Welded joints and their manufacturing methods

Abstract

This invention belongs to the field of machining technology, specifically relating to a welded joint and its manufacturing method, aimed at solving the technical problem of low fatigue strength in welded joints. The welded joint includes at least two sequentially stacked plates, a weld nugget fixing the two adjacent plates together, and a nail-like member. The nail-like member is pressed into at least a portion of the plates and each weld nugget along the stacking direction of the at least two plates, forming receiving holes in the corresponding plates and weld nuggets that are adapted to the nail-like member. The edge region of the weld nugget, at least away from the nail-like member, has compressive residual stress. By suppressing the initiation and growth of cracks through compressive residual stress, fatigue strength is improved, and fatigue fracture of the welded joint is reduced.

Description

Technical Field

[0001] The present invention relates to the field of machining technology, and in particular to a welded joint and its manufacturing method. Background Technology

[0002] In recent years, the automotive industry has adopted thin-walled high-tensile steel sheets in body and other components to improve fuel efficiency and safety. These sheets are then spot-welded at overlapping joints to form welded joints. Spot welding involves clamping multiple overlapping high-tensile steel sheets with electrodes, applying pressure, and simultaneously applying a high current to the electrodes for a short time to create a weld nugget, thus fixing the sheets together. This process requires no filler material, resulting in high production efficiency and ease of automation. However, welded joints typically have lower fatigue strength. Summary of the Invention

[0003] In view of the above problems, embodiments of the present invention provide a welded joint and a method for manufacturing the same, so as to improve the fatigue strength of the welded joint.

[0004] A first aspect of the present invention provides a welded joint comprising at least two plates stacked sequentially, a weld nugget for fixing two adjacent plates, and a nail-shaped member, wherein the nail-shaped member is pressed into at least a portion of the plates and each of the weld nuggets along the stacking direction of the at least two plates, such that a receiving hole adapted to the nail-shaped member is formed in the corresponding plates and the weld nuggets, and the edge region of the weld nugget at least away from the nail-shaped member has compressive residual stress.

[0005] In some possible embodiments, the direction of the compressive residual stress is perpendicular to the stacking direction of at least two plates.

[0006] In some possible embodiments, the compressive residual stress is distributed radially relative to the axis of the nail.

[0007] In some possible embodiments, the hardness of the nail-like element is greater than the hardness of the plate and greater than the hardness of the molten core, and the axis of the nail-like element coincides with the center of the molten core.

[0008] In some possible embodiments, the receiving hole is formed on the first surface of the at least two plates, and a protrusion is formed on the second surface, the protrusion being disposed opposite to the receiving hole, and the first surface and the second surface being disposed opposite to each other along the stacking direction of the at least two plates.

[0009] In some possible embodiments, the nail-like member is self-piercing riveted to the corresponding plate and the fusion core, the nail-like member comprising a self-piercing rivet.

[0010] In some possible embodiments, the self-piercing rivet includes a rivet foot and a rivet head connected to one end of the rivet foot, the rivet head being located within a plate and exposed away from the end face of the rivet foot, the rivet foot penetrating the fusion core and the plate located between the rivet head and the fusion core, and pressing the edge region of the fusion core.

[0011] In some possible embodiments, the at least two plates include a first plate and a second plate, the nail-like element is located within the first plate and penetrates the first plate and the fusion nugget, and extends into the second plate, the edge region of the fusion nugget away from the nail-like element having the compressive residual stress.

[0012] The welded joints of the present invention have at least the following advantages:

[0013] The welded joint of this invention includes a nail-like element pressed into at least two plates, and the nail-like element penetrates at least a portion of the plates and each weld nugget, so that the edge region of the weld nugget at least away from the nail-like element has compressive residual stress, thereby inhibiting the generation and growth of cracks, improving fatigue strength, and reducing fatigue fracture of the welded joint.

[0014] A second aspect of this invention provides a method for manufacturing a welded joint, comprising:

[0015] Stack at least two plates in sequence to form a part to be welded;

[0016] The workpiece to be welded is welded to form a welded part, and a weld nugget is formed inside the welded part. The weld nugget is fixedly connected to two adjacent plates. Along the stacking direction of the at least two plates, the workpiece to be welded has a first surface and a second surface that are disposed opposite to each other.

