Punch Hole Forming Method and Punch Hole Forming Device

Abstract

A punch hole forming method and a punch hole forming device that can suppress a decrease in the temperature of a workpiece due to a machining tool when a hole is formed by punching the workpiece using the machining tool. In the punch hole forming method, when a workpiece that is a plate-like member having a thickness of 0.01 mm or more and 1 mm or less is placed on a die, and a hole is formed by punching the workpiece in the thickness direction using a punch, the workpiece is kept at a temperature at which the workpiece can be punched at least during formation of the hole.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of International Application No. PCT/JP2019/014375 filed Mar. 29, 2019, and claims priority to Japanese Patent Application No. 2018-070339 filed Mar. 30, 2018, the disclosures of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a punch hole forming method of punching a substrate, and a punch hole forming device.

Description of Related Art

In general, when a hole is provided in a workpiece material, which is an object to be punched, a workpiece is placed on a die, and a punch is used to provide a hole in the workpiece material. Japanese Patent Application Publication No, JP H8-309473A (Patent Document 1) discloses a hot forging technique in which a workpiece is punched after the workpiece is heated to reduce the deformation resistance of the workpiece material, namely to increase the deformability thereof. In the case where a workpiece is heated as described above, abrasion, thermal damage, and the like occur in the punch due to the temperature of the heated workpiece itself, friction during punching, and the like, and thus the lifetime of the punch is reduced. Therefore, in the technique disclosed in Patent Document 1, a coolant always flows inside the punch, and the leading end of the punch is cooled by intensively spraying the coolant onto the leading end of the punch.

SUMMARY OF THE INVENTION

In a case of a relatively thin workpiece, when the workpiece is placed on a die and is then punched, the temperature of the workpiece decreases due to the die and the punch, and thereby the deformability thereof is reduced, thus making it difficult to punch the workpiece. As mentioned above, in the technique disclosed in Patent Document 1, the punch is cooled in order to prevent the punch from being heated and thermally damaged due to the very hot workpiece. That is, Patent Document 1 does not disclose a technique in which a workpiece is punched in a state in which the heat of the workpiece is prevented from being transferred to a die, a punch, and the like.

Accordingly, the present invention was made in view of the aforementioned problem, and an object thereof is to provide a punch hole forming method and a punch hole forming device that can suppress a decrease in the temperature of a workpiece due to a machining tool when a hole is formed by punching the workpiece using the machining tool.

In a characteristic configuration of a punch hole forming method according to the present invention, the punch hole forming method is a method of placing a workpiece that is a plate-like member having a thickness of 0.01 mm or more and 1 mm or less on a die, and forming a hole by punching the workpiece in a thickness direction using a punch, and includes keeping the workpiece at a temperature TO at which the workpiece can be punched at least during formation of the hole.

When a relatively thin workpiece having a thickness of 0.01 mm or more and 1 mm or less is placed on a die, the temperature of the workpiece may decrease due to contact with the die. On the other hand, since the workpiece is a relatively thin plate, when the workpiece is excessively heated, there is a possibility that the plate shape of the workpiece cannot be kept, and the workpiece undergoes deformation such as warping.

With this characteristic configuration, while taking these points into account, the workpiece, which is a relatively thin plate, is kept at the temperature TO at which the workpiece can be punched, in a state in which the workpiece is placed on the die. Accordingly, a decrease in the temperature of the workpiece can be suppressed, and the deformation resistance (tensile strength) can be kept small. That is, in the state in which the deformation resistance of the workpiece is kept small and thereby the deformability is increased, a hole can be formed by easily punching the workpiece using a punch. In addition, the resistance is small while a hole is being formed, thus making it possible to suppress deformation of the workpiece itself, which is a relatively thin plate, and to accurately form a hole having a desired diameter. Also, for the reason that the temperature TO is not a temperature at which the shape of the workpiece itself is changed but a temperature at which the workpiece can be punched, a change in the shape of the workpiece itself can be suppressed.

Moreover, since the deformation resistance of the workpiece is small, the possibility of the punch buckling can also be avoided.

In another characteristic configuration of the punch hole forming method according to the present invention, a load applied by the punch to the workpiece while the workpiece at the temperature TO is being punched using the punch is smaller than or equal to a predetermined value.

With this characteristic configuration, the deformation resistance of the workpiece is reduced by keeping the workpiece at the temperature TO at which the workpiece can be punched. Due to the reduction in the deformation resistance of the workpiece, a load (compressive stress applied to the punching blade of the punch) is smaller than or equal to a predetermined value while the workpiece is being punched using the punch. If a workpiece is punched with a large load, a portion of the workpiece located at a position at which a hole is formed and a portion therearound may be pulled in the punching direction, leading to deformation of the workpiece. While a hole is being formed, a load (compressive stress) can be set to be smaller than or equal to a predetermined value by keeping the workpiece at the temperature TO, thus making it possible to suppress the deformation of the workpiece itself, which is a relatively thin plate, and to accurately form a hole having a desired diameter.

A load applied by the punch to the workpiece kept at the temperature TO while a hole is formed in the workpiece using the punch is 10% or more and 30% or less of a load required to form a hole in the workpiece at room temperature using the punch.

With this characteristic configuration, a load required to form a hole in a workpiece that is kept at the temperature TO can be sufficiently reduced compared with a load required to form a hole in the workpiece at room temperature. Accordingly, it is possible to suppress the deformation of the workpiece itself, which is a relatively thin plate, and to accurately form a hole having a desired diameter.

In another characteristic configuration of the punch hole forming method according to the present invention, the temperature TO is 300° C. or higher and 950° C. or lower.

With this characteristic configuration, keeping the temperature TO of the workpiece at a temperature of 300° C. or higher and 950° C. or lower makes it possible to suppress the deformation of the workpiece itself, which is a thin plate, and to accurately form a hole having a desired diameter.

In another characteristic configuration of the punch hole forming method according to the present invention, the workpiece is kept at the temperature TO by placing the workpiece on the die heated to a temperature TD.

