Plate material, plate material tearing method, and suspension

A plate material has a first portion, a second portion, and a fracture portion connecting the first portion and the second portion, and is separated into the first portion and the second portion by tearing the fracture portion. The first portion and the second portion are arranged in a first direction. The fracture portion has thin portions arranged in a second direction crossing the first direction. Widths in the second direction of the thin portions are different from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2019-222871, filed Dec. 10, 2019, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plate material used for a suspension of, for example, a disk drive, a plate material tearing method of tearing the plate material, and a suspension manufactured by tearing the plate material.

2. Description of the Related Art

A hard disk drive (HDD) is used in an information processing apparatus such as a personal computer. The hard disk drive includes a magnetic disk which rotates about a spindle, a carriage which turns about a pivot shaft, and the like. The carriage has an actuator arm, and is turned in a track width direction of the disk about the pivot shaft by a positioning motor such as a voice coil motor.

A disk drive suspension (hereinafter referred to simply as a suspension) is attached to the actuator arm. The suspension includes a base plate, a load beam coupled to the base plate, a flexure arranged overlapping the load beam, and the like. In a gimbal portion formed close to a distal end of the flexure, a slider constituting a magnetic head is provided. In the slider, an element (transducer) for reading data from the disk and writing data to the disk is provided. The load beam, the flexure, the slider and the like constitute a head gimbal assembly.

During the manufacturing of the suspension, from the perspective of efficiency, a chain blank where a plurality of suspensions are coupled together by a frame is manufactured. The frame is integrally connected to a part of the suspension, for example, the load beam. After that, the individual suspensions in the chain blank are separated from the frame.

During the separation of the suspension from the frame, a method of sandwiching a part of the suspension between an upper die and a lower die, pressing the frame by a punch, and applying a shear force to a connection portion of these two may be used. However, in order to realize this separation method, high accuracy is required for a clearance between the punch and the lower die, or the like, and a cutting apparatus costs high. In addition, burrs and particles may occur.

Therefore, in JP 2012-027993 A, a method of providing an easy-to-tear portion where an opening and a thin portion are alternately arranged in a cut portion of the frame and the load beam, and cutting the easy-to-tear portion using a tensile force in an in-plane direction is proposed. According to this method, since high accuracy is not necessarily required for the clearance, the cost of a tearing apparatus can be suppressed. In addition, occurrence of burrs and particles can be suppressed.

Recently, processing with higher accuracy has been required in the suspension. When the cut portion is relatively thick, even if the above easy-to-tear portion is provided, strong vibration still occurs during tearing. This vibration may have various negative impacts on the suspension after separation.

On the other hand, when all the thin portions of the easy-to-tear portion are made thin, vibration during tearing can be suppressed. In this case, however, the strength to support the suspension of the frame is reduced, and the vibration of the suspension during the transportation of the chain blank is increased. Since the suspension may be deformed by this vibration, this vibration causes yield reduction.

As described above, the method of separating the suspension from the frame have various problems which can be improved. Similar problems may also arise during separation of a plate material used for a product other than the suspension.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a plate material and a plate material tearing method which can realize tearing of a fracture portion with excellent quality and to provide a suspension which can realize improvement in yield.

A plate material according to one embodiment has a first portion, a second portion, and a fracture portion connecting the first portion and the second portion, and is separated into the first portion and the second portion by tearing the fracture portion. The first portion and the second portion are arranged in a first direction. The fracture portion has a plurality of thin portions arranged in a second direction crossing the first direction. Furthermore, widths in the second direction of the thin portions are different from each other.

The fracture portion may have a first thin portion, a second thin portion and a third thin portion arranged in the second direction. In this case, a width in the second direction increases in an order of the first thin portion, the second thin portion and the third thin portion. As another example, the width in the second direction of the second thin portion may be less than those of the first thin portion and the third thin portion. As yet another example, the width in the second direction of the second thin portion may be greater than those of the first thin portion and the third thin portion.

