Method for the production of a metal tube, in particular a gas distributor tube for vehicle airbags

Abstract

The invention relates to a method for the production of a metal tube, particularly a gas distributor tube for vehicle airbags. The tube mantle is punched out as a planar metal blank, the outside contour of which corresponds to the developed view of the tube. The planar metal blank is then formed into a profile having a U-shaped cross-section. The U-shaped profile is pressed to form a tube-shaped semi-finished piece that still has an open longitudinal slit. The longitudinal slit, which extends without interruption with an essentially constant gap width over the entire length of the tube, is finally welded closed. In the production of gas distributor tubes, the outside contour of the metal blank corresponds to a developed view of the gas distributor tube, whereby the parting plane for the developed view is laid through the exit openings.

Description

The invention relates to a method for the production of a metal tube, which has at least one reduction in cross-section. According to another embodiment, the tube can contain functional elements, e.g. filter inserts, flow baffles, and the like. The invention specifically also relates to a method for the production of a gas distributor tube, particularly for vehicle air bags, which has a connector cuff, at least one ring-shaped collar, and exit openings on the mantle, which are in a row in the longitudinal direction.

Gas distributor tubes that are used for head and side airbags in vehicles, for example, are long, slim tubes having a plurality of exit openings arranged in the longitudinal direction. The tubes have a connector cuff for a connection to a gas source, as well as a collar, on which an inflatable bag is secured to prevent it from slipping off. Within the scope of the known measures, the exit openings are made in pre-finished tubes that have been cut to size, by means of punching them out. For this purpose, a mandrel has to be introduced into the tube. Any chips and punched parts that occur during the processing must be carefully removed, since even small particles can penetrate the suddenly inflating bag when the airbag deploys. In other processing steps, the ring-shaped collar is formed by means of compression, and the connector cuff is pressed on and crimped. The production method is complicated. The complete removal of all particles and chips from the tube is also a problem. Due to disruptions in the process, it is not always assured that the collar possesses the dimensions and shape that are required for reliable functioning of the gas distributor tube. In order to ensure this, an enormous inspection effort is required.

The invention is based on the task of indicating a production method with which a tube that has changes in cross-section can be produced in a single piece. In this connection, the production of tubes into which functional elements have been firmly integrated or which have exit openings on the mantle, as gas distributor tubes, and are suitable for vehicle airbags, is also supposed to be possible.

The object of the invention and the solution for this task is a method for the production of a metal tube, which has at least one change in cross-section, whereby

• • the tube mantle is punched out as a planar metal blank, the outside contour of which corresponds to the developed view of the tube,
  • the planar metal blank is formed into a profile having a U-shaped cross-section,
  • the U-shaped profile is pressed to form a tube-shaped semi-finished piece that still has an open longitudinal slit, and
  • the longitudinal slit, which extends without interruption with an essentially constant gap width over the entire length of the tube, is welded closed.

The longitudinal slit of the tube-shaped semi-finished piece can be used for aligning the work piece in a longitudinal welding machine, or to align the welding tool on the work piece. The ends of the mantle that are to be joined with one another are pressed together and welded.

The metal blank has segments of different width, which are connected by means of constant transition segments. According to a preferred embodiment of the invention, the metal blank is punched out in a width that corresponds to the outside diameter of the tube, multiplied by the number π. Since the outside diameter of the tube to be produced, not the neutral phase in the tube mantle, is used as the basis for sizing the width of the blank, this results in a slight excess dimension, which is advantageous during the subsequent welding of the longitudinal tube seam, and contributes to the production of defect-free longitudinal seams.

Press die-plates configured as half-shells can be used for the production of the tube-shaped semi-finished piece. It is practical if the shank ends of the U-shaped profile are held at a distance that forms the longitudinal slit, by means of a tongue, during the shaping. A welding tool can be guided along the longitudinal slit of the tube-shaped semi-finished piece, which follows the contour of the tube and welds the longitudinal seam of the tube closed.

The method according to the invention is furthermore suitable for producing a tube with functional elements firmly integrated into it. Functional elements can be flow baffles, filter elements, static mixers, and similar components. Within the course of the deformation of the metal blank, functional elements are inserted, which are fixed in place with a positive lock after completion of the tube. On the lengthwise sides of the planar metal blank, projections are formed, which form an annular space for holding the functional element, after deformation to produce a tube-shaped semi-finished piece. If necessary, the contour forming the annular space can be finished with external shaping tools. According to a preferred embodiment of the invention, projections are formed on the lengthwise sides of the metal blank, which form a bead-shaped widened tube region to hold a disk, after deformation to produce a tube-shaped semi-finished piece. This widened tube region is pressed to form a collar, using shaping tools, in which the related disk is fixed in place with a positive lock.

