BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an induction heating coil, and a method for manufacturing the induction heating coil.

2. Description of Related Art

An induction heating coil may be used in order to, for example, subject metal machine parts such as a shaft to a heat treatment by high frequency induction heating (see JP 2013-136819A, for example). An induction heating coil disclosed in JP 2013-136819A includes a circular ring-shaped coil section which is constituted to surround a shaft serving as a treatment target. A large current is supplied to the coil section to operate it to carry out the induction heating.

This high electrical current is supplied to the coil section via, for example, a metal member (power supply section) that is brazed on the coil section. Furthermore, the coil section is cooled because its temperature increases. For preventing the temperature increased, a cooling water passage is provided in the inside of the power supply section and the inside of the coil section.

Cooling water reaches the inside of the coil section through the inside of the power supply section, and cools the coil section. The cooling water that has passed through the coil section is returned through the inside of the power supply section.

SUMMARY OF THE INVENTION

A coil section is formed in a cylindrical shape with thin shell as a whole, and the inside of this cylindrical portion is a hollow space for cooling water there in. Accordingly, the coil section has a complicated shape, and it is difficult to make the coil section from a single member. The coil section is thus formed in a shape having a hollow space by brazing a plurality of members. Also, this coil section is brazed in the state of abutting against an end portion in the longitudinal direction of the circumferential portion surrounding the cooling water passage of the power supply section. Accordingly, the coil section is fixed to the power supply section.

In order to perform a brazing operation with accuracy, however, proficient skill is needed. And the accuracy in brazing of a plurality of members constituting the coil section, and brazing between the coil section and the power supply section tends to vary widely. Accordingly, the brazing accuracy is largely influenced by the skills of the operator who performs brazing. As a result, it is difficult to keep the brazing accuracy constant for each induction heating coil, and also difficult to make the induction heating coils in mass production with them formed in same (uniform) dimensions or shapes each other.

Furthermore, when the plurality of members constituting the coil section are brazed to each other, and when the coil section and the power supply section are brazed to each other, the brazing temperature is high, and thus heat strain inevitably occurs between the plurality of members constituting the coil section and between the coil section and the power supply section. Accordingly, a special jig is needed for lowering such heat strain, when brazing is performed on the coil section and the power supply section. Design of this jig as well requires a high level intuition and experience for lowering heat strain in the coil section and the power supply section.

Furthermore, when brazing is performed on the coil section and the power supply section, it takes not only time for setting the above-described jig but also a lot of troublesome works to prepare the jig, resulting in a lowered efficiency of producing the induction heating coils. Moreover, processes of brazing and machining the induction heating coil are low in their flexibility to set their conditions. This will reduce the scope of conditions in setting the shape of the induction heating coil for achieving the heat treatment most appropriate for a treatment target subjected to the treatment. Furthermore, since the brazed section has a larger electrical resistivity than that of other parts of the coil section, the brazed section is likely to generate heat, largely expands and shrinks, and is likely to be subjected to fatigue failure. Accordingly, the lifetime (occurrence of crack or breaking) of the brazed section becomes the lifetime of the induction heating coil. Therefore, design of the brazed section requires further intuition and experience.

In view of the above-described circumstances, it is an object of the present invention to provide an induction heating coil manufacturing method by which an induction heating coil so as to have a longer lifetime can be manufactured, and the induction heating coil.

Furthermore, it is another object of the present invention to manufacture the induction heating coil more easily and with higher accuracy, further improving the efficiency of producing the induction heating coil.

(1) In order to solve the above-described problem, an induction heating coil according to an aspect of the present invention includes: a coil section configured to heat a treatment target by induction; a power supply section configured to supply power to the coil section; and a cooling medium passage that is arranged in the power supply section and the coil section, and is configured to supply a cooling medium to the coil section, wherein the coil section, the power supply section, and the cooling medium passage are formed using a metal additive fabrication method.

