Press Working Method

Abstract

A press working mechanism has a punch and a die, which are arranged to be opposed to each other in a vertical direction. A work-piece is set at a position between the punch and the die, so that a press working force is applied by the punch to the work-piece. An upper-side surface of the die has a recessed portion, a shape of which corresponds to a shape of a final press working product. A lower-side surface of the punch has a center projected portion, a shape of which corresponds to the shape of the final press forming product, and an outside projected portion. The work-piece has a main portion and a predetermined first-contact portion. Specifications for a dimensional accuracy of a press work, which is required for the predetermined first-contact portion, is made to be lower than that required for the main portion. The outside projected portion of the punch and the die hold the predetermined first-contact portion of the work-piece prior to the main portion thereof in an initial stage of a press working process, so that a press work is done for the first-contact portion.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on Japanese Patent Application No. 2015-80018 filed on Apr. 9, 2015, the disclosure of which is incorporated herein by reference.

FIELD OF TECHNOLOGY

[0002] The present disclosure relates to a press working method, according to which a punch and a die of a press working mechanism are so arranged as to be opposed to each other, a work-piece is held between the punch and the die, and the work-piece is pressed by the punch to a desired shape. The present disclosure further relates to a press working apparatus for using the press working method and relates to a press forming product or a press working product which is manufactured by the press working method.

BACKGROUND

[0003] In a well-known pressure sensor for an automotive vehicle, a metal diaphragm is incorporated in the sensor. The metal diaphragm is made of a stainless thin plate of a disc shape, in which multiple (corrugated portions) are formed in a concentric fashion. A press working method is generally used for manufacturing the metal diaphragm of this kind, wherein the press working method is carried out by a press working mechanism having a punch and a die.

[0004] In recent years, for example, as disclosed in Japanese Patent Publication No. S61-63320, the punch is made of a metal mold and the die is made of a rubber mold (made of urethane rubber) in order to prevent an occurrence of a flaw on a surface of the stainless thin plate.

[0005] In a case that one of (or both of) the punch and the die is made of elastic material, such as, rubber, it is necessary to decide a shape of the mold for the punch and/or the die by taking into consideration a possible deformation of the mold to which a press working pressure is applied. For example, in a case that the punch is made of an elastic body, a surface of the punch is made with a flat surface and a press working process is carried out together with the die made of a metal mold (a rigid body). More exactly, the punch made of the elastic body mills a work-piece material when it is deformed and then the punch presses the work-piece into the die.

[0006] However, in the case that the punch is made of the elastic body, a press working force to be applied to the work-piece material depends on a deformation by a physicality of the elastic body (Young's modulus, a stress-strain relationship, and so on). It is, therefore, more difficult to uniformly apply the press working force to the work-piece material in view of its characteristic, when compared with a case in which the metal mold of the rigid body is used. As a result, the press working force is locally applied to a portion of the work-piece, for example, a deep portion of a deep-drawing work. Such a press working force may remain as a residual stress in a press forming product (a final product), which may deteriorate a durability of the final product. In addition, since a mechanical and physical property of the elastic body varies depending on a temperature, a lot and so on, it is necessary to provide a margin in order to surely carry out the press working process. However, such a margin may further increase the residual stress.

SUMMARY OF THE DISCLOSURE

[0007] The present disclosure is made in view of the above problem. It is an object of the present disclosure to provide a press working method and a press working apparatus, according to which a work-piece is deformed by a punch and a die and a durability characteristic of a press forming product or a press working product is prevented from becoming worse due to a residual stress in the work-piece.

[0008] According to one of features of the present disclosure, a press working mechanism has a punch and a die, which are arranged so as to be opposed to each other in order to hold a work-piece between them in a press working method of the present disclosure, a press working force is applied by the press working mechanism to the work-piece so that the work-piece is deformed in a desired shape. In an initial stage of a press working process, a predetermined first-contact portion (an outside portion) of the work-piece is at first held by the punch and the die prior to a main press-work portion (a center portion) of the work-piece. At least one of specifications with respect to a dimensional accuracy of a press work, a mechanical, strength and durability, which are required for the predetermined first-contact portion is made to be lower than that required for the main press-work portion of the work-piece.

[0009] According to another feature of the present disclosure, the present disclosure is applied to the press working apparatus. Therefore, like the above feature of the press working method, the press working mechanism of the press working apparatus has the punch and the die, which are arranged so as to be opposed to each other in order to hold the work-piece between them. In the same manner to the above press working method of the present disclosure, the press working force is applied by the press working mechanism to the work-piece so that the work-piece is deformed in the desired shape in the initial stage of the press working process, the first-contact portion of the work-piece is at first held by the punch and the die prior to the main press-work portion of the work-piece. At least one of the specifications with respect to the dimensional accuracy of the press work, the mechanical strength and the durability, which are required for the first-contact portion is made to be lower than that required for the main press-work portion of the work-piece.

[0010] Generally, in a case that a work-piece is plastically deformed by a press working process by use of a punch and a die in order to obtain a desired shape for the work-piece, a specific gripping portion of the work-piece, which is usually an outside portion of the work-piece, is held at first by and between the punch and die in an initial stage of the press working process. Then, in an ending stage of the press working process, a main portion of the work-piece, which is usually a center portion of the work-piece and surrounded by the specific gripping portion (the outside portion) is pressed by the punch so that the main portion is plastically deformed along a shape of the punch and/or the die. During the above press working process, in particular, in the ending stage of the press working process, material of the work-piece cannot sufficiently move from the specific gripping portion to the main portion, because the specific gripping portion is firmly held by and between the punch and the die. Therefore, when a deep drawing process is carried out in the ending stage of the press working process (in which, the material does not easily and sufficiently flow from the specific gripping portion to the main portion), a thickness of the work-piece is reduced in an area of the main portion. As a result, a uniform thickness cannot be obtained in the main portion of the work-piece which is plastically deformed. A relatively large residual stress may remain in a final press working product.

[0011] However, according to the press working method and/or the press working apparatus of the present disclosure, the punch and the die hold the predetermined first-contact portion (for example, the outside portion) of the work-piece prior to the other portion of the work-piece (for example, the main press-work portion, which is generally surrounded by the outside portion). In other words, the main press-work portion of the work-piece is held by the punch and the die after the predetermined first-contact portion (the outside portion) of the work-piece has been held by and between the punch and the die. More exactly, a press work is done for the main press-work portion of the work-piece, after the predetermined first-contact portion is partly (or fully) deformed and thereby the work-piece material flows from the first-contact portion toward the main press-work portion. As a result, it becomes possible that the material of the work-piece can easily and sufficiently move from the first-contact portion to the main press-work portion during the press working process. It is, therefore, possible to suppress the reduction of the thickness at the main press-work portion of the work-piece during the work-piece is plastically deformed. In other words, it is possible to avoid a situation that the work-piece (the final press working product) has a non-uniform thickness in the area of the main press-work portion.

