S hielded M etal A rc W elding (or) M anual M etal A rc W elding (or) Stick welding:

Electrode identification: E XX(X) X X

Electrode:Solid metal core wire covered with a layer of granular flux or covered metal core electrode. No external filler metal is added.

Shielding:Shielding is provided by electrode coating, when gets heated & decomposes. This shielding gas assists the flux in shielding of molten metal in the arc region.

Power supply:Constant current power supply with “Drooping Characteristics”. Polarity may be DCEP, DCEN or AC.Drooping Character: A decrease in arc voltage will result in corresponding increase in arc current. In other way, arc voltage is directly related to the arc length (distance from electrode to work piece).

Advantages: It is used for most materials except for some of the more exotic (unusual) alloys. The equipment is relatively simple and inexpensive. The process is considered quite versatile, due to the availability of numerous types of electrodes.

Disadvantages: Speed will be affected by the periodic change of electrodes. Solidified slag must be removed before depositing the next layer. Low hydrogen type electrodes (suffix with 5, 6 and 8) need electrode holding oven to maintain

their low hydrogen level.

Inherent problems: Porosity

Reason: i) Presence of moisture or contamination in the weld region (i.e.) in the electrode coating, on the surface of the material or from the atmosphere surrounding the welding operation.

ii) Long arc length (Long arcing) when using low hydrogen electrodes.iii) Due to arc blow.

Slag inclusionReason: The molten slag is not flow freely to the surface of the solidifying weld metal.

Incomplete fusion Incomplete penetration Cracking Undercut Overlap Incorrect weld size Improper weld profile

G as M etal A rc W elding (or) M etal I nert G as W elding: 1

Electrode identification:ER XX S - X

Electrode:Solid wire which does not contains flux coating.

Shielding:Shielding is provided by protective atmosphere which is emitted from the welding gun from external sources. Both inert and reactive gases are used for shielding. No external filler metal is added.

Power supply:Self regulating constant potential or voltage system. Polarity is normally DCEP.

Metal transfer: Spray Globular Pulsed arc Short circuiting

These are differing from each other by the amount of heat provided to the work piece.

Metal transfer depends upon several factors. Those are, Shielding gas Current and voltage levels Power supply characteristics

Advantages: The use of gas shielding can reduce the possibility of introducing hydrogen into the weld zone. Due to the non-availability slag, it is well suited for automatic and robotic welding or other high

production situations. Efficiency is further increased by the continuous spool of wire, which does not require changing as

often as the individual electrodes. Metal deposition is based upon lbs/hr, which reduces labour costs. It is relatively clean process because no flux coated electrode is used. It has more visibility during welding. Since no slag is present, the weld region can more easily be

observed the action of the arc and molten puddle to improve control.

Disadvantages: It is not well suited for field welding due to sensitive to drafts or winds, which tend to blow the

shielding gas away and leave the weld metal unprotected. Increased flow rates of shielding gas may draw atmospheric gases into the weld zone will tend to

increase the possibility of porosity. Equipment is more complex. Gun liners and contact rube must be checked frequently. Otherwise altered electrode feeding and

electrical characteristics will result in defective welds. This is also known as “Arc Instability”. Since no flux is used, it is an “open arc” process tends to result in incomplete fusion.

2

Inherent problems: Porosity

Reason: Due to contamination or loss of shielding.

Incomplete fusionReason: Due to the use of short circuiting transfer on heavy sections.

Arc instabilityReason: Caused by worn liners and contact tips known as wire feed problem.

_____________________________________________________________________________________

3

F lux C ored A rc W elding (FCAW):

Electrode identification:E X X T - X

Electrodes: Self shielded electrodes (suffix ending with 3, 4, 7, 8,10 & 11) (external) Gas shielded electrodes (suffix ending with 1, 2 or 5)

Self shielded electrodes are better suited for field welding.

Shielding:FCAW can be performed with or without an external shielding gas.

Power supply:Constant voltage DC power supply. Depends upon the electrode, polarity may be DCEP or DCEN.

