Unilateral friction riveting method and system

Abstract

The invention provides a unilateral friction riveting method. The unilateral friction riveting method comprises the steps that a rivet is clamped, and the axis of the rivet and the preset connecting position of a workpiece to be connected are centered; driving the rivet to rotate and press the rivet into the workpiece to be connected at a first rotating speed and a preset axial pressure; on the basis of real-time monitoring of the riveting process, when a preset critical condition is detected, the rotating speed of the rivet is reduced to a second rotating speed from the first rotating speed, and the preset axial pressure is kept; and when a preset termination condition is met, driving of the rivet is stopped. The invention further provides a single-side friction riveting system. Through constant pressure and staged rotating speed control, heat input and material flowing are optimized, solid-phase welding is achieved through high-speed rotation firstly, then densification is completed through speed reduction, the problems that in a traditional process, heat input is not uniform, and the number of joint defects is large are solved, and the joint quality and strength are remarkably improved. The high-precision mode or the low-precision mode can be selected according to equipment conditions, and the high-quality connection requirement of light-weight materials such as aluminum alloy is met.

Description

Technical Field

[0001] The present disclosure relates to the technical field of material connection, and in particular to a single-sided friction riveting method and system suitable for connecting light alloy profiles. Background Art

[0002] With the increasing demand for lightweight structures in fields such as aerospace, rail transportation, and new energy vehicles, light alloy materials represented by aluminum alloys and magnesium alloys have been widely used. Light alloy profiles have the advantages of high rigidity, strong torsional resistance, and easy forming. The quality of their connection directly affects the safety, reliability, and service performance of the product. Existing light alloy point connection processes include single-sided resistance spot welding, flow drilling riveting, core riveting, backfill stir friction spot welding, etc. Although the above technologies can meet the needs of light alloy connections to a certain extent, they still have shortcomings in terms of sealing, applicable space, structural integrity, material adaptability, and production efficiency, which limits their scope of application.

[0003] Single-sided friction riveting technology generates heat through friction between the rivet and the workpiece at high speed, causing plastic softening of the materials being joined. Under low axial force, the rivet can be inserted without penetrating the underlying plate, forming a threaded-solid composite connection between the plates. This technology offers advantages such as the absence of prefabricated holes, excellent sealing, and minimal equipment loss, making it suitable for single-sided structural connections. However, existing single-sided friction riveting processes lack a comprehensive control strategy. In high-speed applications, the frictional heat generation rate is difficult to precisely match with the plastic flow behavior of the material, leading to defects such as holes, cracks, or unwelded connections at the rivet / workpiece and workpiece / workpiece solid-phase connection interfaces. Furthermore, the vibration of industrial robots during operation can further exacerbate this mismatch, reducing the mechanical properties and service reliability of the joint. Summary of the Invention

[0004] In a first aspect, an embodiment of the present disclosure provides a unilateral friction riveting method, comprising:

[0005] Clamping the rivet and aligning the rivet axis with the predetermined connection position of the workpieces to be connected;

[0006] driving the rivet to rotate and press into the workpiece to be connected at a first rotation speed and a preset axial pressure;

[0007] Based on real-time monitoring of the riveting process, when a preset critical condition is detected, the rotation speed of the rivet is reduced from the first rotation speed to a second rotation speed while maintaining the preset axial pressure;

[0008] When a preset termination condition is met, the driving of the rivet is stopped.

[0009] In some embodiments, the preset axial pressure is determined based on the hot yield strength of the material when the solid phase welding temperature is reached and the effective contact area between the rivet and the workpiece.

[0010] In some embodiments, the first rotational speed is determined based on a heat dissipation rate of the workpieces to be joined.

[0011] In some embodiments, the preset critical condition includes:

[0012] The accumulated total mechanical work reaches a preset energy threshold and the axial feed rate is within a preset rate range; or

[0013] The axial feed rate is within the preset rate range.

[0014] In some embodiments, the preset energy threshold is determined based on energy absorbed by the materials to be connected.

[0015] In some embodiments, the preset rate interval is [a, ∈a], where a represents the feed rate when achieving solid phase connection, and ∈ is determined based on the ratio of the hot yield strength of the material at the solid phase welding temperature and the maximum allowable temperature.

[0016] In some embodiments, the second rotational speed is determined based on the first rotational speed in accordance with a preset proportional relationship.

