Methods for quality assurance of a supporting structure for a vehicle

Abstract

Method for quality assurance of a load-bearing structure for a vehicle, in particular a body longitudinal member (1) or a sheet metal part for a B-pillar, wherein the load-bearing structure has a hard area (3) with a high strength value and a soft area (5) with a lower strength value following in a longitudinal direction (x) of the load-bearing structure and an intermediate transition area (7), wherein in the transition area (7) the strength values ​​are reduced in a predefined, continuous progression from a high strength value in the hard area (3) to the lower strength value in the soft area (5), characterized in that the method checks whether tolerance ranges are maintained in the transition area (7), and in the method the load-bearing structure to be checked is classified as scrap if the actual values ​​recorded for the load-bearing structure to be checked are outside the tolerance ranges, comprising the steps: - Recording actual values ​​of the load-bearing structure in the transition area, - Verification of the actual values ​​of the supporting structure to ensure compliance with tolerance ranges in the transition area, - Classification of the supporting structure as scrap if the recorded actual value is outside the tolerance ranges.

Description

[0001] The invention relates to a method for quality assurance of a supporting structure for a vehicle, in particular a body longitudinal member or a sheet metal part for a B-pillar, according to the preamble of patent claim 1.

[0002] To increase the crash safety of vehicles, their crash-relevant supporting structures, such as longitudinal members or B-pillars, can be divided into zones with different strength values ​​along their longitudinal direction. Such zones of different strength values ​​can be achieved through different heat treatments, different hardening, or different tempering processes.

[0003] EP 2 441 852 A1 discloses a generic support structure for a vehicle, which has a hard region with a high strength value and, in the longitudinal direction, a soft region with a lower strength value, as well as an intermediate transition region. In the hard region and the soft region of the longitudinal member, the strength, hardness, and ductility properties are specifically adjusted by different heat treatments. In contrast to the hard region, the soft region tends to have a more ductile material structure. In the soft region, deformation, such as wrinkling or compression, is therefore favored in the event of a crash without cracking or tearing occurring. In contrast to the soft region, the hard region of the longitudinal member has a substantially martensitic structure with particularly high strength values.The hard area of ​​the longitudinal member therefore ensures that in the event of a crash, the longitudinal member structure in the passenger cell area is maintained as deformation-free as possible.

[0004] In EP 2 441 852 A1, the transition region arranged between the hard region and the soft region is designed to be as short as possible in the direction of extension, in particular less than 20 mm.

[0005] Studies have shown that the material properties in the transition area, in particular, can have a decisive influence on the crash behavior of the entire longitudinal member. Furthermore, when longitudinal members are manufactured and delivered by different suppliers, there is a risk that the material properties of the longitudinal members in the transition area may differ from one another.

[0006] The object of the invention is to provide a supporting structure for a vehicle or a method for producing or quality assurance of such a supporting structure, in which the crash behavior of the supporting structure is improved in a simple manner.

[0007] The problem is solved by the features of patent claim 1. Further developments of the invention are disclosed in the subclaims.

[0008] The invention is based on the fact that, in support structures known from the prior art, the strength values ​​are not defined, especially in the transition region between the hard and soft regions, or that, specifically in the transition region, undesirable crash behavior of the support structure often occurs. Against this background, according to the characterizing part of patent claim 1, the strength values ​​in the transition region between the hard and soft regions are reduced in a predefined, continuous progression from the high strength value in the hard region to the low strength value in the soft region. This results in predefined material properties, especially in the transition region, with which the desired crash behavior of the support structure can be more easily achieved.In addition, when manufacturing and supplying longitudinal members by different suppliers, the risk that the longitudinal members differ from one another in terms of their material properties in the transition area can be eliminated.

[0009] The transition zone can extend in the longitudinal direction of the supporting structure from the hard zone to the soft zone between predefined longitudinal positions over a specified length. The strength values ​​can preferably be continuously reduced over the entire specified transition length until the lower strength value (soft zone) is reached.

[0010] For consistent crash behavior across the longitudinal direction, it is advantageous if the high strength value curve in the hard range is constant. The same applies to the lower strength value curve in the soft range, which is also preferably constant across the longitudinal direction.

[0011] The supporting structure can preferably be a single-piece, uniformly constructed sheet metal component in the longitudinal direction, which can be divided into a hard region, a transition region, and a soft region by different heat treatments or different hardening / cooling processes. The hard region can preferably be treated with a tempering process, while the soft region of the supporting structure is partially tempered or untempered. Tempering is the combination of hardening and tempering of steel at elevated temperatures in order to impart high strength and toughness to the material through this heat treatment. Hardening occurs through rapid cooling from the austenite region of the steel material. Depending on the steel grade and intended use, the tempering process takes place at temperatures between 150°C and 700°C.Depending on the required mechanical properties, the workpieces are kept at this temperature for different lengths of time and are generally cooled in air.

