WO2026019693A1

WO2026019693A1 - Compound frequency induction device for gear heat treatment

Info

Publication number: WO2026019693A1
Application number: PCT/US2025/037505
Authority: WO
Inventors: Hugo BARRAGAN VARGAS; Francisco ROBLES HERNANDEZ; Ricardo CUENCA ALVAREZ; Agustin CRUZ CONTRERAS
Original assignee: Instituto Politecnico Nacional Ipn; University of Houston System
Current assignee: Instituto Politecnico Nacional Ipn; University of Houston System
Priority date: 2024-07-15
Filing date: 2025-07-14
Publication date: 2026-01-22
Anticipated expiration: 2027-01-15

Abstract

An electric induction heating system for heating a workpiece having an undulating perimeter includes a low frequency coil and a high frequency coil arranged to heat the workpiece, a low frequency induction circuit coupled to the low frequency coil to induce a low frequency output less than about 50 kHz, wherein the low frequency induction circuit comprises at least two low frequency power sources, a high frequency induction circuit coupled to the high frequency coil to induce a high frequency output greater than about 100 kHz, wherein the high frequency induction circuit comprises at least two high frequency power sources, and a controller connected to the low frequency induction circuit and the high frequency induction circuit and operable to induce the low frequency output alone, the high frequency output alone, and the low frequency output and the high frequency output simultaneously.

Description

COMPOUND FREQUENCY INDUCTION DEVICE FOR GEAR HEAT TREATMENT TECHNICAL FIELD

[0001] This disclosure relates in general to the field of heat treatment of an electrically conductive workpiece, and more particularly, but not by way of limitation, to an induction heating system for heat treatment of gear's simultaneously utilizing high and low frequencies to selectively heat the gear tip and the gear root.

BACKGROUND

[0002] This section provides background information to facilitate a better understanding of the various aspects of the disclosure and is not an admission of prior art.

[0003] Induction heating generally describes a process in which an alternating current is passed through a coil to generate an alternating magnetic flux. When the coil is placed in close proximity to or wrapped around a metallic object that is to be heated, the alternating magnetic flux inductively couples the load to the coil and generates eddy currents within the metallic object causing it to become heated. Because of its function, the coil is often referred to as a work coil or induction head, and the metallic object to be heated as a load. Induction heating may be used for many purposes including curing adhesives, hardening of metals, brazing, soldering, welding, and other fabrication processes in which heat is a necessary agent or catalyst.

[0004] Several types of induction heating systems having been developed to control power delivered to the induction head and, thus, the heat produced in the load. One type of induction heating system, sometimes referred to as a resonant system, generally comprises a power supply, a resonant induction head typically formed by the work coil and a capacitor, and some type of switching means to control delivery of power to the resonant induction head by the power supply. Generally, the switching means is closed to cause the power supply to provide a current to the resonant induction head resulting in energy being stored in the work coil. When the switching means is opened, the induction head begins to resonant and generate an oscillating voltage and corresponding oscillating current, and the stored energy is discharged to the load as heat.

SUMMARY

[0005] An example electric induction heating system for heating a workpiece having an undulating perimeter includes a low frequency coil and a high frequency coil arranged to heat the workpiece, a low frequency induction circuit coupled to the low frequency coil to induce a low frequency output less than about 50 kHz, wherein the low frequency induction circuit comprises at least two low frequency power sources, a high frequency induction circuit coupled to the high frequency coil to induce a high frequency output greater than about 100 kHz, wherein the high frequency induction circuit comprises at least two high frequency power sources, and a controller connected to the low frequency induction circuit and the high frequency induction circuit and operable to induce the low frequency output alone, the high frequency output alone, and the low frequency output and the high frequency output simultaneously.

[0006] An example method of hardening an undulating perimeter of a cylindrical workpiece includes positioning the workpiece in an inductor comprising a low frequency coil and a high frequency coil and energizing the inductor to induce a compound frequency output comprising a first low frequency output induced by the low frequency coil and a first high frequency output induced by the high frequency coil. [0007] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. As will be understood by those skilled in the ait with the benefit of this disclosure, elements and arrangements of the various figures can be used together and in configurations not specifically illustrated without departing from the scope of this disclosure.

[0009] Figure 1 is a schematic illustration of a system according to one or more aspects of the disclosure.