Suffix with 1, 2, 3, 4, 5, 6 & 8 are normally used with DCEP.Suffix with 7 is normally used with DCEN.

Advantages: It has increased deposition rate (productivity), due to the continuous feeding of electrode reel

which increases the “arc time”. Presence of fusion type discontinuities are less due to aggressive and deeply penetrating arc. It has relatively good performance on contaminated surfaces due to the presence of flux. Comparing with other manual process, it requires less operator skill. Can be used for field welding purpose.

Disadvantages: Since there is a presence of flux, slag will appear. It has to be removed before depositing additional

layer or for visual inspection. Due to the presence of flux, significant amount of smoke will be generated. Prolonged exposure

could cause health problems. Since the smoke extractor system is heavy, it will increase the gun weight and decrease the

visibility. They also may disturb the shielding if an auxiliary gas is being used. The equipment more complex than that of SMAW.

Inherent problems: Porosity

Reason: Due to the loss of shielding when used with external shielding gas.

Slag inclusionReason: Due to flux and less travel speed.

Arc instabilityReason: Due to wire feed problem

_____________________________________________________________________________________G as T ungsten A rc W elding (GTAW):

4

Electrode identification:E W alphabet - number

Electrodes:Electrodes are separated by five classifications. Commonly by colour coding system.

EWP – Pure Tungsten – Green EWCe-2 – 1.8 – 2.2% Ceria – Orange EWLa-1 – 1% Lanthanum Oxide – Black EWTh-1 – 0.8 – 1.2% Thoria – Yellow EWTh-2 – 1.7 – 2.2% Thoria – Red EWZr – 0.15 – 0.40% Zirconia – Brown

Pure tungsten is used for aluminium with ball end.EWTh-2 type is used for ferrous materials.

The electrode used is not consumable because it has the ability to withstand for very high temperature. The deposited weld bead has no slag cover to be removed.

Power supply:Constant current type with flat characteristics. Polarity may be DCEP, DCEN or AC.DCEP – More heating of the electrodeDCEN – More heating of the base metalAC – Alternatively heats the electrode and the base metal

AC is normally used for aluminium because of the increased cleaning action.DCEN is most commonly used for the welding of steels.

Advantages: It has the ability to produce welds of high quality and excellent visual appearance. Since no flux is used, no slag to remove after welding. It can be used for almost all materials, because the electrode is not melted during the welding. Its ability to weld at low currents makes it suitable for use on the thinner materials up to 0.005

inch. Its typically clean and controllable operation which leads to extremely critical operations. Numerous types of filler metals exist for wide range of metals.

Disadvantages: It is among the slowest of the available welding process. It has low tolerance for contamination. It needs high skill level when used manually. It is normally selected in situations where the need for very high quality causes additional cost.

Inherent problems: Its inability to tolerate contamination Porosity due to moisture or contamination Tungsten inclusion

5

S ubmerged A rc W elding (SAW):

Electrode identification:F X X X – E X X X

Electrodes:Two types of electrode

Solid electrode Composite electrode

For alloyed weld deposit, an alloy electrode with neutral flux or a mild steel electrode with an alloy flux. Multiple electrodes can be used.

Power supply:Constant voltage power supply or constant current type. Polarity may be DCEP, DCEN or AC. Polarity will affect both penetration and weld bead contour.

Advantages: Due to high rate of metal deposition, it is quite effective for overlaying or building up material

surface. Less smoke is generated. It has the ability to penetrate deeply.

Disadvantages: It can only be done in the position where the flux can be supported in the weld joint. Need for extensive fixtures and positioning equipment. Slag need to be removed. If welding parameters are improper, slag removal will be difficult. If the arc is not properly directed, incomplete fusion will result.

Inherent problems: If the flux becomes wet, porosity and under bead cracking will occur. If the weld bead having very high width to depth ratio, solidification cracking will occur. (i.e.)

centerline shrinkage cracking.

____________________________________________________________________________________

P lasma A rc W elding (PAW):

6

Plasma is defined as an ionized gas. PAW is named because of the intensity of this plasma region. Both GTAW & PAW uses constant current type.

