Heating coil for high-frequency heating device

Abstract

[Problem] To provide a heating coil that enables efficient application of quenching treatment to a workpiece in a short time, effective prevention of the workpiece from being excessively heated, and easy control of the depth of a hardened layer which is obtained by quenching the workpiece. [Solution] A heating coil 1 is integrally shaped using a forming method in which depositing a powder composed of a conductive substance, and melting, solidifying, and layering the same are repeated on the basis of three-dimensional data, and comprises: grounding parts 2a, 2b to be brought into contact with electrodes; support parts 3a, 3b respectively disposed perpendicular to the grounding parts 2a, 2b; and a heating part 4 provided so as to connect the tips of the support parts 3a, 3b to each other. Additionally, the heating part 4 comprises: an intermediate heating portion 14 for allowing supplied high-frequency current to flow in a first direction; and a lower-side heating portion 15 for allowing the supplied high-frequency current to flow in a second direction opposite to the first direction.

Description

Heating coil for high-frequency heating device

[0001] The present invention relates to a heating coil used in a high-frequency heating device for heating a workpiece by electromagnetic induction using a high-frequency current.

[0002] In order to increase the hardness of the surface portion of a metal workpiece, a process of heating the surface of the workpiece to a temperature above the transformation point (austenite transformation point) of the metal and then rapidly cooling it (so-called quenching) is performed. And, as a method for performing such quenching, a method of heating the workpiece by flowing a high-frequency current through a metal member (heating coil) close to the surface of the workpiece using a high-frequency heating device is widely adopted. Further, as a heating coil used for such quenching, as disclosed in Patent Document 1, an annular coil portion made of a metal pipe for fitting over the workpiece is connected to a conductive plate (copper plate) for supplying a high-frequency power source, and such a structure is known.

[0003] Japanese Patent Application Laid-Open No. 2020-115428

[0004] However, in the above-described conventional heating coil for a high-frequency heating device, since the current always flows in one direction inside the annular coil portion, when a large amount of current flows inside the coil portion, the workpiece is overheated, the crystal grains of the quenched structure of the workpiece become coarsened, and the toughness decreases, resulting in a decrease in mechanical strength. On the contrary, when only a small amount of current flows inside the coil portion, the depth of the hardened layer of the workpiece becomes shallow and the quenching becomes insufficient. Therefore, it has been difficult to control the depth of the hardened layer due to quenching of the workpiece with the conventional heating coil for a high-frequency heating device.

[0005] An object of the present invention is to solve the above-described problems of the conventional heating coil for a high-frequency heating device, to be able to efficiently perform a quenching process on a workpiece in a short time, and to effectively suppress a situation where a portion that is overheated due to the shape of the workpiece occurs, prevent a decrease in the mechanical strength of the workpiece, and to provide a practical heating coil that can easily control the depth of the hardened layer due to quenching of the workpiece.

[0006] The invention described in claim 1 of the present invention is a heating coil for use in a high-frequency heating device for heating a workpiece using electromagnetic induction by a high-frequency current, comprising: a pair of plate-shaped grounding portions for contacting electrodes through which a high-frequency current is passed; a pair of plate-shaped support portions arranged perpendicular to each of the grounding portions; and a series of circumferential heating portions provided to connect the tips of the support portions, wherein the heating portion comprises a first conductive portion that allows the high-frequency current supplied from the grounding portion to flow in a first direction; and a second conductive portion that allows the high-frequency current supplied from the grounding portion to flow in a second direction opposite to the first direction.

[0007] In other words, the invention described in claim 1 utilizes the principle that "when the direction of the high-frequency current flowing through two rings (ring-shaped portions, i.e., the first conductive part and the second conductive part) formed in a coil is reversed, the magnetic flux between those rings cancels out." By positioning a part prone to overheating between rings where the direction of such high-frequency currents is reversed, the temperature rise of that part is suppressed. Furthermore, in the invention described in claim 1, the effect of suppressing the temperature rise of a part prone to overheating can be adjusted by changing the distance between the rings where the direction of the high-frequency currents is reversed. It is also possible to adjust the temperature rise suppression effect by changing the length of the rings where the direction of the high-frequency currents is reversed.

[0008] The invention described in claim 2 is characterized in that, in the invention described in claim 1, the heating section has the first conductive section and the second conductive section arranged vertically.

[0009] The invention described in claim 3 is characterized in that, in the invention described in claim 1, a part of the heating portion is bent in an S-shape or inverted S-shape in the vertical direction, thereby forming the first conductive portion and the second conductive portion.

