Abstract:
A method of roughening metal surfaces of a workpiece such as a cylinder bore of an internal combustion engine to improve the adhesion of layers thermally sprayed thereon. Uniform grooves are formed in the surface and ridges are arranged between the grooves. The grooves may be formed by a process such as turning, drilling, milling or rolling. The ridges are plastically deformed in order to form undercuts in the grooves, with the degree of plastic deformation of the ridges varying regularly in the longitudinal direction of the grooves. Local deformations are produced in the ridge, and these bring about regular undercuts in the groove. This makes it possible to produce the undercuts in identical dimensions with little effort. Furthermore, since the groove is now not completely constricted by undercuts, it can be filled more effectively with spraying material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §DE 10 2009 027 200.3 filed Jun. 25, 2009, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The invention relates to a process for roughening metal surfaces in order to improve the adhesion of layers thermally sprayed thereon. 
         [0004]    2. Background Art 
         [0005]    WO 2007087989 A1 discloses a process for roughening metal surfaces in order to improve the adhesion of layers thermally sprayed thereon, wherein uniform grooves, e.g. rectangular or trapezoidal grooves, are introduced into the metal surface and resulting ridges are plastically deformed in order to form undercuts along the ridges. A disadvantage of this process is that the ridges are plastically deformed over their entire length. This requires a relatively large effort, it being possible to make the shape of the undercuts constant only with difficulty. Furthermore, the formation of the undercuts over the entire length of the grooves ensures that the grooves are filled completely by the spraying material only to a limited extent, since the adjacent undercuts form a narrow point through which only some of the spraying material can penetrate into a groove. 
       SUMMARY 
       [0006]    Since the degree of plastic deformation of the ridges varies regularly in the longitudinal direction of the grooves, the undercuts can be introduced into the ridges in a targeted manner at regular portions. For this purpose, the ridges are each locally deformed by suitable tools in such a way that these undercuts are produced. As seen in the longitudinal direction of the grooves, this leads to a constant, but regular, variation in the shape of the undercuts. In this case, some of the undercuts may not even occur at all since, at certain points, the degree of plastic deformation is only low or no plastic deformation is present at all. 
         [0007]    This regular variation in the groove shape means that the undercuts which then occur regularly can be introduced into the ridges with relatively little effort since, overall, only a small degree of plastic deformation of the ridges is required. Furthermore, the undercuts can be introduced with increased accuracy. As a result, these are produced regularly with identical dimensions along the grooves. This is a major advantage for uniform adhesive strength of the sprayed layer subsequently applied. It is also advantageous that the spraying material to be applied can fill the grooves very well since these regularly do not have any undercuts or have at least relatively small undercuts. In these regions, the spraying material penetrates very well into each groove and can then easily fill the directly adjacent groove regions with the undercuts. 
         [0008]    In one advantageous embodiment, the plastic deformations are knurls on the top face of the ridges. For this purpose, a known knurling tool is moved along the groove. Depending on the form of the knurling tool, this produces the uniform plastic deformations according to the flute shape of the knurling tool. 
         [0009]    In a further embodiment, the plastic deformations are local indentations on the top face of the ridges. This can be introduced by a roller having corresponding projections, points or needles. 
         [0010]    In both cases, the undercuts are produced by pressing the groove with such a force on the top face that the groove is pressed in plastically and, as a result, the groove flanks are deformed plastically toward the side—transversely with respect to the longitudinal direction of the groove. 
         [0011]    In another embodiment, the plastic deformations are local mortices in the ridges transversely with respect to the direction of the grooves. This can be done by moving a roller in the groove, this roller having regular projections, points or shoulders on the radial circumference which deform the groove transversely with respect to the longitudinal direction of the groove. The groove is then bent over plastically transversely with respect to the longitudinal direction thereof. Since the ridges remain undeformed in the groove root, the ridges are subjected to more severe deformation, and virtually inclined, in the transverse direction as their height increases, as a result of which the undercuts are produced in the grooves. 
         [0012]    The plastic deformations can be local indentations of the ridge edges. This can be implemented by appropriately pressing in or crimping the ridge edges at regular intervals, as a result of which the undercuts are produced on the groove flanks. 
