Tube expansion for motor vehicle crash boxes and method of manufacturing the same

Abstract

The invention relates to a motor vehicle crash box having a working direction in the longitudinal axis of the vehicle, which is manufactured from a tube which is expanded into different regions (1, 2, 3, 4) of different strength and diameter by using a steel which even after shaping has a uniform austenitic microstructure by means of the strain hardening effect. The invention also relates to a manufacturing method for such a component.

Description

Technical Field

[0001] This invention relates to a vehicle collision box having an operating direction along the longitudinal axis of the vehicle. The invention also relates to a method of manufacturing such a component. Background Technology

[0002] Existing motor vehicles are equipped with energy-absorbing elements at each end (front and rear) of their longest or longest dimension as collision protection components. These elements are called collision management systems or buffer systems and are typically attached to each other via a crossbeam connecting two existing collision boxes, which in turn are connected to the vehicle body structure. The collision boxes thus absorb the kinetic energy of the impact. The collision boxes undergo irreversible plastic deformation through compression or folding. Therefore, the vehicle body itself should be protected without any structural damage or distortion.

[0003] As a component of a motor vehicle, the crash box typically possesses seemingly contradictory characteristics, such as achieving high crash safety while being lightweight to reduce fuel consumption and thus CO2 emissions, and being cost-effective. Furthermore, the crash box provides protection for pedestrians. Further requirements include ease of assembly with adjacent parts, optimal space utilization, and easy replacement after an impact. The Automotive Repair Research Council has developed test scenarios called the RCAR crash test to assess damage and repair costs following rear-impact collisions at lower speed levels. The results of such tests have a direct impact on insurance ratings for passenger vehicles and are therefore of considerable interest to end users.

[0004] Several different geometries have been used in the design of crash boxes for motor vehicles. Circular and polygonal tubes with multi-chamber profiles or box-shaped constructions, as well as modular designs, can taper in the longitudinal direction of the component. While uniform tubular profiles offer constant force absorption, they are less resistant to lateral forces and bending torques than profiles with other geometries. Tubes are presented as easy to manufacture and therefore offer the highest cost-effectiveness for crash boxes.

[0005] In response to the increasing demand from crash test organizations such as Euro NCAP and US NCAP, a wide range of profile forms, consisting of two half-shells set together and divided into sections of different lengths, are now most common. To allow for the desired crash behavior, indentations or corrugations are introduced into the crash box through uniform folding. Indentation or corrugation forming in the resulting profile or half-shell of the crash box is a further manufacturing step, thus increasing component costs as a direct result.

[0006] Various prior art solutions exist for combining lightweight and crash safety in collision box components. US Patent Application Publication US2017113638A1 describes a crossbeam made of a lightweight metal alloy and configured as a hollow profile to define an internal space, having a top beam and a bottom beam, wherein the top beam and / or bottom beam has recesses defined by edge regions in the form of collars oriented into the internal space of the crossbeam. At the ends of the crossbeam are collision boxes formed with flanges sized to overlap at least one region of the crossbeam in the longitudinal direction of the vehicle. Spacers are arranged in the internal space of the crossbeam and have chamfers for engagement by collar-shaped locking. Fasteners are configured to pass through the recesses and thereby extend in the vertical direction of the vehicle through the spacers and the flanges of each collision box. The use of lightweight metal alloy hollow profiles is costly and results in the manufacture of expensive components.

[0007] In U.S. patent application 9663051B2, the crash box is divided into regions of different lengths. The tapered configuration used in conjunction with the introduction of tire beads indicates extensive effort during the manufacture of the crash box and results in higher component costs.

[0008] Another example of an expensive method of manufacturing a crash box is provided in U.S. Patent Application Publication 2017210319A1, in which multiple support walls are inserted in the longitudinal direction of the crash box. At least one of these support walls is designed as a vault.

[0009] U.S. Patent Application Publication 2013119705A1 discloses a collision box system in which a multi-chamber profile is integrated with additional support elements and fastening profiles for use. Similarly, the integration of weakening tools and longitudinal cracks, known from U.S. Patent Application Publication 2013048455A1, exhibits additional effort during component manufacturing, resulting in higher component costs.

