Abstract:
An ironing ring for use in a press for ironing pressing or drawing of a workpiece. The ironing ring has a work surface which, upon deforming the workpiece, contacts the workpiece, and causes flowing of the workpiece material. In order to prevent friction deposits in the region of the work surface of the ironing ring, a microstructure, differing from the roughness of the work surface, is introduced into the work surface, which forms elevations and/or recesses in the work surface. Material particles remaining on the work surface after the deforming of a workpiece thus adhere less strongly to the work surface and can be stripped off during the next deforming process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part application of pending international application PCT/EP2014/054493 filed Mar. 7. 2014, and claiming the priority of German application No. 10 2013 102 898.5 filed Mar. 21, 2013. The said International application PCT/EP2014/054493 and German application No. 10 2013 102 898.5 are both incorporated herein by reference in their entireties as though fully set forth. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an ironing ring for use in a press for ironing pressing of a workpiece. 
         [0003]    Such ironing rings have been known per se. In a press for ironing pressing or drawing a workpiece, for example a cup, several such ironing rings are successively arranged, as a rule, in the direction of the working stroke in order to intermittently or incrementally reduce the outside diameter of the workpiece. As a result of this, it is possible, for example, to ultimately form a hollow cylindrical can body from a cup. 
         [0004]    During the deforming process, a radially inward facing work surface of the ironing ring comes into contact with the workpiece. Depending on the material of the workpiece, more or less viscous, smeary material build-up or friction deposits occurs. This phenomenon is known. Nowadays, the ironing rings are therefore deinstalled from the press after a certain number of deforming processes, cleaned and subsequently reinstalled. This is labor-intensive and expensive and has caused the shutdown of the press. 
         [0005]    In order to avoid friction deposits, publication DE 22 56 334 A1 discloses the possibility of applying a special lubricant to the ironing ring or the workpiece. However, such lubricants must subsequently be removed again from the deformed workpiece. This option is labor-intensive and expensive as well. Publication DE 22 56 334 A1 suggests that the ironing ring be made of ceramic material. However, if pressure is suddenly removed from the ceramic ironing ring, fissures may form, this being prevented according to DE 22 56 334 A1 in that the end region of the workpiece may immerse into a recess on the ironing stamp in order to avoid the sudden removal of pressure from the ceramic ironing ring. 
         [0006]    Considering this, the object of the present invention may be viewed to be an ironing ring in which the risk of friction deposits is reduced and which does not require any design changes on other press components. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides an ironing ring  10  for use in a press for ironing pressing or drawing of a workpiece  11 . The ironing ring  10  has a work surface  15  which, upon deforming the workpiece  11 , contacts the workpiece  11  and causes flowing of the workpiece material. In order to prevent friction deposits (friction deposits) in the region of the work surface  15  of the ironing ring  10 , a microstructure  22 , differing from the roughness of the work surface, is introduced into the work surface  15 , which forms elevations  23  and/or recesses  24  in the work surface  15 . Material particles remaining on the work surface  15  after the deforming of a workpiece  11  thus adhere less strongly to the work surface  15  and can be stripped off during the next deforming process. 
         [0008]    On its inside, the ironing ring has an interior work surface that comes into contact with the workpiece when the workpiece is being deformed. As a rule, the part of the ironing ring comprising the work surface or the entire ironing ring is made of a metallic material, in particular hard metal or tool steel. In particular on its work surface, the ironing ring is not provided with a coating and can be used without the use of lubricants. In accordance with the invention, the work surface is provided with a microstructure that includes elevations and/or recesses. These elevations and/or recesses form an uneven microstructure in the nanometer-range or micrometer range. The result of the microstructure is that, during a deforming process, particles of the deformed workpiece remaining on the work surface of the ironing ring adhere less strongly and can thus be removed easily, for example, they can be stripped off during one of the subsequent deforming processes. As a result of this, the risk of friction deposits is at least greatly reduced. In this manner, it is possible to avoid cleaning of the ironing ring or to at least drastically reduce the number of cleaning processes. 