[0017] In some embodiments, when a preset termination condition is met, stopping driving the rivet includes:

[0018] When the axial feed rate reaches or falls below a preset termination threshold, driving of the rivet is stopped.

[0019] In some embodiments, the preset termination threshold is an axial feed rate less than 0.1 mm / s.

[0020] In some embodiments, the solid phase bonding achieves microscopic metallurgical bonding at at least one of the following interfaces:

[0021] Between the material in the hollow cavity of the rivet and the underlying workpiece;

[0022] Between the original interfaces of the upper layer workpiece and the lower layer workpiece of the workpieces to be connected;

[0023] between the inner wall of the rivet and the trapped material;

[0024] Between the outer wall of the rivet and the surrounding workpiece material.

[0025] In some embodiments, the rivet is a semi-hollow rivet comprising an integrally formed rivet cover and a rivet body, wherein the inner wall, outer wall, or both of the rivet body form a smooth cylindrical surface or a special-shaped structure selected from at least one of threads, knurling, annular grooves, and axial grooves.

[0026] In a second aspect, an embodiment of the present disclosure provides a unilateral friction riveting system, comprising:

[0027] a drive head configured to clamp the rivet and provide drive for axial feed motion and rotational motion of the rivet during the riveting process; and

[0028] A support frame configured to secure the workpieces to be connected,

[0029] Wherein, the unilateral friction riveting system is configured to implement the unilateral friction riveting method described in the first aspect of the embodiment of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 4 is a flow chart of a unilateral friction riveting method according to an embodiment of the present disclosure.

[0031] Figure 2 Schematic diagram of the effective contact area formed between the semi-hollow rivet and the workpiece during the friction riveting process in an embodiment of the present invention.

[0032] Figure 3 is a block diagram of a single-sided friction riveting system according to an embodiment of the present disclosure.

[0033] Figure 4 The figure is a schematic diagram of the process of a constant pressure two-stage single-sided friction riveting method for connecting two layers of aluminum alloy plates in an embodiment of the present invention.

[0034] Figure 5 It is a schematic diagram of the process of switching from the first stage to the second stage in an embodiment of the present disclosure.

[0035] Figure 6 It is a cross-sectional schematic diagram of a riveted joint formed in an embodiment of the present disclosure.

[0036] Figure 7 1 and 2 are cross-sectional metallographic photographs of the joints according to the embodiments of the present disclosure and the comparative embodiment.

[0037] Figure 8 2 are the shear force-displacement curves of the joints of the disclosed embodiment and the comparative embodiment. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the technical solution of the present disclosure is described in detail below with reference to the accompanying drawings.

[0039] Example embodiments will be described more fully hereinafter with reference to the accompanying drawings, but the example embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art.

[0040] In the absence of conflict, the various embodiments of the present disclosure and the various features therein may be combined with each other.

[0041] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0042] The terms used herein are used only to describe specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a," "an," and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It will also be understood that when the terms "comprising" and / or "made of" are used in this specification, the presence of the features, wholes, steps, operations, elements, and / or components is specified, but the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or groups thereof is not excluded.

[0043] The embodiments described herein may be described with reference to plan views and / or cross-sectional views, with the aid of idealized schematic diagrams of the present disclosure. Thus, the example illustrations may be modified based on manufacturing techniques and / or tolerances. Therefore, the embodiments are not limited to the embodiments shown in the accompanying drawings, but include modifications of the configurations formed based on the manufacturing process. Therefore, the regions illustrated in the accompanying drawings are schematic in nature, and the shapes of the regions shown in the drawings illustrate specific shapes of the regions of the elements, but are not intended to be limiting.

[0044] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted as having an idealized or overly formal meaning unless expressly defined as such herein.

[0045] In this disclosure, unless otherwise specified, the following technical terms should be understood as follows:

[0046] Unilateral friction riveting means that the riveting is completed by applying pressure from only one side of the workpiece;

[0047] Axial pressure refers to the external pressure applied along the axis of the rivet, which is used to push the rivet into the workpiece;

[0048] The axial feed rate refers to the speed at which the rivet is advanced in the axial direction and is used to characterize the rate at which the rivet is pressed into the workpiece;

[0049] Joining workpieces refers to metal sheets or parts that need to be fixed together by a single-sided friction riveting process.