         [0013]    A tool for introducing the plastic deformations can have at least one punch. This punch can advantageously move in a cyclic manner. When the tool is guided over the grooves, the moving punch produces the corresponding plastic deformations of the ridges. In this case, the punch can have an appropriately shaped punch head, and the punch can act on the grooves in any suitable direction in order to produce the optimum shape of undercuts on the ridges. By way of example, the punch can act directly perpendicularly on the top face of the ridges, as a result of which the ridges are pressed from above and the ridge material thereby flows in the transverse direction. However, the punch can also act in the transverse direction with respect to the grooves at a shallow angle, as a result of which the ridges are deformed transversely with respect to the longitudinal direction thereof. 
         [0014]    A tool for introducing the plastic deformations may be guided in, on, or by a groove. Therefore, it is possible for the tool to always be aligned precisely with respect to the ridges and for only one of the adjacent ridges to be machined. Since the tool is guided on, by, or in the grooves, the ridges are always deformed relative to the groove and the deformation can thus be carried out with high precision and repeatability. 
         [0015]    It is particularly advantageous if the plastic deformations in the second process step are introduced in the same operation as the first process step. By way of example, a tool for the plastic deformation can be arranged downstream of a turning, drilling or milling tool. In this case, the tools for the first and second process steps are advantageously mounted on the same tool carrier, e.g. a milling or turning spindle. Therefore, the first and second process steps take place virtually at the same time or in brief succession. In addition to reduced time (no further operation is necessary), the outlay in terms of measurement or apparatus is also reduced for the second process step. Both tools are coupled directly to each other and have to be aligned with respect to each another only once. 
         [0016]    The described methods for producing the plastic deformations and the undercuts can be suitably combined. By way of example, plastic indentations from above can alternate with indentations in the transverse direction and/or deformations of the groove flanks. A tool can introduce various plastic deformations and/or a mixture or superposition of said plastic deformations. It is also possible to suitably combine a plurality of tools for carrying out the second process step in order to produce the most beneficial undercuts possible. 
         [0017]    The disclosed method is particularly suitable for machining and preparing the coating of cylinder blocks of internal combustion engines. The process is readily useable in the relatively small cylinder bore since it is possible to reliably introduce the undercuts required into the ridges in a very uniform manner with little effort. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Further advantageous embodiments of the invention are illustrated in the drawings, in which: 
           [0019]      FIG. 1  shows a section through a workpiece and two tools for carrying out a surface roughening process; 
           [0020]      FIG. 2  shows a plan view of the arrangement shown in  FIG. 1 ; 
           [0021]      FIG. 3  shows the enlarged excerpt A from  FIG. 1 ; 
           [0022]      FIGS. 4   a - d  show sections through ridges with different deformations; 
           [0023]      FIGS. 5   a - d  show perspective views of the deformed ridges shown in  FIG. 4 ; 
           [0024]      FIGS. 6   a - b  show a side view and a section of a roller for indentations; 
           [0025]      FIGS. 7   a - b  show a side view and a section of a roller for ridge edge deformations; 
           [0026]      FIGS. 8   a - c  show a side view and sections of a roller for transverse deformations; 
           [0027]      FIGS. 9   a - b  show a side view and a section of a punch tool for ridge edge deformations; 
           [0028]      FIGS. 10   a - c  show a section and plan views of a punch tool for transverse deformations; and 
           [0029]      FIGS. 11   a - c  show a section and plan views of a twin roller for transverse deformations. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIGS. 1 to 3  show an arrangement for carrying out a surface roughening. The workpiece may be, for example, a cylinder block  1  and has a metal surface  2  which is prepared by means of the process in order to make it possible to apply a sprayed layer. A tool holder  5 , which bears a turning tool  6 , is fastened to a tool spindle  4 . Since the tool spindle  4  rotates and slowly moves downward into the cylinder bore  3 , the turning tool  6  produces, in the metal surface  2 , the grooves  7  which run in the circumferential direction and have the intermediate ridges  8 . 
