JP3932809B2 - Low strain quenching equipment and quenching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a method for performing low strain quenching on a shaft-shaped workpiece.
[0002]
[Prior art]
A technique is known in which a high-frequency current is induced and heated on the work surface, the heated work surface is cooled, and the work surface is quenched. In order to induce a high-frequency current on the work surface, a high-frequency heating coil is placed at a position facing and close to the work surface, and a high-frequency current is induced on the work surface by applying a high frequency to the coil.
[0003]
When the workpiece is long, a ring coil or a line coil is used. According to the ring coil, high-frequency current flows in the circumferential direction of the workpiece, and the workpiece is easily heated uniformly in the circumferential direction. For example, when a key groove extending in the longitudinal direction (axial direction) is formed on the outer periphery of the workpiece, the nonuniformity of heating in the key groove portion and the non-key groove portion is reduced by flowing a current in the circumferential direction by the ring coil. Can do. On the other hand, according to the line coil, a high frequency current flows in the longitudinal direction of the workpiece, and the workpiece is easily heated uniformly in the longitudinal direction. For example, when a screw is formed on the outer periphery of the workpiece, the heating non-uniformity at the screw thread portion and the screw valley portion can be reduced by causing a current to flow in the longitudinal direction by the line coil. This is apparent in contrast to the opposite combination. When a workpiece having a key groove extending in the longitudinal direction on the outer periphery is heated by a line coil, the heating temperature is greatly different between the key groove portion and the non-key groove portion. When a work having a screw formed on the outer periphery is heated by a ring coil, the heating temperature is greatly different between the thread portion and the thread valley portion.
[0004]
Japanese Patent Laid-Open No. 9-315133 discloses a line coil for high-frequency heating of a workpiece in which a large-diameter portion and a small-diameter portion are continuous in the longitudinal direction and a groove extending in the longitudinal direction is formed on the outer periphery of the large-diameter portion. And a technique that uses a ring coil in combination. By using a line coil, heating nonuniformity at the large diameter portion and the small diameter portion is suppressed, and by using a ring coil, heating nonuniformity at the groove portion and the non-groove portion is suppressed.
[0005]
In the present invention, an axial workpiece having a substantially circular cross section is quenched. That is, a workpiece whose cross section is not circular and has a groove extending in the axial direction on the outer periphery is not treated. However, the workpiece is not limited to a workpiece having a completely circular cross section. Although the cross section of the workpiece with the screw formed on the surface does not become a perfect circle, it changes in the axial direction as a whole and has a uniform shape in the circumferential direction, heating the workpiece surface uniformly. For this purpose, a line coil is suitable.
The workpiece to which the present invention is subjected to the quenching process is a workpiece having a shape in which the surface of the workpiece is uniformly heated by using a line coil rather than a ring coil. In this specification, such a workpiece is referred to as an axial workpiece. When heating the shaft-shaped workpiece uniformly, it is obvious from the above that a line coil is naturally used.
[0006]
It is inevitable that the work shape is deformed non-uniformly due to the quenching process and the work is distorted. However, there is a demand for keeping the distortion small.
The shaft-shaped workpiece that is the subject of the quenching process of the present invention is a workpiece having a shape in which the surface of the workpiece is uniformly heated by using a line coil rather than a ring coil. Distortion is suppressed more uniformly when heated and cooled than when unevenly heated and cooled. Therefore, in the past, when using a line coil rather than a ring coil to harden a shaft-shaped workpiece where the workpiece surface is heated uniformly, a system that uses a line coil to uniformly heat and cool the workpiece has been adopted. By doing so, the occurrence of distortion is suppressed. Obviously, the generation of distortion is suppressed as compared with the case where a method of heating and cooling non-uniformly using a ring coil is employed.
[0007]
[Problems to be solved by the invention]
However, there are cases where the distortion cannot still be suppressed. For example, in the case of a power steering rack that requires high dimensional accuracy, a small strain that cannot be suppressed becomes a problem, and thus a step of removing the strain after quenching is required.
Therefore, the present invention has been studied in order to realize a quenching technique that can further suppress distortion.
The inventor's research has confirmed that not only the heating homogeneity but also the time required for heating affects the strain generated in the quenching process. That is, even when the heating homogeneity was the same level, it was confirmed that the strain was suppressed when heated and cooled in a short time, but increased when heated and cooled for a long time.
As a result of further research, heating with a line coil certainly improves the heating uniformity, but the heating takes a long time, so the heating time is shortened without sacrificing the heating uniformity. It was recognized that the distortion can be further suppressed if it can be realized.
The present invention was developed based on this finding, and utilizes the property that distortion can be suppressed if the heating time can be shortened without impairing the homogeneity of heating.