[0010] The invention described in claim 4 is characterized in that, in the invention described in claim 1, it is integrally formed using a molding method that involves repeatedly laying, melting, solidifying, and laminating powder made of a conductive material based on three-dimensional data (hereinafter referred to as a partial welding lamination method for conductive material powder layers), or a molding method that involves laminating molten conductive material based on three-dimensional data (hereinafter referred to as a melt extrusion lamination method for conductive material).

[0011] In the aforementioned partial welding and lamination methods for conductive material powder layers and the melt extrusion lamination method for conductive materials, the conductive material used as the raw material for molding refers to a material that is substantially non-magnetic and possesses good conductivity. Examples of such conductive materials include copper, brass, and silver. Among these conductive materials, copper is preferable because it allows for a reduction in material costs, enables the inexpensive and easy manufacture of heating coils using a 3D printer, and exhibits extremely good conductivity, resulting in high heating efficiency due to electromagnetic induction. Furthermore, while pure copper can be used as the conductive material, it is preferable to use an alloy (high-copper alloy) containing iron, tin, nickel, titanium, beryllium, zirconium, chromium, silicon, etc., in smaller proportions than copper, as this enhances laser absorption and promotes temperature rise. Furthermore, among these copper alloys, using a copper-chromium alloy containing chromium in copper is more preferable because it allows for the effective enhancement of the heating coil's strength while maintaining high manufacturing efficiency with a three-dimensional printer. It is particularly preferable to use an alloy containing chromium and zirconium in predetermined proportions in copper (for example, one containing 98.71 to 99.45% by mass of copper, 0.50 to 1.00% by mass of chromium, and 0.05 to 0.25% by mass of zirconium (high-copper alloy)).

[0012] Furthermore, when fabricating a heating coil according to the present invention using a partial welding and lamination method of conductive material powder layers, it is necessary to melt the laid fabrication material (i.e., powder made of conductive material) by irradiation with a laser or electron beam. Suitable lasers for this purpose include semiconductor lasers, carbon dioxide lasers, excimer lasers, YAG lasers, fiber lasers, etc. However, using a fiber laser (i.e., a laser that uses an optical fiber doped with rare earth elements such as Yb as the laser medium) is preferable because it is possible to obtain laser light without deviation of the optical axis with high output from a small device, and it is possible to manufacture heating coils with high dimensional accuracy very efficiently.

[0013] The heating coil for a high-frequency heating device described in claim 1 (hereinafter simply referred to as a heating coil) has a heating section that heats a workpiece by electromagnetic induction, which includes a first conductive section that allows a high-frequency current supplied from the ground section to flow in a first direction, and a second conductive section that allows a high-frequency current supplied from the ground section to flow in a second direction opposite to the first direction. As a result, the magnetic flux generated by the first conductive section and the magnetic flux generated by the second conductive section cancel each other out. Unlike conventional heating coils in which the heating section only has a conductive section that allows a high-frequency current to flow in a single direction, this prevents the workpiece from being overheated and makes it easy to control the depth of the hardened layer of the workpiece by quenching.

[0014] The heating coil described in claim 2 has a heating section in which a first conductive section and a second conductive section are arranged concentrically above and below each other. This allows for a large amount of mutually canceling magnetic flux (i.e., the amount of magnetic flux generated by the first conductive section and the amount of magnetic flux generated by the second conductive section), thereby more effectively preventing the workpiece from being overheated and enabling very precise control over the depth of the hardened layer of the workpiece due to quenching.

[0015] In the heating coil described in claim 3, a first conductive part and a second conductive part are formed by bending a part of the heating section in an S-shape or inverted S-shape in the vertical direction, so that the amount of current that does not contribute to heating the workpiece can be reduced, and the workpiece can be effectively hardened with less power.

[0016] The heating coil described in claim 4 is formed by a partial welding lamination method of conductive material powder layers based on three-dimensional data or a melt extrusion lamination method of conductive material. Therefore, despite having a complex shape in which a series of circumferential heating sections are provided with a first conductive section and a second conductive section, it can be manufactured inexpensively and very easily. Furthermore, products with the same shape and characteristics can be manufactured efficiently with good reproducibility, regardless of the skill of the manufacturing worker. In addition, since the heating coil described in claim 4 does not have a bonding portion made of silver solder like conventional heating coils, it does not deform even when the temperature rises due to continuous use, and can be subjected to standard heat treatment (quenching treatment) for a long period of time.

