JP2000239735A - Method for controlling hardening depth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of hardening depth, with which the defective work is reduced, and also the hardening depth control with high precision is attained even in the case of changing a hardening apparatus. SOLUTION: When plural works of the same kind are surface-hardened with a high frequency induction heating for the purpose of reserching the relation between the hardening depth and a coil voltage, the heating and hardening are executed with the preset coil voltage, and the allowable range of a pattern of the necessary coil voltage to control the hardening depth in the standard range is found from the relation between the pattern changing with time of the coil voltage and the hardening depth obtd. The changing pattern of the coil voltage in each heating in the practical hardening after this research hardening, is analyzed and the hardening depth is adjusted by judging whether the changing pattern of the coil voltage is controlled with the allowable range or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching depth management method for indirectly managing the quenching depth by surface quenching using high-frequency induction heating without cutting a workpiece.

[0002]

2. Description of the Related Art In surface quenching using high-frequency induction heating,
A high-frequency current is applied to a heating coil facing the surface of the work, the surface is heated by an induced current generated on the surface of the work, and when the temperature reaches a predetermined temperature, the surface of the work is rapidly cooled to quench the surface. Form a layer.

In such surface quenching, usually, the same type of workpiece is continuously quenched. Before a series of quenching, the quenching conditions such as the current value, voltage value, and frequency to be added to the heating coil, the heating time, the amount of cooling water, and the distance (gap) from the coil to the work surface are optimized. Set empirically. However, in the subsequent series of quenching, even if the workpieces are the same type, the quenching depth is reduced due to dimensional variations between the individual workpieces, variations in the material, and variations in the gap during setting. There is a problem that it does not become constant.

[0004] The applicant of the present application has proposed in Japanese Patent Application No. 8-181259, that is, Japanese Patent Application Laid-Open No.
No. 8130 has proposed a quenching depth control method.

In this quenching depth control method, when a plurality of workpieces of the same kind are surface quenched by high-frequency induction heating, heating is performed at a preset current and voltage in order to investigate the relationship between quenching depth and heating power. After performing quenching, the relationship between the time-dependent change pattern of the power obtained during heating and the quenching depth during this survey quenching indicates the power change pattern necessary to manage the quenching depth within the specified range. Determine the allowable range, perform heating while fixing the power supply voltage in the subsequent quenching, investigate the power change pattern for each heating, whether the investigated power change pattern is managed within the allowable range Is determined to determine the quenching depth.

[0006]

However, the above quenching depth management method only examines the results after quenching,
As a result of the investigation, a work that does not fall within the specification range becomes a defective product.

Further, since the power change pattern includes a loss due to a lead or the like between the power supply and the heating coil, the energy input to the work is not monitored. For this reason, if the quenching device is changed and the length of the lead from the power supply to the heating coil changes, the loss also changes, so that even if the power change pattern is monitored, the energy used for actual quenching does not increase. Therefore, it was difficult to accurately control the quenching depth.

For example, since a quenching device used for surface quenching at the stage of trial production of a workpiece is often different from a quenching device for actually performing surface quenching, the power change pattern obtained by the survey quenching is different. Sometimes it makes no sense.

The present invention has been made in view of the above circumstances, and it is possible to reduce the number of defective workpieces and to control the quenching depth with high accuracy even if the quenching device is changed. It aims to provide a depth control method.

[0010]

SUMMARY OF THE INVENTION A quenching depth management method according to the present invention is used for investigating the relationship between quenching depth and coil voltage when surface hardening a plurality of similar workpieces by high frequency induction heating. By performing heating and quenching at a coil voltage set in advance, the quenching depth falls within the standard range from the relationship between the temporal change pattern of the coil voltage obtained at the time of heating in this investigation quenching and the quenching depth. Obtain the allowable range of the coil voltage change pattern required for management, investigate the coil voltage change pattern for each heating in the subsequent main quenching, and manage the checked coil voltage change pattern within the allowable range. The quenching depth is managed by determining whether or not the quenching is performed.

In addition, it is determined whether or not the pattern of the coil voltage for each heating in the main quenching is within the permissible range, and is controlled to return to within the permissible range just before the pattern deviates from the permissible range.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the shape and quenching area of a work, (a) is a longitudinal sectional view, and (b) is a partial front view. FIG. 2 is a configuration diagram of a quenching facility, and FIG. 3 is a schematic perspective view of a heating coil, where (a) shows a stem portion and (b) shows a cup portion. 4A and 4B are graphs showing a change pattern of the coil voltage. FIG. 4A shows the stem portion, and FIG. 4B shows the cup portion.

