JP2004010385A - Press-forming apparatus and press-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely control the temperature of molds; and to realize inexpensive and highly precise press-forming. <P>SOLUTION: A press-forming apparatus 1 produces a desired formed article by heating or pressurizing a raw material G arranged between an fixed upper mold 11 and a movable lower mold 12. The press-forming apparatus 1 is equipped with an induction coil 20 with a tap 20t, which coil is fixed at the periphery of the upper mold 11 and the lower mold 12, and a high-frequency electric power source 21 for supplying high-frequency current to the induction coil 20. It is possible to change the number of windings of the induction coil 20, effective for forming magnetic field at the periphery of the upper mold 11 and the lower mold 12, and to change the position of the magnetic field formed by the induction coil 20 by switching the tap of the induction coil 20 by operating a tap exchanger 22. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a press forming apparatus and a press forming method, and more particularly to a press forming apparatus and a press forming method suitable for forming a glass substrate or the like applied to a magnetic disk or the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, magnetic disks having a substrate made of a raw material such as glass or plastic have been widely used. Since such a magnetic disk substrate is required to have an extremely smooth surface, it is initially manufactured by cutting a glass material or the like into a predetermined size and polishing the surface smoothly. I was However, such a method of manufacturing a disk substrate one by one requires many steps and labor, and has a serious problem in reducing the manufacturing cost of the substrate. For this reason, in recent years, when manufacturing a substrate, a press forming method of transferring a desired shape with high accuracy to a raw material such as glass by heating and pressing the raw material such as glass in a mold has been adopted. It has become to.
[0003]
Such press molding is generally performed according to the following procedure. First, a glass material or the like as a raw material is arranged between upper and lower molds (between a fixed mold and a movable mold), and the periphery of the mold and the like is set to a vacuum or an inert gas atmosphere. Further, the die and the raw material are heated by a predetermined heat source, and when the die and the raw material reach a predetermined temperature, the raw material is pressed between the die. After completion of the pressurization, the molded product is cooled and taken out of the mold. According to such a press molding method, post-processing of a molded article is not required, and high-quality substrates can be mass-produced at low cost.
[0004]
Here, when high processing accuracy is required as in the case of molding a disk substrate, temperature control of a mold is extremely important. For this reason, a high-frequency induction heating method with good temperature controllability is often used as a heating method for the mold and the raw material. In a press forming apparatus employing a high-frequency induction heating method, an induction coil connected to a high-frequency power supply is arranged around a conductive mold. When a high-frequency current (alternating current) is supplied to the induction coil, a magnetic field is formed around the mold, an eddy current flows in the mold, and the mold itself generates heat due to the current loss. According to such a high-frequency induction heating method, it is possible to efficiently heat a mold or the like to be heated in a contacted manner, and it is also possible to reduce the heat capacity of the heated body and to clean the equipment.
[0005]
[Problems to be solved by the invention]
However, when press-forming a substrate for a disk, which eventually has a large ratio between the outer diameter and the plate thickness, a relatively thick spherical or marble-shaped raw material is used as a raw material. The amount of movement must be increased to some extent. For this reason, even if the high-frequency induction heating method is adopted, the relative positional relationship between the induction coil and the mold (particularly, the movable mold) changes, and the heat input state to the two molds changes. The change in the heat input state to each mold causes a temperature difference between the two molds, which hinders the execution of high-precision press molding.
[0006]
In order to solve such a problem, for example, it is conceivable to move the induction coil in the axial direction of the mold, or change the winding pitch of the coil in the axial direction of the mold. However, even if these methods are adopted, it is difficult to control the temperature of each mold so as to favorably follow the movement of the mold. In Japanese Patent Application Laid-Open No. 6-64932, two induction coils are arranged around a fixed type and a movable type, and the oscillating frequency of one high-frequency power source is controlled to supply a high-frequency current to each induction coil. A method is disclosed in which the temperature difference between the molds is suppressed by changing the amount. However, it is not easy to freely change the amount of high-frequency current to each induction coil by such a method, even if an extremely complicated and expensive control circuit is used. It is practically impossible to control to follow the mold clamping well. As a result, with respect to press forming of a disk substrate, etc., it is still necessary to suppress the undulation of the substrate surface to improve the flatness, or to suppress the undulation on the same radius and to improve the dimensional accuracy of the inner and outer diameters of the substrate. Challenges remain.
