Abstract:
The invention relates to a method for manufacturing an axle component having the following steps: arranging a hollow semi-finished product such as a tube in a die for forming the axle component; introduction of fluid into the interior of the hollow semi-finished product; and loading of the fluid with high pressure, in order to deform the hollow semi-finished product in accordance with the die as a result.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention concerns a method for manufacturing an axle component. 
     (2) Description of Related Art 
     Traditionally, axle components such as wheel suspension arms are produced by various manufacturing methods. Examples of such manufacturing methods are casting, forging or welding. Furthermore, there is so-called hydroforming (internal high pressure forming, IHPF), wherein a hollow or tubular part is exposed to liquid pressure, so that the wall of the hollow part lies against a negative mold. However, this method suffers from the drawback that the hollow part has to be preformed and should only have a wall thickness of up to 2.5 mm in order for the hydroforming process (internal high pressure forming, IHPF) to be performed successfully. Furthermore, as a rule, a heat treatment must follow the preforming, in order to restore the material properties for the actual hydroforming process. 
     Accordingly, each of the traditional manufacturing methods for the production of an axle component with a relatively complex shape has the drawback of requiring many process steps in order to make the axle component. As a result, the costs are high for the production of the axle component. 
     SUMMARY OF THE INVENTION 
     The present invention provides an economical production method for an axle component. 
     A method according to the present invention may include the following steps: 
     arranging a hollow, non-preformed, semifinished product such as a tube in a negative mold for the forming of the axle component; 
     introduction of fluid into the interior of the hollow semifinished product; and 
     loading the liquid with high pressure in order to deform the hollow semifinished product in accordance with the negative mold. 
     Preferably, the hollow semifinished product has a wall thickness of at least 2 mm, preferably 3 to 6 mm, most preferred of 4 to 5 mm. 
     Preferably, the pressure lies in the range of 1200 to 2500 bar (120×10 6  Pa to 250×10 6  Pa) preferably in the range of 1800 to 2200 bar (180×10 6  Pa to 220×10 6  Pa). 
     With the hydroforming according to the invention, a conventional semifinished part such as a round tube, an oval tube, or a square tube can be transformed directly into a final shape of the axle component, so that one step of preforming the semifinished part can be omitted. This is accomplished in particular due to the high pressure of the hydroforming method of the invention. Tubes with a wall thickness of more than two millimeters and up to more than five millimeters can be converted directly into a final shape of the axle component by the hydroforming method of the invention. Since the axle component does not have to be preformed, one prevents a local excessive strain, besides avoiding an additional work step. In this way, an axle component with high strength can be produced economically, requiring no further deformation step. Thus, one immediately obtains a closed-wall and highly durable cross section with no welds subjected to stress. 
     Preferably, at least two identical or mirror-symmetrical axle components are formed at the same time, and they are separated after the forming, so that one can make a plurality of axle components with just one forming process. This makes possible further cost reduction and time savings during production. 
     When at least two long axle components, such as wheel suspension arms, have a long shape and overlap in a lengthwise direction when forming the plurality of axle components, one can minimize an overhang at an inlet or outlet of the hydroform, so that excess material, which has to be removed after the forming, is likewise minimized. This results in a further cost benefit. 
     The method may be utilized to manufacture wheel suspension arms with spring seat extensions. Since such spring seat extensions have a smaller dimension in the direction of the vehicle&#39;s height axis Z than another segment of the wheel suspension arm, preferably two wheel suspension arms can be formed at the same time, and the wheel suspension arms can be formed in such a way that the spring seat extensions overlap in the lengthwise direction. After the forming, the two wheel suspension arms are then separated from each other. In this way, the material yield is a maximum. 
     Preferably, the mold for the forming of the axle component is configured such that the spring seat extensions are set off from each other to the side in one transverse direction of the wheel suspension arm. 
