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Posted on Jan 9, 2021
A spot welding machine is also commonly called a resistance spot welder. Spot welding machine can fuse two or more sheet metals via a heating process performed on the welding point, where the pressure is applied after the metal melts.
A spot welding machine is also commonly called a resistance spot welder. The welding equipment is utilized in a metalworking environment to fuse multiple sheet metals together. Welding operations refer to the metal fabrication process which joins a wide variety of metals or plastics together. Many sorts of welding methods need to work at a high temperature in order to melt the metals, and then weld the molten metal area to form the welding joint, the permanent connection.
Spot welding machine can fuse two or more sheet metals via a heating process performed on the welding point, where the pressure is applied after the metal melts. Spot welding is a type of “electric resistance welding”. In resistance spot welding operations, the heat is generated due to the resistance to the electric currents which stably conveyed to the welding area.
Spot welders are suitable for industrial production and assembly lines of automotive and aerospace components as well as the welding applications in the rail industry, electronic, medical, and other industries. The welding process is one of the most classic metal forming processes. With the evolvement and incorporation of robots and other automation techniques, smart spot welders are rapidly increasingly popular for mass metal production.
Spot welding typically uses alloy copper electrodes to deliver the currents through workpieces in the working area. Then the metals will melt because of the high heat generated from the resistance while the power is concentrated to a tiny welding spot under pressure. Copper is the common material the electrodes are made of since the metal has great heat conductivity as well as low electrical resistance. As a result, the heat generated on the surfaces of the metal sheets instead of the electrodes.
Applying a great current to the spot in a short period of time will effectively melt the raw materials in the spot welder to complete the weld. When the electric currents turn off and the electrode pressure keeps working on the joint, the molten sheet metals are fused and later solidified, cooling down by the water cooling system. The energy efficiency of a spot welding machine is defined by the power supply, the magnitude, and also the resistance among electrodes. Also, the metals’ properties, as well as thickness, are also important to productivity.
In general, the thickness of the sheet metal is ranged from 0.5 to 3mm. In the case when the energy transferred to the welding area is not enough to fully melt the raw materials, the resistance spot welder will create a poor weld. However, if supplying too much energy to the joint, the heat may create a hole on the surface eventually.
:: Read more: An Overview of Spot Welding Sheet Metal
The spot welding machine specifications that the user should consider when selecting the best suitable equipment including the rated capacity, the cooling system which is typically air or water type, the range of welding voltage, and the power supply which is typically 220V or 440V, the body size, the throat depths which range from 12’’ to 30’’ and more, and also a different design of frame and electrode holder. The frame is usually a heavy gauge that is made from full steel with a heavy-duty base and welded stiffeners to accommodate light to heavy-duty spot welding applications. On top of that, there are four variables that are essential for the resistance spot welding process, which include the pressure, the welding time, the electric current, and the tip diameter.
When it comes to the required pressure that the spot welding machine should apply to the weld, it is vital since the quality of the joint and the entire product will be significantly affected. If the pressure is not enough during the welding process, the joint will end up very small and weak. On the other hand, if there is too much pressure, cracking might happen eventually in a spot welding machine. In general, high pressure applied in welding areas leads to metal thinning and weakness to some degree. The depth of depression on the surfaces of the materials resulting from the electrodes should not exceed 25% of the thickness of the metal parts.
The weld current (i) and the weld time (t) in a spot welding machine are inversely proportional. The current and time mentioned here are used to bring the metal to welding temperature, typically 1400°C. As for the weld current, the general welding current used in general metalwork shops ranges from 3000 to 5000 A. The weld current as well as the weld time is set by the operators while the resistance is defined by the type of the welded parts. The adjustment of weld current is always more significant and dramatic to the whole spot welding process than the changes in weld time.
Welding current settings are extremely significant for welding machines and also for buyers when selecting the right equipment, especially for today’s vehicle manufacturers. If the weld current is relatively very low, the corresponding weld time should be increased; when the current is higher, the weld time should be decreased. While using lower current in the spot welding machine, it might end up overheating the welding tools as well as the weld transformer.
However, if using a higher weld current, the risks of expulsion are increased. Expulsion refers to the problem of molten metal squirting from the multiple steel layers. In the automotive industry, the galvanized coatings of automotive parts also increase the risks of expulsion during spot welding. Therefore, it is very important to select a spot welder that has the ability to control the weld current well with easier settings.
Last but not least, the welding tip diameter is also vital in the welding process. The tips, which have flat faces when they are new, and the faces quickly crown with use, which is ideal to achieve the crowning radius ranging from 1.5 to 3 inches.
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