[0017] A nail-shaped member is driven into the first surface to form a weld joint. The nail-shaped member penetrates the weld nugget and the plate located on the side of the weld nugget closer to the first surface to form a receiving hole. The edge region of the weld nugget at least away from the nail-shaped member has compressive residual stress.

[0018] In some possible examples, driving the nail into the first surface includes:

[0019] The nail-shaped component is installed inside the punch tool, and the welded component is placed between the punch tool and the die tool, with the punch tool in contact with the first surface;

[0020] The punch tool drives the nail-shaped part into the welded part, the nail-shaped part and the welded part undergo plastic deformation, and the second surface fits into the die tool to form a protrusion adapted to the die tool.

[0021] The method for manufacturing the welded joint according to embodiments of the present invention has at least the following advantages:

[0022] In the manufacturing method of this invention, at least two plates are stacked in sequence and then welded to form a weld nugget between two adjacent plates. A nail-shaped piece penetrates the weld nugget and the corresponding plate, so that the edge area of ​​the weld nugget at least away from the nail-shaped piece has compressive residual stress, thereby inhibiting the generation and growth of cracks, improving fatigue strength, and reducing fatigue fracture of the weld joint.

[0023] In addition to the technical problems solved by the embodiments of the present invention, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions as described above, other technical problems that can be solved by the welding joints and manufacturing methods of the present invention, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific embodiments. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the tensile residual stress of the weld nugget in a welded joint in a related technology;

[0026] Figure 2 This is a schematic diagram of fatigue cracks in related technologies;

[0027] Figure 3 This is a schematic diagram of the structure of the welded joint in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram showing the position of the nail-shaped member before it is pressed into the plate in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram showing the position of the nail-shaped member after it has been pressed into the plate in an embodiment of the present invention;

[0030] Figure 6 This is a top view of the plate and melt core used for testing in an embodiment of the present invention;

[0031] Figure 7 This is a side view of the plate and melt core used for testing in an embodiment of the present invention;

[0032] Figure 8 This is a schematic diagram of the fatigue test results in an embodiment of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1-Panel;

[0035] 2-Melting nucleus;

[0036] 3- Nail-shaped component;

[0037] 4-Punch tool;

[0038] 5-Die tool;

[0039] 6-First surface;

[0040] 7-Second surface;

[0041] 8-Protrusion. Detailed Implementation

[0042] The related technologies often result in welded joints with low fatigue strength. The inventors' research revealed the reason for this: (See [reference]). Figure 1 and Figure 2 During welding, the molten metal expands in volume due to the martensitic phase transformation, but contracts thermally during the subsequent solidification and cooling process. Due to the contraction of the weld nugget 2, pores form in the edge region of the weld nugget 2 and in the nearby plate 1. Figure 1 The equilibrium stress state shown indicates that the edge region of the final melt nugget 2 is under tensile residual stress. Figure 2 As shown, the edge region of the melt nugget 2 is in the same direction as the tensile stress ( Figure 2 A crack initiation occurs in the X direction (as shown), and fatigue cracks develop near the melt, with the fatigue cracks extending towards the plate thickness direction. Figure 2 As shown in the Y direction, fatigue cracks grow, and fatigue fracture occurs when the fatigue cracks reach the surface of plate 1. The tensile residual stress is affected by the shape of the edge region of the weld nugget 2, and even if the strength of plate 1 is increased, the fatigue strength of the weld joint will not increase accordingly.

[0043] Therefore, embodiments of the present invention provide a welded joint and a method for manufacturing the same, by pressing nail-shaped elements into at least two plates, with the nail-shaped elements penetrating at least a portion of the plates and each weld nugget, so that the edge region of the weld nugget at least away from the nail-shaped elements has compressive residual stress, thereby suppressing the generation and growth of cracks, improving fatigue strength, and reducing fatigue fracture of the welded joint.

