Overview of Advanced Welding Processes

An overview of Advanced Welding Process

Dr V.P. Raghupathy

Dept. of Mechanical Engg.PES Institute of Technology

Bangalore -85

WELDING PROCESSES

1Arc welding

Electrical energy sourceSMAW

SAW

GMAW

GTAW

ESW

EGW

Solid state

Mechanical energy source

Pressure

Friction welding

Explosive welding

Ultrasonic welding

Diffusion welding

Resistance weldingElectrical energy sourceSpot, Seam & Projection welding

Flash butt welding

Beam welding

Electro-magnetic energy sourceElectron Beam

LASER welding

2

Brazing methods

Torch, Furnace, Dip, Resistance

3

Soldering methods

Iron, Infra-red, Dip, Oven, resistance

4

SprayingArc,

Flame, Plasma

5

AdhesiveIron,

Hot pressing

SMAW Process• Also referred as

Stick electrode or

covered electrode

welding

• Flux covering

provides the gas and

slag to shield the

molten pool. It also

scavenges , deoxidises

and adds alloying

additions to the weld

• Allows only short

lengths of the weld

• Quality very much

depends on the welder

SMAW Process

• Uses electrode that is quickly consumed

• Uses an equipment that is simple &

portable

• Provides positional flexibility

• It is less sensitive to wind & drafts

• Yields a weld with a variable quality and

appearance depending on operator’s skill

Limitations

• Low productivity

• Interrupted welding

• Requires skill & training of the welder

• High labour costs

SAW Process

SAW Process

Process features

• Flux is used to generate

protective layer of gas &

slag

• Excess flux can be reused

• Slag can be removed

easily

• Thermal efficiency very

high (60% as compared to

25% in SMAW

Deposition rate in SAW is far

higher as compared to SMAW

(only 2 kg/hr)

SAW Process

Process variants

(depends on size & shape of component)

Wire

SAW is operated with a single wire on AC or Dc. Common variants are: Twin wire; Single wire with hot wire addition; Metal powder addition

Flux

• Granulated fusible minerals containing oxides of

Mn, Si, Ti, Al, Zr,Mg and other compounds such as

CaF2 are used as Flux. The constituents are

specifically formulated so that it is compatible with

the wire and base material and yields desired

bead shape and mechanical properties of the weld

• Flux is termed as active if it contains Mn or Si

content

SAW Process

Types of flux : Bonded flux & Fused fluxBonded flux is produced by drying the ingredients & bonding them with with a binding agent such as sodium silicate. These fluxes contain deoxidisers to remove porosity

Fused flux is produced by mixing the ingredients and fusing them to get a homogeneous product. Smooth & stable arc can be achieved and current levels upto 2000A can be obtained

Flux recovery Unit

SAW Process

Applications

• Mainly used for longitudinal &

circumferential joints of Pressure

vessels

• Because of high fluidity of molten

pool, slag layer & fused flux, process

is suitable only for Flat position

(butt welds) and horizontal Position

(FILLET WELDS)

• There is no restriction in number of

passes and hence there is no

limitation in the thickness of the

part to be welded)

• Mainly suited for C-Mn steels

SAW Process

Future prospects – Narrow Gap SAW

GMAW

• Heat is developed through the arc between consumable metal electrode and the work to be welded.• Electrode (bare metal wire) is transferred across the arc and into molten weld puddle.• The wire, the weld puddle, and the area in the arc zone are protected from atmosphere by a gaseous shield.

GMAW Torch cutaway image1. Torch handle2. Moulded

phenolic dielectric (white) threaded metal insert (yellow)

3. Shielding gas nozzle

4. Contact tip5. Nozzle output

face

GMAW

• The control switch, or trigger, when pressed by the operator, initiates the wire feed, electric power, and the shielding gas flow, causing an electric arc to be struck.• The contact tip, normally made of copper, is connected to the welding power source through the power cable and transmits the electrical energy to the electrode • The gas is supplied to the nozzle through a gas hose, which is connected to the tanks of shielding gas. Sometimes, a water hose is also built into the welding gun, cooling the gun in high heat operations

Key parts• control switch• contact tip• power cable• gas nozzle• electrode• gas hose

Torches in GMAW

Function of the welding gun, or torch, is to deliver the welding wire, welding current, and shielding gas to the welding arc.

Guns are available for semi-automatic operation and for automatic operation, where they are fixed in the automatic welding head.