The fracture portion may have a plurality of openings provided between the thin portions adjacent to each other, respectively, and widths in the second direction of the openings may be the same.

The first portion may be a part of a suspension supporting an element for writing data to a disk provided in a disk drive and reading data from the disk. In this case, the second portion may be a frame forming a chain blank by coupling a plurality of the suspensions together.

In a plate material tearing method according to one embodiment, the first portion is arranged between a pad retreatable against an urging force and a punch, the second portion is sandwiched between an upper die and a lower die, and the fracture portion is fractured by applying a tensile force in the first direction to the fracture portion by pressing the pad by the punch.

A suspension according to one embodiment is configured to support an element for writing data to a disk provided in a disk drive and reading data from the disk, and includes a base plate, a load beam including a rigid portion and a pair of spring portions connecting the rigid portion and the base plate, and a flexure connected to the load beam and having a tongue for mounting the element. The pair of spring portions have a first end side and a second end side in a width direction of the suspension, respectively. The first end side and the second end side each have a plurality of thin portions arranged in a longitudinal direction of the suspension, and a concave portion between the thin portions adjacent to each other. Widths in the longitudinal direction of the thin portions are different from each other.

According to the plate material and the plate material tearing method of the above configuration, the fracture portion can be torn with excellent quality. In addition, according to the suspension of the above configuration, the first end side and the second end side can be manufactured as the fracture portion, and therefore the yield can be improved.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described with reference to the accompanying drawings.

In the embodiments, a suspension of a disk drive (HDD), a plate material used during its manufacturing, and a method of tearing the plate material will be illustrated. Note that a plate material and its tearing method having a similar configuration to that of the embodiments can be applied to a component, a member or an apparatus other than a suspension and its manufacturing process.

First Embodiment

FIG. 1is a schematic plan view of a suspension1according to the first embodiment. The suspension1includes a base plate2, a load beam3and a flexure4. In the following explanation, a first direction D1and a second direction D2orthogonal to each other as illustrated will be defined. The first direction D1corresponds to a width direction of the suspension1, and the second direction D2corresponds to a longitudinal direction of the suspension1.

In the base plate2, a boss portion20for attaching the suspension1to an arm provided in a carriage of a disk drive is provided. In the example ofFIG. 1, the base plate2includes a first plate21and a second plate22superposed on the first plate21. The first plate21and the second plate22are formed of, for example, a metal material such as stainless steel, and are coupled together by spot welding. However, the first plate21and the second plate22may be integrally formed from the beginning. The thicknesses of the first plate21and the second plate22are, for example, 150 μm but are not limited to this.

The load beam3includes a rigid portion30, a first spring portion31A and a second spring portion31B. The rigid portion30has a shape tapered toward a distal end (leftward in the drawing). The rigid portion30and the spring portions31A and31B are formed of, for example, a metal material such as stainless steel. The first spring portion31A is coupled to the rigid portion30and the first plate21by, for example, spot welding, respectively, at one end of the suspension1in the first direction D1. The second spring portion31B is coupled to the rigid portion30and the first plate21by, for example, spot welding, respectively, at the other end of the suspension1in the first direction D1. Note that the rigid portion30, the first spring portion31A and the second spring portion31B may be integrally formed from the beginning. In this structure, the load beam3is elastically supported with respect to the base plate2by the spring portions31A and31B. The thickness of the rigid portion30is, for example, 30 μm but is not limited to this example.

The flexure4is arranged along the base plate2and the load beam3, and is coupled to the base plate2and the load beam3by spot welding. The flexure4has a multilayer stack structure including, for example, a metal layer of stainless steel or the like, a copper line for wiring, and an insulating layer of polyimide or the like. The thickness of the metal layer of the flexure4is, for example, 20 μm but is not limited to this example.