[0010] Figure 2 is a schematic illustration of a portion of the system according to one or more aspects of the disclosure.

[0011] Figure 3 is a partial view of an example workpiece illustrating targeted heating of a gear root according to one or more aspects of the disclosure.

[0012] Figure 4 is a partial view of an example workpiece illustrating targeted heating of a gear tip according to one or more aspects of the disclosure.

[0013] Figure 5 is a partial view of an example workpiece illustrating a contoured heating of the gear tip and the gear root using a compound frequency according to one or more aspects of the disclosure.

[0014] Figure 6 is a block diagram of a method according to one or more aspects of the disclosure. DETAILED DESCRIPTION

[0015] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various illustrative embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. For example, a figure may illustrate an exemplary embodiment with multiple features or combinations of features that are not required in one or more other embodiments and thus a figure may disclose one or more embodiments that have fewer features or a different combination of features than the illustrated embodiment. Embodiments may include some but not all the features illustrated in a figure and some embodiments may combine features illustrated in one figure with features illustrated in another figure. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead merely to describe particularly representative examples. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and/or configurations discussed.

[0016] Disclosed is a compound frequency induction system, also referred to as a dual induction system, to heat treat gears. This technology integrates dual-frequency induction, utilizing high and low frequencies to selectively heat the gear tip and the gear root. The device is unique and may include a capacitor bank exchange system, employing three-electrode semiconductor for altering current and a multiplexer to adjust the intensity. This design allows precise penetration depth control, addressing the critical zone of the gear root. Embodiments offer adaptability to various gear geometries, providing a unique solution to the proximity effect in induction heating. It stands as a groundbreaking advancement in controlled and efficient gear heat treatment. A major limitation in the induction treatment furnaces is the inability to identify the needs to treat the tip versus root of the gears.

[0017] Figures 1 and 2 schematical illustrate aspects of an example electric compound frequency induction heating system, generally denoted by the reference number 10, for heating a workpiece 12 with an undulating perimeter 14 of gear tips connected by gear roots. System 10 has an inductor 16 comprising a low frequency coil 18 and a high frequency coil 20. In operation, the low and high frequency coils encircle the workpiece.

[0018] A low frequency induction circuit 22 is coupled to low frequency coil 18 to energize the coil with an alternating current with a low frequency output less than about 50 kHz. Low frequency induction circuit 22 includes at least two low frequency power sources 24 each having a frequency different from the frequency of the other low frequency power sources. According to embodiments each low frequency power source is a band of capacitors. Low frequency induction circuit 22 may include zero voltage circuit 26. An auto-tunable zero voltage circuit can follow the resonance of the coil and capacitors, ensuring efficient and controlled heating. The auto-tuning capability allows dynamic adaptation to change in load and environmental conditions.

[0019] A high frequency induction circuit 28 is coupled to high frequency coil 20 to energize the coil with an alternating current with a high frequency output greater than about 100 kHz. High frequency induction circuit 28 includes at least two high frequency power sources 30 each having a frequency different from the frequency of the other high frequency power sources. According to embodiments each high frequency power source is a band of capacitors. High frequency induction circuit 28 may include zero voltage circuit 26. An auto-tunable zero voltage circuit can follow the resonance of the coil and capacitors, ensuring efficient and controlled heating. The auto-tuning capability allows dynamic adaptation to change in load and environmental conditions.

[0020] A controller 32 is connected to low frequency induction circuit 22 and high frequency induction circuit 28. Controller 32 is operable to energize inductor 16 with the low frequency output alone, the high frequency output alone, and with the low frequency output and the high frequency output simultaneously to apply a compound frequency. Controller 32 can dynamically change the frequencies, including utilizing the at least two low frequency power sources and the at least two high frequency power sources to dynamically change the compound frequency.

[0021] Figure 2 schematic illustrates an electric compound frequency induction heating system 10 according to aspects of the disclosure. Low frequency induction circuit 22 includes a multiplexer 36 in communication with a first low frequency power source 24a, a second low frequency power source 24b, and a third low frequency power source 24c. Each of the low frequency power sources is a bank of capacitors and includes a triode for alternating current (TRIAC) 34. High frequency induction circuit 28 includes a multiplexer 36 in communication with a first high frequency power source 30a, a second high frequency power source 30b, and a third high frequency power source 30c. Each of the low frequency power sources is a bank of capacitors and includes a triode for alternating current (TRIAC) 34. Low frequency induction circuit 22 and high frequency induction circuit 28 can be operated simultaneously to energize both the low frequency coil and the high frequency coil of inductor 16 with a compound frequency 38. Compound frequency 38 can be changed by exchanging the active low frequency power source and/or the active high frequency power source.

