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

Explanation:

Principle of Arc Welding

Definition: Arc welding is a type of welding process that uses an electric arc to create heat to melt and join metals. The process involves creating an electric arc between an electrode and the workpiece, which generates the necessary heat to melt the metal at the welding point.

Working Principle: In arc welding, an electric current is passed through an electrode, creating an arc between the electrode and the workpiece. The intense heat from the arc melts the metal at the joint, and as the electrode is consumed, it deposits filler material into the joint, creating a strong weld upon cooling. The process can be performed using direct current (DC) or alternating current (AC), and the choice depends on the specific requirements of the welding task and materials involved.

Steps Involved:

• Preparation: The workpieces to be welded are cleaned and positioned appropriately to ensure a strong joint.
• Striking the Arc: The welder strikes the electrode against the workpiece to create an arc. This arc generates the heat required to melt the metal.
• Maintaining the Arc: The welder maintains the arc by keeping a consistent distance between the electrode and the workpiece. This distance is crucial for consistent heat and quality of the weld.
• Melting and Joining: As the arc continues, the base metal and the electrode (if it is a consumable electrode) melt, creating a pool of molten metal that fuses the workpieces together.
• Cooling and Solidifying: After the welding is complete, the molten metal cools and solidifies, forming a strong joint between the workpieces.

Advantages:

• High welding speed and efficiency.
• Capability to weld a wide range of metals and thicknesses.
• Strong and high-quality welds.
• Versatility in various welding positions (flat, vertical, overhead).

Disadvantages:

• Requires skilled labor to perform quality welds.
• Potential for harmful radiation and fumes, requiring proper safety measures.
• Initial setup costs for equipment can be high.

Applications: Arc welding is widely used in construction, shipbuilding, automotive industries, and manufacturing of heavy machinery. It is suitable for both large-scale industrial applications and smaller repair works.

Analysis of Incorrect Options:

Option 2: Supplying oxygen and acetylene between the electrodes to melt the metal.

This option describes the principle of oxy-fuel welding (also known as gas welding), not arc welding. In oxy-fuel welding, a flame is produced by burning a mixture of oxygen and acetylene gases, which is used to melt and join metals. This process does not involve the use of an electric arc.

Option 3: Creating a chemical reaction between the electrode and the workpiece to melt the metal.

This option is incorrect because arc welding relies on the heat generated by an electric arc to melt the metal, not on a chemical reaction. While some chemical reactions may occur during the welding process (such as oxidation), they are not the primary mechanism for melting the metal.

Option 4: Creating friction between the electrode and the workpiece to melt the metal.

This option describes the principle of friction welding, not arc welding. In friction welding, heat is generated through mechanical friction between the workpieces, which are then joined under pressure. Arc welding, on the other hand, uses an electric arc to generate the required heat.

Important Information:

Arc welding is a fundamental process in the field of manufacturing and fabrication, offering a high degree of control and precision. It is essential to understand the differences between various welding techniques to choose the appropriate method for specific applications. Safety measures, such as wearing protective gear and ensuring proper ventilation, are crucial to protect welders from potential hazards like ultraviolet radiation, sparks, and toxic fumes.

Explanation:

The heat input in manual arc welding per unit length is given by \( Q = \frac{\eta \cdot V \cdot I}{\text{welding speed}} \), where V is voltage, I is current, η is efficiency, and welding speed is in mm/min.

Given:

Voltage, V = 20 V

Current, I = 100 A

Welding speed = 250 mm/min

Efficiency, η = 0.8

Calculation:

Heat input per unit length, \( Q = \frac{0.8 \cdot 20 \cdot 100}{250} = \frac{1600}{250} = 6.4~\text{J/mm} \)

If welded length = 12 mm, total heat input = \( Q \cdot L = 6.4 \cdot 12 = 76.8~\text{J} \)

Explanation:

Oxygen gas cylinder:

• It is a seamless steel container used to store oxygen gas safely and in large quantity under a maximum pressure of 150 kg/cm2, for use in gas welding and cutting.
• In oxy-acetylene gas welding, the color of the oxygen cylinder is black.