[0050] The present disclosure aims to address the technical problem in existing single-sided friction riveting technology, in which the friction heat generation and the plastic flow of the material are difficult to achieve the best match due to the imprecise control of the process parameters, which makes it easy for defects such as holes, cracks or unwelded parts to appear inside the joint, resulting in a decrease in the mechanical properties and service reliability of the joint. The present disclosure proposes a friction riveting process method that can significantly improve the process stability and the joint forming quality.

[0051] To achieve the above objectives, the present disclosure provides a constant-pressure, two-stage, single-sided friction riveting process. This method uses constant axial pressure as the basic control mode and adjusts the rotational speed in stages during the riveting process. The higher rotational speed in the first stage rapidly generates and accumulates frictional heat, prompting the joined materials to reach a suitable plastic state. The rotational speed is then reduced in the second stage to stabilize material flow and suppress overheating. This allows for precise control of the frictional heat generation rate and material flow behavior, effectively reducing internal joint defects and improving joint forming quality and consistency.

[0052] Figure 1 4 is a flow chart of a unilateral friction riveting method according to an embodiment of the present disclosure.

[0053] First, refer to Figure 1 The present disclosure provides a unilateral friction riveting method, comprising:

[0054] S11, clamping the rivet and aligning the rivet axis with the predetermined connection position of the workpieces to be connected;

[0055] S12, driving the rivet to rotate and press into the workpieces to be connected at a first rotation speed and a preset axial pressure;

[0056] S13. Based on real-time monitoring of the riveting process, when a preset critical condition is detected, reducing the rotation speed of the rivet from the first rotation speed to a second rotation speed while maintaining the preset axial pressure;

[0057] S14. When a preset termination condition is met, stop driving the rivet.

[0058] The above process can be further refined into a constant-pressure, two-stage, single-sided friction riveting method. This method uses a semi-hollow rivet, which is driven by a servo drive to rotate and feed the rivet. While continuously applying constant axial pressure, the following steps 1 to 5 are performed in sequence to screw the rivet into and connect at least two layers of the workpiece to be connected:

[0059] Step 1: In the preparation stage, the panels to be connected are stacked on a support frame, and the drive head clamps the semi-hollow rivet so that the rivet axis is aligned with the predetermined connection point of the workpiece.

[0060] In the disclosed embodiment, at least two layers of panels to be connected can be stacked on a support frame in a predetermined overlapping pattern. After stacking, the panels are positioned using a clamp or locating pins to prevent relative movement during the riveting process and ensure precise alignment of the rivet and workpiece connection positions. The drive head clamps the semi-hollow rivet to prevent slipping during rotation. After clamping, the drive head adjusts its position to precisely align the rivet's axis with the predetermined connection point. This alignment can be achieved using a visual sensor, a laser alignment device, or mechanical limiting methods.

[0061] Step 2: In the first stage (i.e., the frictional heating and solid-phase welding stage), a preset constant axial pressure F is applied to the driving device, and the semi-hollow rivet is driven to rotate at a higher first speed ω1 and pressed into the workpiece to be connected. The high-speed rotation of the rivet generates intense friction with the workpiece contact interface, quickly generating heat, causing the workpiece material in the contact area to heat up to the plastic deformation temperature, thereby softening the material and reducing the rivet penetration resistance. Under the action of constant pressure, the feed rate of the rivet is adaptively adjusted according to the degree of softening of the material. In this stage, under the combined action of high temperature and constant pressure, the material at the contact interface undergoes plastic deformation and stirring and mixing, forming a preliminary solid-phase connection between the rivet / workpiece and the workpiece / workpiece, and promoting dynamic recrystallization of the material and grain refinement.

[0062] In some embodiments, the preset axial pressure is determined based on the hot yield strength of the material when the solid phase welding temperature is reached and the effective contact area between the rivet and the workpiece.

[0063] In some embodiments, the first rotational speed is determined based on a heat dissipation rate of the workpieces to be joined.

[0064] Specifically, the preset axial pressure F is determined by the following formula:

[0065] F=α p ·σ y(hot) ·A (1)

[0066] From formula (1), we can see that the pressure F is positively correlated with the thermal yield strength of the material and the contact area. Therefore, the workpiece material and rivet size are the main factors that determine the pressure.

