13 GMAW Materials

GMAW can be used with a variety of materials.

Carbon Steel

Carbon steel welding with spray transfer can be performed using a 95% to 98% Ar and 2% to 5% O2 mixture. Adding oxygen to the shielding gas mixture provides a more stable arc, minimizes undercutting, and permits faster travel speeds. Straight CO2 may be used for high-speed production welding. However, straight CO2 produces globular transfer with excessive spatter.  Pulsed spray transfer (GMAW-P) can be performed with 90% Ar and 10% CO2.

Welding parameters such as electrode diameter, proper wire feed speed (current) and voltage, and shielding gas flow are set based on the carbon steel thickness.

Aluminum

Welding aluminum is a difference experience to other materials: it has a lower melting point (approximately 1200° F), its thermal conductivity is five times greater than steel, it does not change color as its temperature changes, and oxide on the surface melts at a higher temperature than the base metal (3700° F versus 1200° F). Aluminum is normally welded with GMAW, for thicknesses over 1/8″, or gas tungsten arc welding (GTAW) for thin (less than 3/16″) or intricate parts.

• Either constant current or constant voltage power sources can be used for GMAW work on aluminum.
• Direct current electrode positive (DCEP) or “reverse” polarity is used.
• For the shielding gas, 100% argon is most common, although helium or mixtures of argon and helium can be used.
• Gas flow rate should be between 25 and 40 cubic feet per hour.
• Either push pull systems or spool guns can be used as wire feeders, although only a pull/forehand travel should be used.
• Weaves are not recommended, due to the lack of cleaning action.
• Be aware when welding aluminum that the puddle is very soft and must be within certain parameters. Aluminum is also more prone to crater cracks.

Using short circuiting transfer on aluminum produces a colder arc than is produced with spray transfer, permitting the weld pool to solidify rapidly. This action is especially useful for vertical, overhead, and horizontal welding and for welding thin aluminum. When using GMAW in vertical position, a downhill technique is preferred.

Spray transfer on aluminum is especially suitable for thick sections. With spray transfer, more heat is produced to melt the electrode and the base metal. Vertical, horizontal, and overhead welds are typically more difficult with spray transfer than with short circuiting transfer.

Welding parameters such as edge preparation, electrode diameter, argon flow, proper current and voltage, and electrode feed speed for short circuiting transfer or spray transfer should be set based on aluminum thickness. In general, gas flow should be about 35, voltage at 24, and current at 180.

Stainless Steel

Stainless steel was initially developed to prevent the rusting and corrosion that occurred with carbon steel. Stainless steel is produced at a higher quality level than carbon steels and has fewer impurities, making it a reliable material for welding.

On stainless steel 1/4′′ thick or more, the welding gun should be moved back and forth with a slight side-to-side movement. Thin stainless steel is best welded with a slight back-and-forth motion along the joint. The forehand technique is generally used for welding stainless steel.

Short circuiting transfer can be used on thin stainless steel in overhead or vertical position. Spray transfer with stainless steel is not possible in overhead or vertical positions.

Quality welds can be produced on stainless steel using the spray transfer process with a 1/16′′ diameter electrode and high current. DCEP with argon and 1% to 2% O2 may be used for spray transfer on stainless steel. Proper ventilation is necessary to remove the fumes.

Welding parameters such as edge preparation, electrode diameter, shielding gas flow, proper current and voltage, electrode feed speed, welding speed, and welding passes for short circuiting transfer or spray transfer should be set based on stainless steel thickness.

Copper

Steel backing bars are required for welding copper 1/8′′ thick or less. Preheating at this thickness is not necessary. Preheating at 400°F is advisable on sections 3/8′′ thick or more.

Welding parameters such as edge preparation, electrode diameter, proper current and voltage, electrode feed speed, and welding speed should be set based on copper thickness.