Abstract:
A method for manufacturing an inner cutter for a reciprocating electric shaver, including the steps of: forming a plurality of slits in a thin plate; forming ribs by pressing bridging-portions that remain between the slits so that each rib extends for the length of each bridging-portion and forms a protruding portion that protrudes in the width direction, thus obtaining an intermediate worked member; deep drawing the intermediate worked member that has the ribs into substantially an arch shape with the protruding portions of the ribs facing outward; and grinding the outer surface of the arch-form intermediate worked member, thus forming cutting edges which have blade surfaces and acute rake angles in the protruding portions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to a method for manufacturing an inner cutter adapted to be used in a reciprocating electric shaver in which the cutter blades of the inner cutter make a reciprocating motion while making sliding contact with the inside surface of a substantially arch-form outer cutter.  
         [0003]     2. Description of the Related Art  
         [0004]     In generally known reciprocating electric shavers, an inner cutter makes a reciprocating motion while making sliding contact with the inside surface of an arch-form outer cutter, and hair that enters openings (hair introduction openings) formed in the outer cutter is cut by the reciprocating inner cutter, as seen in, for instance, Japanese Patent Application Publication (Kokoku) No. S59-32151 and Japanese Patent Application Laid-Open (Kokai) Nos. S59-101182 and H10-323461. The inner cutters used in such electric shavers of this type include assembled type inner cutters and integral type inner cutters.  
         [0005]     In the assembled type inner cutters, a plurality of cutter blades formed by stamping a thin plate(s) into an arch-form shape are held on an inner cutter holder with these cutter blades lined up at fixed intervals as disclosed in Japanese Patent Application Publication (Kokoku) Nos. S59-32151 and Japanese Patent Application Laid-Open (Kokai) No S59-101182. In such inner cutters, since it is necessary to make a plurality of cutter blades and attach these cutter blades to a cutter blade attachment member, the number of manufacturing processes is large, and the productivity tends to be poor.  
         [0006]     On the other hand, in the integral type inner cutter, which is typically made of a single metal cylinder or sheet, all of the cutter blades are integrally formed. More specifically, perpendicular slits are formed in a cylindrical body made of a metal, ceramic or the like, and the portions that remain between the slits are used as cutter blades. In another type of integral type inner cutters, a thin plate is bent into an arch-form shape, and cutter blades are formed by making slits in the perpendicular direction with respect to the axis of the arch-form portion. In still another integral type inner cutters, a thin plate in which slits have been made is bent into an arch-form shape as shown in Japanese Patent Application Laid-Open (Kokai) No. H10-323461.  
         [0007]     Meanwhile, it is generally known that the sharpness of inner cutters conspicuously improves by forming the rake angle formed on the cutting edges of the cutter blades in an acute angle. Here, the rake angle is the angle defined by the blade surface, where a cutter blade makes sliding contact with the outer cutter, and the side surface, which is connected with the cutting edge of the cutter blade.  
         [0008]     In the assembled type inner cutters, the cutter blades are independent from each other, and an acute rake angle is formed by, for example, squeezing both surfaces of the cutter blades by pressing.  
         [0009]     However, in the case of the integral type inner cutter, the respective cutter blades are integrally formed or they are formed on a single cylindrical body or on a single arch-form thin plate; accordingly, it is generally difficult to form the rake angle into an acute angle. Nevertheless, various methods for making the rake angle into an acute angle for integral type inner cutters have been introduced.  
         [0010]      FIG. 14  shows the manufacturing process of an integral type inner cutter by a press-molding method, and  FIG. 15  illustrates a detailed working process of the cutter blades of this inner cutter.  
         [0011]     In  FIG. 14 , the reference numeral  10  is a thin plate that will make the inner cutter. In this plate, a contour of an unfolded or extended inner cutter and a plurality of slits  12  that extend in the direction perpendicular to the reciprocating (or lateral) direction (shown by arrow a) of the inner cutter are press-stamped from a thin plate of, for instance, quenchable stainless steel.  FIG. 14A  is a top view of the thin plate  10 , and  FIG. 14B  is a sectional view taken along the centerline  14  of the thin plate  10  of  FIG. 14A .  