[0067] Where: F is the preset axial pressure applied to the rivet, in Newton (N);

[0068] α p It is a dimensionless constant that can be calibrated according to experimental data to correct the difference between theoretical calculation and actual working conditions. Its value range is usually between 1 and 3. The method for determining this constant is: first, based on the experiment, determine the pressure range that can complete riveting under the same workpiece conditions, and then obtain α by fitting the experimental data. pFor different alloy materials, different α p For the same type of workpiece, a unique α p This constant can be determined through the analysis of the material's thermal physical properties test.

[0069] σ y(hot) The workpiece material reaches the target solid phase welding temperature T w The hot yield strength at , in megapascals (MPa);

[0070] A is the effective contact area between the rivet and the workpiece, in square millimeters (mm 2 In this embodiment, the contact surface refers to the geometric projection of the end face of the rivet leg. Since the rivet is a semi-hollow structure, its cavity will be filled during the insertion process, so it can be equivalent to a solid rivet, and its effective contact area is the geometric projection area of ​​the end face of the rivet leg. Figure 2 shown.

[0071] Figure 2 Schematic diagram of the effective contact area formed between the semi-hollow rivet and the workpiece during the friction riveting process in an embodiment of the present invention.

[0072] like Figure 2 As shown, A is the effective contact area between the end face of the rivet leg and the workpiece, that is, the solid phase welding area, and its unit is mm 2 This contact area is determined by the geometric projection of the end faces of the rivet legs. Since the rivet is semi-hollow, during penetration into the workpiece, the rivet cavity gradually fills with the joining material until it becomes solid. Therefore, during the welding phase, the rivet can be considered a solid rivet. In this case, the effective contact area A is the geometric projection of the end faces of the rivet legs.

[0073] Furthermore, the first rotation speed ω1 is determined by the following formula:

[0074]

[0075] Formula (2) shows that the first speed ω1 is closely related to the system's heat dissipation capacity and friction coefficient, so a reasonable selection of the speed helps avoid defects caused by heat accumulation.

[0076] Where: ω1 is the first speed of the rivet, in revolutions per minute (rpm);

[0077] Q diss , is the maximum heat dissipation rate, which means that when the solid phase welding area reaches the target solid phase welding temperature T w The maximum rate at which the system loses heat to the surrounding environment and the workpiece substrate is Q dissIt is related to the contact area between the rivet and the workpiece, the target solid phase welding temperature and the thickness of the lower plate of the workpiece. The unit is kilowatt (kW) and can be calculated according to formula (3);

[0078] F is the constant axial pressure (N) calculated according to formula (1);

[0079] μ is the dynamic friction coefficient between the rivet and the workpiece material, which is determined by different workpiece materials and rivet materials;

[0080] D e is the effective diameter of the rivet, which is calculated as Among them D tool is the total diameter of the rivet leg, in millimeters (mm);

[0081] β is a dimensionless constant calibrated based on experimental data, typically ranging from 1.5 to 4. This constant is obtained by measuring the time required for energy accumulation to reach a threshold at different rotational speeds and fitting the upper and lower limits of β. The magnitude of β indicates how quickly the required energy is reached; larger β values ​​shorten the time to complete the riveting process. However, it should not exceed the critical value of β = 4, as this may lead to overheating or defects. This constant is determined through analysis of the material's thermophysical properties. Its magnitude is independent of the workpiece material and is primarily related to the time it takes to complete the riveting process.

[0082] In the above formula, the maximum heat dissipation rate Q diss The calculation formula is:

[0083]

[0084] in:

[0085] k is the thermal conductivity of the workpiece material, in W / (m·℃);

[0086] A is the contact area between the rivet and the workpiece (mm 2 );

[0087] L is the thickness of the lower plate to be connected, in millimeters (mm);

[0088] T w is the target solid phase welding temperature, in degrees Celsius (℃);

[0089] T0 is the initial temperature of the workpiece or the ambient temperature (°C).

[0090] Through the above formula, the first rotation speed ω1 can be accurately determined in combination with the workpiece thermophysical parameters and structural dimensions, thereby effectively controlling the heat input and material plasticization process in the first stage and ensuring stable joint quality.

[0091] Step three, the phase transition, continues the frictional heating effect of the first phase and determines whether the joint area has achieved solid-phase welding through real-time monitoring of preset critical conditions. If the test results meet the preset critical conditions, the process immediately switches to the second phase, ensuring that the welding effect of the first phase is optimal, thus creating conditions for defect suppression and microstructure control in the second phase.