Conventionally, there has been a problem in that thermal damage and the like occur in a die and a punch due to heating, leading to a reduction in the lifetimes thereof. Therefore, an idea of punching a workpiece after heating a die and the like has been ignored. With this characteristic configuration, the workpiece is relatively thin, and thus the temperature of the workpiece decreases immediately after the workpiece is placed on a die that is not preheated. Based on this fact, a technique is employed in which the die is heated to the temperature TD, which is completely different from conventional techniques. By placing the workpiece on the heated die, the workpiece is kept at the temperature TO due to heat transfer caused by heat conduction, heat radiation, and the like from the heated die.

In another characteristic configuration of the punch hole forming method according to the present invention, the workpiece is kept at the temperature TO by punching the workpiece using the punch heated to a temperature TP.

Conventionally, a punch has not been heated in consideration of the lifetime of the punch. However, with this characteristic configuration, the punch is heated to the temperature TP based on the fact that the workpiece is relatively thin. The workpiece placed on the die is punched using this heated punch. The workpiece is kept at the temperature TO due to not only heat transfer from the die but also heat transfer caused by heat conduction, heat radiation, and the like from the heated punch with which the workpiece is in contact while holes are being formed through punching.

In another characteristic configuration of the punch hole forming method according to the present invention, an aspect ratio defined as a ratio of the thickness of the workpiece to the diameter of a hole (thickness/diameter) is set to be larger than a threshold value in a conventional punch hole forming method. The increased aspect ratio is advantageous because the strength of the workpiece is increased and thus the workpiece can be used in a wider range of applications when being used as a filter, for example. Therefore, the aspect ratio is preferably 2 or more, more preferably 3 or more, and even more preferably 5 or more. It should be noted that an excessively large aspect ratio causes problems in the strength and the durability of the punch and the die, and therefore, the aspect ratio is preferably 30 or less, more preferably 20 or less, and even more preferably 15 or less.

When being punched, the workpiece, which is a relatively thin plate, is kept at the temperature TO at which the workpiece can be easily punched using a punch, and the deformation resistance thereof is kept small. Accordingly, in the state in which the deformation resistance of the workpiece is kept small and thereby the deformability is increased, and a change in the shape of the workpiece itself is suppressed, the workpiece can be easily punched using a punch. Therefore, as in this characteristic configuration, a hole having an aspect ratio of 2 or more and 30 or less can be formed by punching the workpiece, which is a relatively thin plate. The lower limit of the range of the thickness of the thin plate is preferably 0.01 mm or more, more preferably 0.05 mm or more, and even more preferably 0.1 mm or more, from the viewpoint of the processing cost. It should be noted that the upper limit thereof is preferably 1 mm or less, more preferably 0.75 mm or less, and even more preferably 0.5 mm or less.

In another characteristic configuration of the punch hole forming method according to the present invention, the upper limit of the range of the diameter of the hole is 1 mm or less, which is difficult to achieve by a conventional punch hole forming method. It should be noted that the lower limit thereof is preferably 0.005 mm or more, more preferably 0.01 mm or more, and even more preferably 0.02 mm or more, from the viewpoint of the degree of difficulty and the cost of manufacturing of a punch and a die.

In another characteristic configuration of the punch hole forming method according to the present invention, a plurality of the holes are formed in the workpiece. In the case where the workpiece is used as a filter or the like for the purpose of filtration, for example, it is advantageous to provide a larger number of holes because pressure loss of the filter is further reduced. On the other hand, the hole is formed in the workpiece based on the principle that a punch hole is formed through the application of shearing force by a punch. Therefore, if an interval between adjacent holes is too small, defects such as significant deformation and breakage may occur between holes of the workpiece. From this viewpoint, the interval between adjacent holes is preferably two or more times, more preferably three or more times, and even more preferably four or more times as large as the diameter of the punch holes.

In another characteristic configuration of the punch hole forming method according to the present invention, the workpiece is made of a heat-resistant metal material selected from ferrite-based stainless steel, austenite-based stainless steel, and martensite-based stainless steel, and on the other hand, a material to be processed into the punch and the die is a material that is ten or more times as strong as the material of the workpiece at a processing temperature.

Using the material as described in this characteristic configuration to form the workpiece makes it easy to form a desired hole in the workpiece in which at least one of heat resistance, oxidation resistance, and cost reduction is achieved. Accordingly, such a workpiece can be favorably applied to a substrate on which various electrodes and electrolytes for a cell for a fuel cell are to be stacked, a filter provided with a plurality of pores, and the like.

In another characteristic configuration of the punch hole forming method according to the present invention, at least one of the punch and the die is made of a superhard material containing at least one of ceramic and tungsten.

With this characteristic configuration, at least one of the punch and the die is made of a predetermined material having a relatively high hardness. Accordingly, even if the punch and the die are heated when a hole is formed by punching the workpiece, the punch and the die do not undergo deformation due to heating, and do not undergo deformation due to a load during punching, either. Therefore, such a material is preferable.

In another characteristic configuration of the punch hole forming method according to the present invention, a coolant gas is blasted onto the punch after the workpiece has been punched using the punch.

When the workpiece is punched using the punch, the temperature of the punch rises due to friction. With this characteristic configuration, an excessive rise in the temperature of the punch is suppressed by blasting a coolant gas onto the punch. This suppress a reduction in the lifetime of the punch due to thermal damage and oxidation.

In another characteristic configuration of the punch hole forming method according to the present invention, the coolant gas is at least one of oxygen-free carbonic acid gas, nitrogen, and argon.

With this characteristic configuration, the coolant gas is at least one of carbonic acid gas, nitrogen, and argon, thus making it possible to suppress corrosion of the punch.

In another characteristic configuration of the punch hole forming method according to the present invention, the punch includes:

a punch main body having a plate shape with a predetermined thickness:

a punching blade that protrudes and extends from an opposed face of the punch main body opposed to the workpiece and that is used to form a hole in the workpiece; and

a stripper member including a base portion that is located on a face facing in a direction opposite to a protruding direction of the punching blade out of two opposite faces of the punch main body, and a stripper pin that extends from the base portion, passes through the punch main body in the protruding direction of the punching blade, and has a length larger than a thickness of the punch main body,

wherein the stripper pin is retracted so as not to protrude from the opposed face while the workpiece is being punched using the punch, and

after the workpiece has been punched using the punch, a leading end of the stripper pin protrudes from the opposed face and presses the workpiece, and the punching blade is removed from the workpiece together with the punch main body.

