Patent Publication Number: US-2022219216-A1

Title: Stamping apparatus, method of stamping and stamping mold

Description:
BACKGROUND 
     The statement in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art. As illustrated in  FIG. 1-3 , a punching method is known in which a punch  101  is lowered against sheet metal  50  placed on a die  102 , and a workpiece P ( FIG. 3 ) is punched off by punching the sheet metal  50  with the punch  101 . However, the inventors recognized that, in such a punching method, roll-over A 1  was likely to be formed at the lower edge of the periphery of the workpiece P as illustrated in  FIG. 3 . The inventors also recognized that fracture surfaces A 3  and burrs A 4  were likely to be formed above the burnished surface A 2  on the periphery of the workpiece P. The inventors presumed that formation of these fracture surfaces A 3  and burrs A 4  were related to random cracks C formed in the sheet metal  50  as illustrated in  FIG. 2 . The cracks C started from where the corner of the die  102  or the corner of the punch  101  contacts with the sheet metal  50  during the punch  101  is pressing the sheet metal  50 . One approach was to remove the burrs A 4  from the workpiece P after separation from the sheet metal. 
     Alternatively, Japanese Unexamined Patent Application Publication No. 59-082121 (hereinafter referred to as “Patent Document 1”) disclosed a workpiece punching method in which a workpiece part was punched off from sheet metal 3b in two steps. In the first step, the punch 2a having a flat end was driven into the sheet metal 3b to about half of its thickness as illustrated in the FIG. 2 of the same document. In the second step, the workpiece part was separated from the sheet metal 3b with a punch 2b and a die 1b that have larger clearance than the punch 2a and die 1a used in the first step as illustrated in the FIG. 3(a), (b) of the same document. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a conventional stamping apparatus cut in a plane including center line of a punch, illustrating the state before the punch is lowered against sheet metal supported by a die. 
         FIG. 2  is a cross-sectional view of the stamping apparatus of  FIG. 1  cut in the same plane as  FIG. 1 , illustrating the state in which the punch has lowered from the state illustrated in  FIG. 1  and is pressing the sheet metal. 
         FIG. 3  is a cross-sectional view of the stamping apparatus of  FIG. 1  cut in the same plane as  FIG. 1 , illustrating the state in which the punch has further lowered from the state illustrated in  FIG. 2  and a workpiece part of the sheet metal has been separated by the punch. 
         FIG. 4  is a schematic perspective view of the neighborhood of a stamping mold set in a stamping apparatus in accordance with one or more embodiments. 
         FIG. 5  is a perspective view of the work-hardening punch in the stamping apparatus illustrated in  FIG. 4 , viewed from the end side. 
         FIG. 6  is a cross-sectional view of a stamping apparatus in accordance with one or more embodiments cut in a plane including the center line of a work-hardening punch, illustrating the state before the work-hardening punch is lowered against sheet metal supported by a work-hardening die. 
         FIG. 7  is a cross-sectional view of a stamping apparatus of  FIG. 6  cut in the same plane as  FIG. 6 , illustrating the state in which the work-hardening punch has lowered from the state illustrated in  FIG. 6  and is pressing the sheet metal. 
         FIG. 8  is a cross-sectional view of a stamping apparatus in accordance with one or more embodiments cut in a plane including center line of a separation punch, illustrating the state before the separation punch is lowered against sheet metal supported by a separation die. 
         FIG. 9  is a cross-sectional view of a stamping apparatus of  FIG. 8  cut in the same plane as  FIG. 8 , illustrating the state in which the separation punch has lowered from the state illustrated in  FIG. 8  and is pressing the sheet metal. 
         FIG. 10  is a cross-sectional view of a stamping apparatus of  FIG. 8  cut in the same plane as  FIG. 8 , illustrating the state in which the separation punch has further lowered from the state illustrated in  FIG. 9  and a workpiece part of the sheet metal has been separated by the separation punch. 