Guns for GMAW have several characteristics in common. All have a copper alloy shielding gas nozzle, that delivers the gas to the arc area in a nonturbulent, angular pattern to prevent aspiration of air.

The nozzle may be water cooled for semiautomatic welding at high amperage and for automatic welding where the arc time is of long duration.

Welding current is transferred to the welding wire as the wire travels through the contact tip or contact tube located inside the gas nozzle (Refer to Figure). The hole in the contact tip through which the wire passes is only a few thousandths of an inch larger than the wire diameter. A worn contact tip will result in an erratic arc due to poor current transfer.

Welding consumables

Ferrous welding wires

Si – deoxidiser; Mn – strengthener

Al, Ti & Zr – strong deoxidiser

Ni, Cr, V – to improve mechanical properties

ER70S-2 to ER70S-7 welding of Mild steel

ER80S-D2 to ER100S-4 welding of low alloy steel

ER308L ; ER308L-Si ; ER309L, E316L - welding of stainless steel

Non - Ferrous welding wires

ERCuSiA ; ERCuSnA – welding of Cu & brass

Effect of Shielding GasesProperties of shielding gases that affect welding process

- Thermal properties at elevated temperatures

- Chemical reaction of the gas

- Effect of each gas on the mode of metal transfer

Thermal conductivity of CO2 gas is higher and requires more voltage

• Spatter level is high

when CO2 is used

• Penetration level is high

• Steels should have

deoxidising elements to

compensate for the

reactive nature of the gas

GMAW Process

Narrow Gap MIG welding

GTAW Process

GTAW Process

• TIG welding is also called GTAW (Gas Tungsten Arc Welding).

• Arc is started with a tungsten electrode shielded by inert gas and filler rod is fed into the weld puddle separately.

• Gas shielding (Ar) that is required to protect the molten metal from contamination and amperage issupplied during the TIG welding operation.

• TIG welding is a slower process than MIG, but it produces a more precise weld and can be used at lower amperages for thinner metal and can even be used on exotic metals.

• TIG welding has become a popular choice of welding processes when high quality, precision welding is required.

• TIG welding process requires more time to learn than MIG.

Process characteristics

GTAW Process

• Uses a non-consumable tungsten electrode

• Is easily applied to thin materials

• Produces very high-quality, superior welds

• Welds can be made with or without filler metal

• Provides precise control of welding variables (i.e. heat)

• Welding yields low distortion• Leaves no slag or splatter

Advantages

Limitations

• Very slow process

• Thickness limitation

• High operator skill

EBW Process

Electron Beam Welding joins ferrous metals, light metals, precious metals, and alloys, to themselves or each other.

• Multi-axis EB control

• High ratio of depth-to-width

• Maximum penetration with minimal distortion

• Exceptional weld strength

• Ability to weld components up to 10 feet in diameter

• High precision & repeatability with virtually 0% scrap• Versatility from .002" depth to 3.00" depth of penetration

EBW Process

• Maximum amount of weld penetration with the least amount of heat input reduces distortion

• Repeatability is achieved through electrical control systems

• A cleaner, stronger and homogeneous weld is produced in a vacuum

• Exotic alloys and dissimilar materials can be welded

• Extreme precision due to CNC programming and magnification of operator viewing

• yields a 0% scrap rate

Advantages

LBW Process

Laser welding & cutting uses a high intensity laser beam to melt or burn through plastic or metal.

Different types of laser are used, depending on the material and application. Diode lasers are the lowest power and lowest cost and can be used for welding of plastics.

CO2 lasers have higher power and can be used for both welding and cutting of plastics. Nd:YAG lasers can be used at very high powers, making them suitable for welding and cutting of sheet metal and thermoplastics.

LBW Process

• Very high precision welding or cutting• Contact-free, very localised energy means low thermal & mechanical strain on parts• Cleaner than electric arc or gas welding• No consumables, unless filler material is used for welding.

Advantages

Disadvantages

• Very high initial cost• Reflective metals cannot be welded• High cost compared with conventional welding and cutting techniques. • Not practical for manua welding.

Solid state Welding Process Adherent oxide

& contaminated film

It is a group of welding processes which produces coalescence at temperatures essentially below the melting point of the base materials being joined, without the addition of brazing filler metal.