[0044] To make the above-mentioned objectives, features, and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] See Figure 3 This invention provides a welded joint comprising at least two plates 1 stacked sequentially, a weld nugget 2 for fixing the two adjacent plates 1 together, and a nail-like component 3. The number of plates 1 can be two or more, and these plates 1 are stacked sequentially with overlapping areas to facilitate clamping with electrodes and forming the weld nugget 2. The stacking direction of these plates 1 is the plate thickness direction, and the stacking order of these plates 1 is related to their connection relationship, requiring the plates 1 to be fixedly connected to contact each other.

[0046] Plate 1 can be a steel plate or an aluminum alloy plate, etc., and its thickness is relatively thin. When plate 1 is a steel plate, it can be a mild steel plate, a high-tensile steel plate, an ultra-high-tensile steel plate, etc., and its thickness is usually less than or equal to 4mm. When plate 1 is an aluminum alloy plate, its material can be 5000 series aluminum alloy, 6000 series aluminum alloy, etc., and its thickness is usually less than or equal to 3mm.

[0047] Two adjacent plates 1 are fixedly connected by a fusion nugget 2, which is formed by heating the plates 1. When there are more than two plates 1, the fusion nugget 2 is located at the center of the overall thickness of the multiple plates 1 and fixes the plates 1 together. The thickness direction of the fusion nugget 2 is the stacking direction of at least two plates 1, i.e., the depth direction of the melting penetration. The radial direction of the fusion nugget 2 is orthogonal to the thickness direction of the fusion nugget 2, so that the center of the fusion nugget 2 extends radially. The diameter of the fusion nugget 2 is the maximum radial length of the fusion nugget 2.

[0048] Continue reading Figure 3 The nail-shaped member 3 is pressed into at least a portion of the plate 1 and each of the melt nuggets 2 along the stacking direction (i.e., the thickness direction) of the plate 1, so that receiving holes are formed in the corresponding plate 1 and melt nuggets 2. The receiving holes are adapted to accommodate the nail-shaped member 3. The interior of the melt nuggets 2 and the plate 1 has a new structure, and the edge region of the melt nuggets 2 is in a state of compressive residual stress.

[0049] Wherein, along the stacking direction of at least two plates 1, one end of the stacked plate 1 is the press-in end (e.g. Figure 3As shown at the upper end), the nail-shaped member 3 is pressed into the plate 1 and the molten core 2 from the press-in end. The nail-shaped member 3 penetrates each molten core 2 and the corresponding plate 1. For example, the nail-shaped member 3 penetrates each plate 1 located on the side of the molten core 2 near the press-in end to achieve penetration of the molten core 2.

[0050] Due to the compression of the nail-shaped component 3, plastic deformation occurs inside both the weld nugget 2 and the plate 1. At least the edge region of the weld nugget 2 furthest from the nail-shaped component 3 exhibits compressive residual stress. Compared to tensile residual stress, compressive residual stress can suppress crack initiation and growth, thereby improving not only the static and dynamic strength of the welded joint (e.g., impact strength) but also fatigue strength and reducing fatigue fracture. Simultaneously, the nail-shaped component 3 also undergoes plastic deformation, forming a mechanical interlocking structure with the plate 1 and the weld nugget 2, ensuring the strength of the connection.

[0051] The hardness of the nail-shaped component 3 is greater than that of the plate 1 and also greater than that of the molten core 2, to enable the nail-shaped component 3 to be pressed in and to form the receiving hole. The nail-shaped component 3 is located in the central region of the molten core 2, for example, in the exact center of the molten core 2, meaning that the axis of the nail-shaped component 3 coincides with the center of the molten core 2, so that the stress on the edge region of the molten core 2 is more uniform. The compressive residual stress is distributed radially relative to the axis of the nail-shaped component 3, so that the compressive residual stress in the edge region is distributed around the axis of the nail-shaped component 3, and the edge region has compressive residual stress, and the distribution of compressive residual stress in the edge region is more uniform.