[0012] According to the press working process, the predetermined first-contact portion of the work-piece is at first held between and pressed by the punch and the die prior to the other portion (the main press-work portion) of the work-piece. Therefore, the residual stress may be generated due to the thickness reduction and remain in the final press working product. However, the predetermined first-contact portion corresponds to a portion, for which high specifications are not always required with respect to at least one of the dimensional accuracy of the press work, the mechanical strength and the durability. Accordingly, even when the residual stress may remain in the predetermined first-contact portion, it may not adversely affect to the final press working product.

[0013] It is a general practice that specifications for the dimensional accuracy of the press work, the mechanical strength and the durability are uniformly applied to a whole area (every portion) of the work-piece.

[0014] Generally, it is not a usual way that the press working product is directly used as a final product by itself alone. In other words, in most of the cases, the press working product is combined with other parts and/or components, which are separately manufactured by different processes. When incorporating the press working product to the other part(s) or the component(s), the press working product is fixed to the other part (s) or the component (s) by various kinds of fixing methods, such as, a bonding, a pressure bonding, a caulking, a bolting, a welding and so on. It is necessary for the press working product to have a certain area or portion, when the press working product is fixed to the other part (s) or the component (s) independently from which fixing method is used. The dimensional accuracy will be then decreased as a whole, when considering a manufacturing method including the press working process and a fixing process. It is, therefore, reasonable in view of a cost-saving that the certain area or portion (a fixing portion) of the press working product (at which the press working product is fixed to the other part) is defined as a specific portion, for which the specifications of the press work (for example, the specifications with respect to the dimensional accuracy) is made lower than that for the other portion of the work-piece than the fixing portion. A priority for the specifications for the mechanical strength or the durability varies depending on an importance of a fixing function of the fixing portion. However, it is also reasonable that different specifications for the mechanical strength or the durability are chosen for the fixing portion, wherein the specifications for the fixing portion are different from the specifications for the other portion of the press working product with respect to the mechanical strength or the durability.

[0015] In some of exceptional cases, a whole body of the press working product is combined to the other part or the other component. For example, when the work-piece is made of a flat plate, an entire flat plate is incorporated to the other part or component, after the press work is done to the flat plate. In other words, a press-worked main portion as well as its neighboring portion of the work-piece is combined with the other part, wherein the neighboring portion functions as a reinforcing portion or a damper portion, for example. Even in such a case, a pressure or a force received at the press-worked main portion is not always the same to that received at the neighboring portion. It is, therefore, not necessary in the above case that the required specifications with respect to the mechanical strength at the neighboring portion is identical to that at the press-worked main portion. The same thing can be applied to the required specifications with respect to the dimensional accuracy for the press work and the durability.

[0016] It is further known in the art that a coiled material is supplied to an automatic press machine in order to manufacture a large amount of the press working products with a low cost and a high speed. In such a case, a portion of the press working product is cut out in a manufacturing step after the press working process, wherein the portion to be cut out corresponds to a cut-out portion which is not necessary in the final press working product. In this case, a part or a whole area of the cut-out portion is chosen as the specific portion, for which the specifications with respect to at least one of the dimensional accuracy of the press work, the mechanical strength and the durability may be made lower than that for the press-worked main portion.

[0017] According to another feature of the present disclosure, a portion of the work-piece is cut out after the press working process. Such a cut-out portion of the work-piece to be cut out is used as the predetermined first-contact portion which is at first brought into contact with the punch, so that the press work is partly or fully done for the predetermined first-contact portion (that is, the cut-out portion). In this case, it is necessary to make an area of the punch and die larger than that for the other case in which the work-piece has no cut-out portion. However, since the required specifications with respect to the dimensional accuracy for the cut-out portion are low and thereby required specifications for the punch and die are correspondingly low, there exists only a small influence on a cost increase for manufacturing the punch and the die.

[0018] In the case of the above press working product having the cut-out portion, it may be further possible to apply different specifications with respect to the dimensional accuracy to a portion of the work-piece other than the main press-work portion and the predetermined first-contact portion.

[0019] The press working product of the present disclosure is a product manufactured by the press working method of the present disclosure. The press working product of the present disclosure is a metal diaphragm having a surface rigidity in a press working direction, which is larger than that of the work-piece to be press worked.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

[0021] FIGS. 1A to 1D are schematic cross sectional views showing a press working mechanism (including a punch and a die) as well as a work-piece for explaining a press working process according to a first embodiment of the present disclosure;

[0022] FIG. 2 is a schematic perspective view showing a metal diaphragm manufactured by the press working process of the present disclosure;

[0023] FIGS. 3A to 3C are schematic cross sectional views according to a second embodiment of the present disclosure, wherein FIG. 3A shows a press worked shape of the work-piece, FIG. 3B shows relevant portions of a press working mechanism and the work-piece, and FIG. 3C shows a schematic cross sectional view showing a final product;

[0024] FIGS. 4A and 4B are schematic cross sectional views showing a press working mechanism and the work-piece for explaining a press working process according to a third embodiment of the present disclosure;

[0025] FIG. 5 is a schematic cross sectional view showing relevant portions of a press working mechanism and the work-piece according to a fourth embodiment of the present disclosure;

[0026] FIG. 6 is a schematic cress sectional view showing relevant portions of a press working mechanism and the work-piece according to a fifth embodiment of the present disclosure;

[0027] FIG. 7 is a schematic cross sectional view showing relevant portions of a press working mechanism and the work-piece according to a sixth embodiment of the present disclosure;

[0028] FIG. 8 is a schematic cross sectional view showing relevant portions of a press working mechanism and the work-piece according to a seventh embodiment of the present disclosure; and

[0029] FIGS. 9A and 9B are schematic cross sectional views showing a press working mechanism and the work-piece for explaining a press working process according to an eighth embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The present disclosure will be explained hereinafter by way of multiple embodiments and/or modifications with reference to the drawings. The same reference numerals are given to the same or similar structures and/or portions throughout the multiple embodiments and/or modifications. In the following embodiments, the present disclosure is applied to a method for manufacturing a metal diaphragm, which is a press forming body (a press working product).

First Embodiment

[0031] A first embodiment of the present disclosure will be explained with reference to FIG. 1 (FIGS. 1A to 1D) and FIG. 2. FIG. 2 schematically shows a structure of a metal diaphragm 1 of the present embodiment. The diaphragm 1 is made of a metal thin plate having a thickness of 25 .mu.m, for example, a stainless thin plate of a disc shape. Multiple concave portions 1a (corrugated portions 1a) are formed in the metal thin plate in a concentric fashion. Each of the corrugated portions 1a is projected in a downward direction and its cross section is formed in an arc shape (a semi-circular shape). An outer periphery of the metal diaphragm 1 is formed as a flanged portion 1b. As explained below, the metal diaphragm 1 is manufactured by a press working method of the present embodiment, which is applied to a work-piece 5 of a flat plate shape.

