Method for increasing the structural in-service performance of a sheet metal component

Abstract

A method for increasing the structural in-service performance of a sheet metal component having a discontinuity, comprising: Heat treating a zone of the sheet component at a predetermined distance from the discontinuity, thereby reducing the strength of the zone by 15% to 25% and increasing the formability of the zone; and Shifting the deformation caused in the sheet metal component by a subsequent deformation event away from the discontinuity to the zone.

Description

TECHNICAL FIELD

[0001] This document generally concerns the heat treatment of sheet metal components, in particular including sheet metal components used in the manufacture of motor vehicles such as motor vehicle roof panels, trailer panels or other body panels. GENERAL STATE OF THE ART

[0002] The presence of discontinuities, such as a weld seam, a weld heat-affected zone, an edge, an edge bend, a mechanical fastening connection, or a deep-drawn area that has been mechanically deformed during manufacturing, can adversely affect the structural performance of components and assemblies, including, in particular, sheet metal components used in the manufacture of motor vehicles. This is especially true when such sheet metal components are made of work-hardened and / or heat-treated aluminum alloys.

[0003] US 7 618 503 B2 discloses methods for forming steel structures produced by welding two surfaces of hardenable iron alloys by an improved heat treatment after welding.

[0004] From US 2014 / 0 125 090 A1 a method for manufacturing vehicle components is known which involves the welding together of two differently heat-treated aluminum alloys as well as a motor vehicle component manufactured according to the method.

[0005] US 8 448 324 B2 describes a method in which at least one sheet of a magnesium alloy is joined to another by means of fiber-reinforced polymer bodies which, after being guided into congruent holes in an overlapping region of the sheets which is displaced from the plane of the planar overlapping region, are compressed on both sides of the sheets so that the sheets are joined in a corrosion-resistant manner.

[0006] More specifically, the strength and / or ductility of a weld or a zone affected by welding heat is almost always reduced below that of a parent aluminum alloy substrate. Furthermore, the geometry of the weld joint can lead to stress concentration, which can cause cracking under service conditions and impact loading. Furthermore, welds in aluminum alloys generally exhibit lower strength when subjected to peel loading rather than pure tensile shear.

[0007] Heat-treated 6XXX sheet aluminum alloys, such as those commonly used for automotive body parts, are particularly susceptible to these problems. Fig. 1a and Fig. 1b shows such an aluminum roof panel R connected to a door opening panel D via a weld W. If subjected to a sufficient impact load, e.g., from a vehicle accident, the aluminum roof panel R may buckle adjacent to the weld W, resulting in a load concentration at the weld operating in peel mode. See Fig. 1c. Under extreme conditions, this can lead to weld failure.

[0008] This document relates to (a) a method for increasing the in-service structural performance of a sheet metal component having a discontinuity, including, for example, a metal automotive roof panel, and (b) such a roof panel being heat treated to overcome the potential problem. SUMMARY

[0009] For this purpose, a method having the features of independent claim 1, having the features of independent claim 5, and a roof panel having the features of independent claim 9 are provided. Advantageous embodiments can be found in the dependent claims.

[0010] In accordance with the purpose and benefits described herein, a method for increasing the structural in-service performance of a sheet metal component having a discontinuity is provided. The method comprises heat-treating a zone of the sheet metal component at a predetermined distance from the discontinuity, thereby altering the strength and formability of the heat-treated zone. The method further includes shifting the deformation induced in the sheet metal component by a subsequent deformation event away from the discontinuity to the zone.

[0011] In one possible embodiment, the method further includes reducing the strength and increasing the deformability of the zone. In one possible embodiment, the method includes reducing the strength of the material in the zone by 15% to 25%.

[0012] In yet another possible embodiment, the sheet component is a 6XXX aluminum alloy and the method further includes heating the zone of the sheet component to a temperature between 426°C and 482°C for a time period between 0.05 to 1 second.

[0013] In one possible embodiment, the method further includes controlling the heat input into the zone during heat treatment by using a combination of laser energy, laser beam size and configuration, and laser scan speed. In yet another possible embodiment, where the discontinuity in the sheet metal component is a weld, the method further includes shifting the deformation mode, thereby subjecting the weld to a shear rather than peel load.

