TUBULAR ELEMENT FOR GAS PRESSURE VESSEL, GAS PRESSURE VESSEL AND METHOD OF MANUFACTURING A TUBULAR ELEMENT

Abstract

This invention concerns a tubular element for a gas pressure vessel of an airbag module, in particular of a vehicle, wherein the tubular element (1) consists of high-strength steel, has a first and a second end (17, 18) and from the first end (17) to the second end (18) the tubular element (1) has an undeformed section (11), a transition section (12) and a tapering section (13) and on the tapering section (13) at least one radially outwardly extending collar (14) is formed, characterized in that the collar (14) is separated from the transition section (12) by a first length section (130) having an outer diameter (A1) smaller than the outer diameter (A2) of the collar (14) and the wall thickness of the collar (14) is greater than the wall thickness of the first length section (130). Furthermore, the invention concerns a gas pressure vessel and a process for manufacturing a tubular element according to the invention (1).

Claims

1. A tubular element for a gas pressure vessel of an airbag module, in particular of a vehicle, wherein the tubular element (1) consists of high-strength steel, has a first and a second end (17, 18) and from the first end (17) to the second end (18) the tubular element (1) has an undeformed section (11), a transition section (12) and a tapering section (13), and on the tapering section (13) at least one radially outwardly extending collar (14) is formed, characterized in that the collar (14) is separated from the transition section (12) by a first length section (130) having an outer diameter (A1) smaller than the outer diameter (A2) of the collar (14) and the wall thickness of the collar (14) is greater than the wall thickness of the first length section (130).

2. A tubular element according to claim 1, wherein the tubular element (1) is produced by at least one axial semi-hot forming process.

3. A tubular element according to claim 1, wherein the tubular element (1) consists of a quenched and tempered steel having a tensile strength in the range of 800-1500 MPa, in particular 900-1200 MPa.

4. A tubular element according to claim 2, wherein the tubular element (1) in the tapering section (13) is only partially surface-treated after the axial semi-hot forming process.

5. A tubular element according to claim 1, wherein the tapering section (13) comprises a second length section (131) extending from the second end (18) of the tubular element (1) to the collar (14) and the second length section (131) of the tapering section (13) has a smaller or equal inner diameter (13) and a smaller or equal outer diameter (A3) than the first length section (130).

6. A tubular element according to claim 5, wherein in the inside of the second length portion (131) a cylindrical recess is provided which extends up to the second end (18) of the tubular element (1).

7. A gas pressure vessel for an airbag module, characterized in that it comprises a tubular element (1), wherein the tubular element (1) consists of high-strength steel, has a first and a second end (17, 18) and from the first end (17) to the second end (18) the tubular element (1) has an undeformed section (11), a transition section (12) and a tapering section (13), and on the tapering section (13) at least one radially outwardly extending collar (14) is formed, characterized in that the collar (14) is separated from the transition section (12) by a first length section (130) having an outer diameter (A1) smaller than the outer diameter (A2) of the collar (14) and the wall thickness of the collar (14) is greater than the wall thickness of the first length section (130).

8. A process for producing a tubular element (1), wherein the tubular element (1) consists of high-strength steel, has a first and a second end (17, 18) and from the first end (17) to the second end (18) the tubular element (1) has an undeformed section (11), a transition section (12) and a tapering section (13), and on the tapering section (13) at least one radially outwardly extending collar (14) is formed, characterized in that the collar (14) is separated from the transition section (12) by a first length section (130) having an outer diameter (A1) smaller than the outer diameter (A2) of the collar (14) and the wall thickness of the collar (14) is greater than the wall thickness of the first length section (130), characterized in that the tubular element (1) is produced in several stages and comprises at least one semi-hot forming process step which is carried out as axial compression.

9. A process according to claim 8, where the process comprises the following steps: a first step of drawing a tube end of a tube (10) to the outer diameter (A1) of the collar (14), a second step of forming said collar (14) by axial compression, and a third step of drawing the tube end to a final diameter (A3) and end forming the collar (14).

10. A process according to claim 8, wherein at least the process step of the axial semi-hot forming process is carried out at temperatures in the range of 200 C. to 800 C. and below the Ac3 temperature of the steel of which the tubular element consists.

11. A process according to claim 9, wherein in the first process step the tube (10) is compressed by means of an outer die (3) and further wherein the wall thickness of the tube (10) at least in the tapering section (13) and the tube length in the tapering section (13) is increased.

12. A process according to claim 9, wherein in the second process step the collar (14) is pre-formed on the outside of the tapering portion (13).

13. A process according to claim 12, wherein in the second process step the inner shape of the transition section (12) is completely formed.

14. A process according to claim 12, wherein the second process step is carried out with a die (5) which has a mandrel (50) and an annular gap (51) surrounding the mandrel (50), the annular gap (51) having on the open side a shoulder (510) in which the width of the annular gap (51) is increased.

15. A process according to claim 9, where in the third process step the collar (14) and the tube end are finished in the area of the second length section (131) by means of a die (6) which has a bowl-shaped recess (60) whose diameter increases towards the open end.

16. A process according to claim 8, wherein the tubular element (1) is machined in areas of the tapering section (13) after the last axial forming step.

