[Solved] Welding MCQ [Free PDF] - Objective Question Answer for Welding Quiz - Download Now! (2023)

1. Consumable coated electrode and work piece
2. Non-consumable electrode and work piece
3. Consumable bare electrode and work piece
4. Tungsten electrodes and work piece

Explanation:

Submerged arc welding:

• Submerged arc welding is an arc welding process in which heat is generated by an arc which is produced betweenbare consumable electrode wire and the work-piece.
• The arc and the weld zone are completely covered under a blanket of granular, fusible flux which melts and provides protection to the weld pool from the atmospheric gases.
• The molten flux surrounds the arc thus protecting arc from the atmospheric gases.
• The molten flux flows down continuously and fresh flux melts around the arc.
• The molten flux reacts with the molten metal forming slag and improves its properties and later floats on the molten/solidifying metal to protect it from atmospheric gas contamination and retards cooling rate.
• A process of submerged arc welding is illustrated in Figure.

1. Lack of penetration
2. Lack of fusion
3. Burn through
4. Excessive penetration

Explanation:

A fault is an imperfection in the weld which may result in failure of the welded joint while in service.

The following faults occur commonly in gas welding.

1. Undercut:A groove or channel formed in the parent metal at the toe of the weld is called undercut.

Cause:

• When the current setting is too high
• When welding speed is too fast
• By overheating of the job due to continuousheating
• Due to faulty electrode motion
• When electrode angle is wrong

2. Incomplete Penetration:Failure of the weld metal to reach the root of the joint is known as incomplete penetration.

Cause:

• Too narrowedge penetration
• Excessive welding speed
• When the current setting is low
• When a larger diameter electrode is used
• Due to inadequate cleaning or gouging before depositing sealing run

3. Porosity or blow-hole:A group of pin-holes in a weld (porosity) or a larger hole in the weld (blow-hole) are caused by the gas being entrapped.

Cause:

• Presence of contaminantson the job or electrode surface
• Presence of high sulphur in the job or electrode material
• Moisture trapped between joining surfaces
• Freezing of weld at a faster rate

4. Spatters:An unintentional deposit of weld metal, in the shape of small globules on the job surface along the weld is known as spatters.

Cause:

• A too high current setting
• Use of moisture affected electrode
• Wrong polarity
• Use of a long arc
• Arc-blows

5. Overlap:Metal flowing onto the surface of the base metal without fusing it.

Cause:

• Improper welding technique
• High welding current
• By using large electrodes

6. Lack of fusion:If there is no melting of the edges of the base metal at the root face or on the side face or between the weld runs, then it is called lack of fusion.

Cause:

• It occurs because of the low heat input
• Incorrect electrode and torch angle
• Low welding current
• High welding speed

1. work thickness
2. electrode rod thickness
3. arc gap
4. other considerations

Explanation:

Three units are used to describe any arc welding process. They are voltage (V), amperage (A), and wattage (W).

Voltage:

• Voltage is the measurement of electrical pressure.
• Voltage control the maximum gap the electron can jump to form an arc.
• Welding voltage is associated with welding temperature.

Amperage:

• It is the measurement of the total number of electrons flowing.
• Amperage control the size of the arc.
• The higher the amperage setting, the higher the heat produced by the welding arc, and the lower the amperage setting the lower the heat produced.
• Each diameter of the electrode has a recommended minimum and maximum amperage range and therefore a recommended heat range.Amperage is associated with the welding heat.

Wattage:

• It is the measurement of the amount of electrical energy or power in the arc i.e how much heat and temperature an arc produces.

1. Short arc welding
2. Long arc welding
3. Spray arc welding
4. Pulsed arc welding

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 fromShort 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, withShort 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.

1. 1.5 : 1
2. 2 : 1
3. 2.5 : 1
4. 3 : 1

Explanation:

Thermit Welding:

Itis a welding process utilizing heat generated by an exothermic chemical reaction between the components of the thermit(a mixture of metal oxide and aluminium powder).In this process, fine aluminium particles and metal oxide are mixed in and ignited by an external heat source.

The reaction will proceed according to the following equation:

Metal Oxide + Aluminum → Aluminum Oxide + Metal + Heat

Thermit Welding is mainly used for joining steel parts.It is used for repair of steel casings and forgings, for joining railroad rails, steel wires and steel pipes, for joining the large cast and forged parts.For which aluminium is mixed with theiron oxide in the ratio of 1 : 3 by weight.

\(3Fe_3{O_4} + 8Al \to 9Fe + 4A{l_2}{O_3} + \left( {Heat} \right)\)

Due to thethermit chemical mixture reaction, 3 products are produced,

• Iron- Used as filler rod
• Al2O3- Used as a slag
• Heat- Used for the melting of the parent material

Aluminium is mixed with iron oxide in the ratioof 1 : 3 by weight and in the ratioof 8 : 3 by moles which can be approximated to 3 : 1.