[0007]
Accordingly, an object of the present invention is to realize low-cost and high-precision press molding capable of favorably controlling the temperature of a mold.
[0008]
[Means for Solving the Problems]
One embodiment of the present invention is a press forming apparatus that creates a desired molded product by heating and pressing a raw material between a fixed mold and a movable mold. The press forming apparatus is fixed around the fixed mold and the movable mold. An induction coil and a high-frequency power supply that supplies a high-frequency current to the induction coil, and by changing the number of turns of the induction coil effective to form a magnetic field around the fixed and movable types, It is characterized in that the position of the formed magnetic field is varied.
[0009]
This press forming apparatus is capable of supplying a high-frequency current from a high-frequency power supply to an induction coil fixed around a fixed mold and a movable mold, and raising the temperature of the fixed mold and the movable mold and the raw material by induction heating. is there. As described above, in the press forming apparatus having the fixed mold and the movable mold, when the movable mold is moved relative to the fixed mold to heat and pressurize the raw material, the fixed mold and the movable mold are moved with the movement of the movable mold. May cause a temperature difference.
[0010]
In view of this point, this press forming apparatus changes the position of the magnetic field formed by the induction coil by changing the number of turns of the induction coil effective for forming the magnetic field around the fixed mold and the movable mold. It is configured to be able to vary. Thus, in this press molding apparatus, the heating efficiency of the induction coil for one of the fixed mold and the movable mold can be appropriately changed according to the temperature of the fixed mold and the movable mold. Therefore, the temperatures of the fixed mold and the movable mold are controlled very favorably and flexibly, so that the temperature difference between the fixed mold and the movable mold can be constantly maintained at almost zero. As a result, according to this press molding apparatus, distortion and warpage are suppressed, and a molded product having high dimensional accuracy, flatness, smoothness, and the like can be manufactured at low cost.
[0011]
In this case, the induction coil has at least one tap, and the press forming device controls the tap switching means for switching the tap of the induction coil and the tap switching means according to the temperature difference between the fixed mold and the movable mold. It is preferable to further comprise control means. By adopting such a configuration, the number of turns of the induction coil effective for forming a magnetic field around the fixed type and the movable type can be changed, so that the temperature of the fixed type and the movable type is set to a desired value. It is possible to make very good and flexible settings.
[0012]
Another embodiment of the present invention is a press molding method for producing a desired molded article by heating and pressing a raw material between a fixed mold and a movable mold, and the method includes guiding the material around the fixed mold and the movable mold. Fixing the coil, supplying high-frequency current to the induction coil, and increasing the number of turns of the induction coil effective to form a magnetic field around the fixed type and the movable type according to the temperature difference between the fixed type and the movable type And changing the position of the magnetic field formed by the induction coil.
[0013]
In this case, it is preferable that an induction coil having at least one tap is fixed around the fixed type and the movable type, and the taps of the induction coil are switched according to a temperature difference between the fixed type and the movable type.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a press forming apparatus and a press forming method according to the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a schematic configuration diagram showing a first embodiment of a press forming apparatus according to the present invention. The press forming apparatus 1 shown in FIG. 1 is suitable for use in producing a substrate for a magnetic disk from a raw material G such as glass or plastic, and a high frequency induction method is used as a method for heating a mold and the raw material G. To adopt. The press forming apparatus 1 has a frame 2 including a base 3, an upper stage 4 and a lower stage 5. The upper stage 4 is fixed on the base 3 by a plurality of columns 6. The lower stage 5 is slidably supported by a plurality of columns 6, and is connected to a rod 7a of a press unit 7 installed on the base 3. By operating the press unit 7, the lower stage 5 can be moved vertically between the base 3 and the upper stage 4 in the figure.
