Patent Publication Number: US-2009223270-A1

Title: Press, method for manufacturing the metal plate, method for manufacturing the liquid spray head, method for manufacturing the liquid spray apparatus

Description:
The entire disclosure of Japanese Patent Application No. 2008-050903, filed Feb. 29, 2008 is incorporated by reference herein. 
     The entire disclosure of Japanese Patent Application No. 2008-055445, filed Mar. 5, 2008 is incorporated by reference herein. 
     The entire disclosure of Japanese Patent Application No. 2009-032813, filed Feb. 16, 2009 is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressing apparatus, a metal plate manufacturing method, a method for manufacturing a liquid spray head, and a method for manufacturing a liquid spray apparatus. In particular, the invention can be suitably applied to the manufacturing of a liquid spray head nozzle plate through which minute through holes are formed. 
     2. Related-Art Invention 
     For example, a filter that is used for filtering liquid that flows in a flow channel of a liquid spray head is made of a thin metal plate (e.g., stainless plate) through which a plurality of through holes each having a very small diameter is formed. The liquid spray head discharges liquid that is retained in a pressure chamber from a nozzle opening in the form of a liquid drop by making a pressure change occur in the liquid retained therein. A few examples of methods for forming holes through a metal plate are an etching method and a press working (plastic working) method, the latter of which uses a metal mold. 
     As an example of the press working method explained above, a method for forming a through hole that functions as a nozzle opening in a final product by pressing a punch into a thin metal plate, which is the raw material of a nozzle plate, from one surface side of the thin metal plate and thereafter by removing a bulged part that is formed at the other surface side of the thin metal plate that is opposite to the one surface side thereof in a subsequent grinding process is proposed in Japanese Unexamined Patent Application Publication No. 2007-137039 (e.g., Patent Document 1). 
     When a small hole is formed in a thin metal plate by means of the conventional metal plate working method explained above, in some cases, a ring-shaped bump is formed at the peripheral edge of the hole. 
     The reason why such a ring-shaped peripheral elevation is formed is that, when a punch is pressed into a metal plate and makes its way in the metal plate, a part of metal material that is pressed and thus yields to the punching pressure of the punch moves to the peripheral edge of the hole (which can be called as escape of metal material). In order to remove such a bump, a process of lapping the bulged surface and thereby forming it into a smooth surface is required in the conventional method. 
     In view of the foregoing, the present invention has been made with an aim to provide a metal plate pressing apparatus, a metal plate manufacturing method, a method for manufacturing a liquid spray head, and a method for manufacturing a liquid spray apparatus that makes it possible to prevent a bump from forming on a punched-side surface. 
     SUMMARY OF THE INVENTION 
     In order to achieve the objective described above, a pressing apparatus according to an aspect of the invention, which performs plastic working by pressing a punch into a metal material plate, includes: a rough part that is formed at least at a front-end-side area of an outer surface of the punch that is brought into contact with the metal material plate, the level of surface roughness of the rough part being greater than that of other area part. 
     With the configuration described above, since the pressing apparatus performs plastic working by pressing a punch into a metal material plate and includes a rough part that is formed at least at a front-end-side area of an outer surface of the punch that is brought into contact with the metal material plate, the level of surface roughness of the rough part being greater than that of other area part, as the punch makes its way in the metal plate, the rough part of the punch causes the punched part of the metal plate (metal material) to move (i.e., be drawn) in the punching direction by a strong frictional force. Consequently, it is possible to ensure that the metal (material) escapes in the punching direction. Therefore, it is possible to avoid the formation of a bump at the peripheral edge of a hole on the punched-side surface of the metal material plate, thereby saving the trouble of removing the bump formed thereon. In addition, it is possible to prevent the degree of circularity of a minute hole from decreasing, which might otherwise occur if the formed bump collapses and becomes deformed under pressure applied by a metal mold or the like. 
     It is preferable that a pressing apparatus having the configuration described above should further include a smooth part that is formed at a base-end-side area that is located at a relatively base-end side in comparison with the area of the rough part, the smooth part being smoother than the rough part, wherein the diameter of the rough part is not larger than that of the smooth part. 
     With the configuration described above, since the pressing apparatus further includes a smooth part that is formed at a base-end-side area that is located at a relatively base-end side in comparison with the area of the rough part, the smooth part being smoother than the rough part, wherein the diameter of the rough part is not larger than that of the smooth part, it is possible to use an existing punch just by working the outer surface of the existing punch so as to increase the surface roughness level thereof. In addition, it is possible to easily form the rough part not throughout an outer surface of the punch but only on a surface that is necessary to be subjected to surface roughening. 
     In the configuration described above, it is preferable that the punch should be inserted up to a point where the rough part goes beyond one surface of the metal material plate that is opposite to the other surface thereof that is provided at a side at which the insertion of the punch into the metal material plate is started. 
     With the configuration described above, since the punch is inserted up to a point where the rough part goes beyond one surface of the metal material plate that is opposite to the other surface thereof that is provided at a side at which the insertion of the punch into the metal material plate is started, it is less likely that a pattern of streaks (impression) is formed in the metal material plate along the punching direction as the imprinted copy of the rough shape of the rough part within the range of the plate thickness of the metal material plate. In addition, even when such an imprinted pattern is formed therein, it is possible to smooth away the streaks because of smoothening pressure applied by the smooth surface. Thus, the punch-worked surface of the metal material plate is smooth when viewed within the range of the plate thickness of the metal material plate, thereby eliminating a need for another separate process of removing the imprinted copy of the roughness of the rough part within the range of the plate thickness of the metal material plate. 
     In the configuration described above, it is preferable that the punch should include a straight part that is uniform in outer diameter from the front end of the punch toward the base end thereof; and that the rough part should be formed at least at a front-end-side area of an outer surface of the straight part whereas the smooth part should be formed at a base-end-side area that is located at a relatively base-end side in comparison with the area of the rough part. 
