Induction heating uses a high-frequency current output from an induction heating device to generate an alternating magnetic field through an induction coil. This magnetic field creates eddy currents in the metal workpiece placed within the coil, rapidly heating it. The induction coil itself does not generate heat. This method has been around for decades. In the mid-1990s, all-solid-state induction heating equipment based on IGBT modules began to appear, offering 10%-40% energy savings compared to high-frequency tube and thyristor induction heating equipment. Since its introduction, it has become the most ideal heating method in the field of small-scale metal heating due to its numerous advantages, including energy saving, environmental friendliness, high processing quality, ease of operation, safe and reliable operation, and low maintenance costs. Different frequencies of induction heating equipment produce different heating effects, determining the quality of heating; the power determines the heating speed and processing efficiency of the workpiece. Therefore, selecting the correct frequency and power according to the heating requirements of the workpiece is crucial. I. How to Select the Frequency Induction heating equipment can be broadly classified according to its output frequency: ultra-high frequency, high frequency, ultrasonic frequency, and medium frequency. Different heating processes require different frequencies. If the wrong frequency is chosen, the heating requirements may not be met, resulting in slow heating time, low efficiency, uneven heating, or insufficient temperature, which can easily damage the workpiece. To correctly select the frequency, it's essential to understand the product's heating process requirements, which generally fall into the following categories: 1. Through-heating of the workpiece, such as fasteners, standard parts, auto parts, hardware tools, rigging, hot upsetting and hot rolling of twist drills, etc. The larger the workpiece diameter, the lower the frequency should be. For example: Below Φ4mm, high frequency and ultra-high frequency (100-500KHz) are suitable; Φ4-16mm, high frequency (50-100KHz) is suitable; Φ16-40mm, ultra-high frequency (10-50KHz) is suitable; above Φ40mm, medium frequency (0.5-10KHz) is suitable. 2. Heat treatment, such as shafts, gears, quenching, and annealing of stainless steel products, etc. Taking quenching as an example, the shallower the quenching layer, the higher the frequency should be; the deeper the quenching layer, the lower the frequency should be. For example: A quenched layer of 0.2-0.8mm is suitable for 100-250KHz ultra-high frequency and high frequency; 1.0-1.5mm is suitable for 40-50KHz high frequency and ultrasonic frequency; 1.5-2.0mm is suitable for 20-25KHz ultrasonic frequency; 2.0-3.0mm is suitable for 8-20KHz ultrasonic frequency and intermediate frequency; 3.0-5.0mm is suitable for 4-8KHz intermediate frequency; 5.0-8.0mm is suitable for 2.5-4KHz intermediate frequency. 3. Brazing: For brazing of drill bits, lathe tools, reamers, milling cutters, drill bits, etc., and composite welding of different materials for stainless steel pot bottoms, the larger the weld volume, the lower the frequency should be. Taking lathe tool welding as an example: Tools under 20mm are suitable for 50-100KHz high frequency; tools over 20-30mm are suitable for 10-50KHz high frequency and ultrasonic frequency; tools over 30mm are suitable for 1-8KHz intermediate frequency. 4. Smelting precious metals such as gold, silver, copper, and lead depends on the specific furnace and production efficiency. For small-capacity applications, high frequency is optional; for most applications, ultra-high frequency or medium-frequency ultra-high frequency is sufficient to meet general die-casting industry needs, typically melting 200KG of aluminum ingots per hour. II. How to Choose Power After determining the machine's frequency based on your workpiece requirements, the next step is to select the appropriate machine power according to production conditions. Higher power results in faster heating, but also increases the price. Lower power equipment is cheaper but heats more slowly. 1. Induction heating power typically has two types: output power and oscillation power. Induction heating equipment must rectify AC power to obtain oscillation current and voltage; oscillation power is the product of these two. The power usually referred to is the machine's load power, also called output power; oscillation power is only about 60% of the actual output power. For example, a 50KW oscillation power induction heating device and a 30KW output power induction heating device will have the same heating effect under the same conditions. Below is a comparison of output power/oscillation power for commonly used equipment. Currently, there is no nationally standardized model designation method for induction heating equipment, with models 25KW/42KW, 30KW/50KW, 50KW/80KW, and 80KW/125KW. Most manufacturers prefer to label their products as a combination of manufacturer's name identification number and power rating, such as XX-20, YY-60, ZZ-100, etc. Therefore, some manufacturers often label the power rating as oscillation power, while others label it as output power or simply use a general term like "power," misleading customers. Some even omit the power rating altogether, using the input current as the model number, leading customers to mistakenly believe that the following information represents the machine's power. The two are actually quite different. Induction heating equipment is typically not upgraded for a long time after purchase, and customers often regret their purchase when they realize the difference. Therefore, when a company introduces a product to you, don't just focus on the model number; remember to ask about its output power to be fully informed. 