[0016]
An upper mold (fixed mold) 11 made of a conductive material (such as a WC material) is attached to the upper stage 4 via a support member 8. On the other hand, a lower mold (movable mold) 12 made of a conductive material (such as a WC material) is attached to the lower stage 5 via a support member 9, and a regulating ring 14 is attached to the lower mold 12. Further, an upper mold temperature sensor 15 is provided for the upper mold 11, and a lower mold temperature sensor 16 is provided for the lower mold 12. Further, cooling jackets (cooling means) 17 and 18 are arranged between the upper stage 4 and the upper mold 11 and between the lower stage 5 and the lower mold 12. A cooling medium can be circulated in each of the cooling jackets 17 and 18 as shown by a white arrow in FIG. Each of the cooling jackets 17 and 18 can be approached or separated from the back surface of the upper mold 11 (the surface opposite to the transfer surface) or the back surface of the lower mold 12 (the surface opposite to the transfer surface) by a moving mechanism (not shown). .
[0017]
Now, in the press forming apparatus 1, since the high-frequency induction heating method is adopted to heat the upper mold 11 and the lower mold 12 and the raw material G, the induction coil is provided around the upper mold 11 and the lower mold 12. 20 are arranged. The induction coil 20 has a size that can be positioned around both the upper mold 11 and the lower mold 12 at a position where the raw material G comes into contact with the molding surface of the upper mold 11, and between the one end 20a and the other end 20b. Includes a tap 20t at a predetermined position. The induction coil 20 is arranged in a state of being slightly shifted to the lower mold 12 side (downward in FIG. 2) so as to surround both the outer peripheral face of the upper mold 11 and the outer peripheral face of the lower mold 12. I have. Further, the center axis of the induction coil 20 substantially coincides with the center of the mold of the upper mold 11 and the lower mold 12. In the press molding apparatus 1, the upper mold 11, the lower mold 12, the induction coil 20, and the like are housed in a housing member (not shown), and the inside of the housing member can be set to a vacuum or an inert gas atmosphere.
[0018]
As shown in FIG. 1, one end 20 a of the induction coil 20 is directly connected to a high-frequency power supply 21, and the tap 20 t and the other end 20 b of the induction coil 20 are connected to the high-frequency power supply 21 via a tap switch 22. Is connected to The tap changer 22 has a movable contact piece 23, a first fixed contact 24, and a second fixed contact 25. The movable contact piece 23 is connected to the high frequency power supply 21. The first fixed contact 24 is connected to the tap 20 t of the induction coil 20, and the second fixed contact 25 is connected to the other end 20 b of the induction coil 20.
[0019]
Thus, when the movable contact piece 23 is brought into contact with the second fixed contact 25, a high-frequency current of a predetermined frequency is supplied from the high-frequency power supply 21 between the one end 20a and the other end 20b of the induction coil 20. In this case, the induction coil 20 forms a magnetic field that links both the movable lower mold 12 and the fixed upper mold 11. On the other hand, when the movable contact piece 23 of the tap changer 22 is brought into contact with the first fixed contact 24, a high frequency current (alternating current) of a predetermined frequency is supplied from the high frequency power supply 21 between the one end 20 a of the induction coil 20 and the tap 20 t. Is done. As a result, the magnetic field formed by the induction coil 20 moves upward (toward the upper mold 11 which is a fixed mold) along the moving direction of the lower mold 12 (the center axis of the mold).
[0020]
As described above, in the press forming apparatus 1 of the present invention, a magnetic field is formed around the fixed upper mold 11 and the movable lower mold 12 by switching the taps of the induction coil 20 by the tap changer 22. The number of turns of the induction coil 20 which is effective for the above can be changed. In the present embodiment, when the tap changer 22 is switched to the second fixed contact 25 side, the heating efficiency of the induction coil 20 is higher than that of the upper mold 11 relative to the lower mold (movable mold) 12, and the tap switching is performed. When the heater 22 is switched to the first fixed contact 24 side, the size and the mounting position of the induction coil 20 are set such that the heating efficiency of the induction coil 20 is higher for the upper die (fixed die) 11 than for the lower die 12. The position of the tap 20t is determined.
