METHOD AND TOOL FOR MECHANICALLY ROUGHENING A CYLINDRICAL SURFACE

Abstract

A method for mechanically roughening a cylindrical surface of a workpiece, e.g. the piston-bearing surface of a cylinder sleeve in a cylinder crankcase, by producing a defined microstructure of mutually crossing grooves, and by a groove forming tool, operating with or without material removal. A method in which in a first operation, a groove-forming tool is moved axially along the workpiece surface in such a way that at least one axial groove is machined into the workpiece surface; and in a second operation, following the first operation, the groove forming tool is rotated about the cylinder axis by a predefined rotational angle in the axial position reached in the first operation, whereby at least one circumferential groove crossing the axial groove is machined into the workpiece surface; and in a third operation following the second operation, the groove-forming tool is drawn back axially along the workpiece surface.

Claims

1. A method for mechanically roughening a cylindrical surface of a workpiece by generating a defined microstructure of mutually crossing grooves by means of a non-cutting or cutting groove molding tool, the method comprising: a) in a first operation, moving the groove molding tool axially along the workpiece surface in such a way as to introduce at least one axial groove into the workpiece surface; b) in a second operation following the first operation, the groove molding tool in the axial position reached in the first operation is turned around the cylinder axis by a prescribed rotational angle, as a result of which at least one circumferential groove that crosses the axial groove is introduced into the workpiece surface, and c) in a third operation following the second operation, the groove molding tool is retracted axially along the workpiece surface.

2. The method according to claim 1, wherein the forward tool stroke is larger than the axial extension of the workpiece surface to be machined.

3. The method according to claim 1, wherein the prescribed rotational angle measures an integral multiple of an angle obtained from dividing 360 as the dividend and the number of the at least one axial groove as the divisor.

4. The method according to claim 1, wherein, in the event of several axial grooves, the latter is equidistantly distributed around the cylinder axis in the circumferential direction.

5. The method according to claim 1, wherein at least one pair of diametrically opposing axial grooves can be molded into the workpiece surface in the first operation.

6. The method according to claim 4, wherein the prescribed rotational angle measures 180 or 360.

7. The method according to claim 1, wherein the axial and/or circumferential grooves are molded toward a defined final dimension or a defined final cross section.

8. The method according to claim 1, wherein the axial and/or circumferential grooves are given a dovetailed undercut.

9. The method according to claim 1, wherein: d) in a fourth operation d), the groove molding tool is again turned relative to the workpiece around the cylinder axis of the workpiece surface by a prescribed rotational angle differing from the rotational angle of the second operation, and e) the first to third operations are subsequently performed once again.

10. A groove molding tool for mechanically roughening a cylindrical surface of a workpiece, comprising a carrier body that carries at least one axially parallel row of teeth, the at least one row of teeth encompassing at least one axial tooth to form an axial groove and at least one circumferential tooth to form one or more circumferential grooves, both arranged one after the other in an axial direction, the cross-section of each circumferential tooth as viewed in an axial projection in the forward tool stroke direction lying within the cross-section of the at least one axial tooth.

11. The groove molding tool according to claim 10, wherein the at least one axial tooth as viewed in an axial projection in the forward tool stroke direction comprises a dovetailed cross-section.

12. The groove molding tool according to claim 10, wherein the groove molding tool comprises at least two axial teeth, which are axially staggered and whose cross-sections overlap as viewed in an axial projection in the forward tool stroke direction to form an overlapping cross-section.

13. The groove molding tool according to claim 10, wherein the teeth arranged in one and the same row of teeth are formed on one or several tooth elements arranged axially one after the other, which are detachably or permanently secured to the carrier body.

14. The groove molding tool according to claim 13, wherein the at least one axial tooth and the at least one circumferential tooth are formed on various tooth elements.

15. The groove molding tool according to claim 10, wherein the groove molding tool comprises several rows of teeth.

16. The groove molding tool according to claim 10, wherein the at least one circumferential tooth comprises a dovetailed cross section as viewed in the circumferential direction.