1. 6.55 kW
2. 65.5 kW
3. 62.5 kW
4. 6.25 kW

Concept:

Power in welding is given as

P = V × I

where V = voltage (V), I = current (A)

Calculation:

Given:

V = 25 V, I = 250 A

Power required is:

P = V × I

P = 25 × 250 = 6250 W = 6.25 kW

1. Field weld
2. Weld all around
3. Flush contour
4. Chipping finish

Explanation:

Following table represents the weld symbols:

1. tungsten inert gas welding
2. submerged arc welding
3. electroslag welding
4. thermit welding

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.

Thermit Welding: Thermit is a mixture of aluminium powder and metal oxide. Aluminium combines with oxygen and intense heat will be released. It is used for repair of railway track.

1. Surface tension of the molten metal
2. Electromagnetic forces
3. Expansion of gases in the arc
4. Shielding gases

Explanation:-

• The electromagnetic force is a type of physical interaction that occurs between electrically charged particles.
• It acts between charged particles and is the combination of all magnetic and electrical forces.
• The electromagnetic force can be attractive or repulsive.
• A pinch welding gives narrow and long flame which is concentrated on the desired part, it is achieving by an induction coil, which results in electromagnetic forces.

Important Points

Arc blow is the undesirable effect of arc, during arc welding.

1. 18 - 40 volts
2. 40 - 95 volts
3. 100 - 125 volts
4. 130 - 170 volts

Explanation:

The selection of an optimum value of OCV (Open circuit voltage) depends on the type of base metal, a composition of electrode coating, type of welding current and polarity, type of welding process etc.

It generally varies from 50 V - 100 V.

1. Mild steel
2. High carbon steel
3. Grey cast iron
4. Alloy steels

Explanation:

The oxidizing flame is mainly used for welding brass. It is also very suitable for the cutting operations due to nonferrous metals (brasses and bronzes) due to formation of a tenuous oxide film over the molten metal which prevents the vaporization of zinc.

Carbonizing flame is very suitable for the welding steel as the rate of welding is faster by this flame than with the neutral flame. Types of flames for metals required for the different metals.

A carburizing flame is one in which the supply of acetylene is in excess as compared to the oxygen. The temperature attained by these flames vary from 3100°C to 3500°C and the most commonly used temperature is about 3200°C which can be attained without any appreciable amount of difficulty.

1. Neutral flame

• It is used to weld most of the common metals, i.e.mild steel, cast iron, stainless steel, copper and aluminium

2. Oxidizing flame

• Useful for welding ofbrass and for brazingof ferrous metals

3. Carburizing flame

• Useful for stelliting (hard facing), ‘Linde’ welding of steel pipes, and flame cleaning

1. 1-4-2-3
2. 3-4-2-1
3. 4-3-2-1
4. 3-2-4-1

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 zonein 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.

1. One
2. Two
3. Three
4. Four

Explanation:

The essential requirement for oxy-acetylene welding is a well-controlled flame with sufficient heat, which can be easily manipulated to heat and melts without altering the chemical composition of the metal/weld.

Three different types of oxy-acetylene flames as given below can be set.

Neutral flame

• Oxygen and acetylene are mixed in equal proportion in the blowpipe
• It is used to weld most of the common metals, i.e.mild steel, cast iron, stainless steel, copper and aluminium

Oxidising flame

• It contains an excess of oxygen over acetylene as the gases come out of the nozzle
• Useful for welding ofbrass and for brazingof ferrous metals

Carburising flame

• The fuel gas (acetylene) is greater than the oxygen
• Useful for stelliting (hard facing),‘Linde’ welding of steel pipes, and flame cleaning
• This flame has 3 zones i.e. bright luminous inner zone, acetylene feather and outer blue envelope.

1. Leg
2. Face
3. Effective throat
4. Actual throat

Explanation:

Nomenclature of butt and fillet weld:

Throat thickness:The distance between the junction of metals and the midpoint on the line joining the two toes.

Leg length:The distance between the junction of the metals and the point where the weld metal touches the base metal ‘toe’.

Thelength of the legis the distance from the root of the weld to the toe of the weld.

Thetheoretical throatis the perpendicular distance between the root of the weld and the hypotenuse joining the two ends of the length. It is the shortest distance from the root to the face.

Root:The parts to be joined that are nearest together.

Root gap:It is the distance between the parts to be joined.

Root face:The surface formed by squaring off the root edge of the fusion face to avoid a sharp edge at the root.

Reinforcement:Metal deposited on the surface of the parent metal or the excess metal over the line joining the two toes.

The toe of weld:The point where the weld face joins the parent metal.

Weld face:The surface of a weld seen from the side from which the weld was made.

Root penetration:It is the projection of the root run at the bottom of the joint.