[0092] In some embodiments, the preset critical condition includes:

[0093] The accumulated total mechanical work reaches a preset energy threshold and the axial feed rate is within a preset rate range; or

[0094] The axial feed rate is within the preset rate range.

[0095] In the embodiment of the present disclosure, the preset critical condition needs to ensure that the accumulated heat generated by friction is sufficient to enable the materials in the interface area of ​​the workpieces to be connected to reach an ideal solid-phase welding state.

[0096] In high-precision control mode, the preset critical condition must meet the following two indicators at the same time:

[0097] Energy input threshold monitoring: Real-time integration of the total mechanical work E of the riveting process. When E reaches the preset energy threshold E0, the condition is determined to be met. Where F is the axial reaction force, M is the reaction torque, f is the axial feed rate, ω is the rotational angular velocity, and Δt is the accumulated time;

[0098] Rivet Process Window Monitoring: Under constant axial pressure control mode, the rivet's axial feed rate sensitively reflects the material's energy accumulation. When energy is insufficient, the axial feed rate approaches 0 mm / s. When the energy reaches a threshold, the feed rate rapidly increases from near 0 mm / s to over 9 mm / s. Therefore, monitoring the feed rate reflects the softening and flow state of the material. When the axial feed rate exceeds 1 mm / s, it is determined that a sufficient solid-phase weld has been established.

[0099] In some embodiments, the preset energy threshold is determined based on energy absorbed by the materials to be connected.

[0100] Specifically, the preset energy threshold E0 can be obtained by the following formula:

[0101] E0=γ e E absorbed (4)

[0102] E0 is a comprehensive energy index, and its calculation depends on the material absorption energy E absorbed .

[0103] Energy absorbed by the material Eabsorbed Indicates that the metal material in the joint volume is heated from the initial temperature T0 to the target solid phase welding temperature T w The theoretical minimum heat required is calculated as follows:

[0104]

[0105] Where: C is the specific heat capacity of the material, in J / (kg·℃); ρ is the density of the material, in kg / m 3 ; V is the effective volume of the heated solid phase welding core area, unit is mm 3 , the volume is the product of the effective connection area A and the thickness of the lower plate; γ e is a dimensionless constant, and its value range is usually 40 to 100. e Based on the thermophysical properties of the workpiece material, specifically, for the preset alloy material and workpiece thickness, the actual total mechanical work when the joint reaches the target welding state is obtained through experiments; the corresponding theoretical absorbed energy is calculated based on formula (5); the actual total mechanical work is compared with the theoretical absorbed energy to inversely calculate the γ e For different alloy materials, different γ e Value; For the same alloy material and under the same heat dissipation conditions, the γ e Numeric values ​​can be considered fixed.

[0106] When the total mechanical work E reaches the preset energy threshold T0 and the real-time monitored axial feed rate is within the preset rate range, it is determined that the preset critical condition is met and switching is performed.

[0107] In another embodiment, if the riveting system's sensor accuracy is insufficient or uncalibrated, a low-precision control mode can be used. In this mode, only the fundamental process parameter, the axial feed rate, needs to be monitored to determine whether the preset critical condition has been met, thus avoiding complex energy accumulation calculations. This mode significantly simplifies the monitoring process and control system, facilitating stable and cost-effective deployment and application in industrial environments.

[0108] In some embodiments, the preset rate interval is a to ∈a, where a represents the feed rate when achieving solid phase connection, and ∈ is determined based on the ratio of the hot yield strength of the material at the solid phase welding temperature and the maximum allowable temperature.

[0109] In a preferred embodiment of the present disclosure, the preset rate interval ranges from [a to ∈a], where a represents the feed rate when achieving solid-phase connection, which is usually 1 mm / s; ∈ is calculated as follows:

[0110]

[0111] in, Indicates that the material is at the preset maximum allowable temperature T r The hot yield strength under the condition of MPa, the maximum temperature E r It is pre-set based on the thermophysical properties of the material; δ is a dimensionless constant calibrated based on experimental data, and its value range is usually between 1 and 5.

[0112] In a preferred embodiment, the preset energy threshold and rate threshold can be adaptively adjusted according to different workpiece materials and thicknesses, and the corresponding parameters can be automatically loaded by storing a material database and an experimental calibration curve.

