EP0770435A1 - Method for making a construction part and axle support - Google Patents

Abstract

The method is used to form an axle support for a motor vehicle, through bending and hydro- forming a straight, metallic, hollow profile (2). The latter is first loaded by an internal hydraulic pressure and by an axial force on its ends (8), to form bulges (7) and to transfer profile material to the regions (6',7') which are to be deformed. Internal hydraulic pressure is then used to bend the hollow profile, and to finish its shaping process. The bulges may also be achieved by an opposing pressure which acts in the region which is to be deformed.

Description

The invention relates on the one hand to a method for producing a construction workpiece, in particular an axle support for motor vehicles, by bending and hydroforming a straight metallic hollow profile and on the other hand to an axle support.

Construction workpieces such as axle beams of motor vehicles are now consistently designed in a lightweight construction. Such construction workpieces are usually hollow molded parts which are produced from a straight metallic, usually cylindrical tube. The hydroforming process offers a wide range of options for forming the tube. Here, a cylindrical tube is expanded as a starting profile under the pressure of a liquid with simultaneous axial feed movement and pressed against the shape of a divided hollow tool. Hydroforming is described, inter alia, in "WT Werkstattstechnik" 79 (1989), pages 210 to 214. Because of its manufacturing advantages, the hydroforming process is widespread, particularly in the mass production of construction workpieces, for example for the automotive industry.

In the manufacture of curved construction workpieces, the procedure has so far been such that pipes are first pre-bent. Here, the pipes are brought into a shape that corresponds to the later contour of the construction workpiece. The bent hollow profile is then hydroformed into the final shape. This procedure, as described for example in DE-PS 40 17 072, has proven itself in principle.

After the hydroforming process, the construction workpiece is finished from its contour. Now attachments are welded onto the construction workpiece. Such attachments can be reinforcements, for example in the form of gusset plates, which serve to stabilize the construction workpiece. Mostly, however, such attachments are required to fasten the construction workpiece or to fix other components on the construction workpiece.

Subsequent attachment of the attachments is costly and labor intensive. In addition to the quantity and timely provision of the add-on parts, the effort involved in determining the welding technology is high. Accordingly, rationalization of the manufacturing process is desirable.

Starting from the prior art, the invention is based on the object of producing curved construction workpieces to make it more economical and to reduce the number of add-on parts to be subsequently welded onto the construction workpiece. The invention further aims at a simpler and more economically designed axle support for motor vehicles.

The solution to the procedural part of this task consists in the measures listed in the characterizing part of claim 1. The solution to the objective part of the task can be seen in the characterizing features of claim 7.

The basic idea of the invention is to first shift enough material into the zones of the forming on the straight starting profile, as a result of which forming areas are preformed. The contour of the construction workpiece is then produced by bending and hydroforming.

In particular, fastening or reinforcement areas of the construction workpiece can also be hydroformed from the initial profile before the bending process.

The method according to the invention thus makes it possible in any case to replace a large part of the add-on parts that would otherwise have to be welded on after the final shaping.

When manufacturing the construction workpieces, a straight metallic hollow profile in the form of a tube is initially assumed. This is placed in a multi-part press tool. The press tool is designed in such a way that it allows targeted preforming in the required areas without causing disadvantageous wall thinning in these zones. After closing the press tool, the tube is closed with a hydraulic internal pressure and an axial force acting on the ends of the tube.

The axial force is usually transmitted to the pipe on both sides with rigid tools. Usually these are hydraulically moved pistons with appropriately shaped heads that close the tube at both ends. An increasing pressure is then built up in the pipe. As soon as this is so high that the tube is deformed in the area of the pre-deformed areas, the ends of the tube are pressed in the axial direction. This process is controlled depending on the internal pressure. Then there is a shift of profile material to the areas to be deformed. This results in a regionally specific preforming of bulges in the zones of the later bend or the later fastening or reinforcement areas.

An advantage of the method is that with the first manufacturing step, the zones of the forming are first prefabricated on the straight tube. In particular, the zones of maximum deformation, in which the subsequent bending of the preformed hollow profile is carried out, can be specifically prepared accordingly for the subsequent plastic deformation.

The bending process takes place under high internal pressure so that the hydroformed contours remain. Wrinkling or indentation of the pipe is prevented. Preforming the zones of maximum deformation also avoids the elastic springback that is otherwise typical for bending. The subsequent final shaping is also carried out by hydraulic internal pressure. This gives the construction workpiece its final shape. A pushing the ends of the bent Construction workpiece is not required. This is an essential procedural advantage.

Before the hydraulic final shaping, depending on the design, the construction workpiece can also be flattened in certain areas. Here, the preformed bulges and / or sections of the construction workpiece are flattened. This process takes place in the hydroforming tool.

The control devices and the hydraulic devices of the production plant can be used both in the preforming, in the bending process and in the final shaping.

The number of attachments to be welded on is reduced by the method according to the invention. Necessary fastening or reinforcement areas on the body of the construction workpiece can be molded in one piece from the initial profile. The additional effort for the provision and definition of add-on parts is minimized or can even be completely saved, depending on the construction workpiece.