     The term “uniform” in the outer diameter of the punch means that the diameter is substantially the same throughout it with some allowable margin of error, for example, to the extent of the roughness of the rough part or so. 
     With the configuration described above, since the punch includes a straight part that is uniform in outer diameter from the front end of the punch toward the base end thereof; and the rough part is formed at least at a front-end-side area of an outer surface of the straight part whereas the smooth part is formed at a base-end-side area that is located at a relatively base-end side in comparison with the area of the rough part, it is possible to ensure that the rough part that is formed on the straight part draws a part of the metal material plate that has been brought into contact with the punch in the punching direction. On the other hand, the smooth surface of the smooth part is copied on a part of the metal material plate that is in contact with the smooth part without being in contact with the rough part. Thus, this part of the metal material plate is formed to be smooth. 
     In the configuration described above, it is preferable that the punch should include a tapered part that is formed at a relatively base-end side in comparison with the area of the straight part; the diameter of the tapered part should gradually increase from the front-end side toward the base-end side; and the rough part should be formed in the outer surface of the tapered part. 
     With the configuration described above, since the punch includes a tapered part that is formed at a relatively base-end side in comparison with the area of the straight part; the diameter of the tapered part gradually increases from the front-end side toward the base-end side; and the rough part is formed in the outer surface of the tapered part, when punching pressure is applied to the metal material plate, the rough part presses the material of the metal material plate in the punch-pressing direction and thus prevents the material of the metal material plate from moving toward the punched-side surface. By this means, it is possible to avoid the formation of a bump at the peripheral edge of a hole on the punched-side surface of the metal material plate with greater reliability. 
     In the configuration described above, the rough part may be pear-peel finished. 
     A metal plate manufacturing method according to an aspect of the invention is a method for manufacturing a metal plate by forming a hole as a result of pressing a punch into a metal material plate, the metal plate manufacturing method including: a first step of forming a hole by pressing, into the metal material plate, the punch that includes a rough part that is formed at least at a front-end-side area of an outer surface of the punch that is brought into contact with the metal material plate, the level of surface roughness of the rough part being greater than that of other area part. 
     Since the metal plate manufacturing method includes a first step of forming a hole by pressing, into the metal material plate, the punch that includes a rough part that is formed at least at a front-end-side area of an outer surface of the punch that is brought into contact with the metal material plate, the level of surface roughness of the rough part being greater than that of other area part, as the punch makes its way in the metal plate, the rough part of the punch causes the punched part of the metal plate (metal material), which is pressed and thus yields to the punching pressure of the punch, to move in the punching direction by a strong frictional force. Consequently, it is possible to ensure that the metal (material) escapes in the punching direction. Therefore, it is possible to avoid the formation of a bump at the peripheral edge of a hole, thereby saving the trouble of removing the bump formed thereon, which must be done if a conventional method is used. As a consequence thereof, it is possible to easily manufacture a metal plate in which holes are formed by plastic working. In addition, it is possible to prevent the degree of circularity of a hole from decreasing, which might otherwise occur if the formed bump collapses and becomes deformed under pressure applied by a metal mold or the like. 
     In the metal plate manufacturing method described above, in the first step, the punch may be inserted up to a point where the rough part goes beyond one surface of the metal material plate that is opposite to the other surface thereof that is provided at a side at which the insertion of the punch into the metal material plate is started. 
     With the feature described above, in the first step, since the punch is inserted up to a point where the rough part goes beyond one surface of the metal material plate that is opposite to the other surface thereof that is provided at a side at which the insertion of the punch into the metal material plate is started, when the punch is pressed into the metal material plate and makes its way in the metal material plate, the smooth part applies smoothening pressure to the rough surface formed as the imprinted copy of the rough shape of the rough part. Therefore, it is possible to smoothen the inner circumferential surface of a hole that is formed in the metal material plate. 
     It is preferable that the metal plate manufacturing method described above should further include a second step of removing a bulged part that is formed around the hole formed in the first step on the one surface of the metal material plate that is opposite to the other surface thereof that is provided at the side at which the insertion of the punch into the metal material plate is started. 
     The metal plate manufacturing method described above further includes a second step of removing a bulged part that is formed around the hole formed in the first step on the one surface of the metal material plate that is opposite to the other surface thereof that is provided at the side at which the insertion of the punch into the metal material plate is started. Therefore, it is possible to form the hole into a through hole by grinding away the bulged part that was formed on the reverse face of the metal material plate. In addition, it is possible to form the thickness of the metal material plate into a predetermined thickness. 
     The metal plate manufacturing method described above may further include a third step of surface treatment. 
     With the metal plate manufacturing method described above, when the shape of the rough part of the punch is imprinted on the inner circumferential surface of the hole, during the process of liquid-repellent treatment of the metal material plate, it is possible to make it easier to apply liquid for surface treatment and to perform the surface treatment easily. 
     A method for manufacturing a liquid spray head according to an aspect of the invention is characterized in that a metal plate that has been worked by means of the metal plate manufacturing method explained above is mounted as a nozzle plate from the hole of which liquid is ejected. A method for manufacturing a liquid spray apparatus according to an aspect of the invention is characterized in that the liquid spray head described above is mounted so as to eject liquid from the liquid spray head. 
     With the manufacturing methods explained above, since a metal plate through which holes each having high degree of circularity are formed is used as a nozzle plate, it is possible to achieve excellent liquid-traveling performance, that is, the traveling of a liquid drop in air, when the liquid drop is ejected from a nozzle opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an essential-part sectional view that illustrates the configuration of a recording head. 
         FIG. 2  is an exploded perspective view that illustrates the configuration of a fluid channel unit. 
