Weld joint structure between tubular part of extrusion material and tubular part of casting material

Abstract

To provide a new weld joint for joining a tubular part of a casting material having such high rigidity as not to be easily deformed even when impact is applied thereto, and a tubular part of an extrusion material having such high toughness as to be easily compressed and deformed and absorb impact energy so that impact applied thereto is prevented from being transmitted to the casting material, which improves fatigue strength to a tensile load or a bending load as compared to a lap joint, and can make absorption ability of the impact energy when a compression load acts thereon larger than that of a joggled joint.SOLUTION: There is provided a weld joint structure for joining a tubular part of a casting material 10 and a tubular part of an extrusion material 20, wherein the diameter of an end 12 of the tubular part of the casting material is formed so as to be thinner than a body part continued to the end, and a bonded part between a plate thickness center 21 of the tubular part of the extrusion material opposite to the end of the tubular part of the casting material and a weld part 30 is positioned radially inside of a plate thickness center 11 of the body part of the tubular part of the casting material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a welded joint structure of a metal tubular member, and more specifically to a welded joint structure between a tubular portion of an extruded material and a tubular portion of a cast material, which has been improved to have higher fatigue strength against tension and bending and to have greater impact absorption energy during compression. [Background technology]

[0002] For welding metal members together, various joint structures such as lap joints and lap joints are selected depending on the application. For example, Patent Document 1 proposes a fillet weld joint for steel plates in which the upper and lower plates each have a flat portion and an inclined portion, and the end of the upper plate faces the upper surface of the inclined portion of the lower plate, the angle between the inclined portions of the upper plate and the lower plate is 90° or more, so as to reduce stress concentration at the toe and make it difficult for fatigue cracks to initiate at the root. Furthermore, the center of the throat thickness of the weld formed between the end of the upper plate and the upper surface of the inclined portion of the lower plate is located below both the central axis of the thickness of the flat portion of the upper plate and the central axis of the thickness of the flat portion of the lower plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2019-155391 Summary of the Invention [Problem to be solved by the invention]

[0004]

[0003] When a space frame is used in the chassis of a vehicle such as an automobile, the region of the space frame that defines the passenger compartment is formed of a highly rigid cast material so as not to easily deform even when an impact is applied from the front of the vehicle, and the portion in front of the region formed of the cast material is formed of a highly tough extruded material so as to easily compress and deform to absorb impact energy when an impact is applied from the front of the vehicle and to make it difficult for the impact to be transmitted to the passenger compartment, and the tubular portions of the extruded material and the cast material are joined by welding. Since tensile loads and bending loads are constantly applied to the welded joint structure between the tubular portions of the extruded material and the cast material in such a vehicle space frame, it is desirable for the welded joint structure to have high fatigue strength against tensile loads and bending loads, but it is also desirable for the extruded material to be able to deform so as to maximize the energy absorption when a compressive load due to an impact from the front of the vehicle is applied to the welded joint structure. In the case of a commonly used welded joint, a "seamless joint" (Figure 3), the welded joint is located on the extension of the thickness center of the extrusion, which reduces stress concentration under tensile or bending loads, resulting in high fatigue strength. However, because the thickness center of the extrusion is located radially outward of the thickness center of the cast material, the tubular portion of the extrusion bends in the direction of expanding its diameter under compressive loads, resulting in low absorbed energy. In contrast, in the case of a lap joint (Figure 4), another commonly used welded joint, the thickness center of the extrusion is located radially inward of the thickness center of the cast material, which reduces its diameter under compressive loads, resulting in high absorbed energy. However, because the root of the weld is located radially outward of the thickness center of the extrusion, stress concentration is likely to occur at the root under tensile or bending loads, resulting in low fatigue strength and a tendency for fracture.Therefore, if there is a welded joint structure that can increase the impact energy absorption capacity when a compressive load is applied (without increasing the thickness of the member) compared to a butt joint, and can increase the fatigue strength against a tensile load or bending load compared to a lap joint (without increasing the thickness of the member), it can be advantageously used as a welded joint structure when welding a tubular portion of an extruded material in front of a tubular portion of a cast material forward of the passenger compartment in a space frame of a vehicle chassis.

[0005] Thus, the main object of the present invention is to provide a new welded joint that joins a tubular portion of a cast material that is highly rigid so that it does not easily deform even when subjected to an impact, and a tubular portion of an extruded material that is highly tough so that it can easily compress and deform to absorb impact energy and prevent the impact from being transmitted to the cast material, and which has improved fatigue strength against tensile loads or bending loads compared to a lap joint and has a greater ability to absorb impact energy when a compressive load is applied compared to a butt joint. [Means for solving the problem]

[0006] According to the present invention, the above-mentioned object is achieved by a welded joint structure that joins a tubular portion of a cast material and a tubular portion of an extruded material, wherein the diameter of the end of the tubular portion of the cast material is formed to be smaller than that of the main body portion that is continuous with the end, and the center of plate thickness of the tubular portion of the extruded material that faces the end of the tubular portion of the cast material and the adhesive site of the weld are located radially inward of the center of plate thickness of the main body portion of the tubular portion of the cast material.