[0014] According to an additional aspect, a method for increasing the structural in-service performance of a metal automotive roof panel having a discontinuity is provided. The method can be broadly described as comprising the following steps: heat-treating a zone of the metal automotive roof panel at a predetermined distance from the discontinuity, thereby altering the strength and ductility of the zone, and shifting the deformation induced in the metal automotive roof panel by a subsequent deformation event away from the discontinuity to the zone.

[0015] According to yet another aspect, a roof panel for a motor vehicle is provided. This roof panel comprises a sheet metal component having a discontinuity and a heat-treated zone at a predetermined distance from the discontinuity. The heat-treated zone is characterized by reduced strength and increased formability, thereby shifting the deformation caused in the sheet metal component by a subsequent deformation event away from the discontinuity to the zone. In one possible embodiment, a strength reduction of between 15% and 25% has been achieved in the material comprising the roof panel zone.

[0016] In one possible embodiment, the discontinuity is selected from a group of discontinuities consisting of a weld seam, a zone affected by welding heat, an edge, an edge bend, a mechanical fastening connection and a deep-drawn area that were mechanically deformed during manufacturing.

[0017] In one possible embodiment, the discontinuity is a weld seam between the roof panel and a door opening panel. The weld seam runs along an edge of the sheet metal component. In such an embodiment, the zone runs parallel to the weld seam. More specifically, the zone can be spaced from the weld seam by a distance between 1 cm and 30 cm. Furthermore, the zone can have a width between 2 mm and 100 mm. Furthermore, the zone runs along the full length of the weld seam.

[0018] According to an additional aspect, a method is provided for increasing the in-service structural performance of a metal automotive trailer plate or other body panel having a discontinuity. The method can be broadly described as comprising the steps of: heat treating a zone of the metal automotive body panel at a predetermined distance from the discontinuity, thereby altering the strength and ductility of the zone, and shifting the deformation induced in the metal automotive body panel by a subsequent deformation event away from the discontinuity to the zone. According to an additional aspect, a method is provided for increasing the in-service structural performance of a metal automotive body panel having a discontinuity.The method can be broadly described as comprising the following steps: heat treating a zone of the metal automotive body panel at a predetermined distance from the discontinuity, thereby altering the strength and ductility of the zone, and shifting the deformation caused in the metal automotive body panel by a subsequent deformation event away from the discontinuity to the zone.

[0019] In the following description, various preferred embodiments of the method and the roof panel processed by the method are illustrated and described. It should be understood that the method and the roof panel are capable of other, various embodiments, and the various details may be modified in various, obvious aspects without departing from the method and the roof panel as set forth and described in the following claims. Accordingly, the drawings and descriptions are to be interpreted as illustrative and not restrictive. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0020] The accompanying drawing figures, which are incorporated herein and form part of the specification, illustrate several aspects of the process, the sheet metal component, and the roof panel, and, together with the description, serve to explain certain principles thereof. The drawing figures show: Fig. 1a is a view of an untreated roof panel from the prior art and a cooperating door opening panel to which the roof panel is connected via a weld seam; Fig. Figure 1b is a cross-section along line AA showing the weld or joint between the prior art roof panel and the door opening panel; Fig. Figure 1c is a cross-section illustrating the prior art roof panel, door panel and weld after a deformation event, showing the bulging of the roof panel adjacent to the weld; Fig. 2a is a perspective view of a roof panel illustrating the positioning of a heat treatment zone adjacent to the weld discontinuity that increases the structural in-service performance of the roof panel according to the teachings of this document; Fig. 2b a cross section of Fig. 2a, which shows the heat-treated roof panel and the door opening panel to which the roof panel is connected by means of the weld or joint; Fig. 2c a Fig. 2b Similar view, but depicting the cross-section after a deformation event, showing how the roof panel in the heat-treated zone buckles away from the weld or joint to protect the integrity of the weld.

[0021] Reference will now be made in detail to the presently preferred embodiments of the method and roof panel, examples of which are illustrated in the accompanying drawing figures. DETAILED DESCRIPTION

[0022] Reference is now made to Fig. 2a to 2c, which illustrate a motor vehicle roof panel 10 that has undergone a process to increase structural in-service performance. More specifically, the motor vehicle roof panel 10 includes a sheet metal component 12 having a discontinuity 14 and a heat-treated zone 16.

