Method for manufacturing a profiled rod

Abstract

Method for manufacturing a profiled rod from a rod-shaped metal blank including a first deformation step, in which the blank is embedded in a first die arrangement, and subsequently, the blank is axially compressed so as to radially displace blank material within the first die arrangement to form a first surface protrusion structure on the blank, and following the first deformation step, a second deformation step, in which the blank is embedded in a second die arrangement, and subsequently, the blank is axially compressed so as to radially displace blank material within the second die arrangement to form a second surface protrusion structure on the blank, wherein at least a section of the second surface protrusion structure is closer to the first end than the first surface protrusion structure is.

Claims

1-9. (canceled)

10. A method for manufacturing a profiled rod from a rod-shaped metal blank having a first end and a second end located opposite the first end, and having a longitudinal axis extending through the first end and through the second end, the method comprising: a first deformation step, in which the blank is embedded in a first die arrangement, and subsequently, the blank is axially compressed so as to radially displace blank material within the first die arrangement to form a first surface protrusion structure on the blank; and following the first deformation step, a second deformation step, in which the blank is embedded in a second die arrangement, and subsequently, the blank is axially compressed so as to radially displace blank material within the second die arrangement to form a second surface protrusion structure on the blank, wherein at least a section of the second surface protrusion structure is closer to the first end of the blank than the first surface protrusion structure is.

11. The method as recited in claim 10 wherein at least part of the second surface protrusion structure is contiguous with at least part of the first surface protrusion structure.

12. The method as recited in claim 10 wherein a further section of the second surface protrusion structure is closer to the second end than the first surface protrusion structure is.

13. The method as recited in claim 10 wherein in the first deformation step, the blank is axially compressed by simultaneously advancing both the first end and the second end with respect to the first die arrangement, and in the second deformation step, the blank is axially compressed by simultaneously advancing both the first end and the second end with respect to the second die arrangement.

14. The method as recited in claim 10 wherein the first surface protrusion structure and the second surface protrusion structure define at least one helical screw thread structure.

15. The method as recited in claim 10 wherein in the first deformation step, the blank is axially compressed so as to radially outwardly displace blank material within the first die arrangement, and in the second deformation step, the blank is axially compressed so as to radially outwardly displace blank material within the second die arrangement.

16. The method as recited in claim 10 wherein the blank consists of steel.

17. The method as recited in claim 10 further comprising a screw head formation step following the first deformation step and the second deformation step, a screw head being formed on the blank during the screw head formation step.

18. A screw comprising: at least one screw thread, wherein in at least one sectional plane of the screw thread including a longitudinal axis of the screw, all flow lines of the screw thread are strictly convex with respect to the longitudinal axis of the screw.

19. A screw manufactured according to the method as recited in claim 10, the screw comprising: at least one screw thread, wherein in at least one sectional plane of the screw thread including a longitudinal axis of the screw, all flow lines of the screw thread are strictly convex with respect to the longitudinal axis of the screw.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is explained in greater detail below with reference to preferred exemplary embodiments, which are depicted schematically in the accompanying drawings. Individual features of the exemplary embodiments presented below can be implemented either individually or in any combination within the scope of the present invention.

[0031] FIGS. 1 to 11 illustrate consecutive steps of a manufacturing method.

[0032] FIG. 12 illustrates a floating die system that can be used in one or more of the deformation steps of the method of FIGS. 1 to 11.

[0033] FIGS. 13 and 14 illustrate alternative deformation steps applied to a hollow rod-shaped blank 5.

[0034] FIGS. 15 to 18 show sectional views through differently-manufactured screws having a screw thread each, in each case in a sectional plane that includes the longitudinal axis of the screw.

DETAILED DESCRIPTION

[0035] FIGS. 1 to 11 illustrate consecutive steps of an exemplary manufacturing method. In a first step, illustrated in FIG. 1, an elongate, rod-shaped blank 5 is provided. In particular, the blank 5 is generally circular cylindrical and can be a piece of wire. The blank 5 consists of metal, in particular of steel.