Process:A high velocity plasma gas is forced through the copper orifice and past, the welding arc resulting in the constriction of the arc. This process makes the arc more intense.

Plasma arc is classified into two types. Transferred – Arc is created between tungsten electrode and the work piece. Non-transferred - Arc is created between tungsten electrode and the copper orifice.

Transferred arc is used for cutting & welding of conductive materialsNon-transferred arc is used for cutting of non-conductive materials and welding of materials where less amount of heating is required for welding.

Differences between PAW & GTAW:

PAW GTAW Torch will have copper orifice It will not have Plasma control console & source of plasma gas Not needed

is needed Two separate gases are used. One is shielding Only shielding gas is used

and the other one is orifice or plasma gas

PAW uses more localized heat source. It is used for full penetration by the technique “key hole welding”.

Advantages: It provides more localized heat, which increases the welding speed and therefore less distortion. The welder has better visibility. Since the tungsten electrode recessed within the torch, a chance of tungsten inclusion is less. Since plasma arc is less sensitive to changes in arc length, complete penetration and weld

uniformity are possible.

Disadvantages: PAW is possible with 1” or less thickness. Equipment cost is greater. Need greater operator skill. Too high current will melt the copper orifice.

Inherent problems: Tungsten inclusion Tunneling: occurs when the key hole is not completely filled at the end of the weld, leaving a

cylindrical void which may extend entirely through the throat of the weld. Possibility of incomplete fusion if the arc and joints are narrow.

E lectro S lag W elding (ESW):

7

It is made between edge to edge, so that the joint is vertical. Even though it is considered as vertical, the position of the welding is considered flat due to the location of the electrode with respect to the puddle.

Process:It is not considered as an arc welding process. It works heating from the electrical resistance of the molten flux to melt the base metal and the filler metals. During welding, the molten metal is supported on two sides by water cooled shoes.

Advantages: It has high deposition rate. Multiple electrodes can be used for fast welding. No special joint preparation is needed. Since the entire thickness of the joint is fused in single pass, there will be no angular distortion

during or after welding.

Disadvantages: Limited to welding of carbon steel in thickness greater than ¾”. Extensive time required to set up.

Inherent problems: Gross porosity can occur due to wet flux or the presence of leak in one of the water cooled shoes. Centerline cracks due to weld metal shrinkage. Grain growth may occur due to high amount of heat.

_____________________________________________________________________________________

O xy- A cetylene W elding (OAW):

Filler metal identification:8

R G - numbers

Process:It is a chemical welding process, also known as oxy fuel welding. Heat is provided by a chemical reaction. Shielding provided by the flame itself. No flux is needed. Filler metal is externally added.

Flames are of three types. Natural flame: Oxygen and acetylene ratio is almost same Oxidizing flame: Oxygen ratio will be more Carburizing or reducing flame: Acetylene ratio will be more

Advantages: Inexpensive and portable No electrical input is required

Disadvantages: Less heat energy comparing with an arc. Suitable for thin steel sheet and small diameter piping For groove welds, joint preparation should have a thin feather edge for complete penetration. Slow process due to less heat concentration.

_____________________________________________________________________________________

S tud W elding (SW):

Process:It is considered as an arc welding process. The process is performed in four cycles which are timed and sequenced by a control unit once the stud is positioned and the trigger is pulled. DC power supply is used.

Advantages: Little operator skill is required. Economical and effective method for welding various attachments to a surface. No need for hole drilling, tapping or other manual process. Stud can be easily inspected.

Disadvantages: Electrical or mechanical malfunction could produce poor weld quality. Stud shape is limited to the configuration which can be held in the gun’s chuck.

Inherent problems: Lack of 360º flash (reinforcing fillet) Incomplete fusion at the interface.

_____________________________________________________________________________________L aser B eam W elding (LBW):

Laser is an acronym for light amplification by stimulated emission of radiation.

