Welding current
Since the heat generated by the resistance is proportional to the square of the passing current, the welding current is an important factor in generating heat. Butt welding machine. The importance of welding current does not simply refer to the size of welding current, but also the level of current density.
※Nugget: refers to the metal part that solidifies after melting at the joint during lap resistance welding.
pressure
The pressure in the welding process of the spot welder is an important factor in the heat generation. Pressurizing force is the mechanical force applied to the welding place. The contact resistance is reduced by the pressurizing force, and the resistance value is made uniform, which can prevent local heating during welding and make the welding effect uniform.
Power-on time
The power-on time is also an important factor in generating heat. The heat generated by power-on is released by conduction. Even if the total heat is constant, due to the different power-on time, the high temperature of the welding place will be different, and the welding results will be different.
Current waveform
The combination of heat generation and pressure in time is very important to the spot welding machine, so the temperature distribution at each moment in the welding process must be appropriate. According to the material and size of the object to be welded, a certain current flows for a certain period of time, and if the pressure of the contact part is delayed, it will cause local heating and deteriorate the welding effect of the spot welding machine. In addition, if the current is stopped suddenly, cracks and material embrittlement will occur in the welded part due to rapid cooling. Therefore, a small current should be passed before or after the main current, or pulses should be added to the rising and falling currents.
[Example] There is deformation and strain in thick plates and press-formed products. In order to make the plates tightly bonded after welding, a small current is flowed to preheat before the main current.
[Example] For materials that will produce thermal hardening or cracks, after the main current flows, post-heating is performed with a small current to achieve annealing treatment.
surface state of the material
Contact resistance is a factor directly related to the heat generation of the contact part. When the pressure is constant, the contact resistance is determined by the surface state of the solder, that is, after the material is determined, the contact resistance is determined by the small unevenness and oxide film on the metal surface. Small unevenness is beneficial to obtain the desired heating range of the contact resistance, but due to the existence of the oxide film, the resistance increases, which will lead to local heating, so it should be removed.
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