         [0012]     In  FIG. 14A , the reference numeral  16  is a pair of left and right side edge portions that are parallel to the direction of lateral length of the inner cutter (the reciprocating direction, i.e., the direction of the lateral center line  14 ), and  18  indicates bifurcated claws that protrude outward from the centers of the edge portion of side edge portions  16 . The inner cutter (that can be referred to by the reference numeral  10 ) is held on an inner cutter holder (not shown) by these claws  18  and makes a reciprocating motion by this inner cutter holder.  
         [0013]     In  FIG. 14B, 12A  indicates discarded elements resulted from the stamping work of the slits  12 . Bridging-portions  20  that remain after the stamping work and are in the form of being connected to the pair of the side edge portions  16  are formed (or remain) between these slits  12 .  
         [0014]     As shown in  FIG. 15 , forming of the rake angle into an acute angle by press-molding is performed on the bridging-portions  20 . In  FIG. 15 , the reference numeral  22  indicates a flat lower mold (die side), and  24  indicates an upper mold (punch side).  
         [0015]     The flat plate  10  shown in  FIGS. 14A and 14B  is placed on the lower mold  22 . The upper mold  24  is formed with grooves  26  which have substantially the same length as the bridging-portions  20  and which have a width that is narrower than the width of the bridging-portions  20 ; and the grooves  26  are positioned so as to correspond to the respective bridging-portions  20 . Beveled faces  28  that are substantially triangular in cross section are formed in the opening corner of the grooves  26 .  
         [0016]     When the bridging-portions  20  are pressed by the molds  22  and  24 , the bridging-portions  20  undergo plastic deformation from the state shown in step (A) to the states shown in steps (B), (C) and (D). The following description on making the rake angles into an acute angle for the bridging-portions  20  will be made only for one bridging-portion  20  though such a process is made for all the bridging-portions simultaneously.  
         [0017]     More specifically, first, when the upper mold  24  is lowered, the edges of the upper surface of the bridging-portion  20  advance into the groove  26  while being guided by the beveled surfaces  28  of the upper mold  24  in step (B), and the lower portion of the bridging-portion  20  is caused to protrude in the direction of width by the beveled surfaces  28  in step (C). Then, the lower portion of the protruding portion  30  advance into the space between the facing surfaces of the upper and lower molds  22  and  24 ; as a result, the cross section of the bridging-portion  20  assumes substantially the shape of an inverted umbrella or an inverted letter T.  
         [0018]     The thin plate  10  thus makes an intermediate worked member  32  in which, as shown in  FIG. 14C , all the bridging-portions  20  are pressed into a cross-sectional shape that is substantially the shape of an inverted T or an inverted umbrella. The bridging-portions  20  of this intermediate worked member  32  make the ribs  20 A that have protruding portions  30 .  
         [0019]     In step (D) of  FIG. 15 , the intermediate worked member  32  is subjected to deep drawing so as to be into an arch-form shape about the lateral center line  14  (see  FIG. 14A ) so that the protruding portions  30  of the ribs  20 A face outward.  
         [0020]     Then, cutter blades with an acute rake angle α are formed by grinding the outer circumferential surface to the dimension a.  
         [0021]     However, in the above method, since the amount of plastic deformation working of the thin plate is large, braking and cracking tend to occur internally.  
         [0022]     More specifically, noting the position b of the dot symbol near the upper corner part of the bridging-portion  20  shown in step (a) in  FIG. 15 , this position b is, during the deformation work, caused to move, as shown in steps (B) and (C), toward the center in the direction of width of the bridging-portion  20  by the beveled face  28  of the upper mold  24 , and it is further caused to move to the vicinity of the protruding portion  30  as shown in step (D). Here, the deformation limit of the metal tends to exceed as the angle c of the beveled face  28  increases, and as the dimension d increases, so that braking and cracking are more likely to occur internally. Such internal braking and cracking are pushed inward by the molds  22  and  24  in the final stage of pressing in step (D) and are therefore extremely difficult to find from the outside.  
         [0023]      FIGS. 16A and 16B  show the manufacturing process of an integral type inner cutter according to an etching method (see the above-identified Japanese Patent Application Publication (Kokoku) No. S59-22542). In  FIG. 16A , the etching is performed from one side; and in  FIG. 16B , the etching is performed from the both sides.  