With this characteristic configuration, when the workpiece, which is a thin plate, is punched, the punching blade can be easily removed from the workpiece due to the stripper pin pressing the workpiece.

In a characteristic configuration of a punch hole forming device according to the present invention, the punch hole forming device forms a hole in the workpiece using the punch hole forming method described above, and includes:

a die on which the workpiece is to be placed;

a punch for forming a hole by punching the workpiece placed on the die in a thickness direction; and

a control unit that performs control to keep the workpiece at a temperature TO at which the workpiece can be punched while the hole is being formed.

With this characteristic configuration, the workpiece, which is a relatively thin plate, is kept at the temperature TO at which the workpiece can be punched, in a state in which the workpiece is placed on the die. Accordingly, a decrease in the temperature of the workpiece can be suppressed, and the deformation resistance (tensile strength) can be kept small. That is, in the state in which the deformation resistance of the workpiece is kept small and thereby the deformability is increased, a hole can be formed by easily punching the workpiece using a punch. In addition, the resistance is small while a hole is being formed, thus making it possible to suppress deformation of the workpiece itself, which is a relatively thin plate, and to accurately form a hole having a desired diameter. Also, for the reason that the temperature TO is not a temperature at which the shape of the workpiece itself is changed but a temperature at which the workpiece can be punched, a change in the shape of the workpiece itself can be suppressed.

Moreover, since the deformation resistance of the workpiece is small, the possibility of the punch buckling can also be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall configuration of a punch hole forming device.

FIG. 2 is a schematic diagram showing a state in which a punch is used for a workpiece placed on a die.

FIG. 3 is a partially enlarged schematic diagram showing a state in which holes are formed in a workpiece using the punch hole forming device.

DESCRIPTION OF THE INVENTION

Embodiments

Hereinafter, a punch hole forming device and a punch hole forming method according to this embodiment will be described with reference to FIGS. 1 to 3.

(1) Punch Hole Forming Device

First, a punch hole forming device 100 will be described below.

The punch hole forming device 100 includes a die 10 on which a workpiece O to be provided with holes is to be placed, a punch 20 for forming holes by punching the workpiece O placed on the die 10, a stripper member 50 for facilitating removal of punching blades 23 from the workpiece O, a cooling device 60 for cooling the punching blades 23 of the punch 20, and a control unit 30 that performs various types of control when holes are formed by punching the workpiece O.

The workpiece O of this embodiment is a relatively thin plate-like member having a thickness of 0.01 mm or more and about 1 mm or less. As shown in FIG. 2, the workpiece O is set in the punch hole forming device 100 and punched, and thereby a plurality of holes passing through the workpiece O are formed simultaneously. In this embodiment, these holes have a large aspect ratio of 2 or more.

It should be noted that the aspect ratio refers to a ratio of the thickness of the workpiece O to the diameter of each hole (thickness/diameter). In this embodiment, each hole has a diameter of 0.005 mm or more and 0.5 mm or less, for example, and the pitch of the holes is four or more times as large as the diameter of each punch hole.

For example, the workpiece O is made of a heat-resistant metal material selected from ferrite-based stainless steel, austenite-based stainless steel, and martensite-based stainless steel, but the material is not limited thereto. Using such a material to form the workpiece O makes it possible to form desired holes in the workpiece O in which at least one of heat resistance, oxidation resistance, and cost reduction is achieved. Accordingly, such a workpiece O can be favorably applied to a substrate on which various electrodes and electrolytes for a cell for a fuel cell are to be stacked, a filter provided with a plurality of pores, and the like.

In this embodiment, in order to simultaneously form a plurality of holes having a large aspect ratio of 2 or more in the workpiece O as described above, the control unit 30 performs control to form holes by punching the workpiece O placed on the die 10 using the punch 20 in the state in which the workpiece O is kept at a temperature TO. In this case, the control unit 30 performs control to keep the workpiece O at the temperature TO by heating the die 10 and the punch 20.

It should be noted that the die 10 is fixed at a predetermined position, and the movable punch 20 is moved down toward the workpiece O placed on the die 10 and holes are formed in the workpiece O on the die 10 using the punch 20.

The punch 20 includes a punch main body 21 having a substantially plate shape, and a plurality of punching blades 23 protruding from the punch main body 21. The punch main body 21 includes a punch bottom face (opposed face) 21a that is a flat face and is opposed to the die 10, and a punch top face 21b on the other side. The plurality of punching blades 23 are formed protruding downward from the punch bottom face 21a toward the die 10.

As shown in FIG. 3, each of the punching blades 23 includes a main portion 23a having a cylindrical shape, and a tip portion 23b that tapers from the main portion 23a toward the tip. The diameter of the main portion 23a of the punching blade 23 corresponds to the diameter of each hole to be formed in the workpiece O, which is 0.005 mm or more and 0.5 mm or less, and is substantially the same as the diameter of each hole. The pitch of the plurality of punching blades 23 provided on the punch main body 21 is four or more times as large as the diameter of the punch holes, which is a pitch of the hole. The plurality of punching blades 23 that each have such a diameter and are aligned at such a pitch are arranged at positions corresponding to lattice points of a square lattice along a row and a column, for example.

When the punch 20 is moved close to the die 10, the plurality of punching blades 23 are inserted into insertion holes 13 provided in the die 10 as shown in FIGS. 2 and 3.

The punch 20 further includes a punch heater 25 for heating the punch main body 21 to a predetermined temperature TP. The punch heater 25 is provided inside the punch main body 21, for example, and heats the punch main body 21 and the punching blades 23 to the temperature TP. In this case, the punch heater 25 may heat the punch bottom face 21a and the punching blades 23 to be brought into contact with the workpiece O. Alternatively, the punch heater 25 may heat, to the temperature TP, at least the punching blades 23 that come into contact with the workpiece O while the workpiece O is being punched.

In the description below, heating only the entire punch main body 21, only the punch bottom face 21a of the punch main body 21, only the punching blades 23, or any combination thereof in the punch 20 is referred to as “heating of the punch 20”.