2. For processing the same workpiece, different working speeds require significantly different power selections. For example, a fastener company needs to hot-forge Φ30mm, 50mm long screws at a heating temperature of 1000 degrees Celsius and a production speed of 20 pieces/minute. In this case, a machine with an ultrasonic frequency (10-40kHz) and an output power of 80kW should be selected. If the production speed is reduced to 10 pieces/minute, a machine with an ultrasonic frequency (10-40kHz) and an output power of 50kW will suffice. The 80kW machine is more expensive than the 50kW machine. Therefore, manufacturers can choose the most suitable model based on their actual needs to avoid waste. Furthermore, power selection must also consider voltage fluctuations. For users with three-phase AC power, a 10V drop in voltage will reduce the output power by approximately 7%. Generally, when using this equipment, the heating time for a batch of workpieces is fixed. When the voltage drops, to ensure the same heating effect, the machine power should be increased. However, if your heating time is set based on the equipment's maximum power, when the voltage drops, the only way to achieve the same heating effect is to extend the heating time. This requires re-experimentation to obtain the time setting parameters, delaying production and compromising workpiece quality. Therefore, it is recommended to adjust the equipment's power output to around 85-90% of its maximum power, leaving a margin. This extends the equipment's lifespan and allows you to easily cope with the adverse effects of voltage fluctuations. III. How to Avoid Price Traps After determining the machine's frequency and power based on your workpiece requirements, you need to select an appropriate supplier based on your production needs. Price is naturally a major concern, and avoiding price traps will be another issue. Currently, with the widespread use of IGBT induction heating equipment, there are many manufacturers. However, in the small-scale (400KW) field, only a handful of companies nationwide possess independent intellectual property rights, a high-level independent R&D team, and a full range of products. Most companies simply imitate and assemble. Therefore, even between different manufacturers, products with the same power (calibrated) can have significant quality differences. Buying a practical, affordable, and high-quality product is what every user hopes for. Since the price of equipment is closely related to its power output—the higher the power, the higher the price—falsely labeling power output is a common way to mislead customers. This typically manifests in the following ways: 1. Labeling the power as oscillation power. 2. Companies labeling oscillation power as output power or simply stating it as power. 3. Omitting the power output and instead labeling the input current as the model number, misleading customers into believing that the following text indicates the machine's power. 4. Randomly labeling low power as high power. Compared to the above, the following situation is even worse. Some domestic manufacturers, in pursuit of exorbitant profits, adjust certain parameters of IGBT modules to increase the power of low-power equipment. For example, they might adjust a 30KW device to 40-50KW and sell it as a 45KW device. The result is that the equipment is overloaded, shortening its lifespan. A product that should normally last 5 years may become unusable within one or two years. Customers may not notice this in the short term, but it's only a matter of time before it becomes unusable. Furthermore, changes in parameters worsen equipment compatibility, leading to severe mutual interference, frequent malfunctions, and impacting production. The best way to avoid this is to seek out large domestic manufacturers or listen to feedback from peers. In fact, regardless of the situation, it's not difficult to discern the cause with a little attention. A brief explanation follows. 1. Comparison of the same power output: For example, if you decide that your factory will purchase a high-frequency heating device for welding, and you select products from three companies, A, B, and C, the prices are as follows: A-25 (output power 25KW) 14800 yuan, A-40 (output power 40KW) 26800 yuan, B-25 (oscillation power 25KW) 12500 yuan, B-40 (oscillation power 40KW) 18800 yuan, C-25 (oscillation power 25KW) 11000 yuan, and C-40 (oscillation power 40KW) 16800 yuan. Since A-25 is the output power, it is converted to oscillation power. A's oscillation power is 42KW. Therefore, to complete the same work, comparing B and C, the prices are: B-40 (oscillation power 40KW) 18800 yuan and C-40 (oscillation power 40KW) 16800 yuan. Therefore, A-25, at 14800 yuan, is actually the lowest price. This can lead you into the price trap of ethylene and propylene oxide. 