AME 8 Q2

A. MIG welding involves creating an electric arc between a consumable wire electrode and the workpiece, with a shielding gas to protect the weld from atmospheric contamination.

Explanation:

• A. Correct: In MIG welding, a continuous consumable wire electrode is fed through the welding gun, and an electric arc is formed between the wire and the workpiece. A shielding gas (usually argon or a mix of argon and CO2) protects the weld from atmospheric contaminants.
• B. Incorrect: High-frequency electric arcs between non-consumable electrodes describe TIG welding, not MIG welding. MIG welding uses a consumable wire electrode.
• C. Incorrect: Laser welding uses a laser beam rather than an electric arc and does not involve a consumable wire electrode or shielding gas in the same way as MIG welding.
• D. Incorrect: The description of a manual arc with a tungsten electrode and a filler rod describes TIG welding, not MIG welding. MIG welding uses a continuously fed consumable wire electrode and shielding gas.

Correct Answer:

A. The surface should be clean and free of rust, paint, oil, and other contaminants to ensure proper electrical contact and strong welds.

Explanation:

• A. Correct: Clean surfaces are crucial for MIG welding to ensure proper electrical contact between the electrode and the workpiece. Contaminants such as rust, paint, or oil can interfere with the welding process and lead to weak or defective welds.
• B. Incorrect: MIG welding does not require roughening the surface. Clean and smooth surfaces are preferred to avoid issues with weld quality and to ensure proper fusion.
• C. Incorrect: Protective wax coatings are not used in MIG welding. Surface preparation focuses on removing contaminants, not applying additional coatings.
• D. Incorrect: Heating the surface is not a standard practice for MIG welding. Proper cleaning is more important than pre-heating for ensuring strong welds.

Correct Answer:

C. Advantages: High-quality welds with less spatter, ability to weld in all positions, suitable for automation; Limitation: High equipment and consumable costs.

Explanation:

• C. Correct: MIG welding offers high-quality welds with less spatter, can be used in various positions, and is suitable for automation. However, it can be expensive due to the cost of equipment and consumables.
• A. Incorrect: MIG welding is versatile and can be used in various positions, not just flat positions. High welding speed and minimal post-weld cleaning are advantages, but limited position capability is not a limitation.
• B. Incorrect: MIG welding does not necessarily require significant pre-weld surface preparation compared to other methods. It is versatile and can weld in all positions, and continuous welding is an advantage.
• D. Incorrect: MIG welding can be used both indoors and outdoors with proper shielding gas management. Low heat input and minimal distortion are advantages, but equipment costs are not the only limitation.