The die 10 includes a die main body 11 having a substantially plate shape on which the workpiece O is to be placed. The die main body 11 includes a die top face 11a that is a flat face and is opposed to the punch 20, and a die bottom face lib on the other side. The die main body 11 is provided with a plurality of insertion holes 13 that pass through the die main body 11 from the die top face 11a to the die bottom face 11b. The plurality of insertion hole 13 are formed at positions corresponding to the plurality of punching blades 23, and the plurality of punching blades 23 are to be inserted into the plurality of insertion holes 13.

The die 10 further includes a die heater 15 for heating the die main body 11 to a predetermined temperature TD. The die heater 15 is provided inside the die main body 11, for example, and heats the die main body 11 to the temperature TD. In this case, the inner surfaces located inside the insertion holes 13 are also heated to the temperature TD due to heating of the die main body 11. Alternatively, the die heater 15 may heat only the die top face 11a on which the workpiece O is to be placed, only the inner surfaces of the insertion holes 13, or both the die top face 11a and the inner surfaces of the insertion holes 13.

In the description below, heating only the entire die main body 11, only the die top face 11a of the die main body 11, only the inner surfaces of the insertion holes 13, or any combination thereof in the die 10 is referred to as “heating of the die 10”.

Small protrusions 17 (FIG. 3) are formed on the die top face 11a. The small protrusions 17 are formed protruding upward from the die top face 11a. The small protrusions 17 protrude to such a height that the workpiece O placed on the die top face 11a is prevented from being shifted from a predetermined position and is not damaged. It is preferable that the small protrusions 17 have a shape that causes no damage to the workpiece O. As shown in FIG. 1 and the like, the small protrusions 17 are formed at portions located adjacent to the insertion holes 13, for example. It is sufficient that the small protrusions 17 are formed to an extent that the workpiece O is not shifted from a predetermined position on the die top face 11a, and are not necessarily formed corresponding to all the insertion holes 13.

At least one of the die 10 and the punch 20 is made of a superhard material containing at least one of ceramic and tungsten, but the material is not limited thereto. At least one of the punch 20 and the die 10 is made of a material having a relatively high hardness. Accordingly, even if the punch 20 and the die 10 are heated when holes are formed by punching the workpiece O, the punch 20 and the die 10 do not undergo deformation due to heating, and do not undergo deformation due to a load during punching, either. Therefore, such a material is preferable.

Even when a heat-resistant metal material such as ferrite-based stainless steel, austenite-based stainless steel, or martensite-based stainless steel is selected as the material of the workpiece O, the die 10 and the punch 20 made of the above-described material are strong enough to apply an appropriate load to punch the workpiece O.

The control unit 30 performs control to keep the workpiece O at the temperature TO at which holes having an aspect ratio of 2 or more and 30 or less can be formed through punching. More specifically, when holes are formed by punching the workpiece O in the thickness direction of the plate-like member using the punch 20, the control unit 30 performs control to keep the workpiece O at the temperature TO during at least while the holes are being formed.

In this case, the control unit 30 turns on the die heater 15 to heat the die 10 to the temperature TD before punching the workpiece O. The temperature TD is a temperature that allows the workpiece O placed on the die 10 to be kept at the temperature TO. When the temperature TO is lower than the temperature TD, the workpiece can be easily kept at the temperature TO due to the die 10 at a higher temperature, and thus such a temperature relationship is preferable.

In addition, the control unit 30 turns on the punch heater 25 to heat the punch 20 to the temperature TP before punching the workpiece O. The temperature TP is a temperature that allows the workpiece O placed on the die 10 to be kept at the temperature TO while the workpiece O is being punched using the punch 20. When the temperature TO is lower than the temperature TP, the workpiece O can be easily kept at the temperature TO due to the punch 20 at a higher temperature, and thus such a temperature relationship is preferable.

It should be noted that each of the temperature TD of the die 10, the temperature TP of the punch 20, and the temperature TO of the workpiece O may indicate a certain point of temperature or a certain range of temperature. Depending on the materials, the temperature TD, the temperature TP, and the temperature TO are within a range of 300° C. or higher and 950° C. or lower when the workpiece O is a substrate used to form a fuel cell, for example. Setting these temperatures to be within this range makes it possible to suppress deformation of the workpiece O itself, which is a thin plate, and to accurately form holes having a desired diameter.

As described above, the workpiece O is kept at the temperature TO by heating the die 10 and the punch 20. Accordingly, when the workpiece O is punched using the punch 20, a load applied by the punch 20 to the workpiece O at the temperature TO is smaller than or equal to a predetermined value. A load required to punch the workpiece O at the temperature TO using the punch 20 is 10% or more and 30% or less of a load required to punch the workpiece O at room temperature using the punch 20, for example.

After holes are formed by punching the workpiece O placed on the die 10 using the punching blades 23, and then the punching blades 23 are removed from the workpiece O, the cooling device 60 blasts a coolant gas onto the punching blades 23. Examples of the coolant gas include, but are not limited to, carbonic acid gas, nitrogen, and argon.

As shown in FIG. 3, the stripper member 50 includes a base portion 51 that is located on the punch top face 21b side of the punch main body 21, and stripper pins 53 that extend from the base portion 51 in the direction in which the punching blades 23 protrude, pass through the punch main body 21, and have a length larger than the thickness of the punch main body 21. It is preferable that the length of each stripper pin 53 is substantially the same as the sum of the thickness of the punch main body 21 and the length of each punching blade 23 in the protruding direction. The stripper pins 53 includes stripper pins 53a and stripper pins 53b, and are arranged such that a punching blade 23 is located substantially at the center between a pair of stripper pins 53a and 53b. The stripper pins 53 can be slid inside the punch main body 21 in the extending direction of the stripper pins 53. An example of the use of the stripper member 50 will be described later.

(2) Punch Hole Forming Method

Next, a punch hole forming method in which the above-mentioned punch hole forming device 100 is used will be described mainly with reference to FIG. 3.

First, a workpiece O that is a relatively thin plate-like member having a thickness of 0.01 mm or more and 1 mm or less is prepared. Holes to be formed in the workpiece O have a diameter of 0.005 mm or more and 0.5 mm or less, and the pitch of the holes is four or more times as large as the diameter of each punch hole. The holes have an aspect ratio of 2 or more and 30 or less.