[0113] Step 4: During the second phase, namely, the controlled thermal preload, defect suppression, and microstructure densification phase, critical process parameter adjustments are made: while maintaining a constant axial pressure F, the rivet rotational speed is reduced to a second speed ω2, significantly lower than the first speed ω1. This speed reduction reduces the frictional heat generation rate, effectively preventing excessive heat accumulation in the joint area and excessive softening of the material. Under the action of continuous axial pressure, the material in the plastic stirring zone is fully mechanically constrained, achieving stable and orderly plastic flow, resulting in a dense joint with reduced defects.

[0114] In some embodiments, the second rotational speed is determined based on the first rotational speed in accordance with a preset proportional relationship.

[0115] In a specific embodiment, the second rotational speed ω2 can be expressed by the following formula:

[0116] ω2=ω1 / β。

[0117] By maintaining constant axial pressure and reducing the rotational speed during this stage, defects such as pores and inclusions within the joint can be significantly reduced, thereby improving the joint's density and mechanical properties. Experimental results show that when β is controlled within a reasonable range, the resulting joint exhibits superior shear strength and fatigue life compared to the control sample without speed control.

[0118] In some embodiments, the parameter control strategy of the second stage can be widely applicable to single-sided friction riveting of different types of light alloys, steels and dissimilar materials thereof, which helps to expand the material adaptability of the process.

[0119] Step 5: At the end of the process, when the axial feed rate is monitored to decrease to nearly 0 mm / s, the riveting process is complete. At this point, the drive head stops rotating and applying pressure and quickly returns to its initial position, ultimately forming a composite joint with a smooth surface and dense interior on the workpiece.

[0120] In some embodiments, when a preset termination condition is met, stopping driving the rivet includes: stopping driving the rivet when the axial feed rate reaches or falls below a preset termination threshold.

[0121] In some embodiments, the preset termination threshold is an axial feed rate less than 0.1 mm / s.

[0122] Typically, when the real-time monitored rivet axial feed rate decreases to a preset termination threshold close to zero (e.g., less than 0.1 mm / s), it indicates that the bottom of the rivet cap has touched the upper plate material, resulting in the rivet being unable to penetrate further under the current pressure. At this point, the trigger stops rotation and resets, thus ending the riveting process.

[0123] In the embodiment of the present disclosure, the preset termination condition may also include one or more of the following situations: when the axial displacement of the rivet is monitored to reach the preset limit stroke, it indicates that the rivet has been fully inserted and forms the expected connection interface with the workpiece, thereby terminating the driving of the rivet; when it is monitored that the continuously applied axial pressure does not cause obvious rivet displacement, it indicates that the materials are fully compacted, and the driving of the rivet is terminated; or, when the temperature signal or friction heat input curve is monitored in real time to be stable and meets the forming conditions in the process database, the driving of the rivet is terminated. The above-mentioned multi-condition judgment method can be flexibly selected according to different working conditions and workpiece material characteristics to ensure the joint forming quality and process stability.

[0124] In the disclosed embodiment, after the above process is completed and terminated, a stable composite joint is formed between the rivet and the workpiece. This joint is achieved through solid-phase bonding and is characterized by: under the action of thermal-mechanical coupling, the original material interface around the rivet is eliminated, and a microscopic metallurgical bond is generated at at least one of the following interfaces:

[0125] The interface between the workpiece material trapped within the hollow cavity of the rivet and the underlying workpiece body;

[0126] The original interface between the upper and lower workpieces around the outer wall of the rivet;

[0127] The interface between the workpiece material trapped in the hollow cavity of the rivet and the inner wall of the rivet;

[0128] The interface between the outer wall of the rivet and the surrounding workpiece material it is squeezed against.

[0129] In some embodiments, the solid phase ligation occurs at at least one of the following interfaces:

[0130] Between the material in the hollow cavity of the rivet and the underlying workpiece;

[0131] Between the original interfaces of the upper layer workpiece and the lower layer workpiece of the workpieces to be connected;

[0132] between the inner wall of the rivet and the trapped material;

[0133] Between the outer wall of the rivet and the surrounding workpiece material.

[0134] To achieve this process, the semi-hollow rivet used in this disclosure is a one-piece structure, comprising a rivet cap and a rivet body. The top of the rivet cap is provided with a positioning structure for engaging with the drive head and transmitting torque. The positioning structure can be a groove, a boss, or a combination thereof to achieve stable and centered driving.

