Manual Metal Arc Welding - Short Test 2

Practice flashcards covering Manual Metal Arc Welding concepts including backstep welding, AC/DC characteristics, circuit components, and welding defects like porosity and lack of penetration.

What is the explanation for the term backstep welding according to the transcript?

Backstepping reduces the shrinkage force because each run is restrained by the previous run of weld.

What are the specific requirements for the installation and maintenance of the mains supply lead in a welding circuit?

The lead should be as short as possible and it must be installed and maintained by a qualified electrician.

What safety precautions should the welder take regarding their protective equipment in an arc welding circuit?

The welder should use dry gloves and have dry feet.

Interpret the welding symbol described as '6MM Fillet weld all around'.

It indicates a fillet weld with a size of $6\,mm$ to be applied around the entire joint.

What are the four advantages of using an Alternating Current (AC) welding machine (transformer)?

1. Lower cost compared to Direct Current power sources. 2. More efficient compared to engine (petrol and diesel) driven power sources. 3. Maintenance free due to few or no moving parts. 4. No blow arc to cause deflection of the arc during welding.

What are logic-based limitations of using Alternating Current (AC) for welding?

AC is potentially more dangerous in damp conditions (welder, ground, or equipment) and certain metals like cast iron and aluminium are more difficult to weld as electrodes may require DC.

List the general causes of lack of penetration in welding.

Current too low, travel speed too fast, electrode too large, and incorrect joint preparation.

Regarding joint preparation, what specific factors lead to a lack of penetration in MMAW?

Included angle too tight (MMAW requires an angle of at least $60^\circ$), root face too broad, and root gap too tight.

What are the environmental and material cleanliness causes of porosity?

Damp electrodes, damp work, and dirty work containing oil, grease, rust, or millscale.

What are the metallurgical and operational causes of porosity?

Impurities in the parent metal such as sulphur, and arc length being too long or too short, especially at the start or end of welds.