(2-1) FIG. 3(i)

When the holes are formed by punching the workpiece O, the control unit 30 turns on the die heater 15 to heat the die 10 to the temperature TD and turns on the punch heater 25 to heat the punch 20 to the temperature TP before punching the workpiece O.

For example, the control unit 30 may start the step of heating the die 10 and the punch 20 after receiving an instruction to start the punching of the workpiece O from an operator and a separate device.

After the temperatures of the die 10 and the punch 20 reach predetermined temperatures, the control unit 30 plays a sound or shows an image, for example, and thereby notifies the operator that the workpiece O may be placed on the die 10. After receiving the notification, the operator places the workpiece O on the die 10.

Alternatively, after the temperatures of the die 10 and the punch 20 reach predetermined temperatures, the control unit 30 may control a robot arm or the like to place the workpiece O, which is prepared at a predetermined position, on the die 10.

In FIG. 3(i), the workpiece O is placed in accordance with predetermined hole forming positions on the die top face 11a of the die 10 fixed at a predetermined position. The punch 20 is arranged such that the punch bottom face 21a is opposed to the workpiece O placed on the die top face 11a. In this case, the punch 20 is arranged such that the punching blades 23 protruding from the punch bottom face 21a are opposed to the insertion holes 13 of the die 10.

In FIG. 3(i) showing a state before the workpiece O is punched using the punch 20 and subsequent FIG. 3(ii) showing a state in which the workpiece O is being punched using the punch 20, the stripper member 50 is located at a retracted position. That is, regarding the stripper member 50, when the workpiece O is punched using the punch 20, the base portion 51 is pulled up and located above the punch top face 21b, and thereby the pairs of the stripper pins 53a and 53b are retracted in the punch main body 21 so as not to protrude from the punch bottom face 21a. Accordingly, only the punching blades 23 protrude from the punch bottom face 21a.

(2-2) FIG. 3(i) to FIG. 3(ii)

In the state shown in FIG. 3(i), the punch 20 is moved close to the workpiece O placed on the die 10 located at a fixed position, and then holes are formed by punching the workpiece O using the punching blades 23 as shown in FIG. 3(ii). As shown in FIGS. 1 and 2, a plurality of holes are simultaneously formed in the workpiece O using the plurality of punching blades 23. Punch chips Oa produced through punching are pushed out by the punch 20 and separated from the workpiece O.

From the start of the punching of the workpiece O to the end of the punching, the die 10 and the punch 20 are heated to the temperature TD and the temperature TP, respectively, and thus the workpiece O is kept at the temperature TO. It should be noted that the temperature TO is a temperature at which the workpiece O can be punched or is easily punched.

When a relatively thin workpiece O having a thickness of 0.01 mm or more and 1 mm or less is placed on the die 10, the temperature of the workpiece O may decrease due to contact with the die 10. On the other hand, since the workpiece O is a relatively thin plate, when the workpiece O is excessively heated, there is a possibility that the plate shape of the workpiece O cannot be kept, and the workpiece O undergoes deformation such as warping.

While taking these points into account, the workpiece O, which is a relatively thin plate, is kept at the temperature TO at which the workpiece O can be punched, in a state in which the workpiece O is placed on the die 10. Accordingly, a decrease in the temperature of the workpiece O can be suppressed, and the deformation resistance (tensile strength) can be kept small. That is, in the state in which the deformation resistance of the workpiece O is kept small and thereby the deformability is increased, holes can be formed by easily punching the workpiece O using the punch 20. In addition, the resistance is small while holes are being formed, thus making it possible to suppress deformation of the workpiece O itself, which is a relatively thin plate, and to accurately form holes having a desired diameter. Also, for the reason that the temperature TO is not a temperature at which the shape of the workpiece O itself is changed but a temperature at which the workpiece O can be punched, a change in the shape of the workpiece O itself can be suppressed.

Moreover, since the deformation resistance of the workpiece O is small, the possibility of the punch 20 buckling can also be prevented.

Conventionally, there has been a problem in that thermal damage and the like occur in a die 10 and a punch 20 due to heating, leading to a reduction in the lifetimes thereof. Therefore, an idea of punching a workpiece O after heating a die 10 and the like has been ignored. With the configuration described above, the workpiece O is relatively thin, and thus the temperature of the workpiece O decreases immediately after the workpiece O is placed on the die 10 that is not preheated. Based on this fact, a technique is employed in which the die 10 is heated to the temperature TD, which is completely different from conventional techniques. By placing the workpiece O on the heated die 10, the workpiece O is kept at the temperature TO due to heat transfer caused by heat conduction, heat radiation, and the like from the heated die 10.

As described above, conventionally, a punch 20 has not been heated in consideration of the lifetime of the punch 20. However, with the configuration described above, the punch 20 is heated to the temperature TP based on the fact that the workpiece O is relatively thin. The workpiece O placed on the die 10 is punched using this heated punch 20. The workpiece O is kept at the temperature TO due to not only heat transfer from the die 10 but also heat transfer caused by heat conduction, heat radiation, and the like from the heated punch 20 with which the workpiece O is in contact while holes are being formed through punching.

In the methods in which holes are formed in the workpiece O using a boring technique in which a rotary blade such as a drill is used, melting penetration by laser irradiation, and the like, holes are formed one by one. Therefore, when a plurality of holes are formed, it takes a long time to perform processing, which has a harmful influence on mass production. However, with the configuration described above, the workpiece O is kept at the temperature TO at which the workpiece can be punched, that is, a state in which the substantially entire workpiece O can be easily punched is maintained, and therefore, a plurality of holes can be simultaneously formed in a processing region located in a predetermined range of the workpiece O. Accordingly, a plurality of holes can be formed in the workpiece O in a short time. For example, a plurality of holes can be formed in the workpiece O placed on the die 10 by punching the workpiece O using a plurality of punches 20. Accordingly, a large number of workpieces O provided with a plurality of holes can be produced in a short time, and thus the workpieces O can be processed at low cost.

