Process for manufacturing a tie rod housing

This is a continuation of and claims the benefit (35 U.S.C. §120 and 365(c)) of copending International Application PCT/DE 2003/003535 of Oct. 23, 2003, which designated inter alia the United States and which claims the priority of German Application DE 102 49 768.0 of Oct. 24, 2002. The entire contents of each application is hereby incorporated by reference in its entirety.

The present invention pertains to a process for manufacturing a tie rod housing comprising a tie rod head and a shaft element fastened thereto, in which the tie rod head receives its final shape by a mechanical machining process after the manufacture of the tie rod housing blank comprising the shaft element and the tie rod head.

Tie rod housings of the type described at the beginning are used as components of motor vehicle steering mechanisms and are subject to the highest safety-relevant general conditions because of their special intended use. These general conditions are dictated by the motor vehicle manufacturers and are divided in the state of the art, e.g., into the safety classes A, B, C and D, where the tie rod housing described at the beginning are subject to the highest safety level D.

In order to guarantee the required process safety of safety level D within the framework of predetermined loads, the possibility of transmission of preset static and dynamic forces as well as of impact stresses is necessary.

To meet the said criteria, tie rod housing blanks comprising a tie rod head and a shaft element are preformed within the framework of a forging process and are brought to their final shape predetermined by the vehicle manufacturer by a subsequent mechanical machining, so that additional components such as seals and bearing components can be mounted in the tie rod head. The entire manufacture comprising the forging process and the subsequent machining process is extremely cost-intensive, and attempts have recently been made to reduce the processing time for the subsequent machining operations by cold forging operations. Cold forging as a manufacturing process is, on the other hand, again relatively complicated and cost-intensive, so that the overall manufacturing price advantages of the alternative mode of manufacture that can be achieved cannot necessarily be considered to be great.

The object of the present invention is therefore to provide a process for manufacturing a tie rod housing, which can be embodied significantly more favorably in terms of the manufacturing costs compared with the processes known from the state of the art.

This object is accomplished according to the present invention by connecting the shaft element with the tie rod head by means of a resistance welding operation within the framework of the process according to the present invention and by subsequently creating at least two accumulations of material, which connect the two components and are brought about by a welding operation between the outer circumferential surface of the tie rod head and of the shaft element.

The special combination of the said welding operations leads to an overall welded connection between the shaft element and the tie rod head, which meets, analogously to the forged connection that has hitherto been common, all the necessary criteria concerning the transmissibility of static and dynamic forces or in respect to resistance to impact forces. The components involved, namely, the shaft element and the tie rod head, can be manufactured here from suitable bars available at a favorable cost within the framework of preceding machining operations. Moreover, modular versions of tie rod housings, in which it is possible, for example, to combine certain housing heads with shaft elements of different lengths, can be embodied by means of the novel manufacturing process.

The process for manufacturing a tie rod housing provides a tie rod head and a said shaft element fastened thereto. The tie rod head receives its final shape by a mechanical machining process after the manufacture of the tie rod housing blank components comprising the shaft element and the tie rod head. The shaft element is connected with the tie rod head by means of a resistance pressure welding operation. At least two material accumulations are subsequently created between the outer circumferential surface of the tie rod head and of the shaft element. The two material accumulations connect the two components and are brought about by a welding operation.

It proved to be particularly advantageous to arrange the accumulations of material on diametrically opposite sides of the tie rod head and of the shaft element. The opposite arrangement of the material accumulations has an advantageous effect on the dimensions of the tie rod housing, which are of great significance because the space available for installation, in general, in the area of the steering mechanisms of motor vehicles, is small.

The MAG (metal active gas) welding process, which is known from other fields of use and can be carried out at a low cost, has proved to be especially suitable for preparing the material accumulation.

Moreover, it was revealed by experiments that the transmission of the necessary forces between the tie rod head and the shaft element is supported by designing the cross section of the material accumulation as a triangular cross section, wherein the limiting surfaces, which project over the base of the triangle that faces the components to be connected, are sloped at an angle of about 45° in relation to the base.

Moreover, it proved to be advantageous for making it possible to mount adjacent components, for example, sealing elements at the tie rod head, within the framework of the limitation of the overall dimensions, to remove the circular weld seam prepared by the resistance pressure welding operation in partial areas, which are arranged offset by about 90° in relation to the material accumulations, by means of a machining operation and advantageously by a broaching process.

The features of the connection between the tie rod head and the shaft element, which are essential for the present invention and were described at the beginning, make it, moreover, expediently possible to deform the shaft element by a bending operation after the manufacture of the tie rod housing.

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 a preferred embodiment of the invention is illustrated.

FIG. 1 is a perspective view of a state of the process with blanks provided for the tie rod head and the shaft element;

FIG. 2 is a perspective view of a state of the process with the machined tie rod head and the shaft element positioned for connection;

FIG. 3 is a perspective view of a state of the process with showing the results of a resistance pressure welding process used for the tie rod head and the shaft element:

FIG. 4 is a perspective view of a state of the process showing the results of providing material accumulation formed on diametrically opposite sides in the area of the truncated conical end of the connected shaft element;

FIG. 5 is a perspective view of a state of the process showing the weld seam, formed within the framework of the resistance pressure welding process, removed; and

FIG. 6 is a perspective view of a state of the process showing the shaft element bent in another concluding manufacturing step, after the completion of the connection process.

Referring to the drawings in particular, a tie rod housing is manufactured according to the process according to the present invention. A blank is provided, in principle, a tie rod head 1 and a shaft element 2 , which are shown in a perspective view in FIG. 1 . The shaft element 2 is a bar-shaped cylindrical solid material and the tie rod housing is a tubular cylindrical element.

As is apparent from the view in FIG. 2 , the tie rod head 1 as well as the shaft element 2 are provided in a first production step with chamfers 3 , 4 as well as 5 , whose special designs are adapted to the later installation and attachment conditions of the tie rod housing. At its second free end, which is not provided with the chamfer 5 , the shaft element 2 has a truncated conical end 6 at the end of the preparatory measures. With the outer end of the truncated conical end 6 , which has a thinner cross section, the shaft element 2 is pressed against the cylindrical outer surface of the tie rod head 1 and is connected with the tie rod head 1 by means of the resistance pressure welding process by applying a corresponding voltage to the components 1 and 2 as well as by applying corresponding pressing forces. A circular weld seam 7 is formed due to this resistance pressure welding operation.

In the next process step for manufacturing the tie rod housing, a material accumulation 8 and 9 each is formed on diametrically opposite sides in the area of the truncated conical end 6 of the shaft element 2 and in the area of the adjoining cylindrical outer surface of the tie rod head 1 . These material accumulations 8 and 9 form a reinforcing web each and are welded to the areas, the MAG welding process having proved to be suitable corresponding to an advantageous embodiment. The material accumulations 8 and 9 have essentially a triangular cross-sectional shape, and the outwardly projecting limiting surfaces 10 and 11 , which extend obliquely in relation to one another, are sloped at an angle of 45° in relation to the base of the material accumulations.

After the material accumulations 8 and 9 , which are used for reinforcement, have been prepared, the weld seam 7 formed within the framework of the resistance pressure welding process is removed in another operation preferably by means of a broaching tool in the area of the respective chamfers 3 and 4 .

Finally, FIG. 6 shows how the shaft element is bent in another, concluding manufacturing step after the completion of the connection process between the tie rod head 1 and the shaft element 2 in order to adapt it to special installation conditions during the mounting.

While a specific embodiment of the invention has 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.