WO2007121709A1

WO2007121709A1 - Method of producing a motor-vehicle swivel bearing in shell construction

Info

Publication number: WO2007121709A1
Application number: PCT/DE2007/000660
Authority: WO
Inventors: Raphael Fischer; Peter Niebling; Ralf Hund
Original assignee: Schaeffler Kg
Priority date: 2006-04-22
Filing date: 2007-04-17
Publication date: 2007-11-01
Also published as: DE102006018809A1

Abstract

The invention relates to a method of producing a motor-vehicle swivel bearing (12) in shell construction, wherein at least one half shell (9) of the swivel bearing (12) is produced from a sheet-metal blank (5) by deep drawing in a forming tool (1) having a forming space (8). In order to permit simplified production of a swivel bearing having improved properties, provision is made for the sheet-metal blank (5) to be heated in a first step and for the sheet-metal blank (5) to be inserted into the forming tool (1), consisting of die (2) and punch (3), in a second step and for the forming tool (1) to be closed by pressure.

Description

Name of the invention

Method for producing a motor vehicle pivot bearing in shell construction

description

Field of the invention

The invention relates to a method for producing a motor vehicle pivot bearing in shell construction, wherein at least one half shell of the pivot bearing is produced from a sheet metal blank by deep-drawing forming in a forming tool with a mold space.

Background of the invention

Swivel bearings for the front axle of a motor vehicle, which are also referred to as wheel carriers, provide the connection between a damper or shock absorber leg, the wheel bearing and the control arm on the front axle of a motor vehicle. The coupling of the control arm with the pivot bearing takes place via a pivot bearing formed on the pivot bearing. Conventional pivot bearings are usually cast or forged, one-piece steel parts, which are made for example of a cast steel material or of cast aluminum material. It is therefore a solid component in which all functional surfaces have to be machined. The damper strut is usually connected by means of a screw or clamp connection with the pivot bearing.

From DE 199 15 633 A1 discloses a pivot bearing for the front axle of a front-wheel drive motor vehicle with a base of interconnectable sheet metal parts is known, are attached to the sheet metal parts components for the suspension and the wheel guide and for the braking of the wheel. Both the sheet metal parts and other components of the pivot bearing are made of a titanium alloy material. As a manufacturing method is described there that the forming the main body sheet metal parts are produced by a deep drawing process, so that they are present as two complementary shaped sheet metal parts that joined together via a welded joint a hollow body with a plurality of bonding surfaces for receiving the above-described components.

Further details for the production of the pivot bearing are not specified in DE 199 15 633 A1. The pivot bearing described therein offers a number of advantages over one-piece, massive pivot bearings or wheel carriers. In particular, such a pivot bearing by the use of thermoforming sheets on a low weight. However, the material used, namely a titanium-aluminum alloy, for example, TiAl6V4, very expensive, so that the advantages of a lightweight construction, the disadvantages of high material costs preclude. Furthermore, DE 101 62 441 A1 discloses a method for producing motor vehicle parts, in particular chassis parts, body parts, drive parts, engine parts or the like, from metallic materials, in particular aluminum or aluminum alloys, in which high-pressure hot forming is provided by means of active media is produced in a forming tool with a mold space from an initial form an intermediate or final shape. In order to control the flow of material, the mold space region is purposefully tempered by heat supply and / or heat removal by means of softening processes and solidification processes, wherein a forming tool with a partially heated or cooled mold space is used. The hot forming is carried out by means of a hydroforming at temperatures between 150 ° C and 450 ° C. This should be one-piece motor vehicle components made particularly simple and inexpensive.