[0007] In the above configuration, the cast material and the extruded material may be formed from a metal material, such as aluminum, selected appropriately depending on the application. The welded portion may be formed by a welding method (such as arc welding) commonly used in this field. The bonding portion of the welded portion is the portion where the welded portion is bonded to the extruded material and the cast material, respectively.

[0008] According to the above-described configuration of the present invention, the adhesive portion of the weld is located radially inward of the center of thickness of the tubular portion of the extruded material and the center of thickness of the main body portion of the tubular portion of the cast material. Therefore, even if a tensile load or bending load acts in a direction in which the extruded material moves away from the cast material, stress is less likely to concentrate at the root of the weld. As a result, the weld is less likely to break and its fatigue strength against tensile loads or bending loads is improved compared to a lap joint. On the other hand, when a compressive load is applied in a direction pressing the extruded material against the cast material, as described above, the center of thickness of the tubular portion of the extruded material is located radially inward of the center of thickness of the main body of the tubular portion of the cast material, so the tubular portion of the extruded material bends and deforms in a direction reducing its diameter, and the energy absorbed by this deformation is greater than when the diameter is increased.As a result, the ability to absorb impact energy when a compressive load is applied is greater than that of a normal butt joint (in which the center of thickness of the tubular portion of the extruded material is located outside the center of thickness of the tubular portion of the cast material).

[0009] In the above configuration, if necessary, the center of thickness of the tubular portion of the cast material is offset radially outward from the center of thickness of the tubular portion of the extruded material. This offset may extend around the entire circumference of the tubular portion of the extruded material, or, if the cross-sectional shape of the tubular portion of the extruded material is generally polygonal (usually generally rectangular), it may be only the flat portion excluding the corners and their vicinity. In the regions near the corners of the tubular portion, the outer surface of the tubular portion of the cast material may be formed to approximately coincide with the outer surface of the tubular portion of the extruded material. This has the advantages of facilitating welding of the regions near the corners and making it easier for the cast material to support the load from the extruded material, since the extruded material is less likely to absorb impact energy due to deformation in the regions near the corners.

[0010] In the above configuration, in the region (offset region) where the thickness center of the main body part of the tubular portion of the cast material is shifted radially outward from the thickness center of the tubular portion of the extruded material, if the outer surface of the extruded material is located radially inward from the thickness center of the tubular portion of the cast material, the radial inward deformation of the extruded material when a compressive load is applied will be more reliable, so it is preferable that the offset distance of the thickness center of the main body part of the tubular portion of the cast material from the thickness center of the tubular portion of the extruded material is greater than 1 / 2 the thickness of the extruded material. [Effects of the Invention]

[0011] Thus, according to the present invention, in a welded joint structure joining a tubular portion of a cast material and a tubular portion of an extruded material, fatigue strength against tensile loads or bending loads is improved, and it is possible to increase the ability to absorb impact energy when a compressive load is applied. As already mentioned, the configuration of the present invention may be advantageously used in the front portion of the passenger compartment of a vehicle space frame, but it may also be used for other purposes. The structure of the present invention is formed so as to be able to compensate for the weak points of the lap joint and the butt joint, and is also advantageous in that it can achieve the above benefits without increasing the plate thickness of the tubular members being joined, compared to the case of a lap joint and a butt joint.