According to the features of claim 2, the bulging takes place under the influence of a counter pressure which acts specifically in the area to be deformed. This enables precise control of the expansion process. The size of the preformed areas is proportional to the length reduction of the hollow profile. In order to avoid material thinning or even bursting in the area of the bulge that forms, the forehead of the bulge is supported by the counterpressure during the forming.

The back pressure can basically be generated in different ways. In a convenient way Include counter cylinders in the manufacturing process, which are coordinated with the press tool.

Advantageous developments of the method according to the invention can be seen in claims 3 and 4. The construction workpiece can then be subjected to heat treatment by annealing both before the bending process and after the bending process. Here, the residual stresses created by the deformation process are reduced. Distortion of the structure due to the deformation can also be reduced in this way. The material of the construction workpiece accordingly receives the properties desired for further processing.

According to the features of claim 5, the construction workpiece is calibrated during or after the final shaping. In principle, it is possible that the final shaping only includes calibration. With the repressing, the surface roughness is leveled and the dimensional accuracy of the construction workpieces is increased. In addition, the strength is increased during calibration.

In a further step, the construction workpieces can be provided with assembly openings. The mounting openings may be necessary both for fastening additional components and for carrying out other components, such as a brake line. The assembly openings are produced according to the features of claim 6 with the internal pressure acting. In this way it is avoided that the construction workpiece is deformed during the cutting manufacture of the assembly openings, for example by cutting or punching.

A structurally simple and technically economical axle support for motor vehicles is required 7 characterized. Such a curved axle support is made in one piece from a tube with integrated fastening or reinforcement areas. To do this, hydroforming is first carried out with feeding on the straight pipe. The zones of maximum forming are preformed. The hydroformed pipe is then bent under internal pressure. The preformed areas are then pressed flat according to the respective requirements. Fastening or reinforcement areas can be formed in this way. The axle support is given its final shape by hydroforming or calibration. If necessary, the axle carrier is then provided with holes, the punching being carried out under internal pressure as described.

In the axle carrier according to the invention, the number of attachments to be welded on is reduced. As a result, its production is more economical. The saving in add-on parts to be welded on also results in a weight saving. This in turn has a positive effect on the fuel consumption and the pollutant emissions of a motor vehicle equipped with the axle carrier according to the invention.

Figur 1

in einer schematisierten Ablaufdarstellung den Fertigungsprozeß für einen Achsträger;

Figur 2

in der Ansicht, teilweise im vertikalen Längsschnitt ein Pressenwerkzeug bei der Vorformung;

Figur 3

in der Seitenansicht die Darstellung der Figur 2 entlang der Linie III-III;

Figur 4

einen Teilschritt des Biegevorgangs;

Figur 5

eine weitere Darstellung des Biegevorgangs;

Figur 6

die Darstellung eines Achsträgers bei der Endformung in der Draufsicht;

Figur 7

einen Schnitt durch die Darstellung der Figur 6 entlang der Linie VII-VII.

The invention is described below with reference to the accompanying drawings. In all drawings, corresponding components have the same reference numerals. Show it:

Figure 1

in a schematic flow diagram the manufacturing process for an axle beam;

Figure 2

in the view, partially in vertical longitudinal section, a press tool during preforming;

Figure 3

in the side view the representation of Figure 2 along the line III-III;

Figure 4

a sub-step of the bending process;

Figure 5

another illustration of the bending process;

Figure 6

the representation of an axle beam in the final shaping in plan view;

Figure 7

a section through the representation of Figure 6 along the line VII-VII.

FIG. 1 shows the production of an axle support 1 for a passenger car, starting from an initial profile in the form of a straight tube 2 with a round cross section.

The axle support 1 (FIG. 1E and FIG. 1F) essentially comprises two tubular longitudinal sections 3 which are connected to one another via a central section 4. The central section 4 transmits in particular torsional and bending forces which are directed from the longitudinal sections 3 into the central section 4. In the transitions 5 from the longitudinal sections 3 to the central section 4, forming regions 6 are formed on the axle support 1. These can also be used to attach attachments, for example.

For the manufacture of the axle support 1, the tube 2 is provided in a fixed initial length L _A , which is matched to the dimensions of the axle support 1 or to the forming processes carried out during manufacture (FIG. 1A).

First bulges 7 are preformed on the tube 2 (FIG. 1B). The preforming is carried out by means of hydraulic internal pressure, the ends 8 being axially pushed at the same time. In this way, profile material is shifted to the areas 6 'to be preformed. In the example shown, these are the zones 7 ', in which the maximum deformation takes place during the later bending process.

Not necessarily, but advantageously, the preformed tube 2 'thus formed is then subjected to a heat treatment by means of an annealing process. As a result, the inherent stress of the tube 2 'that results from the preforming can be reduced.

The axis contour 2 ″ is then created by bending (FIG. 1C). During the bending process, the tube 2 'is under high internal pressure, so that the hydroformed contour is retained. Heat treatment can also follow the bending process.