         FIG. 3  is a sectional view that illustrates a nozzle opening that is formed through a nozzle plate. 
         FIG. 4  is a sectional view that illustrates the essential part of the configuration of a pressing apparatus according to a first embodiment of the present invention. 
         FIG. 5  is an enlarged sectional view of the surface of a punch. 
         FIG. 6  is an essential-part sectional view that illustrates punching work that is performed by the pressing apparatus illustrated in  FIG. 4 . 
         FIG. 7  is a sectional view that illustrates a metal plate after the removal of a bulged part thereof. 
         FIG. 8  is a sectional view that illustrates the essential part of the configuration of a pressing apparatus according to a second embodiment of the present invention. 
         FIG. 9  is an essential-part sectional view that illustrates punching work that is performed by the pressing apparatus illustrated in  FIG. 8 . 
         FIG. 10  is an enlarged sectional view that illustrates punching work according to a third embodiment of the present invention. 
         FIG. 11  is a sectional view that illustrates a metal plate after the removal of a bulged part thereof. 
         FIG. 12  is an enlarged sectional view that illustrates punching work according to a fourth embodiment of the present invention. 
         FIG. 13  is a sectional view that illustrates the essential part of the configuration of a pressing apparatus according to a fifth embodiment of the present invention. 
         FIG. 14  is a diagram that illustrates the configuration of an ink-jet printer. 
     
    
    
       1  Recording Head,  10  Nozzle Opening,  13  Nozzle Plate,  30  Pressing Apparatus,  31  Metal Plate,  36  Punch,  40  Hole,  43  Small-diameter Straight Part,  46  Tapered Part,  47  Rough Surface Part,  48  Smooth Surface Part 
     EXPLANATION OF PREFERRED EMBODIMENTS 
     With reference to the accompanying drawings, the best mode for carrying out the present invention will now be explained below. Although various specific features are explained in the following exemplary embodiments of the present invention in order to disclose preferred modes thereof, the invention should be in no case interpreted to be limited to the specific embodiments described below unless any intention of restriction is explicitly shown. In the following explanation, a nozzle plate that is used in an ink-jet recording head (which is a kind of a liquid spray head and is hereafter simply referred to as recording head  1 ) mounted on an ink-jet recording apparatus, which is an example of a liquid spray apparatus, is taken as an example of a metal plate, which is a workpiece according to exemplary embodiments of the present invention. 
     First of all, an explanation is given below of the configuration of the recording head  1 . 
       FIG. 1  is an essential-part sectional view that illustrates the configuration of the recording head  1 . In the schematic configuration thereof, the recording head  1  is provided with a filter assembly  5  that includes an ink inlet needle  2 , a filter  3 , an inlet needle unit  4 , and the like, and is further provided with a head unit  9  that includes a head case  6 , a vibrator unit  7  that is encased therein, a fluid channel unit  8 , and the like. An ink flow channel (which is a kind of a liquid flow channel) that leads from an ink cartridge, which is a kind of a liquid supply source, to a nozzle opening  10  of the fluid channel unit  8  is formed inside the recording head  1 . 
     As illustrated in  FIG. 2 , the fluid channel unit  8  is bonded to the front-end surface of the case head  6  with a vibration plate  11 , a fluid channel formation substrate  12 , and a nozzle plate  13  being formed to have a layered structure. 
     The nozzle plate  13 , which is provided at the bottom of the fluid channel unit  8 , is a thin metal plate through which the plurality of nozzle openings  10  is formed with the array pattern of a plurality of lines having a pitch corresponding to a dot formation density (e.g., 180 dpi). The nozzle plate  13  according to the present embodiment of the invention is made of a stainless steel plate material (a metal material plate according to an aspect of the present invention). The plurality of lines of the nozzle openings  10  (i.e., the plurality of nozzle lines) is arrayed in the scanning direction of the recording head  1 . Each of the plurality of nozzle lines is made up of, for example, one hundred eighty nozzle openings  10 . A method for manufacturing the nozzle plate  13  will be explained in detail later. As illustrated in  FIG. 3 , the nozzle opening  10  according to the present embodiment of the invention is a hole that is formed through the nozzle plate  13  in the thickness direction A of the fluid channel formation substrate  12  and the nozzle plate  13 . The nozzle opening  10  is made up of a tapered part  24  and a straight part  25 . The diameter of the tapered part  24 , which is formed at the fluid-channel-formation-substrate ( 12 ) side, decreases gradually. The straight part  25 , which has a uniform diameter, is in communication with the minimum-diameter part of the tapered part  24 . In  FIG. 3 , the reference symbol A 1  denotes the length of the tapered part  24  when viewed in the axial direction, whereas the reference symbol A 2  denotes the length of the straight part  25 . 
     The fluid channel formation substrate  12  is a member that is layered between the nozzle plate  13  and the vibration plate  11 . Cavities that include a common ink chamber  15 , an ink supply port  16 , a pressure chamber  17 , and the like are formed inside the fluid channel formation substrate  12 . These cavities function as an ink flow passage as a whole. The common ink chamber  15  is a kind of a common liquid chamber. The fluid channel formation substrate  12  is manufactured by, for example, etching a silicon wafer. The nozzle plate  13  and the vibration plate  11  seal the openings of each of the cavities mentioned above. 