[0032] The metal diaphragm 1, which is the press forming body, has a surface rigidity in a press working direction (in a direction perpendicular to a surface of the diaphragm). The surface rigidity of the metal diaphragm 1 is higher than that of the work-piece 5 of the flat plate shape before a press working process is carried out to the work-piece 5. Although not shown in the drawings, the metal diaphragm 1 is incorporated into a pressure sensor of a liquid-sealed type, which is mounted in an automotive vehicle for detecting a pressure of exhaust gas emitted from an internal combustion engine. The pressure sensor of the liquid-sealed type has a pressure introducing chamber in a housing thereof, wherein the pressure introducing chamber is divided by the metal diaphragm 1 into a first portion of a pressure introducing side and a second portion of a pressure-sensor chip side. Liquid (oil) is sealed in a space formed by the second portion of the pressure-sensor chip side.

[0033] A method (the press working method) for manufacturing the metal diaphragm 1 will be explained at first with reference to FIGS. 1A to 1D. A press working apparatus to be used in the present embodiment will be explained. Although not showing an entire structure of the press working apparatus, the press working apparatus has a frame, a bed fixed to a lower portion of the frame, a ram movably supported by the frame so that the ram is movable in a vertical direction (in a direction perpendicular to the bed), a driving portion for driving the ram and so on. A die 2 is attached to the bed on its upper-side surface. A punch 3 is attached to a lower side of the ram. A press working mechanism 4 is formed by the die 2, the punch 3 and so on.

[0034] In the present embodiment, each of the die 2 and the punch 3 is made of a rigid body (for example, a tool steel, ceramics, or the like). The die 2 has a shape corresponding to a lower-side shape of the press forming body (the metal diaphragm 1). More exactly, multiple recessed portions 2A and 2B (2B1, 2B2), which are opened in an upward direction, are formed on an upper-side surface of the die 2. On the other hand, the punch 3 has a shape corresponding to an upper-side shape of the press forming body (the metal diaphragm 1). In other words, multiple projected portions 3A and 3B (3B1, 3B2), which are projected in a downward direction, are formed on a lower-side surface of the punch 3. When the press working process is carried out, the work-piece 5, which is made of metal material of a flat thin plate, is set on the upper-side surface of the die 2. In other words, the work-piece 5 is located at such a position that the work-piece 5 is held by and between the die 2 and the punch 3 in the vertical direction (in the direction perpendicular to the die 2).

[0035] In the present embodiment, as shown in FIG. 1A, a high dimensional accuracy for a press work is required at a main press-work portion 5A (a center portion 5A) of the work-piece 5 (the metal diaphragm 1).

[0036] An outer peripheral portion 5B of the work-piece 5, which has an annular shape and surrounding the center portion 5A, corresponds to a portion requiring a lower dimensional accuracy for the press work than that for the center portion 5A (the main press-work portion 5A). In FIGS. 1A to 1D, each showing the cross sectional view of the work-piece 5, the outer peripheral portion 5B is indicated by a left-hand portion 5B1 and a right-hand portion 5B2, each of which is outwardly separated from the center portion 5A in a radial direction. The outer peripheral portion 5B is also referred to as an outside portion 5B (5B1, 5B2).

[0037] In the present embodiment, as explained below, in an initial stage of the press working process (a first step), the punch 3 and the die 2 hold the outside portion 5B of the work-piece 5 prior to a remaining portion of the work-piece 5, that is, the center portion 5A of the work-piece 5 (the main press-work portion 5A). In other words, an outside projected portion 3B (3B1, 3B2) of the punch 3 is at first brought into contact with the outside portion 5B of the work-piece 5 prior to the center portion 5A, before a center projected portion 3A of the punch 3 is brought into contact with the center portion 5A of the work-piece 5. In the present disclosure, the outside portion 5B of the work-piece 5 is also referred to as a predetermined first-contact portion.

[0038] The press working method of the present embodiment, in which the above press working mechanism 4 of the press working apparatus is used, will be explained. Each of FIGS. 1A to 1D shows a condition of the work-piece 5, which is deformed in accordance with the press working process of the press working mechanism 4.

[0039] As shown in FIG. 1A, the work-piece 5 of the flat thin plate is set on the upper-side surface of the die 2 in an opened condition of the molds in which the punch 3 is lifted up from the die 2.

[0040] When the press working process is started, as shown in FIGS. 1B to 10, the punch 3 is successively pushed down so as to apply a press working pressure "P" in the downward direction to the work-piece 5, which is held between the punch 3 and the die 2. A press work (a deep drawing process) is carried out by applying a press working force to the work-piece 5 in a compression direction and/or in a tensile direction so that a plastic deformation is generated in the work-piece 5. In the press working process, the multiple portions 5A and 5B (5B1, 5B2) of the work-piece 5 are pushed into the respective recessed portions 2A and 2B (2B1, 2B2) of the die 2 by each of the projected portions 3A and 3B (3B1, 3B2) of the punch 3. A thickness of the work-piece 5 is reduced, when the work-piece 5 is extended along a concavo-convex shape of the die 2 and the punch 3. Accordingly, the work-piece 5 is deformed so as to have a predetermined shape and a shape of the metal diaphragm 1 is finally obtained, as shown in FIG. 1D.

[0041] In the initial stage of the press working process (the first step), as shown in FIG. 15, the outside projected portion 3B (3B1, 3B2) of the punch 3 is at first brought into contact with the outside portion 5B (5B1, 5B2) of the work-piece 5 (the predetermined first-contact portion 5B), before the center projected portion 3A of the punch 3 is brought into contact with the center portion 5A of the work-piece 5 (the main press-work portion 5A).

[0042] As shown in FIG. 1C (in the first step), the outside portion 5B (5B1, 5B2) of the work-piece 5 is press worked (the deep drawing process) prior to the center portion 5A, so that the thickness of the work-piece 5 is reduced at the outside portion 5B (5B1, 5B2) and material of the work-piece 5 is moved toward a surrounding portion(s) of the outside portion 5B (5B1, 5B2), for example, to the center portion 5A.

[0043] As shown in FIG. 1D, in an ending stage of the press working process (a second step), the press work (the deep drawing process) is further done for the center portion 5A as well as the outside portion 5B of the work-piece 5. In this stage, the material of the work-piece 5 has been already moved to the center portion 5A from its neighboring portion (from the outside portion 5B). Therefore, when the press work is carried out for the center portion 5A, a thickness reduction at the center portion 5A is suppressed. As a result, it is possible to prevent the thickness of the work-piece 5 (the metal diaphragm 1) including an area of the center portion 5A from being non-uniformly deformed.