         [0024]     In  FIG. 16A , resists  36  are formed on one surface (the upper surface) of a thin plate  34  in positions that correspond to the bridging-portions  20  (see  FIG. 14A ), and slits  38  are worked by performing etching with a jet of etching liquid applied from the upper surface as indicated by arrows e. Here, the resists  36  are formed by coating the entire surface with a resist or pasting a dry film of the resist to the entire surface and then exposing a pattern and removing the unnecessary resists (photo-etching method).  
         [0025]     In this case, the deeper in the thin plate from the upper surface (resist surface), the lesser the amount removed by etching, and thus the width of the slits  38  becomes narrower. Accordingly, the acute rake angle α is formed on the side edges of the undersurfaces of the bridging-portions  40 . The method in which etching is thus performed from one side or from one surface takes a longer time to form the slits  38 , thus increasing the working time. In addition, there are restrictions on the adjustment range of the rake angle α.  
         [0026]     Accordingly, performing the etching on a thin plate from both sides has been considered.  
         [0027]     In  FIG. 16B , resists  36  are formed on both sides (surfaces) of the thin plate  34 , and slits  38  are formed by applying a jet of etching liquid from both sides. In this case, protruding strips  42  are formed on the inside walls of the bridging-portions  40 ; accordingly, it is necessary to grind off the portions f that are from one side of the thin plate  34  to these protruding strips  42 . However, since the thin plate involves a plurality of ground portions f, a large amount of thin plate material is wasted.  
         [0028]      FIG. 17  shows the method of grinding or cutting (see the above-identified Japanese Patent Application Laid-Open (Kokai) No. S53-116961).  
         [0029]     In this method, slits  38  are ground using grindstones  46  that are fastened to a rotating shaft that is rotated as shown by circular arrow and are parallel (horizontal) to the thin plate  34 . Here, the outer circumferential edges of the grindstones  46  are beveled to a substantially trapezoidal shape in cross section so that each grindstone is shaped to be thinner outward. As a result, a rake angle of α is formed in positions that correspond to the outer circumferential sides of the grindstone  46  on the bridging-portions  40  that remain between the slits  38 .  
         [0030]     In this method, however, flashes g and h are generated on the cutting edges and the edges on the opposite sides of the bridging-portions  40 . As illustrated in  FIG. 14 (C), the thin plate  34  is deep drawn into an arch-form shape with the blade surfaces  48  on the outside. If flashes g and h remain thereon, the adhesion with the tool (molds) is poor, and the working precision drops; furthermore, scratches caused by the flashes g and h would be formed in the blade surfaces  48  and in the vicinity of the cutting edges, thus lowering the quality of the inner cutter. Accordingly, it is necessary to remove the flashes g and h first and then perform deep drawing.  
         [0031]      FIGS. 18A and 18B  show the method that uses electro-casting (see the above-identified Japanese Patent Application Publication (Kokoku) No. S60-9597.  
         [0032]     In  FIG. 18A  shows the electro-casting, and  FIG. 18B  shows the finished inner cutter. The reference numeral  48  is a matrix mold. In this matrix mold  48 , resists  52  and primary plating layers  54  are formed in parallel on top of a base member  50  that is made of a synthetic resin or copper. An electro-deposition metals  56  are electro-deposited on top of this primary plating layer  54 , and the matrix mold  48  (including the base member  50  and the resists  52 ) is then remove, thus producing the cutter blades of the inner cutter shown in  FIG. 18B .  FIG. 18B  shows the cross section of the cutter blades  58 .  
         [0033]     In the cutter blades  58  of  FIG. 18B , when it is attempted to increase the thickness i, the plating time increases, and the mass production characteristics deteriorate. Furthermore, it also becomes difficult to reduce the rake angle α. Moreover, there are restrictions on the materials that can be used for the thin plate. Ordinarily, the material used is Ni, Ni-cobalt or the like, so that the degree of freedom in selecting materials is restricted.  