[0021]
As shown in FIG. 1, the press forming apparatus 1 includes a control device 27 and a temperature controller 30 for controlling the high frequency power supply 21. The above-described upper mold temperature sensor 15 and lower mold temperature sensor 16 are connected to the control device 27. The control device 27 includes an average temperature calculation unit 28 and a temperature deviation calculation unit 29. The average temperature calculation section 28 of the control device 27, under the indicated temperature (upper die temperature) T _U of the upper mold 11 shown in the signal received from the upper temperature sensor 15, the signal received from the lower temperature sensor 16 and a temperature (lower mold temperature) _{T L} type 12, determining the average temperature _{T AV} of the upper mold 11 and the lower mold 12 as _{T AV = (T U + T} L) / 2. The average temperature T _AV obtained by the control device 27 (average temperature calculation unit 28) is sent to the temperature controller 30. The temperature controller 30 controls the output of the high-frequency power supply 21 so that the average temperature T _AV indicated in the signal received from the control device 27 matches the target average temperature T ₀ in each molding step set by a setting unit (not shown). (PID control).
[0022]
The temperature deviation calculating section 29 of the control device 27, and the upper mold temperature T _U shown in the signal received from the upper temperature sensor 15, and the lower mold temperature T _L as shown in the signal received from the lower temperature sensor 16 from the temperature difference _{T dt} of the upper mold 11 and the lower mold 12 _T dt _{= |} calculated as | T U -T _L. The press forming apparatus 1 includes a relay 31 for switching control of the tap changer 22 described above. The relay 31 is obtained from the control device 27 by the temperature deviation calculator 29. A signal indicating a temperature deviation _Tdt between the upper mold 11 and the lower mold 12 is provided. When T _dt > δ based on the temperature deviation T _dt indicated by the signal received from the control device 27 and the preset threshold value δ of the temperature deviation, the relay 31 The piece 23 is brought into contact with the second fixed contact 25, and when T _dt <−δ, the movable contact piece 23 of the tap changer 22 is brought into contact with the first fixed contact 24.
[0023]
Next, the operation of the above-described press forming apparatus 1 will be described. First, as shown in FIG. 2, in a state where the upper mold 11 and the lower mold 12 are completely opened, the raw material G is arranged by the transfer unit 13 at substantially the center of the lower mold 12 in the housing member. When the raw material G is placed on the lower mold 12, the press unit 7 is operated to extend the rod 7 a, and as shown in FIG. 3, the lower mold is moved until the upper portion of the raw material G contacts the molding surface of the upper mold 11. 12 is made to approach the upper mold 11. Then, in order to prevent the upper mold 11, the lower mold 12, the induction coil 20 and the like from being deteriorated by oxidation at a high temperature, the inside of the housing member housing these members is set to a vacuum or an inert gas atmosphere. . At this stage, the movable contact piece 23 of the tap changer 22 is in the neutral position where it is not in contact with any of the first and second fixed contacts 24 and 25.
[0024]
When the surroundings of the upper mold 11 and the lower mold 12 are made to have a vacuum or an inert gas atmosphere, heating of the upper mold 11 and the lower mold 12 by high-frequency induction heating is started (heating step). That is, when the surroundings of the upper mold 11 and the lower mold 12 become sufficiently vacuum or an inert gas atmosphere, the control device 27 gives a predetermined operation signal to the relay 31 and The piece 23 is brought into contact with the second fixed contact 25. As a result, a high-frequency current of a predetermined frequency is supplied from the high-frequency power supply 21 between one end 20a and the other end 20b of the induction coil 20, and as shown in FIG. A magnetic field m1 interlinking with both the upper mold 11 and the fixed mold 11 is formed. Then, an eddy current flows through the upper die 11 and the lower die 12, and the respective dies 11 and 12 generate heat due to the current loss.