The method known from DE 101 62 441 A1 may bring advantages in a number of automotive components made of aluminum materials, but it is not necessarily transferable to the production of pivot bearings for motor vehicles. Because the geometry of a serving as Radträger- pivot bearing in shell construction can not be chosen arbitrarily due to the spatial boundary conditions, in particular clearance, acting forces of propeller shaft, brake, rim, tie rod, stabilizer or wishbone. The forces acting on the pivot bearing during operation give rise to typical critical areas in which voltage excesses occur, which can lead to premature fatigue cracks and fatigue fractures on the pivot bearing. One way of reducing stress at these points could be a targeted material thickening, for example, by pre-processing of the sheet metal blank by rolling, a doubling or the use of so-called tailored blanks. However, this would lead to an increased production cost or an increased use of materials, which would nullify the advantages of a shell-type pivot bearing.

Object of the invention

The invention has for its object to provide a method for producing a motor vehicle pivot bearing in shell construction, with which a pivot bearing can be produced easily and inexpensively, which is particularly resistant formed at the points of high force application.

Summary of the invention

The invention is based on the finding that the stated object can be achieved in a surprisingly simple manner by producing at least one half shell of the pivot bearing by hot forming in a forming tool consisting of die and male, at least one region of the formed sheet cured by cooling.

The invention is therefore based on a method for producing a motor vehicle pivot bearing or wheel carrier in shell construction, wherein at least one half shell of the pivot bearing is produced from a sheet metal blank by deep-drawing forming in a forming tool with a mold space. In addition, it is provided that, in a first step, the sheet metal blanket is heated, for example to a temperature above room temperature, that in a second step the sheet metal blank is inserted into the forming tool consisting of die and male part and the forming tool is closed with pressure.

In a third step, at least a portion of the sheet may be cooled by, i. active or passive cooling, hardened. In this case, the active cooling can be effected by means of a, in particular through the forming tool or through a part or through parts of the forming tool, guided coolant. The passive cooling can be effected by a heat absorption of the forming tool or a part or parts of the forming tool.

By means of this design, it is advantageously achieved that the sheet can be rapidly and easily shaped into the desired shape by prior heating to a relatively high temperature in the forming tool, and that during selective cooling, in particular selective or selected and / or discrete or separate Areas of the sheet, preferably a sheet of a steel alloy, can achieve a so-called press hardening of these areas.

Alternatively and / or in addition to selective cooling in the tool, the sheet may also be selectively heated prior to forming, i. By means of suitable measures, areas of the sheet are heated to different temperatures and then cooled selectively or homogeneously during forming.

As is known, the steel structure is composed of chemically homogeneous areas, the phases. Upon heating in a high temperature range of approximately 700 ° C to 1000 ⁰ C, the initial microstructure fully transforms into austenite. Preference is given to a temperature above 45O ⁰ C heated, more preferably to a temperature in the range of 700 ° C to 99O ⁰ C, preferably to a temperature of about 800 ⁰ C.

The subsequent cooling of the desired areas, during which the austenite phase can be converted into the four different phases ferrite, perlite, banite and martensite, has a significant influence on the material properties. The pearlite phase, for example, has a low hardness and great formability, whereas martensite has a high external hardness, but also a certain brittleness.

The press-hardening of the initially austenitic sheet thus causes the setting of desired hardening of the pivot bearing produced by the method. Thus, since the material strength after forming in addition to the material composition of the sheet depends on parameters such as the cooling rate and the form fit, and these parameters are locally variable, according to the method, a targeted strength distribution can be generated in the workpiece, which in conjunction with the component geometry the stresses in Operation of a later component takes into account.

By the method according to the invention, further surprising advantages can be achieved. For example, mass reduction can be achieved by optimizing the sheet thickness. Furthermore, otherwise necessary preliminary work, such as the thickening by means of rolling or welding of different sheet metal thicknesses of the sheet can be dispensed with.

It has also been found that the method results in a more uniform material stress and thus lower local thinning during forming, as the glowing sheet material is much easier to shape. As a result, lower pressing forces than usual can be used. After forming and complete cooling of a half-shell is to be expected that only a negligibly small springback of the components is observed, resulting in a higher achievable precision of the components of the pivot bearing.

