Madan Lal Chandravanshi

Assistant Professor

Mechanical Engineering Department

Indian School of Mines Dhanbad

WELDING PROCESS 1

 Welding is the process of joining two metal pieces as a result of significant diffusion of the atoms of the welded pieces into the joint (weld) region.  Welding is carried out by heating the joined pieces to melting point and fusing them together (with or without filler material) or by applying pressure to the pieces in cold or heated state. Advantages of welding:

 Strong and tight joining;  Cost effectiveness;  Simplicity of welded structures design;  Welding processes may be mechanized and automated. Disadvantages of welding:

 Internal stresses , distortions and changes of micro-structure in the weld region;  Harmful effects: light, ultra violate radiation, fumes, high temperature. Applications of welding:

 Buildings and bridges structures;  Automotive, ship and aircraft constructions;  Pipe lines;  Tanks and vessels;  Machinery elements. Classification of welding process

 Gas Welding  Resistance welding  Solid Sate welding Welding processes

 Arc welding  ;  Shielded Metal Arc Welding (SMAW) ;  (SAW) ;  Metal Inert Gas Welding (MIG, GMAW) ;  Inert Gas Arc Welding (TIG, GTAW) ;  Arc Welding (PAW) ;  Resistance Welding (RW) ;  (RSW) ;  (FW) ;  Resistance Butt Welding (UW) ;  Seam Welding (RSEW) ;  Gas Welding (GW) ;  Oxyacetylene Welding (OAW) ;  Oxyhydrogen Welding (OHW) ;  Pressure Gas Welding (PGW) ;  Solid State Welding (SSW) ;  (FOW) ;  Cold Welding (CW) ;  (FRW) ;  Explosive Welding (EXW) ;  Diffusion Welding (DFW) ;  (USW) ;  Thermit Welding (TW) ;  Electron Beam Welding (EBW) ;  (LW) . Gas Welding

 Gas Welding is a welding process , utilizing heat of the flame from a welding torch. The torch mixes a fuel gas with oxygen in the proper ratio and flow rate, providing combustion process at a required temperature. The hot flame fuses the edges of the welded parts, which are joined together a weld after Solidification . Gas Welding equipment:

Gas Welding

 Depending on the proportion of the fuel gas and oxygen in the combustion mixture, the flame may be  chemically neutral (equal ratio of the gases),  oxidizing (excess of oxygen),  carburizing (excess of fuel gas). TYPES OF FLAMES…

 Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (3000 0c)  Has the highest temperature about 3400 0c  Used for welding brass and brazing operation When oxygen and fuel gas has equal ratio, The flame a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (3200 0c)

Used for welding steels, aluminum, copper and cast iron If more oxygen is added as compared to the fuel gas. The flame cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame Gas Welding

 Filler rod is used when an additional supply of metal to weld is required. Shielding flux may be used if protection of weld pool is necessary. 1. Oxyacetylene Welding (OAW)

 Oxyacetylene Welding is a Gas Welding process using a combustion mixture of acetylene (C2H2) and oxygen (O2) for producing gas welding flame. Temperature: 6000°F (3300°C).  Combustion of acetylene proceeds in two stages: 1. Inner core of the flame. C2H2 + O2 = 2CO + H2 2. Outer envelope of the flame: CO + H2 + O2 = CO2 + H2O Arc welding

 Arc welding uses a Electric power supply to create an between an and the base material to melt the metals at the welding point.

 Electric arc between the electrode and work piece closes the electric circuit. The arc temperature may reach 10000°F (5500°C), which is sufficient for fusion the work piece edges and joining them.

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Arc welding

 They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable .  The welding region is sometimes protected by some type of inert or semi-inert gas, known as a , and/or an evaporating filler material.  The process of arc welding is widely used because of its low capital and running costs. Arc Welding process

22 WELDING PROCESS Power Supplies

 To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used.  constant current power supplies  constant voltage power supplies.

 In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input.

23 Power Supplies

 Constant current supply is more important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate.  Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as , flux cored arc welding, and submerged arc welding.

24 Consumable electrode methods

 One of the most common types of arc welding is shielded metal arc welding (SMAW ), which is also known as manual metal arc welding (MMA) or stick welding.  An electric current is used to strike an arc between the base material and a consumable electrode rod or 'stick'.  The electrode rod is made of a material that is compatible with the base material being welded and is covered with a flux that protects the weld area from oxidation and contamination by producing CO 2 gas during the welding process.  The electrode core itself acts as filler material, making a separate filler unnecessary.

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Schematic representation of MIG Welding

WELDING PROCESS 27 MIG Welding

 Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding.  MIG welding is a commonly used high deposition rate welding process.  Wire is continuously fed from a spool.  MIG welding is therefore referred to as a semiautomatic welding process.