Flattening is then carried out in the hydroforming tool in an intermediate step (FIG. 1D). The areas 6 'are flattened here. In the subsequent hydraulic final shaping (FIG. 1E), the axle support 1 receives its final contour with the required dimensional accuracy (calibration). When the internal pressure acts, the assembly openings 9 are further punched. This prevents the contour of the axle support 1 from being pressed in.

In a final manufacturing step (FIG. 1F), the corner regions 10 of the axle support 1 are trimmed.

The preforming, as shown schematically in FIG. 1B, is carried out in a press tool 11 (see FIGS. 2 and 3). The press tool 11 has two tool halves 12, 13. An axial punch 16, 17 is arranged on each of the two end sides 14, 15. Furthermore, in the zones in which the bulges are preformed, the press tool 11 has bulge openings 18 which are adapted there. Here, counter-cylinders 19 are arranged, the pistons 20 of which are designed to match the contour of the bulges.

After inserting the tube 2 into the press tool 11, the tool halves 12, 13 are moved together hydraulically. The tube 2 is closed at both ends 8 by likewise hydraulically moved pistons 21 with correspondingly shaped heads 22. A pressure medium is then applied to the tube 2. The pressure medium is supplied via an internal high-pressure line 23, indicated by dashed lines in FIG. 2, which is led through the pistons 21.

In the next phase, an axial force is exerted on the tube 2, which is created by the two axial punches 16, 17 acting against each other. The heads 22 are pressed into the pipe ends 8 by the axial forces and thus form-fitly seal the interior 24. At the same time, the liquid pressure increases within the tube 2. Due to the internal pressure with simultaneous axial loading, the tube 2 reaches a plastic state and begins to bulge. Controlled depending on the internal pressure, the pistons 20 of the counter-holding cylinders 19 are now retracted. This results in a targeted material shift into the expansion openings 18 while simultaneously axially pushing the pipe ends 8, whereby the desired preformed pipe 2 'is created.

The preformed tube 2 'is then bent. The bending process is shown in Figures 4 and 5. For this purpose, the preformed tube 2 'is picked up by a bending tool 25. The ends 8 are closed by the adapter 26. The tube 2 'is then subjected to internal pressure. Tool parts 27, which are designed to pivot, engage on the longitudinal sections 3 and bend them over the shape contour 28. During the bending process, the center section 4 is fixed by the counter contour 29.

The axle contour 2 ″ preformed in this way is fed to a hydroforming tool 30 after the bending process, in which the final shaping is carried out (FIG. 6). The areas 6 ′ are first flattened in the hydroforming tool, as a result of which the shaping areas 6 receive their configuration. The axis contour 2 ″ is also slightly flattened on the top in the areas 6 ′ (see also FIG. 7). The axle contour 2 ″ is then closed in a form-fitting manner by the adapter 31. The final shaping then takes place hydraulically, in which the axle support 1 is calibrated with the required dimensional accuracy. Following this, the assembly openings 9 are punched out while the internal pressure is acting.

List of reference symbols

1

- axle beam

2nd

- Pipe
2 '- preformed tube
2 '' axis contour

3rd

- longitudinal section

4th

- middle section

5

- Crossing

6

- forming area
6 'area of 6

7

- Bulge 7 '- zone of max. Reshaping

8th

- end of 2nd

9

- assembly opening

10th

- corner area

11

- press tool

12th

- Tool half

13

- Tool half

14

- end of v. 11

15

- end of v. 11

16

- Axial punch

17th

- Axial punch

18th

- Removal opening

19th

- counter cylinder

20th

- piston from 19th

21

- piston from 16 u. 17th

22

- head of 21

23

- Internal high pressure line

24th

- interior v. 2nd

25th

- bending tool

26

- adapter

27

- tool parts

28

- shape contour

29

- counter contour

30th

- hydroforming tool

31

- adapter

L _A

- initial length

Claims (7)

Method for producing a construction workpiece (1), in particular an axle support for motor vehicles, by bending and hydroforming a straight, metallic hollow profile (2), characterized by the following measures: a) loading of the hollow profile (2) with a hydraulic internal pressure and with an axial force acting on the ends (8) of the hollow profile (2), with specific, targeted pre-forming of bulges (7) from the material of the hollow profile (2) and displacement of Profile material to the areas to be deformed (6 ', 7'), b) bending the preformed hollow profile (2 ') under hydraulic internal pressure, c) final shaping by hydraulic internal pressure. A method according to claim 1, characterized in that the bulging is carried out under the influence of back pressure acting in the area to be deformed. A method according to claim 1 or 2, characterized in that the preformed hollow profile is annealed before bending. Method according to one of claims 1 to 3, characterized in that the hollow profile is annealed after bending. Method according to one of claims 1 to 4, characterized in that the construction workpiece (1) is calibrated during or after the final shaping. Method according to one of claims 1 to 5, characterized in that the construction workpiece (1) is provided with assembly openings (9) when the internal pressure acts. Axle support for motor vehicles, characterized in that it is formed in one piece from a tube (2, 2 ', 2'') with integrated forming areas (6) using hydroforming and bending technology.

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