[0008]
[Means, actions and effects for solving problems]
The present invention realizes a quenching apparatus that can suppress the occurrence of distortion to a level impossible in the prior art. This low-distortion quenching device includes a ring coil for preheating a shaft-shaped workpiece, a line coil for main heating the pre-heated workpiece, a cooling means for cooling the heated workpiece, and a shaft-shaped workpiece around the axis. Rotating means for rotating, and feeding means for moving the shaft-shaped workpiece along the axis from the ring coil to the cooling means via the line coil are provided.
[0009]
According to this quenching apparatus, preheating is first performed with a ring coil having good heating efficiency. In this preheating stage, the workpiece is not preheated uniformly in the axial direction. If quenched as it is, it is cooled from a non-homogeneously heated state, so that a large distortion occurs with the quenching process. However, in the present quenching apparatus, in order to cool the preheated shaft-shaped workpiece after the main heating by the line coil, the workpiece is uniformly heated immediately after the completion of the main heating and immediately before the cooling. For this reason, quenching with less distortion can be achieved by heating uniformly and cooling.
In the quenching apparatus of the present invention, since the preheating is performed with a ring coil with good heating efficiency, the entire heating time is shortened, and further, the heating uniformity is impaired because the main heating is performed with a line coil that can be heated uniformly. Absent. Since it is heated uniformly in a short time, distortion can be suppressed to a level that was impossible until now.
[0010]
In this apparatus, it is preferable to use a line coil having a plurality of line portions placed at equal distances from the workpiece rotation axis.
[0011]
According to this configuration, the heating time can be further shortened using the homogeneous heating force of the line coil, and the generation of distortion can be more effectively suppressed.
[0012]
The present invention has also created a quenching method that achieves unprecedented low strain. In this quenching method, the shaft-shaped workpiece is moved in the axial direction while rotating around the rotation axis, so that it is first preheated with a ring coil, then heated with a line coil, and then cooled.
[0013]
According to this quenching method, preheating is first performed with a ring coil with good heating efficiency, and then main heating is performed with a line coil that can be heated uniformly. It is possible to suppress distortion to a small level.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be implemented in the following forms.
(Mode 1) The direction of the current flowing through the ring portion of the ring coil and the direction of the current flowing through the line portion of the line coil are orthogonal to each other, and the ring coil and the line coil are close to each other with a certain distance.
(Mode 2) A plurality of line portions placed at an equal distance from the rotation axis of the workpiece are connected in series.
[0015]
【Example】
A low distortion quenching apparatus according to an embodiment will be described with reference to FIGS. The low distortion quenching apparatus 1 mainly includes a ring coil 4, a line coil 6, a cooling unit 14, a work rotating unit 44, a work feeding unit 46, a power supply unit 42, and a control unit 40.
[0016]
The ring coil 4 is composed of a copper square tube. 2 and 3, the ring coil 4 is a continuous tube from one end 22 to the other end 24 via the ring portion 5. A space 25 is provided at the center of the ring portion 5, and an axial workpiece W (hereinafter referred to as a workpiece W) penetrates in a concentric positional relationship.
The ring coil 4 is connected to the power supply unit 42. The ring coil 4 can flow the current supplied from the power supply unit 42 from the one end 22 to the other end 24 via the ring unit 5 (the reverse direction is also possible).
The inside of the square tube of the ring coil 4 is a cooling water passage 8. A coolant (in this case, water) for preventing the ring coil 4 from overheating when energized can flow through the cooling water passage 8. The cooling water passage 8 of the ring coil 4 extends from one end 22 to the other end 24 via the ring portion 5.
As shown in FIG. 1, the ring coil 4 is fixed by a ring coil frame 18 disposed on the upper surface of the line coil 6. The ring coil frame 18 is made of an insulating material.
[0017]
The line coil 6 is configured by combining copper square tube groups. 4 and 5, the line coil 6 has a plurality of line portions 10 and is a continuous tube from one end 26 to the other end 28 through the plurality of line portions 10. FIG. 6 shows a part of the current path of the line coil 6 as a skeleton. When the trace is traced from one end 26, the line portion 10 for inducing current to the work extends from the top to the bottom with a small radius. Yes. On the other hand, the current path extends from the bottom to the top in the large radius portion. The plurality of line portions 10 of the line coil 6 are connected in series so that the direction of current flow is aligned.
A space 29 is provided at the center of the line coil 6, and the workpiece W penetrates in a concentric positional relationship. The plurality of line portions 10 are placed at an equal distance from the rotation axis of the workpiece W.
The line coil 6 is connected to the power supply unit 42. The line coil 6 can cause the current supplied from the power supply unit 42 to flow from the one end 26 to the other end 28 via the plurality of line units 10 (and vice versa). The direction of the current flowing through the line unit 10 is the same.
The current flowing in the line portion 10 is in the axial direction of the workpiece W, the current flowing in the ring portion 5 of the ring coil 4 is in the circumferential direction of the workpiece W, and both are orthogonal to each other.