[0010] U.S. Patent Application 2011291431A1 describes a collision box using a manganese-boron alloy steel grade that must be press-hardened and further annealed between 300°C and 450°C. A technical disadvantage of this grade is that it is brittle even in its welded regions due to its martensitic microstructure having a significantly lower energy absorption potential than the austenitic ductile microstructure grade. Furthermore, the press-hardening followed by further annealing manufacturing process results in costly production, inefficient cycle times, high investment costs, and unsatisfactory impacts on lifetime cycle assessment. U.S. Patent Application 2011291431A1 specifies the yield strength level R... p0.2=1,150 MPa, with an elongation A5 of 8%. These values ​​contrast with the requirements known from Béla Barény and her DE patent application 854157C for components that are stretchable, deformable, and have lower strength than those for the passenger safety zone of the vehicle body, which is designed for the passenger compartment. The strength decreases continuously or gradually in stages in the direction of the front and rear ends of the vehicle, and therefore, the front compartment and rear end of the car are considered deformable areas.

[0011] Most existing impact chamber systems are mechanical solutions designed to minimize costs during post-impact repair or replacement. Other systems are also available, such as those using sensors known from International Patent Application Publication WO2011073049A1. Furthermore, pneumatic or hydraulic damper solutions are generally technically feasible to meet component requirements.

[0012] In summary, there is no existing collision box system that utilizes a cost-effective tube design to meet practical collision requirements and today's lightweight OEM needs by leveraging the target-oriented strain hardening properties of austenitic steel. Furthermore, existing technologies lack a manufacturing process and use expansion forming to create collision box components. Summary of the Invention

[0013] One object of the present invention is to overcome some of the disadvantages of the prior art and provide a lightweight and cost-effective vehicle collision box having an operating direction in the longitudinal axis of the vehicle. This collision box is manufactured from a tube, such as a circular or polygonal tube, which is expanded into different regions of varying strengths and diameters using steel with a uniform austenitic microstructure exhibiting strain hardening even after forming. Furthermore, the collision box of the present invention is easy to assemble and scale up, depending on the vehicle model and its dimensions.

[0014] This invention relates to a vehicle collision box having an operating direction along the longitudinal axis of a motor vehicle and a method for manufacturing the same. The invention is defined by the independent claims. Preferred embodiments are set forth in the dependent claims. Detailed Implementation

[0015] This invention relates to a vehicle collision box having an operating direction along the longitudinal axis of the vehicle, the collision box being manufactured from a tube, such as a circular tube or a polygonal tube, which is expanded into different regions of varying strengths and diameters using steel having a uniform single-phase microstructure, such as a uniform austenitic microstructure, that exhibits strain hardening even after forming. The invention also relates to a method for manufacturing such a component.

[0016] The embodiments describe a motor vehicle crash box. In one embodiment, the motor vehicle crash box has an operating direction along the longitudinal axis of the vehicle. The motor vehicle crash box is manufactured from a tube that is expanded into an expanded tube by a forming process, the expanded tube comprising at least two regions with different material strengths and different geometries. Thus, in one embodiment, the crash box comprises an expanded tube having at least two regions. Each region has a different material strength and a different shape or geometry. In one embodiment, the tube is a circular tube. In another embodiment, the tube is a polygonal tube. For the purposes of this invention, a circular tube is a tube in which both the inner cavity or internal space of the tube and the outer circumference of the tube are circular and have a non-undulating diameter. In one embodiment, the internal space of the tube has a diameter that is substantially the same along the length of the tube, and similarly, the tube has an outer diameter that is substantially the same along the length of the tube.

