Abstract:
A disc cartridge includes a disc type recording medium housed for rotation in a flat housing formed by a pair of metal shell halves. The housing is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium. At least one of the metal shell halves is provided along its periphery with an erected wall which is formed by bending a part of the edge of the shell half and is bonded to the other shell half and a V-shaped groove which keeps the bending angle of the erected wall at a predetermined angle is integrally formed on the shell half.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a disc cartridge comprising a magnetic disc housed for rotation in a housing having an opening and a shutter for opening and closing the opening, and a method of producing the same.  
           [0003]    2. Description of the Related Art  
           [0004]    In mobile instruments such as a digital camera, there has been used as the recording medium, for instance, a subminiature magnetic disc cartridge called “clik! ®” shown in FIGS. 5A, 5B and  6 . See, for instance, “Perso-Com Kaitai Shinsho” by Atsushi Oshima, Softbank Publishing, Apr. 19, 2000 pps, 52 and 53. The disc cartridge  1  (FIG. 6) can be loaded in a card-type driver (not shown) of type ΠPC employed in a notebook size personal computer. The driver is 53 mm×85 mm ×5 mm respectively in width, depth and thickness, and can be inserted for recording and reproduction into a PC card slot of a notebook size personal computer with a clik loaded therein.  
           [0005]    [0005]FIG. 6 is a perspective view showing the, and FIG. 7 is an exploded perspective view of the same. The magnetic disc cartridge (“clik! ®”)  1  comprises a 40 MB magnetic disc  9  (FIG. 7) 45.7 mm (1.8 inches) in diameter housed for rotation in a flat housing  5  formed by a resin frame  2  and upper and lower shell halves  3  and  4 . Each of the upper and lower shell halves  3  and  4  is formed of metal material (a stainless steel plate about 0.2 mm thick) and the flat housing is 50 mm in width, 55 mm in depth and 1.95 mm in thickness.  
           [0006]    The housing  5  is provided with an opening  6  (FIG. 6) which gives access to the magnetic disc  9  to a magnetic head of a disc drive system into which the magnetic disc cartridge  1  is inserted, and a rotary shutter  7  formed of, for instance, aluminum alloy, which is moved between its closed position where it closes the opening  6  and its open position where it opens the opening  6 . As shown in FIG. 6, the upper and lower shell halves  3  and  4  have peripheral walls  3   k  and  4   k  which are butted against each other and welded together by laser welding at not less than 10 sites P (FIG. 6).  
           [0007]    The rotary shutter  7  comprises upper and lower shutter halves  7 U and  7 D and is supported for rotation between the upper and lower shell halves  3  and  4 . Liners  18  are interposed between the magnetic disc  9  and the upper shutter half  7 U and between the magnetic disc  9  and the lower shutter half  7 D. The magnetic disc  9  is provided with a center core  10 . The frame  2  is interposed between the upper and lower shell halves  3  and  4  to keep a predetermined space therebetween. A coiled spring  14  which urges the rotary shutter  7  toward its closed position and a guide wire  13  which is inserted into the coiled spring  14  to guide the same are disposed along the arcuate inner surface of the frame  2 .  
           [0008]    A shutter lock member  11  for locking the rotary shutter  7  in its closed position is provided on the upper shell half  3 . A circular central opening  4   a  for giving access to a center core  10  of the magnetic disc  9  and an arcuate slit  4   b  concentric with the rotary shutter  7  are formed in the lower shell half  4 . A shutter knob  7   b  which projects outward through the slit  4   b  to be moved along the arcuate slit  4   b  when the rotary shutter  7  is opened and closed is fixed to the lower shutter half  7 D.  
           [0009]    The upper and lower shutter halves  7 U and  7 D have peripheral walls  7 Uk and  7 Dk which are butted against each other and bonded together by welding or the like.  
           [0010]    When the disc cartridge  1  is loaded in a personal computer, the rotary shutter  7  is rotated to its open position where it exposes the magnetic disc  9  through the opening  6  to give access to the magnetic disc  9  to a magnetic head of the computer to record or read data.  