         FIG. 11  is an overview of a stamping apparatus in accordance with one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments provides 
     a method of stamping for separating a workpiece part of sheet metal to obtain a workpiece, the method comprising: 
     a work-hardening step of generating work-hardening at vicinity of outline of the workpiece part of the sheet metal by moving a work-hardening punch having an end side facing the sheet metal toward the sheet metal and locally pressing the vicinity of the outline along the outline with a work-hardening projection provided on the end side of the work-hardening punch; and 
     a separation step of punching the workpiece part of the sheet metal which has finished the work-hardening step with a separation punch and thereby separating the workpiece part from the sheet metal, 
     wherein the work-hardening projection is formed to have V-shaped cross-section with both inner wall and outer wall of the work-hardening projection being inclined to pressing direction of the work-hardening punch. 
     Thus, by performing the work-hardening step, work-hardening is generated in the vicinity of the outline (hereinafter referred to as “outline-vicinity area”) in the sheet metal, making the outline-vicinity area fragile. In addition, a dent is formed on the sheet metal by the work-hardening projection. When the workpiece part is punched in the separation step, cracks are likely to be formed from the bottom of the dent or the vicinity thereof. As a result, an advantage is achieved in that burrs are less likely to be formed on the separated workpiece. In addition, the cracks are likely to be formed in a straight way where the work-hardening is generated. As a result, an advantage is achieved in that fractured surfaces are less likely to be formed on the separated workpiece. Furthermore, by forming the work-hardening projection to have V-shaped cross-section, an advantage is achieved in that the work-hardening projection is less likely to be deformed or broken. 
     One or more embodiments provides 
     a stamping mold for separating a workpiece part of sheet metal to obtain a workpiece, the stamping mold comprising: 
     a work-hardening punch having an end side configured to face the sheet metal, the end side provided with a work-hardening projection, wherein the work-hardening projection is configured to generate work-hardening at vicinity of outline of the workpiece part of the sheet metal by locally pressing the vicinity of the outline along the outline; 
     a work-hardening die provided in pair with the work-hardening punch, wherein the work-hardening die is configured to support the sheet metal on outside of the workpiece part; 
     a separation punch configured to punch the workpiece part of the sheet metal which has pressed by the work-hardening punch, and thereby separate the workpiece part from the sheet metal; and 
     a separation die provided in pair with the separation punch, wherein the separation die is configured to support the sheet metal on outside of the workpiece part, 
     wherein the work-hardening projection is formed to have V-shaped cross-section with both inner wall and outer wall of the work-hardening projection being inclined to pressing direction of the work-hardening punch. 
     One or more embodiments provides a stamping apparatus comprising the stamping mold described in the previous paragraph. 
     In one or more embodiments, the work-hardening projection is provided successively on the end side of the work-hardening punch, and is configured to follow the outline of the workpiece part of the sheet metal. As a result, an advantage is achieved in that work hardening is likely to be generated successively along the outline of the workpiece part, and burrs and fracture surfaces are even less likely to be formed on the separated workpiece. Here, “the work-hardening projection is provided successively” means that the work-hardening projection is in an annular shape or an annular shape with one cut-off portion. The term “annular shape” includes substantially circular rings, substantially elliptical rings, substantially polygonal rings, rings with at least one corner of the substantially polygonal ring rounded, and other irregular shapes. In other embodiments, a plural of work-hardening projections is provided intermittently on the end side of the work-hardening punch, and are configured to follow the outline of the workpiece part of the sheet metal. 
     In one or more embodiments, inner width of the work-hardening die is configured to be equal to outer width of the workpiece. Meanwhile, ridgeline distance of the work-hardening projection is not limited, wherein the “ridgeline distance” refers to, if the work-hardening punch has only one work-hardening projection, a width of an area defined by a ridgeline of the work-hardening projection, and if the work-hardening punch has a plural of work-hardening projections, a width of an area defined by a line connecting all the peaks of the plural of work-hardening projections, the same applies hereinafter. In some embodiments, the ridgeline distance of the work-hardening projection is configured to be substantially equal to outer width of the workpiece (which is, in some embodiments, substantially equal to inner width of the work-hardening die). As a result, the above-mentioned cracks are more likely to be formed parallel to the pressing direction, making it more likely to get a well-formed periphery of the separated workpiece. In other embodiments, peak tip(s) of the work-hardening projection(s) is/are configured to contact slightly outside the outline of the workpiece part of the sheet metal. In other words, the ridgeline distance of the work-hardening projection is configured to be slightly larger than the outer width of the workpiece. In other embodiments, peak tip(s) of the work-hardening projection(s) is/are configured to contact slightly inside the outline of the workpiece part of the sheet metal. In other words, the ridgeline distance of the work-hardening projection is configured to be slightly smaller than the outer width of the workpiece. 