         [0009]    The microstructure is a form design of the work surface that is formed independently of and in addition to the roughness of the work surface. The microstructure of the work surface is directly introduced in the metallic material, in particular hard metal or tool steel, of the ironing ring. Therefore, additional coatings are not necessary. Metallic materials that are standard in ironing rings may be used. The microstructure can be produced by the defined ablation of material, for example by laser ablation. 
         [0010]    In a few exemplary embodiments, the elevations and/or recesses of the microstructure have a regular pattern, for example due to the uniform arrangement of the elevations and/or recesses along the work surface. However, it is also possible to provide irregular microstructures, for example by varying the form, size and arrangement of elevations and/or recesses which may take place stochastically or consistent with a prespecified rule of arithmetic. A combination of regular and irregular sections or regions of the microstructure is also possible. 
         [0011]    With a regular pattern of the microstructure, the center axes or center planes or maxima of adjacent elevations of the microstructure are preferably at the same distance. The contour of the elevations as well as the distance between the center axes or center planes or maxima, of two adjacent elevations can be defined as a function of the material of the workpiece that is to be deformed. For example, elevations may have a spherical, cylindrical or conical contour, or they may have the contour of a truncated cone, a pyramid, a truncated pyramid, a parallelepiped or a cube. Recesses of the microstructure form an intermediate space between these elevations. 
         [0012]    Alternatively or in addition to elevations rising in the direction of the normal vector on the work surface of the ironing ring, there may also be recesses. The distance of the center axes or center planes or minima of respectively adjacent recesses of the microstructure may be the same, so that also in this case a uniformity in the microstructure is achieved. 
         [0013]    The distance between the center axes or center planes or minima or maxima of adjacent elevations or adjacent recesses is preferably less than 50 micrometers. Depending on the material of the workpiece that is to be deformed, this distance may also be less than 1000 nanometers. Preferably, this distance is greater than 50 nanometers. 
         [0014]    The microstructure may be embodied as a 3-dimensional or a 2.5-dimensional structure. If a three-dimensional microstructure is intended, the maximum height difference between the maxima of the elevations and the minima of the recesses measured in the direction of the normal vector on the work surface is at most 500 nanometers. 
         [0015]    In one embodiment of the invention the elevations of the microstructure taper in the direction of the normal vector of the work surface. Therefore, the elevations have lateral flanks that are inclined relative to the normal vector on the work surface. The recess or the distance between two elevations thus increases toward the maximum or toward the free end of the elevation. As a result of this, an additional reduction of the adhesion of particles can be achieved. 
         [0016]    An elevation and/or a recess of the microstructure, preferably measured transversely to the extension direction of the normal vector, may have in one or more dimensions a transverse dimension that is smaller than 10 micrometer and, in particular smaller than 1000 nanometers. 
         [0017]    Preferably, the work surface has two surface sections that subtend an angle. The two surface sections are inclined relative to the longitudinal axis of the ironing ring. An ironing edge may exist in the transition region between the two surface section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Advantageous embodiments of the ironing ring can be inferred from the dependent claims as well as the description. The description is restricted to essential features of the invention. The drawings are to be used for supplementary reference. Hereinafter, exemplary embodiments of the invention are explained in detail with reference to the appended drawings. They show in: 
           [0019]      FIG. 1  a schematic representation of an ironing ring, an ironing stamp, as well as of a workpiece, in a sectional view along the longitudinal axis of the ironing ring; 
           [0020]      FIG. 2  a schematic sectional view of the ironing ring according to  FIG. 1 , along the longitudinal axis of the ironing ring; and, 
           [0021]      FIGS. 3 to 12  show a schematic diagram of elevations and/or recesses of the microstructure of the work surface of the ironing ring. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIGS. 1 and 2  show, greatly schematized, an ironing ring  10  for ironing a workpiece  11 , i.e., a cup in accordance with the example, wherein the workpiece  11  is moved with the aid of a stamp  12  through the ironing ring  10 . The ironing ring  10  is supported by a ring holder  13  in a die  14  of a press that is not specifically shown in detail. By means of the press drive of the press, the stamp  12  with the workpiece  11  is pressed for deformation through the ironing ring  10 . In doing so, the workpiece  11  comes into contact with a radially interior work surface  15  of the ironing ring and is thus deformed. Referring to the exemplary embodiment, the wall thickness of the workpiece  11 , i.e., a cup is reduced as a result of this, whereby the length of the cup increases. Usually, considering presses for ironing drawing or ironing pressing of a workpiece  11  in a die  14 , there are several ironing rings  10  arranged at distance from each other, as a result of which the deformation of the workpiece  11  takes place intermittently or incrementally. 