[0025]
The temperatures of the upper mold 11 and the lower mold 12 heated in this way are detected by the upper mold temperature sensor 15 and the lower mold temperature sensor 16, and each of the temperature sensors 15, 16 outputs a signal indicating the detected value to the control device. 27. The average temperature calculation section 28 of the control device 27 from the upper mold temperature T _U shown in the signal received from the upper temperature sensor 15, a lower mold temperature T _L as shown in the signal received from the lower temperature sensor 16, An average temperature T _AV (= (T _U + T _L ) / 2) of the upper mold 11 and the lower mold 12 is obtained. Then, the control device 27 gives a signal indicating the calculated average temperature T _AV to the temperature controller 30. The temperature controller 30 controls the output of the high-frequency power supply 21 so that the average temperature T _AV indicated in the signal received from the control device 27 matches the target average temperature T ₀ in each molding step set by a setting unit (not shown). Control.
[0026]
In the heating step, the raw material G is heated to a predetermined softening temperature (press temperature) via the upper mold 11 and the lower mold 12. When the temperature of the raw material G rises to the softening temperature, the lower die 12 is further brought closer to the upper die 11 by the press unit 7, whereby the raw material G between the upper die 11 and the lower die 12 is pressurized ( Press process). The raising operation of the lower mold 12 is stopped at the stage where the upper end of the restriction ring abuts on the upper mold 11, so that a molded product having a uniform thickness can be obtained.
[0027]
Here, at the time of the above-described pressing process, the lower die 12 which is a movable die approaches the upper die 11, so that the heating efficiency of the induction coil 20 increases with the movement of the lower die 12. It becomes different between the lower die 12 and, there is a difference between the upper mold temperature T _U and the lower mold temperature T _L occurs. In particular, in the case of the type in which the lower mold 12 is raised as in the press molding apparatus 1, the temperature rising speed of the upper mold 11 is slower than that of the moving lower mold 12.
[0028]
In view of this, the press forming apparatus 1, the temperature deviation calculating section 29 of the control device 27, and the upper mold temperature T _U, which is detected by the upper mold temperature sensor 15, the lower mold, which is detected by the lower temperature sensor 16 temperature deviation _{T dt} of the temperature _{T L is,} T dt _{= |} is obtained as | T U -T _L. Then, a signal indicating the temperature deviation T _dt between the upper die 11 and the lower die 12 obtained by the temperature deviation calculator 29 is given from the control device 27 to the relay 31 that operates the tap changer 22.
[0029]
The relay 31 determines, based on the temperature deviation T _dt indicated in the signal received from the control device 27 and the preset temperature deviation threshold δ, that T _dt > δ (δ is a positive value) The movable contact piece 23 of the tap changer 22 is brought into contact with the second fixed contact 25 (or kept in contact). On the other hand, when the temperature deviation T _dt satisfies T _dt ≦ −δ during the heating step or the pressing step, the relay 31 brings the movable contact piece 23 of the tap changer 22 into contact with the first fixed contact 24.
[0030]
As shown in FIG. 4, when the movable contact piece 23 comes into contact with the first fixed contact 24, a high-frequency current (alternating current) having a predetermined frequency is supplied from the high-frequency power supply 21 between the one end 20a of the induction coil 20 and the tap 20t. Is done. Thereby, the number of turns of the induction coil 20 effective for forming a magnetic field around the upper mold 11 and the lower mold 12 is changed (decreased), and the magnetic field m2 formed by the induction coil 20 is reduced. The mold 12 moves upward along the moving direction (center axis of the mold). In the press forming apparatus 1, when the tap changer 22 is switched to the first fixed contact 24 side, the heating efficiency of the induction coil 20 is higher for the upper mold (fixed mold) 11 than for the lower mold 12. Become. During the heating step and the pressing step, the relay 31 moves the movable contact piece 23 to the first fixed contact 24 side according to the temperature deviation signal from the control device 27 (the temperature deviation calculation unit 29), as shown in FIG. Alternatively, the position of the magnetic field formed by the induction coil 20 is changed by switching to the second fixed contact 25 side.