The work 10 is a constant velocity joint used in a drive system of an automobile here. Hardened layers 11 ′ and 12 ′ are provided on the outer surface of a stem portion 11 and the inner surface of a cup portion 12.
Are respectively formed.

As shown in FIG. 2, the quenching equipment includes an oscillator 20 for generating a high-frequency voltage based on a predetermined power supply voltage.
An output transformer 30 for converting a high-frequency voltage generated by the oscillator 20 to a low voltage to obtain a large current;
A heating coil 40 connected to the heating coil 40, a coil voltage monitor 50 connected to the heating coil 40 and monitoring a coil voltage of the heating coil 40, and a comparison unit 70 for comparing the coil voltage with a change pattern of the coil voltage. Comparison section 70
And a control unit 80 for controlling the oscillator 70 so that the coil voltage falls within the change pattern just before the coil voltage deviates from the change pattern based on the comparison result of the above. The coil voltage monitor 50 detects a voltage applied to the heating coil 50, and displays a temporal change of the coil voltage when heating the work 10 on the display 60.

As for the heating coil 40 for heating the outer surface of the stem portion 11 of the work 10, as shown in FIG. 3 (a), the heating coil 40 is bent corresponding to the axial outer surface shape of the stem portion 2. This is a semi-open saddle coil in which both ends of the straight portions 41, 41 are connected to each other by arc portions 42, 43. Further, the heating coil 40 for heating the inner surface of the cup portion 12 of the work 10 has, as shown in FIG.
This is a spiral coil whose winding diameter is changed in the axial direction so as to face the inner surface of the cup portion 12.

In the quenching operation, after investigating and quenching a small number of works 10, a large number of remaining works 10 are quenched one after another.

To harden the outer surface of the stem 11 of the work 10 in both the investigation hardening and the main hardening, the heating coil 40 is opposed to the stem 11 and the work 10 is rotated in this state. , A predetermined voltage is applied to the oscillator 20. Thus, the quenched portion on the outer surface of the stem portion 110 is heated by the induced current.

In the investigation and quenching, the coil voltage at the time of heating is set to an appropriate value estimated from experience. When this voltage is applied to the oscillator 20, the coil voltage detected by the coil voltage monitor 50 starts to increase at the same time as the voltage is applied, as shown in FIG. It becomes a pattern.

When the heating is completed, the heating portion is rapidly cooled by spraying a quenching liquid to form a quenched layer 11 '. After quenching, the work 10 is cut open to check the depth of the quenched layer 11 '. From the depth and the specified range of the quenching depth, an allowable range of the coil voltage change pattern required to keep the quenching depth within the specified range, that is, an upper limit and a lower limit are obtained. If the power supply voltage needs to be corrected, make the correction. In any case, with respect to a specific power supply voltage, an allowable range of a change pattern of the coil voltage required to keep the quenching depth within the standard range is obtained. This change pattern of the coil voltage is shown in FIG.

In addition, for a few seconds from the start of heating, for a few seconds,
Since the change pattern of the coil voltage is not stable, it is desirable to exclude the change from the allowable range.

The change pattern of the coil voltage (FIG. 4 (a)) obtained by the investigation and quenching is input to the comparison unit 70 in advance, and is used for feedback at the time of main quenching.

The above is Survey Yaki1. After the completion of the survey quenching, the power supply voltage is fixed at a predetermined value, and the outer surface of the stem portion 11 of the work 10 is heated one after another to perform the main quenching. In the main quenching, the power change pattern is checked by the coil voltage monitor 50 for each heating. Then, the comparison unit 70 compares whether or not the change pattern of the coil voltage is within the allowable range obtained by the investigation and quenching for all the works 10. That is, when the change pattern of the coil voltage is within the allowable range, the comparison unit 70 outputs the fact to the control unit 80. As a result, the control unit 80 does not change the voltage oscillated from the oscillator 20.

Before the coil voltage goes out of the permissible range, the comparing section 70 outputs the fact to the control section 80 before the coil voltage goes out of the permissible range, and the oscillator 20 controls the voltage so that the coil voltage falls within the permissible range. To change. For example, the comparison unit 70 determines that the coil voltage is 10% before the upper limit value or 1% below the lower limit value.
At the point of time when it is 0% before, the fact is outputted to the control unit 80. Note that the value of 10% can be changed as appropriate.