It should be noted that, in the methods in which holes are formed in the workpiece O using melting penetration by laser irradiation and the like, a portion of the workpiece O needs to be melted. Therefore, problems arise in that dross such as oxides produced through melting attaches to the inside of the holes and blocks the holes, and in that another processing for removing the attached dross needs to be performed. However, with the configuration described above, holes are formed by punching the workpiece O using the punch 20, and therefore, punch chips Oa produced through punching are pushed out by the punch 20 and separated from the workpiece O. Accordingly, the problem in that holes are blocked is less likely to arise unlike the case where laser irradiation and the like are performed.

It should be noted that, since the workpiece O is kept at the temperature TO, a load (compressive stress applied to the punching blades 23 of the punch 20) required to punch the workpiece O at the temperature TO using the punch 20 is 10% or more and 30% or less of a load required to punch the workpiece O at room temperature using the punch 20, for example.

If the workpiece O is punched with a large load, portions of the workpiece O located at positions at which holes are formed and portions therearound may be pulled in the punching direction while the workpiece O is being punched, leading to deformation of the workpiece O. While holes are being formed, a load can be set to be smaller than or equal to a predetermined value by keeping the workpiece O at the temperature TO, thus making it possible to suppress the deformation of the workpiece O itself, which is a relatively thin plate, and to accurately form holes having a desired diameter.

Holes formed by punching the workpiece O have an aspect ratio of 2 or more and 30 or less. As described above, when being punched, the workpiece O is kept at the temperature TO at which the workpiece O can be easily punched using the punch 20, and the deformation resistance (tensile strength) thereof is kept small. Accordingly, in the state in which the deformation resistance of the workpiece O is kept small and thereby the deformability is increased, and a change in the shape of the workpiece O itself is suppressed, the workpiece O can be easily punched using the punch 20. Therefore, holes having an aspect ratio of 2 or more and 30 or less can be formed by punching the workpiece O, which is a relatively thin plate. For the same reason, holes having a large aspect ratio of 2 or more and 30 or less and a diameter of 0.005 mm or more and 0.5 mm or less can be formed by punching the workpiece O, which is a relatively thin plate, with a pitch that is four or more as large as the diameter of the punch holes.

When holes having an aspect ratio of 2 or more are formed in the workpiece O using the punch 20 through cold forging, which is performed at room temperature or the like without heating the workpiece O, a load (compressive stress applied to the punching blades 23 of the punch 20) applied to the punch 20 during punching is large. Moreover, in the case where the relatively thin workpiece O is punched, even if the workpiece O is placed on the die 10 after the workpiece O has been heated, the workpiece O is cooled due to its small thickness. As a result, compressive stress applied to the punch 20 is large when holes having an aspect ratio of 2 or more are formed in the workpiece O using the punch 20. In this case, compressive stress and buckling stress applied to the punch 20 excess the threshold values, and thus it is difficult to form holes having an aspect ratio of 2 or more.

However, with the configuration described above, by heating the die 10 and the punch 20, the workpiece O is kept at the temperature TO at which the workpiece O can be punched. Accordingly, compressive stress applied to the punch 20 is reduced to a relatively small value, and thus holes having an aspect ratio of 2 or more can be easily formed.

(2-3) FIG. 3(ii) to FIG. 3(iii)

After holes are formed by punching the workpiece O using the punching blades 23 as shown in FIG. 3(ii), the punching blades 23 are removed from the workpiece O as shown in FIG. 3(iii).

When the punching blades 23 are removed, the stripper member 50 is pressed and moved toward the workpiece O, and the punch 20 is moved upward away from the die 10. Thus, the leading ends of the pairs of the stripper pins 53a and 53b protrude from the punch bottom face 21a and press the top face of the workpiece O. Accordingly, the punching blades 23 are easily removed from the workpiece O together with the punch main body 21.

It should be noted that the stripper member 50 may also be manually moved by an operator. Alternatively, the control unit 30 may perform control such that the stripper member 50 is placed at the retracted position until the punching of the workpiece O performed using the punching blade 23 is completed, and the punching blade 23 are removed by moving the stripper member 50 toward the workpiece O and press it against the workpiece O after the punching is completed.

After the punching blades 23 are removed from the workpiece O, an operator performs a manual operation or the control unit 30 performs control such that a coolant gas is blasted from the cooling device 60 onto the punching blades 23. When the workpiece O is punched using the punch 20, the temperatures of the punching blades 23 rise due to friction. By blasting the coolant gas onto the punching blades 23 as described above, a rise in temperatures of the punching blades 23 is suppressed. Thus, a reduction in lifetime of the punch 20 due to thermal damage is suppressed.

Using at least one of carbonic acid gas and argon as the coolant gas makes it possible to suppress corrosion of the punch 20. It should be noted that the coolant gas is not limited to these types of gas as long as corrosion of the punch 20 can be suppressed.

(3) Simulation of Formation of Holes in Workpiece

As described above, when holes are formed in the workpiece O, the control unit 30 performs control to heat the die 10 to the temperature TD and the punch 20 to the temperature TP. Thus, the workpiece O to be punched that is placed on the die 10 is kept at the temperature TO at which the workpiece O can be punched.

The following is a description of a simulation performed to confirm whether or not holes having an aspect ratio of 2 or more and 30 or less can be formed when such a punch hole forming method is used to form holes.

A plate-like member that is made of SUS430 (ferrite-based stainless steel) and has a thickness of 0.3 mm is used as the workpiece O. Holes formed through punching have a diameter of 0.025 mm and an aspect ratio of 12. The punch and the die are kept at 700° C. The punch 20 are provided with cylindrical punching blades 23.

The tensile strength σ₇₀₀ of SUS430 at 700° C. is about a fifth of the tensile strength σ₂₀ at room temperature 20° C., and is about 100 MPa (10.2 kgf/mm²). It should be noted these values are obtained with reference to the thesis “High-Temperature Characteristics of Stainless Steel” by KIKUCHI Masao.

Next, punching force P (kgf) required to perform punching using the punch 20 is calculated based on Formula (1) below.