Acetylene gas storage:

• The acetylene gas used in gas welding is stored in steel bottles (cylinders) painted in maroon color.
• The normal storage capacity of storing acetylene in a dissolved state is 6m3 with the pressure ranging between 15-16 kg/cm2.
• Acetylene is highly flammable and would explode in elevated pressure when reacting with oxygen in the air.
• Due to the danger of explosion, pure acetylene cannot be compressed to pressure more than 0.1 Pa above the atmosphere.
• Therefore acetylene is supplied in cylinders in the form known as dissolved acetylene.
• Acetylene gas is used for welding purposes and is stored in cylinders of liquid acetone contained in the porous material.
• This is for cooling purposes in the event of thermal decomposition and to ensure that there is no free space left for acetylene gas.

Explanation:

• ​Arc stability in welding is generally better with a direct current (DC) power supply compared to an alternating current (AC) power supply.
• When using DC, the welding arc remains relatively stable and predictable due to the consistent flow of current in one direction.
• This allows for better control over the heat input and penetration during welding.
• DC welding also provides better control over the shape and characteristics of the weld bead, making it easier to achieve the desired weld quality.
• On the other hand, with AC welding, the current periodically changes direction, which can cause the arc to flicker or wander.
• This can lead to less stable and more difficult-to-control welding arcs.
• AC welding is typically used for certain applications, such as aluminum welding, where the alternating current helps to prevent oxide formation on the electrode and promotes cleaning action.
• In summary, when it comes to arc stability, DC welding generally provides better results compared to AC welding. 
• Arc stability in welding is generally better with a direct current (DC) power supply compared to an alternating current (AC) power supply.

Explanation:

An electric arc is a type of discharge that occurs between two electrodes, usually in air or another gas. It is characterized by a bright, luminous column of ionized gas called the arc column, which is sustained by a continuous flow of electric current.

During an electric arc, several different zones can be identified, each with its own unique characteristics. These zones are:

A) Cathode spot: This is the region where electrons are emitted by the cathode due to thermionic emission. The electrons move towards the anode due to the potential difference between the electrodes.

B) Anode space: This is the region between the anode and the cathode where the electrons move towards the anode. In this region, the voltage drop is sharp.

C) Anode spot: This is the region where the electrons are absorbed by the anode. 

D) Arc column: This is the central region of the arc where the temperature is high, and the plasma is formed. In this region, the voltage drop is not sharp.

Hence,The correct option is 3: A – 4, B – 1, C – 2, D – 3.

Explanation:

• The selection of an optimum value of OCV (Open circuit voltage) depends on the type of base metal, the composition of electrode coating, type of welding current and polarity, type of welding process etc.
• It generally varies from 50 V - 100 V.

Explanation:

Gas Welding methods

• There are two types of Welding methods
  1. Leftward welding  (forehand welding)
  2. Rightward welding (backhand welding)

Leftward welding

• The welding rod is held in the left hand and the blowpipe is held in the right hand.
• Leftward welding is used for the metal plate thickness up to 3 mm.
• Welding proceeds from right to left.
• It is also known as forwarding or forehand welding.
• The inclination of the welding rod with plate is 30° to 40° and the inclination of the blowpipe with plate is 60° to 70°.

Rightward welding

• Rightward welding is used for thicker plates and proceeds from left to right.
• The inclination of the welding rod is the same as in the leftward welding but the inclination of the blowpipe is 10° to 20° less than that in the leftward welding, i.e. at 40° to 50°. 
• It is also known as backward or backhand welding.

Concept:  

Welding symbol:

A welding symbol has the following basic elements:

1. Reference line

2. Arrow

3. Basic weld symbols (like fillet, butt joints, etc.)

4. Dimensions

5. Supplementary symbols

6. Finish symbols

7. Tail 

Reference Line:

• It is used to apply weld symbols and other data.
• The reference line is always drawn horizontal to the bottom of the print. 
• Lower side of the reference line is termed as arrow side.
• Upper side of the reference line is termed as other side.

Arrow:

• The arrow is used to connect the reference line to the joint area to be welded.

Basic weld symbols:

• Basic symbol and type in mention in the given chart.

Tail:

• Tail is added only when there is a need for including the specification process or other references.