1. P-4, Q-3, R-5, S-1, T-2
2. P-4, Q-2, R-3, S-5, T-1
3. P-4, Q-5, R-1, S-2, T-3
4. P-3, Q-5, R-2, S-1, T-4

Explanation:

Types of welding defects:

Weld porosityis due to atmospheric gases are trapped inside the liquid metal during the solidification of the metal.

Slag inclusion caused by trapping of the compound by oxides, fluxes and electrode coating materials in the weld zone.

Weld crack caused due to non-uniform cooling and internal stresses generated in weld Beed. If stress is more than the strength of the material cracks will be formed.

Weld spatter caused due to high welding current and low welding speed and arc blow.

Incomplete fusion caused due to insufficient heat and too fast/quick travel of torch or electrode.

1. Microstructural changes but does not melt
2. Neither melting nor microstructural changes
3. Both melting and microstructural changes after solidification
4. Melting and retains the original microstructure after solidification

Explanation:

Theheat-affected zone(HAZ) is the area of the base material, either ametalor athermoplastic, which is not melted and has had its microstructure and properties altered byweldingor heat intensive cutting operations.

The extent and magnitude of property change depend primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process.

1. Four
2. Five
3. Three
4. Two

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.

1. Alcohol
2. plastic deformation
3. water jet
4. sand blasting

Concept:

In solid-state welding like cold pressure welding operation, when the force of large amount is applied on the metals, deformation of metals takes place due to which the joinedplates move slightly which leads to removal of the contaminated layer.

Sandblasting is basically used to clean the surface of any material, mainly for the metallic surface. Materials used in sandblasting are sand, copper slog, steel grit, pieces of walnut, powder abrasive, pieces of avocado, and many others.

1. Electric arc welding
2. Plasma arc welding
3. Tungsten inert gas arc welding
4. Submerged arc welding

Explanation:

Flux:

• Flux coating acts as deoxidizers; by forming the slag it will protect the liquid metal from atmospheric gases.
• Slag formation controls the heat transfer rate of liquid metal to the weld pool.

Types of welding, working, and use of flux:

Additional Information

1. Gas welding
2. TIG welding
3. MIG welding
4. Plasma arc welding

Explanation:

Plasma Arc Welding:

• Plasma Arc Welding is the advanced version of TIG welding. In Plasma Arc Welding process the arc is being created between tungsten electrode and the work piece. Plasma is the state of the gas when the gas is heated to high temperature and changes into positive ions, neutral atoms and negative electrons.
• The plasma is allowed to pass through a very constricted nozzle to get a very high velocity of plasma.
• The nozzle constrict the plasma and arc, thus constriction of arc will result into high temperature of the plasma. Thus high velocity and high temperature (30000°C) results into rapid melting of base metal.
• The PAW is used for welding very thin foils due to very less heat affected area and intense heat generation.
• The heat affected region in PAW is less than GTAW process, thus less amount of heat lost and high efficiency as compared to GTAW.
• The energy density in PAW is greater than GTAW process. This result in deeper penetration in base metal and even thicker metal can be melted rapidly.
• PAW is used in welding stainless steel, titanium, metals having very high melting points and super alloys. Also, in aeronautical industry, precision instrument industry and jet engine manufacturing.

Gas Welding:

• In gas welding Heat source is the flame produced by the combustion of fuel gas and oxygen. Acetylene (C2H2) is the principal fuel gas employed in this welding. No pressure is involved in this welding. Filler metal can be added in the form of a wire or rod.
• The Gas welding process uses heat from exothermic chemical reactions.
• Gas welding is used for joining ferrous and non-ferrous metals, e.g.,carbon steels, alloy steels, cast iron, aluminium, copper, etc.
• Gas welding is used in automotive and Aircraft industries, sheet metal fabricating plants, etc.

TIG Welding:

• Tungsten Inert Gas (TIG)or Gas Tungsten Arc (GTA) welding is the arc welding process in which arc is generated between non-consumable tungsten electrode and work piece.
• The tungsten electrode and the weld pool are shielded by aninert gas normally argon and helium.
• TIG welding is used for welding thin materials up to a thickness of 5 mm, without using filler material.
• TIGwelds are stronger, more ductile and more corrosion resistant than welds made with ordinary shield arc welding.
• There is little weld metal splatter or weld sparks that damages the surface of the base metal as in ordinary shield arc welding.

MIG Welding:

• In this process the arc is formed between a continuous, automatically fed,metallic consumable electrodeand welding job in an atmosphere of inert gas, and hence this is called metal inert gas arc welding (MIG) process.
• In MIG welding the consumable electrode is supplied in the form of a spool wire.
• In MIG welding the thickness of base metal is limited to 40 mm.
• It provides higher deposition rate. It is faster than shielded metal arc welding due to continuous feeding of filler metal.
• There is no slag formation and deeper penetration is possible.
• Practically all commercially available metals can be welded by this method.