     The vibration plate  11  is a plate member that is provided between the fluid channel formation substrate  12  and the head case  6 . The vibration plate  11  is configured as a complex plate having a dual-layer structure, which is made up of a supporting plate  21  that is made of a metal such as a stainless steel or the like and an elastic film  22  that is laminated thereon. An island part  19  is formed at a partial region of the vibration plate  11  that is opposite the pressure chamber  17  by, for example, etching away a part of the supporting plate  21  so as to form a ring-shaped region. The front-end surface of the free end of a piezoelectric vibration element  18  is connected to the island part  19 . With such a configuration, this part functions as a diaphragm. That is, the vibration plate  11  is formed so that, as the piezoelectric vibration element  18  operates, the elastic film  22  around the island part  19  deforms elastically. In addition, a part of the vibration plate  11  functions as a compliance part  20 , which seals the opening of the common ink chamber  15  of the fluid channel formation substrate  12 . A partial region of the vibration plate  11  that functions as the compliance part  20  is made up of the elastic film  22  only after etching away, or removing by means of any alternative method other than etching, a part of the supporting plate  21  as done so for the formation of the diaphragm part described above. 
     The recording head  1 , which has an exemplary configuration explained above, can record an image or the like as follows. Upon the activation of the piezoelectric vibration element  18 , a pressure change occurs inside the pressure chamber  17 . As a result of the pressure change, ink that flowed from an ink cartridge into the pressure chamber  17  through the ink flow passage and is now retained inside the pressure chamber  17  is discharged from the nozzle opening  10  as an ink drop. The ink drop discharged through the nozzle opening  10  lands on a sheet of recording paper, which is an example of a recording target medium. In this way, the recording head  1  can perform image recording. 
     Next, with reference to  FIGS. 4-7 , a method for manufacturing the nozzle plate  13  through the plastic working of a pressing machine  30  according to the present embodiment of the invention is explained below.  FIG. 4  is a sectional view that illustrates the essential part of the configuration of the pressing apparatus  30 . 
     In the schematic configuration thereof, the pressing apparatus  30  according to the present embodiment of the invention includes a die  32 , a base  33 , a pressing board  35 , and a punch  36 . A metal plate  31  (metal material plate), which is the raw material of the nozzle plate  13 , is placed on the die  32 . The base  33  is mounted on the lower surface of a ram (which is not illustrated in the drawing). The pressing board  35  is provided under the base  33  with an elastic material  34  such as a spring, elastomer, or the like being provided between the base  33  and the pressing board  35 . With such a structure, the pressing board  35  can move upward/downward with respect to the base  33 . The punch  36  is provided in a downward orientation with its base end being fixed to the base  33 . 
     For example, the metal plate  31  is a plate that is made of invar alloy and has a thickness of 30-100 μm or so. The invar alloy of the metal plate  31  has substantially the same coefficient of linear expansion as that of the fluid channel formation substrate  12  explained earlier. An example of such alloy is “42 Alloy”. Through the adjustment of the nickel content thereof, the metal plate  31  is formed so as to have a coefficient of linear expansion that is approximately equal to that of the fluid channel formation substrate  12 . Therefore, it is possible to prevent the nozzle plate  13  from becoming warped when, after the heat bonding of the fluid channel formation substrate  12  to the metal plate  31  or vice versa with the use of a thermosetting resin having thermo-hardening property or the like at the temperature of 200-300° C., it is cooled down to room temperature, thereby making it further possible to prevent the nozzle plate  13  from coming off the fluid channel formation substrate  12 . 
     The die  32  has punch insertion holes  41  each of which has a diameter that is larger than the diameter of a hole (punch hole)  40  that is to be formed in the metal plate  31 . The die  32  functions as a female mold that is provided for the punch  36 , which functions as a male mold. A guiding through hole  42  is formed through the pressing board  35 . The diameter of the guiding through hole  42  is larger than that of the punch  36 . Apart of the punch  36  from the front end thereof to the middle body thereof is inserted through the guiding through hole  42 . 
     The punch  36  has the shape of a pillar. The punch  36  has a punch body part  45  and a tapered part  46 . The punch body part  45  of the punch  36  is provided at the base ( 33 ) side (base-end side). The tapered part  46  of the punch  36  extends from the front-end part of the punch body  45  thereof. The punch body part  45  has a columnar shape, which is uniform in its outer diameter from the base end thereof to the front end thereof when viewed along the punching direction of the punch  36  (which is shown by an arrow K in  FIG. 4 ). The outer diameter of the punch body part  45  of the punch  36  is 20-30 μm. Roughly speaking, the tapered part  46  has the shape of a truncated cone that has a gentle contour curve in its cross section and has an outer diameter that gradually decreases toward the front end thereof. The front-end part of the tapered part  46  is formed as a small-diameter straight part  43  (which is a kind of a straight part according to an aspect of the present invention). The small-diameter straight part  43  has a columnar shape, which is uniform in its outer diameter from the rear end thereof to the front end thereof when viewed along the punching direction K of the punch  36 . The front-end surface of the small-diameter straight part  43  is flat. 
     A rough surface part  47  (which is a kind of a rough part according to an aspect of the present invention) is formed at least at the front-end-side surface area of the outer surface of the punch  36  that is brought into contact with the metal plate  31 . The level of the surface roughness of the rough surface part  47  is greater than that of other area part. That is, the rough surface part  47  is not formed throughout the outer surface of the punch  36  but formed at the front-end-side surface area thereof, which is a part that is brought into contact with the metal plate  31  when the punch  36  is punched into the metal plate  31 . The rough surface part  47  according to the present embodiment of the invention, which is illustrated in  FIG. 4 , is formed throughout the surface areas of the small-diameter straight part  43 , the tapered part  46 , and the front-end area part of the punch body part  45 . For example, the surface roughness Ra of the rough surface part  47  is 0.6 μm or greater. The rough surface part  47  is formed so as to increase a coefficient of friction that works when the punch  36  is punched into the metal plate  31 . Any kind of surface treatment may be applied so as to form the rough surface part  47  as long as a frictional force that acts on the metal plate  31  is increased thereby. In the present embodiment of the invention, as illustrated in  FIG. 5 , a minute uneven pattern is formed in the outer surface of the punch  36  through surface treatment such as arc, blast, etching, or the like, where such minute ruggedness is formed by concaving the outer surface of the punch  36  toward the axial center of the punch  36  at each concavity. Specifically, after the cutting and machining of a round bar steel, which is the material of the punch  36 , with the use of a lathe, the circumference surface of the punch  36  is subjected to surface working so that the level of the surface roughness of the contour face of the punch  36  after the surface treatment is greater than the level of the surface roughness of the contour face of the punch  36  immediately after the cutting and machining thereof. As a result, the diameter of the concavity thereof thereafter is smaller than that of the original surface before the working. Therefore, in the configuration of the punch  36  according to the present embodiment of the invention, the diameter of the rough surface part  47  is not larger than that of a smooth surface part  48 . Note that shot peening may be used so as to form a so-called pear-peel finished surface, which is a surface on which fine irregularities are formed. 