[0012] With regard to the crash behaviour of the supporting structure, the strength values ​​that have proven to be particularly important are the yield strength R P, 0,2 , the tensile strength R m and hardness (especially Vickers hardness) have proven to be particularly meaningful material properties.

[0013] The longitudinal positions and the strength values, especially of the transition area of ​​the supporting structure, can vary by specified tolerances without affecting the crash behavior of the supporting structure. For example, the longitudinal positions can vary by a tolerance of ± 10 mm in the longitudinal direction. Furthermore, the Vickers hardness can be between 400 HV and 520 HV in the hard range and between 210 HV and 240 HV in the soft range. Alternatively or additionally, the yield strength R P , 0,2 in the hard range between 1000 and 1300 MPa and in the soft range between 430 and 550 MPa. In addition, the tensile strength R m in the hard range between 1300 and 1650 MPa and in the soft range between 650 and 750 MPa.

[0014] A quality assurance procedure for the supporting structure specifically checks whether the tolerance ranges specified above are met in the transition area. If the recorded actual values ​​for the supporting structure under inspection lie outside the tolerance ranges specified above, the supporting structure under inspection is classified as scrap:

[0015] For example, the quality assurance process can record the hardness profile specifically in the transition area. For this purpose, the actual hardness values ​​directly at the longitudinal positions I1, I2, as well as additional hardness values ​​located between the longitudinal positions I1 and I2, are recorded. A check is then carried out to determine whether the recorded hardness values ​​lie within the tolerance ranges specified above. Alternatively or in addition to these actual hardness values, actual values ​​relating to the tensile strength or yield strength can also be recorded.

[0016] Hardness is the mechanical resistance a material offers to the mechanical insertion of a harder test specimen. The definition of hardness differs from the definition of tensile strength, which represents the resistance of a material to separation.

[0017] The 0.2 percent yield strength R used as the strength value p, 0,2 Describes a mechanical longitudinal strain in which the residual strain, relative to the initial length of the specimen, after unloading is exactly 0.2%. At even higher loads, either pronounced plastic deformation occurs or the tensile strength is exceeded, resulting in fracture of the material.

[0018] The advantageous embodiments and / or further developments of the invention explained above and / or reproduced in the subclaims can - except, for example, in cases of clear dependencies or incompatible alternatives - be used individually or in any combination with one another.

[0019] The invention and its advantageous developments and further developments as well as their advantages are explained below with reference to drawings.

[0020] They show: Fig. 1 shows a partial side view of a section of a body longitudinal member for a motor vehicle; Fig. 2 a diagram illustrating the course of the yield strength over the length of the body longitudinal member; Fig. 3 a diagram illustrating the tensile strength curve along the length of the body longitudinal member; and Fig. 4 a diagram illustrating the hardness progression over the length of the body longitudinal member.

[0021] In the Fig. 1 shows a longitudinal body member 1 as an example of a supporting structure for a vehicle. The longitudinal body member 1 has, in its longitudinal direction x, i.e., in the vehicle longitudinal direction x, a hard region 3 and a soft region 5 following in the vehicle longitudinal direction x, and a transition region 7 arranged therebetween. The longitudinal body member 1 is manufactured throughout the various sub-regions 3, 5, 7 as a single-piece and uniformly material sheet steel component. The hard region 3 of the longitudinal member 1 has high strength values, as described later, while the soft region 5 of the longitudinal member 1 has comparatively lower strength values. In the transition region 7, as shown in the Fig. 3 to 4, the strength values ​​are reduced in a predefined continuous progression from the high strength value in the hard range 3 to the low strength value in the soft range 5.

[0022] According to the Fig. 1, the transition area 7 extends in the vehicle's longitudinal direction x from the hard area 3 to the soft area 5 between two predefined longitudinal positions I1 and I2, specifically over a specified length ΔI. The length ΔI of the transition area 7 is, for example, in a range of 200 mm, with an exemplary tolerance of ± 20 mm.

[0023] With regard to the crash behaviour of the longitudinal member 1, the strength values ​​that have proven particularly suitable are the yield strength R P, 0,2 , the tensile strength R mand hardness (especially Vickers hardness, optionally also other hardness measurement methods) have proven to be particularly meaningful material properties. Their progression along the longitudinal member 1 is shown in the diagrams of Fig. 2 to 4 shown.

[0024] According to the Fig. 2, the yield strength R of the longitudinal member 1 is P, 0,2 in the hard range 3 constant at 1200 MPa, while the tensile strength R m is constant at 1500 MPa and the Vickers hardness is constant at 450 HV. In the soft area 5 of the longitudinal member 1, however, the yield strength R p, 0,2 in the vehicle longitudinal direction x constant at 500 MPa, the tensile strength constant at 700 MPa and the hardness constant at 230 HV.

[0025] To produce the hard area 3, the longitudinal member is subjected to a tempering process up to the longitudinal position I1, while the longitudinal member 1 remains untempered in the soft area 5 starting from the second longitudinal position I2.

[0026] The longitudinal positions I1 and I2 defined above, as well as the strength values ​​of the transition area 7 of the longitudinal member 1, can vary by specified tolerances without affecting the longitudinal member's crash behavior. For example, the longitudinal positions I1 and I2 can vary by a tolerance of ± 10 mm in the longitudinal direction x. Furthermore, the Vickers hardness in the hard area 3 can be between 400 HV and 520 HV, and in the soft area 5 between 210 HV and 240 HV. Alternatively or additionally, the yield strength R P, 0,2 in the hard range 3 between 1000 and 1300 MPa and in the soft range 5 between 430 and 550 MPa. In addition, the tensile strength R m in hard range 3 between 1300 and 1650 MPa and in soft range 5 between 650 and 750 MPa.

[0027] The following describes a quality assurance procedure for the vehicle longitudinal member 1, specifically at its transition area 7. Compliance with the above tolerance ranges is checked. If the recorded actual values ​​for the longitudinal member 1 under inspection lie outside the above-specified tolerance ranges, the longitudinal member 1 under inspection is classified as reject:

[0028] In the quality assurance process, for example, the hardness profile can be recorded specifically in transition area 7. For this purpose, the actual hardness values ​​directly at the longitudinal positions I1, I2, as well as additional actual hardness values ​​located between the longitudinal positions I1 and I2, are recorded. A check is then carried out to determine whether the recorded actual hardness values ​​lie within the tolerance ranges specified above. Alternatively or in addition to these actual hardness values, actual values ​​relating to the tensile strength or yield strength can also be recorded.

Claims

[1] Method for quality assurance of a supporting structure for a vehicle, in particular a body longitudinal member (1) or a sheet metal part for a B-pillar, wherein the supporting structure has a hard region (3) with a high strength value and a soft region (5) following in a longitudinal direction (x) of the supporting structure with a lower strength value and an intermediate transition region (7), wherein in the transition region (7) the strength values ​​are reduced in a predefined, continuous course from a high strength value in the hard region (3) to the lower strength value in the soft region (5), characterized by that the procedure checks whether tolerance ranges are complied with in the transition area (7), and that the supporting structure to be checked is classified as reject if the recorded actual values ​​for the supporting structure to be checked lie outside the tolerance ranges, comprising the steps: - Recording actual values ​​of the supporting structure in the transition area, - Checking the actual values ​​of the supporting structure for compliance with tolerance ranges in the transition area, - Classification of the supporting structure as scrap if the recorded actual value is outside the tolerance ranges. [2] Method according to claim 1, characterized by that the transition region (7) is defined by predetermined longitudinal positions (I1, I2) which are spaced apart from one another in the longitudinal direction (x) over a predetermined length (ΔI), and that in particular the strength values ​​over the entire length (ΔI) between the longitudinal positions (I1, I2) can be continuously reduced. [3] Method according to claim 1 or 2, characterized bythat the course of the high strength value in the hard region (3) is constant over the longitudinal direction (x), and / or that the course of the lower strength value in the soft region (5) is constant over the longitudinal direction (x). [4] Method according to one of the preceding claims, characterized by that the supporting structure (1) is a one-piece sheet metal component made of the same material throughout the longitudinal direction (x). [5] Method according to one of the preceding claims, characterized by that the regions (3, 5, 7) of the supporting structure are formed by different heat treatments, and that in particular the hard region (3) is tempered and the soft region (5) is partially tempered or untempered. [6] Method according to one of the preceding claims, characterized by that the length (ΔI) of the transition area (7) is 200 mm, in particular with a tolerance of ± 20 mm. [7] Method according to one of the preceding claims, characterized by that the longitudinal positions (I1, I2) can be positioned with a tolerance of in particular ± 10 mm in the longitudinal direction (x). [8] Method according to one of the preceding claims, characterized by that the strength value is the hardness, in particular the Vickers hardness (HV), and / or the tensile strength (R m ) and / or the yield strength (R P, 0,2 ) is provided. [9] Method according to claim 8, characterized by that the Vickers hardness in the hard range (3) is between 400 HV and 520 HV and in the soft range (5) between 210 HV and 240 HV, and / or that the yield strength (R P, 0,2 ) in the hard range (3) is between 1000 and 1300 MPa and in the soft range (5) is between 430 and 550 MPa, and / or that the tensile strength (R m ) in the hard range (3) between 1300 and 1650 MPa and in the soft range (5) between 650 and 750 MPa.

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