     Outer width of the separation punch is not limited. Inner width of the separation die is not limited either. In some embodiments, outer width of the separation punch is configured to be smaller than outer width of the workpiece (which is, in some embodiments, substantially equal to inner width of the work-hardening die), and inner width of the separation die is configured to be larger than outer width of the workpiece. As a result, an advantage is achieved in that whisker burrs are less likely to be formed on the periphery of the separated workpiece. In other embodiments, outer width of the separation punch is configured to be substantially equal to the outer width of the workpiece. In other embodiments, inner width of the separation die is configured to be substantially equal to the outer width of the workpiece. 
     One or more embodiments further comprises a counter-punch placed inside a die opening of the work-hardening die, wherein the counter-punch is configured to pressure hold the workpiece part from the opposite side of the work-hardening punch when the sheet metal is pressed by the work-hardening punch. The counter-punch is intended to prevent warping of the workpiece part during pressing by the work-hardening punch by pressure holding the workpiece part from the opposite side of the work-hardening punch. As a result, an advantage is achieved in that the dimensional accuracy of the separated workpiece is likely to be increased. 
     One or more embodiments further comprises means for transferring the sheet metal that has pressed by the work-hardening punch from the work-hardening die to the separation die. As a result, an advantage is achieved in that the workpieces can be produced efficiently and continuously. 
     Hereinafter, one or more embodiments of a stamping apparatus, a method of stamping, and a stamping mold are described with reference to the drawings. In some of the drawings, x-axis, y-axis, and z-axis are illustrated. Directions of the x-axis, y-axis, and z-axis are kept consistent in different figures. For convenience of explanation, the positive side in the z-axis direction is sometimes referred to as “upper” side and the negative side in the z-axis direction is sometimes referred to as “lower” side hereinafter. 
       FIG. 4  is a schematic perspective view of the neighborhood of a stamping mold  1  set in a stamping apparatus in accordance with one or more embodiments. In one or more embodiments, the stamping mold  1  comprises a work-hardening section  10  and a separation section  20  as illustrated in  FIG. 4 . The work-hardening section  10  is designed to perform a work-hardening step in which work-hardening is generated at a certain part of sheet metal  50 . Meanwhile, the separation section  20  is designed to perform a separation step in which a workpiece P (see  FIG. 10  below) is obtained by punching and separating a certain part of the sheet metal  50 . 
     After completing the work-hardening step in the work-hardening section  10 , the sheet metal  50  is transferred to the separation section  20 , where the separation step is performed. Thus, the workpiece P is obtained by sequentially performing the work-hardening step at the work-hardening section  10  and the separation step at the separation section  20 . 
     Hereafter, the work-hardening section  10  and the separation section  20  of the stamping mold  1  are described in more detail. 
     In one or more embodiments, the work-hardening section  10  comprises a work-hardening punch  11 , a work-hardening die  12  and a counter-punch  30  (see  FIG. 6 ) as illustrated in  FIG. 4 . The work-hardening punch  11  has an end side configured to face the sheet metal. A work-hardening projection  11   a  is provided on the end side of the work-hardening punch  11 .  FIG. 5  is a perspective view of the work-hardening punch  11  in the stamping apparatus illustrated in  FIG. 4 , viewed from the end side. In some embodiments, the work-hardening projection  11   a  is annularly provided at the edge on the end side of the work-hardening punch  11 . The work-hardening die  12  has a die opening  12   a  to accept the work-hardening punch  11 . In one or more embodiments, diameter of the die opening  12   a  (inner width W 2  of the work-hardening die  12 ) is configured to be substantially equal to outer width W 5  (see  FIG. 10 ) of the workpiece P. 