The change in coil voltage reflects not only a change in impedance on the work side due to a change in the material of the work 10 and a change in the gap, but also a change in impedance on the hardening equipment side due to deterioration of the heating coil 40, deterioration of the core, and the like. You.
Since the quenching depth changes due to these impedance changes, the quenching depth is managed by the coil voltage change pattern, so that the management is performed accurately.

When the inner surface of the cup portion 12 is hardened,
First, investigation and quenching are performed to determine an allowable range of a coil voltage change pattern as shown in FIG. 4B.
Then, in the main quenching after the investigation quenching, heating quenching is performed at a predetermined power supply voltage, and a change pattern of the coil voltage is examined by the coil voltage monitor 50 for each heating. Then, the comparison unit 70 compares whether or not the change pattern of the coil voltage is within the allowable range obtained by the investigation and quenching for all the works 10. The operation of the control unit 80 based on the result of the comparison is the same as that in the case of the main quenching of the stem unit 11 described above, and thus a detailed description is omitted.

Thus, the quenching depth of the inner surface of the cup portion 12 is accurately controlled.

The present embodiment is a method for managing the quenching depth when the work 10 is a constant velocity joint, but it is needless to say that the present invention is not limited to this and can be applied to surface quenching of other works.

[0028]

As described above, the quenching depth management method according to the present invention investigates the relationship between the quenching depth and the coil voltage when surface hardening a plurality of similar workpieces by high-frequency induction heating. For this purpose, heat quenching is performed at a preset coil voltage, and the relationship between the quenching depth and the time-dependent change pattern of the coil voltage obtained during heating during this survey quenching is used to set the quenching depth within a specified range. Determine the allowable range of the coil voltage change pattern necessary to manage within, and investigate the coil voltage change pattern for each heating in the subsequent main quenching, and the investigated coil voltage change pattern is within the allowable range. The quenching depth is managed by determining whether or not the quenching is performed.

Therefore, in the case of the quenching depth control method according to the present invention, when quenching a plurality of similar workpieces to the surface, the quenching depth is estimated from the change pattern of the coil voltage in each heating. It can be determined with high accuracy whether the quenching depth is within the standard range. In particular, since the quenching depth is estimated from the conventional power change pattern, the energy input to the work itself is monitored without loss due to leads etc. between the power supply and the heating coil.
Since the quenching device is changed and the change in the coil voltage due to the change in the length of the lead from the power supply to the heating coil is included, a more accurate quenching depth management method becomes possible. For this reason, even if the quenching device used for surface quenching in the trial production stage of the workpiece is different from the quenching device that actually performs surface quenching, the change pattern of the coil voltage obtained by the survey quenching is different. Is not meaningless.

In addition, it is determined whether or not the pattern of the coil voltage for each heating in the main quenching is within the allowable range, and the control is performed so as to return to within the allowable range just before the pattern deviates from the allowable range. It becomes possible to reduce the work which becomes defective.

[Brief description of the drawings]

1A and 1B show a shape and a quenching region of a work, wherein FIG. 1A is a longitudinal sectional view, and FIG.

FIG. 2 is a configuration diagram of a quenching facility.

FIGS. 3A and 3B are schematic perspective views of a heating coil, wherein FIG. 3A shows a stem portion and FIG. 3B shows a cup portion.

FIG. 4 is a graph showing a change pattern of a coil voltage;
(A) shows about a stem part, (b) shows about a cup part.

[Explanation of symbols]

 Reference Signs List 10 Workpiece 20 Oscillator 30 Output transformer 40 Heating coil 50 Coil voltage monitor 60 Display 70 Comparison unit 80 Control unit

Claims (2)

[Claims] In order to investigate the relationship between the quenching depth and the coil voltage when performing surface quenching of a plurality of similar workpieces by high-frequency induction heating, heating and quenching are performed at a preset coil voltage. From the relationship between the temporal change pattern of the coil voltage obtained during quenching heating and the quenching depth, the allowable range of the coil voltage change pattern required to manage the quenching depth within the specified range was calculated. By examining the coil voltage change pattern for each heating in the subsequent main quenching, determine whether the investigated coil voltage change pattern is managed within the allowable range, the quenching depth A quenching depth management method characterized by management. 2. The method according to claim 1, further comprising: determining whether a coil voltage pattern for each heating in the main quenching is within the allowable range, and performing control to return the coil voltage to within the allowable range just before the pattern deviates from the allowable range. The quenching depth management method according to claim 1.