Process variables : PressureTemperatureTime

This group of welding processes includes

- cold welding- diffusion welding- explosion welding- forge welding- friction welding- ultrasonic welding

Principle: Break or dislodge adherent oxide & contaminated surface film and produce clean surfaces

Even out the undulations in the surface

Friction Welding

It that allows more materials and material combinations to be joined than with any other welding process. A whole range of different material combinations, such as steel/copper, steel/aluminum or aluminum/magnesium, can also be joined without difficulty. With friction welding, joints are possible not only between two solid materials or two hollow parts: solid material/hollow part combinations can also be reliably welded. Friction-welded parts are characterized by great accuracy in their length and eccentricity. The process is distinguished by very short welding times and thus extremely short cycle times

Friction Welding

Friction Stir Welding

Friction Stir Welding

Explosive Welding

Coalescence is effected by high-velocity movement together of the parts to be joined produced by a controlled detonation.

The resultant composite system is joined with a durable, metallurgical bond.

A no. of combinations of metals, which are impossible, by other means can be welded

Explosive velocity , m/sRDX (Cyclotrimethylene trinitramine 8100

PETN (Pentaerythritol tetranitrate) 8190

TNT (Trinitrotoluene) 6600Tetryl Trinitrophenylmethylinitramine, 7800Lead azide 5010Ammonium nitrate 2655

Explosive Welding

• Joining of pipes and tubes

• Tube sheets and pressure vessels

• Tube Plugging

• Remote joining in hazardous

environments

• Joining of dissimilar metals -

Aluminium to steel, Titanium alloys to Cr – Ni steel, Cu to stainless steel, Tungsten to Steel, etc

• Attaching cooling fins

Applications

Ultrasonic Welding

Ultrasonic Welding

Ultrasonic welding is a solid state welding process which produces coalescence by the local application of high-frequency vibratory energy as the work parts are held together under pressure. Welding occurs when the ultrasonic tip or electrode, the energy coupling device, is clamped against the work pieces and is made to oscillate in a plane parallel to the weld interface.

Applications

Ultrasonic welding is widely used in electronic industry

Diffusion Welding

Selection of Welding Process

1.) The joint to be welded is analyzed in terms of its requirements.

2.) The joint requirements are matched with the capabilities of available processes. One or more of the processes are selected for further examination.

3.) A checklist of variables is used to determine the ability of the selected processes(s) to meet the particular application.

4.) Finally, the proposed process or processes deemed most efficient are reviewed with an informed consultant

Four easy steps to aid selection


Analysis of Joint to be welded

• Analyze the size of the weld metal

• Base metal thickness whether thick or thin

• Type of base metal

• Position of weld

• Express the need of the joint in four terms

Fast-Fill (high deposition rate)

Fast-Freeze (the joint is out-of-position

overhead or vertical)

Fast-Follow (high arc speed and very

small welds)

Penetration (the depth the weld penetrates

the base metal)

STEP 1


Fast-FillThis is required when a large amount of weld metal is needed to fill the joint. A heavy weld bead can only be laid down in minimum arc time with a high deposition rate.

Fast-Freeze

implies that a joint is out-of-position, and therefore requires quick solidification of the molten crater. Not all semiautomatic processes can be used on fast-freeze joints.

Fast-Follow

suggests that the molten metal follows the arc at rapid travel speed, giving continuous, well-shaped beads, without "skips" or islands. This trait is especially desirable on relatively small single-pass welds, such as those used in joining sheet metal

Penetrationvaries with the joint. With some joints, penetration must be deep to provide adequate mixing of the weld and base metal and with others it must be limited to prevent burn-through or cracking.

STEP 1

Selection of Welding Process STEP 2

Matching Joint Requirements with Processes

• Carefully examine the capabilities

of the process

• Select appropriate equipment

• Consider the options of using

alternate consumables


Volume of Production. Cost of welding equipment should be commensurate with amount of work, or productivity

Weld Specifications. Rule out a process if it does not provide the weld properties specified by the code governing the work.

Operator Skill. Operators may develop skill with one process more rapidly than another. Train your operators according to his capabilities

Auxiliary Equipment. Every process has a recommended power source and other items of auxiliary equipment. If a process makes use of existing auxiliary equipment, the initial cost in changing to that process can be substantially reduced.

Accessory Equipment. Availability and cost of necessary accessory equipment - chipping hammers, deslagging tools, flux lay-down and pickup equipment, exhaust systems, et cetera - should be taken into account.

Check list


Base-Metal Conditions. Rust, oil, fit-up of the joint, weldability of the steel, and other conditions must be considered. These factors could limit the usefulness of a particular process.

Arc Visibility. Is there a problem following irregular seams? Then open-arc processes are advantageous. On the other hand, if there's no difficulty in correct placement of the weld bead, there are "operator-comfort" benefits with the submerged-arc process; no head-shield required and heat from the arc is reduced.

