According to the use, the spot welding machine has a universal type (universal type) and a special type; according to the number of solder joints welded at the same time, there are single-point type, double-point type, and multi-point type; Bilateral; according to the transmission mode of the pressurizing mechanism, there are pedal type, motor-cam type, pneumatic type, hydraulic type, composite type (pneumatic-hydraulic type); according to the characteristics of operation, there are non-automation and automation; according to The installation method is divided into fixed type, mobile type or portable type (suspension type); according to the moving direction of the movable electrode (usually the upper electrode) of the welding machine, there are vertical stroke (the electrode moves in a straight line) and arc stroke; According to the power supply mode, there are power frequency welding machine (using 50 Hz AC power supply), pulse welding machine (DC pulse welding machine, energy storage welding machine, etc.), variable frequency welding machine (such as low frequency welding machine).
When the workpiece and the electrode are fixed, the resistance of the workpiece depends on its resistivity. Therefore, the resistivity is an important property of the material to be welded. The metal with high resistivity has poor conductivity (such as stainless steel) and the metal with low resistivity has good conductivity (such as aluminum alloy). Therefore, it is easy to generate heat and dissipate heat when spot welding stainless steel, and it is difficult to generate heat and dissipate heat easily when spot welding aluminum alloy. When spot welding, the former can use a small current (several thousand amperes), while the latter must use a large current (a few thousand amperes). million amps). The resistivity depends not only on the type of metal, but also on the heat treatment state, processing method and temperature of the metal.
In order to ensure the size of the nugget and the strength of the welding spot, the welding time and the welding current can complement each other within a certain range. In order to obtain a solder joint of a certain strength, high current and short time (strong condition, also known as hard specification) can be used, or small current and long time (weak condition, also known as soft specification) can be used. The choice of hard or soft specification depends on the properties of the metal, the thickness and the power of the welding machine used. There is an upper and lower limit for the current and time required for metals with different properties and thicknesses, which shall prevail when used.
The electrode pressure has a significant effect on the total resistance R between the two electrodes. With the increase of the electrode pressure, R decreases significantly, while the increase of the welding current is not large, which cannot affect the reduction of heat generation caused by the decrease of R. Therefore, the joint strength always decreases as the welding pressure increases. The solution is to increase the welding current while increasing the welding pressure.