[0017] In another implementation, the region has a strength of 6.0 N / mm². 3 –9.0N / mm 3 Strength [N / mm] 2 The ratio of [ ] to diameter [mm]. Strength is measured according to the method of DIN EN 10216, in which tensile testing of a region of the steel tube is performed at room temperature under quasi-static conditions. The hardening behavior of stable single-phase steel is known from tensile testing according to DIN EN ISO 6892-1:2017-02, which is performed at room temperature under flat and quasi-static conditions. By understanding the strain hardening rate of the material under flat conditions, the resulting strength of the tube after expansion, in relation to the degree of forming, can be calculated.

[0018] In one embodiment, the minimum strength Δ between different regions, measured according to the method described above, is ΔRm ≥ 75 MPa, preferably ΔRm ≥ 120 MPa. The strength difference between regions is optimized to form a collision buffer for absorbing impact kinetic energy, as described in the embodiment below, wherein, depending on the respective minimum diameter, the expansion tube having its different regions is first folded by the region with the minimum diameter, and then by the other regions.

[0019] In other words, in one implementation, the region has foldability inversely proportional to its diameter. This means that the region with the smallest diameter folds first, and the region with the largest diameter folds last on impact.

[0020] In another embodiment, the expansion tube is configured to reach the block length of the system after impact, preferably L. B ≥80mm, more preferably L B ≥100mm is used to provide a residual safety zone. This limits the transmission of force to the vehicle's passenger compartment.

[0021] In one implementation, the center in the longitudinal direction is used as a mirror axis, and the region is characterized from the outside to the center, with the diameter of the region decreasing towards the center.

[0022] In a preferred embodiment, at least one end of the expansion tube is widened to provide a flange around the circumference of the tube end, the flange being substantially perpendicular to the longitudinal axis of the tube housing and its operating direction. The flange provides a surface for attaching the crash box to adjacent vehicle parts, such as a bumper or chassis of a car. The flange can be welded as a lap joint, for example as a fillet, or mechanically attached to the adjacent vehicle parts in a lap joint state, for example by screws or other mechanical attachments, such as rivets, nails, nuts, bolts, etc. Such attachment components provide easy assembly and minimize downstream costs when installing the crash box in a motor vehicle.

[0023] Another embodiment relates to a method for manufacturing a motor vehicle collision box having an operating direction along the longitudinal axis of the vehicle. In one embodiment, the tube is manufactured as a longitudinally welded tube, preferably by high-frequency welding. Welded tubes are generally significantly less expensive than cold-drawn seamless tubes. Welding, especially high-frequency welding, provides the highest production speed. Furthermore, high-frequency welding has the lowest possible heat input. The heat input in this method is concentrated at the surface to be welded. This concentration of heat input makes the method ideal for welding thin tubes, such as tubes with a steel thickness of 0.8 mm ≤ t ≤ 2.5 mm. This reduces thermal distortion and lowers the internal stress of the tube.

[0024] In another embodiment, the tube is expanded using a mechanical drift expansion process in a mechanical drift expansion machine. Mechanical drift expansion machines are relatively inexpensive. These machines can be used to test weld quality and perform expansion forming steps.

[0025] In a preferred embodiment, the mechanical drift expansion process machine uses at least two different expansion mandrels for at least two different regions of the impact box. The process is optimized by using different mandrels.

[0026] In a suitable implementation, the mechanical drift expansion process machine has a mirrored longitudinal axis to form a symmetrical collision box.

[0027] In one embodiment, the tube is made of strain-hardenable fully austenitic steel, preferably austenitic stainless steel, which has an initial yield strength R measured by tensile testing at room temperature under flat and quasi-static conditions according to DIN EN ISO 6892-1:2017-02. p0.2 ≥380MPa and initial elongation A 80 ≥40%.

[0028] In one specific embodiment, the tube has an initial thickness of 0.8 mm ≤ t ≤ 2.5 mm, and the ratio of the initial diameter to the thickness is 24 ≤ r. d / t ≤125, more preferably between 40≤r d / t The thickness and diameter are ≤55. The thickness and diameter can be measured using various methods known to those skilled in the art, such as calipers or mechanical micrometers. Further methods for measuring the diameter include optical methods, such as laser distance measurement. The described thickness-to-inner-diameter ratio is optimal for molding collision boxes used in cars, trucks, buses, or agricultural vehicles.