     Next, an explanation is given below of a punching process (a first step) that is performed with the use of the pressing machine  30  that has the configuration explained above. It is assumed herein that the die  32  is fixed on a supporting stage of the pressing machine  30  such as a bolster or the like that is not illustrated in the drawing and that the base  33  is mounted on the lower surface of a ram. In addition, it is further assumed herein that all tryout mold adjustments such as the adjustment of the relative positions of the die  32  and the base  33  (punch  36 ), the adjustment of the bottom dead point of the punch  36 , and the like have been completed in advance. 
     First of all, the metal plate  31  that is made of 42 Alloy or the like is placed on the die  32  at a predetermined set position. Then, with the front end of the punch  36  being oriented toward the metal plate  31 , the base  33  is lowered. As a result, as illustrated in  FIG. 4 , the lower surface of the pressing board  35  is brought into contact with the surface of the metal plate  31 . Thereafter, the base  33  is further moved downward against the urging force of the elastic member  34 . As the base  33  is further lowered, the front-end part of the punch  36  is pushed into the metal plate  31  as guided through the guiding through hole  42  of the pressing board  35 . Thereafter, the punch  36  is further lowered to the bottom dead point. By this means, as illustrated in  FIG. 6 , a hole  40  that has a mating shape as the counterpart copy of the shape of the punch  36  is formed in the metal plate  31 . In this process, as the punch  36  makes its way, the metal material of the punched part of the metal plate  31  that is pressed and thus yields to a punching force of the punch  36  mainly moves (i.e., is drawn) toward the front-end side of the punch  36  in the direction K (i.e., plate thickness direction), which is indicated with an arrow in the drawing. As a result, the most part thereof bulges on the reverse face  31   b  of the metal plate  31  so as to form a bump  49 . On the other hand, even if the metal plate  31  is made of a relatively soft material such as 42 Alloy or the like, no bulged part is formed on the front face  31   a  of the metal plate  31 , which is the punched-side surface, unlike conventional art according to which a bulged part is formed also on the front face of a metal plate when a conventional punch (whose surface is not rough) is punched therein. 
     More specifically, as the punch  36  gradually makes its way deeper into the metal plate  31  from the front face  31   a  thereof, the metal material of the front-face ( 31   a ) part (at a side at which the punching insertion of the punch  36  is started) of the metal plate  31  and in the neighborhood thereof is pressed by the rough surface part  47  of the punch  36  and thus yields thereto so as to move in the arrowed direction K as drawn thereby. That is, since the punch  36  moves deeper and deeper into the metal plate  31  while drawing the part of the metal material of the metal plate  31  in the arrowed direction K by the rough surface part  47  thereof, the bulged part  49  only is formed on the reverse face  31   b  of the metal plate  31 , which is opposite to the front face  31   a  thereof, without forming any other bulged part around the punched area on the front face  31   a  thereof (that is, no bump is formed at the punched front-face  31   a  side). 
     In this way, the hole  40  that has the same shape as that of the punch  36  is formed in the metal plate  31 . Note that the hole  40  illustrated in  FIG. 6 , which is formed in the metal plate  31 , is not a through hole. After the formation of the hole  40 , the bulged part  49  is removed in a grinding process, which will be explained later. As a result, the hole  40  is formed into the nozzle opening  10 , that is, into a through hole. 
     After the formation of the funnel-shaped hole  40  in the metal plate  31  through the downward movement of the punch  36  to its bottom dead point, the punch  36  is moved upward. As the base  33  moves upward together with the upward movement of the ram, the pressing board  35  starts to move upward at a point in time that is slightly later than the start of the upward movement of the base  33  due to the returning of the elastic material  34  to its original form. Then, the pressing board  35  comes away from the surface of the metal plate  31  and goes up to its top dead point. In this way, a series of punching operations for one hole ends. 
     Then, a feeder moves the metal plate  31  by a predetermined pitch for the purpose of carrying out the next punching. After the movement of the metal plate  31 , a series of punching operations explained above is performed again so as to form the next hole  40  through the metal plate  31  at the predetermined pitch. Through the repetition of the operations explained above, it is possible to sequentially form the plurality of holes  40  through the metal plate  31  at the predetermined pitch. 
     After the completion of the punching process, the metal plate  31  is demounted from the pressing machine  30  and then is transported to a grinding machine (which is not shown in the drawing). The grinding machine carries out a bump removal process (a second step) as the next step. In the bump removal process, the bulged part  49 , which was formed during the punching process on the reverse face  31   b  of the metal plate  31 , is ground away. As illustrated in  FIG. 7 , the bump  49  is removed in this grinding process so as to form the hole  40  into the nozzle opening  10 , which is a through hole. In addition, the metal plate  31  is polished so as to make the thickness thereof equal to a predetermined plate thickness. After the bump removal process, a lapping process (processing) is carried out. In the lapping process, a part of the surface of the metal plate  31  that was brought into contact with the rough surface part  47  of the punch  36  (more specifically, a rugged pattern of the inner circumferential surface of the nozzle opening  10  that was formed at the surface area thereof corresponding to the rough surface part  47  of the punch  36  as a result of the imprinting of, that is, as the transferred counterpart copy of, the rugged shape of the rough surface part  47  of the punch  36 ) is removed. Therefore, even when a pattern of streaks (impression)  50  is formed in the surface of the metal plate  31  along the punching direction that is shown by the arrow K as the imprinted copy of the rugged shape of the rough surface part  47  of the punch  36 , the streaks  50  are smoothed away in this process so as to ensure that the inner circumferential surface of the nozzle opening  10  is not rough. In this way, the nozzle plate  13  through which the nozzle openings  10  are formed is manufactured. 