According to this configuration, the cooling medium passage in the coil section and the power supply section is formed using a metal additive fabrication method. In the metal additive fabrication method, it is possible to form any three-dimensional shape by repeatedly performing an operation in which a powder metal layer is selectively heated and melted, and then this melted metal is allowed to harden. Therefore, even when the cooling medium passage formed in the coil section and the power supply section has a complicated shape, it is possible to form the coil section and the power supply section as a single member of unified structure. Accordingly, no brazed section needs to be provided either on the coil section itself or between the power supply section and the coil section. This eliminates the need for a brazing operation that requires proficiency. Furthermore, the metal additive fabrication method enables mass production of uniformly-shaped induction heating coils with high mechanical accuracy. It is thus possible to mass-produce induction heating coils with uniform dimensions.

Moreover, since the formation of the coil section itself does not need brazing, and also the coil section and the power supply section do not need to be brazed, heat strain that is caused by a brazing operation does not occur in the coil section itself and does not occur between the power supply section and the heating coil section.

Therefore, no special jig for lowering such heat strain is needed, making it possible to manufacture the induction heating coil more easily.

Furthermore, since an operation for setting the above-described jig for brazing is not needed, it is possible to raise the efficiency of producing the induction heating coil. Moreover, when the metal additive fabrication method is used, the flexibility in setting the shape is high. This can achieve a high flexibility in setting the shape of the induction heating coil for achieving the heat treatment most appropriate for a treatment target subjected to the treatment. Furthermore, since a brazed section, in which electrical resistance is discontinuous, is not needed, it is possible to reduce imbalance in heat stress in the coil section and a connection section at which the power supply section and the coil section are connected to each other. Accordingly, the lifetime of the induction heating coil can further be extended.

Therefore, according to the above-described configuration, it is possible to manufacture the induction heating coil so as to have a longer lifetime. It is furthermore possible to manufacture the induction heating coil more easily and with higher accuracy, and to further improve the efficiency for producing the induction heating coil.

(2) It is preferable that a support section configured to support a predetermined portion of the induction heating coil is formed when the induction heating coil is formed by the metal additive fabrication method, and the induction heating coil has a post-removal section that remains after the support section has been removed.

According to this configuration, the support section can be used for preventing, for example, the coil section serving as a predetermined portion and a projection projecting from the power supply section, from causing positional aberration such as sinking of the coil section into the metal powder layer due to its own weight, during fabrication by the metal additive fabrication method. Accordingly, it is possible to improve the dimensional accuracy of the induction heating coil. The induction heating coil formed with such a support section will have a post-removal section.

(3) It is more preferable that the coil section has a height that is smaller than that of the power supply section, and is formed in a shape projecting from the power supply section, and the support section is formed so as to support the coil section that serves as the predetermined portion when the induction heating coil is formed by the metal additive fabrication method.

According to this configuration, the induction heating coil having the thin coil section can be formed with accuracy.

(4) It is preferable that the cooling medium passage includes a power supply section side passage formed in the power supply section, and a coil section side passage formed in the coil section, and a connection section at which the power supply section side passage and the coil section side passage are connected to each other has a cross-sectional area that changes continuously in the traveling direction of the cooling medium.

Ordinarily, the shape of the connection section at which the power supply section and the coil section are connected to each other changes largely, and heat stress is likely to increase locally in the connection section. In the periphery of this connection section, the shape of the cooling medium passage changes continuously. Accordingly, it is possible to suppress imbalance in heat stress in the connection section. It is thus possible to further extend the lifetime of the induction heating coil.

(5) It is preferable that the cooling medium passage includes a coil section side passage formed in the coil section, the coil section side passage has a rising and falling section, and the rising and falling section extends in the circumferential direction of the coil section while rising and falling in the thickness direction of the coil section.

According to this configuration, a larger contact area between the coil section and the cooling medium can be ensured. Accordingly, it is possible to absorb the heat generated by the coil section by the cooling medium more efficiently, making it possible to more reliably suppress imbalance in heat stress due to overheating of the coil section. The ease of manufacturing of the induction heating coil including the cooling medium passage having such a complicated three-dimensional shape will become significant by the use of the additive fabrication method.