         [0031]    A rotatable knurling roller  9  is arranged on the tool holder  5  and acts on the ridges  8  by means of regular projections  10  which are arranged on the circumference and, when the rotary spindle  4  rotates, plastically deform the ridges  8  at regular intervals in the form of knurls or flutes  11 . These flutes  11  in turn produce the undercuts  13  on the groove flanks  12  of the ridges  8 . 
         [0032]    The knurling roller  9  is set back axially—as seen in the axial direction of movement of the rotary spindle—with respect to the turning tool  6 , as a result of which the knurling roller  9  always interacts only with a ridge  8  which has just been produced. 
         [0033]      FIGS. 4   a  to  4   d  show sections through ridges with different deformations and  FIGS. 5   a  to  5   d  show the associated perspective views. 
         [0034]      FIGS. 4   a ,  5   a  show the plastic deformation of a ridge  8   a , into the top face  15  of which regular central indentations  14  are introduced. The indentations  14  result in plastic deformations, as a result of which the regular undercuts  13  are formed on the groove flanks  12 . In this context, regular means that the indentations or undercuts always occur at roughly the same intervals, as seen in the longitudinal direction of the grooves. 
         [0035]      FIGS. 4   b ,  5   b  show plastic deformations of a ridge  8   b  which are produced by a knurling roller, as has also already been shown in  FIG. 3 . The depressions or knurls or flutes  11  which are produced result in plastic deformation of the ridge material in the transverse direction with respect to the grooves, as a result of which the undercuts  13  are formed. 
         [0036]      FIGS. 4   c ,  5   c  show the plastic deformations of the ridge edges  16 . Since the ridge edges  16  are regularly pressed in, the regular undercuts  13  are formed. 
         [0037]      FIGS. 4   d ,  5   d  show the plastic deformations of the ridge  8   d  itself, in that said ridge is regularly and alternately bent toward the side in one direction and the other in the transverse direction with respect to the longitudinal direction of the grooves. As a result, the undercuts  13  are formed alternately—as seen in the longitudinal direction of the grooves—on the groove flanks  12 . 
         [0038]    Various tools for producing the ridges as described herein are shown in the subsequent Figures. These tools can also be combined with each other such that different deformations are produced by one tool; however, it is also possible for a plurality of these tools to be arranged alongside each other or in succession, in order to obtain different plastic deformations. 
         [0039]      FIGS. 6   a  and  6   b  show a roller  9   a  which can be used to introduce indentations  14  into the top face  15  of a ridge  8 . In  FIG. 6   a , the roller  9   a  is cut in its center plane. 
         [0040]      FIG. 6   b  shows the section A-A shown in  FIG. 6   a . Cone points  17  are integrally formed on the outer circumference of the roller  9   a  at regular intervals. When the roller  9   a  rolls on the top face  15  of a ridge  8   a  in the direction of the grooves, the indentations  14  are formed as plastic deformations in the ridge  8   a  and form the undercuts  13  already described in  FIGS. 4   a  and  5   a . The roller  9   a  is guided on the ridge  8   a  via two radially protruding guide disks  18   a  which are arranged on the sides of the roller  9   a . Therefore, the roller  9   a  centers itself with respect to the middle of the ridge  8   a , and it is ensured that the indentations  14  are always made precisely in the middle of the top face  15 . So that the guide disks  18   a  do not become blocked with the plastically deformed ridge  8  in the region of the indentations  14 , the guide disks  18   a  are cut out radially and axially in the region of the cone points  17 . 
         [0041]      FIGS. 7   a  and  7   b  show a roller  9   c  which is used to plastically deform ridge edges  16 . In  FIG. 7   a , the roller  9   c  is cut in its center plane.  FIG. 7   b  shows the section B-B shown in  FIG. 7   a . The roller  9   c  is also guided on the ridge  8   c  via two radially protruding guide disks  18   c  which are arranged on the sides of the roller  9   c . Triangular shoulders  19  are integrally formed on the outer circumference of the roller  9   c  at regular intervals. The guide disks  18   c  and roller  9   c  are expediently formed integrally so as to provide the shoulders with a higher strength. When the roller  9   c  rolls on the top face  15  of a ridge  8   a  in the direction of the grooves, the ridge edges  16  are plastically deformed at regular intervals. These deformations are indentations or crimped portions of the ridge  8   c  and the ridge edges  16 , as a result of which the undercuts  13  already described in  FIGS. 4   c  and  5   c  are formed. 