           [0011]    In addition to the “click!”, there has been known a rectangular flat magnetic disc cartridge which is employed in a type Π, PC card. (See, for instance, Japanese Unexamined Patent Publication No. 2001-243736.) The disc cartridges of this type comprises a rectangular flat base plate of resin holding therein a magnetic disc medium and a pair of metal cover plates disposed on opposite sides of the base plate. The cover plates are provided with peripheral walls which are bonded together by spot welding or the like.  
           [0012]    When a cylindrical projection as a tubular shaft for rotatably supporting the rotary shutter  7  is to be formed in a thin sheet metal member such as the upper and lower shell halves  3  and  4  of the housing  5 , a method of processing generally called “barring” is employed.  
           [0013]    [0013]FIGS. 8A to  8 E are for illustrating an example of barring employed when a projection is formed in a sheet metal. A base hole  51  of a small diameter is first formed in a sheet metal member  50  (e.g., one of the shell halves  3  and  4 ) as shown in FIG. 8A. Then a barring tool  60  comprising cylindrical smaller and larger diameter portions  61  and  63  provided on opposite end portions of a conical body portion  62  which is a truncated cone in shape is prepared and the smaller diameter portion  61  of the tool  60  is inserted into the base hole  51  as shown in FIG. 8B.  
           [0014]    When the tool  60  is subsequently forced upward, a part  52  of the sheet metal member  50  circumscribing the base hole  51  is expanded as shown in FIG. 8C as the conical body portion  62  enters the base hole  51 . When the tool  60  is further forced upward with the part about the base hole  51  held by a jig  65  having a circular opening  65   a,  the part  52  of the plate member  50  is further expanded and stretched to be plastically deformed as the larger diameter portion  63  enters the hole  51  as shown in FIG. 8D. The sheet metal member  50  is thus processed to a member having a cylindrical projection  53  with a central opening  54  as shown FIG. 8E. Though not shown, the jig  65  shown in FIG. 8D is also used in the steps shown in FIGS. 8B and 8C.  
           [0015]    The cylindrical projection  53  is used as a tubular shaft for supporting the rotary shutter  7  for rotation. In such a case, after a plate member  55  having an axial opening  55   a  (e.g. one of the upper and lower shutter halves  7 U and  7 D) is loosely fit on the cylindrical projection  53  as shown in FIG. 9A, the free end portion of the cylindrical projection  53  is caulked to form a flange  53   a  for preventing dismounting of said plate member  55  from the cylindrical portion  53  as shown in FIG. 9B.  
           [0016]    When the free end portion of the cylindrical projection  53  is caulked, a caulking jig  70  such as shown in FIG. 10 is generally employed. The caulking jig  70  comprises a lower die  71  and an upper die  72 . The lower die  71  is provided with a flat upper surface  71   a  on which the sheet metal member  50  is placed, and a locator cylindrical body  73  on which the central opening  54  of the cylindrical projection  53  is fitted is erected from the upper surface  71   a.    
           [0017]    The upper die  72  is provided on its lower surface  72   a  with a cylindrical body  74  which is coaxial with, is shorter than and is of the same diameter as the cylindrical body  73  of the lower die  71 . The diameter of a root portion of the cylindrical body  74  is curvedly enlarged toward the lower surface  72   a,  thereby forming a caulking wall surface  75 .  
           [0018]    When the flange  53   a  is formed on the free end portion of the cylindrical projection  53 , the upper die  72  is moved downward with the plate member  55  having the axial opening  55   a  loosely fitted on the cylindrical projection  53  and with the cylindrical bodies  73  and  74  of the caulking jig  70  inserted into the central opening  54  from below and above, whereby the free end portion of the cylindrical projection  53  is expanded by the caulking wall surface  75  and a flange  53   a  is formed on the free end portion of the cylindrical projection  53 .  