Fixturing Requirements. A change to a semiautomatic process requires some fixturing if productivity is to be realized. Appraise the equipment to find out if it can adapt to processes.

Check list

Selection of Welding Process STEP 3Check list

Production Bottlenecks. If the process reduces unit fabrication cost, but creates a production bottleneck, its value is lost. Highly complicated equipment that requires frequent servicing by skilled technicians may slow up your actual production thereby diminishing its value.

The completed checklist should contain every factor known to affect the economics of the operation. Some may be specific to the weld job or weld shop. Other items might include:

•Protection Requirements

•Range of Weld Sizes

•Application Flexibility

•Seam Length

•Setup Time Requirements

•Initial Equipment Cost

•Cleanliness Requirements

Selection of Welding Process STEP 4Review & Consult

• Review of the Application & selection of

equipment with expert

• Establish Systems. A system is of no

value unless it is used.

• Create a chart and follow the steps to

determining process.

• By taking the time to analyze each new

weld joint, your operation will become

more productive and your welding

experience will be more fulfilling.

Weldability – definition & significance

Weldability

Process weldability

Focus on Choice of Process:

• Fusion welding

• Solid state welding

Fabrication weldability

Focus on :

• Process parameters

• Welding conditions

Material weldability

Focus on :

• Material quality

• Structure

• Composition

• Steel making practice

Service weldability Focus on Weldment properties

• Strength

• Toughness

• Fatigue

• Creep

Problems encountered in welding

• Hydrogen Assisted cracking• Solidification cracking• Reheat cracking• Lamellar tearing• Formation of Local Brittle Zones (LBZ) in the

weld metal and hardening of HAZ• Toughness of weld metal & HAZ

Hydrogen Assisted CrackingStressCaused by restraint, stress concentration and high weld metal yield strength.

HydrogenCaused by moisture in the electrode coating and flux, Lubricants on the wire (oil, drawing compounds, and rust) and paint contaminants

Microstructure.It's affected by chemical composition (“high carbon, high-alloy steels are more likely to have cold cracking”) and weld cooling rate.

Low temperatureHAC occurs below 150°C.

CE = C + Mn/6 + [Cr+Mo+V]/5 + [Ni+Cu]/15

Solidification cracking

• Hot cracks are found at the grain boundaries, and tend to grow along the weld centerline, involving low- melting eutectic liquid films

• They are sensitive to alloy composition and the weld thermal cycle

• Between two solid grains, if a liquid film is being pulled apart, the liquid goes into a state of tension and it becomes unstable. It will either cavitate or produce decohesion of oxides.

Reheat cracking

Reheat cracking also called Post Heat Treatment cracking, strain – age cracking, stress rupture racking and stress relief cracking can occur during Post Weld Heat Treatment or during high temperature service of some low alloy and Cr-Mo steels.

Reheat cracks are inter-granular and usually occur in the coarse grain regions of the HAZX, although they sometimes occur in weld metals. Reheat cracking results from embrittlement of prior austenite grain boundaries caused by minor alloying elements such as P, Sn, Sb and As. Report cracking has been reported in some Cr-Mo-V steels such as ASTM A 514, A517, A 508Cl II and in in ASTM A 710 HSLA steels.

Lamellar cracking

Lamellar tearing mainly occurs in fillet welds of corner or T joints which results in high welding stresses in the base metal adjacent to the weld metal.

High tensile stresses can develop perpendicular to the mid-plane of the steel plate as well as parallel to it. The magnitude of the stresses depends on the size of the weld, welding procedures and the restraint imposed on the weldment design.

This tearing is usually associated with poor elongation in the through-thickness direction of plates. It is aided by inclusions in the steel and usually progresses in a step-like manner. Elongated Sulphide inclusions increases the sensitivity of lamellar tearing.

Welding stress

Local Brittle Zones

Local Brittle Zones occur in reheated multi-pass welding of the steels. In these zones, small islands of martensite and austenite are formed, when the weld beads are heated to inter-critical temperature by subsequent passed and cooled.

It is reported that such localized brittle zones in high strength steel reduces its resistance to cleavage fracture.

In the steels, in view of high hardneability, HAZ gets hardened and all care should be taken during like appropriate selection of heat input and pre-heat temperatures so as to limit the hardness to within 450 Vickers.

As strength level is high, the weldment apart from possessing requisite strength must also have adequate toughness.