       FIG. 6  and  FIG. 7  are cross-sectional views of a stamping apparatus in accordance with one or more embodiments cut in a plane including the center line of the work-hardening punch  11 .  FIG. 6  illustrates the state before the work-hardening punch  11  is lowered against the sheet metal  50  supported by the work-hardening die  12 .  FIG. 7  illustrates the state in which the work-hardening punch has lowered from the state illustrated in  FIG. 6  and is pressing the sheet metal  50 . 
     In the work-hardening section  10 , the work-hardening punch  11  is lowered against the sheet metal  50  supported by the work-hardening die  12  as illustrated in  FIG. 6  and  FIG. 7 . Then, as illustrated in  FIG. 7 , the work-hardening punch  11  locally presses the sheet metal  50  in vicinity of outline (outline-vicinity area α) of a workpiece part  51  (a part of the sheet metal  50  that is to be the workpiece P) along its outline with the work-hardening projection(s)  11   a . Thus, work-hardening (a phenomenon in which hardness of metal increases due to plastic deformation when stress is applied to it) is likely to be efficiently generated in the outline-vicinity area α. 
     In the work-hardening step of the embodiments illustrated in  FIG. 6  and  FIG. 7 , the work-hardening punch  11  is lowered until just before the end peak(s) of the work-hardening projection(s)  11   a  reaches the top surface of the work-hardening die  12 . When the work-hardening step is completed, an annular dent β (dent groove) is formed by the work-hardening projection  11   a  in the outline-vicinity area α along the outline of the workpiece part  51 . At this point, the workpiece part  51  and a part(s) of the sheet metal  50  located outside of the workpiece part  51  (scrap part(s)  52 ) are connected only by thin sheet-like part(s) in the outline-vicinity area α. Although hardened by the work-hardening described above, this sheet-like part(s) is/are very easy to get cracks and fragile due to its hardness and thinness. 
     During the work-hardening step, the workpiece part  51  of the sheet metal  50  comes down into the die opening  12   a  of the work-hardening die  12  as illustrated in  FIG. 7  as it is pressed downward (toward the die opening  12   a ) by the end side of the work-hardening punch  11 . At this point, the outline-vicinity area α of the workpiece part  51  receives upward resistance force (tensile force) from the scrap part(s)  52  of the sheet metal  50 . In addition, the outer periphery of the workpiece part  51 , which has come down into the die opening  12   a , receives upward resistance force (frictional force) from the inner periphery of the work-hardening die  12  (the inner wall of the die opening  12   a ). Due to these forces, the workpiece part  51  is likely to warp convexly to the lower direction during the work-hardening step. 
     In this regard, one or more embodiments is provided with a counter-punch  30  placed inside the die opening  12   a  of the work-hardening die  12 . The counter-punch  30  is biased upward (to the work-hardening punch  11  side) by biasing means  31 . In some embodiments, the biasing means  31  is a coil spring. The counter-punch  30  pressure holds the workpiece part  51  upward when the workpiece part  51  is pressed downward by the work-hardening punch  11 . In other words, the workpiece part  51  is sandwiched between the work-hardening punch  11  and the counter-punch  30 . Thus, the workpiece part  51  is more likely to be kept in a substantially flat state during the work-hardening step, and less likely to get warped. As a result, an advantage is achieved in that the dimensional accuracy of the obtained workpiece P is likely to be increased. The counter-punch  30  also functions as means for removing the sheet metal  50  from the work-hardening die  12 , which is a so-called knockout. 
     The cross-sectional shape of the work-hardening projection(s)  11   a  of the work-hardening punch  11  (in some embodiments, cross-sectional shape in the plane including the center line of the work-hardening punch  11 ) is V-shaped, as illustrated in  FIG. 6 . In other words, the inner wall  11   a   1  (wall facing the center side of the work-hardening punch  11 ) and the outer wall  11   a   2  (wall facing the periphery side of the work-hardening punch  11 ) of the work-hardening projection(s)  11   a  are inclined with respect to pressing direction (direction in which the work-hardening punch  11  is lowered) so that the distance between them increases from the end side (negative side in the z-axis direction) to the base side (positive side in the z-axis direction). 