           [0019]    However, production of the housing and/or the shutter of the disc cartridge in accordance with the prior art gives rise to the following problem. That is, bending of sheet metal to form parts of disc cartridge, e.g., metal shell halves, metal shutter and the like, causes a phenomenon of spring back in erected walls. It is difficult to control the spring back and to bend the sheet metal through a desired right angle, which results in increased labor. When the spring back cannot be successfully controlled, inclination of the erected walls, strain of the surface around the erected wall and/or the like can be generated.  
           [0020]    Recently, miniaturization of systems such as a portable personal computer, a digital camera and a PC card are required and accordingly, miniaturization of a disc cartridge which is employed in such systems as a recording medium is required. In order to meet such requirements, the disc cartridge must be precisely formed of a thin sheet metal. As the thickness of the sheet metal becomes smaller, inclination of the erected walls, strain of the surface around the erected wall and/or the like become more apt to be generated. When such defect is generated, there arises fear that the disc cartridge cannot be loaded in the system. Further, inclination of the erected walls can reduce the rigidity of the disc cartridge.  
           [0021]    Further, in the case of a cylindrical projection  53  which is employed as a tubular shaft for supporting for rotation the rotary shutter  7 , the flange  53   a  for preventing dismounting of the shutter  7  is formed on the free end portion of the cylindrical projection  53  by caulking. However, the free end portion of the cylindrical projection  53  cannot be always of an ideal shape shown in FIG. 9B but the peripheral wall of the cylindrical projection  53  is often inclined outward so that the cylindrical projection  53  becomes larger in diameter toward its free end to be brought into contact with the plate member  55  to prevent rotation thereof as shown in FIG. 9C.  
           [0022]    In order to avoid such trouble, conventionally, the speed of the upper die  72  has been controlled or the upper die  72  has been caused to work in an increased number of steps. However, these approaches have not been effective and the defect results in deterioration of the quality of the products and/or the yield of the products.  
         SUMMARY OF THE INVENTION  
         [0023]    In view of the foregoing observations and description, the primary object of the present invention is to provide a method of producing a disc cartridge which can suppress occurrence of spring back and strain of the surface around the erected wall and to provide a disc cartridge in which spring back and strain of the surface around the erected wall are suppressed.  
           [0024]    Another object of the present invention is to provide a method of producing a disc cartridge in which when a cylindrical projection employed as a tubular shaft for supporting for rotation a rotary shutter is formed with a flange for preventing dismounting of the shutter on the free end portion thereof by caulking, inclination of the cylindrical projection can be prevented.  
           [0025]    In accordance with a first aspect of the present invention, there is provided a disc cartridge comprising a disc type recording medium housed for rotation in a flat housing which comprises a pair of metal shell halves and is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium, wherein at least one of the metal shell halves is provided along its periphery with an erected wall which is formed by bending a part of the edge of the shell half and is bonded to the other shell half and an angle keeping means which keeps the bending angle of the erected wall at a predetermined angle is formed on the shell half integrally therewith.  
           [0026]    In accordance with a second aspect of the present invention, there is provided a disc cartridge comprising a disc type recording medium housed for rotation in a flat housing which comprises a pair of metal shell halves and is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium, and a shutter for opening and closing the opening, wherein the shutter is formed by a pair of metal shutter halves, at least one of the shutter halves is provided along its periphery with an erected wall which is formed by bending a part of the edge of the shutter half and is bonded to the other shutter half and an angle keeping means which keeps the bending angle of the erected wall at a predetermined angle is formed on the shutter half integrally therewith.  
           [0027]    The angle keeping means may be, for instance, a groove which is V-shaped in cross-section and formed along the inner side of the erected wall.  
           [0028]    Otherwise, the angle keeping means may be a triangular rib which is embossed on the inner side of the erected wall substantially in perpendicular thereto.  
           [0029]    In accordance with a third aspect of the present invention, there is provided a method of producing a disc cartridge comprising a disc type recording medium housed for rotation in a flat housing which comprises a pair of metal shell halves and is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium, wherein the improvement comprises that when forming an erected wall, which is bonded to the other shell half, on at least one of the shell halves by bending a part of the edge of the shell half, both the sides of the shell half are held under a pressure by a jig, along the part along which the shell half is bent to form the erected wall, so that the sides are not pulled toward the erected wall to be deformed upon bending the shell half.  