[0017] This is a perspective view of the heating coil (coil body). This is a front view of the heating coil (coil body). This is a top view of the heating coil (coil body). This is a left side view of the heating coil (coil body). This is a right side view of the heating coil (coil body). This is a vertical cross-sectional view of the grounding part (section along line A-A in Figure 3). This is a vertical cross-sectional view of the support part (section along line B-B in Figure 3). This is a vertical cross-sectional view of the connecting part (section along line C-C in Figure 3). This is a vertical cross-sectional view of the heating part (section along line D-D in Figure 3). This is an explanatory diagram showing how the heating coil is manufactured (a is a top view and b is a vertical cross-sectional view). This is an explanatory diagram showing the operation of the heating coil (left side view).

[0018] Hereinafter, an embodiment of the heating coil according to the present invention will be described in detail with reference to the drawings. <Structure of the heating coil> The heating coil consists of a metal coil body, an insulating plate (not shown) formed in sheet form from a synthetic resin (fluororesin) having insulating and heat-resistant properties, and screw members such as bolts and nuts (not shown). Figures 1 to 9 show the coil body of the heating coil, and the coil body 1 is integrally formed from a copper alloy (high copper alloy) and has dimensions of length (front to back) × width (width) × height = 300 mm × 150 mm × 100 mm (length, width, and height are all the maximum lengths).

[0019] The coil body 1 is formed by a three-dimensional printing method described later, and has grounding portions 2a and 2b for contacting the electrodes of a high-frequency power supply, a series of circumferential heating portions 4 for heating the workpiece by induction heating, and support portions 3a and 3b for supporting the heating portions 4 at positions away from the grounding portions 2a and 2b. The support portions 3a and 3b and the heating portions 4 (separated portions on the left and right of the base end) are connected by connecting portions 5a and 5b. In addition, a series of cooling medium channels for cooling the coil body 1 and the workpiece by allowing a cooling medium (such as water) to flow through are provided so as to penetrate the inside of the grounding portions 2a and 2b, the support portions 3a and 3b, the connecting portions 5a and 5b, and the heating portions 4 (described later).

[0020] The heating section 4 is for heating the workpiece while it is inserted. The heating section 4 is a series of ring-shaped components separated at its base ends, and includes a roughly arc-shaped upper left heating section 21 (with a central angle of approximately 150°), a roughly arc-shaped intermediate heating section 14 (with a central angle of approximately 30°), an upper left connecting section 24 connecting the upper left heating section 21 and the intermediate heating section 14, a roughly arc-shaped lower heating section 15 (with a central angle of approximately 180°), a lower left connecting section 26 connecting the intermediate heating section 14 and the lower heating section 15, a roughly arc-shaped upper right heating section 22 (with a central angle of approximately 60°), and a right connecting section 25 connecting the lower heating section 15 and the upper right heating section 22. As will be described later, the intermediate heating section 14 functions as a first conductive section that allows the applied high-frequency current to flow in a first direction, and a part of the lower heating section 15 (the part located below the intermediate heating section 14) functions as a second conductive section that allows the applied high-frequency current to flow in a second direction opposite to the first direction.

[0021] Furthermore, the upper left heating section 21, the intermediate heating section 14, and the upper right heating section 22 have a shape formed by bending a rectangular prism-shaped body with chamfered edges into an arc. In addition, the outer surface of the lower heating section 15 forms a tapered surface that slopes inward so that the diameter gradually decreases from top to bottom. Also, on the left side of the heating section 4, as shown in Figure 4, the upper left heating section 21, the upper left connecting section 24, the intermediate heating section 14, the lower left connecting section 26, and the lower heating section 15 are arranged in a roughly inverted S-shape.

[0022] In addition, in the inverted S-shaped portion, as shown in the vertical cross-sectional view (end view) of the heating section 4 in Figure 9, the lower part of the intermediate heating section 14, which functions as the first conductive section, and the upper part of the lower heating section 15, which functions as the second conductive section, each form parallel, opposing flat surfaces (horizontal surfaces), and a predetermined gap S (approximately 2.0 mm) is formed between the lower surface of the intermediate heating section 14 and the upper surface of the lower heating section 15. Furthermore, the lower surface of the intermediate heating section 14 and the upper surface of the lower heating section 15 overlap vertically with a predetermined width (approximately 5.0 mm, γ in Figure 9). Moreover, a cooling medium flow path 6 is provided inside the heating section 4 in a hollow shape along the shape of the heating section 4 for cooling the heating section 4 itself and the workpiece by allowing a cooling medium (such as water) to flow down.