[0036] The blank 5 comprises a first end 51 and a second end 52, wherein the first end 51 is located opposite the second end 52 on the blank 5. The blank 5 furthermore comprises a longitudinal axis 59, which passes through both the first end 51 and the second end 52. In the present embodiment, the blank 5 is solid, i.e. without an internal cavity.

[0037] In a first deformation step, which is illustrated in FIGS. 2 and 3, the blank 5 is arranged in a first die arrangement 10, so that the first die arrangement 10 surrounds the lateral surface of the blank 5 in an annular manner, as shown in FIG. 2. The first die arrangement 10 is provided with a first cavity 31 intended to receive blank material when the blank 5 is axially (with respect to its longitudinal axis 59) compressed. When the blank 5 is embedded in the first die arrangement 10 as intended (i.e. when the first die arrangement 10 surrounds the blank 5 in an annular manner), the first cavity 31 projects radially outwardly (with respect to the longitudinal axis 59) from the blank 5. In the present embodiment, the first cavity 31 is helical and has the form of an internal thread.

[0038] As shown in FIG. 3, the blank 5 is then axially (with respect to the longitudinal axis 59) compressed. In particular, the blank 5 is axially compressed by displacing both the first end 51 and the second end 52 relative to the first die arrangement 10 into the first die arrangement 10. This is achieved by means of a punch 61 that acts upon the first end 51 and a counterpunch 62 that acts upon the second end 52, wherein both the punch 61 and the counterpunch 62 are displaced relative to the first die arrangement 10. Simultaneous advancement of both the punch 61 and the counterpunch 62 into the first die arrangement 10 can be achieved using a floating die system like that shown in FIG. 12, and described in more detail below.

[0039] The mentioned axial compression of the blank 5 causes blank material to be displaced and to flow radially outwardly, away from the longitudinal axis 59, into the first cavity 31. In this way, a first surface protrusion structure 1 is formed on the lateral surface of the blank 5. The first surface protrusion structure 1 geometrically corresponds to the first cavity 31 and therefore, the first surface protrusion structure 1 is a helical external thread section in the present embodiment. The resulting blank 5 is illustrated in FIG. 4.

[0040] In a second deformation step, which follows the first deformation step, and which is illustrated in FIGS. 5 and 6, the blank 5 is arranged in a second die arrangement 20, so that the second die arrangement 20 surrounds the lateral surface of the blank 5 in an annular manner, as shown in FIG. 5. The second die arrangement 20 is provided with a supporting cavity 38 for receiving the first surface protrusion structure 1. The second die arrangement 20 is furthermore provided with a second cavity 32 intended to receive blank material when the blank 5 is axially (with respect to its longitudinal axis 59) compressed. When the blank 5 is embedded in the second die arrangement 20 as intended (i.e. when the second die arrangement 20 surrounds the blank 5 in annular manner), the supporting cavity 38 and the second cavity 32 project radially outwardly (with respect to its longitudinal axis 59) from the blank 5.

[0041] As shown in FIG. 6, the blank 5 is then axially (with respect to the longitudinal axis 59) compressed. In particular, the blank 5 is axially compressed by displacing both the first end 51 and the second end 52 relative to the second die arrangement 20 into the second die arrangement 20. This is achieved by means of a punch 61 that acts upon the first end 51 and a counterpunch 62 that acts upon the second end 52, wherein both the punch 61 and the counterpunch 62 are displaced relative to the second die arrangement 20. Simultaneous advancement of both the punch 61 and the counterpunch 62 into the second die arrangement 20 can again be achieved using a floating die system like that shown in FIG. 12, and described in more detail below.

[0042] The mentioned axial compression of the blank 5 causes blank material to be displaced and to flow radially outwardly, away from the longitudinal axis 59, into the second cavity 32. In this way, a second surface protrusion structure 2 is formed on the lateral surface of the blank 5. The second surface protrusion structure 2 geometrically corresponds to the second cavity 32.