         [0034]     In the above-described press-molding method ( FIGS. 14A through 14D  and  15 ), braking and cracking occurring inside the bridging-portions  20  are easily overlooked; accordingly, problems occur in the durability of the cutting edges of the inner cutter, and there is a danger that this will lead to a quality drop. Furthermore, since the amount of pressing involved is large, it is necessary to use expensive molds that have a high precision and high strength. Moreover, since the pressing pressure is high, it is necessary to use a large size pressing machine, and the thin plate needs to be of an expensive material that has good pressing characteristics. Furthermore, different molds must be used for different shape deformations of inner cutters, and it is difficult to manufacture inner cutters that have a complicated shape.  
         [0035]     As seen from the above, in the method that uses etching ( FIGS. 16A through 16D ), the manufacturing time is long, and there is considerable waste of material. Furthermore, the problem of restrictions on the adjustment range of the rake angle also arises.  
         [0036]     In the case of a method that uses grinding (cutting) ( FIG. 17 ), it is necessary to remove the flash that is generated. Thus, the procedure required is bothersome, and the productivity is poor, and further, it is very difficult for this method to handle inner cutters that have a complex shape.  
         [0037]     In the method that uses electro-casting ( FIG. 18 ), there are problems. The mass production characteristics are poor, the adjustment range of the rake angle is small, and there are restrictions on the degree of freedom of material selection for the thin plate.  
       BRIEF SUMMARY OF THE INVENTION  
       [0038]     The present invention is to overcome the above-described problems, and it solves at one time the various problems encountered in the conventional methods.  
         [0039]     More specifically, the object of the present invention is to provide a method for manufacturing an integral type inner cutter which has a broad rake angle adjustment range, makes it possible to reduce the rake angle, allows easy handling of inner cutters that have a complicated shape, and makes it possible to produce an inner cutter with high durability.  
         [0040]     The above object is accomplished by unique steps of the present invention for a method for manufacturing an inner cutter for a reciprocating electric shaver in which an integral inner cutter makes a reciprocating motion while causing a plurality of cutter blades thereof to make sliding contact with the inside surface of an arch-form outer cutter; and in the present invention, the method includes the steps of: 
        (a) forming a plurality of slits in a thin plate so that the slits are substantially perpendicular to the reciprocating direction of the inner cutter and are defined by uneven surfaces with respect to the depth of the slits (or to the thickness of the thin plate),     (b) forming ribs by pressing bridging-portions that remain between the slits so that the ribs extend in the direction of length of the bridging-portions and are in a form of protruding portions that protrude in the direction of width and toward a blade surface, thus obtaining an intermediate worked member,     (c) deep drawing the intermediate worked member that has ribs formed in step (b) into substantially an arch shape with the protruding portions of the ribs facing outward, and     (d) grinding the outer circumferential surface of the arch-form intermediate worked member, thus forming cutting edges that have blade surfaces and acute rake angles in the protruding portions.        
 
         [0045]     In the present invention, the slits that are formed in step (a) are defined by the worked wall surfaces that are uneven or inclined with respect to the direction of depth of the slits (or in the direction of the thickness of the thin plate); accordingly, the amount of plastic deformation working that is performed during the pressing work in step (b) is reduced. Consequently, the amount of deformation occurred during the pressing work of the thin plate is small, and braking and cracking tend not to occur internally. The inner cutter obtained by the present invention thus has an improved durability in the cutting edges. Furthermore, since the amount of deformation of the thin plate is small, the selection range of the materials for the thin plate is high, and the method can use the mold that has a reduced strength and pressing pressure; as a result, the pressing machine can be simple in structure and small in size.  
         [0046]     Meanwhile, since the protruding portions are formed on the blade surface sides of the ribs in step (b), the rake angle of the cutting edges can be formed as an acute angle by grinding the outer surfaces of the protruding portions in step (d); and the rake angle can be adjusted for a broad range by adjusting the shape of these protruding portions and the amount of outer surface grinding. In particular, when deep drawing the intermediate worked member into an arch-form shape is performed in step (c), both side edges of the protruding portions on the outer circumferential sides of the ribs are drawn toward the inner circumferential side; accordingly, the outer circumferential surfaces of the protruding portions are slightly bent in cross section perpendicular to the direction of length of the ribs. However, since these protruding portions protrude further toward the blade surface side than the surfaces formed as blade surfaces by the grinding in step (d), the blade surfaces can be ground to make surfaces that are parallel to the reciprocating direction of the inner cutter. Furthermore, since the amount of working by pressing in step (b) is small, inner cutters that have complicated shapes can easily be handled.  