[0012] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0013] [Figure 1]Fig. 1(A) is a schematic cross-sectional view of one embodiment of a welded joint structure between a tubular portion of a cast material and a tubular portion of an extruded material according to this embodiment, viewed from a direction perpendicular to the axial direction of the tubular portion. Figs. 1(B) and 1(C) are schematic end views of the tubular portion of a cast material and the tubular portion of an extruded material according to this embodiment. Fig. 1(D) is a schematic cross-sectional view of the tubular portion near a corner of the welded joint structure between a tubular portion of a cast material and a tubular portion of an extruded material according to this embodiment, viewed from a direction perpendicular to the axial direction (the cross-section taken along (D)-(D) in Figs. 1(B) and 1(C)). Fig. 1(E) is a schematic diagram showing the behavior of stress when a tensile load acts on the welded joint structure between a tubular portion of a cast material and a tubular portion of an extruded material according to this embodiment. FIG. 1(F) is a diagram showing the deformation direction of the tubular portion of the extruded material when a compressive load acts on the welded joint structure between the tubular portion of the cast material and the tubular portion of the extruded material according to this embodiment. [Figure 2] 2(A) and (B) are schematic cross-sectional views of another embodiment of the welded joint structure (butt joint) between the tubular portion of the cast material and the tubular portion of the extruded material according to this embodiment, viewed from a direction perpendicular to the axial direction of the tubular portion. (A) shows a flat portion of the tubular portion, and (B) shows a corner portion of the tubular portion. [Figure 3] Figure 3(A) is a schematic cross-sectional view of a welded joint structure when a tubular portion of a cast material and a tubular portion of an extruded material are welded using a common "seam joint," viewed from a direction perpendicular to the axial direction of the tubular portion. Figures 3(B) and 3(C) are schematic end views of the tubular portion of the cast material and the tubular portion of the extruded material in the welded joint structure of Figure 3(A). Figure 3(D) is a schematic diagram showing how stress acts when a tensile load acts on the seam joint structure. Figure 3(E) is a diagram showing the deformation direction of the tubular portion of the extruded material when a compressive load acts on the seam joint structure. [Figure 4]Figure 4(A) is a schematic cross-sectional view of a welded joint structure when a tubular portion of a cast material and a tubular portion of an extruded material are welded using a typical "lap joint," viewed from a direction perpendicular to the axial direction of the tubular portion. Figures 4(B) and 4(C) are schematic end views of the tubular portion of the cast material and the tubular portion of the extruded material in the welded joint structure of Figure 4(A). Figure 4(D) is a schematic diagram showing how stress acts when a tensile load is applied to the lap joint structure. Figure 4(E) is a diagram showing the deformation direction of the tubular portion of the extruded material when a compressive load is applied to the lap joint structure. [Explanation of symbols]

[0014] 10...Tubular portion of cast material, 11...Plate thickness center of tubular portion of cast material, 12...End of tubular portion of cast material, 20...Tubular portion of extruded material, 21...Plate thickness center of tubular portion of extruded material, 30...Weld, F...Load, C...Center axis of tubular portion BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0016] General welded joint structure When joining a tubular portion of an extruded metal material to a tubular portion of a cast metal material in a vehicle space frame or the like so that their axial directions coincide, fillet welding is used to weld the fillets of the ends of the tubular portions together using an arc welding method.

[0017] More specifically, in the case of a fillet welded joint, which is one of the common welded joint structures, as shown schematically in Figures 3(A) to 3(C), the outer surfaces of the end of the cast material 10 and the end of the extruded material 20 are positioned so that they are substantially aligned, and they are joined by a weld 30. In this case, the bonding position of the weld 30 on the cast material 10 side and the extruded material 20 side is on an extension of the thickness center 21 on the extruded material 20 side, so that when a tensile load F is applied by tension or bending, as shown in Figure 3(D), the stress t acting on the weld 30 is on an extension of the thickness center of the extruded material 20 on both the cast material 10 side and the extruded material 20 side, which makes it difficult for local stress concentration to occur and enables a relatively high fatigue strength against tensile loads. However, in the case of a butt joint, as shown in Figure 3(E), the center of thickness 21 on the extruded material 20 side is usually located radially outward from the center of thickness 11 on the cast material 10 side. Therefore, when a compressive load F acts from the extruded material 20 side, such as when the vehicle space frame is hit from the front, the tubular portion of the extruded material 20 will bend radially outward as shown by arrow b in the figure. As a result, when viewed in cross section, the tubular portion of the extruded material 20 will deform in the direction in which the angle R of the corner region (Figure 3(C)) widens, and the ability to absorb impact energy will not be very great.

[0018] On the other hand, in the case of a lap joint, which is another common welded joint structure using fillet welding, as shown in Figures 4(A) to (C), if the tubular portions of both extruded material 20 and cast material 10 are overlapped and welded so that the center of thickness 21 of the extruded material 20 is located radially inward of the center of thickness 11 of the cast material 10, as shown in Figure 4(E), when a compressive load F is applied from the extruded material 20 side, the tubular portion of the extruded material 20 will bend radially inward as shown by arrow b in the figure.As a result, the angle R of the corner region (Figure 4(C)) when viewed in cross section of the tubular portion of the extruded material 20 will deform in a direction narrowing, making it possible to increase the impact energy absorption capacity compared to a cut-off joint. However, in this case, the weld 30 is located radially outward of the center of thickness 21 on the extruded material 20 side, between the outer surface of the extruded material 20 and the end face of the cast material 10. Therefore, when a tensile load F is applied by pulling or bending, stress t acts in a different direction at the root r of the weld 30, causing stress concentration and making it more likely to break from the root R. As a result, the fatigue strength against tensile loads is lower than in the case of a butt joint.