[0044] According to the present embodiment, the punch 3 and die 2 hold the outside portion 5B of the work-piece 5 (the predetermined first-contact portion 5B) prior to the other portion of the work-piece 5 (the center portion 5A) in the initial stage of the press working process (the first step).

[0045] In the first step, the press work is partly (or fully, as the case may be) done for the outside portion 5B, so that the material is moved from the outside portion 5B to the center portion 5A. Thereafter, in the second step, the press work is further carried out for the center portion 5A and the outside portion 5B, of the work-piece 5.

[0046] Therefore, it is possible to avoid a situation that the work-piece 5 has non-uniform thickness in the area of the work-piece 5 including the center portion 5A. In other words, it is possible to prevent, the durability characteristic from becoming worse due to the residual stress in the work-piece 5.

[0047] Specifications related to the dimensional accuracy required for the press work at the outside portion 5B of the work-piece 5 is not necessarily as high as that for the center portion 5A. Therefore, the non-uniform thickness of the outside portion 5B (the predetermined first-contact portion 5B) of the work-piece 5 has no adverse influence on the final product, that is, the metal diaphragm 1.

[0048] In the present embodiment, the outside portion 5B of the work-piece 5, for which the required specifications related to the dimensional accuracy are not always as high as that for the center portion 5A of the work-piece 5, is selected as the predetermined first-contact portion. However, any portion(s) of the work-piece 5, for which the required specifications related to at least one of the dimensional accuracy, strength and durability are lower than that for the center portion 5A of the work-piece 5, may be selected as the predetermined first-contact portion.

[0049] As above, the press working process of the present embodiment includes the first step equal to the initial stage of the press working process and the second step equal to the ending stage of the press working process. The press working process is applied to the press working product which has a center recessed portion to be formed at the center portion 5A (the main press-work portion 5A) and an annular recessed portion to be formed at the outside portion 5B (the predetermined first-contact portion 5B), wherein the annular recessed portion surrounds the center recessed portion so that the center recessed portion and the annular recessed portion are formed in the concentric fashion.

[0050] In the first step, the outside projected portion 3B of the punch 3 is at first brought into contact with the outside portion 5B of the work-piece 5 in order to carry out the press work (for example, the deep drawing process) and to partly or fully deform the outside portion 5B. The material of the work-piece 5 is, therefore, moved from the outside portion 5B toward the center portion 5A during the press work (the deep drawing process) of the first step.

[0051] In the second step, the center projected portion 3A of the punch 3 is brought into contact with the center portion 5A of the work-piece 5, so that the press work (the deep drawing process) is further applied to both of the center portion 5A and the outside portion 5B of the work-piece 5. As a result of the second step, the center recessed portion and the annular recessed portion are respectively formed at the positions corresponding to the center portion 5A and the outside portion 5B of the work-piece 5.

[0052] According to the above press working process, it is possible to obtain the press working product (the metal diaphragm 1) having the uniform thickness at the area corresponding to the center portion 5A of the work-piece 5.

Second Embodiment

[0053] FIGS. 3A to 3C show a second embodiment of the present disclosure. The second embodiment differs from the first embodiment in that an outside portion 6B of a work-piece 6 is formed as a cut-out portion 6B (6B1, 6B2), which is cut out in a manufacturing step after the press working process.

[0054] As shown in FIG. 3A, a center portion 6A of the work-piece 6 corresponds to a main press-work portion, for which the high dimensional accuracy (that is, the high shape accuracy) of the press work is required. The outside portion 6B (a left-hand side portion 6B1 and a right-hand side portion 6B2 in the drawing) surrounding the center portion 6A corresponds to a predetermined first-contact portion, for which the high dimensional accuracy of the press work is not required, because the outside portion 6B of the work-piece 6 corresponds to the cut-out portion 6B (6B1, 6B2). In the drawing of FIG. 3A or 3B, which is a cross sectional view, two cut-out portions 6B1 and 6B2 are indicated. However, since the outside portion 6B is formed in an annular recessed shape in the embodiment, there exists one annular cut-out portion 6B including the portions 6B1 and 6B2.

[0055] In the present embodiment, the press work (the deep drawing process) is carried out to the work-piece 6 by the press working mechanism, in order that the work-piece 6 is deformed so as to have a predetermined shape. Then, the work-piece 6 is transferred to a cut-out press machine for punching out the cut-out portion 6B (6B1, 6B2). As shown in FIG. 3B, the cut-out press machine has a punching die 7 and a cut-out punch 8. The cut-out press machine punches out the cut-out portion 6B (6B1, 6B2) at a boundary portion between the center portion 6A and the cut-out portion 6B. According to the above process, as shown in FIG. 3C, the center portion 6A of the work-piece 6 is punched and a final product 9 is finished, wherein the cut-out portion 6B is finally cut out from the work-piece 6.

[0056] According to the present embodiment, since the work-piece 6 is deformed by the press work by use of the punch 3 and the die 2 in the same manner to the first embodiment, it is possible to prevent the durability characteristic from becoming worse due to the residual stress in the work-piece 6. In addition, in the present embodiment, since the outside portion 6B (the predetermined first-contact portion) is chosen as the cut-out portion 6B, which is cut out after the press working process, the final product. 9 can be used as the metal diaphragm 1 without causing any problems.

Third Embodiment

[0057] FIGS. 4A and 4B show a third embodiment of the present disclosure. In the present embodiment, either one of a punch 12 and the die 2 of a press working mechanism 11 is made of an elastic body. More exactly, the punch 12 is made of the elastic body in the present embodiment. In other words, the punch 12 is made of a material for a hyper-elastic body, for example, rubber, urethane or the like, which has Poisson ratio close to 0.5 so that the material has incompressibility and restoring property. The die 2 is made of the rigid body (for example, the tool steel).

[0058] According to the above structure, as shown in FIG. 4A, an outside projected portion 12B (12B1, 12B2) of the punch 12 is at first brought into contact with the outside portion 5B (5B1, 5B2) of the work-piece 5 in the initial stage of the press working process in a condition that a center projected portion 12A of the punch 12 is not yet in contact with the center portion 5A of the work-piece 5. The outside projected portion 12B (12B1, 12B2) pushes the outside portion 5B (5B1, 5B2) of the work-piece 5 to the die 2, while the outside projected portion 12B (12B1, 12B2) is elastically deformed, for example, elastically expanded in a lateral direction. As a result, a squeezing effect can be increased at the outside portion 5B (the predetermined first-contact portion 5B). Therefore, in the same manner to the first embodiment, the outside portion 5B is partly deformed in the initial stage of the press working process (the first step).

