This is a detailed guide to the use of high frequency welding that will help you understand how HF welding equipment works in a welded pipe production line.
Unlike other welding methods, High Frequency Welding (HFW) is a method of joining materials using electromagnetic energy (high frequency electromagnetic waves) to produce a strong, reliable weld, and HFW is an important step in the welded pipe production process. Confusing terminology such as rectifier cabinets, SCRs, IGBTs, etc. can be overwhelming.
This article will explain what HF welding is, the workflow of HF welding and its application in the welded pipe industry.
Table of Contents
What is High Frequency Welding
High Frequency Welding is an advanced method that uses electromagnetic energy to efficiently fuse materials with strong and durable results. Unlike traditional welding methods that rely on heat from an external source, HF welding generates heat internally within the materials being welded. This unique feature allows for precise control over the welding process, resulting in high-quality welds that are often stronger than the materials themselves.
HF welding is highly versatile, capable of joining multiple layers of thermoplastic materials simultaneously. This makes it ideal for applications requiring airtight, gas-tight, and waterproof welds, such as medical supplies, automotive components, and technical textiles.
The main function of high frequency welding equipment is to create precise and durable welds through controlled energy application, ensuring consistent seam quality without the need for adhesives.
The Development of High Frequency Welding
Since the invention of high-frequency welding technology based on Faraday’s principle of electromagnetic induction at the beginning of the 20th century, its industrialized application in the field of welded pipe has experienced three key stages:
1. HF Welding Technology germination (1920s-1950s)
High-frequency induction heating was first applied to sheet metal welding, 1930s German engineers successfully developed the first HF welding pipe unit, At this time, the HF welding technology is limited by the bottleneck of thyristor technology, the frequency can only be stabilized at 10-20 kHz, the main production of small-diameter (DN150 or less) low-pressure pipe.
2. Industrialization maturity period (1960s-1990s)
With the innovation of power electronic devices (e.g. thyristor, IGBT), the welding frequency breaks through to 50-100 kHz, and the thermal efficiency increases by 30%. The U.S. API standard promoted the large-scale application of the technology in the field of oil and gas pipelines, and the successful welding of X65 high-strength steel in the 1980s marked the entry of HF welded pipes into the mainstream market of long-distance pipelines. Japanese companies such as Sumitomo developed a multi-stage hydraulic servo pressure roller system to increase the welding speed to 8-12 m/s.
3. Intelligent upgrading period (2000-present)
The integration of digital twin technology and 5G communication enables real-time parameter feedback accuracy of ±0.01%, and the high-frequency-laser composite welding process realizes high-speed welding of 0.5 mm ultra-thin plates (30 roots/minute). China used 80 kHz high-frequency welding machine in the second line of the West-East Natural Gas Transmission Project, the weld pass rate of 99.92%, the annual production capacity of a single production line exceeded 500,000 tons, and the energy consumption is 65% lower than the traditional resistance welding. Currently, the technology is expanding to the field of welding dual-phase steel (such as X80) for marine engineering, and the heat-affected zone is controlled within 1.2 mm through nanoscale surface treatment.
High Frequency Welding Process in The Field of Welded Pipe
High frequency welding machines are an integral part of the steel pipe manufacturing process. Generally called solid state high-frequency welding.
Solid state welders are mainly categorized into two topologies: series-type welders and parallel-type welders. Parallel type high frequency welding equipment adopts DC voltage regulator + slot road adjustment to realize impedance matching. Series-type high frequency welding equipment adopts inverter-side power regulation technology to realize the impedance matching of the welder.
IGBT chopper regulator + IRF460mosfet low voltage inverter + parallel resonance
It consists of five major parts: SCR full-wave rectification, IGBT high-frequency inverter + PWM voltage regulation, high-frequency transformer, FRED fast recovery diode module high-frequency rectification, and E-type bridge inverter output. Among them, the rectifier + PWM AC voltage regulation is completed by a circuit board. Embedded in the motherboard PWM control unit board, unit board by the microcontroller + PWM control system to complete the main functions, combined with the motherboard’s double closed-loop PI regulator to complete the voltage regulation and feedback control, alarm control by the digital circuit for the control core combined with the hardware’s fast response to make the protection action sensitive.
Solid-state high-frequency integrated machine due to the use of full-wave rectifier IGBT inverter power modulation, do not need to adjust the SCR phase-shifting angle, so it has a high power factor, power-saving effect is good, and at the same time can save the incoming cable cross-sectional area and other advantages!
SCR Rectifier + SiC Silicon Carbide High Voltage Inverter + Series Resonance
Series-connected solid-state HF welding machine is a typical AC-DC-AC inverter structure. The rectifier adopts three-phase bridge thyristor phase-controlled rectifier circuit, and the DC side adopts inductor and capacitor to form LC filter to meet the working requirements of voltage inverter.