The inside of the square tube of the line coil 6 is a cooling water passage 12. A coolant (in this case, water) can be passed through the cooling water passage 12 to prevent the line coil 6 from overheating when energized. The cooling water passage 12 of the line coil 6 extends from one end 26 to the other end 28 via the plurality of line portions 10.
As shown in FIG. 1, the line coil 6 is fixed by a line coil frame 16 disposed above the cooling unit 14. The line coil frame 16 is made of an insulating material.
[0018]
The cooling unit 14 has a coolant injection port (not shown) that ejects a coolant (for example, water) for quenching the heated workpiece W toward the workpiece W. The coolant rebounded from the surface of the workpiece W by the coolant sprayed from the coolant spray port of the cooling unit 14 is configured not to flow backward to the line coil 6.
[0019]
The work rotation unit 44 holds one end of the work W by holding means (not shown), and rotates the work W around the rotation axis J (in the direction of arrow K). The rotation axis J of the workpiece W coincides with a straight line connecting the center of the space 25 and the center of the space 29. The rotation axis J of the workpiece W is orthogonal to the direction of the current flowing through the ring portion 5 of the ring coil 4 and parallel to the direction of the current flowing through the line portion 10 of the line coil 6.
[0020]
The workpiece feeding section 46 holds one end of the workpiece W by holding means (not shown), and moves the workpiece W along the axis J. The moving direction J of the workpiece W coincides with a straight line connecting the center of the space 25 and the center of the space 29.
[0021]
The operation when quenching the workpiece W will be described. In the operation preparation stage, water starts to flow through the cooling water passage 8 of the ring coil 4 and the cooling water passage 12 of the line coil 6. Cooling water continues to flow during operation of the quenching equipment.
The holding means group of the work rotating part 44 and the work feeding part 46 is operated to hold the work W. After holding the workpiece W, the workpiece rotating unit 44 rotates the workpiece W around the axis J (in the direction of arrow K) at the number of rotations controlled by the control unit 40. While rotating the workpiece W, the workpiece feeding unit 46 moves the workpiece W in the axis J direction at a moving speed controlled by the control unit 40. The moving speed is set based on the required quenching quality (mainly the quenching depth). The workpiece W first passes through the ring coil 4 while rotating, then passes through the line coil 6, and finally reaches the cooling unit 14.
[0022]
When quenching from the tip of the workpiece W, energization of the ring coil 4 is started before the tip of the workpiece W reaches the ring coil 4. When quenching the intermediate portion of the workpiece W, energization of the ring coil 4 is started immediately before the tip of the quenching area of the workpiece W arrives at the ring coil 4. The frequency and current value of the high-frequency current that flows through the ring coil 4 are set in advance to values appropriate for preheating.
When the ring coil 4 is energized with a high frequency current, an induced current IR flowing in the circumferential direction is induced in the vicinity of the surface of the work W, and the temperature in the vicinity of the work surface is increased. By using the ring coil 4, the workpiece W can be efficiently preheated in a short time.
[0023]
When quenching from the tip of the workpiece W, energization of the line coil 6 is started before the tip of the workpiece W reaches the line coil 6. When quenching the intermediate portion of the workpiece W, energization of the line coil 6 is started immediately before the tip of the quenching area of the workpiece W reaches the line coil 6. The frequency and current value of the high-frequency current passed through the line coil 6 are set in advance to values appropriate for the main heating of the preheated workpiece.
When the line coil 6 is energized with a high-frequency current, an induced current IL flowing in the axial direction is induced near the surface of the workpiece W, and the temperature near the workpiece surface increases. Since the workpiece W is preheated by the ring coil 4 in advance, the temperature range increase required by the line coil 6 is narrow. The line coil 6 is heated by slightly raising the temperature of the preheated workpiece surface. Since the main heating is performed by the line coil, the workpiece surface is heated uniformly.
[0024]
When heating is performed with an efficient ring coil, when the power consumption is the same, the workpiece can be heated in a shorter time than when heating with only the line coil, and the workpiece feeding speed can be increased. Although it is slow compared with the case of heating only by the ring coil, it can be heated more uniformly than the case of heating only by the ring coil.
The apparatus 1 of the present embodiment can obtain the advantages of the line coil 4 and the ring coil 6 and can heat them uniformly in a short time.
[0025]
The main heated workpiece W is quenched and quenched by the coolant sprayed from the coolant spray port of the cooling unit 14. Since the cooled workpiece W has been heated by the line coil 6 before cooling, the workpiece W is cooled from a state of being heated uniformly. Therefore, the distortion of the workpiece W after quenching (after cooling) is very small.
