4. Joining Processes

Joining Processes in this standard refers specifically to welding. Welding should not be confused with soldering or brazing. Welding is a method of taking two pieces of exactly the same metal and fusing it together by melting it with some source of heat. Welding is such a large topic with a wide range of welding methods and techniques that it is a trade qualification by itself. We will only touch on five welding methods, and we will not go too deep into the topic. Level 1 only covers the basics.

Arc/stick Welding

The most common form of electrical welding is arc, or stick, welding. This type of welding uses high voltages and amps to create a lightning bolt between a sacrificial electrode and the metal you are welding.

This bolt of lightning is hot enough to melt the electrode and the base metal, creating a molten pool of steel that fuses with your metal pieces. As the weld cools it sets and the two pieces of metal become one. The electrode has a flux around it that melts with the electrode. This flux creates a protective gas that prevents oxygen from reaching the molten pool of steel.

As the metal weld cools, the flux forms a layer of glassy slag on the weld bead. This slag has to be removed by a metal brush and tack hammer to inspect the welds. Arc welding can be done on aluminium and iron, but the correct electrodes will have to be procured and used. Arc welding works really well on thick metals, as it generates a lot of heat and a big molten weld pool.

Mig Welding

MIG welding stands for Metal Inert Gas Welding. As the name suggests, the metal electrode is shielded with an inert gas. An inert gas is a gas that will not react with the molten steel pool, but protect it.

The different gasses that can be used are Argon, Carbon Dioxide, or a mixture of the two. This gas only protects the weld pool from interacting with oxygen (4). The actual welding process is the same as described in Arc welding. It is done with electricity, and the electrode (3) is melted as you weld. However, unlike Arc welding, MIG welding has a continuous electrode wire (3) that feeds through the welding gun and does not get shorter as you use it.

Aluminium and steel can be mig welded, but the electrode wire will have to be changed to accommodate the different metals.

It is important to keep the gas shield clean as any blockages will prevent the shield gas from properly protecting the molten weld pool (5). MIG welding is good for thick metals or thin metals, as the heat setting and pulse duration can be adjusted on the welder.

TIG welding

TIG welding stands for Tungsten Inert Gas Welding. It is the most difficult form of welding to master, but the most versatile type of welding out there. It can be done on steel, stainless steel, aluminium, brass, and even copper.

As the name suggests, it uses an inert gas just like MIG welding. Unlike MIG welding, TIG welding does not have a continuous electrode that feeds through the welding gun. Instead, it has a tungsten electrode that creates the molten weld pool and you have to feed in an additional filler rod with your other hand. This two-handed form of welding is difficult to learn, but if you can master it, it will be the most useful skill you have.

As with Arc and MIG, TIG uses electricity to form a weld pool. Tungsten is used for the electrode because it does not melt easily but conducts electricity well. The initiation of the weld is controlled either on the welding gun with a push button or by foot with a foot pedal. TIG welding is also referred to as GTAW, short for Gas Tungsten Arc Welding.

SPOT welding

Spot welding, as the name suggests, only welds one spot at a time. There is no filler material used, and this type of welding is mostly used on thin sheet metal.

Spot welding is used mainly in the automotive industry. It is the main method of welding used to build a car frame. Two electrodes that are made from copper push down onto two pieces of sheet metal. A high amperage electrical current is passed through the electrodes and sheet metal in turn causing the sheet metal to heat up and melt together in that spot.

The copper does not heat up and melt because it has a very low resistance to electrical flow. It is important not to use the spot welder continuously or without sheet metal between the electrodes. Spot welding can only be done on sheet metal up to 1mm thick. Bigger industrial spot welders can go thicker, but not the small handheld welders.

Gas Welding

As stated earlier, to melt metal you need to generate heat; Gas welding is the oldest form of welding and uses combustable gasses that are accelerated with oxygen to melt metal and form a weld pool.

Some types of gas welding are Oxy-Acytylene welding and Oxy-Propane welding. In both types of gas welding, the fuel gas and oxygen gas are mixed in the torch. The ratio of fuel to oxygen is important to get the most efficient and hottest flame. If a flame is red, it has too much fuel, and if a flame is blue with a gap between the torch and the flame, it has too much oxygen.

Do not confuse a welding torch and a cutting torch as one is for cutting through metals and one is for welding metals together.

Because this form of welding uses combustible gasses, it is inherently dangerous. These gasses can accumulate and either combust or suffocate someone. Always check that the gas bottles are properly closed and inspect them for leaks often.

Gas lines need to be replaced every three years.

SAFETY

As with all forms of welding, PPE is essential. The radiation from electrical welding can cause damage to your DNA which can cause cancers. The gasses used with electrical and gas welding can combust or suffocate you. Always think about safety before welding.

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