[0059] As shown in FIG. 4B, in the ending stage of the press working process (the second step), the press work is further done for the center portion 5A of the work-piece 5 in addition to the outside portion 5B. In this stage, the material of the work-piece 5 has been already moved to the center portion 5A from its neighboring portion. Therefore, the press work is carried out for the center portion 5A in such a manner that the thickness reduction at the center portion 5A is suppressed. As a result, it is possible to prevent the thickness of the work-piece 5 (the metal diaphragm 1) including the area of the center portion 5A from becoming non-uniform. In other words, the press work can be done for the center portion 5A of the work-piece 5, wherein the center portion 5A has a higher dimensional accuracy, strength and durability.

[0060] According to the present embodiment, the punch 12 is made of the hyper-elastic body. However, a similar advantage can be obtained when the punch 12 is made of a commonly-used elastic body, for example, a rubber mold. Alternatively, the same function and the same effect can be also obtained, when the punch 12 is made of the rigid body and the die 2 is made of the elastic body or the hyper-elastic body.

Fourth & Fifth Embodiments

[0061] Each of FIG. 5 and FIG. 6 shows a fourth embodiment and a fifth embodiment of the present disclosure. In the same manner to the third embodiment, a punch 15/19 is made of a hyper-elastic body (or an elastic body), while a die 16 is made of a rigid body (a tool steel) in the fourth and the fifth embodiments. In a press working mechanism 14 or 18 of the fourth or the fifth embodiment, a portion 15B/19B of the punch 15 (FIG. 5) or the punch 19 (FIG. 6), which is at first brought into contact with a predetermined first contact portion of the work-piece 5 (the outside portion 5B), is projected in the downward direction toward the work-piece 5. In other words, a projection amount of an outside projected portion 15B (15B1, 15B2) in FIG. 5 or a projection amount of an outside projected portion. 19B (19B1, 19B2) in FIG. 6 is larger than that of any other portions (for example, a center projected portion 15A/19A) of the punch 15 in FIG. 5 or the punch 19 in FIG. 6.

[0062] More exactly, FIG. 5 shows the fourth embodiment. In the fourth embodiment, the press working mechanism 14 has the punch 15 made of the hyper-elastic body (or the elastic body) and the die 16 made of the rigid body. A recessed portion 16A is formed in the die 16 at a position opposing to the center portion 5A of the work-piece 5, so that a shape of an upper-side surface of the die 16 corresponds to a shape of a final press forming product. The center projected portion 15A is formed in the punch 15 at a position opposing to the recessed portion 16A of the die 16, so that a shape of a lower-side surface of the punch 15 corresponds to the shape of the final press forming product.

[0063] The outside projected portion 15B (15B1, 15B2) is formed in the punch 15 at such a position, at which the outside projected portion 15B (15B1, 15B2) is at first brought into contact with the predetermined first-contact portion (the outside portion 5B (5B1, 5B2) of the work-piece 5. The outside projected portion 15B (15B1, 15B2) is projected in the downward direction to the work-piece 5, in such a manner that the projection amount of the outside projected portion 15B (15B1, 15B2) is larger than that of any other portions of the punch 15 (for example, the center projected portion 15A).

[0064] According to the present embodiment, the outside projected portion 15B of the punch 15 is at first brought into contact with the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B) prior to the center projected portion 15A of the punch 15. In other words, the punch 15 and the die 16 hold the outside portion 5B of the work-piece 5 prior to the main press-work portion 5A of the work-piece 5 (the center portion 5A).

[0065] In the initial stage of the press working process, the work-piece 5 is pressed by the outside projected portion 15B of the punch 15 so that the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B) is partly (or fully) deformed and flattened out. In the ending stage of the press working process, during which the material of the work-piece 5 further flows to an area of the center portion 5A from a neighboring portion of the center portion 5A, the press work is done for the center portion 5A and the outside portion 5B of the work-piece 5, wherein a reduction of the thickness at the center portion 5A is suppressed.

[0066] In the present embodiment, according to which the work-piece 5 is deformed by the press work by use of the punch 15 and the die 16, it is possible to avoid the situation that the area of the work-piece 5 including the center portion 5A has non-uniform thickness. It is, therefore, possible to prevent the durability characteristic from becoming worse due to the residual stress in the work-piece 5.

[0067] In addition, in the present embodiment, it is possible to form the outside projected portion 15B at any position of the punch 15, independently from a press forming shape of the work-piece 5 (the shape of the final product). In other words, it is possible to easily form the outside projected portion 15B at such a position opposing to the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B). As a result, a manufacturing cost for the molds (the punch 15 and/or the die 16) can be reduced.

[0068] FIG. 6 shows the fifth embodiment in the fifth embodiment, the press working mechanism 18 has the punch 19 made of the hyper-elastic body (or the elastic body) and the die 16 made of the in rigid body.

[0069] In the same manner to the fourth embodiment, the recessed portion 16A is formed in the die 16 at the position opposing to the center portion 5A of the work-piece 5. The center projected portion 19A is formed in the punch 19 at a position opposing to the recessed portion 16A of the die 16, so that a shape of the center projected portion 19A corresponds to a shape of the recessed portion 16A.

[0070] The outside projected portion 19B (19B1, 19B2) is formed in the punch 19 at such a position, at which the outside projected portion. 19B (19B1, 19B2) is at first brought into contact with the predetermined first-contact portion 5B (the outside portion 5B) of the work-piece 5. More exactly, in the present embodiment, the outside projected portion 19B (19B1, 19B2) is formed with a tapered surface, which comes closer to the die 16 (that is, the upper-side surface of the work-piece 5) in a radial-outward direction. A radial-outward end portion of the tapered surface 19B (19B1, 19B2) has a projection amount in the downward direction to the die 16 (to the work-piece 5), which is larger than that of any other portions of the punch 19 (for example, a center projected portion 19A).

[0071] According to the present embodiment, in the initial stage of the press working process, the outside projected portion 19B of the punch. 19 (that is, the tapered surface) is at first brought into contact with the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B) prior to the other portions of the punch 19, such as the center projected portion 19A. More exactly, the tapered surface 19B is successively brought into contact with the work-piece 5 from its radial-outward end in a radial-inward direction. Accordingly, the punch 19 and the die 16 hold the outside portion 5B of the work-piece 5 prior to the other portion of the work-piece 5 (the center portion 5A).

[0072] In the same manner to the fourth embodiment, in the initial stage of the press working process, the work-piece 5 is pressed by the outside projected portion 19B (the tapered surface 19B) of the punch 19 so that the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B) is deformed and flattened out. In the ending stage of the press working process, during which the material of the work-piece 5 also flows to the area of the center portion 5A from the neighboring portion of the center portion 5A, the press work is done for the center portion 5A of the work-piece 5, wherein the reduction of the thickness at the center portion 5A is suppressed.

[0073] In the present embodiment, according to which the work-piece 5 is deformed by the press work by use of the punch 19 and the die 16, it is also possible to avoid the situation that the area of the work-piece 5 including the center portion 5A has non-uniform thickness. It is, therefore, possible to prevent the durability characteristic from becoming worse due to the residual stress in the work-piece 5. In addition, in the present embodiment, the above advantages can be obtained by simply forming the tapered surface 19B in the punch 19 made of the hyper-elastic body. As a result, a manufacturing cost for the molds (the punch 19 and/or the die 16) can be likewise reduced.