At a position overlapping the load beam3, the flexure4includes a pair of wiring portions40A and40B arranged in the first direction D1. In an end portion of the wiring portions40A and40B on a distal end side (leftward in the drawing), a plurality of terminals41arranged in the first direction D1are provided. In addition, the flexure4has a tongue42close to the terminals41. The tongue42is provided with a slider5constituting a magnetic head. The slider5includes an element (transducer) for reading data from a disk and writing data to the disk, and is electrically connected to the terminals41.

The flexure4further includes a pair of outriggers43A and43B located respectively on both outer sides of the tongue42in the first direction D1. The tongue42, the outriggers43A and43B and the like constitute a gimbal portion.

The load beam3has a first end side SA at one end in the first direction D1and a second end side SB at the other end in the first direction D1. In the present embodiment, the first end side SA and the second end side SB are parts of the spring portions31A and31B, respectively, and extend in the second direction D2.

FIG. 2is an enlarged schematic plan view of the first spring portion31A close to the first end side SA. The first end side SA has a first thin portion61, a second thin portion62and a third thin portion63which project in the first direction D1. In addition, the first end side SA has a first concave portion71between the first thin portion61and the second thin portion62, and a second concave portion72between the second thin portion62and the third thin portion63.

The thin portions61to63are arranged in order in the second direction D2. In the present embodiment, the first thin portion61has a width W1in the second direction D2, the second thin portion62has a width W2greater than the width W1in the second direction D2, and the third thin portion63has a width W3greater than the width W2in the second direction D2. The widths W1to W3are, for example, the widths at respective distal ends of the thin portions61to63. As another example, the widths W1to W3may be defined as the widths in respective middle portions of the thin portions61to63or the average values of the widths from respective proximal ends to respective distal ends of the thin portions61to63. In the present embodiment, the widths W1to W3are in a range of greater than or equal to twice the thickness of the first spring portion31A but less than or equal to four times the thickness of the first spring portion31A.

In the example ofFIG. 2, the widths in the second direction D2of the concave portions71and72are the same. However, the widths of the concave portions71and72may be different from each other. For example, the widths of the concave portions71and72are greater than or equal to the width W1but less than or equal to the width W3.

Since the shape of the second spring portion31B close to the second end side SB is similar to the example ofFIG. 2, explanation will be omitted. Note that the number of thin portions provided in each of the end sides SA and SB is not limited to three but may be two or greater than or equal to four.

Next, an example of a manufacturing method of the suspension1will be explained. During the manufacturing of the suspension1, a chain blank where the suspensions1are coupled together is manufactured.

FIG. 3is a schematic plan view of a chain blank100according to the present embodiment.FIG. 4is a schematic exploded diagram of elements constituting the chain blank100.

The chain blank100includes a frame8in addition to the respective elements of the suspension1which are also shown inFIG. 1. The frame8includes a coupling portion80extending in the first direction D1, and a first arm81A and a second arm81B extending in the second direction D2from the coupling portion80. The frame8further includes pin holes82A and82B for fixing the position of the frame8in a tearing process which will be described later. In the example ofFIGS. 3 and 4, the pin holes82A and82B are provided close to distal ends of the arms81A and81B, respectively.

The suspension1is arranged between the arms81A and81B. The first arm81A is connected to the first spring portion31A in a first fracture portion9A (first end side SA). The second arm81B is connected to the second spring portion31B in a second fracture portion9B (second end side SB). The fracture portions9A and9B can be referred to also as easy-to-tear portions. The frame8and the spring portions31A and31B are integrally formed using a metal material such as stainless steel.

The chain blank100includes a plurality of sets of the arms81A and81B shown inFIG. 3and the suspension1supported by them. These sets are arranged at intervals in the first direction D1, for example.

FIG. 5is a flowchart showing an example of a manufacturing process of the suspension1. The suspension1is manufactured through a component artwork process P1, a bending process P2, an assembling process P3and a tearing process P4. The tearing process P4can be referred to also as a cutting process or a separation process.

In the component artwork process P1, those of the elements shown inFIG. 4which are made of metal are formed by punching, etching or the like to a plate which is to be their material.