If required, moreover, a flexible design of the distribution of strength during production can be achieved, for example by selectively changing the forming parameters, in particular the temperatures and the pressures in the mold.

In addition, it has been found to be an advantage of the method that less internal stresses are introduced into the component, which has a positive effect not only during welding, but also during the load of the finished pivot bearing in operation. Until now, there has been the danger that, in the worst case, the strength of the material will be largely used up by such residual stresses.

In addition, it can be provided that a coolant is fed into the forming tool for selective hardening of the areas to be hardened.

In other practical developments it can be provided that the areas with a resulting tensile strength R _mm aχvon 600 to 1400 MPa are cured. The tensile strength R _m max of 1400 MPa corresponds to an elongation at break of about 5%, and the tensile strength R _m m _a x of 600 MPa corresponds to an elongation at break of about 20%.

Other practical embodiments of the invention are characterized in that the sheet metal blank is provided prior to insertion into the forming tool with a Oberflächenverzunderung preventing coating, said coating can be based on a further development of aluminum silicon or graphite. Furthermore, according to further embodiments, it can be provided that at least two half shells produced according to the invention are connected to one another to form the pivot bearing or wheel carrier, wherein this configuration can be further expanded by welding the half shells together.

A further practical embodiment of the method according to the invention provides that a receptacle for a damper tube is formed on the pivot bearing, wherein the receptacle is formed by corresponding ein¬ckige formations on the half-shells. Finally, an embodiment of the invention is particularly advantageous, which is characterized in that a steel alloy is used as the material for the sheet metal blank.

Brief description of the drawings

The invention will be explained in more detail below with reference to the accompanying drawings. It shows

1a to 1d process steps of a method according to the invention, and

Fig. 2 is a manufactured according to the method according to the figures 1a to 1d pivot bearing.

Detailed description of the drawings

The sequence of a production method according to the invention is therefore shown schematically in FIGS. 1a to 1d. In Fig. 1a, a forming tool 1 is shown in cross section, which consists of a die 2 and a male part 3 or an embossing die.

In a gap 4 between hold-down and die 2, a sheet metal plate 5 is inserted from sheet steel, which was heated to a temperature of ≥ 800 ° C before inserting. The sheet metal plate 5 forms after completion of the process, a half-shell of a motor vehicle pivot bearing or wheel carrier.

Between top 6 of the male part 3 and the inside 7 of the die 2, between which the sheet metal plate 5 is arranged, a mold space 8 is formed. Before the sheet metal plate 5 is heated and placed in the forming tool 1, the sheet metal plate 5 was provided with a coating which prevents surface Verzunderung. Such a coating may be based on aluminum-silicon or graphite.

In Fig. 1b, a manufacturing state is shown, in which the forming tool 1 is closed by moving together of the die 2 and male part 3. The still glowing hot sheet metal plate 5 has deformed according to the topographies of the die 2 and male part 3 to a half-shell 9 and fills the mold space 8 completely. Because the sheet metal blank 5 has been heated to a comparatively high temperature, the steel material of the sheet metal blank 5 is relatively soft, so that a smaller force must be used to close the forming tool 1 than in a cold forming method.

In Fig. 1c, the state of Fig. 1b is shown in more detail, wherein in dotted marked areas 10 and 11, which represent areas of high loads of the subsequent pivot bearing, cooling of the sheet half-shell 9 is carried out, thereby curing the sheet in these areas 10 and 11 to reach. For this purpose, a cooling medium is fed into the forming tool 1 via lines not shown, whereby the temperature of the half-shell 9 is lowered to a value which is lower than the temperature of the remaining half-shell 9. After the (cooled) press-hardening of the areas 10 and 11 is the Half shell 9 formed and removed from the forming tool 1.

A cross section through the finished and cooled half shell 9 is shown in Fig. 1d. Again, the now hardened areas 10, 11 are shown dotted. The hardness of these regions 10 and 11 is greater than the hardness of the remaining half-shell 9.