Sixth & Seventh Embodiments

[0074] Each of FIG. 7 and FIG. 8 shows a sixth embodiment and a seventh embodiment of the present disclosure. In the sixth and the seventh embodiments, a punch 22 is made of the hyper-elastic body (or the elastic body) and a die 23/26 is made of the rigid body (the tool steel or the like).

[0075] In the sixth and the seventh embodiments, a convex portion 23B/26B is formed in the die 23/26 at a portion or an entire portion of an outside area, which is at first brought into contact with the predetermined first-contact portion. 5B of the work-piece 5 (the outer portion 5B). In the initial stage of the press working process, the convex portion 23B/26B is brought into contact with the predetermined first-contact portion 5B of the work-piece 5 prior to any other portion (for example, the center portion 5A). More exactly, the punch 22 and the die 23/26 (the convex portion of the die) hold the predetermined first-contact portion 5B of the work-piece 5 prior to the center portion 5A of the work-piece 5, when starting the press working process.

[0076] More exactly, FIG. 7 shows the sixth embodiment in the sixth embodiment, a press working mechanism 21 has the punch 22 made of the hyper-elastic body (or the elastic body) and the die 23 made of the rigid body. A lower-side surface of the punch 22 is formed with a flat surface. A recessed portion 23A, which corresponds to a shape of the final product, is formed in the die 23 at a position opposing to the center portion 5A of the work-piece 5. The convex portion 23B (23B1, 23B2) having a step shape is formed in the die 23 at a position, at which the die 23 is at first brought into contact with the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B). The convex portion 23B is upwardly projected toward the work-piece 5 more than any other portion of the die 23 (for example, the recessed portion 23A formed at the position opposing to the center portion 5A of the work-piece 5).

[0077] According to the above structure, in the initial stage of the press working process (the first step), the convex portion 23B of the die 23 is at first brought into contact with the predetermined first-contact portion 5B (the outside portion 5B of the work-piece 5), so that the die 23 and the punch 22 hold the outside portion 5B prior to the center portion 5A of the work-piece 5. In the initial stage of the press working process, the punch 22 is deformed so as to apply the press working force to the outside portion 5B of the work-piece 5, so that a part of the material flows from the outside portion 5B to the center portion 5A of the work-piece 5. In the ending stage of the press working process (the second step), during which the material of the work-piece 5 further flows to the area of the center portion 5A from the neighboring area of the center portion 5, the press work is done for the center portion 5A of the work-piece 5, so that the reduction of the thickness at the center portion 5A is suppressed.

[0078] In the present embodiment, according to which the work-piece 5 is deformed by the press work by use of the punch 22 and the die 23, it is possible to avoid the situation that the area of the work-piece 5 including the center portion 5A has non-uniform thickness. It is, therefore, possible to prevent the durability characteristics from becoming worse due to the residual stress in the work-piece 5.

[0079] In addition, in the present embodiment, it is possible to form the convex portion 23B at any position of the die 23 independently from the press forming shape of the work-piece 5 (that is, the shape of the final product). In other words, it is possible to easily form the convex portion 23B at such a position corresponding to the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B). Furthermore, since the shape of the punch 22 has a simple shape having no concave and/or convex, it is possible to further reduce the cost for manufacturing the mold for the punch 22.

[0080] Furthermore, FIG. 8 shows the seventh embodiment. In the seventh embodiment, a press working mechanism 25 has the punch 22 made of the hyper-elastic body (or the elastic body) and the die 26 made of the rigid body. A recessed portion 26A is formed at an upper-side surface of the die 26 at a position opposing to the center portion 5A of the work-piece 5, wherein the recessed portion 26A corresponds to the shape of the final product. The convex portion 26B (26B1, 26B2) having a tapered surface is further formed on the upper-side surface of the die 26 at a position, at which the die 26 is at first brought into contact with the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B). The tapered surface 26B is upwardly inclined toward the work-piece 5 in the radial-outward direction. In other words, the tapered surface 26B comes closer to the work-piece 5 in the radial-outward direction.

[0081] According to the above structure, in the initial stage of the press working process (the first step), the tapered surface 26B of the die 26 is at first brought into contact with the predetermined first-contact portion 5B of the work-piece 5 (the outside portion 5B), so that the die 26 and the punch 22 hold the outside portion 5B prior to the other portion of the work-piece 5 (the center portion 5A). In the press working process, the punch. 22 is deformed so as to apply the press working force to the outside portion 5B of the work-piece 5, so that a part of the material flows from the outside portion 5B to the center portion 5A of the work-piece 5. In the ending stage of the press working process (the second step), during which the material of the work-piece 5 further flows to the area of the center portion 5A from the neighboring area of the center portion 5A, the press work is done for the center portion 5A of the work-piece 5, so that the reduction of the thickness at the center portion 5A is suppressed.

[0082] In the present embodiment, according to which the work-piece 5 is deformed by the press work by use of the punch 22 and the die 26, it is possible to avoid the situation that the area of the work-piece 5 including the center portion 5A has non-uniform thickness. It is, therefore, possible to prevent the durability characteristics from becoming worse due to the residual stress in the work-piece 5. In addition, in the present embodiment, since it is possible to easily form the tapered surface 26B on the upper-side surface of the die 26 and the punch 22 has the simple shape having no concave and/or convex, it is possible to further reduce the cost for manufacturing the molds for the punch 22 and the die 26.

[0083] In the above fourth to the seventh embodiments, the punch is made of the hyper-elastic body (or the elastic body), while the die is made of the rigid body. However, the punch may be made of the rigid body, while the die may be made of the hyper-elastic body (or the elastic body). In such a case, the position of the projected portion, the convex portion or the tapered surface is also reversed from that of the fourth to the seventh embodiments.

[0084] In addition, in the above fourth to the seventh embodiment the press work is done by one cycle of the press working process for obtaining the final product (the press forming product). However, a multi-stage press work (that is, a progressive press work) is actually done by multiple, press working processes in order to obtain a complex shape.

[0085] Generally, in the case that the punch or the die is made of the elastic body (in particular, the hyper-elastic body), an amount of the expansion deformation is larger than that of the compression deformation. Therefore, the projected portion or the convex portion may be preferably formed in the punch or the die, which is made of the rigid body, so that the press work can be effectively done.

[0086] Therefore, when the multi-platen press work is done, it is preferable that a portion (the projected portion, the convex portion or the like) of the rigid body is at first brought into contact with the predetermined first-contact portion of the work-piece. Therefore, the punch and/or the die may be changed as the case may be. Alternatively, a surface direction of the work-piece may be changed upside-down.

