Spot Welding

 

Another type of commercial and industrial welding is so-called “spot” welding. The car in your driveway was manufactured with hundreds of spot welds, on the frame, the body, the suspension, etc.

When you see those big robotic machines welding cars in automobile factories, what they’re most-likely doing is spot welding. And appliances like washing machines and dishwashers are constructed with spot welds as well, as is the toolbox in your garage.

Almost any factory or process that involves joining pieces of sheet metal together uses spot welding for the task. This type of automated resistance welding is accomplished by taking the two components that are to be joined and placing them between the electrodes of the spot welding unit. The actual weld only takes an instant, due to the high electrical current involved, making this a very fast way of joining sheet metal parts.

The electrode or electrodes used by spot welders conduct large amounts of current to the weld point, fusing and forging the two work pieces together. The weld cycle is controlled by the amount of time involved, the amount of pressure applied to the work pieces, and the amount of current flowing through the electrode. All three are need to raise a volume of molten metal and form a weld pool. Then the current is removed and the weld pool is allowed to cool under pressure, until the weld has set and the two pieces are permanently joined together. This is also known as the welder hold time.

If any of the above three parameters are changed without then adjusting the other two, a poor weld is usually the result. All three need to work in balance for the optimum bond to take place. For example, if the electrode current is increased, and without adequate pressure being applied, then excessive weld splash will be the result. On the other hand, if the pressure is changed without adjusting the current and time, then the result could be a poor quality weld as well.

With this type of resistance welding, the welding efficiency will be reduced considerably by electrical impedance. And this type of electrical impedance is measured by how much opposition is presented by an electrical circuit to the passage of current when a voltage is applied. In spot welding, or other resistance welding, this resistance is increased when the distance that the current needs to follow through to the welding electrodes is increased, and reduced when the distance is reduced.

Spot welding is cost effective

While spot welding is used in large-scale manufacturing, that doesn’t mean it’s a welding method that’s beyond the capabilities of smaller operations as well. Just about any metal fabrication shop can utilize spot welding without having to invest in a lot of expensive equipment.

Mild and low-carbon steel can be spot welded with inexpensive equipment, for example. And a body shop spot welder can be operated from most TIG, MIG and arc welding power supplies with no additional modifications.

The only exception to this is for spot welding aluminum. It takes a large, very expensive spot welder to weld aluminum, as this metal takes a lot more precision to weld then does regular steel.

 


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