In the bending process P2, those of the elements shown inFIG. 4which require bending are bent by an appropriate method. In the process P2, for example, working for forming a dimple which supports the slider with respect to the rigid portion30is included.

In the assembling process P3, the elements shown inFIG. 4are assembled by, for example, spot welding using a laser. In the process P3, welding of the first plate21and the second plate22, welding of the first plate21and the spring portions31A and31B, welding of the rigid portion30and the spring portions31A and31B, welding of the flexure4and the rigid portion30, and the like are included.

In the tearing process P4, the suspension1is separated from the frame8by tearing the fracture portions9A and9B shown inFIGS. 3 and 4by a tearing apparatus200which will be described later.

FIG. 6is a schematic plan view of the first fracture portion9A in the present embodiment. In the first fracture portion9A, the first thin portion61, the second thin portion62and the third thin portion63which are also shown inFIG. 2are provided. In the example ofFIG. 6, these thin portions61to63are connected to the first spring portion31A and the first arm81A.

The first thin portion61is located between a first notch73which is recessed in the second direction D2at the boundary between the first arm81and the first spring portion31A and a first opening74which is adjacent to the first notch73. The second thin portion62is located between the first opening74and a second opening75which is adjacent to the first opening74. The third thin portion63is located between the second opening75and a second notch76which is recessed in the second direction D2at the boundary between the first arm81A and the first spring portion31A. This first fracture portion9A can be formed by, for example, etching or pressing.

The first fracture portion9A is torn along, for example, a fracture line L shown by a dashed dotted line. After tearing, parts of the thin portions61to63remaining on a first spring portion31A side form the thin portions61to63projecting from the first end side SA shown inFIG. 2, respectively. In addition, parts of circumferential edges of the openings74and75remaining on the first spring portion31A side form the concave portions71and72shown inFIG. 2, respectively.

The magnitude relationship of the widths W1to W3of the thin portions61to63are as described above. However, since the thin portions61to63are stretched to some extent during tearing, the widths W1to W3of the thin portions61to63shown inFIG. 2may be less than those shown inFIG. 6. The widths in the second direction D2of the openings74and75are, for example, the same. The depths in the second direction D2of the notches73and76are, for example, less than any of the width W1and the widths of the openings74and75.

In the example ofFIG. 6, the first spring portion31A and the first arm81A are arranged in the first direction D1. In addition, the thin portions61to63, the notches73and76and the openings74and75are arranged in the second direction D2. In the present embodiment, the first spring portion31A and the first arm81A are an example of a “first portion” and a “second portion”. Furthermore, in the present embodiment, the first spring portion31A and the first arm81A (frame8) before tearing are an example of a “plate material”.

FIG. 7is a schematic cross-sectional view of the tearing apparatus200in the present embodiment. The tearing apparatus200includes an upper pad210of an upper die, a die220of a lower die opposed to the upper pad210, a punch230adjacent to the upper pad210, and a lower pad240opposed to the punch230.

The punch230is supported movably along an upward/downward direction inFIG. 7. The lower pad240is elastically supported by an urging member such as a coil spring. When the punch230moves down toward the lower pad240and presses the lower pad240, the lower pad240retreats downward against an urging force.

The punch230has a punch surface231opposed to the lower pad240, a guide surface232overhanging toward the upper pad210with respect to the lower pad240, an end surface233opposed to the upper pad210, and a corner portion234between the guide surface232and the end surface233. In the present embodiment, the guide surface232is located more upward in the drawing (in a direction away from the lower pad240) than the punch surface231. Accordingly, a step235is formed between the punch surface231and the guide surface232. In addition, the corner portion234in the present embodiment has an R portion234ahaving a cross section rounded in an arc shape.

