Basic principle of high frequency welding

The so-called high frequency refers to the AC current frequency of 50 Hz, and generally refers to a high frequency current of 50 KHz to 400 KHz. There are two peculiar effects when high-frequency current passes through metal conductors: skin effect and proximity effect. High-frequency welding is the use of these two effects to weld metal tubes. So, what are these two effects?
Skin effect: It means that when an alternating current of a certain frequency passes through the same conductor, the current density is not evenly distributed across all sections of the conductor, it will mainly concentrate on the surface of the conductor, that is, the current density on the surface of the conductor is large, The density inside the conductor is small, so we visually call it: "skin effect". The skin effect is usually measured by the penetration depth of the current. The smaller the penetration depth value, the more significant the skin effect. This penetration depth is proportional to the square root of the conductor's resistivity and inversely proportional to the square root of frequency and permeability. In layman's terms, the higher the frequency, the more concentrated the current is on the surface of the steel plate; the lower the frequency, the more dispersed the surface current. It must be noted that although steel is a conductor, its magnetic permeability will decrease with increasing temperature, that is, when the temperature of the steel plate increases, the magnetic permeability will decrease and the skin effect will decrease.
Proximity effect: It means that when high-frequency current flows in the reverse direction between two adjacent conductors, the current will concentrate on the edges of the two conductors. Even if the two conductors have a shorter side, the current does not follow With a shorter route flow, we call this high-frequency machine_high-frequency welding machine type effect: "proximity effect".
The proximity effect is essentially due to the inductive reactance, which plays a dominant role in high-frequency currents. The proximity effect increases as the frequency increases and the distance between adjacent conductors becomes closer. If a magnetic core is added around the adjacent conductors, the high-frequency current will be more concentrated on the surface of the workpiece.
These two effects are the basis of high-frequency welding of metals. High-frequency welding uses the skin effect to concentrate the energy of high-frequency current on the surface of the workpiece; and uses the proximity effect to control the position and range of the high-frequency current flow path. The speed of the current is very fast. It can heat and melt the edges of the adjacent steel plates in a short time, and realize the butt joint by extrusion.