         [0047]     The thin plate can be formed so as to have a contour of an intended inner cutter in step (a). For example, in cases where etching is used in step (a), the contour is made by etching. The contour or external shape can also be made by stamping when pressing is performed in step (b). In this case, step (a) is performed on a large thin plate for a plurality of inner cutters, and the resulted plurality of intermediate worked members are simultaneously formed in step (b); accordingly, the productivity is high.  
         [0048]     It is advisable to use photo-etching in step (a). With photo-etching, high-precision working is easily performed. Furthermore, by way of executing etching from both sides (or both surfaces) of the thin plate, the time of the etching treatment can be shortened. However, etching can be performed from only one surface (the opposite surface from the blade surface). In this case, though it takes longer processing time, the amount of deformation caused by the pressing in step (b) can be greatly reduced, thus enhancing the advantages of the present invention. Some other method such as electrolytic working, laser beam working or the like can be used instead of photo-etching.  
         [0049]     Furthermore, reinforcing portions can be formed in the insides (inner circumferential sides) of the cutting edges of the cutter blades in order to prevent chipping of these cutting edges during the pressing performed in step (b). More specifically, reinforcing portions can be worked at the same time as the protruding portions by using a mold that has a shape to form the reinforcing portions in addition to a shape that form the protruding portions. The reinforcing portions can be formed by a mold in which a slight amount of working for the shape for the reinforcing portions is made therein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0050]      FIG. 1  is a schematic front view of a reciprocating electric shaver for which the inner cutter of the present invention is adapted to be used;  
         [0051]      FIG. 2  is a schematic side view thereof;  
         [0052]      FIGS. 3A through 3E  shows process of manufacturing method for the inner cutter according to the present invention  
         [0053]      FIG. 4  shows the steps of the manufacturing process of the inner cutter of the present invention;  
         [0054]      FIG. 5  shows in cross section the side view of the inner cutter of the present invention;  
         [0055]      FIG. 6  is an enlarged cross-sectional view taken along the line VI-VI in  FIG. 5 ;  
         [0056]      FIG. 7  is an enlarged perspective view of a part of a cutter blade of the inner cutter of the present invention seen from the inside;  
         [0057]      FIG. 8  is a top view of the inner cutter according to one embodiment of the present invention unfolded;  
         [0058]      FIG. 9  is a top view of the inner cutter of another embodiment of the present invention unfolded;  
         [0059]      FIG. 10  is a top view of the inner cutter of still another embodiment of the present invention unfolded;  
         [0060]      FIG. 11  is a top view of the inner cutter of still another embodiment of the present invention unfolded;  
         [0061]      FIG. 12A  is a top view of the inner cutter of further embodiment of the present invention unfolded, and  FIGS. 12B and 12C  are enlarged views, respectively, of the cutter blades;  
         [0062]      FIG. 13A  is a top view of the inner cutter of still further embodiment of the present invention unfolded, and  FIG. 13B  is an enlarged view of the cutter blades thereof;  
         [0063]      FIGS. 14A through 14D  show the manufacturing process of an inner cutter by a conventional press-molding method;  
         [0064]      FIG. 15  shows in detail the manufacturing steps (A) through (D) of the cutter blades thereof;  
         [0065]      FIGS. 16A and 16B  show the manufacturing steps of an inner cutter in a conventional etching method;  
         [0066]      FIG. 17  shows the manner of manufacturing an inner cutter in a conventional grinding/cutting method; and  
         [0067]      FIG. 18A  shows the manner of manufacturing an inner cutter in a conventional electro-casting, and  FIG. 18B  illustrates the completed inner cutter.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0068]      FIG. 1  shows schematically the internal structure of a reciprocating type electric shaver according to one embodiment of the present invention, the internal structure of the shaver being omitted; and  FIG. 2  shows the shaver from the side.  