9

Process:It’s a non contact fusion joining process. Produces coalescence of material with the heat obtained from a concentrated beam of coherent (all the light waves are in phase), monochromatic light impinging on the joint to be welded. Laser beam is directed by flat optical elements, and then focused to a small spot at the workplace using either reflecting focusing elements or lenses. Key hole technique is utilized for welding.

Inert gas shielding is generally employed. Filler metal may or may not be added.

Most commonly used laser beams are, 1.06µm wavelength YAG (Yttrium Aluminium Garnet) & the 10.6 µm wavelength CO2 laser.

Advantages: Heat input is only to the required amount to melt the metal. Thus,

metallurgical effects in HAZ are less. Up to 1 ¼” thickness can be welded in a single pass without a filler metal. Since no electrodes are used, electrode contamination will not occur. Since optical elements or lenses are used, welding in areas not easily

accessible also is possible by focusing the beam. The joining of small, closely spaced components with tiny welds are possible. Wide variety of materials in combinations can be welded. Used as an automatic and high speed welding. Thin metals and small diameter wires can be welded. Not like arc & electron beam welding, LBW can not be affected by magnetic

field. Depth to width ratio 10:1 can be attainable by forming a cavity in the metal

such as keyhole technique. No vaccum or X-ray shielding is required. Beam can be transmitted to more than one work station by sharing. Electrically resistance materials can also be welded.

Disadvantages: Joints must be accurately positioned. Clamping mechanism must ensure that

the final position of the joint is accurately aligned with the beam focal point. Aluminium and copper alloys can affect their weldabilty due to their high

reflectivity and high thermal conductivity. Plasma control console must be used when performing moderate to high

power laser welding. Porosity and brittleness can be expected due to rapid solidification. Equipment is expensive.

_____________________________________________________________________________________

E lectron B eam W elding (EBW):

10

Process:It’s a fusion joining process. Produces coalescence of materials with heat obtained by impinging a beam of high energy electrons on the joint to be welded. It utilizes key hole technique.

The rate of energy input to the weld joint is controlled by four basic variables. Beam current: the number of electrons per second being impinged on to the work piece. Beam acceleration voltage: The magnitude of velocity of these electrons. Focal beam spot size: The degree to which the beam is concentrated at the work piece. Welding speed: The travel speed with which the work piece or electron beam is being moved.

Advantages: This process is extremely efficient because EBW directly converts electrical energy into beam

output energy. Single pass welding of thick joints are possible due to high width-to-depth ratio. The heat input per unit length for a given depth of penetration is much lower than the arc. So less

distortion & narrow heat affected zone. Vaccum environment for welding minimizes contamination of the metal by oxygen or nitrogen. The beam can be projected from a distance allows it to weld inaccessible location. Increased travel speed due to high melting rate. Square butt joints of thick & thinner plates can be welded without filler metal in single pass. Hermetic closures can be welded with high or medium vaccum. It can be magnetically deflected to produce various shaped welds 7 magnetically oscillated to

improve penetration. Dissimilar metals & metals with high thermal conductivity can be welded.

Disadvantages: Equipment is expensive. Rapid solidification rate may cause solidification crack in highly constrainded & low ferrite

stainless steel. For high & medium vaccum welding, work chamber size must be large. The time needed to

evacuate the chamber will influence production cost. Partial penetration welds with high depth –to- width ratios are susceptible to root voids and

porosity. Radiation shielding must be maintained. Ventilation is required with non-vaccum to remove ozone and other noxious gases.

_____________________________________________________________________________________

Brazing & Soldering:

11

It is accomplished without any melting of the base metal. The heat is only sufficient enough for melting the filler metal.

Brazing and soldering are differentiated by the temperature at which the filler metal melts. Filler melting above 840º F or 450º C are considered braze materials, while those melting below this temperature are considered Soldering. For brazing joint is designed to have a large surface area, clearance or gap between the two pieces to be joined is kept to a minimum.

Process:First, the joint surface to be thoroughly cleaned. Once the parts are cleaned and fitted together, heat is applied in some manner. When the parts have been heated to a temperature above the melting point of the braze filler metal, it will be drawn into the joint when placed in contact with the parts as a result of capillary action. To maintain the cleanliness of the joint during the application of heat, brazing fluxes are often used.