           [0030]    In accordance with a fourth aspect of the present invention, there is provided a method of producing a disc cartridge comprising a disc type recording medium housed for rotation in a flat housing which comprises a pair of metal shell halves and is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium, and a shutter for opening and closing the opening, wherein the improvement comprises that the shutter is formed by a pair of metal shutter halves, and when forming an erected wall, which is bonded to the other shutter half, on at least one of the shutter halves by bending a part of the edge of the shutter half, both the sides of the shutter half are held under a pressure by a jig, along the part along which the shutter half is bent to form the erected wall, so that the sides are not pulled toward the erected wall to be deformed upon bending the shutter half.  
           [0031]    For example, the jig may comprise a bending punch having a protrusion which extends along the erected wall and presses a side of the sheet metal (the shell half or the shutter half) adjacent to the inner side of the erected wall and a flat surface which is substantially flush with the side of the sheet metal, and a bearer which is positioned on the side of the sheet metal opposite to the bending punch.  
           [0032]    In accordance with a fifth aspect of the present invention, there is provided a method of producing a disc cartridge comprising a disc type recording medium housed for rotation in a flat housing which comprises a pair of metal shell halves and is provided with an opening for giving a recording/reproducing head of a disc driver access to the disc type recording medium, and a rotary shutter which is for opening and closing the opening and is formed by a pair of shutter halves, wherein the improvement comprises that when a cylindrical projection is formed on one of the housing and the rotary shutter and a free end portion of the cylindrical projection is caulked with the other of the housing and the rotary shutter engaged for rotation with the cylindrical projection, thereby forming a flange for preventing disengagement of said the other of the housing and the rotary shutter from the cylindrical projection, a groove which is V-shaped in cross-section and extends in a circumferential direction of the cylindrical projection is formed on the peripheral surface of the cylindrical projection at the base of the flange prior to the caulking.  
           [0033]    The cylindrical projection may be formed, for instance, by barring.  
           [0034]    In the disc cartridge in accordance with the first aspect of the present invention, the angle keeping means prevents spring back of the erected wall of the shell half and suppresses strain of the surface around the erected wall.  
           [0035]    In the disc cartridge in accordance with the second aspect of the present invention, the angle keeping means prevents spring back of the erected wall of the shutter half and suppresses strain of the surface around the erected wall.  
           [0036]    When the angle keeping means is a groove which is V-shaped in cross-section and formed along the inner side of the erected wall, spring back of the erected wall is prevented and at the same time bending of the shell half or the shutter half is facilitated.  
           [0037]    When the angle keeping means is a triangular rib which is embossed on the inner side of the erected wall substantially in perpendicular thereto, spring back of the erected wall is prevented and at the same time the erected wall is reinforced by the triangular rib, whereby the bending angle of the erected wall can be kept at a predetermined angle more surely.  
           [0038]    In the method of producing a disc cartridge in accordance with the third aspect of the present invention, since both the sides of the shell half are held under a pressure by a jig, along the part along which the shell half is bent to form the erected wall, so that the sides are not pulled toward the erected wall to be deformed upon bending the shell half, deformation of the surface around the erected wall involved by formation the erected wall is prevented.  
           [0039]    In the method of producing a disc cartridge in accordance with the fourth aspect of the present invention, since both the sides of the shutter half are held under a pressure by a jig, along the part along which the shutter half is bent to form the erected wall, so that the sides are not pulled toward the erected wall to be deformed upon bending the shutter half, deformation of the surface around the erected wall involved by formation of the erected wall is prevented.  
           [0040]    When the jig comprises a bending punch having a protrusion which extends along the erected wall and presses a side of the sheet metal (the shell half or the shutter half) adjacent to the inner side of the erected wall and a flat surface which is substantially flush with the side of the sheet metal, and a bearer which is positioned on the side of the sheet metal opposite to the bending punch, the sides by the erected wall can be more strongly pressed and accordingly, deformation of the surface can be prevented more surely.  