[0029] Therefore, other embodiments relate to the use of the expansion tube. One embodiment describes the use of the expansion tube as a crash box in a motor vehicle. In one embodiment, the motor vehicle in which the crash box is integrated is a car, truck, bus, or agricultural vehicle. In another embodiment, the motor vehicle in which the crash box is integrated is a fully electric vehicle.

[0030] In another implementation, the collision box is used as an energy-absorbing element in a crash barrier, protective rail, or inside a rail vehicle.

[0031] According to the invention, the expansion tube impact box is manufactured from a longitudinally welded continuous tube, preferably a circular tube, which is cut into the required component length in a first step. Then, the tube is expanded from at least one side, preferably from both ends, by a mechanical drift expansion process to the length of the cut tube. To provide an economically attractive component, the longitudinal welding process is preferably a high-frequency welding process, which further provides high ductility and electrical transmission in the weld area using austenitic steel. Alternatively, a laser beam welding process can be used to satisfy the method of the invention.

[0032] The cut tube is expanded by a forming process, preferably by a mechanical drift expansion process, into at least two regions with different material strengths and geometries, particularly tube diameters. By using austenitic steel with a cold-formable strain hardening mechanism, the larger expanded region with the higher resulting diameter provides a higher strength level. As a result of impact in the longitudinal direction of a motor vehicle, the expanded tube's impact box folds together, with the region having the smallest diameter and therefore the lowest strength level folding first. Because the highest elongation exists in this region, the energy absorption potential for converting impact kinetic energy into material-related plastic deformation is at its highest. If the impact force is not mitigated by folding the first region, the same effect occurs in the region with the second smallest diameter, and so on. In low-energy impacts, the region with the lowest strength and the thinnest diameter folds. In higher-energy impacts, regions with increased diameter and increased strength also fold successively, allowing energy to be continuously absorbed by the impact box. Thus, the impact box absorbs impact kinetic energy, protecting the vehicle body and, in particular, the occupants within the vehicle from these effects.

[0033] Resistance to impact is increased in two ways using the impact box and method of the present invention: firstly, in a material-related manner, because the strain-hardening austenitic steel used will increase its strength during impact due to its hardening mechanism. Utilizing this effect, the yield strength [N / mm²] in the corresponding region is increased. 2 The ratio of [ ] to diameter [mm] can be defined as a design factor for component engineers. For the method of this invention, utilizing a combination of an expansion tube impact box and strain-hardenable austenitic steel, the ratio is suitable at 6.0 N / mm. 3 –9.0N / mm 3 Between. Resistance to impact will increase in a second way, which is geometry-related, because the continuous folding of the lower diameter region to the higher diameter region results in more material having to be folded during the corresponding next folding step. At the end, the part condition is reached, where the block length L is obtained. B This can be defined as a residual safety zone, where maximum resistance to impact is exhibited. Preferably, the block length of the impact box reaches a length of L. B ≥80mm, preferably length L B ≥100mm.

[0034] In a preferred embodiment, there are three regions (1, 2, 3) each having three diameters (d1, d2, d3), see [reference]. Figure 1Therefore, the center in the longitudinal direction is used as a mirror axis. Regions are characterized from the outside towards the center, with the diameter of the region decreasing. To achieve the desired folding behavior of different regions, the diameter is preferably constructed in such a way that the minimum strength Δ between different regions is ΔRm ≥ 75 MPa, preferably ΔRm ≥ 120 MPa.

[0035] Using the above-described construction, the necessary machine for expanding the tube using the mechanical drift expansion process must be fully adapted to the design requirements. Therefore, the machine is designed with tools having at least two different expansion mandrels for at least two different regions of the impact box. Preferably, the main mandrel tool is formed on one side of a mirror axis, into which the tube is inserted. To allow for rapid and cost-effective production of high vehicle volumes, more preferably, the machine has a mirrored longitudinal axis to form a symmetrical impact box, allowing the mandrel tools to be inserted from both sides of the tube's longitudinal axis, so that the tube expands simultaneously to its mirror axis from both sides.