(6) It is preferable that the induction heating coil further includes a second cooling medium passage and a spray nozzle through which a treatment target cooling medium for cooling the treatment target that was induction-heated by the coil section passes, wherein the second cooling medium passage and the spray nozzle are formed using the metal additive fabrication method, the spray nozzle is connected to the second cooling medium passage, and the spray nozzle is open toward portions where the coil section is opposite to the treatment target during the heat treatment of the treatment target, and is capable of spraying the treatment target cooling medium onto the treatment target.

According to this configuration, it is possible to cool the treatment target that was induction-heated by the coil section by the treatment target cooling medium. Accordingly, the ease of manufacturing of the induction heating coil including the second cooling medium passage in addition to the cooling medium passage will become significant by the use of the additive fabrication method.

(7) In order to solve the above-described problem, a method for manufacturing an induction heating coil according to an aspect of the present invention includes a metal additive fabrication step of forming, using a metal additive fabrication method, a coil section configured to heat a treatment target by induction, a power supply section configured to supply power to the coil section, and a cooling medium passage that is arranged in the power supply section and the coil section, and is configured to supply a cooling medium to the coil section.

According to this configuration, the cooling medium passage in the coil section and the power supply section is formed using the metal additive fabrication method. In the metal additive fabrication method, it is possible to form any three-dimensional shape by repeatedly performing an operation in which a powder metal layer is selectively heated and melted, and then this melted metal is allowed to harden. Therefore, even when the cooling medium passage formed in the coil section and the power supply section has a complicated shape, it is possible to form the coil section and the power supply section as a single member of unified structure. Accordingly, no brazed section needs to be provided either on the coil section itself or between the power supply section and the coil section. This eliminates the need for a brazing operation that requires proficiency. Furthermore, the metal additive fabrication method enables mass production of uniformly-shaped induction heating coils with high mechanical accuracy. It is thus possible to mass-produce induction heating coils with uniform dimensions.

Moreover, since the formation of the coil section itself does not need brazing, and also the coil section and the power supply section do not need to be brazed, heat strain that is caused by a brazing operation does not occur in the coil section itself and does not occur between the power supply section and the heating coil section. Therefore, no special jig for lowering such heat strain is needed, making it possible to produce the induction heating coil more easily.

Furthermore, since an operation for setting the above-described jig for brazing is not needed, it is possible to raise the efficiency of producing the induction heating coil. Moreover, when the metal additive fabrication method is used, the flexibility in setting the shape is high. This can achieve a high flexibility in setting the shape of the induction heating coil for achieving the heat treatment most appropriate for a treatment target subjected to the treatment. Furthermore, since a brazed section, in which electrical resistance is discontinuous, is not needed, it is possible to reduce imbalance in heat stress in the coil section and the connection section at which the power supply section and the coil section are connected to each other. Accordingly, the lifetime of the induction heating coil can further be extended.

Therefore, according to the above-described configuration, it is possible to manufacture the induction heating coil so as to have a longer lifetime. It is furthermore possible to manufacture the induction heating coil more easily and with higher accuracy, and to further improve the efficiency for producing the induction heating coil.

(8) It is preferable that the metal additive fabrication step forms a support section configured to support a predetermined portion of the induction heating coil, and the method further includes a removal step of removing the support section.

According to this configuration, the support section can be used for preventing, for example, the coil section serving as a predetermined portion and a projection projecting from the power supply section, from causing positional aberration such as sinking of the coil section into the metal powder layer due to its own weight, during fabrication by the metal additive fabrication method. Accordingly, it is possible to improve the dimensional accuracy of the induction heating coil.

(9) In order to solve the above-described problem, an induction heating coil according to an aspect of the present invention includes: a coil section configure to heat a treatment target by induction; a power supply section configured to supply power to the coil section; and a cooling medium passage that is arranged in the power supply section and the coil section, and is configured to supply a cooling medium to the coil section, wherein the coil section, the power supply section, and the cooling medium passage are formed in one piece using a single member of unified structure.