Calculations:

Given:

Here the symbol is of fillet weld on lower side of the reference line that represents arrow side.

Here the symbol is of fillet weld on the upper side of the reference line that represents the other side.

∴ combining the two, 6 on the lower side represents the arrow side and 12 on the upper side represents the other side.

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.

Concept:

Duty cycle:

It is defined as the ratio of arc on time to total time.

i.e. \({\bf{Duty}}\;{\bf{cycle}} = \frac{{{\bf{Arc}}\;{\bf{on}}\;{\bf{time}}}}{{{\bf{Total}}\;{\bf{time}}}}\)

Calculation:

Given:

Total time = 10 min, Dwell time = 4 min, Arc on time = 5 min, Duty cycle = ?

Now, we know that

\({\bf{Duty}}\;{\bf{cycle}} = \frac{{{\bf{Arc}}\;{\bf{on}}\;{\bf{time}}}}{{{\bf{Total}}\;{\bf{time}}}}\)

\({\bf{Duty}}\;{\bf{cycle}} = \frac{5}{{10}} = \frac{1}{2}\)

∴ % Duty cycle = 50 %

Explanation:

Shielded metal arc welding:

• A consumable electrode is provided for the welding
• The coating on the electrode basically gets vapourised and creates a shielded environment for welding.

Submerged arc welding:

• A consumable electrode is used 
• Instead of electrode coating, external flux is provided to avoid the oxidation of welding material
• Only used for the horizontal positions

Tungsten inert gas welding:

• A non-consumable tungsten electrode is used
• Inert gas argon or helium is used 
• A separate filler material is used for welding 
• It is also called gas tungsten arc welding 

Explanation:

Welding defects:

• Cracks
• Cavities
• Solid inclusions
• Incomplete fusion
• Imperfect shape or unacceptable contour

Welding cracks:

• Fracture-type interruptions either in the weld or in base metal adjacent to the weld.
• Serious defect because it is a discontinuity in the metal that significantly reduces strength.
• Caused by embrittlement or low ductility of weld and/or base metal combined with high restraint during contraction.
• In general, this defect must be repaired.

Concept:

Coding of Electrodes

It consists of the following letters and numerals and shall be followed in the order stated:

a) a prefix letter 'E' shall indicate a covered electrode for manual metal arc welding, manufactured by extrusion process

b) a letter indicating the type of covering

c) first digit indicating the ultimate tensile strength in combination with the yield stress of the weld metal deposit

d) second digit indicating the percentage elongation in combination with the impact values of the weld metal deposited

e) third digit indicating welding position(s) in which the electrode may be used

f) fourth digit indicating the current condition in which the electrode is to be used

From the chart, it is clear that the third digit i.e. 2 is for the flat and horizontal welding position category, so option 4 is the correct answer.

Explanation:-

Gas metal arc welding (MIG):

Metal Inert Gas Welding (Gas Metal Arc Welding) is an arc welding process, in which the weld is shielded by an external gas (Argon, helium, CO₂, Argon + Oxygen, or other gas mixtures). 

Process:

Consumable electrode wire, having a chemical composition similar to that of the parent material, is continuously fed from a spool to the arc zone.

The arc heats and melts both the workpiece's edges and the electrode wire. The fused electrode material is supplied to the surfaces of the workpieces, fills the weld pool, and forms joints.

Due to the automatic feeding of the filling wire (electrode), the process is referred to as semiautomatic.

The operator controls only the torch positioning and speed.

Advantage - 

• The continuous weld may be produced (no interruptions);
• A high level of operators skill is not required;
• Slag removal is not required (no slag).

Disadvantages - 

• Expensive and non-portable equipment is required;
• Outdoor applications are limited because of the effect of wind, dispersing the shielding gas.

Concept:

Current - Duty cycle relation is given by

I²D = Constant 

From the above relation,

I_r²D_r = I_d²D_d

where I_r and D_r are rated current and duty cycle, I_d and D_d are desired current and duty cycle respectively.

Calculation:

Given:

I_r = 250 A, D_r = 100%, D_d = 50%, I_d = ?

Now, we know that

Ir²Dr = Id²Dd

250² × 1 = I_d² × 0.5

∴ I_d = 353.55 A