           [0041]    In the method of producing a disc cartridge in accordance with the fifth aspect of the present invention, the groove facilitates formation of the flange and prevents inclination of the cylindrical projection involved by caulking of the free end portion of the cylindrical projection. Accordingly, contact between the cylindrical projection and the member to be supported for rotation by the cylindrical projection (the shutter or the housing) can be avoided, whereby the yield and the quality of the of the products can be improved and the cost of the products can be reduced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]    [0042]FIG. 1A is a fragmentary cross-sectional view showing a part of the peripheral wall erected on an edge of the lower shell half of a magnetic disc cartridge in accordance with a first embodiment of the present invention together with the jig,  
         [0043]    [0043]FIG. 1B is a fragmentary plan view of the part of the peripheral wall of the lower shell half of the magnetic disc cartridge in accordance with the first embodiment of the present invention,  
         [0044]    [0044]FIG. 2A is a fragmentary cross-sectional view showing an edge of the lower shell half of a magnetic disc cartridge in accordance with a second embodiment of the present invention before an erected wall is formed,  
         [0045]    [0045]FIG. 2B is a fragmentary cross-sectional view of the same after the erected wall is formed,  
         [0046]    [0046]FIG. 3 is a fragmentary perspective view of a magnetic disc cartridge in accordance with a third embodiment of the present invention showing the erected wall of the same,  
         [0047]    [0047]FIG. 4A is a fragmentary cross-sectional view showing the lower shell half after bumping,  
         [0048]    [0048]FIG. 4B is a fragmentary plan view showing the same after bumping,  
         [0049]    [0049]FIGS. 5A and 5B are view illustrating formation of a flange by caulking on the free end portion of a cylindrical projection of a disc cartridge in accordance with a fourth embodiment of the present invention,  
         [0050]    [0050]FIG. 6 is a perspective view of a disc cartridge,  
         [0051]    [0051]FIG. 7 is an exploded perspective view of the disc cartridge shown in FIG. 6,  
         [0052]    [0052]FIGS. 8A to  8 E are views for illustrating the barring,  
         [0053]    [0053]FIGS. 9A and 9B are cross-sectional views illustrating formation of a flange by caulking on the free end portion of a cylindrical projection of a disc cartridge in accordance with the prior art,  
         [0054]    [0054]FIG. 9C is a cross-sectional view for illustrating the problem involved by the conventional caulking, and  
         [0055]    [0055]FIG. 10 is a cross-sectional view of the caulking jig. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0056]    A disc cartridge in accordance with a first embodiment of the present invention will be described with reference to FIGS. 1A and 1B, hereinbelow. FIG. 1A is a fragmentary cross-sectional view showing a peripheral wall (erected wall)  24   k  erected on en edge of the lower shell half  24  of the disc cartridge in accordance with the first embodiment together with the jig employed, and FIG. 1B is fragmentary plan view of the lower shell half  24 . The structure of the disc cartridge of this embodiment is basically the same as that shown in FIGS. 6 and 7 and will not be described here.  
         [0057]    In the first embodiment, the jig  26  shown by the chained line in FIG. 1A is employed when the lower shell half  24  is bent. The jig  26  comprises a bending punch  25  and a bearer  32 . The bending punch  25  comprises a vertical surface  27  extending to press the lower shell half  24 , a protrusion  28  which projects from the base of the vertical surface  27  in perpendicular to the vertical surface  27  and extends along the vertical surface  27 , and a flat surface  30  which projects from the edge of the protrusion  28  in perpendicular to the vertical surface  27  with an inclined shoulder  29  intervening between the protrusion  28  and the flat surface  30  and extends along the protrusion  28 . In this particular embodiment, the bearer  32  has a flat surface  34  facing upward.  
