METHOD AND APPARATUS FOR THE PRODUCTION OF A TUBULAR STRUCTURE FOR A GAS GENERATOR, AND GAS GENERATOR TUBULAR STRUCTURE

Abstract

In a method of producing a tubular structure for a gas generator, a tubular body is positioned relative to a forming device having inner and outer tools, which are moved relative to an end portion of the tubular body until an inner circumferential surface of a neck of the end portion rests against a support surface of the inner tool to reduce a diameter of the end portion by a tool contour of the outer tool and thereby form a shoulder. The outer tool is held in position upon the end portion and the neck inner circumferential surface is calibrated by a calibrating surface on a calibrating member of the inner tool while an outer circumferential surface of the neck is supported by the outer tool, as the inner tool is removed from the end portion. The outer tool is then removed from the end portion of the tubular body.

Claims

1. A method of producing a tubular structure for a gas generator, said method comprising: positioning a tubular body in relation to a forming device; moving an inner tool and an outer tool of the forming device in relation to an end portion of the tubular body until an inner circumferential surface of a neck of the end portion rests against a support surface of the inner tool to reduce a diameter of the end portion by a tool contour of the outer tool and thereby form a shoulder; holding the outer tool in its position upon the end portion; calibrating the inner circumferential surface of the neck by a calibrating surface on a calibrating member of the inner tool while an outer circumferential surface of the neck is supported by the outer tool, as the inner tool is removed from the end portion; and removing the outer tool from the end portion of the tubular body.

2. The method of claim 1, wherein the inner tool and the outer tool of the forming device are moved in relation to the end portion of the tubular body in a time-staggered sequence, with the inner tool and the calibrating member thereof being first inserted and positioned into the end portion and then moving the outer tool in relation to the end portion.

3. The method of claim 2, further comprising guiding the outer tool on the end portion, when the outer tool moves in relation to the end portion.

4. The method of claim 1, wherein the inner tool and the outer tool of the forming device are moved concurrently in relation to the end portion of the tubular body.

5. The method of claim 1, further comprising sliding the end portion along the support surface, as the neck is formed.

6. The method of claim 1, wherein the tubular body is made in an area of the inner circumferential surface of the neck of a material which is plastically deformable during calibration.

7. The method of claim 1, wherein during forming of the end portion the neck has a wall thickness which is greater than a wall thickness of the tubular body by 5% to 25%.

8. The method of claim 1, wherein during forming of the end portion the neck has a wall thickness which is greater than a wall thickness of the tubular body by 8% to 15%.

9. Apparatus for producing a tubular component for a gas generator, said apparatus comprising: an outer tool having a funnel-shaped tool contour, said outer tool including an entry zone, a reduction zone, and a support zone, with the tool contour tapering from the entry zone via the reduction zone to the support zone; and an inner tool including a mandrel having a calibrating member which defines a calibrating surface, said mandrel defining a support surface.

10. The apparatus of claim 9, wherein the inner tool has a mandrel bar, said mandrel being arranged on the mandrel bar, said calibrating member defined by a diameter which is greater than a diameter of the mandrel bar.

11. The apparatus of claim 9, wherein the calibrating member transitions via a transition zone into the mandrel bar.

12. The apparatus of claim 9, wherein the calibrating member is arranged on a free end of the mandrel bar.

13. A tubular structure for a gas generator, comprising a tubular body having an end portion defined by a diameter which is smaller than a remainder of the tubular body, said end portion having a tapering shoulder and a neck, said neck having a surface with an residual stress which deviates by a maximum of 5% from an average tensile strength of a material of the tubular body, with the deviation amounting to a maximum of 50 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0036] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

[0037] FIG. 1 is a simplified schematic illustration of seven process steps involved in a production of a tubular structure for a gas generator in accordance with the present invention; and

[0038] FIG. 2 is a simplified schematic illustration of six process steps involved in an alternative production of a tubular structure for a gas generator in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments may be illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

[0040] Turning now to the drawing, and in particular to FIG. 1, there is shown a simplified schematic illustration of seven process steps a) to g) involved in a production of a tubular structure 1 for a gas generator in accordance with the present invention. The tubular structure 1 includes a tubular body 2 which has an end portion 3 to be pulled or drawn into a forming device 6 for reduction of the diameter, as shown in step a). The forming device 6 includes an outer tool 7 and an inner tool 8. Both, the outer and inner tools 7, 8 are shown here only by way of a cutaway detail. It will be understood by persons skilled in the art, that the outer tool 7 is configured rotation-symmetrical about a longitudinal center axis ML. This is equally true for the tubular structure 1.

[0041] The outer tool 7 has a funnel-shaped tool contour 9 which has an entry zone 10, a reduction zone 11, and a cylindrical support zone 12 which adjoins the reduction zone 11, The tool contour 9 tapers from the entry zone 10 via the reduction zone 11 in the direction of the support zone 12. The reduction zone 11 has hereby a curved course of its wall.