[0023] Furthermore, each support portion 3a and 3b is formed as a pair of flat rectangular parallelepipeds (plates), and is arranged adjacent to each other on the left and right with a predetermined distance (approximately 2.0 mm) between them, with one plate surface facing the other. The upper front of each support portion 3a and 3b is beveled in an arc shape. As shown in Figure 7, cooling medium channels 9a and 9b are formed inside each support portion 3a and 3b, respectively, so as to communicate with the cooling medium channel 6 inside the heating portion 4.

[0024] On the other hand, each of the ground contact portions 2a and 2b is formed as a pair of flat rectangular parallelepipeds (plates), with their inner sides facing each other and positioned adjacent to each other on the left and right sides, separated by a predetermined distance (approximately 2.0 mm). The inner edges of each ground contact portion 2a and 2b are connected to the base edges of the left and right support portions 3a and 3b, and the plate surfaces of each ground contact portion 2a and 2b are perpendicular to the plate surfaces of each support portion 3a and 3b.

[0025] Furthermore, within each grounding portion 2a, 2b, cooling medium passages 11a, 11b are formed in a roughly L-shaped, hollow form for cooling the grounding portions 2a, 2b themselves by allowing a cooling medium to flow down. In addition, cylindrical outlets 7a and 7b are provided approximately in the center (approximately in the left-right direction) of the upper surface of each grounding portion 2a, 2b, and these outlets 7a and 7b are in communication with the cooling medium passages 11a, 11b formed inside each grounding portion 2a, 2b. Furthermore, these cooling medium passages 11a, 11b are connected (in communication) with the cooling medium passages 9a, 9b inside each support portion 3a, 3b.

[0026] In addition, as described above, the heating coil 1 has cooling medium flow channels 9a, 9b and 11a, 11b formed not only inside the heating section 4, but also inside the left and right support sections 3a, 3b and the left and right grounding sections 2a, 2b, respectively, for allowing the cooling medium to flow down. These cooling medium flow channels 9a, 9b, 11a, 11b, and the cooling medium flow channels 10a, 10b inside the left and right connecting sections 5a, 5b are connected in a continuous line with the cooling medium flow channel 6 inside the heating section 4.

[0027] Furthermore, although not shown in the diagram, a sheet-like insulating plate of a predetermined thickness (approximately 2.0 mm) is sandwiched between the left and right grounding portions 2a and 2b of the coil body 1, between the left and right support portions 3a and 3b, and between the left and right base portions of the heating portion 4. In this state, the left and right support portions 3a and 3b and the insulating plate are screwed together by screw members (bolts and nuts, not shown) through screw holes 8, 8. These screw members are screwed together with the support portions 3a and 3b and the insulating plate via bushings made of synthetic resin (glass epoxy resin) that has insulating and heat-resistant properties, so that the support portions 3a and 3b do not have electrical contact with each other through the bolts.

[0028] <Method for Manufacturing a Heating Coil> Figure 10 shows the process of forming the coil body 1 of a heating coil. The three-dimensional printer device M for forming the coil body 1 includes a frame F with a rectangular parallelepiped-shaped concave portion in the center, a lifting member provided to be vertically movable relative to the frame F, an irradiation means S for irradiating a laser L, a reflection means R for reflecting the laser, a driving means (not shown) for raising and lowering the lifting member, and so on. The lifting member is provided with a table T having approximately the same area as the opening of the concave portion of the frame F.

[0029] When manufacturing the coil body using the three-dimensional printer device M, first, copper alloy (high-copper alloy) powder is laid on the surface of the table T of the lifting member in the raised position to a predetermined thickness (for example, 30 μm) (the copper powder is laid only in the gap between the surface of the table T and the surface of the outer frame F). Then, a laser (fiber laser) L of a predetermined output is irradiated onto the copper alloy powder in a predetermined shape to melt a portion of the copper alloy powder, and then cooled and solidified to form a part of the coil body 1.

[0030] As described above, after forming a part of the coil body 1, the table T of the lifting member is lowered to a predetermined height (for example, 30 μm) by the driving means. At that height, a series of operations is repeated: "laying copper alloy powder on the upper side of the previously formed part of the coil body 1 → irradiating the copper alloy powder with a laser L → cooling and solidifying the molten copper alloy (solidification by solidification)." By repeating the above series of operations a predetermined number of times (for example, 5,000 times), the coil body 1 made of copper alloy can be formed integrally.