2. Comparison of Similar Workpieces: As the saying goes, "It's not that you don't know the goods, it's that you don't compare them." Take the workpiece to the aforementioned suppliers and you'll get different heating times. The one with the shortest heating time has the highest power. Compare them and find models with similar functions for selection. IV. How to Choose a Good Product A good product should have the following characteristics: good stability, good cost-effectiveness, good adaptability, and fast and comprehensive after-sales service. When choosing a product, you should consider not only its overall long-term operating costs, including downtime losses, parts replacement, post-warranty repairs, upgrade capabilities, and many other factors. Practice is the only standard for testing a product. You can ask the supplier to install the equipment in your factory for on-site testing. If possible, it's best to try it out for a few days. Good equipment has a clean appearance, clear markings, and is easy to use. Usually, for low-power equipment (oscillation power below 30KW), most companies use LEDs to display the current, but this cannot accurately display the power; it can only be used as a reference for adjusting the power. When the oscillation power exceeds 30KW, standard voltage (oscillation) and current (oscillation) meters should be used. During equipment operation, the operating voltage (oscillation) and current (oscillation) should be displayed clearly, preventing companies from falsifying data and allowing operators to objectively and accurately grasp the machine's operating status. If such high-power equipment still uses LEDs for display, caution is advised. High-power equipment typically separates the main power supply and the induction coil transformer. The transformer's performance directly affects the induction coil's efficiency. Some transformers use oil-immersed methods; these are outdated, easily contaminated, and once damaged, almost impossible to repair, and therefore obsolete. Most companies now use dry-type transformers. Even with the same main unit, the transformer may differ depending on the workpiece. For example, when a 30KW induction heating device is used for welding, its induction coil has 1-2 turns. When the induction heating device is used for annealing, its induction coil has 4-8 turns. Under the premise of ensuring normal power output, the more turns of the induction coil, the more uniform the workpiece is heated, and the stronger the equipment's ability to handle irregularly shaped workpieces. However, some companies' equipment transformers can only support 1-2 induction coils. When encountering large workpieces, the induction coil can only be made using parallel tubes, which is complex and has low heating efficiency. I once encountered a situation where heating a stainless steel pot with a diameter of 16 cm and a height of 20 cm was performed using a certain type of 30KW equipment for stainless steel annealing. The induction coil had 7 turns, and the output power reached 32KW, completing the annealing in just 13 seconds. With the same induction coil and the same workpiece, when tested on another brand's machine that claimed to be 40KW, the heating speed was more than 90 seconds, making it almost unusable. The number of coil turns was reduced to 3-4 turns to barely heat the workpiece, and a rotating device had to be added to the bottom of the workpiece. If possible, you can request the equipment manufacturer to open the chassis. A good device will have a reasonable layout of electronic components and neat wiring. You can see the materials used in key components such as IGBT power modules and power capacitors. The overall appearance and weight of the equipment provide a deeper understanding. Most manufacturers lack independent, high-level R&D teams and their own core technologies, resulting in severe product homogenization. Most companies integrate the main control circuit board and the driver circuit board. When one driver circuit fails, the entire circuit board must be replaced, which usually happens after the warranty period, increasing the burden on users. Therefore, it's best to choose products with separate main control and driver circuit boards for lower repair costs. You can ask the manufacturer's technical staff about this. Reputable companies have ample spare parts, offer fast and efficient service, and provide comprehensive after-sales support. They can also provide backup equipment to minimize disruption to production. By now, you may have a basic understanding of IGBT induction heating equipment, but it cannot meet all needs in metal heating applications. The physical characteristics of IGBT power modules dictate that their power cannot be manufactured to a very high level. Currently, some foreign companies have developed equipment with an input power of 4000KW, while only a few domestic companies are capable of producing equipment with a power of around 1000KW. High-power heating equipment still uses traditional transistor and vacuum tube technologies. In addition, the technology for using IGBTs in the ultra-high frequency field still needs further breakthroughs.