Method and System for Producing a Threaded Bolt

Abstract

The invention relates to a method for producing a threaded bolt. A blank is introduced into a threaded-bolt negative mold. The blank has a bolt-shaped portion. Fibers which are aligned in the longitudinal direction of the bolt-shaped portion are embedded in a plastics material in the blank. Pressure is exerted on the blank in order to deform the blank in the negative mold such that a threaded structure is formed on a circumferential face of the bolt-shaped portion. The invention moreover relates to a threaded bolt which is manufacturable by this method, and to a system which is conceived for carrying out the method. Lightweight and hard-wearing threaded bolts may be manufactured by the method according to the invention.

Claims

1. A method for producing a threaded bolt comprising: providing a blank of plastic material with embedded fibers aligned in a longitudinal direction of a cylindrical portion of said blank; inserting said blank into a mold defining a cavity in the form of the threaded bolt to be produced; exerting pressure on the blank to deform the blank within the cavity, whereby a threaded structure is formed on a circumferential face of said cylindrical portion.

2. The method of claim 1, wherein said step of providing comprises providing a blank of thermoplastic material.

3. The method of claim 2, wherein said thermoplastic material is polyetheretherketone (PEEK).

4. The method of claim 1, comprising the step of: before said step of inserting, heating said blank to a temperature at least 80% of a melting temperature of said plastic material.

5. The method of claim 1, comprising the step of: before said step of inserting, heating said blank to a temperature at least 90% of a melting temperature of said plastic material.

6. The method of claim 1, comprising the step of: heating said mold to a temperature that is higher than a melting temperature of said plastic material.

7. The method of claim 1, comprising the step of: heating the radial periphery of said cylindrical portion to a temperature higher than a melting temperature of the plastic material before the step of exerting pressure on the blank.

8. The method of claim 1, wherein said step of exerting pressure on the blank comprises: applying a pressure between 150 MPa and 400 MPa on the blank in a direction aligned with the longitudinal direction of the cylindrical portion of the blank.

9. The method of claim 8, wherein said pressure is between 200 MPa and 300 MPa.

10. The method of claim 1, wherein said cavity extends axially beyond a portion defining said threaded structure and includes an axial end face axially spaced from said threaded structure and said step of inserting comprises: inserting said blank into said cavity so that an axial end of the blank is axially spaced from said axial end face prior to said step of exerting pressure on the blank; and the blank is deformed to bear on said axial end face following said step of exerting pressure on the blank.

11. The method of claim 1, comprising: forming a head on a rear portion of said blank opposite the cylindrical portion, said step of forming comprising: heating said rear portion to a temperature greater than a melting point of said plastic material; and exerting pressure against the rear portion to form the head.

12. The method of claim 11, wherein said step of forming a head is performed after said threaded structure is formed on a circumferential face of said cylindrical portion.

13. The method of claim 11, wherein a radial depth of said blank is heated beyond a melting point of the plastic material during formation of said threaded structure, and said step of heating said rear end comprises: heating an axial extent of the rear end is heated to a temperature greater than a melting point of said plastic material, said axial extent being greater than said radial depth.

14. The method of claim 1, comprising: filling a region of said cavity corresponding to a head of the threaded bolt with an insert piece surrounding a rear portion of the blank during formation of said threaded structure; removing said insert piece; and exerting pressure against the rear portion of the blank to form a head.

15. The method of claim 15, comprising: heating the blank along with said insert piece prior to said step of inserting said blank.

16. A threaded bolt manufactured according to the method of claim 1.

17. A system for manufacturing a threaded bolt, the system comprising: a mold defining a cavity in the form of the threaded bolt to be produced; and a die arranged for exerting pressure on a blank inserted into said cavity to deform the blank in the cavity so that a threaded structure is formed on a circumferential face of a cylindrical portion of said blank.

18. The system of claim 17, wherein said mold includes an insert piece configured to support a rear portion of said blank during formation of said threaded structure, and said a first die arranged to exert pressure on said blank to form said threaded structure; and a second die arranged to form a head of the threaded bolt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention will be described hereunder in an exemplary manner with reference to the appended drawings and by means of advantageous embodiments. In the drawings:

[0029] FIG. 1 shows a schematic illustration of a system according to the invention, in various states A to D;

[0030] FIG. 2 shows a schematic illustration of a blank;

[0031] FIG. 3 shows a schematic illustration of the method according to the invention; and

[0032] FIG. 4 shows a threaded bolt which has been manufactured by the method according to the invention.

DETAILED DESCRIPTION

[0033] In FIG. 1, a system according to the invention comprises a molding tool 14 in which a threaded-bolt negative mold cavity 15 in the shape of the threaded bolt to be produced. The molding tool 14 is received in a heating and cooling installation 19 which surrounds the molding tool 14 laterally and on the lower side. The molding tool 14 is assembled from two halves which bear on one another along a vertical separation joint. According to FIG. 1A, the system according to the invention moreover comprises an insert piece 16 having a central through opening in which a blank 17 is disposed.

