Classification of Welding MCQ Quiz - Objective Question with Answer for Classification of Welding - Download Free PDF

Concept:

Arc welding

• Arc welding is the most commonly used welding type.
• It uses the heat-produced electric arc to weld metals together
• The arc occurs from the base material to the electrode, the welding rod or wire, and melts the metal. Then the welder can fuse the molten metal and craft it into a weld.
• In Arc Welding process, welding cables are used for conduction of current from the welding machine to the electrode holder.

The different types of arc welding is 

1. Shielded metal arc welding 

2. Gas metal arc welding

3. Flux-cored arc welding

4. Gas Tungsten Arc Welding (TIG welding)

5. Carbon arc welding

6. Submerged arc welding

7. Electroslag welding

       8. Drawn Arc (DA) stud welding

Gas Tungsten Arc Welding (TIG welding)

This method uses a non-consumable tungsten electrode and constant current power source to create a plasma arc between metals and can be conducted with or without filler material. Inert shielding gas protects the weld area and electrode from the atmosphere.

TIG welding can be difficult to learn and technically demanding. It requires more operator control than similar processes, but there are both manual and automatic methods available.

The process produces high-quality, clean, and strong welds but can be time-consuming. It’s primarily suitable for welding thin materials and non-ferrous metals but isn’t ideal for thicker metal joints.

Additional Information

Arc welding uses an electric arc to generate heat and join together two metals. The power supplied to the electric arc can be alternating current (AC) or direct current (DC). AC arc welders are often inexpensive while DC arc welders offer a smoother arc that works better on thin materials, however they are more expensive.

All arc welding processes use an electric arc to weld and have at least the following:

An electrode
An electrode cable
A work cable and clamp
Power supply
Metals to join

 The welding arc during the process of any type of arc welding will be around 3500°C. 

During the arc welding process, the welder works with two types of metal.

Parent Material: This is the metal parts that are joined together during the welding process. 

Consumables Material: This is the additional materials that are heated up in the arc and deposited over the joints to create a stronger bond. 

In a basic arc welding process, the power supply is switched on, and the electrode is brought near the base material. Then, intense heat is generated to produce the electric arc. The heat then melts the base metal, electrode core and flux coating. The flux coating then provides a shielding environment to weld. The molten metal is deposited between the two metal work pieces to join them together. Once this solidifies, it forms a strong bond between the two materials. Then, the metal work pieces are left to cool down. 

Explanation:

Welding torch:

• A welding torch is a critical tool used in gas welding processes to mix oxygen and acetylene gases in the appropriate proportions for combustion. This mixture, when ignited, produces a high-temperature flame, which is used to melt and join materials such as metals. The welding torch ensures precise control over the gas flow, allowing the welder to achieve the desired flame characteristics for effective welding.
• In gas welding, oxygen and acetylene are stored separately in high-pressure cylinders. The welding torch has two inlets—one for oxygen and one for acetylene. These gases pass through individual control valves, allowing the welder to adjust their flow rates. Inside the welding torch, the gases mix in a mixing chamber before exiting through the torch nozzle, where they are ignited to produce the flame. By adjusting the proportions of oxygen and acetylene, the welder can control the flame type (neutral, oxidizing, or carburizing) to suit the specific welding application.

Working Principle of a Welding Torch:

• Gas Supply: Oxygen and acetylene are supplied from their respective cylinders through hoses to the welding torch.
• Mixing Chamber: Inside the welding torch, the gases are mixed in a controlled manner to achieve the desired ratio.
• Nozzle: The mixed gases are expelled through the nozzle of the torch, where they are ignited using a spark lighter or similar tool.
• Flame Control: The welder adjusts the control valves to regulate the gas flow, ensuring a stable and efficient flame.

The welding torch is designed to handle the high temperatures and pressures associated with gas welding. It is ergonomically designed to provide comfort and precision to the welder, making it an indispensable tool in welding operations.