[0052] See Figure 3 The direction of the compressive residual stress is perpendicular to the stacking direction of at least two plates 1, that is, the direction of the compressive residual stress is consistent with the rolling direction of plate 1. Since cracks typically propagate in the rolling direction (…), Figure 2 The plate is stretched and opened in the X direction (as shown), towards the thickness direction ( Figure 2 The crack grows and develops in the Y direction. By aligning the direction of the compressive residual stress with the radial direction of the melt nugget 2 (i.e., with the rolling direction of the plate 1), the tensile residual stress in the rolling direction disappears, and the compressive residual stress is maintained in the direction perpendicular to the crack growth. This helps to keep the crack opening closed and can more effectively suppress the crack.

[0053] In some examples, the nail-like component 3 is self-piercing riveted (SPR) to the corresponding plate 1 and ferrule 2. The nail-like component 3 includes a self-piercing rivet. That is, power is provided by a hydraulic cylinder or servo motor to directly press the self-piercing rivet into the plate 1 and ferrule 2. The plate 1, ferrule 2 and self-piercing rivet all undergo reflective plastic deformation under pressure, thereby forming a stable connection.

[0054] Self-piercing rivets can be cylindrical rivets. Specifically, a self-piercing rivet includes a rivet foot and a rivet head connected to one end of the rivet foot. The rivet head is located within a plate 1 and its end face away from the rivet foot is exposed. The rivet foot penetrates the weld nugget 2 and the plate 1 located between the rivet head and the weld nugget 2, and presses against the edge area of ​​the weld nugget 2. The rivet head can be cylindrical, and the rivet foot is turned outwards in all directions to securely connect the plate 1. When there are multiple rivet feet, the distance between adjacent rivet feet increases in the direction away from the rivet head.

[0055] Continue reading Figure 3 At least two plates 1 form a stack, and a nail-like member 3 is pressed into the first surface 6 (e.g., the upper surface) of the at least two plates 1 (i.e., the stack), where the first surface 6 forms a receiving hole. A protrusion 8 is formed on a second surface 7 (e.g., the lower surface) of the at least two plates 1 (i.e., the stack) opposite to the first surface 6. The protrusion 8 is opposite to the receiving hole, and the first surface 6 and the second surface 7 are opposite each other along the stacking direction of the at least two plates 1.

[0056] In the laminate formed by at least two plates 1, the two surfaces of the two plates 1 on both sides that are opposite to each other are the first surface 6 and the second surface 7, respectively. The nail-shaped member 3 is located in the laminate formed by at least two plates 1, with one end exposed and the other end not exposed.

[0057] In some possible examples, each plate 1 and the molten core 2 has a protrusion facing the second surface 7, and the protrusion of the plate 1 located at the bottom of the receiving hole forms a protrusion 8. During the pressing of the nail-shaped member 3, pressure is applied to each plate 1 and the molten core 2 in the same direction as the pressing (e.g., vertically downward), and each plate 1 and the molten core 2 deforms accordingly under the pressure, forming a protrusion in the same direction as the pressing. The protrusion of the outermost plate 1 away from the opening direction of the receiving hole is the protrusion 8 of the laminate formed by at least two plates 1.

[0058] In the example of self-piercing riveting of nail 3 to plate 1 and fusion nugget 2, see [reference needed]. Figure 4 and Figure 5 The self-piercing rivet is disposed inside the punch tool 4. At least two plates 1 are disposed between the punch tool 4 and the die tool 5. Among the at least two plates 1, the plate 1 closer to the punch tool 4 is the top plate, and the plate 1 closer to the die tool 5 is the bottom plate. The self-piercing rivet pierces through the top plate and each melt nugget 2 through the punch tool 4 and enters into the bottom plate. The rivet foot expands to a certain diameter in the bottom plate, and the material of the bottom plate flows into the die tool 5 to form a protrusion that matches the die tool 5.

[0059] In some possible examples, at least two plates 1 include a first plate and a second plate, with the first plate disposed on top of the second plate. There are two plates 1, and a weld nugget 2 is fixedly connected to the first and second plates. A nail-like element 3 is located within the first plate, penetrating both the first plate 1 and the weld nugget 2, and extending into the second plate. The edge region of the weld nugget 2 away from the nail-like element 3 has compressive residual stress. The compressive residual stress is perpendicular to the stacking direction of the first and second plates to give the welded joint high fatigue strength.