17. A process according to claim 16, wherein in the inside of the tapering section (13) a cylindrical recess (15) is introduced by machining the surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention is described in more detail in the following with reference to the enclosed figures, wherein:

[0038] FIG. 1: shows a schematic longitudinal cross-sectional view of an embodiment of the tubular element according to the invention;

[0039] FIG. 2: shows another detailed view of the second end area of the tubular element according to FIG. 1;

[0040] FIG. 3: shows another detailed view of the second end area of the tubular element according to FIG. 1;

[0041] FIG. 4: shows a second end area of the tubular element after a third process step;

[0042] FIG. 5: shows a schematic representation of a first process step of an embodiment of the inventive process;

[0043] FIG. 6: shows a schematic representation of a second process step of an embodiment of the inventive process; and

[0044] FIG. 7: shows a schematic representation of a third process step of an embodiment of the inventive process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] FIGS. 1 to 3 show an embodiment of tubular element 1 according to the invention. The tubular element 1 has a first end 17 and a second end 18. The undeformed section 11 of the tubular element 1 extends from the first end 17. The undeformed section 11 is followed by a transition section 12 in which the diameter of the tubular element 1 decreases. The transition section 12 is followed by a tapering section 13 which extends to the second end 18 of the tubular element 1. At the tapering section 13 a collar 14 is formed, which can also be called undercut or flange. The collar 14 is separated from the transition section 12 by a first length section 130 of the tapering section 13. Between the collar 14 and the second end 18 lays a second length 131 of tapering section 13.

[0046] In the undeformed section 11, the tubular element 1 has a wall thickness W0.

[0047] In the undeformed area 11, tubular element 1 has an inner diameter 10 and an outer diameter A0. In the first length portion 130 of the tapering section 13, the tubular element 10 has an outer diameter A1 which is smaller than the outer diameter A0, and an inner diameter 11 which is smaller than the inner diameter 10. The inner diameter 12 in the region of the collar 14 is equal to the inner diameter 11 of the first length portion 130 in the represented design form. The outer diameter A2 of the collar 14 is larger than the outer diameter A1 and smaller than the outer diameter A0 in the embodiment. The inner diameter 13 of the second length 131 is smaller than the inner diameter 11 and 12. The outer diameter A3 is smaller than the outer diameter A1.

[0048] FIG. 4 shows the shape of the end section of an embodiment of tubular element 1 according to FIG. 1 after the third forming step. As can be seen from this view, according to the invention, tubular element 1 has a smooth surface inside the transition between first length 130, collar 14 and second length 131, without any bulges. In this way, turbulences can be prevented inside the tubular element according to the invention, which can have a negative effect on the operation of a gas generator.

[0049] On the outside of the shown embodiment the slope of the second length section 131 to the collar 14 is small. If a steeper slope is required, the area marked 16 can be removed, e.g. milled. On the inside, a cylindrical recess can be made, e.g. milled, according to the internal milling marked 15 in the tubular element 1 according to the invention.

[0050] Any overhang at the second end of tubular element 1 can also be removed by milling or other machining.

[0051] FIGS. 5 to 7 schematically show the processing steps according to an embodiment of the inventive process. The tools are not shown in these figures.

[0052] In a first step, a tube 10 is inserted into a first die which closely surrounds it. The length of the first die is less than the length of the tube 10. An outer die is also provided. The outer die has a through hole. The through hole has a tapering part and an adjoining cylindrical part. The largest diameter of the tapering part is larger than or equal to the diameter of the tube 10. The cylindrical part has a smaller diameter.

[0053] The tube 10 is at least partially heated to a higher temperature than the rest of the tube 10 in the area where it overhangs the first die. By moving the first die with the tube towards the outer die, the tube 10 passes into the through hole and is formed. After the first step, the tube 10 thus has the shape shown in FIG. 5 on the right. In particular, the transition section is finished on the outside by the tapering part of the outer die through hole and the smaller diameter tapering section is pre-formed by the cylindrical part. In particular, the wall thickness of the tapering section and its length are increased. Prior to this process step, tube 10, for example, is heated to 700 C. at the part that forms the tapering section, while the rest of the tube is heated to 200 C., for example.

[0054] FIG. 6 shows the second step of the process. In this step, the tube 10 pre-formed in step 1 is inserted into a first die. The tube 10 is inserted into the first die so that the undeformed section and the transition section are in the first die. For this purpose, a tapering corresponding to the transition section is provided in the first die. In addition, the first length section of the tapering section lies in the first die and is enclosed by it from the outside. The remaining part of the tapering section extends through a plunge of the first die. A second die used in this step has a mandrel and an annular gap surrounding it. If the first die and the second die are moved towards each other, for example by a punch, the mandrel enters the inside of the tapering section of the pre-formed tubular element 1. The dies are moved towards each other to such an extent that the second end of the tubular element enters the annular gap and touches its base. The depth of the annular gap is less than the length of the overhang of the tapering section over the first die. This results in the shape of the tubular element shown in FIG. 6 at the end of the second step. In this state, the collar is pre-formed and the transition section is finished on the inside. The collar is formed from above by the plunge of the first die and from below by the shoulder of the annular gap.

[0055] FIG. 7 schematically shows the third step of the process. The tubular element 1 pre-formed in step 2 is fixed in the first die. A second die is also provided, in which a cup-shaped recess is provided. If this second die is moved towards the first die, the tapering section, in particular the second length section, enters the recess. By moving the dies further together, the tubular element 1 is given the shape shown in FIG. 7 on the right.

[0056] After this process step, the tubular element 1 can be machined as described above, for example by milling.

REFERENCE CHARACTER LIST

[0057] 1 tubular element [0058] 10 tube [0059] 11 undeformed section [0060] 12 transition section [0061] 13 tapering section [0062] 130 first length section [0063] 131 second length section [0064] 14 collar [0065] 140 forging burr [0066] 15 internal milling [0067] 16 outside milling [0068] 17 first end [0069] 18 second end [0070] A0 outer diameter of the outlet [0071] A1 first outer diameter [0072] A2 second outer diameter [0073] A3 third outer diameter [0074] I0 inner diameter of the outlet [0075] I1 first inner diameter [0076] I2 second inner diameter [0077] I3 third inner diameter [0078] W0 output wall thickness