According to this configuration, no brazed section needs to be provided either on the coil section itself or between the power supply section and the coil section. Accordingly, heat strain that is caused by a brazing operation does not occur between the power supply section and the heating coil section. Therefore, no special jig for lowering such heat strain is needed, making it possible to produce the induction heating coil more easily. Furthermore, since an operation for setting the above-described jig for brazing is not needed, it is possible to raise the efficiency of producing the induction heating coil. Furthermore, since a brazed section, in which electrical resistance is discontinuous, is not needed, it is possible to reduce imbalance in heat stress in the coil section and the connection section at which the power supply section and the coil section are connected to each other. Accordingly, the lifetime of the induction heating coil can further be extended.

According to the above-described configuration, it is thus possible to manufacture the induction heating coil so as to have a longer lifetime.

(10) In order to solve the above-described problem, an induction heating coil according to an aspect of the present invention includes: a coil section configured to heat a treatment target by induction; a power supply section configured to supply power to the coil section; and a cooling medium passage that is arranged in the power supply section and the coil section, and is configured to form a void through which a cooling medium is supplied to the coil section, wherein the coil section is formed in one piece of unified structure from the same electrically-conductive metal material, the coil section does not have a brazed configuration at any position thereof, and variation in electrical resistivity of the metal material per unit volume (mm3) is 5% or less.

According to this configuration, no brazed section is provided in the coil section. Therefore, heat strain that is caused by a brazing operation does not occur in the coil section. Accordingly, since a brazed section, in which electrical resistance is discontinuous, is not needed, it is possible to reduce imbalance in heat stress in the coil section. Accordingly, the lifetime of the induction heating coil can further be extended. Furthermore, the coil section is formed in one piece of unified structure from the same electrically-conductive metal material. Therefore, as compared with the conventional coil section that is formed by brazing to combine a plurality of pieces which are made from different kind of metal materials respectively, variation in electrical resistivity per unit volume in the entire region of the coil section is small. Furthermore, variation in electrical resistivity (Ω·m) per unit volume (1 mm3) in the entire region of the coil section is 5% or less. Therefore, there is not likely to be a difference in the variation in expansion and shrinkage amount of the coil section when the coil section expands and shrinks due to heat. Accordingly, fatigue failure in the coil section can be prevented, and the extension of the lifetime of the coil section can further extend the lifetime of the induction heating coil.

According to the above-described configuration, it is thus possible to manufacture the induction heating coil so as to have a longer lifetime.

(11) It is more preferable that the coil section and the power supply section are formed in one piece of unified structure from the same metal material, the coil section and the power supply section do not have a brazed configuration at any position thereof, and a variation in electrical resistivity of the metal material per unit volume (mm3) is 5% or less.

According to this configuration, no brazed section is provided in the coil section and the power supply section. No brazed section is thus provided in the connection section at which the coil section and the power supply section are connected to each other either. Accordingly, heat strain that is caused by a brazing operation does not occur in the coil section and the power supply section. Accordingly, since a brazed section, in which electrical resistance is discontinuous, is not needed, it is possible to reduce imbalance in heat stress in the coil section and the power supply section. Accordingly, the lifetime of the induction heating coil can further be extended. Furthermore, the coil section and the power supply section are formed in one piece of unified structure from the same electrically-conductive metal material. Therefore, as compared with the conventional coil section and power supply section that are formed by brazing to combine a plurality of pieces which are made from different kind of metal materials respectively, variation in electrical resistivity per unit volume in the entire region of the coil section and the power supply section is small. Furthermore, variation in electrical resistivity (Ω·m) per unit volume (1 mm3) in the entire region of the coil section and the power supply section is 5% or less. Therefore, there is not likely to be a difference in the variation in expansion and shrinkage amount of the coil section and the power supply section in case of the expansion or shrinkage caused on the sections under thermally-stressed conditions. Accordingly, fatigue failure in the coil section and the power supply section can be prevented, and the extension of the lifetime of the coil section and the power supply section can further extend the lifetime of the induction heating coil.

Note that the foregoing and other objects, features, and advantages of the present invention will become apparent by reading the description below with reference to the accompanying drawings.