[0026]
When quenching to the rear end of the workpiece W, the energization of the ring coil 4 is stopped after the rear end of the workpiece W has passed through the ring coil 4, and after passing through the line coil 6, Stop energization. Further, when quenching the intermediate part of the workpiece W, the energization to the ring coil 4 is stopped immediately after the rear end of the quenching area of the workpiece W passes the ring coil 4, and immediately after the line coil 6 is passed. Stop energizing 6.
This quenching apparatus can perform low distortion quenching from the front end of the quenching area of the workpiece W to the rear end of the quenching area. By turning on and off the coil intermittently, a quenching region and a non-quenching region can be alternately arranged in one workpiece W.
When the quenching area length (axial length) of the workpiece W is significantly longer than the axial thickness of the ring portion 5 and the axial length of the line portion 10, the axial quenching is performed. The time obtained by dividing the entry area length by the moving speed is defined as the energization time.
[0027]
The quenching apparatus 1 and the quenching method according to the present embodiment are not limited to the length of the workpiece W to be quenched. Moreover, it is not limited to the thickness or surface shape of the workpiece W.
[0028]
In the quenching apparatus 1 and the quenching method according to the present embodiment, since the workpiece W is preheated in advance using the ring coil 4 with good heating efficiency, and then the main heating is performed with the line coil 6, efficient heat treatment is performed. Can be implemented. That is, an efficient quenching process can be performed.
After the main heating is performed on the workpiece W using the line coil 6, quenching is performed in the cooling unit 14, so that low strain quenching can be performed.
[0029]
Since the workpiece quenched by the quenching apparatus according to the present embodiment has a small distortion, the distortion removing step is omitted from the manufacturing process of a product having a high required quality of dimensional accuracy after quenching (for example, a power steering rack). Is possible.
[0030]
The quenching apparatus according to the embodiment includes a shaft-shaped workpiece having a step (for example, a drive shaft and a rear axle shaft), and a shaft-shaped workpiece (for example, a power steering rack) Suitable for low distortion quenching to ball screws. It is also suitable for low strain quenching to a shaft-shaped workpiece (for example, a side impact beam) having a hollow portion.
[0031]
Although the low distortion quenching apparatus and quenching method according to the embodiment have been described, the present invention is not limited to the above embodiment, and various modifications and improvements have been made based on the knowledge of those skilled in the art. Can be implemented.
For example, in the above-described embodiment, the case of a ring coil or line coil made of a copper square tube has been described as an example, but the ring coil or line coil to which the quenching apparatus and quenching method of the present invention can be applied. The material and the tube cross-sectional shape are not limited thereto. It may be a ring coil or a line coil made of a circular tube made of another material having good electrical conductivity and thermal conductivity. Moreover, although the case where the number of turns of the ring coil is 1 has been described as an example, the number of turns of the ring coil to which the quenching apparatus and the quenching method of the present invention can be applied is not limited thereto. The number of turns of the ring coil may be plural. Furthermore, the hardening apparatus provided with the some ring coil may be sufficient. Furthermore, a quenching apparatus including a plurality of line coils between the ring coil and the cooling unit may be used.
Moreover, although the case of the cooling part which quenches a workpiece | work by ejecting a cooling liquid was demonstrated as an example, the form of the cooling part which can apply the hardening apparatus and hardening method of this invention is not restricted to it. The present invention can also be applied to a quenching apparatus and a quenching method using a cooling unit in a form in which the workpiece immediately after the main heating is immersed in a cooling bath. This is particularly effective when quenching a workpiece that is not relatively long.
Moreover, you may make it move relatively by rotating or sending a coil with respect to the fixed workpiece | work.
[Brief description of the drawings]
FIG. 1 shows a quenching apparatus according to an embodiment.
FIG. 2 is a plan view of a ring coil according to an embodiment.
FIG. 3 is a side view of a ring coil according to an embodiment.
FIG. 4 is a plan view of a line coil according to an embodiment.
FIG. 5 is a side view of a line coil according to an embodiment.
FIG. 6 is a skeleton diagram in the current direction of the line coil.
[Explanation of symbols]
1: quenching device 4: ring coil 6: line coil 10: line part 14: cooling part

Claims (3)

A ring coil for preheating the shaft-shaped workpiece, a line coil for main heating the pre-heated workpiece, a cooling means for cooling the main heated workpiece, a rotating means for rotating the shaft-shaped workpiece around the axis, and a shaft shape A low distortion quenching apparatus comprising a feeding means for moving a work along an axis from a ring coil to a cooling means via a line coil. The low strain quenching apparatus according to claim 1, wherein the line coil has a plurality of line portions placed at equal distances from the workpiece rotation axis. A low-distortion quenching method characterized in that a shaft-shaped workpiece is moved in the axial direction while rotating around a rotation axis, whereby preheating is first performed with a ring coil, then main heating is performed with a line coil, and then cooling is performed.

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