Spot welder working principle

Update:15 Nov 2019

The process of spot welding is to open the cooling wate […]

The process of spot welding is to open the cooling water; the surface of the weldment is cleaned and assembled accurately, and then fed between the upper and lower electrodes, and the pressure is applied to make the contact good; the contact between the two workpieces is heated and partially melted. The nugget is held; after the power is turned off, the pressure is maintained, and the nugget is cooled and solidified under pressure to form a solder joint; the pressure is removed, and the workpiece is taken out. Spot welding process parameters such as welding current, electrode pressure, energization time and electrode working surface size have a significant impact on welding quality.

The spot welder uses the high temperature arc generated by the positive and negative poles in an instantaneous short circuit to melt the material to be welded between the electrodes to achieve the purpose of combining them. The structure of the spot welder is very simple. To put it bluntly, it is a high-power transformer that turns 220V AC into a low-voltage, high-current power source, which can be either DC or AC. The electric welding transformer has its own characteristics, which is characterized by a sharp drop in voltage.

After the welding rod is ignited, the voltage drops, and the working voltage of the welding machine is adjusted. In addition to the 220/380 voltage conversion once, the secondary coil also has a tap change voltage, and there is also an iron core to adjust the adjustable iron core. The electric welder is generally a high-power transformer made by the principle of inductance. When the inductance is turned on and off, a large voltage change occurs, and the high-voltage arc generated by the positive and negative poles in an instantaneous short-circuit is used to melt the solder on the electrode. To achieve the purpose of combining them.

Spot welding is a method of resistance welding of solder joints by soldering the joints and pressing them between the two electrodes, using a resistance heat to melt the base metal. Spot welding is often used for thin-plate connections such as aircraft skins, aero-engine chimneys, and car cab casings. The spot welder welding transformer is a spot welding appliance, and its secondary has only one loop. The upper and lower electrodes and the electrode arm are used both to conduct welding current and to transmit power. The cooling water passage passes through the transformer, the electrode, etc., so as to avoid heat welding, the cooling water should be passed first, and then the power switch is turned on. The quality of the electrodes directly affects the welding process, weld quality and productivity. The electrode material is commonly made of copper, cadmium bronze, chrome bronze, etc.; the shape of the electrode is various, and is mainly determined according to the shape of the weldment. When installing the electrode, be careful that the upper and lower electrode surfaces are kept parallel; the electrode surface should be kept clean and usually sanded or trowel trimmed. The welding cycle of spot welding and projection welding of welding cycles consists of four basic stages (spot welding process):

(1) Preloading phase—The electrode is lowered to the current-on phase to ensure that the electrode is pressed against the workpiece so that there is proper pressure between the workpieces.

(2) Welding time - the welding current passes through the workpiece, and heat is generated to form a nugget.

(3) Maintenance time - The welding current is cut off and the electrode pressure is maintained until the nugget solidifies to a sufficient strength.

(4) Rest time - the electrode starts to lift until the electrode begins to fall again, starting the next welding cycle.

In order to improve the performance of welded joints, it is sometimes necessary to add one or more of the following to the basic cycle:

(1) Increase the pre-pressure to eliminate the gap between the thick workpieces and make them fit snugly.

(2) Use the preheating pulse to improve the plasticity of the metal, so that the workpiece can be easily fitted tightly and prevent splashing; in the case of projection welding, multiple bumps can be uniformly contacted with the flat plate before energization welding to ensure uniform heating at each point.