Spot Welding Machine Introduction

Spot welding machines are divided into universal type (general type) and special type according to their uses; single-point type, double-point type and multi-point type according to the number of welding points welded at the same time; single-sided type and double-sided type according to the conduction method; foot-operated type, motor-cam type, pneumatic type, hydraulic type and compound type (pneumatic and hydraulic type) according to the transmission method of the pressure mechanism; non-automatic type and automatic type according to the operation characteristics; fixed type, mobile type or portable type (hanging type) according to the installation method; vertical stroke (electrode moves linearly) and circular stroke according to the moving direction of the active electrode (usually the upper electrode) of the welding machine; industrial 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) according to the supply method of electric energy.
When the workpiece and the electrode are fixed, the resistance of the workpiece depends on its resistivity. Therefore, resistivity is an important property of the welded material. Metals with high resistivity have poor conductivity (such as stainless steel) and metals with low resistivity have good conductivity (such as aluminum alloy). Therefore, it is easy to generate heat but difficult to dissipate heat when spot welding stainless steel, and it is difficult to generate heat but easy to dissipate heat when spot welding aluminum alloy. When spot welding, the former can use a smaller current (several thousand amperes), while the latter must use a large current (tens of thousands of amperes). 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 molten core and the strength of the weld, the welding time and welding current can complement each other within a certain range. In order to obtain a weld of a certain strength, a large current and a short time (strong condition, also known as hard specification) can be used, or a small current and a long time (weak condition, also known as soft specification) can be used. Whether to use hard or soft specifications depends on the performance, thickness and power of the metal welding machine used. There is an upper and lower limit for the current and time required for metals of different performance and thickness, which shall prevail when used.
The electrode pressure has a significant effect on the total resistance R between the two electrodes. As the electrode pressure increases, R decreases significantly, while the increase in welding current is not large and cannot affect the reduction in heat generation caused by the reduction in R. Therefore, the strength of the weld spot always decreases as the welding pressure increases. The solution is to increase the welding current while increasing the welding pressure.