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

1 . A method for production of an airbag tube, the method comprising:

a step a) of providing a steel tube having an axial length, an outer diameter which is perpendicular to the axial length, and an inner diameter which is parallel to the outer diameter, wherein the axial length is greater than each of the outer diameter and the inner diameter;

a step b) of shaping the steel tube into a pre-geometry, the shaping being performed by axially moving the steel tube into an outer tool so as to thereby provide the pre-geometry with the outer diameter which is reduced in an end region in the outer tool, wherein the shaping in step b) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant;

a step c) of calibrating an inner diameter of the pre-geometry, the calibrating being performed while the pre-geometry is arranged within the outer tool by,

introducing an inner mandrel having an outer diameter which corresponds to the inner diameter of the pre-geometry into the end region of the pre-geometry, and

pressing the pre-geometry against the outer tool so that the inner diameter of the pre-geometry is calibrated via a shaping in the end region,

wherein the shaping in step c) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant, without a preheating and without heated tools;

a step d) of removing the pre-geometry from the outer tool and removing the inner mandrel from the pre-geometry;

a step e) of axially moving the pre-geometry into a drawing tool comprising a roll-in contour which comprises a concave shape, thereby simultaneously shaping the pre-geometry into the airbag tube comprising a rotationally symmetrical outlet opening which is positioned centrally in an end face, wherein the shaping in step e) is performed via a hot forming together with a temperature-resistant lubricant or via a semi-hot forming together with a temperature-resistant lubricant; and

a step f) of removing the airbag tube from the drawing tool,

wherein,

in each of the step b) and the step d), no rotation of the pre-geometry with respect to the outer tool is performed, and

the airbag tube has a tensile strength of at least 700 MPa.

2 . The method as recited in claim 1 , wherein the shaping in the step b) takes place as a cold forming or as a cold drawing.

3 . The method as recited in claim 1 , wherein the shaping in the step c) takes place as a cold forming.

4 . The method as recited in claim 1 , wherein the shaping in the step e) takes place as a hot forming or as a semi-hot forming.

5 . The method as claimed in claim 1 , further comprising:

providing a calibration or a finish-forming of at least one of the end region and of outlet opening of the pre-geometry by,

inserting a second inner mandrel which has an outer contour which corresponds to an inner contour of the end region of the airbag tube to be produced into the outlet opening of the pre-geometry, and

axially moving the second inner mandrel and the pre-geometry into a second outer tool which has an inner contour which corresponds to an outer contour of the end region of the airbag tube to be produced.

6 . The method as recited in claim 5 , wherein, for the calibration or the finish-forming of the outlet opening, the second inner mandrel comprises a rotationally symmetrical element which is positioned centrally in an end face of the second inner mandrel, the outer contour of the rotationally symmetrical element corresponding to the inner contour of the outlet opening of the airbag tube to be produced.

7 . The method as claimed in claim 6 , wherein the calibration of the at least one of the end region and of the outlet opening is performed in a residual heat of a hot forming or of a semi-hot forming which is generated when performing the step e).

8 . The method as recited in claim 7 , wherein the residual heat of the hot forming or of the semi-hot forming which is performed in the step e) has a temperature of at least 473 K or a temperature lower than an Ac1 temperature of a steel or a steel alloy of the airbag tube.

9 . The method as recited in claim 6 , further comprising:

prior to the step e), heating the pre-geometry to >an Ac3 temperature; and

after the step e) or after the outlet opening is calibrated, actively cooling the pre-geometry so as to form an at least partially hardened grain structure in a steel alloy.

10 . The method as recited in claim 1 , wherein the steel tube comprises as a steel a steel alloy.

11 . The method as recited in claim 1 , wherein the steel tube comprises a steel which comprises iron and unavoidable melt-induced contaminants comprising:

0.07 to 0.50 wt-% of C, 0.05 to 0.55 wt-% of Si,

0.2 to 2.5 wt-% of Mn,

<0.025 wt-% of P,

<0.02 wt-% of S,

<2 wt-% of Cr,

<0.03 wt-% of Ti,

<0.6 wt-% of Mo,

<0.6 wt-% of Ni,

0.001 to 0.05 wt-% of Al,

<0.5 wt-% of V, and

<0.1 wt-% of Nb.