WELDING PROCESS 28 MIG Welding Shielding Gas

 The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool.  There are three primary metal transfer modes: - Spray transfer - Globular transfer - Short circuiting transfer WELDING PROCESS 29 The primary shielding gasses

 Argon  Argon - 1 to 5% Oxygen

 Argon - 3 to 25% CO 2  Argon/Helium

 CO 2 is also used in its pure form in some MIG welding processes.  However, in some applications the presence

of CO 2 in the shielding gas may adversely affect the mechanical properties of the weld.

WELDING PROCESS 30 MIG Welding taking place

WELDING PROCESS 31 Glow of MIG Welding Process

WELDING PROCESS 32 Photographic view of MIG Weld

WELDING PROCESS 33 (GTAW, TIG)

 GTAW or tungsten inert gas (TIG) welding, is a manual welding process that uses a non- consumable electrode made of tungsten , an inert or semi-inert gas mixture, and a separate filler material.  Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds.

WELDING PROCESS 34

Gas tungsten arc welding(GTAW)

 It can be used on nearly all weldable metals, though it is most often applied to and light metals.  It is often used when quality welds are extremely important, such as in aircraft and naval applications.

WELDING PROCESS 36 GTAW Welding

 Gas Tungsten Arc Welding (GTAW) is frequently referred to as TIG welding.  TIG welding is a commonly used high quality welding process.  TIG welding has become a popular choice of welding processes when high quality, precision welding is required.

WELDING PROCESS 37 Schematic View of the TIG Welding Process

WELDING PROCESS 38 TIG Welding taking place

WELDING PROCESS 39 Welded surface of TIG welding

WELDING PROCESS 40 TIG

WELDING PROCESS 41 TIG Welding Benefits

 Superior quality welds  Welds can be made with or without  Precise control of welding variables (heat)  Free of spatter  Low distortion

WELDING PROCESS 42 Shielding Gases of TIG Welding

 Argon  Argon + Hydrogen  Argon/Helium  Helium is generally added to increase heat input (increase welding speed or weld penetration).  Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen

cracking. WELDING PROCESS 43 The Plasma Arc Welding Process

 The plasma welding process was introduced to the welding industry in 1964 as a method of bringing better control to the arc welding process in lower current ranges.  Today, plasma retains the original advantages it brought to industry by providing an advanced level of control and accuracy to produce high quality welds in miniature or precision applications and to provide long electrode life for high production requirements. WELDING PROCESS 44 The Plasma Arc Welding Process

 Plasma Arc Welding is a welding process utilizing heat generated by a constricted arc struck between a tungsten non-consumable electrode and either the work piece (transferred arc process ) or water cooled constricting nozzle (non-transferred arc process ).

 Plasma is a gaseous mixture of positive ions, electrons and neutral gas molecules.

WELDING PROCESS 45  Transferred arc process produces plasma jet of high energy density and may be used for high speed welding and cutting of Ceramics , steels , Aluminum alloys , Copper alloys , Titanium alloys , Nickel alloys .

 Non-transferred arc process produces plasma of relatively low energy density. It is used for welding of various metals. Since the work piece in non- transferred plasma arc welding is not a part of electric circuit, the plasma arc torch may move from one work piece to other without extinguishing the arc.

Plazma Arc Welding Process

WELDING PROCESS 48 How Plasma Welding Works

 A plasma is a gas which is heated to an extremely high temperature and ionized so that it becomes electrically conductive.  Similar to GTAW (TIG), the plasma arc welding process uses this plasma to transfer an electric arc to a work piece.  The metal to be welded is melted by the intense heat of the arc and fuses together.

WELDING PROCESS 49 How Plasma Welding Works

 In the plasma welding torch a Tungsten electrode is located within a copper nozzle having a small opening at the tip.  A pilot arc is initiated between the torch electrode and nozzle tip.  This arc is then transferred to the metal to be welded.

WELDING PROCESS 50 How Plasma Welding Works

 By forcing the plasma gas and arc through a constricted orifice, the torch delivers a high concentration of heat to a small area.  With high performance welding equipment, the plasma process produces exceptionally high quality welds.

WELDING PROCESS 51 How Plasma Welding Works

 Plasma gases are normally argon.  The torch also uses a secondary gas, argon, argon/hydrogen or helium which assists in shielding the molten weld puddle thus minimizing oxidation of the weld.