17. The groove molding tool according to claim 10, wherein the groove molding tool comprises at least one pair of diametrically opposed rows of teeth.

18. The groove molding tool according to claim 17, wherein the cross-section of at least one circumferential tooth of one of the two rows of teeth and the cross-section of at least one circumferential tooth of the diametrically opposing other of the two rows of teeth overlap as viewed in the circumferential direction.

19. The groove molding tool according to claim 10, wherein the groove molding tool comprises a clamping shaft for clamping the groove molding tool to a separation point or interface of a machine tool system.

20. The method according to claim 1, wherein the workpiece is metallic.

21. The method according to claim 1, wherein the cylindrical surface is a piston bearing surface of a cylinder sleeve in a cylinder crankcase.

22. The groove molding tool according to claim 12, wherein the overlapping cross-section is undercut.

23. The groove molding tool according to claim 12, wherein the overlapping cross-section is dovetailed.

24. The groove molding tool according to claim 15, wherein the several rows of teeth are equidistantly distributed in a circumferential direction of the groove molding tool.

25. The groove molding tool according to claim 17, wherein the cross section of at least one circumferential tooth of one of the two rows of teeth and the cross section of at least one circumferential tooth of the diametrically opposing other of the two rows of teeth overlap as viewed in the circumferential direction to form a dovetailed, overall cross section.

Description

[0042] A method according to the invention and a groove molding tool according to the invention will be introduced below using the attached drawings, in which:

[0043] FIG. 1 presents a highly simplified sketch of an initial state;

[0044] FIG. 2 presents a highly simplified sketch of a first operation of the method according to the invention;

[0045] FIG. 3 presents a highly simplified sketch of a second operation of the method according to the invention;

[0046] FIG. 4 presents a highly simplified sketch of a third operation of the method according to the invention;

[0047] FIG. 5 shows a simplified, perspective view of an exemplary embodiment of a groove molding tool according to the invention for implementing the method sketched on FIGS. 1 to 4;

[0048] FIG. 6 shows a magnified view of a region of an axial tooth longitudinal section denoted with dashed lines on FIG. 5;

[0049] FIG. 7 shows a magnified view of a circumferential tooth longitudinal section denoted with dot-dashed lines on FIG. 6;

[0050] FIG. 8 shows another circumferential tooth longitudinal section, similarly to FIG. 7;

[0051] FIG. 9 shows a front view of the groove molding tool from FIG. 5; and

[0052] FIG. 10 shows a magnified view of a front section denoted with dot-dashed lines on FIG. 9.

[0053] In the following, FIGS. 1 to 4 will first be used to outline the essential operations of a method according to the invention, and also to introduce the basic structure of a groove molding tool according to the invention.

[0054] FIG. 1 shows an initial state. Visible on the bottom left is a highly simplified top view of a cylinder sleeve 10 of a cylinder crankcase 11 (workpiece). The inner surface 12 of the cylinder sleeve 10 comprises the surface to be roughened. FIG. 1 further shows a developed view of the inner surface 12 of the cylinder sleeve 10 on the bottom right, and a schematized view of a groove molding tool 20 on the top right. In the initial state sketched on FIG. 1, the groove molding tool 20 is positioned axially above the cylinder sleeve 10, specifically in such a way that the longitudinal center line 21 of the groove molding tool 20 coincides with the cylinder axis 13 of the cylinder sleeve 10, or expressed differently, the groove molding tool 20 is aligned coaxially to the cylinder sleeve 10.