[0023] In the illustrated embodiment, the discontinuity comprises a weld or joint 14 between the roof panel 10 and a door opening panel 20, which runs along an edge of the sheet metal component 12. As illustrated, the heat-treated zone 16 runs parallel to the weld 14. In one possible embodiment, the heat-treated zone 16 is spaced from the weld 14 by a distance of between 1 cm and 30 cm. Furthermore, the heat-treated zone 16 has a width of between 2 mm and 100 mm. Furthermore, the zone 16 runs along the full length of the weld 14.

[0024] It will be appreciated that the automotive roof panel 10, which is the subject of this document, has undergone a process for increasing the in-service structural performance of a sheet metal component 12, wherein the sheet metal component includes a discontinuity such as weld 14. It will be appreciated that weld 14 is purely exemplary of the discontinuity. Other examples include, but are not limited to, a weld heat-affected zone or area, an edge, an edge bend, a mechanical fastener connection, and a deep-draw area that have been mechanically deformed during manufacturing and have hardened or become more brittle as a result.

[0025] The method includes heat treating zone 16 of sheet metal component 12 at a predetermined distance from discontinuity / weld 14, thereby altering the strength and formability of the zone. As described in more detail below, the method also includes shifting the deformation caused in sheet metal component 12 by a subsequent deformation event away from discontinuity / weld 14 to zone 16.

[0026] In a particularly useful embodiment, the method includes reducing the strength and increasing the formability of zone 16 through heat treatment. In another possible embodiment, the strength of the zone may be increased where appropriate, and the formability may be reduced as needed. In other possible embodiments, multiple zones may be provided to increase the structural in-service performance of sheet metal component 12 in a desired manner.

[0027] In a particularly useful embodiment, the material comprising zone 16 undergoes a strength reduction due to heat treatment of between 15% and 25%. If the sheet component 12 is a 6XXX aluminum alloy, the method may include heating the zone of the sheet component to a temperature between 426°C and 482°C for a sufficient time (e.g., 0.05 to 1 second) to provide a 15% to 25% reduction in the strength of the material in the zone.

[0028] In one possible embodiment, the heat treatment is performed with a laser, and the amount of heat delivered to zone 16 during the heat treatment is controlled by using a combination of laser energy, laser beam size and configuration, and laser travel speed. In another possible embodiment, the heat treatment is performed by induction.

[0029] Reference is now made to Fig. 2b and Fig. 2c, which illustrate some beneficial effects provided by the heat treatment process. As in Fig. As shown in Figure 2b, the heat-treated zone 16 with reduced strength and increased ductility is provided at a predetermined distance from the weld 14. This predetermined distance may, for example, be between 1 cm and 30 cm. Furthermore, the heat-treated zone 16 has a width between 2 mm and 100 mm. Both the distance between the heat-treated zone 16 in the weld 14 and the width of the heat-treated zone 16 are adjusted as needed to provide the desired structural in-service performance based on experimental testing and / or component testing and / or computer numerical modeling. Fig. Figure 2c shows the same cross-section after deformation induced in the sheet metal component 12 by a deformation event such as a motor vehicle accident. As shown, after deformation begins in zone 16, the stresses are distributed within this zone of more deformable material. The more deformable material of zone 16 absorbs more of the impact energy, thus reducing the likelihood of cracking of the remaining roof panel material. In addition, the selectively heated zone 16 serves to relocate the bulge and lift the roof panel away from the weld 14, thereby maintaining the weld integrity. In contrast, during impact loading of the untreated roof panel R made of Fig. 1a to 1c the deformation of the roof panel is concentrated at the weld joint or seam W.

[0030] As a result, the weld seam W of the roof panel R from the state of the art, which is in Fig.1a to 1c, is subjected to peel mode deformation. This contrasts sharply with the roof panel 10, which has undergone the heat treatment process described herein to provide the heat-treated zone 16, which shifts the deformation away from the weld 14 to the zone 16, thus shifting the deformation mode to shear rather than peel. Since a shear mode weld is stronger than a peel mode weld, it will be appreciated that the roof panel 10 serves to increase weld integrity.

[0031] Reference is now made to the following examples to further illustrate the procedure.