12 . The method as recited in claim 1 , wherein the steel tube comprises a steel which comprises iron and unavoidable melt-induced contaminants comprising:

0.07 to 0.20 wt-% of C,

0.05 to 0.55 wt-% of Si,

0.4 to 0.8 wt-% of Mn,

<0.025 wt-% of P,

<0.02 wt-% of S,

0.8 to 1.0 wt-% of Cr,

<0.015 wt-% of Ti,

0.25 to 0.4 wt-% of Mo,

0.2 to 0.3 wt-% of Ni,

0.02 to 0.04 wt-% of Al,

<0.1 wt. % of V, and

<0.06 wt-% of Nb.

13 . The method as recited in claim 1 , wherein the steel alloy is a steel which has a tensile strength of at least 700 MPa.

14 . A method for production of an airbag tube, the method comprising:

a step a) of providing a steel tube having an axial length, an outer diameter which is perpendicular to the axial length, and an inner diameter which is parallel to the outer diameter, wherein the axial length is greater than each of the outer diameter and the inner diameter;

a step b) of shaping an end region the steel tube into a pre-geometry, the shaping being performed by axially moving the steel tube into an outer tool so as to thereby provide the pre-geometry with the outer diameter which is reduced in the end region in the outer tool and so that an end part of a length of the end region is parallel to a rest of the steel tube which was not shaped, wherein the shaping in step b) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant;

a step c) of calibrating an inner diameter of the pre-geometry, the calibrating being performed while the pre-geometry is arranged within the outer tool by,

introducing an inner mandrel having an outer diameter which corresponds to the inner diameter of the pre-geometry into the end region of the pre-geometry, and

pressing the pre-geometry against the outer tool so that the inner diameter of the pre-geometry is calibrated via a shaping in the end region,

wherein the shaping in step c) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant, without a preheating and without heated tools;

a step d) of removing the pre-geometry from the outer tool and removing the inner mandrel from the pre-geometry;

a step e) of axially moving the pre-geometry into a drawing tool comprising a roll-in contour which comprises a concave shape, thereby simultaneously shaping the pre-geometry into the airbag tube comprising a rotationally symmetrical outlet opening which is positioned centrally in an end face, wherein the shaping in step e) is performed via a hot forming together with a temperature-resistant lubricant or via a semi-hot forming together with a temperature-resistant lubricant; and

a step f) of removing the airbag tube from the drawing tool,

wherein,

in each of the step b) and the step d), no rotation of the pre-geometry with respect to the outer tool is performed, and

the airbag tube has a tensile strength of at least 700 MPa.

15 . A method for production of an airbag tube, the method comprising:

a step a) of providing a steel tube having a tensile strength of at least 700 MPa, axial length, an outer diameter which is perpendicular to the axial length, and an inner diameter which is parallel to the outer diameter, wherein the axial length is greater than each of the outer diameter and the inner diameter;

a step b) of shaping the steel tube into a pre-geometry, the shaping being performed by axially moving the steel tube into an outer tool so as to thereby provide the pre-geometry with the outer diameter which is reduced in an end region in the outer tool, wherein the shaping in step b) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant;

a step c) of calibrating an inner diameter of the pre-geometry, the calibrating being performed while the pre-geometry is arranged within the outer tool by,

introducing an inner mandrel having an outer diameter which corresponds to the inner diameter of the pre-geometry into the end region of the pre-geometry, and

pressing the pre-geometry against the outer tool so that the inner diameter of the pre-geometry is calibrated via a shaping in the end region,

wherein the shaping in step c) is performed via a cold forming together with a lubricant or via a cold drawing together with a lubricant, without a preheating and without heated tools;

a step d) of removing the pre-geometry from the outer tool and removing the inner mandrel from the pre-geometry;

a step e) of axially moving the pre-geometry into a drawing tool comprising a roll-in contour which comprises a concave shape, thereby simultaneously shaping the pre-geometry into the airbag tube comprising a rotationally symmetrical outlet opening which is positioned centrally in an end face, wherein the shaping in step e) is performed via a hot forming together with a temperature-resistant lubricant or as a semi-hot forming together with a temperature-resistant lubricant; and

a step f) of removing the airbag tube from the drawing tool,

wherein,

in each of the step b) and the step d), no rotation of the pre-geometry with respect to the outer tool is performed, and

the airbag tube has a tensile strength of at least 700 MPa.