     As explained above, since the rough surface part  47  whose surface roughness level is greater than that of a base-end-side part of the outer surface of the punch body part  45  is formed in the outer surface of the punch  36  of the pressing machine  30  according to the present embodiment of the invention, as the punch  36  makes its way in the metal plate  31 , the rough surface part  47  of the punch  36  causes the punched part of the metal plate  31  (metal material), which is pressed and thus yields to the punching pressure of the punch  36 , to move (i.e., be drawn) in the direction K that is indicated with the arrow in the drawing. Consequently, it is possible to ensure that the metal (material) escapes in the arrowed direction K in the punching process. Therefore, it is possible to avoid the formation of a bump at the peripheral edge of the hole  40  on the front face  31   a  of the metal plate  31 , thereby saving the trouble of removing the bump formed thereon. As a consequence thereof, it is possible to easily manufacture the metal plate  31  in which the minute holes  40  are formed by plastic working. In addition, it is possible to prevent the degree of circularity of the minute hole  40  from decreasing, which might otherwise occur if a bump that was formed at the peripheral edge of the hole  40  on the front face  31   a  of the metal plate  31  collapses and becomes deformed under the pressure applied by the pressing board  35 . 
     Moreover, if the metal plate  31  that has been worked by the pressing machine  30  described above is mounted as the nozzle plate  13  of the recording head  1  (a fourth step), it is possible to ensure high degree of circularity of the nozzle opening  10 . Because of high degree of roundness of the nozzle opening  10 , it is possible to expect an improvement in the characteristics of the traveling of a liquid drop in air when the liquid drop is ejected from the nozzle opening  10 . 
     Next, with reference to  FIGS. 8 and 9 , an explanation is given below of the punch  36  of the pressing machine  30  according to a second embodiment of the invention. The punch  36  according to the present embodiment of the invention is characterized in that the rough surface part  47  is formed at the front-end-side surface area of a metal-contact part of the outer surface of the punch  36  that is brought into contact with the metal plate  31  when the punch  36  is punched into the metal plate  31 . In addition, the punch  36  according to the present embodiment of the invention is characterized in that a smooth surface part  48  (which is a kind of a smooth part according to an aspect of the present invention) that is smoother than the rough surface part  47  is formed at a base-end-side surface area of the metal-contact part of the outer surface of the punch  36  that is located relatively closer to the base end in comparison with the formation area of the front-end-side rough surface part  47 . Specifically, the rough surface part  47 , which has a rough surface, is formed throughout the surface areas of the front-end area part of the tapered part  46  and the small-diameter straight part  43 , whereas the smooth surface part  48 , which has a relatively smooth surface, is formed throughout the surface areas of the base-end area part of the tapered part  46  and the straight part  45 . That is, the rough surface part  47  is formed at the front-end surface area of the punch  36 , whereas the smooth surface part  48  is formed at a relatively base-end surface area thereof when viewed from the rough surface part  47 . For example, the surface roughness Ra of the rough surface part  47  is 0.6 μm or greater. The surface roughness Ra of the smooth surface part  48  is less than 0.6 μm. 
     Next, an explanation is given below of a punching process (step) that is performed with the use of the pressing machine  30  that has the configuration explained above. In the same manner as in the foregoing first embodiment of the invention, as the punch  36  gradually makes its way deeper into the metal plate  31  from the front face  31   a  thereof, the metal material of the front-face ( 31   a ) part of the metal plate  31  and in the neighborhood thereof is pressed by the rough surface part  47  of the punch  36  and thus yields thereto so as to move in the arrowed direction K as drawn thereby. That is, the punch  36  moves deeper and deeper into the metal plate  31  while drawing the part of the metal material of the metal plate  31  in the arrowed direction K by the rough surface part  47  thereof. In addition, when the punch  36  makes its way in the metal plate  31 , the smooth surface part  48  thereof smoothens the surface of the metal material that has been pressed away. Accordingly, the bulged part  49  only is formed on the reverse face  31   b  of the metal plate  31  without forming any other bulged part around the punched area on the front face  31   a  thereof (that is, no bump is formed at the punched front-face  31   a  side). In addition, although the rugged shape of the rough surface part  47  is imprinted on the inner circumferential surface of the hole  40  that is now being formed in the metal plate  31  when the rough surface part  47  draws the part of the metal material of the metal plate  31  in the arrowed direction K, it is possible to ensure that the smooth surface part  48  smoothens the rugged pattern formed on the inner circumferential surface of the hole  40  thereafter. In this way, the hole  40  that has the same shape as that of the punch  36  is formed in the metal plate  31 . Then, the bulged part  49  is removed in a grinding process. As a result, the hole  40  is formed into the nozzle opening  10 , which is a through hole. 
     Next, with reference to  FIGS. 10 and 11 , an explanation is given below of the punch  36  of the pressing machine  30  according to a third embodiment of the invention. The punch  36  according to the present embodiment of the invention is characterized in that the rough surface part  47  is formed throughout the front-end-side area (denoted as E in  FIG. 10 ) of the circumferential surface of the small-diameter straight part  43  and on the front-end plane of the small-diameter straight part  43 . In addition, the punch  36  according to the present embodiment of the invention is characterized in that the smooth surface part  48  is formed at a base-end-side area of the circumferential surface of the small-diameter straight part  46  that is located relatively closer to the base end in comparison with the formation area of the front-end-side rough surface part  47  and at the surface area of the tapered part  46 . 