[0032] Example 1. In this example, a laser beam is used to selectively heat treat a linear zone in an aluminum 6022-T4 alloy body panel. The laser increases the temperature of the zone between 426 °C and 482 °C. The heat treatment reduces the T4 temper of the 6022 body panel (approximately 100 Vickers hardness) to a fully annealed temper (approximately 80 Vickers hardness), reducing the strength of the material in the heat-treated zone by 20%.

[0033] Example 2. In another embodiment, the laser increases the temperature of the zone between 315°C and 371°C. The heat treatment increases the T4 temper of the 6022 body sheet (about 100 Vickers hardness) to a harder temper (about 120 Vickers hardness), thereby increasing the strength of the material by 20%.

[0034] In both examples, the width of the zone can vary depending on the laser beam size and configuration, as well as the laser travel speed. The strength and hardness of the zone increases or decreases depending on the heat input to that zone. The heat input is controlled by using a combination of laser energy, laser beam size and configuration, and laser travel speed. The process parameters vary depending on the material being treated (e.g., (1) precipitation-hardenable 6XXX aluminum, (2) work-hardenable 5XXX aluminum, (3) steel, etc.), the specific alloy composition (e.g., 6022 vs. 6111 vs. 6082), the proximity of the zone to the edge of the sheet metal component or part being treated (especially for aluminum with a high thermal conductivity), the gauge of the material being treated, and the part size and geometry of the material being treated (e.g., is the part a sheet, a component, or a subassembly).

Claims

[1] A method for increasing the structural in-service performance of a sheet metal component having a discontinuity, comprising: Heat treating a zone of the sheet component at a predetermined distance from the discontinuity, thereby reducing the strength of the zone by 15% to 25% and increasing the formability of the zone; and Shifting the deformation caused in the sheet metal component by a subsequent deformation event away from the discontinuity to the zone. [2] The method of claim 1, wherein the sheet component is a 6XXX aluminum alloy, the method further including heating the zone of the sheet component to a temperature between 426°C and 482°C or between 315°C and 371°C. [3] The method of claim 1, comprising controlling heat input to the zone during heat treatment by using a combination of laser energy, laser beam size and configuration, and laser scan speed. [4] The method of claim 1, wherein the discontinuity is a weld, the method further including shifting the deformation mode whereby the weld can be loaded with a shear rather than a peel load. [5] A method for increasing the structural in-service performance of a metal automotive roof panel having a discontinuity, comprising: Heat treating a zone of the metal automotive roof panel at a predetermined distance from the discontinuity, thereby reducing the strength of the zone by 15% to 25% and increasing the ductility of the zone; and Transferring the deformation caused in the metal automotive roof panel by a subsequent deformation event away from the discontinuity to the zone. [6] The method of claim 5, wherein the metal automotive roof panel is a 6XXX aluminum alloy, the method further including heating the zone of the metal automotive roof panel to a temperature between 426°C and 482°C or between 315°C and 371°C. [7] The method of claim 5, comprising controlling heat input to the zone during heat treatment by using a combination of laser energy, laser beam size and configuration, and laser scan speed. [8] The method of claim 5, wherein the discontinuity is a weld, the method further including shifting the deformation mode whereby the weld can be loaded with a shear rather than a peel load. [9] Roof panel for a motor vehicle, comprising: a sheet metal component having a discontinuity and a heat-treated zone at a predetermined distance from the discontinuity, wherein the heat-treated zone has a strength and a formability that differs from a remaining untreated portion of the sheet metal component, wherein the deformation caused in the sheet metal component by a subsequent deformation event is shifted away from the discontinuity to the zone, wherein the discontinuity is a weld, and where the zone runs along a full length of the weld. [10] A roof panel according to claim 9, wherein the zone has between 15% and 25% less strength than the remaining untreated portion of the sheet component. [11] Roof panel according to claim 10, wherein the zone has a width between 2 mm and 100 mm. [12] Roof panel according to claim 9, wherein the discontinuity is a weld seam that has been mechanically deformed during manufacture. [13] A roof panel according to claim 9, wherein the discontinuity is a weld between the roof panel and a door opening panel running along an edge of the sheet metal component. [14] Roof panel according to claim 13, wherein the zone is parallel to the weld seam. [15] Roof panel according to claim 14, wherein the zone is spaced from the weld seam by a distance of between 1 cm and 30 cm.

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