[0060] To study the fatigue strength of the welded joints in the embodiments of the present invention, taking two plates 1 as examples, tensile and shear fatigue strength tests were conducted on welded joint A (welded only), welded joint B (compression processed after welding), and welded joint C (self-piercing riveting welded after welding) in the embodiments of the present invention.

[0061] For details, please refer to Figure 6 and Figure 7 The two stacked plates 1 are both 780MPa grade cold-rolled steel plates (DP780) with dimensions of 1.8mm x 38mm x 125mm. Here, 125mm is the length L1 of plate 1, 1.8mm is the thickness t of plate 1, 38mm is the width L3 of plate 1, and is also the length L2 of the overlapping area of ​​the two plates 1. Accordingly, the total length L4 of the two stacked plates 1 is 212mm.

[0062] The diameter of weld nugget 2 is φ7.5mm. The specific welding conditions are as follows: a conical-R type electrode with a diameter of 20mm and a front end diameter of φ8mm (R40) is used; the electrode pressure is 4.4kN; the welding current is 7.7kA; and the energizing time is 490ms. After welding the two plates 1 under the above conditions, a welded joint A is obtained.

[0063] The welded joint A, which was obtained by welding only, was subjected to compression processing using a universal testing machine and a boron steel cylindrical punch (φ10mm). Specifically, the center axis of the punch was aligned with the center of the weld nugget 2, and pressure was applied from the plate surface in the thickness direction of the plate, with a maximum load of 100kN and a holding time of 10 seconds, to obtain the welded joint B after compression processing.

[0064] The welded joint A, which was obtained by welding only, was self-piercing riveted using hard rivets (φ5×L6mm, 540HV). The central axis of the hard rivet was aligned with the center of the weld nugget 2, and it was driven into the plate from the plate surface in the thickness direction. The maximum load during driving was 82kN, resulting in the welded joint C that was self-piercing riveted after welding.

[0065] Fatigue tests were conducted on welded joints A, B, and C. Specifically, a servo-hydraulic fatigue testing machine was used, with a frequency f = 60 Hz, a stress ratio R ≈ 0, and a cycle count of 1 × 10⁻⁶. 7The fatigue endurance limit is defined as the fatigue endurance limit, and the evaluation of fatigue results, such as the LN (load amplitude - number of fracture cycles) curve, is based on ISO-14324.

[0066] See Figure 8 Welded joint C exhibits the highest time-dependent strength under all loads, causing the LN curve to shift to the upper right. Compared to welded joint B, welded joint C demonstrates higher and more stable fatigue strength, meaning that welded joint C shows less deviation in the tested structure under the same load. In the comparison of fatigue endurance limits (maximum load without fracture at 1×10⁷ cycles), welded joint C is 2.9 times that of welded joint A, and compared to welded joint B, welded joint C represents a 2-fold improvement. Therefore, the fatigue strength of the welded joint in this embodiment of the invention is significantly improved.

[0067] In summary, the welded joint in the embodiments of the present invention includes a nail-shaped member 3 pressed into at least two plates 1, and the nail-shaped member 3 penetrates at least a portion of the plates 1 and each weld nugget 2, so that the edge region of the weld nugget 2 at least away from the nail-shaped member 3 has compressive residual stress, thereby suppressing the generation and growth of cracks, improving fatigue strength, and reducing fatigue fracture of the welded joint.

[0068] This invention also provides a method for manufacturing a welded joint, see below. Figures 3 to 5 The manufacturing method specifically includes the following steps:

[0069] Step S100: Stack at least two plates in sequence to form a part to be welded.

[0070] The number of plates 1 can be two or more, and these plates 1 are stacked sequentially with overlapping areas to form a part to be welded. The stacking direction of these plates 1 is the thickness direction, and the stacking order of these plates 1 is related to their connection relationship, requiring the plates 1 that need to be fixedly connected to be in contact.