[0022] The system operates with two distinct frequencies, a high frequency, for example 100 kHz to 1 MHz for targeted heating of the gear tip and a low frequency, for example 1 kHz to 40 kHz, for precise treatment of the gear root. This compound frequency approach mitigates the proximity effect, providing a more uniform and controlled heating process.

[0023] The low frequency power sources have a frequency of less than about 50 kHz and in particular’ below about 40 kHz. In a non-limiting example, utilizing three low frequency power sources such as illustrated in FIG. 2, first low frequency capacitor bank 24a has a frequency of about 100 Hz, second low frequency capacitor bank 24b has a frequency of about 10 kHz, and third low frequency capacitor bank 24c has a frequency of about 40 kHz.

[0024] The high frequency power sources have a frequency of greater than about 100 kHz. In a non-limiting example, utilizing three high frequency power sources such as illustrated in FIG. 2, first high frequency capacitor bank 30a has a frequency of about 100 Hz, second high frequency capacitor bank 30b has a frequency of about 10 kHz, and third high frequency capacitor bank 30c has a frequency of about 40 kHz.

[0025] FIGS. 3 to 5 illustrate portions of a workpiece 12 having an undulating perimeter 14 of gear tips 40 connected by gear roots 42. The compound frequency induction system introduces the flexibility to choose between targeted heating of gear root 42 (FIG. 3), targeted heating of gear tip 40 (FIG. 4), and full contoured heating (FIG. 5) of gear tip 40 and gear root 42 with a compound frequency. With reference to FIG. 5, the heating process is performed in a single step, using both low and high frequency coils simultaneously, while also providing the capability to adjust heat penetration depth in both coils, thereby enabling a flexible heating process. This adaptability is a significant improvement over rigid heating approaches.

[0026] The compound frequency induction system addresses critical challenges in the conventional gear heat treatment process, providing solutions for example to the problems of proximity effect in induction heating, rigidity of contouring patterns, limited adaptability to gear variability, lack of control over penetration depth, lack of energy efficiency, inability to tailor treatments to gear requirements, and complex gear manufacturing processes.

[0027] Conventional induction heating methods often encounter the proximity effect, leading to uneven heating in gears. The disclosed compound frequency induction system, or dual induction device, mitigates this issue by employing dual frequencies, allowing targeted heating of the gear tip and root, ensuring a more uniform and controlled heat distribution.

[0028] Existing contouring heating patterns might not be universally suitable for all gear types. The disclosed technology introduces flexibility enabling operators to choose between a full contouring pattern and targeted heating of the gear tip or gear root. This addresses the rigid application of heating patterns and allows for customized treatments. Limited adaptability to gear variability is overcome with the compound frequency induction system. Gears come in various shapes and sizes, and conventional methods may lack adaptability to different gear geometries. The dual induction device overcomes this limitation with its dual-frequency operation and the ability to exchange capacitor banks, ensuring adaptability to a wide range of gear configurations that it is unique and not reproducible by other systems. [0029] The compound frequency induction system may improve control over penetration depth. Achieving precise control over the penetration depth, especially in critical zones like the gear root, is crucial. This is usually lacking in prior techniques. The compound frequency induction system provides a solution by incorporating a capacitor bank exchange system, enabling operators to dynamically adjust the penetration depth and overall depth of induction heating.

[0030] Traditional induction heating methods may lead to inefficient energy usage, with unnecessary heating of areas not requiring treatment. The dual induction device optimizes energy efficiency by allowing the selective application of frequencies and heating patterns, minimizing energy needs.

[0031] Different gears may have unique treatment based on the required or final properties. The dual induction device facilitates customized treatment strategies, ensuring that each gear receives the precise heat treatment necessary for its intended use.

[0032] The complexity of gear manufacturing processes can hinder efficiency. The dual induction device simplifies the heat treatment stage by offering a user-friendly control interface and adaptable features, streamlining operations, and reducing processing times.