     Next, an explanation is given below of a punching process (step) that is performed with the use of the pressing machine  30  that has the configuration explained above. The bottom dead point of the punch  36  according to the present embodiment of the invention has been set at such a position that the rough surface part  47  of the punch  36  passes through the metal plate  31  by a depth that is at least equal to the thickness of the metal plate  31  (where the plate thickness is denoted as D in  FIG. 10 ) when the punch  36  is lowered to its bottom dead point. Specifically, the bottom dead point of the punch  36  according to the present embodiment of the invention has been set at such a position that a combined surface area (which is denoted as “d” in  FIG. 10 ) that is made up of the rough surface part  47 , which is formed in the small-diameter straight part  43  of the punch  36 , and a front-end-side area part of the smooth surface part  48  formed therein passes through the plate thickness D of the metal plate  31 . That is, the bottom dead point of the punch  36  according to the present embodiment of the invention has been set at such a position that, when the punch  36  is lowered to its bottom dead point, the combined surface area “d” that is made up of the rough surface part  47 , which is formed in the small-diameter straight part  43  of the punch  36 , and the front-end-side area part of the smooth surface part  48  formed therein overpasses (goes beyond) the reverse face  31   b  of the metal plate  31 . 
     First of all, the metal plate  31  that is made of 42 Alloy or the like is placed on the die  32  at a predetermined set position. Then, the punch  36  is lowered to the bottom dead point while the front end of the punch  36  is pressed against the metal plate  31  so as to make its way. As a result, as illustrated in  FIG. 10 , the combined surface area “d” that is made up of the rough surface part  47 , which is formed in the small-diameter straight part  43  of the punch  36 , and the front-end-side area part of the smooth surface part  48  formed therein passes through the plate thickness D of the metal plate  31 . As a result, the hole  40  that has an imprinted shape corresponding to the shape of the punch  36  is formed in the metal plate  31 . In this process, as the punch  36  makes its way, the metal material of the punched part of the metal plate  31  that is pressed and thus yields to the punching pressure of the punch  36  mainly moves (i.e., is drawn) toward the front-end side of the punch  36  in the direction K (i.e., plate thickness direction), which is indicated with an arrow in the drawing. As a result, the most part thereof bulges on the reverse face  31   b  of the metal plate  31  so as to form a bump  49 . On the other hand, even if the metal plate  31  is made of a relatively soft material such as 42 Alloy or the like, no bulged part is formed on the front face  31   a  of the metal plate  31 , which is the punched-side surface, unlike conventional art according to which a bulged part is formed also on the front face of a metal plate when a conventional punch (whose surface is not rough) is punched therein. 
     Specifically, as the punch  36  gradually makes its way deeper into the metal plate  31  from the front face  31   a  thereof, the metal material of the front-face ( 31   a ) part of the metal plate  31  and in the neighborhood thereof is pressed by the rough surface part  47  of the punch  36  and thus yields thereto so as to move in the arrowed direction K as drawn thereby. Although the rugged shape of the rough surface part  47  is imprinted on the inner circumferential surface of the hole  40  that is now being formed in the metal plate  31  when the rough surface part  47  draws the part of the metal material of the metal plate  31  in the arrowed direction K, it is possible to ensure that the smooth surface part  48  smoothens the rugged pattern formed on the inner circumferential surface of the hole  40  thereafter. More specifically, a pattern of streaks (impression)  50  is formed in the inner circumferential surface of the hole  40  at an area (which is denoted as “e” in  FIG. 10 , where e&lt;d) corresponding to the area of the rough surface part  47  of the punch  36  that is positioned at the bottom dead point along the punching direction that is shown by the arrow K as the imprinted copy of the rugged shape of the rough surface part  47 . In this way, the hole  40  that has the same shape as that of the punch  36  is formed in the metal plate  31 . Then, the bulged part  49  is removed in a grinding process. As a result, the hole  40  is formed into the nozzle opening  10 , that is, into a through hole. In addition, as a result of the grinding, the inner circumferential surface of the straight part  25  of the nozzle opening  10  is formed as a smooth surface in its entirety. 
     After the completion of the punching process, the metal plate  31  is demounted from the pressing machine  30  and then is subjected to the next bump removal process. In the bump removal process, the bulged part  49 , which was formed during the punching process on the reverse face  31   b  of the metal plate  31 , is ground away. As illustrated in  FIG. 11 , the bump  49  is removed in this grinding process so as to form the hole  40  into the nozzle through hole  10 . In addition, the metal plate  31  is polished so as to make the thickness thereof equal to a predetermined plate thickness. In this way, the pattern of streaks  50  that was formed in the inner circumferential surface of the hole  40  is removed when the bulged part  49  is ground away. As a result, it is possible to manufacture the nozzle plate  13  through which the nozzle openings  10  each having a smooth inner circumferential surface at the straight part  24  and a smooth inner circumferential surface at the tapered part  25  are formed. 