WELDING PROCESS 52 Equipment List of Plasma Arc Welding

 Power Supply  Plasma Console (sometimes external, sometimes built in)  Water re-circulator (sometimes external, sometimes built in)  Plasma Welding Torch  Torch Accessory Kit (Tips, ceramics, collets, electrodes set-up gages)

WELDING PROCESS 53 Resistance Welding

 Resistance Welding is a welding process , in which work pieces are welded due to a combination of a pressure applied to them and a localized heat generated by a high electric current flowing through the contact area of the weld. Resistance Welding

 Heat produced by the current is sufficient for local melting of the work piece at the contact point and formation of small weld pool (”nugget”). The molten metal is then solidifies under a pressure and joins the pieces.  Process parameters:  Time of the process  Applied pressure  flowing current  resistance Resistance Welding

 AC electric current (up to 100 000 A) is supplied through copper electrodes connected to the secondary coil of a welding transformer.  The most popular methods of Resistance Welding are:

 Spot Welding (RSW) ;  Flash Welding (FW) ;  Resistance Butt Welding (UW) ;  Seam Welding (RSEW) . Spot Welding (RSW)

 Spot Welding is a Resistance Welding (RW) process, in which two or more overlapped metal sheets are joined by spot welds.

 The method uses pointed copper electrodes providing passage of electric current. The electrodes also transmit pressure required for formation of strong weld.

 Diameter of the weld spot is in the range 1/8” - 1/2” (3 - 12 mm).

 Spot welding is widely used in automotive industry for joining vehicle body parts.

Flash Welding (FW)

 Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld.

The welded parts are held in electrode clamps, one of which is stationary and the second is movable.

Resistance Butt Welding (UW)

 Resistance Butt Welding is a Resistance Welding (RW) process, in which ends of wires or rods are held under a pressure and heated by an electric current passing through the contact area and producing a weld

Resistance Butt Welding (UW)

 The process is similar to Flash Welding , however in Butt Welding pressure and electric current are applied simultaneously in contrast to Flash Welding where electric current is followed by forging pressure application.  Butt welding is used for welding small parts. The process is highly productive and clean. Butt Welding provides joining with no loss of the welded materials. Seam Welding (RSEW)

 Seam Welding is a Resistance Welding (RW) process of continuous joining of overlapping sheets by passing them between two rotating electrode wheels. Heat generated by the electric current flowing through the contact area and pressure provided by the wheels are sufficient to produce a leak-tight weld.

Advantages of Resistance Welding:

 High welding rates;  Low fumes;  Cost effectiveness;  Easy automation;  No filler materials are required;  Low distortions.  Disadvantages of Resistance Welding:  High equipment cost;  Low strength of discontinuous welds;  Thickness of welded sheets is limited - up to 1/4” (6 mm); Brazing  Brazing is a metal-joining process.  Brazing is when a filler metal or alloy is heated to its melting temperature above 450 °C.  It is then distributed in liquid form between two or more close-fitting parts by capillary action.  The filler metal is then brought slightly above its melting temperature.  It then interacts with a thin layer of the base metal (known as wetting) and is then cooled quickly.  This forms a sealed joint.  Brazed joints are generally stronger than the individual filler metals that have been used to make them.  This is because of the geometry of the joint and the metallurgical bonding that occurs. Advantages of brazing

 It's easy to learn.  You can join virtually any dissimilar metals.  The bond line can be very neat in appearance.  Joint strength is strong enough for most non- heavy-duty use applications

Soldering

 Soldering is a process in which two or more metals are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400 °C.  The filler metal used in the process is called solder.  Soldering is distinguished from brazing as the filler metal used has a lower melting point.  Soldering is normally done by melting the solder with a soldering iron and applying it to the two metals that are going to be joined together. Solder Process

Heat both items at the same time by applying the soldering iron to the copper pad and the component lead. 1 Continue heating and apply a few millimeters of solder. Remove the iron and allow the solder joint to cool naturally. 2

It only takes a second or two to make the perfect joint, which should appear shiny. 3 Advantages of soldering

 Low power is required;  Low process temperature;  No thermal distortions and residual stresses in the joint parts;  Microstructure is not affected by heat;  Easily automated process;  Dissimilar materials may be joined;  High variety of materials may be joined;  Thin wall parts may be joined;  Moderate skill of the operator is required. Disadvantages of soldering

 Disadvantages of soldering  Careful removal of the flux residuals is required in order to prevent corrosion;  Large sections cannot be joined;  Fluxes may contain toxic components;  Soldering joints can not be used in high temperature applications;  Low strength of joints.

Safety issues

 Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the use of new technology and proper protection the risks of injury or death associated with welding can be greatly reduced.  Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant.  To prevent them, wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and sparks.  Additionally, the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes.

WELDING PROCESS 76 Safety issues

 Goggles and helmets with dark face plates are worn to prevent this exposure and, in recent years, new helmet models have been produced featuring a face plate that self-darkens upon exposure to high amounts of UV light.  To protect bystanders, transparent welding curtains often surround the welding area.  These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.

WELDING PROCESS 77 Safety issues  Welders are also often exposed to dangerous gases and particulate matter.  Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides.  The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger.

WELDING PROCESS 78 Safety issues  Additionally, many processes produce various gases (most commonly carbon dioxide and ozone, but others as well) that can prove dangerous if ventilation is inadequate.  Furthermore, the use of compressed gases and flames in many welding processes pose an explosion and fire risk; some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.

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