Welding
In the context of welding, what does the term ‘submerged’ refer to in Submerged Arc Welding (SAW)?
- The arc is buried under a blanket of granular fusible flux
- The welding is performed completely underwater
- The weld pool is shielded by a submerged gas bubble
- The electrode is submerged in a cooling liquid
Explanation:
- The arc is buried under a blanket of granular fusible flux, which is the defining characteristic of SAW, providing shielding and stabilizing the arc.
- The welding is performed completely underwater describes a different process, like hyperbaric welding.
- The weld pool is shielded by a submerged gas bubble is not a standard description for SAW.
- The electrode is submerged in a cooling liquid is incorrect; the electrode is a continuous wire fed through the flux.
Which of the following is a primary function of the shielding gas \( \text{CO}_2 \) in \( \text{CO}_2 \) welding (GMAW)?
- To significantly increase the arc temperature
- To act as a fuel for the exothermic reaction
- To displace atmospheric gases and prevent weld contamination
- To dissolve into the weld metal and increase hardness
Explanation:
- To significantly increase the arc temperature is not its primary function; argon is better for a hotter arc.
- To act as a fuel is incorrect; \( \text{CO}_2 \) is not combustible in this context.
- To displace atmospheric gases and prevent weld contamination is the core purpose of any shielding gas.
- While \( \text{CO}_2 \) can dissociate and affect the chemistry, its primary role is shielding, not deliberately adding carbon.
Atomic hydrogen welding utilizes a stream of hydrogen gas. What is the primary role of the atomic hydrogen (\( \text{H} \)) at the arc?
- It acts as the primary filler metal for the joint.
- It cools the tungsten electrodes rapidly.
- It recombines into molecular hydrogen (\( \text{H}_2 \)) on the workpiece surface, releasing intense heat.
- It forms a protective slag over the finished weld.
Explanation:
- It acts as the primary filler metal is incorrect; a separate filler rod is typically used.
- It cools the electrodes is not its function.
- It recombines into molecular hydrogen (\( \text{H}_2 \)) on the workpiece surface, releasing intense heat is the fundamental principle of the process, providing the energy for welding.
- It forms a protective slag is incorrect; it is a slag-free process.
Ultrasonic welding (USW) is a solid-state welding process. What is the primary mechanism that creates the bond between the two workpieces?
- Melting and solidification of the base metals
- A chemical reaction facilitated by a reactive gas
- The simultaneous application of high-frequency vibration and pressure
- The generation of an electric arc between the parts
Explanation:
- Melting and solidification describes fusion welding processes, not solid-state welding like USW.
- A chemical reaction is not the primary mechanism.
- The simultaneous application of high-frequency vibration and pressure is correct. This scrubs away surface films and allows atomic bonding without bulk melting.
- An electric arc is not involved in ultrasonic welding.
Which welding process uses a non-consumable electrode and requires a separate filler rod?
- Gas Tungsten Arc Welding (TIG)
- Gas Metal Arc Welding (MIG)
- Flux-Cored Arc Welding
- Shielded Metal Arc Welding
Explanation:
- TIG welding uses a non-consumable tungsten electrode to create the arc. The welder must manually feed a separate filler rod into the weld pool if needed.
- MIG welding uses a continuously fed consumable wire electrode that also acts as the filler material.
- Flux-Cored Arc Welding uses a continuously fed tubular wire filled with flux.
- Shielded Metal Arc Welding uses a consumable electrode coated in flux.
In MIG welding, the primary purpose of the shielding gas is to:
- Increase the travel speed of the weld.
- Cool the welding gun.
- Protect the molten weld pool from atmospheric contamination.
- Provide the electrical current for the arc.
Explanation:
- The shielding gas (e.g., Argon, CO₂, or mixtures) is inert or semi-inert and displaces the surrounding air, preventing oxygen and nitrogen from contaminating the molten metal and causing porosity or weakness.
- While gas flow can have a minor cooling effect, it is not its primary purpose.
- The electrical current is provided by the power source and travels through the wire.
Which of the following is a key advantage of MIG welding over TIG welding?
- Superior weld quality and cleanliness on exotic metals.
- Greater operator control over the weld bead.
- Higher deposition rates and faster travel speeds.
- Ability to weld without a shielding gas.
Explanation:
- MIG welding’s continuous wire feed allows for much higher rates of filler metal deposition, making it significantly faster than the manual process of TIG welding.
- Superior weld quality on metals like aluminum and stainless is a hallmark of TIG welding.
- TIG welding offers finer control due to the separate control of the arc and filler metal.
- While some MIG processes like Flux-Cored don’t require external gas, standard MIG (GMAW) does.
A TIG welder is preparing to weld aluminum. To effectively remove the oxide layer and ensure a clean weld, they should use:
- Direct Current Electrode Positive (DCEP).
- Direct Current Electrode Negative (DCEN).
- Alternating Current (AC).
- Pulsed Direct Current.
Explanation:
- Alternating Current (AC) provides a unique cleaning action. During the electrode positive (EP) portion of the cycle, electrons leave the base metal, breaking up the tenacious aluminum oxide layer.
- DCEN is used for deep penetration on most metals but offers no cleaning action on aluminum.
- DCEP provides cleaning action but poor penetration and is hard on the tungsten electrode.
The heat input (\( H \)) for a weld can be calculated by the formula \( H = \frac{60 \times E \times I}{S \times 1000} \) where \( E \) is voltage, \( I \) is current, and \( S \) is travel speed in mm/min. If a MIG weld is made at 24V, 180A, and a speed of 300 mm/min, what is the heat input in kJ/mm?
- 0.648 kJ/mm
- 0.864 kJ/mm
- 0.864 J/mm (or 0.000864 kJ/mm)
- 1.240 kJ/mm
Explanation:
- Plug the values into the formula: \( H = \frac{60 \times 24 \times 180}{300 \times 1000} \)
- First, calculate the numerator: \( 60 \times 24 \times 180 = 259,200 \)
- Then, calculate the denominator: \( 300 \times 1000 = 300,000 \)
- Now, divide: \( H = \frac{259,200}{300,000} = 0.864 \)
- The units from this calculation are kJ/mm *if* the speed is in mm/min. However, 0.864 kJ/mm is an impractically large value. The standard result is 0.864 J/mm. To express it in kJ/mm, it would be 0.000864 kJ/mm, making the third option the most accurately stated answer.