Induction coil design can have a major impact on part quality, process efficiency, and manufacturing costs. How do you know if your coil design is best for your part and process? Here are some induction coil basics and five tips to optimize your design.
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The induction coil determines how effectively and efficiently a workpiece is heated. Induction coils are water-cooled conductors made of copper tubing that is readily formed into the shape of the coil for the induction heating process. Induction heating coils do not themselves get hot as water flows through them.
Work coils range in complexity from a simple helical- or solenoid-wound coil (consisting of a number of turns of copper tube wound around a mandrel) to a coil that is precision machined from solid copper and brazed.
Coils transfer energy from the power supply to the workpiece by generating an alternating electromagnetic field due to the alternating current flowing in them. The coil’s alternating electromagnetic field (EMF) generates an induced current (eddy current) in the workpiece, which generates heat due to I Squared R losses (core losses).
The current in the workpiece is proportional to the coil’s EMF strength. This transfer of energy is known as the transformer effect or eddy current effect.
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Induction coil design has a major impact on process efficiency and final part quality, and the best coil design for your product largely depends on your application. Certain coil designs tend to work best with specific applications, and a less than optimal coil-application pairing can result in slow or irregular heating, higher defect rates, and lower quality products.
Start with understanding where the heat needs to be generated in the part to perform the process, and then design the coil to achieve the heating effect. Similarly, frequency selection will depend on the induction heating application you’ll be using for your part.
Before designing your induction coil, consider these three factors along with your induction application:
Part motion relative to coil- Several applications rely on part movement with the help of conveyors, turntables, or robots. A properly designed induction coil incorporates these individual handling requirements without the loss of heating efficiency.
Frequency- Higher frequencies are used for applications like brazing, soldering, annealing or heat treating, where surface heating is desired. Lower frequencies are preferred for applications requiring through-heating of the parts to the core like forging and die heating.
Power-density requirements- Higher power densities are required for short cycle heating applications requiring high temperatures. Higher power densities may also be required to keep the hot zone confined to a small area, reducing the heat affected area.
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Coupling is the transfer of energy that occurs in the space between the heating portion of the coil and the workpiece. So, coupling distance is how big that space needs to be to balance efficiency and manufacturing requirements.
Generally, distance increases with the diameter of the part, typical values being 0.75, 1.25, and 1.75 inches (19, 32 and 44 mm) or billet-stock diameters of approximately 1.5, 4 and 6 inches (38, 102, and 152 mm), respectively.
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Magnetic flux tends to concentrate toward the center of the length of a solenoid work coil. This means the heating rate produced in this area is generally greater than that produced toward the ends. Further, if the part being heated is long, conduction and radiation remove heat from
the ends at a greater rate. The coil can be modified to provide better heating uniformity along the part length. The technique of adjusting the coil turns, spacing, or coupling with the workpiece to achieve a uniform heating pattern is sometimes known as “characterizing” the coil.
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6 ways to improve uniformity of heating...
The type and design of the induction coil determines how effectively and efficiently a workpiece is heated. Work coils range in complexity from a simple helical- or solenoid-wound coil (consisting of a number of turns of copper tube wound around a mandrel) to a coil that is precision-machined from solid copper and brazed.
The helical solenoid coil is the most ubiquitous induction coil design. It provides a wide range of heating behaviors since the part or heating area is located within the coil, in the area of greatest magnetic flux. Flux lines in a solenoid coil are concentrated inside the coil, providing the maximum heating rate at that location.
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Choosing the right induction heating equipment requires consideration of many different features of the equipment and aspects of the supplier. The induction heating equipment should be long-lasting and reliable, so making the right choice is critical. These are our recommendations of how to choose a supplier and how to ensure that you make the right choice:
Applications Experience: Does the supplier have extensive experience and reputable customers in the induction heating field and in the application you are interested in?
Induction Technology: Does the Induction Heating solution provide the latest advancements in power conversion technology and digital controls to ensure the highest heating precision with a long service life? Is the induction heating technology advanced, flexible and scalable?
Power Rating: How is the power rated? Many low-cost off shore competitors rate their equipment at the input power with a specific coil. The power delivered to the heated part can be 30% lower or more depending on the technology used.
Flexibility and Load matching: Does the Induction Heating system provide an easy to use matching solution for your project? Many Induction Heating systems are factory tuned to a specific application and require extensive effort to match to different applications.
Service and Support: If your systems are shipped to different parts of the world, does the supplier have global support? Does the equipment have remote diagnostics features?
Safety: Is the equipment CE or UL certified and does it meet all safety requirements?
Engineering Support: Does the supplier have a strong engineering team available to help with custom solutions and special applications?
Equipment Origin: Is the supplier a domestic manufacturer with robust and reliable local service and technical support backed by experienced service engineers? Is it an actual manufacturer or a reseller? Many vendors in the market resell product manufactured by other companies. They may provide good initial sales support but have limited post sale service and support capabilities.
Size and Efficiency: Is the equipment compact and energy efficient?
Interfaces and Usability: If you are planning to integrate the equipment into your system or on a production line,
a. Does the equipment have the necessary interfaces to connect with PC or PLC?
b. Does it have temperature control and monitoring options?
c. What is the turn-on response time (very important if short and precise heating cycles are required)?
Coil-making Capabilities and Optional Equipment: Does the supplier offer coil-making services? Do they have advanced design tools and algorithms to optimize the induction coil design? Do they offer optional equipment such as remote control panels, flexible water-cooled leads, remote heat stations, etc.?
For OEMs and System Integrators: Does the supplier offer OEM solutions, such as modules and equipment suitable for integrating into large systems or on conveyor lines?
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