         [0069]     In  FIGS. 1 and 2 , the reference number  100  is an arch-shaped outer cutter, and  102  is an arch-shaped inner cutter that makes a reciprocating motion within or under the outer cutter  100 . The outer cutter  100  is fastened to a frame  104  of the shaver body (not shown). The outer cutter  100  is made of a thin plate of stainless steel, etc., and a plurality of openings (hair introduction openings) are formed in this thin metal plate by, for instance, press-stamping or etching. The outer cuter  100  can be made by electro-casting.  
         [0070]     The inner cutter  102  is driven in a reciprocating motion by an electric motor  106 . More specifically, a plane oscillator  110  made of a synthetic resin is suspended from the upper end surfaces of a pair of supporting columns  108  that extend in an upright attitude from the frame  104  of the shaver so that the oscillator  110  is free to oscillate laterally (or to the left and right), and a crank pin  112  that is fastened to the rotating shaft of the motor  106  is engaged with a long groove formed in the oscillator  110 . As a result, when the rotating shaft of the motor  106  installed in the shaver body rotates, the oscillator  110  makes a lateral (or left and right) reciprocating motion.  
         [0071]     A supporting column  114  is provided so as to protrude from this oscillator  110 , and a holding portion  116  for the inner cutter  102  is held on the supporting column  114 . The holding portion  116  is guided by the supporting column  114  so that the holding portion  116  is free to make an upward and downward motion; and a return inertia oriented in the upward direction toward the outer cutter  100  is applied to the holding portion  116  by a coil spring  118 . As a result, the inner cutter  102  is driven in a reciprocating motion by the motor  106  while being held in elastic contact with the inside surface of the outer cutter  100  by the coil spring  118 .  
         [0072]      FIGS. 3A through 3E  show the working process of the inner cutter  102 ,  FIG. 4  shows the manufacturing process of the inner cutter  102 ,  FIG. 5  is a sectional side view of the inner cutter  102 ,  FIG. 6  is a sectional view of the inner cutter,  FIG. 7  is an enlarged perspective view of a part of the cutter blades seen from the inside, and  FIG. 8  is a top view of the inner cutter unfolded or before being turned into an arch-shape.  
         [0073]     In  FIG. 3A , the reference numeral  120  indicates a thin plate made of stainless steel or the like.  
         [0074]     Patterns (as shown in  FIG. 8 , for instance) of the inner cutter  102  are formed by photo-resists  122  and  124  on both sides (on both surfaces) of this thin plate. The resists  122  and  124  are formed by applying a coating of a resist liquid or pasting a dry film (see step S 200  in  FIG. 4 ), exposing the pattern of the inner cutter  102  (step S 202 ), and developing the exposed pattern (step S 204 ). The resists in the portions corresponding to the slits  126  are removed. Here, the resists  122  and  124  cover the portions that will become both side edges  128  (see  FIG. 8 ), the bridging-portions  130  and the claws  132 .  
         [0075]     The thin plate  120  on which the resists  122  and  124  are formed is etched from both sides (surfaces) as show in  FIG. 3B . More specifically, etching is performed by applying a jet of etching liquid to both sides (or both surfaces) simultaneously or one at a time, so that the slits (grooves)  126  are formed. Since the etching liquid etches only places where there is no resist  122  or  124 , the slits  126  are formed between the resists (step S 206 ).  
         [0076]     Etching proceeds in the direction of thickness of the thin plate  120  from the gaps between the resists  122  and from the gaps between the resists  124 ; accordingly, the worked wall surfaces that define the slits  126  are uneven or inclined with respect to the direction of depth as shown in  FIG. 3B , taking substantially an arc shape in cross section to have curved surfaces. Since etching is performed on both sides of the thin plate, slits are defined by uneven or arc shaped wall surfaces on their both sides with the wall surfaces having protruding strips  134 . Since these protruding strips  134  later make the protruding portions  144  when the pressing working is executed, it is desirable that these protruding strips  134  be formed in positions close to the protruding portions  144 . For this purposes, the amount of etching liquid that is applied is set at a larger amount on the front upper side (or upper side in  FIG. 3B ) of the thin plate, and at a smaller amount on the back (or lower) side. It is also possible that the width of the resist  122  on the front side be set at a width that is narrower than the width of the resist  124  on the back side.  
         [0077]     When etching is completed, the resists  122  and  124  on the front surface and back surface are removed (step S 208 ).  