In a subsequent, not shown step, the half-shell 9 is welded with a second half-shell to a finished pivot bearing or Radträger-, where appropriate, other components can be welded or screwed to the pivot bearing.

In Fig. 2 a finished pivot bearing 12 is shown. This consists of two half-shells welded together, wherein in Fig. 2, only the half-shell 9 can be seen, while the other half-shell forms the back of the pivot bearing 12. The pivot bearing 12 has, as usual, a steering lever 13, two tabs for brake connection 14 and 15, a wheel bearing receptacle 16 and a receptacle 17 for a damper tube of a shock absorber. The receptacle 17 is in this case integrally formed on the pivot bearing 12, wherein the forming process took place in the forming tool 1. In the area of the receptacle 17, both half-shells were provided with a corresponding depression, which together form the receptacle 17. As in FIGS. 1c and 1d, dotted areas 10, 11, 18 and 19 also indicate in FIG. 2 those areas which were hardened during the manufacturing process according to the invention by targeted cooling. These areas 10, 11, 18 and 19 represent those areas in which otherwise particularly high mechanical stresses prevail. Outside of these areas 10, 11, 18 and 19, the material hardness is lower in favor of a higher material toughness.

LIST OF REFERENCE NUMBERS

1 forming tool 2 die

3 patrix

4 gap 4 between hold-down and die 2

5 sheet metal plate

6 top side of the male part 5 7 inside of the female part 2

8 shape space

9 half shell

10 range of curing

11 Curing area 12 Swivel bearings

13 steering lever

14 brake frame

15 brake frame

16 Wheel bearing receiver 17 Mounting of a damper tube

18 area of hardening

19 area of hardening

Claims

claims

1. A method for producing a motor vehicle pivot bearing (12) in shell construction, wherein at least one half-shell (9) of the pivot bearing (12) from a sheet metal blank (5) by deep-drawing forming in a forming tool (1) with a mold space (8) is characterized

that in a first step the sheet metal blank (5) is heated, in particular to a temperature above room temperature,

in a second step, the sheet metal blank (5) is inserted into the forming tool (1) consisting of die (2) and male part (3), and the forming tool (1) is closed by pressure.

2. The method according to at least one of the preceding claims, characterized in that in a third step at least a portion of the sheet is cured by cooling.

3. The method according to at least one of the preceding claims, characterized in that in a third step selective or selected and / or discrete or separate areas of the sheet are cured by cooling.

4. The method according to at least one of the preceding claims, characterized in that a coolant in the forming tool (1) for curing at least one region to be hardened (10, 11, 18, 19) of the sheet is fed.

5. The method according to at least one of the preceding claims, characterized in that to a temperature above 450 ⁰ C, in particular to a temperature from a range of 700 ⁰ C to 990 ⁰ C, preferably to a temperature of about 800 ⁰ C, is heated.

6. The method according to at least one of the preceding claims, characterized in that areas of the sheet metal blank (5) are selectively heated before forming.

7. The method according to at least one of the preceding claims, characterized in that the regions (10, 11, 18, 19) are hardened with a resulting tensile strength R _{m max} of 600 to 1400 MPa.

8. The method according to at least one of the preceding claims, characterized in that the sheet metal blank (5) before its insertion into the forming tool (1) is provided with a Oberflächenverzunderung preventing coating.

9. The method according to claim 8, characterized in that the coating is based on aluminum-silicon or graphite.

10. The method according to at least one of the preceding claims, characterized in that at least two half-shells (9) are interconnected to form the pivot bearing (12).

11. The method according to at least one of the preceding claims, character- ized in that the half-shells (9) are welded together.

12. The method according to at least one of the preceding claims, characterized in that on the pivot bearing (12) a receiving means (17) is formed for a damper tube, wherein the receptacle

(17) is formed by corresponding one-piece formations on the half-shells (9).

13. The method according to at least one of the preceding claims, character- ized in that as material for the sheet metal blank (5) a

Steel alloy is used.