[0031] <Method of Use and Operation of the Heating Coil> The heating coil 1, configured as described above, has its left and right grounding parts 2a and 2b grounded to electrodes. With a workpiece inserted into the series of circumferential heating parts 4, an external power supply (high-frequency power supply) is applied via the electrodes, and the workpiece can be heated (hardened) using the electromagnetic induction phenomenon. Furthermore, by injecting a cooling medium (water) from the injection port 7b of the right grounding part 2b, passing through the cooling medium flow path 11b, the cooling medium flow path 9b of the right support part 3b, and the cooling medium flow path 6 of the heating part 4, then passing through the cooling medium flow path 9a of the left support part 3a and the cooling medium flow path 11b of the left grounding part 2a, and finally draining from the discharge port 7a of the left grounding part 2a, the heating part 4, support parts 3a and 3b, and grounding parts 2a and 2b can be efficiently cooled, thereby accurately preventing damage to the insulating plate 31 due to melting. Moreover, by allowing the cooling medium to flow down into the heating part 4 in this manner, the workpiece can be rapidly cooled. Then, by rapidly cooling the workpiece after it has been heated in this manner, the workpiece is subjected to a hardening process.

[0032] Furthermore, as described above, when a workpiece is subjected to heat treatment, the current (alternating current) applied from the ground flows through the interior and surface of the heating section 4. However, as shown in Figure 11, the direction of the current flowing through the intermediate heating section 14, which functions as the first conductive section (first direction, α direction in Figure 11), and the direction of the current flowing through the lower heating section 15, which functions as the second conductive section (second direction, β direction in Figure 11) are in opposite directions (in reality, since alternating current flows through the interior and surface of the heating section 4, the current flowing through the first conductive section and the current flowing through the second conductive section are in opposite phase). Therefore, the magnetic flux generated by the intermediate heating section 14 and the magnetic flux generated by the lower heating section 15 cancel each other out. Therefore, even when a large current is passed through the heating section 4 (when a high voltage is applied), the portion of the workpiece located inside the intermediate heating section 14 and the lower heating section 15 (inside the heating section 4 in the radial direction) will not be excessively heated, making it possible to adjust the depth of the hardened layer by quenching to be thin.

[0033] <Effects of the heating coil> The heating coil (coil body 1), as described above, has a pair of plate-shaped grounding portions 2a and 2b for contacting electrodes through which high-frequency current is passed, a pair of plate-shaped support portions 3a and 3b arranged perpendicular to each of the grounding portions 2a and 2b, and a series of circumferential heating portions 4 provided to connect the tips of the support portions 3a and 3b. The heating portion 4 includes an intermediate heating portion (first conductive portion) 14 that allows the high-frequency current supplied from the grounding portions 2a and 2b to flow in a first direction (α direction in Figure 11), and a lower heating portion (second conductive portion) 15 that allows the high-frequency current supplied from the grounding portions 2a and 2b to flow in a second direction opposite to the first direction (β direction in Figure 11). Therefore, with this heating coil, the magnetic flux generated by the first conductive part 14 and the magnetic flux generated by the second conductive part 15 cancel each other out. Unlike conventional heating coils in which the heating part 4 only has conductive parts that allow high-frequency current to flow in a single direction, this prevents the workpiece from being overheated and makes it easy to control the depth of the hardened layer of the workpiece by quenching.

[0034] Furthermore, since the heating coil (coil body 1) has an intermediate heating section (first conductive section) 14 and a lower heating section (second conductive section) 15 arranged concentrically above and below each other at a predetermined distance (approximately 2.0 mm), the amount of magnetic flux that cancels each other out (i.e., the magnetic flux generated by the intermediate heating section 14 and the magnetic flux generated by the portion of the lower heating section 15 located below the intermediate heating section 14) can be increased. This effectively prevents the workpiece from being overheated and allows for more precise control of the depth of the hardened layer of the workpiece due to quenching.

[0035] Furthermore, the heating coil (coil body 1) has a heating section 4 that is bent in an inverted S-shape in the vertical direction, forming an intermediate heating section 14 and a lower heating section 15. This reduces the amount of current that does not contribute to heating the workpiece, allowing for effective heat treatment of the workpiece with less power.

