The present invention pertains to a cold forming process for manufacturing ball pivots with a ball area, a cone area and a thread area for installation in ball and socket joints.
Machining as well as non-machining manufacturing processes are used, in principle, to manufacture ball pivots that are intended for installation in ball and socket joints. Larger amounts of waste material, which must be disposed of, take place during machining. In addition, there is a disadvantage that the waste material must first be purchased as a semifinished product. In addition, it is disadvantageous that cycle times that would substantially exceed a number of 10 pieces per minute are not possible on the machine tools that are commonly used at present. Moreover, it is necessary in case of machining that at least the thread area must be machined by a rolling operation in order to prepare the necessary threads in this area. The cycle times of such rolling operations are likewise in the above-mentioned range of about 10 pieces per minute.
As an alternative to machining, it is known in the state of the art that ball pivots can be manufactured according to the cold or hot process by pressing. The pressing operations can be carried out in the direction of the longitudinal axis of the ball pivot, in which case a residual flash is formed at one end of the ball pivot blank, or they are carried out horizontally in a two-part pressing die, in which case a burr is formed circularly around the entire pressed blank. The burrs formed are removed by a finishing machining operation corresponding to the state of the art. Thus, cost-intensive and time-consuming operations are generated until the ball pivot is manufactured in case of non-machining forming of the ball pivot as well.
In addition, ball pivots that have a multipart design are known from the state of the art, but their manufacture shall not be discussed in greater detail here, because the process according to the present invention pertains to the manufacture of one-part ball pivots.
The object of the present invention is to provide a process for manufacturing ball pivots with a ball area, a cone area and a thread area, in which the number of pieces per unit of time for manufacturing individual ball pivots can be substantially reduced, so that the necessary manufacturing costs can be significantly reduced.
This object is accomplished according to the present invention by providing a ball pivot blank with a formed cone area and with cylindrical areas for the thread wherein the ball is first manufactured from a bar-shaped semifinished bar stock by means of extrusion, the extrusion flash being arranged at the free end of the area intended for forming the ball. The ball area is subsequently formed in another operation by means of a triggered synchronized rolling process by rolling forming bodies.
Any machining can be done away with due to the novel combination of the process steps described. During the pressing operation and the subsequent rolling alike, the cycle times are approx. 100 pieces per minute during pressing and in the range of about 50 pieces per minute during rolling.
The rolling process may be a so-called flat jaw rolling process or a round-jaw rolling process.
Due to the combination of the manufacturing operations, it is thus possible to manufacture a considerably greater number of ball pivots than has hitherto been known from the state of the art. This becomes possible, among other things, due to the fact that a plurality of functional areas, for example, the ball area, the cone area and the thread area, can be machined simultaneously by a tool during flat jaw rolling or round-jaw rolling. Moreover, the disposal of any waste material, which is absolutely necessary in case of manufacture by machining, is obviously eliminated.
Since the investment for a rolling machine is in the same cost range as for purchasing a lathe, the new inventive solution also leads to cost advantages in the area of the initial investment for manufacturing ball pivots due to the higher output of workpieces.
Moreover, it proved to advantageous in the process according to the present invention to form at first a neck area between the cone area and the cylindrical area intended for forming the ball during the flat-jaw or round-jaw rolling. Examples of strength measurements on ball pivots manufactured according to the novel process have revealed that the fatigue strength of the ball pivots can be increased by up to 50% by forming a neck area by rolling. Due to the increase in the fatigue strength by rolling a neck, it also becomes possible to use steels with microalloying elements, whose purchase price is substantially lower than that of the heat-treatable steels necessary for heat treatments. The cold forming of the C—Mn steels alloyed with microalloying elements is sufficient especially in the neck area to reach a sufficient strength. The increase in the strength values can be used to reduce the overall size of corresponding ball pivots at equal external loads.
Furthermore, it proved to be expedient as another special embodiment of the process according to the present invention that a blind hole-like recess, which is open on the front side, is pressed before the rolling operation into the free end of the ball pivot blank, which free end is intended for forming the ball area. The blind hole-like recess may be formed by the upper die used for pressing. The recess facilitates the forming of the cylindrical partial area of the ball pivot intended for forming the ball area to its final spherical shape. In addition, the recess does, of course, represent saving of material. If the blind hole-like recess, the so-called pole hole, is still present at least partly after the manufacture of the ball area of the ball pivot, the recess may be used, for example, to receive sensors or used as a grease reservoir. Closing the pole hole, for example, by means of a plastic cover is, of course, also conceivable in this connection.
The operations during both flat-jaw rolling and round-jaw rolling will be explained in greater detail below on the basis of the attached drawings. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Referring to the drawings in particular, the ball pivot blank shown in
Thus, the ball pivot blank, designated by 1 as a whole, comprises, according to the view in
In principle, three possible variants of rolling process are available for the final shaping of the ball pivot blank 1 by means of a triggered synchronized rolling process by rolling forming bodies. These three different processes will be explained below on the basis of the drawings.
At first, the so-called flat-jaw rolling process is presented as a variant of the rolling process. The corresponding rolling device used in this rolling process comprises two flat jaws 9 and 10, one of the flat jaws, the one designated by 9 in this view in
The final forming of the ball head 18 to its final shape is then performed during the further course of the rolling operation between the area of the section lines B-B and C-C, the mobile flat jaw 10 assuming position III indicated by dotted line in
The described course of the rolling operation for manufacturing the finished ball pivot may also be carried out, as an alternative to the flat jaw rolling process, by means of devices whose rolling jaws have a curved shape. A first shape of round-jaw rolling will be explained below at first on the basis of the views in
The views in
Devices in which one rolling jaw is formed by a rolling cylinder 23 similar to that of the above-described first variant, whereas the second rolling jaw is formed by a hollow rolling cylinder 24 concentrically surrounding the rolling cylinder, are suitable as another variant of a so-called round-jaw rolling process. Analogously to the above-described alternative rolling processes, a roll gap 11, into which the ball pivot blank 1 to be formed is introduced, is obtained between the rolling cylinder 23 and the hollow rolling cylinder 24 surrounding this, corresponding to
The forming of the ball pivot may also be carried out with a round-jaw rolling device, which is known per se, as it is shown as an example in
The ball pivot blank 1 is processed in this case by rolling the symmetrical rolling cylinders 25 and 26, which rotate about their axes of rotation. The ball pivot blank 1 is arranged between the rolling cylinders 25, 26 in the roll gap 11. The ball pivot blank 1 receives its spherical shape due to the correspondingly shaped circumferential geometry of the rolling cylinders 25, 26. A negative contour, which may also form the cylindrically shaped area 5 of the ball pivot blank 1, is molded in the respective jacket surfaces 27 and 28 of the rolling cylinders 25, 26. The rotating rolling cylinders 25, 26 are at first moved toward the ball pivot blank 1. This feed motion may be brought about, for example, by means of a hydraulic cylinder.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
Number | Date | Country | Kind |
---|---|---|---|
103 56 111.0 | Nov 2003 | DE | national |
This application is a United States National Phase application of International Application PCT/DE 2004/002614 and claims the benefit of priority under 35 U.S.C. § 119 of German Patent Application DE 103 56 111.0 filed Nov. 27, 2003, the entire contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/DE2004/002614 | 11/25/2004 | WO | 00 | 10/24/2008 |