[0043] The second cavity 32 comprises two helical sections and extends on both sides of the first cavity 31, i.e. the supporting cavity 38 is axially embedded in the first cavity 31. As a consequence, the second surface protrusion structure 2 has a helical first section 2′, which is located closer to the first end 51 of the blank 5 than the first surface protrusion structure 1 is, as well as a helical second section 2″, which is located closer to the second end 52 of the blank 5 than the first surface protrusion structure 1 is. In other words, the second surface protrusion structure 2 extends, axially, on both sides of the first surface protrusion structure 1. In the present embodiment, both sections of the second cavity 32 are helical and have the form of an internal thread. The first cavity 31 and the second cavity 32 are so dimensioned that the first surface protrusion structure 1 and the second surface protrusion structure 2 form a contiguous helical thread structure.

[0044] The supporting cavity 38 can be so dimensioned that it rests snugly against the first surface protrusion structure 1 when the blank 5 is inserted into the first die arrangement 10. Alternatively, the supporting cavity 38 can be, at least regionally, larger than the first surface protrusion structure 1, so that the first surface protrusion structure 1 is further deformed in the second deformation step.

[0045] The blank 5 resulting from the second deformation step is illustrated in FIG. 7.

[0046] The present embodiment includes a third deformation step, illustrated in FIGS. 8 and 9. The third deformation step is analogous to the second deformation step, wherein in the third deformation step, the contiguous helical thread structure is further extended towards the first end 51 and towards the second end 52 of the blank. The blank 5 resulting from the third deformation step is shown in FIG. 10.

[0047] Finally, in an screw head formation step, a screw head 58 is formed on the first end 51 of the blank 5, as shown in FIG. 11, for example by upsetting the blank 5.

[0048] FIG. 12 shows a floating die system, which can be used for the method illustrated in FIGS. 1 to 11. In such a floating die system, the respective die arrangement (for example the first die arrangement 10 or the second die arrangement 20) is spring-suspended both with respect to the punch 61 intended for acting against the first end 51 of the blank 5, and with respect to the counterpunch 62 intended for acting against the second end 52 of the blank 5. If the punch 61 is advanced towards the counterpunch 62, the spring-suspension will transform this movement into simultaneous movement of both the punch 61 and the counterpunch 62 into the respective die arrangement 10 or 20 (as also described in U.S. Pat. No. 4,274,276).

[0049] In the previous embodiments, the blank 5 was solid, i.e. without an internal cavity. It is, however, also possible to use a hollow blank 5. In this case, the respective die arrangement 10 or 20 could include a support mandrel 66, which is inserted into the hollow blank 5 during the first and/or second deformation step. The support mandrel 66 can be generally cylindrical, as shown in FIG. 13, or it could comprise at least sections of the first cavity 31 or second cavity 32, respectively, for forming internal first surface protrusion structures 1 or internal second surface protrusion structures 2, respectively, as shown in FIG. 14. Thus, internal thread structure could also be manufactured by means of the described method.

[0050] The method by which a screw thread is manufactured can be determined from the flow lines of the metal material. FIGS. 15 to 18 show, schematically, cross sections of screws 90 each having a screw thread 91 that has been manufactured by different methods, respectively, in each case in an exemplary sectional plane of the screw thread 91 that includes the longitudinal axis 99 of the screw 90.

[0051] In case of FIG. 15, the screw thread 91 has been manufactured by cutting, and all of the flow lines 95 of the screw thread 91 in the sectional plane are generally parallel, in particular to the longitudinal axis 99 of the screw 90.

[0052] In case of FIG. 16, the screw thread 91 has been manufactured by rolling. In this case, some of the flow lines 95 of the screw thread 91 in the sectional plane are generally convex with respect to the longitudinal axis 99 of the screw 90. However, some flow lines 95 close to the crest of the screw thread 91 have some concavity and are therefore not strictly convex with respect to the longitudinal axis 99 of the screw 90.

[0053] In case of FIGS. 17 and 18, the screw thread 91 has been manufactured by lateral impact extrusion, i.e. by axially compressing a blank so as to radially displace blank material to give the screw thread 91. In this case, all of the flow lines of the screw thread 91 in the sectional plane are strictly convex with respect to the longitudinal axis 99 of the screw 90, wherein the flow lines could be either symmetric (see FIG. 17) or also tilted (see FIG. 18), depending on process details such as friction, thread pitch, geometry and/or others.