     As a result, an advantage is achieved in that the work-hardening projection(s)  11   a  become more strong and less likely to be deformed or broken. This advantage is more helpful in embodiments in which the work-hardening projection(s)  11   a  is/are very fine structure(s) with its height H 1  ranging from about 0.5 mm to 3 mm. The height H 1  of the work-hardening projection(s)  11   a  is determined according to the thickness of the sheet metal  50  and/or other factors, and is not particularly limited. In some embodiments, as illustrated in  FIG. 6 , inclination angle θ 1  of the inner wall  11   a   1  is substantially the same as inclination angle θ 2  of the outer wall  11   a   2 . As a result, when the work-hardening projection(s)  11   a  is/are pressed into the sheet metal  50 , the outward component of the force that the inner wall  11   a   1  receives from the sheet metal  50  becomes substantially equal to the inward component of the force that the outer wall  11   a   2  receives from the sheet metal  50 , making the work-hardening projection(s) even less likely to be deformed or broken. 
     The inclination angle θ 1  of the inner wall  11   a   1  and the inclination angle θ 2  of the outer wall  11   a   2  are not particularly limited as long as they are larger than 0° and smaller than 90°. In one or more embodiments, at least one of the inclination angle θ 1  or θ 2  is more than 10°. In some embodiments, at least one of the inclination angle θ 1  or θ 2  is more than 15°. In at least one embodiment, at least one of the inclination angle θ 1  or θ 2  is more than 20°. The larger the inclination angle θ 1  or θ 2  is, the easier it is to maintain strength of the work-hardening projection(s)  11   a . In one or more embodiments, at least one of the inclination angle θ 1  or θ 2  is less than 60°. In some embodiments, at least one of the inclination angle θ 1  or θ 2  is less than 50°. In at least one embodiment, at least one of the inclination angle θ 1  or θ 2  is less than 45°. The smaller the inclination angle θ 1  or θ 2  is, the easier it is for the work-hardening projection(s)  11   a  to get into the sheet metal  50 . 
     The ridgeline distance W 1  (see  FIG. 6 ) of the work-hardening projection  11   a  is not particularly limited. In some embodiments, the ridgeline distance W 1  is configured to be substantially equal to inner width W 2  of the work-hardening die  12 . In other words, the ridgeline of the work-hardening projection(s)  11   a  is positioned directly above the inner surface of the work-hardening die  12 . As a result, in the separation step described below, cracks C, which are formed starting from near the bottom of the dent β, are more likely to be formed parallel to the pressing direction (z-axis direction) as illustrated in  FIG. 9 , making it more likely to get a well-formed periphery of the separated workpiece P. In other embodiments, the ridgeline distance W 1  is configured to be slightly larger than inner width W 2  of the work-hardening die  12 . In other embodiments, the ridgeline distance W 1  is configured to be slightly smaller than inner width W 2  of the work-hardening die  12 . 
     When the work-hardening step in the work-hardening section  10  is completed, the work-hardening punch  11  is raised, then the sheet metal  50  is transferred from the work-hardening section  10  to the separation section  20 , where the separation step is performed. 
     In one or more embodiments, the separation section  20  comprises a separation punch  21  and a separation die  22  as illustrated in  FIG. 4 . In some embodiments, the separation punch  21  has a flat end side. The separation die  22  has a die opening  22   a  to accept the separation punch  21 . 
       FIG. 8-10  are cross-sectional views of a stamping apparatus in accordance with one or more embodiments cut in a plane including center line of the separation punch  21 .  FIG. 8  illustrates the state before the separation punch  21  is lowered against the sheet metal  50  supported by the separation die  22 .  FIG. 9  illustrates the state in which the separation punch  21  has lowered from the state illustrated in  FIG. 8  and is pressing the sheet metal  50 .  FIG. 10  illustrates the state in which the separation punch  21  has further lowered from the state illustrated in  FIG. 9  and a workpiece part  51  of the sheet metal  50  has been separated by the separation punch  21 . 