Brazing methods: Torch brazing (TB): Uses oxy fuel flame. Furnace brazing (FB): Furnace with a controlled atmosphere. Induction brazing (IB): Induction coil with high frequency electric current Resistance brazing (RB): Electrical resistance on either side of the braze joint Dip brazing (DB): Molten bath for heating Infrared brazing (IR): Heating by radiant energy.

Advantages: It can be used for joining dissimilar metals Metals which don’t lend themselves to welding can be welded Since brazing uses lower temperature than welding, thin metals are joined without melt through or

distortion.

Disadvantages: Parts must be extremely cleaned prior to brazing Need sufficient surface area to develop the required strength

Inherent problems: Formation of voids or unbonded areas within the joint Accidental localized heat applied to the base metal results in erosion of the base metal Corrosion of the base metal by some of the extremely reactive fluxes

_____________________________________________________________________________________

Cutting ProcessOxy-Fuel Gas Cutting (OFC):

12

The equipment used for OFC is slightly different from OAW (Oxy-acetylene welding). Instead of welding tip, a cutting attachment is added with an additional valve or lever to turn on cutting oxygen.

Process:It is a chemical cutting process. Cutting is done by heating the part using a preheat flame which is an oxy fuel mixture. When the metal reaches its “kindling temperature”, the cutting oxygen is turned on to oxidize the hot metal. This exothermic reaction provides necessary heat to rapidly melt the metal.

Kindling temperature is, the temperature needed to oxidize or burn the metal by an oxy fuel flame.

Fuel gases may be acetylene, methane (natural gas), propane, gasoline & methyl acetylene proadine (MPS).

Kerf : Width of the cut made by the flameDrag: The amount of offset between the cut entry and exit points measured along the cut edge.

For effective oxy fuel cutting, the material must comply with the following criteria. It must have the capability of burning in a stream of oxygen Its ignition temperature for burning must be lower than its melting point Its heat conductivity should be relatively low The metal oxides produced must melt at some temperature below the melting point of the metal The formed slag must be of low viscosity

Advantages: The equipment is relatively inexpensive and portable It can be used to cut thin & thick sections. Ease of cutting usually increases with thickness More economical process Multiple torches can be used to cut several parts at once

Disadvantages: It is limited to the cutting of carbon and low alloy steels If the amount of alloying elements increase, the steel may become more difficult to cut or may

give rise to hardness or heat checked cut surfaces Finished cut may require additional cleaning or grinding to prepare for welding

_____________________________________________________________________________________

Air Carbon Arc Cutting (CAC-A):

13

A special holder having copper jaws to hold the carbon electrode is used. One of the jaw will have a series of holes through which the compressed air passes.

Process:The carbon electrode is brought close to the work to create an arc. Once the arc melts the metal, a stream of compressed air blows away the molten metal to produce a gauge or cut. Constant current power supply is used for this process.

Advantages: It has the ability to cut any metals Its an efficient method Equipment cost is less

Disadvantages: It’s a very noisy and dirty process Finished cut may require some cleanup prior to additional welding

__________________________________________________________________________________

Plasma Arc Cutting (PAC):

The process is similar to PAW (plasma arc welding). Power required is higher than that used for welding. The torch used is water cooled internally. Actual cutting may take place under water to reduce noise and particulate level.

Advantages: Primary application is for the cutting of non-ferrous metals It can also be used for cutting of carbon steels It has the ability to cut metals which can not be cut with OFC

Disadvantages: Kerf is generally quite large and the cut edge may not be square Higher cost of equipment

_____________________________________________________________________________________

Mechanical Cutting:

Shearing14

Sawing Grinding Milling Turning Shaping Drilling Planing Chipping

Advantages:Used for

Joint preparation Weld contouring Parts preparation Surface cleaning Removal of defective welds

Disadvantages: Porosity and cracking may occur if the cutting fluids are not fully removed

_____________________________________________________________________________________

15