     As explained above, since the rough surface part  47  is formed throughout the front-end-side outer surface of the punch  36  of the pressing machine  30  according to the present embodiment of the invention whereas the smooth surface part  48  is formed at a base-end-side outer surface thereof that is located relatively closer to the base end in comparison with the formation area of the front-end-side rough surface part  47 , as the punch  36  makes its way in the metal plate  31 , the rough surface part  47  of the punch  36  causes the punched part of the metal plate  31  (metal material), which is pressed and thus yields to the punching pressure of the punch  36 , to move (i.e., be drawn) in the direction K that is indicated with the arrow in the drawing. In addition, when the punch  36  makes its way in the metal plate  31 , the smooth surface part  48  thereof smoothens the surface of the metal material that has been pressed away. Consequently, it is possible to ensure that the metal (material) escapes in the arrowed direction K in the punching process. That is, the punch  36  has a front-end-side part that draws the metal material of the metal plate  31  and a relatively-base-end-side part that smoothens the inner circumferential surface of the hole  40  at the base-end side. With such a structure, it is possible to avoid the formation of a bump at the peripheral edge of the hole  40  on the front face  31   a  of the metal plate  31 , thereby saving the trouble of removing the bump formed thereon, which is a necessary step according to conventional art. As a consequence thereof, it is possible to easily manufacture the metal plate  31  in which the minute holes  40  are formed as a result of presswork. In addition, it is possible to prevent the degree of circularity of the minute hole  40  from decreasing because a bump that was formed at the peripheral edge of the hole  40  on the front face  31   a  of the metal plate  31  does not collapse and become deformed under the pressure applied by the pressing board  35 . 
     Moreover, if the metal plate  31  that has been worked by the pressing machine  30  described above is mounted as the nozzle plate  13  of the recording head  1 , it is possible to ensure that the inner circumferential surface of the straight part  25  of the nozzle opening  10  is formed as a smooth surface. Therefore, it is possible to achieve quick vibration of meniscus (i.e., the surface of ink at the opening side) of ink inside the nozzle opening  10 . Thus, it is possible to achieve stable discharging performance for liquid drops that are ejected from the nozzle orifices  10 . 
     In the configuration of the punch  36  of the pressing machine  30  according to the third embodiment of the present invention explained above, the rough surface part  47  is formed at the front-end-side area E of the outer surface of the small-diameter straight part  43 . As illustrated in  FIG. 12 , the punch  36  of the pressing machine  30  according to a fourth embodiment of the present invention may be configured as follows. The rough surface part  47  is formed at the front-end-side area E of the outer surface of the small-diameter straight part  43  whereas the smooth surface part  48  is formed at a base-end-side area of the outer surface of the small-diameter straight part  43  that is located relatively closer to the base end in comparison with the formation area of the front-end-side rough surface part  47 . In addition, another rough surface part  47 ′ is formed in a metal-contact surface area of the tapered part  46  that is brought into contact with the metal plate  31  when the punch  36  is punched into the metal plate  31  (which is denoted as E′ in  FIG. 12 ). 
     Note that the present invention is not limited to the specific embodiments described above. That is, the invention may be modified into a variety of modes on the basis of the recitations of appended claims. 
     In each of the exemplary embodiments of the invention described above, the punch  36  includes the punch body part  45 , the tapered part  46 , and the small-diameter straight part  43 . Notwithstanding the above, however, as illustrated in  FIG. 13 , the pressing machine  30  according to a fifth embodiment of the invention may be configured as follows. The pressing machine  30  according to the fifth embodiment of the invention is provided with a straight unit  55 . A part of the straight unit  55  that is to be punched into a metal plate has a uniform diameter as viewed from the front end thereof. The rough surface part  47  is formed only at the front-end-side area of the circumferential surface of the straight unit  55 . That is, it suffices if the rough surface part  47  is formed at least at a metal-contact area part of the outer surface of the punch  36  that is brought into contact with the metal plate  31  when the punch  36  is punched into the metal plate  31 . With a rough surface part being formed at the front-end-side area of the circumferential surface of a straight unit as explained above, it is possible to use an existing punch just by working the outer surface of the existing punch so as to increase the surface roughness level thereof. As explained above, since the rough surface part  47  is formed only at the front-end-side area of the circumferential surface of the straight unit  55 , it is possible to easily work the outer surface of an existing punch so as to increase the surface roughness level thereof and to use the worked existing punch. 
     In the configuration of the pressing machine  30  mentioned above, the nozzle opening  10  is formed through the metal plate  31  through the punching process and the bump removal process. Notwithstanding the above, however, in the configuration of the pressing machine  30  according to an exemplary embodiment of the invention, the metal plate  31  may be punched through with the use of the punch  36 . That is, the bottom dead point of the punch  36  may be adjusted into a position that is further lower than the reverse face  31   b  of the metal plate  31  so as to form a through hole in the metal plate  31  without performing the bump removal process. 
     Moreover, when the shape of the rough surface part  47  of the punch  36  is imprinted on the inner circumferential surface of the hole  40  of the metal plate  31  in the direction of the arrow K, during the process of surface treatment (a third step) of the inner circumferential surface of the hole  40 , it is possible to make it easier to apply treatment liquid such as a repellent that repels ink that is ejected by the recording head and to perform the surface treatment easily. 
     In the configuration of the pressing machine  30  according to an exemplary embodiment of the invention, the nozzle plate  13  that is used in the recording head  1 , which is a kind of a liquid spray head, is taken as an application example of the metal plate  31  in which the hole  40  is formed. Notwithstanding the above, however, the invention can be applied to the metal plate  31  that is used in other application. 
     In the foregoing explanation, the recording head  1  is taken as an example of a liquid spray head. Notwithstanding the foregoing, however, the invention is directed to various kinds of liquid spray heads; and therefore, the invention is also applicable to a variety of liquid spray heads that eject liquid other than ink. For example, the invention can be applied to a variety of recording heads such as an ink-jet recording head or the like that are used in an image recording apparatus such as a printer or the like, a color material ejection head that is used in the production of color filters for a liquid crystal display device or the like, an electrode material ejection head that is used for the electrode formation of an organic EL display device, an FED (field emission display), and the like, or a living organic material ejection head that is used for production of biochips. In addition, although the foregoing explanation is given while taking the recording head  1  as an example of a liquid spray head, it can be applied to a liquid spray apparatus that uses other liquid spray head explained above.