         [0023]    In the exemplary embodiment, the ironing ring  10  consists of metal and, in particular, of hard metal or tool steel. About its longitudinal axis L, this ring is completely closed. The work surface  15  is arranged on the interior surface  16  of the ironing ring  10  facing the longitudinal axis L. In doing so, the work surface  15  may be a component of the interior surface  16  or be formed by the entire interior surface  16 . In the exemplary embodiment, the work surface  15  has a first surface section  15   a  and a second surface section  15   b.  Both surface sections  15   a,    15   b  are inclined relative to the longitudinal axis L and have the form of the circumferential surface of a truncated cone. At the location of transition between the two surface sections  15   a,    15   b  there is formed an ironing edge  17  that, in modification of the schematic drawings of  FIGS. 1 and 2 , may also be provided with a radius. The diameter of the work surface  15  is the smallest at the ironing edge, in which case the diameter increases in the direction of the longitudinal axis L in both directions. 
         [0024]    When ironing the workpiece  11 , the work surface  15  comes into contact with the workpiece  11 . Due to the friction and the pressure between the workpiece  11  and the work surface  15  it may happen that particles of the workpiece material cling to the ironing ring  11  and adhere there due to the action of the pressure between the workpiece  11  and the ironing ring  10 . This process is also referred to as friction deposits. These material adhesions to the ironing ring  10  cause the form to change in the region of the work surface  15  and to thus no longer result in the desired deformation of the workpiece  11 . Therefore, until now, the ironing ring  10  must be deinstalled and cleaned after a certain number of deforming processes. During this time, the press is stopped. 
         [0025]    According to the invention such friction deposits during deformation is avoided or at least reduced. This is accomplished in that the work surface  15  and/or the entire interior surface  16  of the ironing ring  10  are provided with a microstructure  22  that is shown highly schematized in dotted lines in  FIG. 2 . In modification of the illustration as in  FIG. 2 , the microstructure  22  can also be provided on the entire interior surface  16 . The microstructure  22  is directly formed in the material of the ironing ring  10 . The ironing ring  10  is not provided with a coating in the region of the work surface  15  and, in particular, in the region of the entire interior surface  16 . In the exemplary embodiment, the ironing ring  10  is completely made of a uniform metal material. 
         [0026]    The microstructure  22  has elevations  23  and/or recesses  24 , as a result of which a regular pattern of elevations  23  and thus of interspaced recesses  24  is formed in the work surface  15  of the ironing ring  10  in accordance with the example. Alternatively, it would also be possible to distribute the elevations  23  and/or the recesses  24  irregularly and, for example, stochastically, within the work surface  15 , which is only shown in an exemplary manner in the schematic of  FIG. 12 . The microstructure  22  has the form design of the work surface  15  that is created independently of or in addition to the roughness of the work surface  15 . 
         [0027]      FIGS. 3 to 12  schematically illustrate different forms and/or exemplary embodiments of elevations  23  to produce a microstructure  22 . It is also possible to use the contours or forms of these elevations  23  for the recesses  24  and, as it were, provide recesses complementary to the elevations and thus obtain a microstructure  22 . Likewise, a combination of such recesses with the depicted elevations  23  is possible. 
         [0028]    Transversely to the normal vector N relative to the work surface  15  or a surface section  15   a,    15   b  of the work surface  15 , the elevations  23  and/or recesses  24  have at least one dimension of a transverse measurement Q that, in accordance with the example, is less than 20 micrometers and, in particular, less than 1000 nanometers. In the respectively other dimension transversely to the normal vector N, the dimension of the elevation  23  or the recess  24  can be greater, in which case these may be, in particular, also so-called linear elevations  23  and recesses  24  that are configured so as be closed in a ring form around the longitudinal axis L or may end at the ends of the work surface  15 —viewed in the direction of the longitudinal axis L. Such examples of linear elevations or recesses are schematically illustrated in cross-section by  FIGS. 8 to 11 . 
         [0029]    Due to the microstructure  22 , it is possible to avoid or at least reduce friction deposits on the work surface  15  of the ironing ring  10 . When the workpiece  11  is being deformed it may happen that particles of the workpiece material remain clinging to the work surface  15  of the ironing ring  10 . Due to the microstructure  22 , the contact surface between such particles and the work surface  15  is reduced. Consequently, adhesion is decreased. The result of this is that, during the next deforming process, such particles located on the work surface  15  can be readily stripped off, thus clearly reducing the risk of friction deposits. 
         [0030]    Depending on the concrete deforming task, the design and dimensioning of the microstructure  22  may vary. For example, the form and dimensioning of elevations  23  and recesses  25  is dependent on the material of which the workpiece  11  is made. In doing so, in particular the pairing of materials between the material of the ironing ring  10  and the material of the workpiece  11  must be taken into account. When cups are being ironed for the deformation of can bodies, aluminum or tinplate are frequently used, the latter also being potentially coated with plastic material, depending on the purpose of use of the can. 
         [0031]    It is thus possible to vary the design and dimensioning of the irregularities  23 ,  24  of the microstructure  22 . The use of linear elevations  23  or recesses  24  ( FIGS. 8 to 11 ) as well as the use of bump-like elevations  23  or recesses  24  is possible.  FIGS. 3 to 7  illustrate—only as examples—a few designs of bump-like elevations  23 , between which grid-like, linear recesses  24  are provided, said recesses separating the individual elevations  23  from each other. 
         [0032]    In the exemplary embodiment, the maximum height difference H between the maxima S or peaks of the elevations  23  and the minima G or the bottom of the recesses  24  is less than 500 nanometers. The height difference H is measured in the direction of the normal vector N on the work surface  15  or the respective work surface section  15   a,    15   b.    
         [0033]      FIGS. 3 to 7  show, highly schematized, different exemplary embodiments of microstructures  22 . In these exemplary embodiments, the individual elevations  23  are separated from each other by linear, groove-like recesses  24 . The elevations  23  may have the form of parallelepipeds or cubes ( FIG. 3 ), the form of a cylinder ( FIG. 4 ), the form of a truncated cone ( FIG. 5 ), be ring-shaped ( FIG. 6 ) or have the form of a pyramid or tetrahedron ( FIG. 7 ). Other forms such as, for example, honeycomb-shaped elevations  23  or spherical elevations  23  can also be used. These mentioned embodiments are only exemplary. There exists a multitude of possibilities of configuring the elevations  23 . Important is that the support surface or contact surface between the material of the workpiece  11  and the ironing ring  10  is reduced, thus reducing the adhesion between a material particle of the workpiece material and the work surface  15 . 
         [0034]    The elevations  23  may by rotation-symmetrical about their respective longitudinal center axis M ( FIGS. 4 to 6 ). They may also taper toward their free end, this being illustrated, for example, by the form of a truncated cone in  FIG. 5  and by the form of a pyramid in  FIG. 7 . Instead of the pyramid or tetrahedron form in  FIG. 7 , it would thus be possible to provide, for example, elevations  23  having the form of a truncated pyramid or a truncated tetrahedron. Considering such embodiments of the elevations  23 , flanks  25  being inclined relative to the center axis M are formed. The angle of inclination a measured between such a flank  25  and the center axis M or a parallel line relative to the center axis M may be in the range of 110° to 160°. 
         [0035]    In accordance with the example, the distance between two elevations  23  is defined between the center axes M and the center planes E, respectively, of two adjacent elevations  23 . Accordingly, the distance A between two adjacent recesses  24  is defined as the distance A between their center axes M and their center planes E, respectively. If, based on the form, a center axis M or a center plane E cannot be determined at an elevation  23  or a recess  24 , the distance A between two adjacent elevations  23  or two adjacent recesses  24  between the maxima S of the adjacent elevations  23  or the minima G between adjacent recesses  24  can be measured. In the case of irregular microstructures  22 , it is also possible—as illustrated in an exemplary manner by FIG.  12 —to determine the distance A between the centroids of the elevations  23 . Accordingly, this distance determination can also be used with adjacent recesses  24 . 