FIG. 8is a schematic cross-sectional view for explaining a plate material tearing method using the tearing apparatus200. The chain blank100shown inFIG. 3is arranged on the die220and the lower pad240. In this state, the frame8(first arm81A) is sandwiched between the upper pad210and the die220, and the first spring portion31A and the first plate21are sandwiched between the punch230and the lower pad240. The first fracture portion9A is located close to the step235, and is at least partly opposed to the guide surface232. Since the step235is provided, a part of the first fracture portion9A which is opposed to the guide surface232is not held by the punch230.

Note that, although not shown in the cross section ofFIG. 8, the second arm81B is also sandwiched between the upper pad210and the die220similarly to the first arm81A, and the second spring portion31B is also sandwiched between the punch230and the lower pad240similarly to the first spring portion31A. In addition, positioning pins are inserted in the pin holes82A and82B shown inFIG. 3.

In the example ofFIG. 8, the punch230is pressed in a third direction D3shown in the drawing, and the first spring portion31A is located more downward than the first arm81A. While the punch230is pressed, the first arm81A is slid along the R portion234aand the guide surface232and is bent along the R portion234a. Close to the guide surface232, a tensile force F substantially parallel to the first direction D1(in-plane direction of the first spring portion31A and the first arm81A) acts on the first arm81A. When the punch230is sufficiently moved down, the tensile force F is increased, and eventually the first fracture portion9A is fractured. In the shape of the first fracture portion9A shown inFIG. 6, a stress applied to the thin portions61and63increases, and the first fracture portion9A can be efficiently fractured.

Here, the thicknesses of the first spring portion31A and the first arm81A will be defined as t as shown inFIG. 8. According to experiments by inventors, when the thickness t of each of the first spring portion31A and the first arm81A formed of SUS 304 is greater than or equal to 15 μm but less than or equal to 100 μm, if the widths W1to W3of the thin portions61to63shown inFIG. 6are less than twice the thickness t, the thin portions61to63are stretched a lot during tearing, and if the widths W1to W3are greater than four times the thickness t, the thin portions61to63are less easily torn. Therefore, when the thickness t of each of the first spring portion31A and the first arm81A is greater than or equal to 15 μm but less than or equal to 100 μm, the widths W1to W3should preferably be greater than or equal to twice the thickness t but less than or equal to four times the thickness t.

In addition, as shown inFIG. 6, the widths in the first direction D1of the openings74and75will be defined as W, the distance in planar view between the fracture line L and the end surface233of the punch230will be defined as D. In the example ofFIG. 6, the width W and the distance D are substantially the same.

FIGS. 9 and 10are plan views schematically showing a state where the first fracture portion9A is torn by the tensile force F. The example ofFIG. 9corresponds to a case where the first arm81A (frame8) is loosely sandwiched between the upper pad210and the die220. In this case, the first arm81A can rotate in a plane including the respective directions D1and D2. Therefore, when the punch230is pressed, the thin portion61having a small width is stretched and the first arm81A is slanted in the plane, and the thin portion61is fractured first, the thin portion62is fractured second, and the thin portion63is fractured last.

On the other hand, the example ofFIG. 10corresponds to a case where the first arm81A (frame8) is firmly sandwiched between the upper pad210and the die220. In this case, since the first arm81A does not rotate in the plane including the respective directions D1and D2, the thin portion63having a large width and stretched little is fractured first, the thin portion62is fractured second, and the thin portion61is fractured last.

For example, in order to determine which of the methods ofFIGS. 9 and 10to use for tearing the first fracture portion9A, one of which can produce an excellent fracture surface after tearing may be selected according to the material qualities of the first spring portion31A and the first arm81A, the widths W1to W3of the thin portions61to63, and the like.

Note that the configuration described regarding the first spring portion31A and the first arm81A with reference toFIGS. 6 to 10can also be applied to the second spring portion31B and the second arm81B.

According to the present embodiment described above, since the fracture portions9A and9B are torn mainly by the tensile force F in the in-plane direction (first direction D1) while the tearing of the plate material (frame8and spring portions31A and31B), bending hardly acts on the fracture portions9A and9B. Therefore, occurrence of burrs after tearing can be suppressed. Since the thin portions61to63are provided in the fracture portions9A and9B, tearing can be easily carried out, and occurrence of particles after tearing can be suppressed.