Eighth Embodiment

[0087] FIGS. 9A and 9B show an eighth embodiment of the present disclosure. In the eighth embodiment, a press working mechanism 28 has a punch 29 made of the hyper-elastic body (or the elastic body) and a die 30 mace of the rigid body (the tool steel or the like).

[0088] Multiple recessed portions 30A and 30B (30B1, 30B2) are formed in the die 30, wherein each of the recessed portions 30A and 30B (30B1, 30B2) corresponds to a shape of a lower side of a press forming product. Multiple projected portions 29A and 29B (29B1, 29B2) are formed in the punch 29, wherein each of the projected portions 29A and 29B (29B1, 29B2) corresponds to a shape of an upper side of the press forming product. The work-piece 5 has the center portion 5A, for which high dimensional accuracy of the press work is required, and the predetermined first-contact portion 5B (the outside portion 5B), which is located at the outside of the center portion 5A.

[0089] As shown in FIG. 9A, a thickness size "u" in a press working direction of the punch 29 made of the elastic body is made larger than a deformation size of the work-piece 5, which is press worked in the press working direction. More exactly, each of the projected portions 29A, 29B (29B1, 29B2) of the punch 29 has a height "a", a height ".beta.1" and a height ".beta.2" in its height direction (in the press working direction). The thickness size ".mu." of the punch 29 (a main body of the punch 29 made of the elastic body) is larger than the deformation size of the work-piece 5. For example, the thickness size ".mu." is larger than any one of the heights ".alpha., .beta.1, .beta.2" of the projected portions.

[0090] As shown in FIG. 9B, the press work is done while the punch 29 is elastically deformed. Since the thickness size ".mu." is made to be sufficiently large, the deformation amount can be correspondingly and sufficiently increased.

[0091] According to the above structure, the punch 29 can be easily and elastically deformed along a shape of the die 30. It can increase the effect for suppressing the situation that the work-piece 5 (in particular, the area including the center portion 5A) has non-uniform thickness. In other words, a press load necessary for obtaining the desired deformation can be decreased. As a result, it is possible to reduce wear amount of the die 30 and/or the punch 29, to elongate a life duration of the press working mechanism 28, and to make the press working mechanism 28 smaller.

Further Embodiments and/or Modifications

[0092] Some further embodiments of the present disclosure will be further explained, although not shown in the drawings.

[0093] In recent years, technologies for a so-called hydraulic press method have been developed in addition to the conventional press working process using the metal molds. In the hydraulic press method, a compression, an extrusion, a forging or a cutting process can be carried out by use of hydraulic pressure of water, oil or the like.

[0094] In the third to the eighth embodiments of the present disclosure, either one of the punch and the die, which is made of the elastic body may be replaced by liquid including water, oil or the like. In other words, the liquid (including the water, the oil or the like) is used as the elastic body for the punch or the die, and the press working force is applied by the hydraulic pressure to the press forming surface of the work-piece.

[0095] The liquid is in-compressible. It is possible to uniformly apply the pressure to the press forming surface of the work-piece when the liquid is continuously supplied. This hydraulic press method can be regarded as an equivalent to the press working process, in which the punch (or the die) made of the hyper-elastic body having Poisson ratio 0.5 is pressed to the work-piece.

[0096] In addition, when the supply of the liquid is stopped, the hydraulic pressure disappears. This means that the stop of the liquid supply has an effect equivalent to that of the elastic body, which is moved back to its initial condition according to its restoring characteristics. In a case of the hydraulic press method, it is not possible to generate a negative pressure. This is a point of the hydraulic press method different from the elastic body (the hyper-elastic body).

[0097] As above, when the press working process is carried out by the liquid pressure, the liquid plays a role of either the punch or the die for applying the press working force to the work-piece. A part of the punch or the die, which is made of the rigid body and which is at first brought into contact with the predetermined first-contact portion of the work-piece in order to receive the press working, force, is formed in a projected or convexed shape. The portion of the punch or the die (whichever is made of the rigid body) of the projected or convexed shape is at first brought into contact with the predetermined first-contact portion of the work-piece and then a remaining portion of the punch or the die is brought into contact with a remaining portion of the work-piece. In other words, the punch or the die, which is made of the elastic body (in this case, the liquid), and the punch or the die, which is made of the rigid body, hold the predetermined first-contact portion of the work-piece prior to the other portion of the work-piece in the first stage of the press working process, so that the predetermined first-contact portion of the work-piece is at first deformed by the press working force applied by the liquid pressure. According to the above structure, the same advantages to those of the above first to the eighth embodiments can be also obtained in such a modified embodiment.

[0098] In the above embodiments, the metal thin plate is used as the work-piece. When the press working method of the present disclosure is applied to a high-volume manufacturing equipment, a band-like metal material wound in a roll shape may be used as the work-piece, wherein the band-like metal material is supplied by a transport mechanism to a press working mechanism in a continuous manner. In this case, for example, a pawl portion is formed at a periphery of the band-like metal material, so that the metal material is transferred by the transport mechanism. Since such a pawl portion is not necessary for the final product, the pawl portion is cut out after the press working process. Therefore, the pawl portion which is formed in the metal material and used for transferring the metal material can be used as a portion, for which high specifications are not required with respect to at least one of the dimensional accuracy of the press work, the mechanical strength and the durability characteristics. Therefore, the pawl portion of the metal material can be used as the predetermined first-contact portion of the work-piece.

[0099] The metal diaphragm 1 of the present disclosure may be applied not only to the pressure sensor of the above embodiments but also to any other products (or a part and/or component of the product), such as, a pressure measuring device, an air-tightness holding device (which is called as a sealing device), a hermetic seal device, a metallic part including a heat radiating part, a product including a part of spring material, and so on. Not only the metal material but also any other material, such as natural resin, synthetic resin (including carbonaceous resin), fiber material, paper material, wood and so on may be used as the press working product.

[0100] In addition, the shape of the press forming product (the metal diaphragm 1) is not limited to the shape of the above embodiments. Furthermore, any kinds of materials may be used for the punch and/or the die. The present disclosure is not limited to the above embodiments but can be further modified in various manners without departing from a spirit of the present disclosure.

Claims

1. In a press working apparatus, which comprises; a press working mechanism having a punch and a die, which are arranged at positions to be opposed to each other in order to hold a work-piece between the punch and the die and to apply a press working force to the work-piece so that the work-piece is deformed in a desired shape, a press working method comprising; a step for holding a predetermined first-contact portion of the work-piece prior to a main press-work portion of the work-piece in an initial stage of a press working process, wherein at least one of specifications with respect to a dimensional accuracy of a press work, a mechanical strength and durability, which are required for the predetermined first-contact portion is made to be lower than that required for the main press-work portion of the work-piece.

2. The press working method according to claim 1, wherein the predetermined first-contact portion of the work-piece corresponds to a cut-out portion, which is cut out after the press working process.