[0019] Thus, if there were a welded joint structure that had high fatigue strength against tensile loads, similar to that of a lap joint, and that had a high impact energy absorption capacity when a compressive load F was applied, similar to that of a lap joint, this would be advantageous in the space frame of a vehicle body, etc.

[0020] Welded joint structure according to this embodiment (improved welded joint) In view of the above circumstances, the inventors of this embodiment have developed a new welded joint structure, as shown schematically in Figures 1(A) to 1(C), which has high fatigue strength against tensile loads, similar to that of a welded joint, and which can increase the ability to absorb impact energy when a compressive load F is applied, similar to that of a lap joint.

[0021] 1(A) to 1(C), in the "improved butt joint" which is the welded joint structure of this embodiment, the tubular portion on the cast material 10 side has a main body portion (on the left side in the figure) that is enlarged in diameter relative to the tip 12, and the thickness center 21 on the extruded material 20 side is positioned radially inward of the thickness center 11 of the tubular portion on the cast material 10 side, with the weld 30 positioned on an extension of the thickness center 21 on the extruded material 20 side, just like in the case of a butt joint. With this configuration, as shown in FIG. 1(E), in response to a tensile load F, the stress t at the weld 30 is on an extension of the thickness center of the extruded material 20 on both the cast material 10 side and the extruded material 20 side, just like in the case of a butt joint, so that local stress concentration is unlikely to occur and high fatigue strength against tensile loads is obtained. On the other hand, as shown in Figure 1(F), when a compressive load F is applied, the thickness center 21 of the extruded material 20 is located radially inward of the thickness center 11 of the cast material 10, so the tubular portion of the extruded material 20 bends radially inward as shown by arrow b in the figure, and the angle R of the corner region (Figure 1(C)) when viewed in cross section of the tubular portion of the extruded material 20 is deformed in a direction narrowing. Thus, as with a lap joint, a high impact energy absorption capacity is obtained.

[0022] In the structure of the improved joint, it is preferable that the offset width x of the thickness center 11 on the cast material 10 side from the thickness center 21 on the extruded material 20 side radially outward is greater than half the thickness Δ on the extruded material 20 side. This positions the outer surface of the extruded material 20 radially inward from the thickness center of the cast material 10, making it possible to more reliably ensure that the extruded material 20 bends radially inward when a compressive load is applied.

[0023] The improved weld joint structure described above is applied to the flat areas between corners in the tubular portion of the cast material 10. A structure similar to a conventional weld joint, as shown in Figure 1(D), may be employed near the corners of the tubular portion. Generally, when performing arc welding, significant differences in the heights of the components being welded (i.e., the distance to the tip of the welding rod) can easily cause uneven weld beads. In particular, the orientation of the tip of the welding rod relative to the tubular component changes at the corners of the tubular component, making welding somewhat more difficult. Therefore, employing a conventional weld joint structure, in which the outer surfaces of the components are approximately aligned, near the corners of the tubular portion simplifies the welding process and ensures the integrity of the weld. Furthermore, because the extrusion material is less likely to bend at the corners of the tubular portion, employing a conventional weld joint structure at the corners also has the advantage of allowing the cast material to withstand frontal impacts.

[0024] As another aspect of the welded joint structure of the present embodiment, as shown in Fig. 2(A), a configuration may be used in which, in a butt joint, the tubular portion on the cast material 10 side has a main body portion (on the left side in the figure) expanded in diameter relative to the tip 12, and the weld 30 is positioned on an extension of the thickness center 21 on the extruded material 20 side, with the thickness center 21 on the extruded material 20 side positioned radially inward from the thickness center 11 of the tubular portion on the cast material 10 side. In this case, too, a normal butt joint may be used at the corner of the tubular portion, as shown in Fig. 2(B).

[0025] Thus, according to this embodiment, the diameter of the end of the tubular portion of the cast material is made smaller than that of the main body portion continuing from that end, and a welded joint structure is formed so that the center of the thickness of the tubular portion of the extruded material facing the end of the tubular portion of the cast material and the bonding site of the weld are located radially inward of the center of the thickness of the main body portion of the tubular portion of the cast material, thereby improving fatigue strength against tensile loads or bending loads and making it possible to increase the ability to absorb impact energy when a compressive load is applied. As already mentioned, the configuration of this embodiment may be advantageously used in the front portion of the passenger compartment of a vehicle space frame, but may also be used for other purposes.

[0026] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A welded joint structure joining a tubular portion of a cast material and a tubular portion of an extruded material, wherein the diameter of the end of the tubular portion of the cast material is formed to be smaller than that of a main body portion continuing from the end, and the center of thickness of the tubular portion of the extruded material facing the end of the tubular portion of the cast material and the adhesive site of the weld are located radially inward of the center of thickness of the main body portion of the tubular portion of the cast material.

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