High Frequency Welding: Classification and Development

High Frequency Welding: Classification and Development

High frequency welding is a popular welding technique that offers many advantages over traditional welding methods. It is divided into two categories: high frequency resistance welding and high frequency induction welding.

High frequency resistance welding involves using a roller or contact point to guide high frequency current into the workpiece. This method is suitable for continuous longitudinal seam welding of pipes, spiral lap welding, boiler fin tubes, and heat exchanger spiral fins. It can weld pipes with an outside diameter of 1200mm, wall thickness of 16mm, and thick flanges of I-beams up to 9.5mm. It has a high production rate.

On the other hand, high frequency induction welding uses an induction coil to heat the workpiece. It is suitable for welding small-diameter pipes with an outer diameter of 9mm and thin-walled pipes with a wall thickness of 1mm. It is commonly used for longitudinal seam welding of medium and small-diameter steel pipes and brass pipes, as well as for circular seam welding. However, its power loss is higher than that of high frequency resistance welding. The main parameters affecting the quality of high-frequency welding are the frequency, power, angle of the workpiece, extrusion force, distance between electrodes (or induction coils) and extrusion rollers, and welding speed. The main equipment includes a high-frequency power source, a workpiece shaping device, and an extrusion mechanical device. High-frequency welding provides stable quality, high productivity, and lower cost. It is suitable for efficient automatic production lines and is an advanced method for producing seamless pipes.

Equipment for High Frequency Welding

Understanding the principles of high frequency welding is not enough; it needs to be implemented using the necessary technical means. High-frequency welding equipment is an electrical-mechanical system used to implement high-frequency welding. It consists of a high-frequency welding machine and a pipe forming machine. The high-frequency welding machine usually consists of two parts: a high-frequency generator and a feed device. Its function is to generate high-frequency current and control it. The shaping machine consists of an extrusion roller frame, which is used to extrude the part melted by high-frequency current, remove the oxide layer and impurities on the steel plate surface, and completely fuse the steel plate.

The earlier high-frequency generators used in welding pipe units were three circuits: a high-frequency power generator, a solid-state frequency converter, and an electronic high-frequency oscillator. Later they were mostly improved to single circuit ones. There are many methods for adjusting the output power of the high-frequency oscillator, such as autotransformer, reactance method, thyristor method, etc.

Feed Device

This is used to transmit high-frequency current to the tube and includes electrode contacts, induction coils, and impedance devices. In contact welding, wear-resistant copper-tungsten alloy electrode contacts are generally used, while purple-copper induction coils are used in induction welding. The main component of the impedance device is the magnetic core, which increases the surface impedance of the tube to reduce the ineffective current and improve the welding speed. The magnetic core of the impedance device is made of ferrite, and its Curie point temperature should not be lower than 310°C. The Curie point temperature is an important indicator of the magnetic core. The higher the Curie point temperature, the closer it can be to the weld seam, the higher the welding efficiency.

CRU and IMC are the two main parts of the machine. CRU includes a rectifier section with a main isolating switch and a full bridge diode rectifier (which converts AC to DC), and a controller with control devices and external control equipment interfaces. IMC includes an inverter module, a matching transformer, and a capacitor group that provides reactive power necessary for the induction coil. Since the introduction of high-frequency welding technology from abroad in the 1950s, it has been widely used in industrial production. High frequency welding technology has received high attention from the National Construction and Science and Technology departments, and has been listed as a key promoted technology for science and technology achievements in the National Construction Department. The National Construction Department has also issued national industry standards for high-frequency welding. Since then, this welding technology has continuously gained market share in the construction field.

Currently, China’s high-frequency welding technology has developed rapidly. Its excellent welding quality and economic effects have broadened its application fields, especially in the steel structure industry. Major projects such as the Shanghai Qingpu Sports Center, the Pearl Line Light Rail, the Shanghai Railway Station, the Nanjing Railway Station, and the Dalian Shipyard Project all use this high-frequency welding technology. The development of China’s high-frequency welding technology has enhanced its innovation capability, and the demand for it in the market is very strong. However, weak foundations still exist for its development. In the next ten to fifteen years, China’s high-frequency welded steel pipe industry will enter a stage of rapid development.


If you are looking for a reliable and efficient welding technique, consider high frequency welding. With its stable quality, high productivity, and lower cost, it offers many benefits compared to traditional welding methods. If you are interested in implementing high frequency welding, make sure to use the necessary technical means, including a high-frequency welding machine and a pipe forming machine. Don’t hesitate to explore this advanced method for producing seamless pipes and improve your business’s efficiency. Contact us today to learn more about how high frequency welding can benefit your industry.