P=LH×t×S×k  (1)

In this formula, LH is the entire circumferential length (mm) of each hole formed in the workpiece O using the punch 20. t is the thickness (mm) of the workpiece O, S is the shearing stress (kgf/mm²), and k is the safety factor.

It should be noted that S is commonly 0.8 times as large as the tensile strength, and therefore, S is determined by multiplying the tensile strength σ₇₀₀ by 0.8.

k is commonly 1.2, but in this description, k is set to 1.0 in order to calculate a collapse safety factor K, which will be described later, for improved safety.

The following values are substituted into Formula (1): 0.025 mm×3.142 for LH, 0.3 mm for t, 0.8×10.2 kgf/mm² for S, and 1.0 for k Thereby, a value 0.1923 (kgf) below is obtained.

$P=\left(0.025\times 3.14\right)\times \left(0.3\right)\times \left(0.8\times 10.2\right)\times \left(1\mathrm{.0}\right)=0.1923\left(\mathrm{kgf}\right)=1.886\left(N\right)$

Accordingly, the punching force P required to form a single hole through punching is 0.1923 (kgf), namely 1.886 (N).

When each cylindrical punching blade 23 of the punch 20 for forming a single hole through punching has a cross-sectional area of A (mm²), compressive stress op applied to each cylindrical punching blade 23 is determined based on Formula (2) below.

σp=P/A  (2)

If the diameter of the cylindrical punching blade 23 is the same as the diameter of the hole, the cross-sectional area A is determined as follows.

A=(0.025/2)×(0.025/2)×3.142

Accordingly, the compressive stress σp is determined as follows by applying this formula to Formula (2).

$\mathrm{op}=\left(0.1923\right)/\left(\left(0.025/2\right)\times \left(0.025/2\right)\times 3.142\right)=391.7\left(\mathrm{kgf}/{\mathrm{mm}}^2\right)$

The punch 20 is made of M78 (manufactured by NJS Co., Ltd.). M78 has a compressive strength on of 8.120 MPa (828.0 kgf/mm²) at 700° C.

Accordingly, the collapse safety factor K for compression failure of the cylindrical punching blade 23 is determined as follows: K=σ_n/σ_p=2.1. It is clear from this value that the punching blade 23 does not undergo compression fracture at 700° C.

It should be noted that since the holes have a large aspect ratio of 12, buckling of the punching blades 23 also needs to be tested. Each punching blade 23 is formed to have a length LP of 0.35 mm, which is longer than the thickness of the workpiece O of 0.3 mm, and a diameter of 0.025 mm, which is the same as the diameter of the hole.

In this case, each punching blade 23 has a slenderness ratio of 14.0 (0.35 mm/0.025 mm). Commonly, buckling needs to be taken into consideration when the slenderness ratio is 15 or more, and therefore, the punching force P is compared with the Euler's buckling load Pcr (N). The Euler's buckling load Pcr (N) is determined based on Formula (3) below.

Buckling load Pcr(N)=m×((3.142)²×E×I)/LP²  (3)

In this formula, m is 0.25 under the condition that one end is fixed, and LP is 0.35 mm.

E is the Young's modulus (Pa), and I is the cross-sectional secondary moment (mm⁴). E×I is the bending moment and commonly corresponds to deflective strength in die machining. The nominal value of the deflective strength of M78 is 1500 (MPa) (1500 (N/mm²)).

Accordingly, the buckling load Pcr (N) is determined as follows by substituting the values into Formula (3).

$\mathrm{Buckling}\mathrm{load}\mathrm{Pcr}=0.25\times {\left(3.142\right)}^2\times 1500/{\left(0.35\right)}^2=3.022\times 10^4\left(N\right)$

The punching force P (kgf) is 1.886 (N), and is smaller than the buckling load Pcr of 3.022×10⁴(N) (Pcr>>P). It is thus clear that the punching force P is sufficiently smaller than the buckling load Pcr, and the punch 20 does not buckle even when the punching force P is applied to the punch 20 in order to punch the workpiece O.

For example, the entire load PP required to simultaneously form a million holes in a single punching step is determined based on Formula (4) below.

Entire load PP=punching force P×number of holes  (4)

Accordingly, the entire load PP is determined as follows: 0.1973 (kgf)×1000000 (holes)=197300 (kgf)=198 (ton). In the case of performing punching using a conventional method, a five-fold larger load applying ability is needed, and therefore, a large-sized pressing machine of a 1000-ton class is needed. However, it is clear that, with the present invention, a small-sized pressing machine of a 200-ton class can be used to perform punching.

Other Embodiments

The configuration disclosed in the embodiment described above (including the other embodiments; the same applies to the following) can be applied in combination with configurations disclosed in the other embodiments as long as no contradiction arises. Also, the embodiments disclosed in this specification are illustrative, embodiments of the present invention are not limited to the disclosed embodiments, and appropriate modifications can be made without departing from the object of the present invention.

(1) In the embodiment described above, a plurality of holes having a large aspect ratio of 2 or more are formed in the workpiece O. Therefore, the control unit 30 performs control to heat the die 10 to the temperature TD and the punch 20 to the temperature TP, and thus the workpiece O is kept at the temperature TO at which the workpiece O can be punched.

However, the control to heat the die 10 and the punch 20 in order to keep the workpiece O at the temperature TO at which the workpiece O can be punched as described in the embodiment above can be applied to a case where a plurality of holes having a small aspect ratio of less than 2 are formed in the workpiece O.

As in the embodiment above, even when a plurality of holes having a small aspect ratio of less than 2 are formed, keeping the workpiece O at the temperature TO makes it possible to form holes by easily punching the workpiece using a punch in the state in which the deformation resistance of the workpiece is kept small and thereby the deformability is increased. In addition, the resistance is small while holes are being formed, thus making it possible to suppress deformation of the workpiece itself, which is a relatively thin plate, and to accurately form holes having a desired diameter.

(2) In the embodiment described above, after holes are formed by punching the workpiece O using the punch 20, the punching blades 23 are removed from the workpiece O using the stripper member 50. However, the stripper member 50 may be omitted.