The voltage inverter adopts a modular parallel structure to extend the power supply, the power switching device used in the inverter module is SIC-MOSFET, and it adopts a unidirectional H-bridge circuit, and each inverter module is connected through a high-frequency matching transformer and a series resonance slot circuit.
Matching transformer on the one hand to achieve power synthesis and impedance matching, on the other hand, to achieve electrical isolation of the load and power supply. The whole HF welder has a compact structure, small size, easy maintenance and low failure rate. For effective and fast protection against voltage type inverter overcurrent faults
SiC-MOSFET Solid State High Frequency Welder
Development of semiconductor materials
Semiconductor (Semiconductor) is the physical cornerstone of the modern electronic information society, power semiconductor devices is precisely the semiconductor industry is one of the subcategories of the large industry, from the power grid, high-speed rail, industrial electrical products and other high-power equipment, to home appliances, digital products, cell phones and other low and medium-power daily consumer electronics, power semiconductor devices play an indispensable role in the conversion of electrical energy, the role of the supply.
1906 Lee DeForest invented the vacuum tube (electron tube)
The first generation of semiconductor materials: germanium (Ge), silicon (Si), silicon-based semiconductor materials, solid-state power electronics era
Second-generation semiconductor materials: gallium arsenide (GaAs), indium phosphide (InP)
Third-generation semiconductor materials: silicon carbide (SiC), gallium nitride (GaN), the era of wide-band semiconductor materials
Performance characteristics of SiC, a third-generation semiconductor material
With the continuous application of 5G technology, the RF chip market is evolving towards high frequency and high power, and GaN will become the most important solution material in this field.
When the power conversion field advances to high voltage and high power, SiC will become the most effective semiconductor material in the field of power devices due to its advantages in high temperature, high voltage and high frequency.
Applications of Power Semiconductor Devices
Three advantages of silicon carbide MOSFETs over silicon-based devices
Low resistance: Silicon carbide devices have higher thermal conductivity and power density, which can simplify the heat dissipation system, thus realizing device miniaturization and lightweight.
low loss, high frequency: silicon carbide device operating frequency up to 10 times the silicon-based devices, and the efficiency does not decrease with the increase in operating frequency, can reduce the energy loss of nearly 50%; at the same time, due to the frequency of the enhancement of the inductors, transformers, and other peripheral components to reduce the size of the composition of the system after the cost of the volume and other components
High-temperature and high-pressure resistance: Silicon carbide power devices can theoretically reach an operating temperature of more than 600 ℃, which is four times that of the equivalent silicon-based devices, and the pressure resistance is 10 times that of the equivalent silicon-based devices, so they can withstand more extreme operating environments.
Advantages of SiC-MOSFET high frequency welding machine
(1) MOS device loss reduction of 68% ! Welder body efficiency increased by 8-16%, HF welding efficiency increased by about 5-10%!
(2) SiC-MOSFET internal integration of anti-parallel SiC-Diod, external wiring is greatly simplified, reducing the failure point, reducing external electromagnetic radiation, and improve the overall safety of the high frequency welding machine.
(3) The layout of resistive-capacitive absorption circuit (R+C) has been optimized, and the shorter RC leads bring good absorption effect, perfect inverter waveform, and heat generation of the inverter unit is greatly reduced.
(4) The original Si-MOSFET withstand voltage 1000V, in order to ensure the safety of the welder DC voltage rated at 450V, mesh-side power factor of about 0.9; the new SiC-MOSFET withstand voltage 1200V, in order to ensure the safety of the premise of the welder DC voltage rated at 500V, mesh-side power factor of about 0.95.
(5) The new SiC-MOSFET package is exactly the same as the original Si-MOSFET; the new power unit and the original power unit installation method, installation size is completely compatible with the site upgrade and transformation is simple and easy.
(6) The new SiC-MOSFET device loss is only 32% of the original Si-MOSFET, so under the premise of certain cooling conditions, the switching frequency can be higher. Can be directly produced at frequencies higher than 600kHz welder (the original Si-MOSFET welder using frequency doubling technology), greatly reducing the size of the welder, reducing the cost of the welder.
(7) The new Si-MOSFET high-frequency welder has a DC voltage as high as 500V, small net-side AC current, low harmonic current and high power factor, which greatly reduces the cost of power supply and distribution for customers and effectively improves the efficiency of power supply.
Process structure of SiC-MOSFET high frequency welding machine
(1) Using SOT227 package single tube module, exactly the same as the original Si-MOS package, good replaceability;
(2) 62mm half-bridge module structure is being developed, which can greatly improve the integration degree of the welder and reduce the size of the welder;
(3) can produce high-frequency induction heating power supply with larger power level (>4500kW).
