Taylor Made: Welding 101
Like machining, welding is a highly refined skill that requires an extensive knowledge base. Welding is the process of fusing materials, mainly metals, together using heat. The weld arc or flame melts the materials at their border so that they solidify as one surface.
Fuel gas welding is done using a gas torch with dual, pressurized feeds of fuel, such as acetylene gas, and oxygen. The fuel coming out of the torch is spark-lit to create a flame, and then oxygen is added to increase the flame’s heat and strength. The combustion reaction occurring in the flame creates a carbon dioxide shielding gas that prevents oxides from forming on the weld. In order to maintain the shielding gas, the flame needs to be kept close to the base material (material being welded).
Filler rods can be used to strengthen the weld and are matched to the base material, e.g. steel rod for steel and aluminum rod for aluminum. The rod blends with the base materials by being dipped into the puddle created by the torch.
Other types of welding use an arc instead of a flame. The arc requires a circuit that consists of the welding machine (power source), electrode, base metal, and ground clamp (attached to the base metal or metal work surface). When the electrode is in close proximity to the base metal, the arc can jump across the gap to complete the circuit.
Shielded metal arc welding (SMAW) uses flux-coated, consumable electrodes in place of filler rods. A clamp connected to the welding machine holds the electrode. Current is passed through the clamp to the electrode at different levels according to the type of electrode being used (e.g. 75-90 amps AC for a 6013 electrode). The arc is started by either scraping or striking the electrode on the base metal for AC or DC respectively. SMAW does not use a shielding gas; instead, a by-product of the burning electrode, called slag, forms a protective layer over the weld. The slag is removed once the weld has been completed.
Gas metal arc welding (i.e. mig welding) has a consumable wire electrode fed at a set rate through the torch. The electrode starts the arc by touching the base metal and then fuses with the base metals to form the weld. Pulling the trigger on the torch starts the electrode feed and shielding gas flow.
Gas tungsten arc welding (tig) uses a non-consumable electrode, meaning that the electrode is only used to convey the arc and does not touch the base metal or become part of the weld. Instead, a foot pedal is used to start the arc and shielding gas flow when the electrode is in close proximity to the metal and a filler rod is added to the puddle to strengthen the weld.
Brazing is similar to welding but is not a welding process. Often performed using a gas torch, the brazing rod is melted using the heat of the base metal. The base metal is only heated to an orange heat instead of reaching melting temperature, meaning that the brazing rod basically acts as a glue that holds the metals together. Brazing is performed above 840 degrees Fahrenheit, while its sister process, soldering, is done below 840 degrees.
Any welding or brazing process requires crucial protection and safety standards as well as lots of practice. I highly recommend taking a class or workshop series, for example on campus or over at Parkland, if you are interested in learning these skills.
Shout out to Stephanie Ott-Monsivais for suggesting this topic.