[0071] Plate 1 can be a steel plate or an aluminum alloy plate, etc., and its thickness is relatively thin. For example, plate 1 can be a mild steel plate, a high-tensile steel plate, an ultra-high-tensile steel plate, a 5000 series aluminum alloy, a 6000 series aluminum alloy, etc. The materials of each plate 1 can be the same or different.

[0072] Step S200: Weld the parts to be welded to form a welded part. A weld nugget is formed inside the welded part. The weld nugget is fixedly connected to two adjacent plates. Along the stacking direction of at least two plates, the welded part has a first surface and a second surface that are arranged opposite to each other.

[0073] The workpieces to be welded are held by electrodes, and pressure and current are applied to the electrodes to perform spot welding, forming a welded part. A weld nugget 2 is formed within the welded part, centered on the contact surface of two adjacent plates 1, thereby fixing the corresponding two plates 1 together. Along the stacking direction of at least two plates 1, the welded part has a first surface 6 that is disposed opposite to each other. Figure 4 The upper surface shown) and the second surface 7 (shown) Figure 4 (See the lower surface shown). Welding conditions during spot welding (such as welding current, power-on test, pressure, etc.) can all be adjusted according to process requirements.

[0074] Step S300: A nail-shaped member is driven into the first surface to form a welded joint. The nail-shaped member penetrates the weld nugget and the plate located on the side of the weld nugget closer to the first surface to form a receiving hole. The edge region of the weld nugget at least away from the nail-shaped member has compressive residual stress.

[0075] A nail-shaped member 3 is driven into the first surface 6 of the weldment to form a weld joint. The nail-shaped member 3 penetrates the weld nugget 2 and the plate 1 located on the side of the weld nugget 2 closest to the first surface 6, thus forming a receiving hole in the corresponding plate 1 and the weld nugget 2. The receiving hole is adapted to the nail-shaped member 3. The receiving hole is a blind hole, that is, the bottom of the receiving hole is located in one of the plate 1, for example, the bottom of the receiving hole is located in the plate 1 furthest from the opening of the receiving hole.

[0076] The hardness of the nail-shaped component 3 is greater than that of the plate 1 and also greater than that of the melt core 2, to enable the nail-shaped component 3 to be pressed in and to form the receiving hole. The nail-shaped component 3 is located in the central region of the melt core 2, for example, in the exact center of the melt core 2, meaning that the axis of the nail-shaped component 3 coincides with the center of the melt core 2, so that the stress on the edge region of the melt core 2 is more uniform. The compressive residual stress is distributed radially relative to the axis of the nail-shaped component 3, so that the compressive residual stress in the edge region is distributed around the axis of the nail-shaped component 3, and the edge region has compressive residual stress, and the distribution of compressive residual stress in the edge region is more uniform.

[0077] After the nail-shaped part 3 is driven into the welded part, the direction of the compressive residual stress in the weld nugget 2 is perpendicular to the stacking direction of at least two plates 1, that is, the direction of the compressive residual stress is consistent with the rolling direction of the plates 1, so that the tensile residual stress in the rolling direction disappears, and the compressive residual stress is maintained in the direction perpendicular to the crack growth, which is conducive to keeping the crack opening closed and can more effectively suppress the crack.

[0078] The nail-shaped member 3 can be self-riveted into the welded part. Specifically, in some possible implementations, the nail-shaped member is driven into the first surface (step S300), including:

[0079] Step S301: The nail-shaped part is installed inside the punch tool, and the welded part is placed between the punch tool and the die tool, with the punch tool in contact with the first surface.

[0080] See Figure 4 The nail-shaped member 3 is located at the punch tool 4, and the punch tool 4 contacts the first surface 6 of the weldment, so that the nail-shaped member 3 also remains in contact with the first surface 6 of the weldment. The die tool 5 contacts the second surface 7 of the weldment, and the weldment is located between the punch tool 4 and the die tool 5, with the first surface 6 and the second surface 7 respectively in close contact with the punch tool 4 and the die tool 5. The punch tool 4 and the die tool 5 are arranged opposite to each other, and the second surface 7 of the weldment is exposed in the receiving cavity of the die tool 5.

[0081] Step S302: The punch tool drives the nail-shaped part into the welded part, the nail-shaped part and the welded part are plastically deformed, and the second surface fits with the die tool to form a protrusion that is compatible with the die tool.