[0031]
As described above, in the press forming apparatus 1, by changing the number of turns of the induction coil 20 effective for forming a magnetic field around the upper die 11 as a fixed die and the lower die 12 as a movable die, The position of the magnetic field formed by the induction coil 20 is changed. Then, in the press forming apparatus 1, the heating efficiency of the induction coil 20 for one of the upper mold 11 and the lower mold 12 is appropriately changed in accordance with the temperature deviation _Tdt between the upper mold 11 and the lower mold 12.
[0032]
Therefore, the temperatures of the upper mold 11 as the fixed mold and the lower mold 12 as the movable mold are controlled very well and flexibly, and the temperature difference between the upper mold 11 and the lower mold 12 is always kept almost zero. Become. As a result, according to the press molding apparatus 1, distortion and warpage are suppressed, and molded articles having high dimensional accuracy, flatness, smoothness, and the like, particularly for disks having a large ratio between the outer diameter and the plate thickness. The substrate can be manufactured at low cost.
[0033]
After the pressurization is completed, the movable contact piece 23 of the tap changer 22 is returned to the neutral position where it is not in contact with any of the first and second fixed contacts 24 and 25, whereby the high-frequency induction heating is stopped. You. Thereafter, a cooling jacket 17 (see FIG. 1) is pressed against the back surface of the upper mold 11 and a cooling jacket 18 (see FIG. 1) is pressed against the back surface of the lower mold 12 (cooling step), and the molded product in the mold is pressed. Cooled. After the cooling is completed, the lower mold 12 is lowered, the mold is opened, and the molded product is taken out.
[0034]
【The invention's effect】
As described above, according to the present invention, it is possible to control the temperature of a mold extremely and flexibly, and to suppress a distortion and a warp to reduce a molded product having high dimensional accuracy, flatness and smoothness. Can be manufactured at cost.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a press molding apparatus according to the present invention.
FIG. 2 is a schematic diagram for explaining the operation of the press forming apparatus of FIG.
FIG. 3 is a schematic view for explaining the operation of the press forming apparatus of FIG. 1;
FIG. 4 is a schematic view for explaining the operation of the press forming apparatus of FIG.
FIG. 5 is a schematic diagram for explaining the operation of the press forming apparatus of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Press molding apparatus 4 Upper stage 5 Lower stage 7 Press unit 11 Upper die 12 Lower die 15 Upper die temperature sensor 16 Lower die temperature sensor 20 Induction coil 20a One end 20b Other end 20t Tap 21 High frequency power supply 22 Tap changer 23 Moving piece 24 First fixed contact 25 Second fixed contact 27 Controller 28 Average temperature calculator 29 Temperature deviation calculator 30 Temperature controller 31 Relay G Raw material

Claims (4)

In a press molding apparatus that creates a desired molded product by heating and pressing the raw material between a fixed mold and a movable mold,
An induction coil fixed around the fixed type and the movable type,
A high-frequency power supply that supplies a high-frequency current to the induction coil,
A press, wherein the position of the magnetic field formed by the induction coil is changed by changing the number of turns of the induction coil effective for forming a magnetic field around the fixed type and the movable type. Molding equipment. The induction coil has at least one tap, a tap switching unit that switches the tap of the induction coil, and a control unit that controls the tap switching unit according to a temperature difference between the fixed type and the movable type. The press forming apparatus according to claim 1, further comprising: In a press molding method of creating a desired molded product by heating and pressing the raw material between the fixed mold and the movable mold,
An induction coil is fixed around the fixed type and the movable type, and a high-frequency current is supplied to the induction coil, and the fixed type and the movable type are changed according to a temperature difference between the fixed type and the movable type. A press forming method characterized by changing the number of turns of the induction coil effective for forming a magnetic field in the periphery and changing the position of a magnetic field formed by the induction coil. An induction coil having at least one tap is fixed around the fixed type and the movable type, and the taps of the induction coil are switched according to a temperature difference between the fixed type and the movable type. The press molding method according to claim 3.

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