308A Welding and Soldering for Sheet Metal 4

Question 1

What is the AWS classification for a common MIG welding wire used on mild steel sheet metal?

Accepted Answer

ER70S-6

Answer

ER70S-6 is the most common MIG wire for mild steel. The 'ER' indicates electrode/rod, '70' indicates 70,000 PSI tensile strength, 'S' indicates solid wire, and '6' indicates the chemical composition with added deoxidizers.

Question 2

What is 'sweat soldering' and when is it used in sheet metal work?

Accepted Answer

Pre-tinning both surfaces with solder, assembling them, then reheating to fuse the solder layers together

Answer

Sweat soldering involves pre-tinning (applying a thin coat of solder to) both mating surfaces, placing them together, then reheating until the solder reflows and bonds the surfaces. It is used for flat seams and patches.

Question 3

What polarity setting is typically used for MIG welding sheet metal?

Accepted Answer

DCEP (Direct Current Electrode Positive / Reverse Polarity)

Answer

MIG welding uses DCEP (reverse polarity) where the electrode wire is positive. This provides deeper penetration, stable arc transfer, and proper cleaning action. DCEN would cause an unstable arc with MIG.

Question 4

What is the purpose of a 'heat sink' when welding thin sheet metal?

Accepted Answer

To absorb excess heat and prevent distortion or burn-through by drawing heat away from the weld zone

Answer

Heat sinks (copper bars, aluminum blocks, or wet rags) placed near or behind the weld joint absorb excess heat, reducing the risk of burn-through and minimizing warping on thin sheet metal.

Question 5

What is the difference between 'acid core' and 'rosin core' solder?

Accepted Answer

Acid core has an aggressive flux for sheet metal and steel; rosin core has a mild flux for electrical work and must not be used on sheet metal

Answer

Acid core solder contains an aggressive acid flux suitable for sheet metal work on steel and galvanized surfaces. Rosin core solder has a mild, non-corrosive flux designed for electrical connections and is not effective on sheet metal.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A Welding and Soldering for Sheet Metal 4