Another embodiment of the method according to the invention provides that a flow insert arranged between two support disks is laid into the profile within the course of the deformation process, and that the support disks are fixed in place, with a positive lock, in beads that are formed during the course of the deformation of the metal blank, and finished using shaping tools.

According to another preferred embodiment of the invention, which is particularly suitable for the production of gas distributor tubes, the lengthwise edges of the metal blank have a profile with back-sets, which complement one another during the deformation of the metal blank, to form exit openings on the mantle, which are in a row in the longitudinal direction.

It is practical if the profiles of the lengthwise sides of the metal blank also have projections from which a collar and a connector cuff are formed during the deformation of the metal blank to form a tube.

The metal blank can have a segment with a lesser width, which forms a narrowed cross-section of the tube after deformation of the metal blank.

Gas distributor tubes that are used in head or side airbags of vehicles have a length that frequently amounts to between 1 m and 2 m. According to a preferred embodiment of the invention, the metal blank used for the production of the tube is punched out of a piece of sheet metal, in segments, whereby the length of the segments is selected to be such that the transitions lie in the region of the back-sets on the edges of the metal blank that form the exit openings. Inaccuracies at these transitions are harmless, since no weld seam has to be formed in the region of the exit openings.

In a final work step, the tube that has been produced from the planar metal blank and welded longitudinally can be given a predetermined spatial progression adapted to the application, by means of bending.

Alternatively, a bending deformation that shapes the work piece in the longitudinal direction can take place at the same time with the deformation of the metal blank and/or during the subsequent pressing to form a tube-shaped semi-finished piece. In this way, the work piece is given a spatial progression adapted to the application, before the longitudinal slit of the tube-shaped semi-finished piece is welded closed. Preferably, the metal blank is deformed into a work piece having a U-shaped cross-section, by means of bending in a forging die or edge rolling, which piece is curved in the longitudinal direction and subsequently pressed into a tube shape using press die-plates, the shaping cavity of which is adapted to the shape of the work piece.

The work piece is already given a spatially curved progression during the deformation of the metal blank and/or during the subsequent pressing process to form a tube-shaped semi-finished piece, which is adapted to the later use of the tube, e.g. as a gas distributor tube. Subsequent bending of the finished, welded tube is not required, or at least can be restricted to segments that are very greatly curved. The method according to the invention particularly does not preclude the possibility that segments curved in arc shape, for example, are deformed subsequently, by means of bending of the tube that has already been shaped three-dimensionally and welded at the longitudinal seam.

In the following, the invention will be explained using a drawing that represents merely an exemplary embodiment. The drawing schematically shows:

FIG. 1 a metal tube produced according to the invention, in a side view,

FIG. 2 a metal blank for the production of the tube shown in FIG. 1,

FIG. 3 a first deformation of the metal blank shown in FIG. 2, to form a U-shaped profile,

FIG. 4 a second deformation step for the production of a tube-shaped semi-finished piece made from the intermediate product shown in FIG. 3,

FIG. 5 a metal tube produced according to the method according to the invention, with integrated functional elements,

FIG. 6 a preferred embodiment of the metal tube produced according to the invention, having exit openings on the mantle, in a row in the longitudinal direction, which can be used as a gas distributor tube for a vehicle airbag,

FIG. 7 a metal blank for the production of the gas distributor tube shown in FIG. 6,

FIG. 8a a curved gas distributor tube produced according to the invention, for a vehicle airbag, in a side view,

FIG. 8b a top view of the object of FIG. 8a,

FIG. 9 another embodiment of a gas distributor tube produced according to the method according to the invention.

The tube 1 shown in FIG. 1 has changes in cross-section, e.g. for a connector cuff 2 as well as for a ring-shaped collar 3.

The mantle for the metal tube shown in FIG. 1, having changes in cross-section, is punched out as a planar metal blank 4. The metal blank 4 is shown in FIG. 2. Its outside contour corresponds to the developed view of the tube 1. The width of the metal blank results from the outside diameter of the tube multiplied by the number π. With reference to the neutral phase running in the wall of the mantle, there is a slight excess dimension, which promotes the subsequent defect-free longitudinal welding of the tube.

In a first deformation step, shown in FIG. 3, the metal blank 4 is deformed to produce a profile 5 having a U-shaped cross-section. Subsequently, the U-shaped profile 5 is inserted between two die-plates 6, 6′ of a press, which are configured as half-shells, and pressed to form a tube-shaped semi-finished piece 7, which has a cross-section progression that corresponds to the tube 1, and a longitudinal slit that is still open. From FIG. 4, it is evident that during this shaping, the shank ends of the U-shaped profile are held at a distance that forms the longitudinal slit, by means of a tongue 8 that is inserted into the die-plate 6.