[0033] This dual induction device and compound frequency induction system addresses problems associated with uneven heating, lack of adaptability, and inefficiency in conventional gear heat treatment processes. It introduces a flexible and precise approach, allowing operators to tailor treatments to specific gear requirements while optimizing energy usage and simplifying manufacturing processes. The penetration depth can be changed manually, or the process can be used with smart controls to work autonomous. [0034] The versatility of the compound frequency induction system is ideal to heat treat intricate and simple architectures in-operando or after additive manufacturing printing is completed. This uniqueness facilitates tuning the heat treatment for a variety of geometries in addition to gears.

[0035] To enhance adaptability, the system incorporates a capacitor bank exchange system controlled by TRIACs and a multiplexer to facilitate the interchangeability of capacitor banks, allowing adjustments to the natural frequency of the RLC (Resistor - Inductor - Capacitor) circuit. This feature enables the control of penetration depth and the overall depth of the induction heating.

[0036] The ability to exchange capacitor banks and adjust frequencies enhances the adaptability of the system to a wide range of gear geometries. This innovation ensures that the heat treatment process can be precisely tailored to accommodate different gear configurations. This addresses the common limitation in traditional induction treatment systems. The compound frequency induction system tunes the treatment to any gear geometry and additive manufacturing or other intricate or simple structures without compromising the quality of the treatment.

[0037] The central control system oversees and regulates frequencies, capacitor banks, and other key parameters of the heating process. This control device can be manually adjusted or programmed to meet specific heat treatment requirements. To facilitate operation, an intuitive user interface is included, allowing operators to control and monitor the heating process. The interface can display information such as temperatures, processing times, and current configurations.

[0038] An example of operation includes powering on the compound frequency induction system and selecting the desired heating parameters through the user interface. The auto-tunable zero voltage circuits dynamically follow the resonance of coils and capacitors, adapting to the load. The high frequency is applied for heating the tip, while the low frequency is used for root heating. When adapting to different gear geometries is necessary, the operator can exchange capacitor banks using TRIACs, thereby adjusting the natural frequency of the LC circuit. With the correct frequencies and settings, the prototype carries out the heating process, ensuring a uniform distribution of heat in the targeted areas of the gear. Once the heating cycle is complete, the operator concludes the process through the user interface. The prototype is safely powered down.

[0039] Figure 6 is a block diagram of an example method 600 of hardening an undulating perimeter of a cylindrical workpiece comprising gear tips connected by gear roots. Method 600 is described with reference to the other figures. At block 602, workpiece 12 is positioned in an inductor 16 comprising a low frequency coil 18 and a high frequency coil 20. At block 604, inductor 16 induces a compound frequency output 38 by simultaneously energizing the low frequency coil with a first low frequency power source inducing a first low frequency output and energizing the high frequency coil with a first high frequency power source inducing a first high frequency output. At block 606, compound frequency output 38 is changed by changing the low frequency coil output from the first low frequency output to a second low frequency output that is different from the first low frequency output. At block 608, compound frequency output 38 is changed by changing the high frequency coil output from the first high frequency output to a second high frequency output that is different from the first high frequency output.

[0040] Although relative terms such as “outer,” “inner,” “upper,” “lower,” and similar terms have been used herein to describe a spatial relationship of one element to another, it is understood that these terms are intended to encompass different orientations of the various elements and components in addition to the orientation depicted in the figures. Furthermore, as used herein, the terms “connect,” “connection,” “connected,” “in connection with,” and “connecting” may be used to mean in direct connection with or in connection with via one or more elements. Similarly, the terms “couple,” “coupling,” and “coupled” may be used to mean directly coupled or coupled via one or more elements. The terms “substantially,” “approximately,” “generally,” and “about” are defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. The extent to which the description may vary will depend on how great a change can be instituted and still have a person of ordinary skill in the art recognized the modified feature as still having the required characteristics and capabilities of the unmodified feature.

[0041] The foregoing outlines features of several embodiments so that those skilled in the ail may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.

Claims

WHAT IS CLAIMED IS:

1 . An electric induction heating system for heating a workpiece having an undulating perimeter of gear tips connected by gear roots, the induction heating system comprising: a low frequency coil and a high frequency coil arranged to heat the workpiece; a low frequency induction circuit coupled to the low frequency coil to induce a low frequency output less than about 50 kHz, wherein the low frequency induction circuit comprises at least two low frequency power sources with different frequencies; a high frequency induction circuit coupled to the high frequency coil to induce a high frequency output greater than about 100 kHz, wherein the high frequency induction circuit comprises at least two high frequency power sources with different frequencies; and a controller connected to the low frequency induction circuit and the high frequency induction circuit, wherein the controller is operable to apply the low frequency output alone, the high frequency output alone, and the low frequency output and the high frequency output simultaneously.

2. The induction heating system of claim 1, wherein: each high frequency power source of the at least two high frequency power sources and each low frequency power source of the at least two low frequency power sources comprise a triode for alternating current (TRIAC).

3. The induction heating system of any one of claims 1 and 2, wherein the at least two low frequency power sources comprise: a first low frequency capacitor bank with a first low frequency; a second low frequency capacitor bank with a second low frequency; and a third low frequency capacitor bank with a third low frequency, wherein the first low frequency, the second low frequency and the third low frequencies are different.

4. The induction heating system of any one of claims 1 and 2, wherein the at least two low frequency power sources comprise: a first low frequency capacitor bank with a frequency of about 100 Hz; a second low frequency capacitor bank with a frequency of about 10 kHz; and a third low frequency capacitor bank with a frequency of about 40 kHz.

5. The induction heating system of any of the preceding claims, wherein the at least two high frequency power sources comprise: a first high frequency capacitor bank with a first high frequency; a second high frequency capacitor bank with a second high frequency; and a third high frequency capacitor bank with a third high frequency, wherein the first high frequency, the second high frequency and the third high frequencies are different.

6. The induction heating system of any one of claims 1 to 4, wherein the at least two high frequency power sources comprise: a first high frequency capacitor bank with a frequency of about 100 kHz; a second high frequency capacitor bank with a frequency of about 500 kHz; and a third high frequency capacitor bank with a frequency of about 1 MHz.

7. A method of hardening an undulating perimeter of a cylindrical workpiece where the undulating perimeter comprises gear tips connected by gear roots, the method comprising: positioning the workpiece in an inductor comprising a low frequency coil and a high frequency coil; and energizing the inductor to induce a compound frequency output comprising a first low frequency output induced by the low frequency coil to heat the gear roots and a first high frequency output induced by the high frequency coil to heat the gear tips.

8. The method of claim 7, wherein the first low frequency output is less than 50 kHz, and the first high frequency output is greater than 100 kHz.

9. The method of any one of claims 7 and 8, further comprising changing the low frequency coil output from the first low frequency output to a second low frequency output thereby changing the compound frequency output.

10. The method of any one of claims 7 to 9, further comprising changing the high frequency coil output from the first high frequency output to a second high frequency output thereby changing the compound frequency output.

11. The method of any one of claims 7 to 9, further comprising: a low frequency induction circuit coupled to the low frequency coil to induce the low frequency output less than about 50 kHz, wherein the low frequency induction circuit comprises a low frequency power source comprising at least two low frequency capacitor banks with different frequencies; and a high frequency induction circuit coupled to the high frequency coil to induce a high frequency output greater than about 100 kHz, wherein the high frequency induction circuit comprise a high frequency power source comprising at least two high frequency capacitor banks with different frequencies.

12. The method of claim 11, wherein the low frequency power source comprises: a first low frequency capacitor bank with a first low frequency; a second low frequency capacitor bank with a second low frequency; and a third low frequency capacitor bank with a third low frequency, wherein the first low frequency, the second low frequency and the third low frequencies are different frequencies.

13. The method of claim 11, wherein the low frequency power source comprises: a first low frequency capacitor bank with a frequency of about 100 Hz; a second low frequency capacitor bank with a frequency of about 10 kHz; and a third low frequency capacitor bank with a frequency of about 40 kHz.

14. The method of any one of claims 11 to 13, wherein the high frequency power source comprises: a first high frequency capacitor bank with a first high frequency; a second high frequency capacitor bank with a second high frequency; and a third high frequency capacitor bank with a third high frequency, wherein the first high frequency, the second high frequency and the third high frequencies are different frequencies.

15. The method of any one of claims 11 to 13, wherein the high frequency power source comprises: a first high frequency capacitor bank with a frequency of about 100 kHz; a second high frequency capacitor bank with a frequency of about 500 kHz; and a third high frequency capacitor bank with a frequency of about 1 MHz.