         [0058]    When bending the lower shell half  24  by the jig  26 , the lower shell half  24  is inserted between the bending punch  25  and the bearer  32 , and the lower shell half  24  is located with respect to the bending punch  25  so that bending punch  25  extends along the bending part  36  along which the lower shell half  24  is to be bent to form the peripheral wall (erected wall)  24   k.  Then the bending punch  25  is moved toward the bearer  32  and presses the upper surface  42  of the lower shell half  42 , whereby the protrusion  28  of the bending punch  25  compresses the upper surface  42  of the lower shell half  24  to form a groove  40 . Substantially simultaneously with the compression, a bending jig  35  bends upward the edge of the lower shell half  24  to form the peripheral wall  24   k.    
         [0059]    The groove  40  is formed by compressing the lower shell half  24  within the range of height of the shoulder  29 . By this compression, the upper and lower surfaces  42  and  43  of the lower shell half  24  are held between the bending punch  50  and the bearer  32  and the surface around the peripheral wall  24   k  is prevented from being pulled toward the peripheral wall  24   k  when the lower shell half  24  is bent to form the peripheral wall  24   k,  whereby the peripheral wall  24   k  can be precisely formed and there is no fear that the upper and lower surfaces  42  and  43  of the lower shell half  24  are deformed. This method is effective to prevent deformation of the arcuate slit  4   b  of the lower shell half  24  shown in FIG. 6. Though being continuous in the embodiment described above, the protrusion  28  may be discontinuous. When the protrusion  28  is discontinuous, the groove  40  formed also becomes discontinuous.  
         [0060]    It is preferred that the depth D of the groove  40  be ⅕ to ¼ of the thickness t of the lower shell half  24  and the width W of the groove  40  be substantially the same as the thickness t of the lower shell half  24 .  
         [0061]    Though, in the first embodiment, the present invention is applied to form the erected wall  24   k  of the lower shell half  24 , the present invention may be applied to form the erected wall  3   k  of the upper shell half  3 , the erected wall  7 Uk of the upper shutter half  7 U and the erected wall  7 Dk of the lower shutter half  7 D.  
         [0062]    The disc cartridge in accordance with a second embodiment of the present invention will be described with reference to FIGS. 2A and 2B, hereinbelow.  
         [0063]    [0063]FIGS. 2A and 2B are views for illustrating an erected wall of a disc cartridge in accordance with a second embodiment of the present invention. FIG. 2A is a fragmentary cross-sectional view showing an edge of the lower shell half of the magnetic disc cartridge in accordance with the second embodiment of the present invention before an erected wall is formed, and FIG. 2B is a fragmentary cross-sectional view of the same after the erected wall is formed. In FIGS. 2A and 2B, the elements analogous to those shown in FIGS. 1A and 1B are given the same reference numerals and will not be described here. In the disc cartridge of the second embodiment, a groove (an angle keeping means)  44  which is V-shaped in cross section is formed on the upper surface  42  of the lower shell half  24  along the bending part  36  along which the lower shell half  24  is to be bent to form the peripheral wall (erected wall)  24   k.  The groove  44  is angled by 90°, and accordingly when the edge of the lower shell half  24  is bent along the groove  44  by a jig not shown, the erected wall  24   k  is erected by 90° to the upper surface  42  of lower shell half  24  as shown in FIG. 2B.  
         [0064]    In this second embodiment, when the lower shell half  24  is bent to form the erected wall  24   k,  material of the upper surface  42  is not pulled toward the erected wall  24   k  and the lower shell half  24  is easily bent. Accordingly, there is no fear that the surface around the erected wall  24   k  is deformed. Further, since the bending stress acting on the bending part  36  is small, the erected wall  24   k  can be kept at a right angle. It is preferred that the depth of the groove  44  be about ⅓ of the thickness of the sheet metal. Also in accordance with the second embodiment, the erected wall  3   k  of the upper shell half  3 , the erected wall  7 Uk of the upper shutter half  7 U and the erected wall  7 Dk of the lower shutter half  7 D can be formed.  