Safe welding Procedures

Pcm = C + Si/30 + Mn/20 + Cu/20 +Ni/60 +Cr/20 +Mo/15 +V/10 +5B

AWS Structural Welding Code for C - Mn Steels

Step 1

Evaluate Composition parameter, Pcm

Step 2

SI = 12 Pcm + log H

Evaluate Susceptibility index (SI)

ASTM Grade C – Mn steels

Specification

A 572 Gr 42

A 633 Gr A

A 710 Gr A

C

0.21

0.22

0.07

Mn

1.35

1.00

0.40

Si

0.30

0.15

0.60

Cr

-

0.40

0.60

Ni

-

0.50

0.70

Others

0.20 Cu

0.05 Nb

1.30 Cu

TS

413 MPa

572 Mpa

620 MPa


Step 3

Identify the Group

Susceptibility Index

Group

Up to 3.0 A

3.0 – 3.5 B

3.6 – 4.0 C

4.1 – 4.5 D

4.6 – 5.0 E

5.1 – 5.5 F

5.6 – 7.0 G

Step 4

Identify Restraint level

Low restraint

Weld joints with reasonable freedom of movement

Medium restraint

Weld joints with reduced freedom of movement (assembly joints)

High restraint

Weld joints with no freedom of movement (very thick plates and repair welds)

Welding of C - Mn Steels


Restraint level

Thicknessmm

Min. preheat & inter-pass temperature in °C

A B C D E F G

Low < 9.5 < 18 < 18 < 18 < 18 60 138 149

9.5 – 19.1 < 18 < 18 < 18 60 99 138 149

19.1 - 38.0 < 18 < 18 < 18 80 110 138 149

38.1 - 76 < 18 < 18 < 18 93 121 138 149

Medium < 9.5 < 18 < 18 < 18 < 18 71 138 160

9.5 – 19.1 < 18 < 18 18 80 116 143 160

19.1 - 38.0 < 18 <18 74 110 134 149 160

38.1 - 76 18 80 110 130 149 149 160

High < 9.5 < 18 18 66 104 138 160 160

9.5 – 19.1 18 85 116 138 149 160 160

19.1 - 38.0 116 130 149 149 160 160 160

38.1 - 76 116 130 149 149 160 160 160

Selection of Pre heat and inter-pass temperatures



Selection of Filler

Grade Matching Filler

SMAW Process

Electrode

E 7015, E 7016, E 7018, E 7028

YS : 414 MPa min. TS : 496 MPa

SAW Process

Electrode

F 7XX - EXX


SAW Process

Electrode

F 7XX - EXX


A 242 Gr 1

A 572 Gr 42

A 588 Gr A

A 633 Gr A

A 710 Gr A


Safe welding Procedures Welding of QT Steels

Specification

C Mn Si Cr Ni Others YSMPa

TSMpa

A 514 0.15 0.80 0.40 0.50 - 0.20 Mo` 620 689

A 515 0.14 0.95 0.15 1.00 1.20 0.40 Mo 620 689

A 533 0.25 1.15 0.15 - - 0.45 Mo 344 551

A 537 0.24 0.70 0.15 0.25 0.25 0.08 Cu 317 482

HY 80 0.12 0.10 0.15 1.00 2.00 0.20 Mo 551 -

HY 100 0.12 0.10 0.15 1.00 2.25 0.20 Mo 689 -

Typical Grades of QT steels

Safe welding Procedures Welding of QT Steels

Thickness A514 A517 A533 A537 HY80 HY100

Up to 13 mm

10°C 10°C 10°C 10°C 20°C 25 – 65°C

13 – 20 mm

10°C 10°C 40°C 10°C 50 - 150°C 25 – 65°C

21 - 40 50°C 50°C 95°C 40°C 95 - 150°C 95 - 135°C

41 - 63 80°C 80°C 95°C 65°C 95 - 150°C 95 - 150°C

> 64 105°C 105°C 105°C 105°C 95 - 150°C 95 - 150°C

Preheat & inter-pass temperatures

Filler metal

Steel SMAW SAW GMAW

A 514 E 1X01X-M F1XXX-Exxx-MX

ER1X0S-1

A 517 E 1X01X-M F1XXX-Exxx-MX

ER1X0S-1

A 533 E901X-M F9XX-EXXX-FX ER100S-1

HY 80 E 1101X-M F11XX-EXXX-MX

ER110S-1

HY 100 E 1101X-M F11XX-EXXX-MX

ER120S-1

Documents

Overview of Advanced Welding Processes