon + 1% to 5% oxygen Stainless steel

CO2Carbon steel up to 0.4%, low alloy steel

Argon + 5% to 25% CO2Carbon and low alloy steels

Argon + 15% nitrogen Copper and its alloys

75% helium + 25% argon Aluminium and copper

75% helium + 25% argon + CO2 trace Austenitic stainless steel

High purity argon Titanium, Zirconium alloys

Note: A H2 trace may be added to most gases to increase arc voltage and therefore overall deposition rates.

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CO2 gas cannot sustain spray transfer, as the Ionisation Potential of the gas is too high. Affects on welding are :

• High ionisation potential• High thermal conductivity and produces low arc

density• Very good penetration• Unstable arc (at high current value) and lots of

spatter.• 1.5 (Specific gravity of gas with respect to air)

Helium has a high Ionisation potential and produce a high arc energy in plasma column. • Very high thermal conductivity and produces

very low arc density• Deep penetration• Stable arc• 0.14 (Specific gravity of gas with respect to air)

Shielding gases

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Argon has a much lower Ionisation potential and can sustain spray transfer above 24 welding volts. Argon gives :

• Very stable arc• Little spatter• Low thermal conductivity and produces high arc density• Lower penetration than CO2.• 1.4 (Specific gravity of gas with respect to air)• We mix both argon and CO2 gas in mixtures of between 5 –

20% CO2 in argon to get the benefit of both gases i.e. good penetration with a stable arc and very little spatter (smoother profile). CO2 gas is much cheaper than argon or its mixtures.

Shielding gases

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Electrode

Solid Wire

Alloy Composition

Rod

ER 70 S - 6

Ultimate Tensile Strength

AWS 5.18 Carbon Steel Filler

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SELECTION OF FILLER WIRES

MATERIAL TYPE

1. CARBON STEEL ER70 S-6

AWS CLASS

2. STAINLESS STEEL ER 308L, ER316L, ER347L

3. ALUMINIUM ER1188, ER4043, ER5356

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Applicable to MIG/MAG process in dip transfer mode.

The electrode is fed slowly through the arc until it touches the weld pool, at this point the output from the power supply is short circuited and a very high current flows through the electrode. If this was allowed to continue, the wire would melt and eject excessive amounts of spatter.

The inclusion of the choke in the welding circuit controls the rate at which the current rises so that the electrode tip is melted uniformly without excessive spatter

Inductance or Choke

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Flux Cored Arc Welding

Insulated extension nozzle

Current carrying guild tube

Flux cored hollow wire

Flux powder

Arc shield composed of vaporized and slag forming compounds

Metal droplets covered with thin slag coating

Molten weld poolSolidified weld

metal and slag

Flux core

Wire joint

Flux core wires

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SELECTION OF FILLER WIRES

MATERIAL TYPE

1. CARBON STEEL E70T-1

AWS CLASS

2. STAINLESS STEEL E 308LT, E316LT, E 347LT

3. ALUMINIUM ER1188T, ER4043T, ER5356T

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Sub-arc (SAW)

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Sub-arc (SAW)

- +

Power supply

Filler wire spool Flux hopper

Wire electrodeFlux

Slide rail

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Fused SAW Fluxes

Agglomerated SAW Fluxes

Sub-arc (SAW) Fluxes

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APPLICATION S.A.W. IN THE FABRICATION

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Sub-arc Fluxes

Fused Flux Flaky appearance

Lower weld quality

Low moisture intake

Low dust tendency

Good re-cycling

Very smooth weld

profile

Agglomerated Flux Granulated appearance

High weld quality

Addition of alloys

Lower consumption

Easy slag removal

Smooth weld profile

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QU 1. State the possible problems when using damp and contaminated fluxes when using the sub-arc process

Questions

QU 2. State the two flux types used in the sub-arc welding process.

QU 3. What power source characteristic is required for a 500 amp out-put sub-arc welding plant

QU 4. State three main items of sub-arc fluxes, which require inspection

QU 5. State the advantages and disadvantages of the sub-arc welding process

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Process Comparisons

Process Electrical characteristic Electrode current type

MMA Drooping / constant current DC+ve, DC-ve, AC

TIG Drooping / constant current DC-ve, AC

MIG/MAG Flat / constant voltage DC+ve,

MAG FCAW Flat / constant voltage DC+ve, DC-ve,

Sub-arc DC+ve, DC-ve, AC

Electro-slag Flat / constant voltage DC+ve,

Drooping / constant current > 500amps

Flat / constant voltage < 500amps

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