         [0065]    A third embodiment of the present invention will be described with reference to FIG. 3, hereinbelow. FIG. 3 is a fragmentary perspective view of the magnetic disc cartridge in accordance with the third embodiment of the present invention showing the erected wall  24   k  of the same. Also the third embodiment of the present invention will be described in conjunction with erecting a wall on the lower shell half  24 . In this embodiment, a triangular rib (an angle keeping means)  46  is formed by embossment from outside at the bending part  36  when forming the erected wall  24   k.  When erected wall  24   k  is formed long along the bending part  36 , a plurality of triangular ribs  46  may be formed at predetermined intervals.  
         [0066]    Since the triangular rib  46  is formed integrally with the lower shell half  24  to connect the erected wall  24   k  and the upper surface  42  of the lower shell half  24 , the rising angle of the erected wall  24   k  is surely held and at the same time, the erected wall  24   k  is greatly reinforced by the rib  46 .  
         [0067]    In order to improve the flatness of the upper and lower surfaces  42  and  43  of the lower shell half  24 , a number of recesses may be formed on the upper and lower surfaces  42  and  43  by bumping at predetermined intervals as shown in FIGS.  4 A and  4 B.  
         [0068]    Generally, a workpiece such as a sheet metal deteriorates in its flatness as the processing step progresses. Bumping is carried out for maintaining the flatness of the workpiece, and in the bumping, a member having a number of two-dimensionally erected pointed projections is pressed against both the surfaces of the sheet metal to form a number of fine conical recesses  48  thereon. It is preferred that the depth of each of the recesses  48  be 0.2 times the thickness t of the sheet metal and the space between adjacent recesses  48 , i.e., the pitch of the recesses  48 , be 0.7 to 2 times the thickness t of the sheet metal. It is further preferred that the angle which the inner surface of each of the recesses  48  be 90° to 120°. When such bumping is carried out before forming the erected walls  3   k,    4   k,    7 Uk  7 Dk, the orthogonality of these erected walls can be stabilized.  
         [0069]    A fifth embodiment of the present invention will be described with reference to FIGS. 5A and 5B, hereinbelow.  
         [0070]    [0070]FIGS. 5A and 5B are views for illustrating formation of a flange  53   a  by caulking on the free end portion of a cylindrical projection  53  formed on one  50  of the upper and lower shell halves with one  55  of the shutter halves of the rotary shutter  7  fitted for rotation on the cylindrical projection  53 , thereby preventing disengagement of the shutter half  55  from the cylindrical projection  53 . FIGS. 5A and 5B respectively correspond to FIGS. 9A and 9B for illustrating formation of a flange  53   a  by caulking in accordance with the prior art. In FIGS. 5A and 5B, elements analogous to those shown in FIGS. 9A and 9B are given the same reference numerals and will not be described here. In the fourth embodiment, a groove  58  which is V-shaped in cross-section and extends in a circumferential direction of the cylindrical projection  53  is formed on the peripheral surface of the cylindrical projection  53  at the base of the flange  53   a  as shown in FIG. 5A prior to the caulking.  
         [0071]    When the free end portion of the cylindrical projection  53  is caulked in this state, the flange  53   a  for preventing disengagement can be formed on the free end of the cylindrical projection  53  without inclination of the cylindrical projection  53 .  
         [0072]    Though, in the fourth embodiment, the cylindrical projection  53  for supporting for rotation the rotary shutter  7  is formed on one of the shell halves of the housing  5 , the cylindrical projection  53  may be formed on one of the shutter halves of the rotary shutter  7 .  
         [0073]    Though, the present invention has been described in detail with reference to the first to fourth embodiments, the embodiments are given only for describing the present invention and may be variously modified. In view of the availability, processability and strength of the disc cartridge produced, it is preferred that the sheet metal material for forming the shell halves be a stainless steel sheet which is 0.15 to 0.2 mm in thickness (SUS304), and the sheet metal material for forming the shutter halves be an aluminum alloy sheet which is 0.15 to 0.2 mm in thickness (A5052P). Especially preferably, the sheet metal material for forming the shell halves is a stainless steel sheet which is 0.2 mm in thickness, and the sheet metal material for forming the shutter halves is an aluminum alloy sheet which is 0.15 mm in thickness.