[0036] In addition, since the heating coil (coil body 1) is formed by a molding method using a three-dimensional printer device M (i.e., a partial welding and lamination method of conductive material powder layers based on three-dimensional data), it can be manufactured very easily despite the complex shape of the series of circumferential heating sections 4 having an intermediate heating section (first conductive section) 14 and a lower heating section (second conductive section) 15. Furthermore, products with the same shape and characteristics can be manufactured efficiently with good reproducibility, regardless of the skill of the manufacturing worker. Moreover, since the heating coil (coil body 1) is formed by a molding method using a three-dimensional printer device M, there are no bonding parts made by silver solder like in conventional heating coils. Therefore, it does not deform even when the temperature rises due to continuous use, and standard heat treatment (quenching treatment) can be performed for a long period of time.

[0037] Furthermore, the heating coil (coil body 1) is configured such that the lower part of the adjacent intermediate heating section (first conductive section) 14 and the upper part of the lower heating section (second conductive section) 15 form parallel flat surfaces (horizontal planes). As a result, the magnetic flux generated by the intermediate heating section (first conductive section) 14 and the magnetic flux generated by the lower heating section (second conductive section) 15 intersect at a long distance (γ in Figure 11). This results in a large amount of magnetic flux canceling each other out, which is highly effective in preventing the workpiece from being overheated, and allows for extremely precise control of the depth of the hardened layer of the workpiece due to quenching.

[0038] <Examples of modifications to the heating coil> The heating coil according to the present invention is not limited in any way to the embodiments described above, and the material, size, grounding portion, support portion, heating portion (first conductive portion, second conductive portion), shape and structure of the cooling medium flow path, etc. can be appropriately modified as necessary without departing from the spirit of the present invention.

[0039] For example, the heating section is not limited to having an annular shape in plan view, as in the above embodiment, but can be changed to have a rectangular periphery in plan view, etc. Also, the heating section is not limited to having one pair of first conductive parts and second conductive parts, as in the above embodiment, but can be changed to having two or more pairs of first conductive parts and second conductive parts. When the heating section is formed by creating multiple pairs of first conductive parts and second conductive parts in this way, it becomes even easier to control the depth of the hardened layer by quenching the workpiece.

[0040] In addition, the heating coil according to the present invention is not limited to one in which a pair of grounding parts and a pair of support parts are insulated by an insulating plate made of fluororesin (PTFE, PFA, FEP, ETFE, PCTFE, ECTFE, PVDF), as in the above embodiment, but can also be changed to one in which a pair of grounding parts and a pair of support parts are insulated by an insulating plate made of other synthetic resins having insulating and heat-resistant properties such as polyacetal (POM), polyphenylene sulfide (PPS), or polyetheretherketone (PEEK).

[0041] As the heating coil according to the present invention exhibits the excellent effects described above, it can be suitably used as a component for heating a workpiece using electromagnetic induction.

[0042] 1...Heating coil 2a, 2b...Grounding part 3a, 3b...Support part 4...Heating part 6...Cooling medium flow path 7a...Discharge port 7b...Inlet 9...Cooling medium flow path 10...Cooling medium flow path 11...Cooling medium flow path 14...Intermediate heating part (first conductive part) 15...Lower heating part (second conductive part)

Claims

1. A heating coil for use in a high-frequency heating device for heating a workpiece using electromagnetic induction by a high-frequency current, comprising: a pair of plate-shaped grounding portions for contacting electrodes through which a high-frequency current is passed; a pair of plate-shaped support portions arranged perpendicular to each of the grounding portions; and a series of circumferential heating portions provided to connect the tips of the support portions, wherein the heating portions comprise a first conductive portion that allows the high-frequency current supplied from the grounding portion to flow in a first direction, and a second conductive portion that allows the high-frequency current supplied from the grounding portion to flow in a second direction opposite to the first direction.

2. The heating coil for a high-frequency heating device according to claim 1, characterized in that the first conductive part and the second conductive part are arranged concentrically in the upper and lower directions at a predetermined distance apart.

3. The heating coil for a high-frequency heating device according to claim 1, characterized in that a part of the heating section is bent in an S-shape or inverted S-shape in the vertical direction, thereby forming the first conductive section and the second conductive section.

4. A heating coil for a high-frequency heating device according to claim 1, characterized in that it is integrally formed using a fabrication method that involves repeatedly laying, melting, solidifying, and layering powder made of a conductive material based on three-dimensional data, or a fabrication method that involves layering molten conductive material based on three-dimensional data.

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