The longitudinal slit of the tube-shaped semi-finished piece is subsequently welded closed, preferably by means of laser welding. In this connection, the welding tool can be guided along the longitudinal slit.

The method is also suitable for the production of a tube into which functional elements 9 are firmly integrated. In the case of an exemplary embodiment shown in FIG. 5, a flow insert 9, e.g. in the form of a static mixer, is arranged within the tube 1 and fixed in place between ring disks 10, as a functional element. The ring disks 10 are fitted into collars 11 of the tube 1 that are formed in the mantle side, with a positive lock. The production of the tube 1 takes place in the manner described above. First, a planar metal blank is punched out, the outside contour of which corresponds to the developed view of the tube and has projections for forming bead-shaped widened regions of the tube. The ring disks 10 and the flow insert 9, e.g. a static mixer, are inserted into the profile during the course of deformation of the metal blank, and the profile is then pressed to form a tube-shaped semi-finished piece. The bead-shaped widened tube regions are finished using shaping tools, whereby the collars shown in FIG. 5 are formed. The ring disks 10 are fixed in place in the collars 11, with a positive lock, and hold the flow insert 9. The longitudinal seam of the tube 1 is welded before and after the final deformation.

FIG. 6 shows another preferred embodiment of a tube 1′ produced according to the invention. The tube 1′ is intended for use as a gas distributor tube for an airbag in a vehicle, particularly for so-called head airbags or side airbags. This is a long, slim tube having a length of 1 m to 2 m, and a diameter of about 15 mm. The gas distributor tube 1′ has a connector cuff 2 for a connection to a gas source, as well as a ring-shaped collar 3, to which a bag, not shown, can be attached. Several exit openings 13 are arranged in a row in the longitudinal direction.

The mantle for the gas distributor tube 1′ shown in FIG. 6, which is straight and provided with areas having a widened cross-section, for the connector cuff 2 and the collar 3, is punched out as a planar metal blank 4. The metal blank 4 is shown in FIG. 7. Its outside contour corresponds to the developed view of the gas distributor tube 1′, whereby the parting plane 14 for the developed view has been laid through the exit openings 13. Accordingly, the lengthwise sides of the metal blank 4 each have a profile with projections 15 and back-sets 16. The projections 15 are assigned to the regions of the gas distributor tube 12 having a widened cross-section, in other words the connector cuff 2 and the ring-shaped collar 3. The back-sets 16 punched out on the edges complement one another when the metal blank 4 is deformed in tube shape, to form the exit openings 13, and form the edges of the exit openings 13. The width of the metal blank corresponds to the outside diameter of the gas distributor tube 1′, multiplied by the number π. With reference to the neutral phase that runs through the wall of the mantle, there is a slight excess dimension, which promotes the subsequent defect-free longitudinal welding of the gas distributor tube 1′.

The deformation of the metal blank 4 as well as the welding of the tube-shaped semi-finished piece 7 takes place analogous to the method of procedure described above (see FIG. 3 to 4).

The metal blank 4 can be punched out of a piece of sheet metal, e.g. a zinc-plated piece of sheet steel. In this connection, it is practical to select the length of the punched segments in such a manner that the transitions from one punched segment to the next lie in the region of the back-sets 16 of the metal blank 4 that form the exit openings 13.

The tubes 1, 1′ shown in FIGS. 1 and 6 can be given a predetermined spatial progression that corresponds to their use, by means of bending.

Alternatively, a bending deformation that shapes the work piece in the longitudinal direction can also take place at the same time with deformation of the metal blank 4 and/or with the subsequent pressing to form a tube-shaped semi-finished piece 7. In this way, the work piece is given a spatial progression adapted to the application, before the longitudinal slit of the tube-shaped semi-finished piece 7 is welded closed. Preferably, the metal blank 4 is formed into a work piece having a U-shaped cross-section, by means of bending in a forging die or edge rolling, which piece is curved in the longitudinal direction, and subsequently is pressed to form a tube, using press die-plates whose shaping cavity is adapted to the shape of the work piece. FIGS. 8a and 8b show a curved gas distributor tube 1′ produced according to this bending method. In the views shown, the exit openings 13 cannot be seen.

Segments curved in arc shape, shown in FIG. 9, can be shaped by means of bending the gas distributor tube 1′ that has already been deformed three-dimensionally and welded closed at the longitudinal seam.

The method according to the invention is characterized, in comparison with the state of the art, by a lesser number of work steps. It has the advantage that even tubes, preferably gas distributor tubes, having a small diameter and large exit openings on the mantle can be produced. In particular, tubes having an inside diameter of 12 mm or less can also be produced according to the method according to the invention. The metal blank 4 can also have a segment having a lesser width, which forms a region of the tube having a narrowed cross-section, after deformation of the metal blank, as shown in FIGS. 8a, 8b, and 9. The work piece is given a spatial progression that is adapted to the subsequent use, as early as during the deformation of the metal blank 4. Subsequent bending deformation of the finished tube is not required, or can be restricted to end segments angled off in arc shape, for example.