         [0042]      FIG. 8   a  shows a side view of a roller  9   d  which can be used to plastically deform the ridges  8   d  in the transverse direction.  FIG. 8   b  shows the section A-A, and  FIG. 8   c  the section B-B, shown in  FIG. 8   a . The roller  9   d  has a central guide disk  18   d  which is integrated in the roller  9   d  and is guided in a groove  7 ′. At regular intervals, the guide disk  18   d  has conical projections  20  which start on the outer circumference, i.e. are not yet present there, and then increase toward the axis of rotation of the roller  9   d -radially inward. When the roller  9   d , guided by the guide disk  18   d , rolls in a groove  7 , the conical projections  20  result in regular plastic deformation of the ridges  8   d , in such a manner that the latter are bent toward the side in the region of the projections  20 , as a result of which the undercuts  13  are produced. 
         [0043]    In order that a ridge  8   d  is bent both to the right and to the left, it is necessary, when the roller  9   d  is guided in the groove  7 ″ adjacent to the groove  7 ′, for the ridge  8   d  to be deformed by the projections  20  on the other side of the roller  9   d  in a correspondingly different direction. This can be seen in  FIG. 8   b , where the roller  9   d  is guided in the first groove  7 ′ and bends the ridge  8   d ′ to the left and the ridge  8   d ″ to the right. In  FIG. 8   c , the roller  9   d  passes through the groove  7 ″ adjacent to the groove  7 ′ and accordingly deforms the ridge  8   d ″ to the left and the ridge  8   d ″′ to the right. In order for this bending to take place alternately to the right and left in a ridge, the rotation of the roller  9   d  is aligned between the grooves  7 ′ and  7 ″. This is carried out in that the guide disk  18   d , in the region between two projections  20 , always has a recess  21  which corresponds to the ridge  8   d ″ bent over to the right. Therefore, the right-hand shoulder  20 ′ can only ever bend the ridge  8   d ″ to the left between two bending movements of the ridge  8   d ″ to the right. 
         [0044]      FIG. 9   a  shows the section through a punch tool  22  for the plastic deformation of the ridge edges  16  (not shown). A punch  23  is mounted in a spring-elastic manner in the punch tool  22  and periodically extends when the punch tool  22  moves along a ridge  8 . The movement of the punch can be produced by any suitable actuator or else mechanically by cam disks which are arranged, for example, on the rotary spindle. The punch head  24  has the negative form for the plastic deformation which the punch is intended to exert on the ridge edges  16 .  FIG. 9   b  shows the front view of the punch head  24 . 
         [0045]      FIG. 10   a  shows the section through a punch tool  22 ′ for the plastic transverse deformation of a ridge  8 . Two punches  23   a  and  23   b  are mounted in a spring-elastic manner in the punch tool  22 ′ and periodically alternately extend when the punch tool  22  moves along the ridge  8 . The punches  23   a, b  are arranged so as to be inclined in the transverse direction with respect to the grooves  7 , in order that the punch heads  24   a, b  can move at least partially into the groove  7  in order to hit the ridge  8 . In this case too, the movement of the punch can be produced by any suitable actuator or mechanically. The plan view of the punch tool  22 ′ in  FIG. 10   b  shows the extended punch  23   a  which deforms the ridge  8  upward.  FIG. 10   c  shows—in the meantime, the punch tool  22 ′ has moved on along the ridge  8 —the downward deformation of the ridge  8  by the punch  23   b.    
         [0046]      FIGS. 11   a - 11   c  show a further embodiment for transverse deformation. A twin-roller tool  25  has the two skew rollers  26   a ,  26   b . The two skew rollers are arranged on both sides of the ridge  8  to be deformed. They are inclined in relation to each other and engage one into the other with their undulating circumferential profile  27 , the ridge  8  to be deformed being arranged between the skew rollers  26   a ,  26   b . When the twin-roller tool  25  moves along the ridge  8  and the skew rollers  26   a ,  26   b  rotate, the ridge  8  is alternately bent upward and downward, as can be seen from the plan views in  FIGS. 11   b  and  11   c.