[0055] In the exemplary embodiment shown on FIG. 1, the groove molding tool 20 has six rows of teeth 23, of which three are visible on FIG. 1. The rows of teeth 23 are arranged on a central carrier body 22, parallel to the longitudinal center line 21. The number, radial position and circumferential distribution of the rows of teeth 23 in relation to the longitudinal center line 21 corresponds to the axial grooves to be introduced into the inner surface 12. In terms of function, each of the rows of teeth 23 can be divided into two longitudinal sections 24 and 25. The front longitudinal section 24 as viewed in the forward tool stroke direction (see arrow on FIG. 1) encompasses at least one tooth to form an axial groove (hereinafter: axial tooth or axial teeth), while the longitudinal section of each row of teeth 23 lying behind the longitudinal section 24 as viewed in the forward tool stroke direction encompasses at least one, but normally a plurality of teeth to form a corresponding plurality of circumferential grooves (hereinafter: circumferential tooth or circumferential teeth). Reference numbers 24 and 25 on FIG. 1 thus indicate at least one axial tooth or at least one circumferential tooth.

[0056] In a case where several, for example two, axial teeth are provided in one and the same row of teeth, the latter are axially staggered one after the other just as in a progressive tool so as to successively form one and the same axial groove to a prescribed final dimension and/or a prescribed final cross section. For example, the several axial teeth can be designed in such a way as to successively form an axial groove toward a prescribed radial depth and/or circumferential width. Simultaneously or alternatively, the several axial teeth can be configured in such a way as to successively form the groove flanks of the axial groove toward a prescribed final cross section. As sketched on FIGS. 2 to 4, the final cross section can have a simple rectangular design, or exhibit a dovetailed undercut, for example. An undercut cross section can help achieve a better toothing for a surface coating with the cylinder sleeve 10 to be applied to the roughened inner surface 12 at a later time.

[0057] As opposed to the axial teeth, each circumferential tooth of a row of teeth forms another circumferential groove, as has yet to be explained drawing upon FIGS. 3 and 4. In the event that several circumferential teeth are provided in one and the same row of teeth 23, they are arranged one after the other like a comb. However, each circumferential tooth is designed in such a way, as viewed in an axial projection in the forward tool stroke direction, that its cross section lies within a cross section of the at least one axial tooth. In the case where one row of teeth 23 has exactly one axial tooth, the cross section of each ensuing circumferential tooth as viewed in the axial projection thus lies within the cross section of the one axial tooth. In the case where a row of teeth 23 has several axial teeth, the cross section of each ensuing circumferential tooth lies within a cross section referred to as the overlapping cross section, which as viewed in the axial projection results from an overlapping of cross sections of each of the several axial teeth. This measure ensures that the circumferential tooth/teeth do(es) not collide with the cylinder sleeve 10, i.e., the workpiece, during the purely axial movement of the groove molding tool 20 performed in the first operation, but instead run(s) within the axial groove that the at least one leading axial tooth in the forward tool stroke direction has already formed.

[0058] The above notwithstanding, the circumferential teeth in a row of teeth can have basically the same, but also differing cross sections. In terms of having a good toothing with a surface coating to be applied to the inner surface 12 at a later time, it can be advantageous for the circumferential teeth to have a dovetailed cross section. However, dovetailed undercut circumferential grooves can also be generated by having the circumferential teeth of two diametrically opposing rows of teeth be oppositely oriented, and thereby each form one of the two flanks of a respective circumferential groove during a 360 rotation.

[0059] Important to remember in this conjunction is that the term tooth generally refers to a tooth-shaped contour on the groove molding tool for forming an axial or circumferential groove, regardless of whether the tooth in question is configured for non-cutting and cutting machining processes. Therefore, a tooth has a geometrically defined or geometrically undefined blade for groove machining with cutting, e.g., resembling a tusk of a groove slotting tool, a cutting tooth, a broaching needle or a honing stone of a honing tool, etc., or a contour for machining by shaping and not cutting. For this reason, the microgroove structure to be formed on the inner surface 12 of the cylinder sleeve 11 with the method according to the invention can basically be formed without cutting and/or by cutting. Therefore, the groove molding tool 20 can be designed as purely a shaping or cutting tool, or as a tool that combines the aforementioned machining types of cutting (e.g., by clearing, punching, engraving, milling, honing, etc.) and shaping (via embossing, impressing).