If the thin portions61to63and the openings74and75are not provided in the fracture portions9A and9B, in order to make the frame8and the spring portions31A and31B easy to tear, the widths of the entire fracture portions9A and9B need to be reduced. In this case, the suspension1in the chain blank100swings easily with respect to the frame8and is not stable. On the other hand, when the thin portions61to63and the openings74and75are provided in the fracture portions9A and9B, the widths of the fracture portions9A and9B can be increased while ease of tearing is maintained. Accordingly, the suspension1is stably supported by the frame8. Furthermore, the position of the fracture line L is also stabilized by providing the thin portions61to63and the openings74and75.

In the tearing apparatus200according the present embodiment, since the guide surface232where a part of the punch230is overhung with respect to the lower pad240is formed, even if the pitch of the suspension1is slightly changed by heat influence during the material joining of the chain blank100, the change in pitch can be absorbed. Furthermore, in the tearing apparatus200, high accuracy is not required for a clearance between the punch230and the die220. Therefore, the cost of the tearing apparatus200can be suppressed.

When the thin portions61to63and the openings74and75are provided in the fracture portions9A and9B, a load which should be applied to the fracture portions9A and9B by the tearing apparatus200is reduced. Accordingly, the miniaturization and energy saving of the tearing apparatus200are facilitated.

As the thicknesses of the spring portions31A and31B and the frame8increase, vibration during tearing increases. For example, when these have a thickness of greater than or equal to 35 μm, strong vibration occurs. By this vibration, the bending angles of the respective parts in the suspension1after tearing may be changed, or the product may be displaced inside the dies and scratches may occur. In addition, the spring portions31A and31B and the frame8cannot be held during tearing, and this may cause a problem with the fracture position, or the like. In order to prevent this, the load for holding the spring portions31A and31B and the frame8needs to be increased, and high rigidity is required for the respective elements of the tearing apparatus200. Furthermore, since the respective elements in the tearing apparatus200loses balance easily by vibration, the frequency of maintenance needs to be increased.

Meanwhile, a countermeasure to suppress vibration during tearing which is conceived is making all the thin portions61to63sufficiently thin. In this case, however, the suspension1is more easily vibrated during the transportation of the chain blank100, and this may cause deformation of the suspension1.

On the other hand, when the widths W1to W3of the thin portions61to63are made different from each other as in the present embodiment, as shown inFIGS. 9 and 10, the thin portions61to63are fractured in order. In this case, vibration during tearing is reduced, and the above problems caused by this vibration can be suppressed. In addition, as compared with a case where all the thin portions61to63are made thin, the vibration of the suspension1during the transportation of the chain blank100can also be suppressed.

In a case where the suspension1is manufactured using the plate material tearing method according to the present embodiment, the first end side SA and the second end side SB of the suspension1have the shape shown inFIG. 2. From another point of view, it is possible to apply the plate material tearing method according to the present embodiment to the manufacturing of the suspension1by forming the suspension1in the shape ofFIG. 2. Accordingly, occurrence of burrs and particles during manufacturing can be suppressed, and the yield of the suspension1can be improved.

Note that the shapes of the fracture portions9A and9B are not limited the shape shown inFIG. 6. In the following second to fifth embodiments, other shapes applicable to the fracture portions9A and9B will be illustrated.

Second Embodiment

FIG. 11is a schematic plan view of the first fracture portion9A according to the second embodiment. In the example of this drawing, the width W2of the second thin portion62is less than the case ofFIG. 6. The width W2is, for example, the same as the width W1of the first thin portion61. A similar shape can also be applied to the second fracture portion9B.

For example, the chain blank100having these fracture portions9A and9B is arranged in the tearing apparatus200such that the arms81A and81B can rotate in the plane including the respective directions D1and D2similarly toFIG. 9, and the punch230is moved down. At this time, since the widths W1and W2are sufficiently less than the width W3, the arms81A and81B rotate more easily than the case ofFIG. 6.