         [0078]     Next, pressing is performed (step S 210 ). This pressing work uses a lower mold  136  and an upper mold  138  as shown in  FIG. 3C . These molds  136  and  138  have substantially the same cross-sectional shapes as the molds  22  and  24  shown in the above-described  FIG. 15 . In other words, the lower mold  136  is flat, and the upper mold  138  has grooves  140  and beveled faces  142 .  
         [0079]     The grooves  140  of the upper mold are aligned with the bridging-portions  130 , and then the upper mold  138  is lowered and pressed toward the lower mold  136 ; as a result, the bridging-portions  130  are deformed as shown in  FIG. 3D . More specifically, the lower portions of the bridging-portions  130  protrude along the beveled faces  142  of the upper mold  138 , and these protruding portions  144  are squeezed in the gaps between the upper and lower molds  138  and  136 , so that ribs  130 A that have a cross-sectional shape that is substantially the shape of an inverted umbrella or an inverted T are formed as shown in  FIG. 3E . The blade surface sides (the bottom side in  FIG. 3E ) of these protruding portions  144  protrude sufficiently further in the direction of the blade surfaces than the blade surfaces that are after the finishing-work, so that grinding can be performed sufficiently when the outer circumferential surface is ground in a subsequent process (step S 216 ).  
         [0080]     In this embodiment, the position j of the dot symbol in the vicinity of the protruding strip  134  shown in  FIG. 3B  is caused to move into the protruding portions  144  by the pressing work; however, the amount of this movement is extremely small. In other words, the amount of plastic deformation is small. Accordingly, braking and cracking do not tend to occur internally.  
         [0081]     The thus pressed ribs  130 A are formed as a result that the bridging-portions  130  which are connected at both ends to the side edge portions  128  (see  FIG. 8 ) are worked. A plate-form intermediate worked member  102 A that has thus been worked and obtained is deep drawn into an arch-form shape (step S 212 ). More specifically, deep drawing is performed as shown in  FIG. 5  about a centerline  150  that passes through the center in the direction of width (see  FIG. 8 ,) and is parallel to the reciprocating direction of the inner cutter  102 .  FIG. 5  is a sectional View taken along the line  152  in  FIG. 8  after arch-form shaping.  
         [0082]     The outer circumferential surface of the intermediate worked member  102 B that has thus been deep drawn into an arch-form shape as shown in  FIG. 5  is ground and finished (step S 216 ) after being quenched (step S 214 ). As a result, the ribs  130 A formed after the pressing work of the bridging-portions  130  make cutter blades  130 B, as seen in  FIG. 6 , that has blade surfaces  154  on the outer circumferential surfaces. Both edges of the blade surfaces  154  of these cutter blades  130 B protrude in the form of eaves, and the tip ends of these eaves form cutting edges  156 . The rake angle α of the cutting edges  156  is an acute angle.  
         [0083]     In the above process, when the flat plate form intermediate worked member  102 A ( FIG. 8 ) is deep drawn and worked into an arch-shaped intermediate worked member  102 B shown in  FIG. 5  (step S 212 ), side edges of the protruding portions  144  are pulled toward the inner circumferential side; accordingly, the outer circumferential surfaces of the protruding portions  144  inevitably bend in a plane perpendicular to the direction of length of the ribs  130 A. In the present invention, however, the amount of protrusion of the protruding portions  144  toward the blade surface is sufficiently ensured; accordingly, the outer circumferential surfaces are ground to make surfaces parallel to the reciprocating direction of the inner cutter in the subsequent grinding process (step S 216 ).  
         [0084]     In the above embodiment, in order to prevent chipping of the eave-form cutting edges  156 , reinforcing portions  158  are formed so as to support the eaves from the inside (see  FIGS. 5, 6  and  7 ). The reinforcing portions  158  can be formed by using a mold in which a plurality of sub-grooves  160  (see  FIGS. 3C, 3D  and  3 E) for forming these reinforcing portions  158  are formed at an appropriate spacing (in five locations in  FIG. 5 ) for each cutter blade  130 B in each one of the grooves  140  of the upper mold  138  ( FIG. 3 ) that is used for the pressing work (step S 210  in  FIG. 4 ). With the thus formed reinforcing portions  158 , it is possible to make the rake angle α of the cutting edges  156  further acute angle, so that the inner cutter has improved sharpness.  