(3) In the embodiment described above, the workpiece O is kept at the temperature TO while holes are being formed by punching the workpiece O. In order to keep the workpiece O at the temperature TO, the die 10 is heated using the die heater 15 and the punch 20 is heated using the punch heater 25. However, a configuration may also be employed in which only the die 10 is heated using the die heater 15 without heating the punch 20 in order to keep the workpiece O at the temperature TO.

Also, the workpiece O may be heated in advance and then placed on the heated die 10.

The method for keeping the workpiece O at the temperature TO while holes are being formed by punching the workpiece O is not limited to the method described in the embodiment above. For example, the workpiece O can be kept at the temperature TO by keeping the atmosphere in which the workpiece O is punched at the temperature TO. Also, the workpiece O can be kept at the temperature TO by applying a voltage to the workpiece O, for example.

(4) In the embodiment described above, each of the punching blades 23 of the punch 20 includes the cylindrical main portion 23a and the tapering tip portion 23b. In consideration of load pressure applied to the punch 20, the tapering shape of the tip portion can be changed as appropriate. Also, a configuration may be employed in which each of the punching blades 23 does not include the tip portion 23b and is constituted by the main portion 23a.

(5) In the embodiment described above, after the workpiece O is punched using the punch 20, the coolant gas is blasted from the cooling device 60 onto the punching blades 23 of the punch 20 in order to cool the punching blades 23. However, the coolant gas is not necessarily blasted onto the punching blades 23, and the cooling device 60 may be omitted.

(6) In the embodiment described above, as shown in FIG. 2 and the like, the workpiece O is placed on the die top face 11a of the die 10 from above the die 10. However, the workpiece O may be slid along a groove-like guide (not shown) provided on the die 10 and placed on the die top face 11a. Alternatively, the punch hole forming device 100 may be provided with a pressing member (not shown) for pressing the workpiece O placed on the die top face 11a from above.

(7) In the embodiment described above, the die 10 is fixed at a predetermined position, and the punch 20 is moved toward the die 10. However, a configuration may also be employed in which the punch 20 is fixed at a predetermined position, and the die 10 is moved toward the punch 20.

(8) In the embodiment described above, the small protrusions 17 are formed in order to prevent the positional shift of the workpiece O placed on the die 10. However, the small protrusions 17 may be omitted.

DESCRIPTION OF REFERENCE SIGNS

• • 10: Die
  • 20: Punch
  • 23: Punching blade
  • O: Workpiece

Claims

1. A punch hole forming method comprising placing a workpiece that is a plate-like member having a thickness of 0.01 mm or more and 1 mm or less on a die, and forming a hole by punching the workpiece in a thickness direction using a punch,

wherein the workpiece is kept at a temperature TO at which the workpiece can be punched at least during formation of the hole.

2. The punch hole forming method according to claim 1, wherein a load applied by the punch to the workpiece while the workpiece at the temperature TO is being punched using the punch is smaller than or equal to a predetermined value.

3. The punch hole forming method according to claim 2, wherein a load applied by the punch to the workpiece kept at the temperature TO while a hole is formed in the workpiece using the punch is 10% or more and 30% or less of a load required to form a hole in the workpiece at room temperature using the punch.

4. The punch hole forming method according to claim 1, wherein the temperature TO is 300° C. or higher and 950° C. or lower.

5. The punch hole forming method according to claim 1, wherein the workpiece is kept at the temperature TO by placing the workpiece on the die heated to a temperature TD.

6. The punch hole forming method according to claim 5, wherein the workpiece is kept at the temperature TO by punching the workpiece using the punch heated to a temperature TP.

7. The punch hole forming method according to claim 1, wherein an aspect ratio defined as a ratio of a thickness of the workpiece to a diameter of the hole, thickness/diameter, is set to 2 or more and 30 or less.

8. The punch hole forming method according to claim 7, wherein the diameter of the hole is 1 mm or less.

9. The punch hole forming method according to claim 1, wherein a plurality of the holes are formed in the workpiece.

10. The punch hole forming method according to claim 1, wherein the workpiece is made of a heat-resistant metal material selected from ferrite-based stainless steel, austenite-based stainless steel, and martensite-based stainless steel.

11. The punch hole forming method according to claim 1, wherein at least one of the punch and the die is made of a superhard material containing at least one of ceramic and tungsten.

12. The punch hole forming method according to claim 1, wherein a coolant gas is blasted onto the punch after the workpiece has been punched using the punch.

13. The punch hole forming method according to claim 12, wherein the coolant gas is at least one of carbonic acid gas, nitrogen, and argon.

14. The punch hole forming method according to claim 1,

wherein the punch includes: a punch main body having a plate shape with a predetermined thickness: a punching blade that protrudes and extends from an opposed face of the punch main body opposed to the workpiece and that is used to form a hole in the workpiece; and a stripper member including a base portion that is located on a face facing in a direction opposite to a protruding direction of the punching blade out of two opposite faces of the punch main body, and a stripper pin that extends from the base portion, passes through the punch main body in the protruding direction of the punching blade, and has a length larger than a thickness of the punch main body,

wherein the stripper pin is retracted so as not to protrude from the opposed face while the workpiece is being punched using the punch, and

after the workpiece has been punched using the punch, a leading end of the stripper pin protrudes from the opposed face and presses the workpiece, and the punching blade is removed from the workpiece together with the punch main body.

15. A punch hole forming device for forming a hole in the workpiece using the punch hole forming method according to claim 1, the device comprising:

a die on which the workpiece is to be placed;

a punch for forming a hole by punching the workpiece placed on the die in a thickness direction; and

a control unit that performs control to keep the workpiece at a temperature TO at which the workpiece can be punched while the hole is being formed.

16. The punch hole forming method according to claim 2, wherein the temperature TO is 300° C. or higher and 950° C. or lower.

17. The punch hole forming method according to claim 3, wherein the temperature TO is 300° C. or higher and 950° C. or lower.

18. The punch hole forming method according to claim 2, wherein the workpiece is kept at the temperature TO by placing the workpiece on the die heated to a temperature TD.

19. The punch hole forming method according to claim 3, wherein the workpiece is kept at the temperature TO by placing the workpiece on the die heated to a temperature TD.

20. The punch hole forming method according to claim 4, wherein the workpiece is kept at the temperature TO by placing the workpiece on the die heated to a temperature TD.