[0060] The teeth situated in one and the same axial row can be located on one or several elements arranged axially one after the other, e.g., inserts, plates, strips or the like, which can be exchanged via bolting, clamping, bonding, soldering, etc. on the carrier body 22 of the groove molding tool 20, or are permanently secured in place. These elements are preferably arranged in receiving pockets open to the outer periphery on the carrier body 22, and bolted with the carrier body 22 or clamped against the carrier body 22. The at least one axial tooth and the at least one circumferential tooth are advantageously formed on various, separate elements.

[0061] In the initial state shown on FIG. 1, the inner surface of the cylinder sleeve 10 has still not been machined.

[0062] In the first operation of the method according to the invention sketched on FIG. 2, the groove molding tool 20 is moved axially along the inner surface 12 of the cylinder sleeve 10 in the forward tool stroke direction denoted by the arrow, causing the at least one axial tooth of each row of teeth 23 to form an axial groove 14 on the inner surface 12. According to the invention, the groove molding tool 20 is moved downwardly until such time that at least just the one axial tooth on FIG. 1b is positioned axially outside of the cylinder sleeve 10 at the end of the movement or the first operation, as visible on FIG. 2. Therefore, the forward tool stroke is larger than the axial extension of the cylinder sleeve 10 or the inner surface 12 to be machined. The axial grooves 14 are thus continuous. They extend over the entire length of the cylinder sleeve 10 or inner surface 12. FIG. 2 shows the result of the first operation. Visible corresponding to the number of rows of teeth 23 are six axial grooves, each with a rectangular cross section per the graphic depiction.

[0063] FIG. 3 sketches the second operation that follows the first operation, in which the groove molding tool 20 in the axial position reached in the first operation Is turned around a prescribed rotational angle, 360 in the sketched example, around the cylinder axis 13 or longitudinal center line 21, as a result of which a number of circumferential grooves 15 corresponding to the number of circumferential teeth 25 is additionally introduced into the inner surface 12, crossing the axial grooves 14 at a right angle. FIG. 3 presents a highly simplified illustration of a plurality of circumferential grooves 15, which are annular in shape owing to the 360 rotation. Because the axial teeth 24 of each row of teeth 23 of the groove molding tool 20 are located axially outside, and hence not engaged with the cylinder sleeve 10 during the second operation, they are not exposed to any stress whatsoever. The circumferential grooves 15 are formed solely via the axial circumferential tooth/teeth 25. As mentioned above, once the circumferential teeth of two diametrically opposing rows of teeth 23 come to be oppositely oriented, the 360 rotation allows the circumferential teeth of the diametrically opposing rows of teeth 23 to each form one of the two flanks of a respective circumferential groove, e.g., with a dovetailed undercut.

[0064] FIG. 4 sketches the third operation that follows the second operation, in which the groove molding tool 20 in the rotational position reached in the second operation is axially retracted back into its initial position corresponding to the initial state along the inner surface 12 of the cylinder sleeve 10 in the return tool stroke direction denoted by the arrow.

[0065] In summation, according to the invention, the groove molding tool 20 is thus moved purely axially forward in the first operation, i.e., during the forward tool stroke, purely turned in the axial position achieved in the first operation during the second operation that follows the first operation, and moved purely axially back in the rotational position reached in the second operation during the third operation that follows the second operation, i.e., during the return tool stroke. The forward tool stroke in the first operation is preferably larger than the axial extension of the inner surface 12 to be machined, so that the at least one axial groove 14 introduced into the inner surface 12 in the first operation extends over the entire length of the cylindrical inner surface 12, i.e., is axially continuous. The return tool stroke, i.e., the distance of the groove molding tool 20 in the third operation, advantageously corresponds to the forward tool stroke, i.e., the distance of the groove molding tool 20 in the first operation, so that the groove molding tool, after going through the first to third operations, again arrives at its starting position. The third operation takes place idly in the sketched method, i.e., without any further machining of the inner surface 12.