     In the separation section  20 , the separation punch  21  is lowered toward the sheet metal  50  supported by the separation die  22  as illustrated in  FIG. 8-10 . The workpiece part  51  of the sheet metal  50 , in which work hardening has generated in the outline-vicinity area α in the work-hardening step, is pressed to the die  22  side (lower side) by the separation punch  21 , and is separated from the scrap part(s)  52  as illustrated in  FIG. 10 . The separated workpiece part  51  (workpiece P) falls into the die opening  22   a . The workpiece P is used either as a final product or a intermediate product. 
     As already described, work-hardening has been generated and sheet-like part(s) have been formed in the outline-vicinity area α in the work-hardening step. Therefore, when the separation punch  21  presses the workpiece part  51  in the separation step, cracks C starting at the bottom of the dent β are likely to be formed in the most fragile part in the outline-vicinity area α (that is, the thinnest part) as illustrated in  FIG. 9 . As the dent β is formed in a cross-sectional V-shape according to the shape of the work-hardening projection(s)  11   a , the cracks C are likely to be formed straight down from the bottom of the dent  1 . As a result, the part of the sheet metal  50  where the cracks C are formed is likely to be smooth burnished surface rather than rough fractured surface, making it more likely to get a smoother periphery of the separated workpiece P with less fracture surface. 
     Moreover, because of the dent β formed on the upper side of the outline-vicinity area α, and of the smooth cracks C described above, burrs are less likely to be formed on upper end of the periphery of the separated workpiece P. As a result, an advantage is achieved in that the post-process of removing burrs from the workpiece P can be eliminated, and the workpiece P can be produced continuously and efficiently. 
     In some embodiments, outer width W 3  of the separation punch  21  is configured to be smaller than outer width W 5  of the workpiece P, and inner width W 4  of the separation die  22  is configured to be larger than outer width W 5  of the workpiece P. As a result, an advantage is achieved in that whisker burrs are less likely to be formed on the periphery of the separated workpiece P. In other embodiments, at least one of the outer widths W 33  or a diameter of the die opening  22   a  (that is, the inner width W 4 ) is configured to be substantially equal to the outer width W 5  (see  FIG. 10 ) of the workpiece P. 
       FIG. 11  is an overview of a stamping apparatus in accordance with one or more embodiments. In one or more embodiments, the sheet metal  50  is automatically transferred from the work-hardening section  10  to the separation section  20  by a sheet metal transfer means. In some embodiments, the stamping apparatus is a progressive stamping apparatus comprising an uncoiler  91 , a feeder  92  as the sheet metal transfer means, and a stamping press  93 , as illustrated in  FIG. 11 . In this case, the stamping mold  1  is attached to the stamping press  93 . In at least one embodiment, the feeder  92  is a roll feeder that feeds the sheet metal  50  with rotating rollers. In at least one other embodiment, the feeder  92  is a gripper feeder that feeds the sheet metal by gripping the sheet metal with grippers. In other embodiments, the stamping apparatus is a transfer press apparatus comprising fingers, which hold the sheet metal  50  and/or the workpiece P, as the sheet metal transfer means. In other embodiments, the sheet metal  50  is manually transferred from the work-hardening section  10  to the separation section  20 . 
     As described so far, the stamping apparatus of one or more embodiments makes it possible to obtain a workpiece P with less burrs and fractured surfaces, while having a relatively simple structure and being easy to maintain and operate. In the embodiments illustrated in  FIG. 4-10 , the work-hardening punch  11  and the removal punch  21  are both substantially cylindrical, as they are intended to separate the substantially disk-shaped workpiece P. In other words, the work-hardening punch  11  and the removal punch  21  have a substantially circular cross-sectional shape when cut in a plane perpendicular to the pressing direction. In other embodiments, cross-sectional shape (when cut in a plane perpendicular to the pressing direction) of at least one of the work-hardening punch  11  or the separation punch  21  is, for example, but not limited to, a substantially oval shape, a substantially polygonal shape, a substantially polygonal shape with at least one corner rounded, or any other irregular shapes, according to shape of the workpiece P.