[0034] The threaded-bolt negative mold cavity 15 extends from an opening at the upper end to an end face at the lower end. The end face delimits a first cylindrical portion, the diameter thereof being smaller than the diameter of the blank 17. A second cylindrical portion, the diameter thereof being somewhat larger than the diameter of the blank 17 adjoins the first cylindrical portion. The first cylindrical portion has a smooth shell surface. A threaded structure 18 is configured in the wall of the second cylindrical portion (cf. FIG. 3). The second cylindrical portion transitions into a third portion, the latter widening in a conical manner toward the opening. The first, the second, and the third portion together form the threaded-bolt negative mold in which the threaded bolt has a threadless front portion, a shaft provided with a thread, and a countersunk head.

[0035] The insert piece 16 has a protrusion 23 which matches the third portion of the threaded-bolt negative mold and tapers off toward the bottom in a conical manner. If the insert piece 16 is guided toward the molding tool 14 (FIG. 1B), the protrusion 23 of the insert piece 16 fills the third portion of the threaded-bolt negative mold. The central through opening in the insert piece 16 is disposed in the extension of the cylindrical portions of the threaded-bolt negative mold.

[0036] The system furthermore comprises a first die 20 and a second die 21 which are conceived for exerting pressure in the axial direction on the rear end of the blank 17. The first die 20 is cylindrical, having a diameter matching the diameter of the through bore in the insert piece 16. The second die 21 is likewise cylindrical, having a diameter which is at least as large as the opening at the upper end of the threaded-bolt negative mold cavity 15. The second die 21 is provided with a heating installation 22 which is conceived for heating the rear portion of the blank 17.

[0037] An enlarged illustration of the blank 17 is shown in FIG. 2. The blank is composed of PEEK having embedded carbon fibers. PEEK is a thermoplastic plastics material with a melting temperature of 335° C. The parallel vertical lines in FIG. 2 that extend in the longitudinal direction of the blank show the preferred direction of the carbon fibers.

[0038] The sequence of the method according to the invention is as follows. The insert piece 16 together with the blank 17 which has been inserted into the through opening is heated in an oven (not illustrated) to a temperature of the magnitude of the melting temperature of PEEK. In parallel therewith, the molding tool 14 by way of the heating installation 19 is elevated to a temperature of approximately 400° C. The die 20 is heated to a temperature of approximately 300° C.

[0039] The insert piece 16 having the blank 17 disposed therein is guided toward the molding tool 14 such that the protrusion 23 of the insert piece 16 engages in the upper portion of the threaded-bolt negative mold cavity 15. The blank 17 is pushed downward by the first die 20 which is introduced into the through opening of the insert piece 16 such that said blank 17 penetrates into the threaded-bolt negative mold. FIG. 1B shows the state in which the blank 17 is introduced into the negative mold to the extent that the front end face of the blank 17 bears on the shoulder face which delimits the first portion of the threaded-bolt negative mold.

[0040] In this state, the system is idle for a time span of 30 seconds, for example, such that the external region of the blank 17 that bears on the 14 is elevated to a temperature beyond the melting temperature of PEEK. Upon termination of this heating phase, the external region of the blank 17 may have a temperature of 380° C., for example. By contrast, the temperature in the core of the blank 17 remains below the melting temperature of PEEK.

[0041] The die 20, at a high pressure of 250 MPa, for example, is then guided further forward such that the blank 17 advances up to the end face of the threaded-bolt negative mold. The deformation of the blank 17 that is associated therewith leads to the material of the blank 17 penetrating into the threaded structure of the molding tool 14 such that a threaded structure is created on the external side of the blank.

[0042] As is shown in FIGS. 3 and 4, the alignment of the carbon fibers in the core region of the structure is substantially maintained in the case of this forming procedure. It is only in the external region in which the thread is formed that the fibers adapt to the threaded structure, the fibers preferably not being severed. The thread which is produced in this manner has very high stability and, at the same time, is of light weight.

[0043] Upon the threaded structure having been molded, the first die 20 and the insert piece 16 are removed from the molding tool 14. Instead, the second die 21 which is provided with the heating installation 22 is moved toward the rear-side end face of the blank 17. The second die 21 is heated to a temperature of more than 400° C., enabling the rear portion of the blank 17 to be heated to a temperature above the melting temperature of PEEK by way of contact with the second die 21 (cf. FIG. 1C).

[0044] Upon termination of this heating phase, the second die 21 at very high pressure is guided forward such that the rear portion of the blank 17 is deformed, filling the conical region of the threaded-bolt negative mold. In this way, this portion of the blank 17 is formed to a countersunk head of the threaded bolt (cf. FIG. 1D).

[0045] Compressed air is subsequently directed into ducts which are configured in the heating and cooling installation 19 of the molding tool 14, so as to cool the molding tool 14. Upon having been sufficiently cooled, the two halves of the molding tool 14 are separated, enabling the finished threaded bolt 24 to be removed from the mold (cf. FIG. 4).