[0066] Therefore, the three operations in the method according to the invention are characterized by purely axial or rotational movements of the groove molding tool 20 relative to the inner surface 12. These movements can be easily realized with the lowest time outlay from the standpoint of control technology. As a result, the method according to the invention yields a microgroove structure on the workpiece surface, which is defined by at least one axial groove and at least one circumferential groove running transverse to the at least one axial groove. The grooves forming the microstructure have a very small depth, e.g., ranging from 0.05 to 0.15 mm, roughly from 0.05 to 0.07 mm, in particular measuring roughly 0.06 mm, and width, e.g., ranging from 0.10 to 0.20, roughly 0.13 to 0.17 mm.

[0067] The movements of the groove molding tool 20 discussed above can be executed and controlled relatively easily with a conventional NC or CNC-controlled machine tool. To this end, the carrier body 22 of the groove molding tool 21 can further exhibit a clamping shaft not shown on FIGS. 1 to 4, e.g., a known HSK, SK or cylinder shaft, with which the groove molding tool 20 can in a known manner be joined to a separation point or interface of a modular machine tool system, for example.

[0068] FIGS. 5 to 10 present schematic views of an exemplary embodiment of a groove molding tool according to the invention for implementing the method sketched on FIGS. 1 to 4.

[0069] According to FIG. 6, the groove molding tool 20 has two axial teeth 24 24 per row of teeth 23, which are axially staggered as in a progressive tool in such a way as to successively form one and the same axial groove toward a prescribed final dimension and/or a prescribed final cross section. In addition, the axial teeth 24 24 are formed on a strip-shaped tooth element 24a, which is detachably fastened to the carrier body 22 via clamping with a clamping plate 24b. As further evident from FIG. 6, the strip-shaped tooth element 24a is arranged in a receiving pocket 22a open on the outer periphery on the carrier body 22, and bolted to the carrier body 22 or clamped against the carrier body 22. In the groove molding tool 20, a plurality of circumferential teeth 25, 25, etc. per row of teeth 23 is further formed on a strip-shaped tooth element 25a differing from the tooth element 24a, which similarly to the tooth element 24a is arranged in a receiving pocket open on the periphery on the carrier body 22 (not indicated in any more detail). As may be gleaned from FIG. 5, the groove molding tool 20 exhibits a plurality of such tooth elements 25a per row of teeth 23, with a respective plurality of circumferential teeth that are arranged in an axial row with the tooth element 24a.

[0070] As evident from FIG. 6, the axial and circumferential teeth 24, 25 of each row of teeth 23 of the depicted groove molding tool are designed as cutting teeth. For example, the axial teeth 24 are designed as a kind of broaching needle of a broaching tool. The groove molding tool 20 shown on FIGS. 5 and 6 thus represents a purely cutting tool with geometrically definite cutting contours.

[0071] FIGS. 7 to 10 present further views and sections of the groove molding tool.

[0072] As stated at the outset, however, the axial and/or circumferential teeth can also be designed for non-cutting machining, etc., as an alternative to the groove molding tool shown on FIGS. 5 to 10. In addition, the teeth arranged in one and the same axial row can be formed on one or several elements arranged axially one after the other, e.g., inserts, plates, strips or the like, which are exchangeable or permanently fastened to the carrier body via bolting, bonding, soldering, etc., instead of via clamping.

[0073] In addition, fewer or more rows of teeth can be provided instead of the depicted six rows of teeth 23, which can basically be circumferentially distributed equidistantly or unequally around the longitudinal center line of the groove molding tool. Depending on the number and distribution of rows of teeth, the rotational angle in the second operation can also differ from 360. According to claim 4, in the event of several axial grooves, the latter can preferably be equidistantly distributed around the cylinder axis in the circumferential direction, as already explained at the outset.

[0074] Additional variations and modifications of the method and groove molding tool according to the invention may be derived by the expert from the feature combinations discussed at the outset and/or the feature combinations in the claims. Such variations and modifications are the subject matter of the invention, and can serve as the basis for subsequent claim formulations.