[0036] To allow connection to adjacent parts of the crash box, at least one end, but preferably both ends, of the expansion tube are widened to provide a flange around the circumference of the tube end, which is substantially perpendicular to the longitudinal axis of the box and its operating direction. The flange provides a surface for attaching the crash box to adjacent vehicle parts, such as bumpers or chassis of a car. The flange can be welded as a lap joint, for example, as a fillet, or mechanically attached to adjacent vehicle parts in a lap joint state, for example, by screws or other mechanical attachments, such as rivets, nails, nuts, bolts, etc. Such attachment components provide easy assembly and minimize downstream costs when installing the crash box in a motor vehicle.

[0037] The advantage of this design is that the position and orientation of the joint are optimized to better resist stress during impacts from the front or rear of the vehicle.

[0038] The initial material form prior to pipe manufacturing is flat steel with a thickness t ≤ 3.0 mm, preferably between 0.8 mm ≤ t ≤ 2.5 mm, and is typically supplied to the pipe manufacturer in the form of coils or strips. It is further adapted to define the ratio of the initial diameter to the thickness of the pipe, which is 24 ≤ r. d / t ≤125, more preferably between 40≤r d / t ≤55. Individual tubes can be manufactured from sheets or plates; however, using strips and coils as starting materials for continuous tube manufacturing provides a cost-effective and large-scale industrial crash box manufacturing for larger vehicle volumes.

[0039] In one embodiment, an austenitic steel, preferably stainless steel, with a cold-formable and strain-hardening mechanism is used, having an initial yield strength R. p0.2≥380MPa and initial elongation A 80 ≥45%. In another embodiment, stable single-phase austenitic steel is used, which provides TWIP (twin-induced plasticity) strain hardening effect even after forming and welding of fully austenitic steel.

[0040] To provide a lightweight impact box with good or optimal impact resistance, meaning safety, it is suitable for use with an initial strength level R p0.2 ≥380MPa, more preferably R p0.2 High-strength steel with a strength ≥450MPa. Besides strength, the ductility of the expansion tube is also an important characteristic. During a collision, the material's ductility is further required as a key characteristic of the component—energy absorption potential. The higher the energy absorption of the impact chamber, the lower the forces and accelerations transmitted to the passenger compartment and thus to the occupants. Due to the ductility of the impact chamber material, the impact chamber can continuously absorb impact energy and gently reduce the forces on the occupants in the vehicle. Therefore, the value of ductility, described as elongation after fracture, is A. 80 ≥40%, preferably A 80 ≥50% of the initial material is suitable for this invention. The desired combination of strength and elongation is provided by steels with an austenitic microstructure and strain hardening mechanism (especially austenitic stainless steels) having a chromium content of ≥10.5%. The strain hardening property allows vehicle engineers to achieve the final strength-ductility combination after the component manufacturing is completed (in this case, after the expansion tube impact box). For austenitic steels, there are two different hardening mechanisms: the first hardening occurs during cold forming, including manufacturing, and the second hardening occurs during impact impacts throughout the component's service life. Steels with a metastable austenitic microstructure exhibit a TRIP (transformation-induced plasticity) hardening effect, in which austenite transforms into martensite during forming loads. For the method of this invention, it is preferred to use steels with a fully austenitic microstructure exhibiting a so-called TWIP (twin-induced plasticity) hardening effect, which has a chromium content between 20 mJ / m 2 With 30mJ / m 2 The specific stacking fault energy (SFE) combination between them. The advantage of TWIP hardened austenitic steel is that during tube expansion, the microstructure remains in the initial ductile-austenitic conditions without the presence of a brittle martensite phase, and therefore the parts have a uniform microstructure.

[0041] Furthermore, due to its natural and re-passivated chromium oxide surface layer, austenitic stainless steel offers significantly higher corrosion resistance than low- or non-alloy steels. This eliminates the need for additional dip-coating processes on components, thus reducing the overall cost of impact box components. Additionally, it improves environmental impact over its lifecycle. Stainless steel impact box components are fully recyclable; they can be melted down in an electric arc furnace at the end of their lifespan.

[0042] The expansion tube impact box can be used in any motor vehicle, preferably in the interior of a passenger car, but can also be used in the interior of trucks, buses, or agricultural vehicles. The method of the invention can also be adapted for use in rail vehicles by changing the thickness and diameter to higher values. Furthermore, the expansion tube impact box can also be integrated as an energy-absorbing element into crash barriers or guardrail systems to protect intruding vehicles and their occupants during an impact. Attached Figure Description

[0043] The invention is illustrated in more detail with reference to the accompanying drawings.

[0044] Figure 1 An embodiment of the invention is shown schematically by way of a side view.

[0045] Figure 2 The relationship between component strength and longitudinal length is shown.

[0046] Figure 3 The side view shows the condition of the component geometry from the initial vehicle mounting (left) and the forming behavior during an impact (right).

[0047] Figure 4 The behavior of the component during the impact reaching the block length is shown in the side view.

[0048] Figure 5 The side view shows the welded connection between the expansion tube and adjacent vehicle parts.

[0049] Description of the embodiments of the present invention

[0050] Figure 1 The expanded tube collision box after manufacturing is shown in a side view. The dashed line indicates the longitudinal axis of symmetry. In this embodiment of the invention, there are three regions (1), (2), and (3) that are symmetrical in the transverse direction, such that region 1 (1), with the smallest diameter d1, is located in the central region. From the center outwards longitudinally, the diameter of the regions increases, as shown in regions 2 (2) and 3 (3).

[0051] Figure 2 against Figure 1 The components shown illustrate the relationship of strength in the longitudinal direction of components with different regions, whereby the transition region (4) is located from Figure 1 Between the main regions (1), (2), and (3). The horizontal dashed line (5) shows the starting point where the regional changes and therefore the changes in diameter and intensity occur. Region 1, with the smallest diameter d1, has the lowest intensity level. As the diameter increases, the intensity level also increases. Figure 1The implementation scheme results in two strength differences named ΔRm(6). The strength differences between each diameter are essentially the same.

[0052] Figure 3 The forming behavior of the component during an impact from the longitudinal side is shown, thereby derived from... Figure 1 The region with the lowest diameter and therefore the lowest strength level (1) is folded. Depending on the specific strength level, the region with the higher diameter will slide over the region with the lower diameter.

[0053] Figure 4 Showing from Figure 3 The length is called block length L B (7) The ongoing impact at its end position, where the component's energy is exhausted. Block length L B (7) Further equals the residual safety zone, in which other components can be located and will not be affected by the impact.

[0054] Figure 5 A preferred embodiment of the invention is shown, wherein at least one end of the expansion tube is widened in such a way that the end (8) is bent along the longitudinal axis of the tube collision box and in its working direction to enable engagement with an adjacent vehicle part (10) at a lap joint (9). The engagement can be performed as welding with a fillet, or as a mechanical engagement similar to a lap joint such as a threaded connection.

Claims

1. A motor vehicle collision box having a working direction along the longitudinal axis of the vehicle, wherein, The component is made of a tube, which is made of austenitic steel having a uniform austenitic microstructure that exhibits strain hardening even after forming. The austenitic steel is expanded into an expanded tube by a forming process, and the expanded tube includes at least two regions (1, 2, 3) with different material strengths and different geometries. The feature is that the center of the expansion tube in the longitudinal direction serves as a mirror axis, and the at least two regions (1, 2, 3) are formed in such a way that they start from the outer longitudinal direction and move towards the center, and the diameters (d1, d2, d3) of the at least two regions (1, 2, 3) decrease from the outer longitudinal direction to the center, such that the region with the smallest diameter among the at least two regions is located in the central region.

2. The vehicle collision box according to claim 1, characterized in that, The at least two regions (1, 2, 3) have a strength of 6.0 N / mm. 3 –9.0N / mm 3 The ratio of strength to diameter.

3. The motor vehicle collision box according to claim 1 or 2, characterized in that, The minimum intensity Δ between different regions (1, 2, 3) in the at least two regions is ΔRm≥75MPa.

4. The vehicle collision box according to claim 3, characterized in that, The minimum intensity Δ between different regions (1, 2, 3) in the at least two regions is ΔRm≥120MPa.

5. The motor vehicle collision box according to claim 1 or 2, characterized in that, The at least two regions (1, 2, 3) have foldability that is inversely proportional to the diameters (d1, d2, d3) of the at least two regions (1, 2, 3).

6. The motor vehicle collision box according to claim 1 or 2, characterized in that, The expansion tube is configured to reach the system's block length L after impact. B To provide a safe zone for the remaining population.

7. The vehicle collision box according to claim 6, characterized in that, The block length L B ≥80mm.

8. The vehicle collision box according to claim 6, characterized in that, The block length L B ≥100mm.

9. The motor vehicle collision box according to claim 1 or 2, characterized in that, At least one end of the expansion tube is widened to provide a flange around the circumference of the end of the expansion tube, the flange being substantially perpendicular to the longitudinal axis of the vehicle crash box and its operating direction, the flange providing a surface for attaching the vehicle crash box to an adjacent vehicle component.

10. A method for manufacturing a motor vehicle collision box according to any one of claims 1 to 9, characterized in that, The tube is manufactured as a longitudinally welded tube.

11. The method according to claim 10, characterized in that, The tube is manufactured as a longitudinally welded tube by high-frequency welding.

12. The method according to claim 10 or 11, characterized in that, The tube is expanded in a mechanical drift expansion process machine.

13. The method according to claim 12, characterized in that, The mechanical drift expansion process machine uses at least two different expansion mandrels for at least two different regions of the vehicle collision box.

14. The method according to claim 12, characterized in that, The mechanical drift expansion process machine has a mirrored longitudinal axis to form a symmetrical vehicle collision box.

15. The method according to claim 10 or 11, characterized in that, The tube is made of strain-hardenable fully austenitic steel with an initial yield strength R. p0.2 ≥380MPa and initial elongation A 80 ≥40%.

16. The method according to claim 15, characterized in that, The fully austenitic steel is austenitic stainless steel.

17. The method according to claim 10 or 11, characterized in that, The tube has an initial thickness of 0.8 mm ≤ t ≤ 2.5 mm, and the ratio of the initial diameter to the initial thickness of the tube is 24 ≤ r. d / t ≤125.

18. The method according to claim 17, characterized in that, The ratio of the initial diameter to the initial thickness of the tube is 40 ≤ r d / t ≤55.

19. An expansion tube made of austenitic steel for use in a motor vehicle crash box according to any one of claims 1 to 9, said austenitic steel having a uniform austenitic microstructure exhibiting strain hardening even after forming, said austenitic steel being expanded into an expansion tube by a forming process to serve as a motor vehicle crash box, said expansion tube comprising at least two regions (1, 2, 3) having different material strengths and different geometries, characterized in that, The motor vehicle collision box is integrated into a car, truck, or bus.

20. An expansion tube made of austenitic steel for use in a motor vehicle crash box according to any one of claims 1 to 9, said austenitic steel having a uniform austenitic microstructure exhibiting strain hardening even after forming, said austenitic steel being expanded into an expansion tube by a forming process to serve as a motor vehicle crash box, said expansion tube comprising at least two regions (1, 2, 3) having different material strengths and different geometries, characterized in that, The vehicle whose collision box is integrated is an agricultural vehicle.

21. An expansion tube made of austenitic steel for use in a motor vehicle crash box according to any one of claims 1 to 9, said austenitic steel having a uniform austenitic microstructure exhibiting strain hardening even after forming, said austenitic steel being expanded into an expansion tube by a forming process to serve as a motor vehicle crash box, said expansion tube comprising at least two regions (1, 2, 3) having different material strengths and different geometries, characterized in that, The vehicle collision box is an energy absorption element located in a crash barrier, a protective rail, or inside a rail vehicle.

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