         [0085]     In the above-described embodiment, as is clear from  FIG. 8 , the cutter blades  130 B (bridging-portions  130 , ribs  130 A) have a rectilinear shape that is perpendicular to the reciprocating (or lateral) direction (in the direction of extension of the center line  150 ) of the inner cutter  102 . However, the cutter blades  130 B are not limited to such a shape, and various configurations are possible.  FIGS. 9 through 13  show the cutter blades of various configurations. In  FIGS. 9 through 13 , the inner cutters are shown unfolded as in the same manner as in  FIG. 8 .  
         [0086]     In the inner cutter  102   a  shown in  FIG. 9 , the cutter blades  130   a  are inclined at a fixed angle with respect to the reciprocating (lateral) direction of the inner cutter  102   a . In this embodiment, the cutter blades  130   a  cut the hair obliquely, and the cutter blades  130   a  have improved sharpness.  
         [0087]     In the inner cutter  102   b  shown in  FIG. 10 , some of the cutter blades  130   b  (those in the right half of  FIG. 10 ) have a wave-shape. In this embodiment, the length of the wave-shape cutter blades  130   b  can be smaller than the length of the cutter blades  130   a  in  FIG. 9 . The wave-shape cutter blades  130   b  have an increased strength compared to the strength of the cutter blades in  FIG. 9 .  
         [0088]     The inner cutter  102   c  shown in  FIG. 11  has a plurality of bent regions (three bent regions) p, q and r that are different in inclinations with respect to the reciprocating (lateral) direction of the inner cutter  102   c . In the central bent region q, the cutter blades are inclined and the inclination of adjacent cutter blades  130   c  varies slightly next to each other; and in the other regions p and r at both ends, the cutter blades are perpendicular to the reciprocating (lateral) direction of the inner cutter. Accordingly, when adjacent cutter blades  130   c  within the region q cut across the same hair introduction opening of an outer cutter, these cutter blades contact the same hair at different angles, so that the positions of the opening edges of the outer cutter contacted by the hair are varied. As a result, it is possible to extend the useful life of the outer cutter and to improve the sharpness.  
         [0089]     In the inner cutter  102   d  shown in  FIG. 12A , deformed portions  162  that have different width in the reciprocating (lateral) direction are formed in the cutter blades  130   d , and positions of these deformed portions  162  are varied in the direction of length of adjacent cutter blades  130   d  (i.e., in the direction perpendicular to the reciprocating (lateral) direction).  FIG. 12A  shows the inner cutter  102   d  unfolded, and  FIGS. 12B and 12C  show the deformed portions  162  in enlarged view. The deformed portions  162  of the cutter blades  130   d  in the right half of  FIG. 12A  have a substantially oval ring shape as shown in  FIG. 12B , while the deformed portions  162 ′ of the cutter blades  130   d ′ in the left half of  FIG. 12A  have a substantially diamond ring shape as shown in  FIG. 12C . In this inner cutter  102   d , the shapes of the cutter blades  130   d  and  130   d ′ are different in the right half and left half; however, this is mere an example of two different shapes that can be taken as the shape of the deformed portions in the cutter blades.  
         [0090]      FIG. 13A  shows the unfolded inner cutter  102   e  of still another embodiment of the present invention, and  FIG. 13B  is an enlarged view of a part of the cutter blades  130   e  and  130   e ′ of this inner cutter  102   e . In this embodiment, among the adjacent cutter blades  130   e  and  130   e ′, the cutter blades  130   e  are in a rectilinear shape that is perpendicular to the reciprocating (lateral) direction of the inner cutter  102   e , while the other cutter blades  130   e ′ are formed with deformed portions  164  in an oval ring shape.  
         [0091]     In the inner cutters shown in  FIGS. 12A and 13A , when adjacent cutter blades  130   d  and  130   d ′ or  130   e  and  130   e ′ cut across the same hair introduction opening of the outer cutter, the inclination angle (intersection angle) is different. Accordingly, the outer cutter has extended useful life and improved sharpness.  
         [0092]     In the present invention, cutter blades that have complicated shapes such as those shown in  FIGS. 10 through 13 B can be formed.