Importance of Proper Gas Mixing:

The correct mixture of oxygen and acetylene is essential for achieving the desired flame characteristics:

• Neutral Flame: The oxygen and acetylene are mixed in equal proportions, producing a balanced flame with a well-defined inner cone. This flame is suitable for most welding applications.
• Oxidizing Flame: A higher proportion of oxygen results in an oxidizing flame, which is useful for specific applications like brazing but can cause oxidation in certain metals.
• Carburizing Flame: A higher proportion of acetylene results in a carburizing flame, which is used for specific tasks requiring additional carbon in the weld.

Explanation:

Thermit Welding in Railway Track Joining

Definition: Thermit welding is a process that utilizes the exothermic reaction between a metal oxide and aluminum powder to produce intense heat for welding. This process is particularly advantageous for joining large sections of metal, such as railway tracks, due to its ability to generate high temperatures and melt the steel, creating a strong, homogenous joint.

Working Principle: In thermit welding, a mixture of iron oxide and aluminum powder is ignited to initiate a highly exothermic reaction. The reaction can reach temperatures of about 2500°C (4500°F), which is sufficient to melt steel. The molten steel produced by the reaction flows into the mold prepared around the joint, filling the gap between the railway tracks. As the molten steel cools and solidifies, it forms a robust weld that is integral to the tracks.

Procedure: The thermit welding process typically involves the following steps:

• Preparation: The ends of the railway tracks to be joined are cleaned and aligned. A mold is then placed around the joint area to contain the molten steel.
• Ignition: The thermit mixture is placed in a crucible and ignited using a special ignition device. The reaction starts, producing molten steel.
• Pouring: Once the reaction is complete, the crucible is tilted, and the molten steel is poured into the mold, filling the gap between the track ends.
• Cooling: The molten steel is allowed to cool and solidify, forming a strong weld. The mold is then removed, and any excess material is ground away to ensure a smooth joint.

Advantages:

• Ability to produce high-quality welds that are strong and durable.
• Suitable for welding large sections of metal, such as railway tracks.
• Portable and can be performed in the field without the need for extensive equipment.

Disadvantages:

• The process generates extremely high temperatures, which require careful handling and safety precautions.
• The initial setup and preparation can be time-consuming.

Applications: Thermit welding is extensively used in the railway industry for joining and repairing railway tracks. Its ability to produce strong and durable welds makes it ideal for ensuring the structural integrity of rail networks.

Analysis of Other Options:

1) Electron Beam Welding:

Definition: Electron beam welding (EBW) is a fusion welding process where a beam of high-velocity electrons is applied to the materials to be joined. The kinetic energy of the electrons is converted into heat upon impact, melting the materials and forming a weld.

Advantages:

• High precision and control over the welding process.
• Ability to weld a wide range of materials, including refractory metals.

Disadvantages:

• Requires a vacuum environment, which can limit its application in the field.
• High equipment and operational costs.

Applications: Electron beam welding is used in industries requiring high precision and control, such as aerospace, automotive, and electronics manufacturing. It is not typically used for railway track joining due to the need for a vacuum environment and high costs.

2) Ultrasonic Welding:

Definition: Ultrasonic welding is a solid-state welding process that uses high-frequency ultrasonic vibrations to create a weld. The vibrations generate heat through friction, causing the materials to fuse without melting.

Advantages:

• Rapid welding process with low energy consumption.
• Suitable for welding thermoplastics and some metals.

Disadvantages:

• Limited to thin materials and certain types of metals and plastics.
• Not suitable for welding large sections or thick materials like railway tracks.

Applications: Ultrasonic welding is commonly used in the electronics, automotive, and medical device industries for joining small components and assemblies. It is not suitable for railway track joining due to its limitations in handling large and thick materials.

4) Laser Beam Welding:

Definition: Laser beam welding (LBW) is a welding technique that uses a focused laser beam to melt and join materials. The high energy density of the laser allows for deep penetration and precise control over the welding process.

Advantages:

• High precision and control, allowing for fine and intricate welds.
• Ability to weld a wide range of materials with minimal distortion.

Disadvantages:

• High equipment costs and the need for precise alignment.
• Not suitable for field applications where portability is required.