Third Embodiment

FIG. 12is a schematic plan view of the first fracture portion9A according to the third embodiment. In the example of this drawing, the width W2of the second thin portion62is greater than the case ofFIG. 6. The width W2is, for example, the same as the width W3of the third thin portion63. A similar shape can also be applied to the second fracture portion9B.

When the chain blank having these fracture portions9A and9B is torn by a similar method toFIG. 9, the arms81A and81B rotate less easily than the case of the fracture portions9A and9B having the shape ofFIG. 6.

Fourth Embodiment

FIG. 13is a schematic plan view of the first fracture portion9A according to the fourth embodiment. In the example of this drawing, the width W2of the second thin portion62is greater than either of the width W1of the first thin portion61and the width W3of the third thin portion63. In addition, the width W1and the width W3are the same. A similar shape can also be applied to the second fracture portion9B.

When the chain blank having these fracture portions9A and9B is torn by a similar method toFIG. 9, since the fracture portions9A and9B have a bisymmetrical shape with respect to the center in the second direction D2, the arms81A and81B rotate less easily than the case of the fracture portions9A and9B having the shape ofFIG. 6.

Fifth Embodiment

FIG. 14is a schematic plan view of the first fracture portion9A according to the fifth embodiment. In the example of this drawing, the width W2of the second thin portion62is less than either of the width W1of the first thin portion61and the width W3of the third thin portion63. In addition, the width W1and the width W3are the same. A similar shape can also be applied to the second fracture portion9B.

When the chain blank100having these fracture portions9A and9B is torn by a similar method toFIG. 9, similarly to the fourth embodiment, the arms81A and81B rotate less easily. When the widths W1and W3of the thin portions61and63at both ends are greater than the width W2of the second thin portion62at the center as in the present embodiment, the effect of rotation suppression becomes more significant.

The fracture portions9A and9B disclosed in the above first to fifth embodiments can be appropriately used depending on whether or not to rotate the arms81A and81B during tearing. The fracture portions9A and9B disclosed in these embodiments can produce various other favorable effects. In the embodiments, the number of thin portions provided in each of the fracture portions9A and9B is not limited to three but may be two or greater than or equal to four.

The configuration of the tearing apparatus200is not limited to the configuration shown inFIGS. 7 and 8. In the following sixth and seventh embodiments, other shapes applicable to the tearing apparatus200will be illustrated.

Sixth Embodiment

FIG. 15is a schematic cross-sectional view of the tearing apparatus200according to the sixth embodiment. In the example of this drawing, the punch surface231and the guide surface232are located at the same height. A concave portion236is formed between the punch surface231and the guide surface232. According to this configuration, the tensile force F applied to the fracture portions9A and9B during tearing as shown inFIG. 8can be made parallel to the first direction D1.

Seventh Embodiment

FIGS. 16(a), 16(b) and 16(c)are schematic cross-sectional views of the corner portion234of the punch230provided in the tearing apparatus200according to the seventh embodiment. The corner portion234shown inFIG. 16(a)has an inclined surface234binclined with respect to the guide surface232and the end surface233, a first R portion234cbetween the inclined surface234band the guide surface232, and a second R portion234dbetween the inclined surface234band the end surface233.

The corner portion234shown inFIG. 16(b)has the inclined surface234bsimilarly to the example ofFIG. 16(a)but does not have the R portions234cand234d.

The corner portion234ofFIG. 16(c)has a first inclined surface234e, a second inclined surface234fand a third inclined surface234gwhich are inclined with respect to the guide surface232and the end surface233. Angles which these inclined surfaces234eto234gform with the guide surface232and the end surface233are different from each other. R portions may be provided between the guide surface232and the first inclined surface234e, between the first inclined surface234eand the second inclined surface234f, between the second inclined surface234fand the third inclined surface234g, and between the third inclined surface234gand the end surface233.