[0042] The inner tool 8 includes a mandrel bar 13 and a mandrel 30 arranged at a free end of the mandrel bar 13 and defining a calibrating member 14. The calibrating member 14 is cylindrical and has a calibrating surface 15 on an outer surface area thereof. The calibrating member 14 is defined by a diameter D.sub.K which is greater than a diameter D.sub.S of the mandrel bar 13. The calibrating member 14 transitions via a conical transition zone 16 into the mandrel bar 13. A section 17 of the mandrel 30 and the mandrel bar 13 defines a support surface 18 which is part of an outer circumferential surface of the mandrel bar 13.

[0043] The tubular body 2 represents the starting product for the production of the tubular structure 1. The tubular body 2 is cut to size as tube piece from a hot-rolled, cold-drawn and heat-treated tube string.

[0044] In step a), the tubular body 2 is positioned in relation to the forming device 6 and held in place by a not shown holding device.

[0045] The inner tool 8 of the forming device 6 is then moved toward a confronting end portion 3 of the tubular body 2, as shown in step b) and indicated by arrow P1, for entering the end portion 3. The calibrating member 14 of the inner tool 8 is positioned in the tubular body 2 and the inner tool 8 is held in place in this position.

[0046] Subsequently, the outer tool 7 is moved in relation to the end portion 3 in the direction of arrow P2 and pushed over the end portion 3, as shown in step c).

[0047] As the outer tool 7 moves in relation to the end portion 3, the end portion 3 is reduced in diameter by the tool contour 9 of the outer tool 7 to thereby form a shoulder 4. With progressing reduction in diameter, an inner circumferential surface 19 of a neck 5 of the end portion 3 ultimately contacts the support surface 17 of the inner tool 8. At the same time, the support zone 12 slides on the outer circumferential surface 20 of the neck 5, as shown in step d). As the end portion 3 is drawn-in, the neck 5 is supported on the inside by the support surface 18 on the mandrel bar 13 of the inner tool 8 and on the outside by the support zone 12.

[0048] Once the end portion 3 has been drawn-in, the inner tool 8 is pulled out of the end portion 3 of the tubular body 2, as indicated by left-pointing arrow P3 in steps d) and e).

[0049] As the inner tool 8 is removed, the outer tool 7 is held in place on the end portion 3. The inner circumferential surface 19 of the neck 5 is calibrated by the calibrating surface 15 that is formed on the calibrating member 14 of the inner tool 8. At the same time, the outer circumferential surface 20 of the neck 5 is supported in the support zone 12 by the outer tool 7. During calibration, the inner circumferential surface 19 of the neck 5 is slight deformed plastically and its inner dimension precisely dimensioned. The outer support in the support zone 12 of the outer tool 7 results also in a precise dimensioning of the outer circumferential surface 20 of the neck 5.

[0050] After the inner tool 8 has been removed from the end portion and calibration has been concluded, the outer tool 7 is removed from the end portion 3 of the tubular body 2, as indicated by arrow P4 in step f).

[0051] The finished end portion 3 is shown in step g), once the forming device 6 is removed. The end portion 3 of the tubular member 2 of the tubular structure 1 thus is reduced in diameter and includes the tapered shoulder 4 and the neck 5. The tubular body has an outer diameter D1 and the neck of the drawn-in end portion 3 has an outer diameter D2.

[0052] Referring now to FIG. 2, there is shown a simplified schematic illustration of six process steps involved in an alternative production of a tubular structure 100 for a gas generator in accordance with the present invention. Parts corresponding with those in FIG. 1 are denoted by identical reference numerals and not explained again. This applies to steps a), c) to f) correspond to steps a), d) to g), respectively. The description below will thus center only on the differences between the embodiments.

[0053] In this embodiment, provision is made for the inner tool 8 and the outer tool 7 to be moved concurrently in relation to the end portion 3 as shown in step b) and indicated by arrows P1 and P2. The inner tool 8 enters hereby the interior of the end portion 3 (arrow P1) and is positioned there. At the same time, the outer tool 7 is moved in the direction of arrow P2 and pushed over the end portion 3. During this movement, the end portion 3 is reduced in diameter by the tool contour 9 of the outer tool 7 until the outer tool 7 has reached its end position on the end portion 3 and the inner circumferential surface 19 of the neck 5 rests upon the support surface 18 of the inner tool 8. The neck 5 is supported on the inside by the support surface 18 upon the mandrel bar 13 of the inner tool 8 and on the outside by the support zone 12 of the outer tool 7.

[0054] It will be understood by persons skilled in the art that the inner tool 8 leads the outer tool 7 when moving into the end portion 3 so that the calibrating member 14 of the inner tool 8 is prevented from colliding with the inner circumferential surface of the end portion 3 of the tubular body 2.

[0055] The mandrel bar 13 and the support surface 18 as well as the support zone 12 have a cylindrical configuration. The neck 5 is formed in the gap between outer diameter of the support surface 18 and the inner diameter of the support zone 12 and supported during the forming and calibration processes.

[0056] While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0057] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: