METHOD FOR PRODUCTION OF A STEEL TUBULAR PRODUCT, IN PARTICULAR AN AIRBAG TUBULAR PRODUCT, AND A STEEL TUBULAR PRODUCT PRODUCED USING THIS METHOD, IN PARTICULAR AN AIRBAG TUBULAR PRODUCT

Abstract

The invention concerns a method for production of a steel tubular product (1), in particular an airbag tubular product, with the following steps: a) provision of a steel tube (2), b) shaping of the steel tube (2) into a pre-geometry (3), wherein in an end region (4), an outer diameter (5) of the steel tube (2) is reduced by axial movement into an outer tool, c) calibration of an inner diameter (7) of the pre-geometry (3), wherein the pre-geometry (3) is still laid in the outer tool, and an inner mandrel, with an outer diameter corresponding to the inner diameter (7) of the calibrated pre-geometry (3), is introduced into the end region (4) of the pre-geometry (3), and the pre-geometry (3) is pressed against the outer tool such that the inner diameter (7) of the pre-geometry (3) is calibrated by shaping, d) removal of the pre-geometry (3) from the outer tool (5) and removal of the inner mandrel from the pre-geometry (3), e) axial movement of the pre-geometry (3) into a drawing tool with a roll-in contour having a pot-like concavity, with simultaneous shaping of the pre-geometry (3) into the tubular product (1) with a rotationally symmetrical outlet opening (8) positioned centrally in the end face, f) removal of the tubular product (1) from the drawing tool.

Claims

1. Method for production of a steel tubular product (1), in particular an airbag tubular product, with the following steps: a) provision of a steel tube (2), b) shaping of the steel tube (2) into a pre-geometry (3), wherein in an end region (4), an outer diameter (5) of the steel tube (2) is reduced by axial movement into an outer tool, c) calibration of an inner diameter (7) of the pre-geometry (3), wherein the pre-geometry (3) is still laid in the outer tool, and an inner mandrel, with an outer diameter corresponding to the inner diameter (7) of the calibrated pre-geometry (3), is introduced into the end region (4) of the pre-geometry (3), and the pre-geometry (3) is pressed against the outer tool such that the inner diameter (7) of the pre-geometry (3) is calibrated by shaping, d) removal of the pre-geometry (3) from the outer tool (5) and removal of the inner mandrel from the pre-geometry (3), e) axial movement of the pre-geometry (3) into a drawing tool with a roll-in contour having a pot-like concavity, with simultaneous shaping of the pre-geometry (3) into the tubular product (1) with a rotationally symmetrical outlet opening (8) positioned centrally in the end face, f) removal of the tubular product (1) from the drawing tool.

2. The method as claimed in claim 1, characterized in that the shaping in step b) takes place as cold forming or cold drawing.

3. The method as claimed in any of the preceding claims, characterized in that the shaping in the further step takes place as cold forming.

4. The method as claimed in any of the preceding claims, characterized in that the shaping in step d) takes place as hot forming or semi-hot forming.

5. The method as claimed in any of the preceding claims, characterized by a finish-forming of the end region (4) and outlet opening (8) of the tubular product (1) by insertion of a second inner mandrel, which has an outer contour corresponding to the inner contour of the end region (4) to be produced of the tubular product (1), and an axial movement of the second inner mandrel and tubular product (1) into a second outer tool, the inner contour of which corresponds to the outer contour of the end region (4) to be produced of the tubular product (1).

6. The method as claimed in claim 5, characterized in that for calibration or finish-forming of the outlet opening (8), the second inner mandrel is used with a rotationally symmetrical element positioned centrally in the end face, the outer contour of which element corresponds to the inner contour of the outlet opening to be produced of the tubular product (1).

7. The method as claimed in claim 5 or 6, characterized in that the calibration of the end region (4) and/or the outlet opening (8) takes place in a residual heat of a hot forming or semi-hot forming carried out in step e), in particular at a temperature of at least 473 K or lower than a Ac1 temperature of the used steel or used steel alloy.

8. The method as claimed in any of the preceding claims, characterized in that before step d) (rolling-in), the tubular product is heated to >Ac3 temperature, and after step d), or in the case of calibration of the outlet opening, is actively cooled so that an at least partially hardened grain structure is formed in the steel alloy.

9. The method as claimed in any of the preceding claims, characterized in that as steel for the steel tube, a steel alloy and in particular a hardenable ultra-high strength steel is used.

10. The method as claimed in claim 8, characterized in that as a material of the tube or tubular product to be produced, a steel is used which, as well as iron and unavoidable melt-induced contaminants, comprises the following alloy elements as percentage by weight: C 0.07 to 0.50. preferably 0.07 to 0.20; Si 0.05-0.55; Mn 0.2 to 2.5, preferably 0.4 to 0.8; P less than 0.025; S less than 0.02; Cr less than 2, preferably 0.8 to 1.0; Ti less than 0.03, preferably less than 0.015; Mo less than 0.6, preferably 0.25 to 0.4; Ni less than 0.6, preferably 0.2 to 0.3; Al 0.001 to 0.05, preferably 0.02 to 0.04; V less than 0.5, preferably less than 0.1; Nb less than 0.1, preferably less than 0.06.

11. The method as claimed in any of the preceding claims, characterized in that the tubular product (1) produced has a tensile strength of 700 MPa, preferably at least 900 MPa.

12. Tubular product (1), in particular an airbag tubular product, produced according to a method as claimed in any of claims 1 to 12.

Description

[0049] FIG. 1: shows an exemplary embodiment of a steel tube to be provided for production of a tubular product with the method according to the invention,

[0050] FIG. 2: shows the steel tube from FIG. 1 after an inventive method step for production of an uncalibrated pre-geometry,

[0051] FIG. 3: shows the pre-geometry from FIG. 2 after a calibration, and

[0052] FIG. 4: shows the final produced tubular product.

[0053] FIG. 1 shows a steel tube 2 which serves as a starting product for production of a tubular product according to the invention using a method according to the invention. The steel tube 2 is here configured as a rotationally symmetrical element with a constant outer diameter 5, which has a rotational axis 10 configured as a longitudinal axis.

[0054] After provision of the steel tube 2, this is shaped into a pre-geometry 3, wherein in an end region 4, an outer diameter of the steel tube 2 is reduced by axial movement into an outer tool (not shown here). Such a reduced outer diameter 6 is shown in FIG. 2, in which the end region 4 has already been shaped accordingly but not yet calibrated. This calibration takes place when the pre-geometry 3 is laid in an outer tool (not shown here), in which an inner mandrel (also not shown here), with an outer diameter corresponding to the inner diameter 7 of the calibrated pre-geometry 3, is introduced into the end region of the pre-geometry 3. Thus the inner diameter 7 of the pre-geometry 3 is calibrated by this shaping.

[0055] By the reduction of the outer diameter 5 of the steel tube 2 to the outer diameter 6 of the pre-geometry 3, naturally the wall thickness in the end region 4 of the pre-geometry 3 increases in comparison with the wall thickness in the end region 4 of the steel tube 2.

[0056] This increased wall thickness is thinned out again by the calibration described. This thinning-out of the wall thickness in the end region facilitates the rolling (described below) of the end region and makes this reproducible. Such a calibrated pre-geometry 3 is shown in FIG. 3.

[0057] The shaping of the steel tube 2 and pre-geometry 3 described above were all carried out by cold forming or cold drawing. In cold forming or cold drawing, the shaping takes place between room temperature and a temperature lower than 473 K, in particular without preheating and without heated tools. So that the steel tube 20 and pre-geometry 3 can slide on one another and on the inserted tools and mandrels more easily, simple lubricant may be used between the individual parts during shaping.

[0058] In order now to shape the pre-geometry into the definitive tubular product 1, the pre-geometry is axially displaced into a drawing tool (not shown in the figures) with a roll-in contour having a U-shaped cavity, with simultaneous shaping of the pre-geometry into the tubular product with a rotationally symmetrical outlet opening positioned centrally in an end face.

[0059] In the context of the invention, U-shaped or pot-like means an at least partially curved course of a wall between the outlet opening and the unshaped tube portions, e.g. also hemispherical.

[0060] This shaping takes place as hot forming or semi-hot forming between a temperature of 473 K up to an Ac1 temperature of the steel used, which lies at 1173 K for the steels and steel alloys used for the tubular product.

[0061] The end region 4 and outlet opening 8 of the tubular product 1 are shaped by insertion of a second inner mandrel (also not shown here), which has an outer contour corresponding to the inner contour of the calibrated end region 4 of the tubular product 1, and axial movement of the second inner mandrel and tubular product into a second outer tool (also not shown here), the inner contour of which corresponds to the outer contour of the calibrated end region 4 of the tubular product 1.

[0062] In this final step of shaping by hot forming, during rolling of the end region 4 and subsequent insertion of the second inner mandrel, a transverse wall thickness 11 on the end face is again slightly reduced, wherein the geometry of the outlet opening 8 is optimized at the same time. Simultaneously, the inner radii 12 and outer radii 13 are reduced in the rolling region of the end region 4.

[0063] In the exemplary embodiments shown here, the end region 4 of the steel tube 2 is drawn over the length which is necessary for rolling of the pre-geometry 3 and for forming the outlet opening 8. In a further exemplary embodiment (not shown here), the drawing may take place over a larger end region of the starting steel tube 2. The later rolling however does not concern the entire drawn end region, so that the inner and outer radius of the final tubular product in the unrolled end region is reduced accordingly in comparison with the longitudinal extent of the tubular product lying outside the end region 4.

LIST OF REFERENCE SIGNS

[0064] 1 Tubular product [0065] 2 Steel tube [0066] 3 Pre-geometry [0067] 4 End region [0068] 5 Outer diameter [0069] 6 Outer diameter [0070] 7 Inner diameter [0071] 8 Outlet opening [0072] 10 Rotational axis [0073] 11 Thickness [0074] 12 Inner radius [0075] 13 Outer radius