Applications: Laser beam welding is used in industries requiring high precision and control, such as aerospace, automotive, and electronics manufacturing. It is not typically used for railway track joining due to the high costs and need for precise alignment.

Explanation:

Non-Consumable Electrodes in Welding

Definition: Non-consumable electrodes are those that do not melt or get consumed during the welding process. Instead, these electrodes serve as a conductive medium for the arc and may also help in transferring filler material (if any) to the weld pool. The primary function of non-consumable electrodes is to establish an arc and sustain it, without adding material to the weld.

Processes Using Non-Consumable Electrodes:

Among the given options, the processes that use non-consumable electrodes are:

(i) Atomic Hydrogen Welding (AHW): In this process, two tungsten electrodes are used, and an arc is struck between them in an atmosphere of hydrogen gas. The hydrogen gas disassociates into atomic hydrogen due to the high temperature of the arc. When the atomic hydrogen recombines into molecular hydrogen on the surface of the workpiece, it releases a large amount of heat, which is used to weld the materials. Tungsten electrodes are non-consumable as they do not melt or get consumed during the welding process.

(iii) Plasma Arc Welding (PAW): This welding process uses a non-consumable tungsten electrode to create a plasma arc. The arc is formed between the tungsten electrode and the workpiece or between the tungsten electrode and a constricting nozzle. The plasma arc is highly focused and has high energy density, making it suitable for precision welding. The tungsten electrode remains intact and does not get consumed during the welding process.

Therefore, the correct option is 3, which includes (i) Atomic Hydrogen Welding and (iii) Plasma Arc Welding.

Other Processes and Electrodes:

To analyze why the other processes mentioned in the options are not correct:

(ii) MIG Welding (Metal Inert Gas Welding): Also known as Gas Metal Arc Welding (GMAW), this process uses a consumable wire electrode that is continuously fed through the welding gun. The wire electrode melts and becomes part of the weld pool, making it a consumable electrode process.

(iv) SAW (Submerged Arc Welding): This welding process uses a consumable wire electrode that is fed into the weld zone under a blanket of granular flux. The wire electrode melts and contributes to the weld pool, classifying it as a consumable electrode process.

Conclusion:

In summary, the processes that use non-consumable electrodes among the given options are Atomic Hydrogen Welding and Plasma Arc Welding, making option 3 the correct answer. This differentiation is crucial in welding technology as the choice of consumable versus non-consumable electrodes impacts the welding process's efficiency, application, and outcome.

Explanation:

Submerged Arc Welding (SAW)

• Submerged Arc Welding (SAW) is an arc welding process that produces coalescence of metals by heating them with an arc between a bare metal electrode and the workpiece.
• The arc and molten metal are shielded by a blanket of granular fusible flux which is fed through a tube directly over the weld zone. This flux not only shields the arc but also stabilizes it and prevents spatter and sparks as the arc is completely submerged under the flux.
• In SAW a continuouslyfed consumable electrode is used which creates an arc between the electrode and the workpiece. The arc is submerged beneath a layer of flux which melts to form a protective slag and gas shield around the weld pool.
• This prevents contamination by atmospheric gases ensuring a clean and highquality weld. The flux also serves several additional functions such as deoxidizing the weld area and aiding in the formation of the weld bead.

Advantages:

• High deposition rates making it suitable for thick materials and long welds.
• Minimal welding fumes and spatter due to the submerged arc.
• Excellent weld quality with deep penetration and uniformity.
• High welding speeds can be achieved improving productivity.

Disadvantages:

• Limited to horizontal or flat welding positions due to the flow characteristics of the flux.
• Not suitable for thin materials as the high heat input can cause warping.
• The process setup and equipment can be more complex and costly compared to some other welding methods.

Applications: SAW is widely used in industries requiring high productivity and highquality welds such as shipbuilding pressure vessel fabrication structural steel construction and large diameter pipes manufacturing.

Explanation:

Grey cast iron is welded by gas welding.

In welding grey cast iron Neutral flame is used. Sometimes slightly oxidized flame can also be used for grey cast iron welding.

The grey iron castings are widely used for machine tool bodies, automotive cylinder blocks, heads, housings, fly‐wheels, pipes, and pipe fittings, and agricultural implements.

The grey cast iron is designated by the alphabet ‘FG’ followed by a figure indicating the minimum tensile strength in MPa or N/mm². For example, ‘FG 150’ means grey cast iron with 150 MPa or N/mm² as minimum tensile strength.

Heat Affected Zone (HAZ):  

• The area of the base material of metal which is affected by the heat of the welding process. Melting of the base material does not occur here only microstructure is changed.
• Heat affected zone may range from small to large depending on the rate of heat input. A process with low rates of heat input will result in a large HAZ.
• The size of HAZ also increases as the speed of the welding process decreases.

\({\rm{Size\;of\;HAZ}}\; \propto \frac{1}{{speed\;of\;welding}}\)

So, order of welding processes in increasing speed is

Arc welding → Submerged Arc welding → MIG welding → Laser Beam welding

Therefore, the order of size of the heat affected zone in increasing sequence is

Laser Beam welding → MIG welding → Submerged Arc welding → Arc welding 

Important Points

Butt welding:  Joining of metal by its whole cross section side by side.

Explanation:

TIG Welding: 

• Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA) welding is the arc welding process in which an arc is generated between a non-consumable tungsten electrode and workpiece.
• The tungsten electrode and the weld pool are shielded by an inert gas normally argon and helium.
• The principle of tungsten inert gas welding process is shown below

Concept:

Flash butt welding

• In flash welding (FW), also called flash butt welding, heat is generated very rapidly from the arc as the ends of the two members begin to make contact and develop an electrical resistance at the joint.
• After the proper temperature is reached and the interface begins to soften, an axial force is applied at a controlled rate and a weld is formed by plastic deformation of the joint.
• The mechanism is called hot upsetting, and the term upset welding (UW) also is used for this process.
• Some molten metal is expelled from the joint as a shower of sparks during the process-hence the name flash welding. 
• It is used for joining of HSS drill bit to the carbon steel shank.

The advantages of flash butt welding are:

1) Less requirement of power

2) When the surfaces being joined, it requires only less attention.

3) Weld obtained is so clean and pure; due to the foreign metals appearing on the surfaces will burn due to flash or arc.

Soldering:

• Soldering is a non-fusion and non-pressure welding operation.
• The mechanism by which the joint formation taking place is wetting and surface alloying.
• The filler material used having a melting temperature less than 427°c
• Borax is used as Flux material.
• The filler material used is an alloy of lead and tin known as solder.
• Filler material entered into the workpiece by means of capillary action.

Brazing:

• It is also a non-fusion and non-pressure welding operation. 
• Filler material- Alloy of Cu and Zn, Cu and Ag, Cu and Al
• Flux material- Borax
• Filler material entered into the workpiece by means of capillary action.
• Filler material melting temperature greater than 427°c and less than the melting point of the base material

Braze welding:

• It is also a non-fusion and non-pressure welding operation.
• Filler material – an alloy of Cu and Tn (Bronze).
• The strength of the joint is more than brazing and soldering.
• Filler material entered into the workpiece by gravity force.

Explanation:

Welding technology

• The stability of a DC arc with a consumable electrode depends largely on how the molten metal is transferred in the arc.
• One can be distinguished essentially between two different types of arcs, depending on material transport.
  1. Spray arc
  2. Short arc

Short arc welding

• The heat input from Short arc welding is low, which makes the process suitable for welding in thinner materials.
• The drops from the electrode dip into the weld pool.
• This can be repeated up to 200 times per sec.
• If the short circuit current is too high, it has a considerable effect on the pinch-off forces, causing weld spatter.
• Some means of limiting the short-circuit current must therefore be provided in the power unit, e.g. through the use of an inductor coil.
• It is not easy, with Short arc welding, to achieve a completely stable arc.
• The objective is to achieve a consistent, high short-circuiting frequency, resulting in small droplets being transferred to the workpiece and spatter droplets being so fine that they do not adhere to the workpiece.