[0082] The punch tool 4 pushes the nail-shaped piece 3 to pierce the first surface 6 of the weldment and enter the weldment. The nail-shaped piece 3 undergoes plastic deformation to form a mechanical interlocking structure with the weldment. The weldment undergoes plastic deformation, and the material of the plate 1 layer in the weldment that contacts the die tool 5 enters the die tool 5, causing the second surface 7 of the weldment to fit against the die tool 5, forming a protrusion adapted to the die tool 5. At the same time, the weldment and the nail-shaped piece 3 form a weld joint.

[0083] In summary, in the manufacturing method of the welded joint in the embodiments of the present invention, at least two plates 1 are stacked in sequence and then welded to form a weld nugget 2 between two adjacent plates 1. The weld nugget 2 and the corresponding plates 1 are penetrated by a nail-shaped member 3, so that the edge area of ​​the weld nugget 2 at least away from the nail-shaped member 3 has compressive residual stress, thereby inhibiting the generation and growth of cracks, improving fatigue strength, and reducing fatigue fracture of the welded joint.

[0084] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0085] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0086] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welded joint, characterized in that The at least two plates are sequentially stacked, and a nugget is formed in the welding joint, the nugget fixedly connects two adjacent plates, and the welding joint has oppositely arranged first and second surfaces. The direction of the compressive residual stress is perpendicular to the stacking direction of the at least two plates. The compressive residual stress is radially distributed relative to the axis of the nail-shaped member. The axis of the nail-shaped member coincides with the center of the nugget.

2. The welded joint of claim 1, wherein, The hardness of the nail-shaped member is greater than the hardness of the plates and greater than the hardness of the nugget.

3. The welded joint according to any one of claims 1-2, characterized in that, The first surface of the at least two plates is formed with the accommodating hole, and the second surface is formed with a protrusion, the protrusion being oppositely arranged with the accommodating hole, and the first surface and the second surface being oppositely arranged along the stacking direction of the at least two plates.

4. The welded joint according to any one of claims 1-2, characterized in that The nail-shaped member is self-piercing riveted between the corresponding plate and the nugget, and the nail-shaped member comprises a self-piercing rivet.

5. The welded joint of claim 4, wherein, The self-piercing rivet comprises a rivet shank and a rivet head connected to one end of the rivet shank, the rivet head being located in one of the plates and the end surface away from the rivet shank being exposed, the rivet shank penetrating the nugget and the plate between the rivet head and the nugget and extruding the edge region of the nugget.

6. The welded joint of claim 1, wherein, The at least two plates comprise a first plate and a second plate, the nail-shaped member being located in the first plate and penetrating the first plate and the nugget and extending into the second plate, and the edge region of the nugget away from the nail-shaped member having the compressive residual stress.

7. A method of manufacturing a welded joint, characterized by The method comprises: sequentially stacking at least two plates to form a to-be-welded member; welding the to-be-welded member to form a welded member, the welded member having a nugget formed therein, the nugget fixedly connecting two adjacent plates, and the to-be-welded member having oppositely arranged first and second surfaces along the stacking direction of the at least two plates; driving a nail-shaped member from the first surface to form a welded joint, the nail-shaped member penetrating the nugget and the plate on the side of the nugget close to the first surface to form an accommodating hole, and at least the edge region of the nugget away from the nail-shaped member having a compressive residual stress; the direction of the compressive residual stress being perpendicular to the stacking direction of the at least two plates; the compressive residual stress being radially distributed relative to the axis of the nail-shaped member; the axis of the nail-shaped member coinciding with the center of the nugget.

8. The manufacturing method according to claim 7, wherein Driving the nail-shaped member from the first surface comprises: the nail-shaped member being installed in a convex die tool, and the welded member being placed between the convex die tool and a concave die tool, the convex die tool being in contact with the first surface; the convex die tool driving the nail-shaped member into the welded member, the nail-shaped member and the welded member being plastically deformed, and the second surface being in abutment with the concave die tool to form a protruding head adapted to the concave die tool.

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