3. The press working method according to claim 1, wherein one of the punch and the die is made of an elastic body, while the other of the punch and the die is made of a rigid body.

4. The press working method according to claim 3, wherein the elastic body, of which one of the punch and the die is made, is composed of a hyper-elastic body having an incompressibility and a restoring characteristic, and the hyper-elastic body includes rubber and urethane.

5. The press working method according to claim 3, wherein a portion of the punch or the die, which is at first brought into contact with the predetermined first-contact portion of the work-piece, is more projected or convexed toward the work-piece than a remaining portion of the punch or the die.

6. The press working method according to claim 3, wherein a portion of the punch or the die, which is made of the rigid body, is projected or convexed toward the work-piece, and such a projected or convexed portion is brought into contact with the predetermined first-contact portion of the work-piece prior to the main press-work portion of the work-piece, so that the punch and the die hold the predetermined first-contact portion prior to the main press-work portion of the work-piece in the press working process.

7. The press working method according to claim 3, wherein the punch or the die, which is made of the elastic body, has a thickness in a press working direction, and the thickness of the elastic body is larger than a deformation size of the work-piece during the press working process.

8. The press working method according to claim 3, wherein one of the punch and the die is made of the elastic body, which is composed of liquid including water and oil, and a liquid pressure of the liquid is applied to the work-piece as the press working force.

9. The press working method according to claim 8, wherein one of the punch and the die is made of the elastic body, which is composed or the liquid and applies the press working force to the work-piece, the other of the punch and the die is made of the rigid body for receiving the press working force together with the work-piece, a portion of the rigid body is projected or convexed toward the work-piece, and such a projected or convexed portion is brought into contact with the predetermined first-contact portion of the work-piece prior to the main press-work portion of the work-piece, so that the punch and the die hold the predetermined first-contact portion prior to the main press-work portion of the work-piece in the press working process.

10. The press working method according to claim 1, wherein the work-piece is made of a flat-plate type thin metal material or a band-like thin metal material.

11. The press working method according to claim 10, wherein the work-piece is made of the band-like thin metal material wound in a roll shape, and the band-like thin metal material is continuously transferred by a transport mechanism to the press working mechanism.

12. A press working apparatus comprising; a press working mechanism having a punch and a die, which are arranged at positions to be opposed to each other in order to hold a work-piece between the punch and the die and to apply a press working force to the work-piece so that the work-piece is deformed in a desired shape, wherein the punch and the die holds a predetermined first-contact portion of the work-piece prior to a main press-work portion of the work-piece, in an initial stage of a press working process, wherein at least one of specifications with respect to a dimensional accuracy of a press work, a mechanical strength and durability, which are required for the predetermined first-contact portion is made to be lower than that required for the main press-work portion of the work-piece.

13. The press working apparatus according to claim 12, wherein the predetermined first-contact portion of the work-piece corresponds to a cut-out portion, which is cut out after the press working process.

14. The press working apparatus according to claim 12, wherein one of the punch and the die is made of an elastic body, while the other of the punch and the die is made of a rigid body.

15. The press working apparatus according to claim 14, wherein the elastic body, of which one of the punch and the die is made, is composed of a hyper-elastic body having an incompressibility and a restoring characteristic, and the hyper-elastic body includes rubber and urethane.

16. The press working apparatus according to claim 14, wherein a portion of the punch or the die, which is at first brought into contact with the predetermined first-contact portion of the work-piece, is more projected or convexed toward the work-piece than a remaining portion of the punch or the die.

17. The press working apparatus according to claim 14, wherein a portion of the punch or the die, which is made of the rigid body, is projected or convexed toward the work-piece, and such a projected or convexed portion is brought into contact with the predetermined first-contact portion of the work-piece prior to the main press-work portion of the work-piece, so that the punch and the die hold the predetermined first-contact portion prior to the main press-work portion of the work-piece in the press working process.

18. The press working apparatus according to claim 14, wherein the punch or the die, which is made of the elastic body, has a thickness in a press working direction, and the thickness of the elastic body is larger than a deformation size of the work-piece during the press working process.

19. The press working apparatus according to claim 14, wherein one of the punch and the die is made of the elastic body, which is composed of liquid including water and oil, and a liquid pressure of the liquid is applied to the work-piece as the press working force.

20. The press working apparatus according to claim 19, wherein one of the punch and the die is made of the elastic body, which is composed of the liquid and applies the press working force to the work-piece, the other of the punch and the die is made of the rigid body for receiving the press working force together with the work-piece, a portion of the rigid body is projected or convexed toward the work-piece, and such a projected or convexed portion is brought into contact with the predetermined first-contact portion of the work-piece prior to the main press-work portion of the work-piece, so that the punch and the die hold the predetermined first-contact portion prior to the main press-work portion of the work-piece in the press working process.

21. The press working apparatus according to claim 12, wherein the work-piece is made of a flat-plate type thin metal material or a band-like thin metal material.

22. The press working apparatus according to claim 21, wherein the work-piece is made of the band-like thin metal material wound in a roll shape, and the band-like thin metal material is continuously transferred by a transport mechanism to the press working mechanism.

23. A press working product comprises; a product manufactured by the press working method according to claim 1.

24. The press working product according to claim 23, wherein the press working product is a metal diaphragm, a surface rigidity of the metal diaphragm after the press working process is higher than that of the work-piece before the press working process in the press working direction.

25. The press working product according to claim 24, wherein the metal diaphragm is applied to one of the following products; a pressure sensor; a pressure measuring device; an air-tightness holding device including a sealing part; a hermetic seal; a metal part including a heat radiating part; and a product including a part of spring material.

26. The press working product according to claim 23, wherein the press working product is made of one of the following materials; a metal material; a natural resin; a synthetic resin including carbonaceous resin; a fiber material; a paper material: and a wood.

27. In a press working product, the press working product comprises a metal diaphragm made of a thin plate material and having a center recessed portion and an outside recessed portion of an annular shape, wherein the outside recessed portion surrounds the center recessed portion so as to be concentric with the center recessed portion, and the press working product is manufactured by a press working mechanism, which comprises a punch and a die so arranged as to be opposed to each other in a vertical direction, wherein the punch is movable with respect to the die in order to carry out a press work to a work-piece which is set between the punch and the die, and wherein the punch has a center projected portion and an outside projected portion each of which is projected in a direction to the die, a press working process comprising; a first step for moving down the punch of the press working mechanism to the die in order that the outside projected portion is at first brought into contact with a predetermined first-contact portion of the work-piece prior to a center portion of the work-piece, so that the first-contact portion of the work-piece is partly or fully deformed by a downward movement of the punch in order to move a part of work-piece material from the first-contact portion in a direction to the center portion; and a second step for further moving down the punch to the die so that the center projected portion is brought into contact with the center portion of the work-piece in order to carry out the press work to the center portion.