         [0036]    In the exemplary embodiment, the distance A determined in one of the mentioned ways between two adjacent elevations  23  or two adjacent recesses  24  is less than 50 micrometers and, preferably, less than 1000 nanometers. Preferably, this distance A is greater than 50 nanometers. 
         [0037]    Such microstructures  22  in the nanometer range or the micrometer range can be generated on the work surface  15  by laser ablation. For example, several laser beams may be interferometrically superimposed in order to produce the desired structures on the work surface  15 . 
         [0038]    In regular microstructures  22 , the distance A between two adjacent recesses  24  or two adjacent elevations  23  is constant. As a result of this, a regular, uniform pattern of the microstructure  22  along the entire work surface  15  is achieved. It is also possible to provide different microstructures  22  in different sections or regions of the work surface  15 . For example, it is possible to provide a different microstructure  22  in the region of the first surface section  15   a  than in the second surface section  15   b.    
         [0039]      FIGS. 8 to 11  show elevations  23  and recesses  24  that, in accordance with the example, extend closed in the form of a ring around the longitudinal axis L, so that ring-shaped elevations  23  or ring-shaped recesses  24  are formed. As illustrated schematically and in an exemplary manner by  FIGS. 8 and 9 , the elevations  23  or recesses  24  need not be symmetrical with respect to a radial plane relative to the longitudinal axis L. Starting at a maximum S of an elevation  23 , for example, the steepness of the flanks may be different in the opposite direction. Viewed in the direction of movement of the workpiece  11  through the ironing ring  10 , the workpiece is only or mainly in contact with the flatter flanks  25   a  increasing to the maximum S, as is schematically illustrated by  FIGS. 8 and 9 . A sawtooth-shaped microstructure  22 , as it were, can be achieved, wherein the edges in the region of the maxima S of the elevations and/or in the region of the minima G of the recesses can be embodied so as to have a sharp edge or be rounded. 
         [0040]    According to  FIG. 10 , the elevations  23  have a bump-like cross-section and thus form annular ribs. All previously described contours for the elevations  23  can also form—as a negative profile—recesses  24  in the work surface  15  or in the respective surface section  15   a,    15   b.    FIG. 11  illustrates an example of this. Instead of the ring-shaped rib-like elevations  23  ( FIG. 10 ), it is also possible to form ring-shaped recesses  24  having the appropriate cross-sectional contour. 
         [0041]    In modification of the representations of  FIGS. 3 to 11 , the center axes M or center plane E need not have the same orientation as the normal vector N of the respective surface sections  15   a,    15   b  or the work surface  15 . 
         [0042]    The contours of the elevations  23  and recesses  24  described in conjunction with  FIGS. 3 to 11  may also be used in any desired combination. Inasmuch as the distance of the work surface  15  from the longitudinal axis L is not consistent due to the inclination of the surface sections  15   a,    15   b,  the pressure between the workpiece  11  and the work surface  15  increases as the distance of the work surface  15  from the longitudinal axis L decreases. Therefore, it may be advantageous to configure the microstructure  22  in regions of higher pressure differently from regions of lower pressure. 
       LIST OF REFERENCE SIGNS 
       [0043]      10  Ironing ring 
         [0044]      11  Workpiece 
         [0045]      12  Stamp 
         [0046]      13  Ring holder 
         [0047]      14  Die 
         [0048]      15  Work surface 
         [0049]      15   a  First surface section 
         [0050]      15   b  Second surface section 
         [0051]      16  Interior surface 
         [0052]      17  Ironing edge 
         [0053]      22  Microstructure 
         [0054]      23  Elevation 
         [0055]      24  Recess 
         [0056]      25  Flank 
         [0057]      25   a  Flank with a smaller inclination 
         [0058]    A Distance 
         [0059]    G Minimum 
         [0060]    E Center plane 
         [0061]    H Height difference 
         [0062]    L Longitudinal axis 
         [0063]    M Center axis 
         [0064]    N Normal vector 
         [0065]    Q Transverse dimension 
         [0066]    S Maximum