Explanation:

TIG Welding: 

Gas Tungsten Arc Welding (GTAW), also known as tungsten inert gas (TIG) welding is a process that produces an electric arc maintained between a non-consumable tungsten electrode and the part to be welded.

Inert Gas in TIG Welding

The heat-affected zone, the molten metal, and the tungsten electrode are all shielded from atmospheric contamination by a blanket of inert gas fed through the GTAW torch.

Inert gas is inactive or deficient inactive chemical properties. The shielding gas serves to blanket the weld and excludes the active properties in the surrounding air. Inert gases, such as Argon and Helium, do not chemically react or combine with other gases.

The principle of the tungsten inert gas welding process is shown below

Explanation:

Types of flames in gas welding:

• Neutral flame:
  • ​The neutral flame has a 1:1 ratio of oxygen and acetylene by volume. Structurally it consists of two parts namely the inner cone and the outer envelope.
  •  It has a clear, well-defined, or luminous inner cone indicating that the combustion is complete. Such a flame makes a hissing sound and is the most used type of flame for welding metals.
  • It normally does not affect the chemistry of the weld metal and usually produces a clean-looking weld having properties comparable to the base metal. It is most often used for welding low-carbon structural steel and aluminum.​
• Carburizing Flame:
  • ​The carburizing flame has a 0.85:0.95 ratio of oxygen and acetylene by volume. 
  • The inner zone has white color, the intermediate zone which is red in color and the outer cone has a blue color. The inner cone temperature is about 2900° Centigrade. This flame is used to weld medium carbon steel, nickel, etc.
• Oxidizing Flame:
  • The oxidizing flame has a 1.15:1.5 ratio of oxygen and acetylene by volume. 
  • The inner zone has a very bright white color and has a temperature of about 3300 degrees centigrade. The outer flame has blue in color. This flame is used to weld oxygen-free copper alloys like brass, bronze, etc.

Explanation:

Metal inert gas welding or gas metal arc welding:

• it uses continuous solid wire consumable electrode.
• the electrode is heated and fed into the weld pool from the welding gun.
• MIG welding is done in an inert gas atmosphere.
• The shielding gases for MIG welding are mixtures of argon, oxygen and carbon dioxide and a special gas mixture may contain helium.
• Excessive speed or irregularity in wire feed results in the welding spatter. Spatter occurs when the filler material enters the weld pool. 
• Direct current power supply is used to weld the workpiece.

Explanation:

Resistance spot welding occurs in four steps. They are as follows:

Squeeze time:

• The time required for the electrodes to align and clamp the work-piece together and provide necessary electrical contact.

Weld time:

• Time the current flows through the work-piece till they are heated to melting temperature.

Hold time:

• Time till the pressure is maintained, without the current, wherein the pieces are expected to get forge weld.

Off time:

• When the pressure of the electrode is taken off so that plates can be positioned for the next spot.

Resistance welding:

• This process makes use of the electrical resistance for generating heat that is required for melting the work-piece.
• Generally used to and join thin plate structures.
• Also considered as a green process since it does not generate gases and flames as in metal arc welding and gas welding.
• The heat generated in Resistance welding is given by H = I²Rt

H = Heat generated, I = Current, R = Resistance of joint, t = Time of flow of current.

• Resistance depends upon:
  • work-piece to be joined
  • electrode used
  • gap resistance

Types:

Spot welding

• Individual weld is produced by momentary application of pressure and resistance into the work-piece.

Seam welding

• It can produce continuous fast and leak-proof weld mainly used for thin metallic sheets, galvanized roofing, small tanks, etc

Projection welding

• A dimple is embossed into one of the work-piece at the locations where the weld is desired.

Explanation:

Submerged arc welding: In submerged arc welding the arc is completely submerged into the granular flux powder and forming a blanket.

Tungsten inert gas welding: In this type of welding non-consumable tungsten electrode will be used to generate the arc. A gas shield is provided around the welding.

Electro slag Welding: Welding is started by generating the electric arc and completed by resistance heating effect of slag material and if shielding gas is provided it is called as Electro Gas Welding.