(4) Using SOT227 package single tube module, exactly the same as the original Si-MOS package, good replaceability;
(5) 62mm half-bridge module structure is being developed, which can greatly improve the integration degree of the welder and reduce the size of the welder;
(6) can produce high-frequency induction heating power supply with larger power level (>4500kW).
Load Matching for Solid State HF Welders
Load Matching (Impedance Matching)
A poor load match is one in which the voltage reaches the rated value first and the current is less than the rated value (light load, left side of the graph), and two in which the current reaches the rated value first and the voltage is less than the rated value (heavy load, right side of the graph).
Commonly used methods of regulating load matching:
1) Adjusting the number of inductor turns, diameter, and width;
2) change the parameters of the groove road (parallel type welder, change the series and parallel adjustable reactor);
(3) change the matching transformer ratio (series-type welder, the adjustment level difference is large and discontinuous);
(4) welding machine inverter side adjustment (series-type welder specific).
- adjust the frequency (20kHz or less intermediate frequency / ultra-audio power supply, power device loss)
pulse phase shift (small adjustment range, power device loss)
pulse density (PDM, large adjustment range, power fluctuations)
pulse shielding (PSM)
Pulse shielding technology
Pulses Shielded Modulation (PSM) is a new type of inverter-side power regulation technology, which is an upgrade of the traditional uniform pulse density technology (PDM). This technology regulates the output power of the welder by dynamically adjusting the duty cycle of the inverter pulses (which is equivalent to automatically changing the refractory impedance of the load) after ensuring that the DC voltage reaches the maximum rated value.
1) The best way to solve the load matching problem of the welding machine
For pipe welding of different sizes or different welding methods, the rated power output can be achieved without changing any parameters of the welder, giving full play to the capabilities of the solid-state high-frequency welder while ensuring a relatively minimum operating current. Figures 6 and 7 depict the V-I volt-ampere characteristics of pulse shielding technology.
The most typical load mismatch application is the contact/induction bifunctional welder, where pulse shielding technology does not require any adjustment of the electrical parameters or electrical structure to switch weld states and ensure that the rated power output can be achieved in both modes.
2) High power factor, low harmonic content
The solid-state HF welder with pulse shielding technology (PSM) has the highest constant power factor (>0.9) and the smallest harmonic current. Therefore, the welder does not need to add additional reactive power compensation and harmonic elimination devices, reducing the capacity of the power supply transformer, reducing the incoming cable loss, and significantly improving the overall power efficiency.
3）Safety and reliability are significantly improved
Pulse shielding technology (PSM) so that the MOS tube has been working in the resonant soft switching state, the lowest switching loss. Conventional frequency control, pulse phase-shift control and other inverter power control methods, the operating environment destroys the resonant soft switching conditions of the MOS tube, in the realization of part of the load matching (generally not more than 20%) function, increases the switching loss of the MOS device, reduces the safety and reliability of the welder.
Advantages of high-frequency welded pipe
HF Welded Pipe has the following significant advantages:
High efficiency and energy saving: High-frequency current rapidly heats up the weld area through electromagnetic induction, with concentrated energy and high thermal efficiency, the welding speed can be up to 20-50 meters/minute, which greatly improves the production efficiency, and at the same time, the energy consumption is reduced by more than 30% compared with that of traditional electric arc welding.
Excellent weld quality: HF welding through the pressure extrusion of molten metal, the formation of dense and uniform weld, the strength of the base material can reach more than 90%, and the heat-affected zone is narrow, small deformation, and significantly improve the mechanical properties of the pipe and dimensional accuracy.
Strong material adaptability: can weld carbon steel, stainless steel, alloy steel and other metals, especially suitable for the production of thin-walled pipe (0.5-12mm), widely used in oil and gas transportation, automotive exhaust, building structures and other fields.
Environmental protection and low consumption: no need for welding rods, flux and other filler materials, reducing fume and slag pollution, in line with the trend of green manufacturing.
Cost advantage: continuous automated production to reduce manual intervention, equipment maintenance is simple, the overall cost is lower than submerged arc welding or laser welding or other welding methods, suitable for high-volume industrialized manufacturing.
HF welded pipe has become one of the preferred technologies for pipe manufacturing in modern industry by virtue of its high cost performance, stability and process flexibility.
Conclusion
In the field of pipe welding, whether it is parallel HF welding or series HF welding, there are application scenarios, the new SiC-MOS HF welding machine + pulse shielding technology has its unique advantages. high efficiency, stability and intelligence is the eternal pursuit of the steel pipe high frequency welding industry!
Get the best HF welding equipment solutions
New Victor Tube Mills is a Chinese manufacturer of HF welding pipe production line, known for its superior quality High frequency pipe welding equipment. We provide professional and customized welded pipe solutions to customers all over the world. Make your business a success with the New Victor. Contact us today!