Claims

1. Method for the production of a metal tube, which has at least one change in cross-section, wherein

the tube mantle is punched out as a planar metal blank (4), the outside contour of which corresponds to the developed view of the tube (1, 1′),

the planar metal blank (4) is formed into a profile (5) having a U-shaped cross-section,

the U-shaped profile (5) is pressed to form a tube-shaped semi-finished piece (7) that still has an open longitudinal slit, and

the longitudinal slit, which extends without interruption with an essentially constant gap width over the entire length of the tube, is welded closed.

2. Method according to claim 1, characterized in that the metal blank (4) has segments of different width, which are connected by means of constant transition segments.

3. Method according to claim 1 or 2, characterized in that the metal blank is punched out in a width that corresponds to the outside diameter of the tube, multiplied by the number π.

4. Method according to one of claims 1 to 3, characterized in that press die-plates (6, 6′) configured as half-shells are used for the production of the tube-shaped semi-finished piece (7) and that the shank ends of the U-shaped profile (5) are held at a distance that forms the longitudinal slit, by means of a tongue (8), during the shaping.

5. Method according to one of claims 1 to 4, characterized in that a welding tool, for example one controlled by an automatic welding machine, is guided along the longitudinal slit of the tube-shaped semi-finished piece (7), which follows the spatial progression and the contour of the tube and welds the longitudinal seam closed.

6. Method according to one of claims 1 to 5, characterized in that within the course of the deformation of the metal blank (4), functional elements (9) are inserted, which are fixed in place with a positive lock, by means of the wall profile, after completion of the tube (1, 1′).

7. Method according to claim 6, characterized in that projections are formed on the lengthwise sides of the metal blank (4), which form an annular space for holding a functional element (9), after deformation to produce a tube-shaped semi-finished piece, and that the contour forming the annular space is finished with external shaping tools.

8. Method according to claim 6 or 7, characterized in that projections are formed on the lengthwise sides of the metal blank (4), which form a bead-shaped widened tube region to hold a disk (10), after deformation to produce a tube-shaped semi-finished piece (7), and that the widened tube region is pressed to form a collar (11), using shaping tools, in which the disk (10) is fixed in place with a positive lock.

9. Method according to one of claims 6 to 8, characterized in that a flow insert (9) arranged between two support disks (10) is laid into the profile within the course of the deformation process, and that the support disks are fixed in place, with a positive lock, in collars (11) that are formed during the course of the deformation of the metal blank (4), and finished using shaping tools.

10. Method according to one of claims 1 to 9, characterized in that the lengthwise edges of the metal blank (4) have a profile with back-sets (16), which complement one another during the deformation of the metal blank (4) to form a tube (1′), to form exit openings (13) on the mantle, which are in a row in the longitudinal direction.

11. Method according to one of claims 1 to 10, characterized in that the lengthwise edges of the metal blank (4) have a profile with projections (15), from which a collar (3) and a connector cuff (2) are formed during the deformation of the metal blank (4) to form a tube (1′).

12. Method according to one of claims 1 to 11, characterized in that the metal blank (4) has a segment with a lesser width, which forms a narrowed cross-section of the tube after deformation of the metal blank.

13. Method according to one of claims 10 to 12, characterized in that the metal blank (4) is punched out of a piece of sheet metal, in segments, whereby the length of the segments is selected to be such that the transitions lie in the region of the back-sets (16) on the edges of the metal blank (4) that form the exit openings (13).

14. Method according to one of claims 1 to 13, characterized in that the tube that has been produced from the planar metal blank (4) and welded longitudinally is given a predetermined spatial progression adapted to the application, by means of bending.

15. Method according to one of claims 1 to 13, characterized in that a bending deformation that shapes the work piece in the longitudinal direction takes place at the same time with deformation of the metal blank (4) and/or with the subsequent pressing to form a tube-shaped semi-finished piece (7), and that in this way, the work piece is given a spatial progression adapted to the application, before the longitudinal slit of the tube-shaped semi-finished piece (7) is welded closed.

16. Method according to claim 15, characterized in that the metal blank (4) is deformed into a work piece having a U-shaped cross-section, by means of bending in a forging die or edge rolling, which piece is curved in the longitudinal direction and subsequently pressed into a tube shape using press die-plates (6, 6′), the shaping cavity of which is adapted to the shape of the work piece.

17. Method according to claim 15 or 16, characterized in that segments curved in arc shape are deformed subsequently, by means of bending of the tube that has already been shaped three-dimensionally and welded at the longitudinal seam.