     Furthermore, the hydroforming method of the invention offers the benefit that, in the case of a wheel suspension arm, the spring seat extensions can easily be set off to the side by appropriate design of the negative mold in one transverse direction of the vehicle in the case of a trailing arm. As a result, for example, a trailing arm can be molded that has outstanding wheel steering properties, since the axle sockets of a pair of trailing arms have a large distance from each other and are situated near a wheel of the wheel suspension, while at the same time the springs are set off away from the wheel—looking in the direction toward the middle of the vehicle in the transverse direction of the trailing arm—so that the installation configuration of the springs can be improved. In other words, the trailing arms can be at maximum spacing from each other, while the springs can be arranged closer to each other. 
     Preferably, the method moreover has the step of welding a bushing into a joint socket for the pivotable fastening of the wheel suspension arm on a vehicle frame. 
     Preferably, the stiffness of a trailing arm produced by the hydroforming method of the invention is increased in that an essentially triangular piece is cut out from the pair of side walls at one end lying at the pivot axis of the trailing arm, and an upper or lower wall (upper or lower flange) or a tonguelike segment of the upper and lower wall resulting from the cutting out is bent toward a joint socket so that this upper or lower wall can be welded to the side walls of the trailing arm. In this way, one gains the benefit of achieving great rigidity of the trailing arm in the region of the pivot axis. 
     Furthermore, one or more indentations or bulges can be formed in the walls of the axle component produced by the hydroforming method of the invention. Such indentations and bulges can have virtually any desired shape, and they are best determined with a finite element method (FEM) in this regard. Only the mechanical properties of the starting material or semifinished material and especially the plastic deformability will be a constraint for this. Moreover, preferably, a part of the indentation or bulge can be cut out essentially in the middle thereof, if this middle segment only needs to withstand low forces, so that an axle component produced by the hydroforming method can have less weight. 
     A major advantage of the hydroforming method of the invention is that local rates of strain of the formed axle component do not exceed a given magnitude. 
     Furthermore, the hydroforming can achieve a closed cross section for an axle component, without there being any heavily loaded welded seams in the cross section. For example, a pair of trailing arms can be produced at the same time with only a single die and one stroke of the hydroforming device. 
     The invention shall now be explained more closely by means of sample embodiments in connection with the enclosed drawings. However, the sample embodiments show only the manufacture of a wheel suspension arm as an illustration. As the practitioner can easily discern, however, the invention can also be applied to other axle components and superstructure components of a vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first sample embodiment of a trailing arm, in which a spring seat extension is arranged at basically the same height as a pivot bearing of the trailing arm. 
         FIG. 2  shows an alternative sample embodiment in which, contrary to the sample embodiment shown in  FIG. 1 , a spring seat extension is arranged higher than a joint axis of the trailing arm. 
         FIG. 3  shows a tube after the hydroforming, from which two basically identical or mirror symmetrical trailing arms can be cut out. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As is shown in  FIG. 3 , a hollow body is produced by hydroforming from a tube, preferably a round steel tube made of a steel with a high fracture strain in the region of around 10 to 15%, preferably around 10%. Suitable refined steel grades can be used when there are higher requirements on the fracture strain or the plastic deformability during the production process and/or the corrosion behavior. A multiphase steel can also be used if there are high demands on the strength of the hollow body. The described method offers additional benefits here in particular, since only a single deformation process is needed, so that a multiphase steel will preserve its additional strength. An additional deformation process, such as preforming, would rule out the prospect of using such steels. Likewise, nonferrous metals such as aluminum alloy with suitable material properties can also be considered as the material used for the semifinished blank. Furthermore, depending on the desired shape, one can also use a square tube, oval tube, or other tube cross sections as a semifinished blank for the hydroforming. 
     After the hydroforming, it is still necessary to remove an excess at a front and rear end, which results from the inlet and outlet. From the hollow bodies shown in  FIG. 3 , one ultimately produces two trailing arms  10 ,  20 , as shown in  FIG. 1 , by separating the hollow body of  FIG. 3  in the middle according to the shape of the spring seat extensions  11 ,  21  of the pair of trailing arms  10 ,  20 . 
     The shape of the trailing arms  10 ,  20  can be optimized by a finite element method, so that the trailing arms  10 ,  20  have a preferred bending and torsional rigidity and favorable tensile and compressive stress levels. To increase the rigidities, the trailing arms  10 ,  20  are provided with indentations  17 ,  27  and  28 . In order to reduce the weight of the trailing arms  10 ,  20 , a middle or central segment of the indentations  17 ,  27 ,  29  is removed, for example, by laser cutting. Furthermore, a bushing (not shown) for a pivot bearing of the trailing arm  10 ,  20  is welded to a joint socket  12 ,  22  already configured by the hydroforming. In order to improve the introduction of corresponding forces into the pivot bearing of the bushing of the trailing arm  10 ,  20  (not shown), a triangular piece is cut out from the side walls  13 ,  14  and  23 ,  24  of the pair of trailing arms  10 ,  20  at the end of the trailing arm  10 ,  20  in the vicinity of the joint socket  12 ,  22 , again, for example, by laser cutting. After this, a tonguelike segment  15   a ,  25   a  of a lower wall or a lower flange  15 ,  25  of the trailing arm  10 ,  20  is bent toward the cutting edge of the side walls  13 ,  14  and  23 ,  24  and welded to the side walls  13 ,  14  and  23 ,  24 . In this way, the tonguelike segment  15   a ,  25   a  of the lower walls  15 ,  25  can introduce corresponding tensile and compressive loads into the joint socket  12 ,  22 . 
     In this way, one creates a trailing arm with a hollow profile, having no other highly loaded welded seams than the welded seam at the joint socket  12 ,  22  and the welded seam at the tonguelike segment  15   a ,  25   a . Thus, a trailing arm  10 ,  20  with a hollow profile can be made by a simple method, having a minimum of welded seams. Depending on the configuration of the trailing arm  10 ,  20  or some other frame or wheel suspension component of a vehicle, one can totally eliminate the separating of the triangular parts to obtain the tonguelike segments  15   a ,  25   a.    
     By making a pair of trailing arms  10 ,  20  with only one hydroforming step—unlike the molding of only one component—surplus material of an excess which results from the inlet or outlet is reduced to less than half. The reason is that the described method makes it possible to maintain the circumferential lengths of the tube ends  110 ,  120  on the same order of magnitude as the circumferential length of the semifinished blank. Thus, the method-related inlets and outlets can be kept very short. Since, what is more, the spring seat extensions  11 ,  21  have a smaller dimension in a vertical direction Z of the vehicle than the other segments of the trailing arms  10 ,  20 , the spring seat extensions  11 ,  21  can overlap in the longitudinal direction X of the trailing arms  10 ,  20  during the hydroforming of the pair of trailing arms  10 ,  20 . In this way, even more excess material is economized. 
       FIG. 2  shows an alternative sample embodiment, likewise of trailing arms  30 ,  40  for a wheel suspension of a vehicle. The trailing arms  30 ,  40  shown in  FIG. 2  have essentially the same components as the trailing arms  10 ,  20  of  FIG. 1 . Therefore, these elements have been given the same reference numbers and shall not be further discussed here. We shall therefore only go more closely into the difference between the trailing arms  30 ,  40  of  FIG. 2  and the trailing arms  10 ,  20  of  FIG. 1 . 
     For the trailing arms shown in  FIG. 1 , a spring seat extension  11 ,  21  lies essentially at the same height in a vertical direction Z of the vehicle as the joint socket  12 ,  22 . In other words, an upper wall  21   a  of the spring seat extension  21  basically forms a linear or horizontal extension of an upper wall  26  of the trailing arm  20 . The same holds for the other trailing arm  10  of  FIG. 1 , since the trailing arms  10 ,  20  are fashioned to be identical or mirror symmetrical. In contrast to this, an upper wall  31   a  of a spring seat extension  31  of the trailing arm  30  forms an extension of a lower wall  36  of the trailing arm  30 . In this way, a spring seat extension  31  and thus its upper wall  31   a  can be situated higher than a joint socket in a vertical direction Z of the vehicle. In this way, the riding height, i.e., the distance between the lower edge of the chassis and the axle center of a particular vehicle and/or a spring installation configuration can be varied from the first sample embodiment. In other respects, the pair of trailing arms  30 ,  40  of  FIG. 2  is configured exactly the same as the pair of trailing arms  10 ,  20  of  FIG. 1 . 
     Basically, the spring seat extensions  31  can also be very short or eliminated entirely. In this case, the springs (not shown) are supported against the axle tube (not shown) and/or partly against the very short spring seat extensions  31 . In this design, little or no offset bending is needed for the trailing arms  10 ,  20 ,  30 ,  40 . Hence, the length of the material can be further reduced, since the overall length of the thus produced trailing arms  10 ,  20 ,  30 ,  40  is also smaller. 
     The method for manufacturing these trailing arms  10 ,  20 ,  30 ,  40  will now be explained in detail. First, a tube of suitable material with good deep drawing properties, i.e., with a strain fracture of at least 10%, is placed in a negative mold made of steel configured according to the shape of the trailing arms  10 ,  20 ,  30 ,  40  being manufactured. After this, both ends of the tube are tightly closed and liquid is filled into the tube. This liquid is now placed under a high pressure of around 1800 to 2200 bar by a pressure generating device. Due to this high pressure, the material of the steel tube flows and conforms to the wall of the negative mold, adopting its shape. 
     After this, the thus-formed hollow part can be removed from the negative mold after the pressure is released and the liquid is drained. Excess parts of an inlet or outlet of the negative mold are removed from the molded hollow part by sawing or a laser treatment, so that one gets a hollow part as shown in  FIG. 3 . 
     Water with suitable additives is used preferably as the liquid for the hydroforming of the hollow part. 
     The hollow part shown in  FIG. 3  is then cut along a roughly S-shaped line in the middle, so that a pair of identical or mirror symmetrical trailing arms  10 ,  20  or  30 ,  40 , as shown in  FIGS. 1 and 2 , are formed. 
     Afterwards, a joint bushing (not shown) is placed in a joint socket  12 ,  22  of the trailing atm  10 ,  20 , for example, it is welded. In order to further improve the bending and torsional strength of the trailing arm  10 ,  20 , an essentially triangular part can further be cut out from the side walls  13 ,  14  or  23 ,  24  in the vicinity of the joint socket  12 ,  22 . 
     Then, a tonguelike segment  15   a ,  25   a  of the lower wall  15 ,  25  is bent upward to the joint socket  12 ,  22  so that the tonguelike segment  15   a ,  25   a  can be welded to the side walls  13 ,  14  or  23 ,  24 . 
     In order to save on weight and/or to create room for further running gear components, a central segment of the indentations  17 ,  27 ,  29  is then cut out, for example, by means of a laser. The essentially circular axle sockets  18 ,  28  are cut out from the trailing arms  10 ,  20 , e.g., by means of a laser. 
     After this, cover plates are placed on the spring seat extensions to accommodate the springs (not shown) for the trailing arms  30 ,  40  shown in  FIG. 2 . These plates can be secured preferably by welding, and these welded seams are not subject to any increased strain. 
     The invention is not confined to the trailing arms  10 ,  20 ,  30 ,  40  described here. In particular, other wheel suspension components such as transverse links, tilted links, and space rods can also be made with the method of the invention. Furthermore, frames and structure or chassis components can also be made with the invented method. The wall thickness of the tube is 3 to 4 mm prior to the hydroforming, but due to the high pressure of 1800 to 2200 bar, a tube with 5 to 6 mm wall thickness can also be formed. The shape will be determined in advance, for example, by a finite element method, so as to achieve a high tensile, compressive, flexural and torsional strength of the finished trailing arm, on the one hand, and to avoid segments with excessive strain, on the other hand. 
     Although not shown here, the trailing arm can also have a shape wherein the spring seat extension  11 ,  21  is set off inwardly in the vehicle&#39;s transverse direction Y. In this way, on the one hand, the axle can be supported by the trailing arms  10 ,  20  near the wheels of the vehicle, while on the other hand the springs can be moved inward toward the middle of the vehicle, so that the installation conditions for the springs can be varied at will.