[0135] In an optional embodiment, the rivet body is hollow and tubular, and its end may be provided with a wedge-shaped or tapered chamfer to facilitate initial screwing. The inner and / or outer walls of the rivet may be smooth cylindrical, or may be formed with at least one of the following special-shaped structures: threads, knurling, circumferential grooves, and axial grooves to enhance mechanical interlocking and guide plastic flow of the material during the riveting process.

[0136] In some embodiments, the rivet is a semi-hollow rivet comprising an integrally formed rivet cover and a rivet body, wherein the inner wall, outer wall, or both of the rivet body form a smooth cylindrical surface or a special-shaped structure selected from at least one of threads, knurling, annular grooves, and axial grooves.

[0137] Based on the above-mentioned friction riveting process and rivet structure, the present disclosure further provides a single-sided friction riveting system for implementing the above-mentioned friction riveting method, comprising a drive head and a support frame for supporting and fixing the workpieces to be connected; the drive head is configured to be adapted to the semi-hollow rivet to provide controlled axial feed motion and rotational motion during the riveting process; the support frame can be arranged below the workpieces to be connected, for positioning and clamping the connecting material during the riveting process, so as to ensure the riveting quality and position accuracy.

[0138] The present disclosure has the following beneficial effects:

[0139] Improve joint quality: Through the synergistic effect of constant pressure control and two-stage speed control, the heat input and material flow state during the welding process can be precisely adjusted, effectively suppressing the generation of defects such as holes and cracks in the joint area, thereby obtaining high-quality welded joints with dense structure and no obvious defects.

[0140] Improve process stability: The constant pressure control method reduces the dependence on complex process parameters. Combined with the real-time monitoring of process signals such as axial feed rate, energy input or displacement, it can accurately determine the switching timing of the process stage, thereby significantly improving process consistency and process stability, and facilitating engineering promotion and application.

[0141] Enhanced mechanical properties: Due to the significant improvement in the internal quality of the joint, key mechanical performance indicators such as the tensile and shear strength of the joint are improved, and the discreteness of the performance data is reduced, thereby improving the overall reliability of the connection structure.

[0142] Figure 3is a block diagram of a single-sided friction riveting system according to an embodiment of the present disclosure.

[0143] Secondly, refer to Figure 3 The present disclosure provides a single-sided friction riveting system, comprising:

[0144] A drive head 301 is configured to clamp the rivet and provide drive for the axial feed motion and rotational motion of the rivet during the riveting process; and

[0145] The support frame 302 is configured to fix the workpiece to be connected,

[0146] Wherein, the unilateral friction riveting system is configured to implement any one of the above-mentioned unilateral friction riveting methods.

[0147] In the disclosed embodiment, the unilateral friction riveting system may further include a control unit. The control unit may be a numerical control unit (NC), a programmable logic controller (PLC), or a microprocessor-based embedded control device, which stores an instruction program for executing the unilateral friction riveting method.

[0148] Specifically, the control unit can output control signals to the drive head based on preset process parameters (such as speed, downforce, and hold time), causing the drive head to execute the driving action according to the steps. Through the centralized control of the control unit, the riveting process can be automated and the parameters can be accurately repeated.

[0149] Furthermore, the drive head 301 can be integrated with the control unit to form an integrated intelligent drive device; or it can be connected to the control unit through an external signal to achieve speed switching and pressure regulation.

[0150] In a further embodiment, the instruction program may be stored in a computer-readable medium, which may include but is not limited to ROM, RAM, a hard disk, a flash memory, or other non-volatile memory. By running the instruction program in the control unit, the single-sided friction riveting system can implement any of the single-sided friction riveting methods described above, thereby achieving process consistency and traceability.

[0151] It should be noted that the control unit and computer-readable medium are only an optional implementation method to further enhance the intelligence of the system. In some scenarios, the movement of the drive head can also be achieved through manual operation or simple electrical control, which is not limited in this disclosure.

[0152] In some embodiments, the single-sided friction riveting system further includes: a control unit configured to monitor real-time state parameters during the riveting process and control the rotation speed and pressure of the driving head.

[0153] Example 1

[0154] Figure 4 This is a schematic diagram of the process of a constant-pressure, two-stage, single-sided friction riveting method for connecting two layers of aluminum alloy plates in an embodiment of the present invention, wherein: 1 - driving head; 2 - semi-hollow rivet; 3 - pressure sleeve; 4 - upper workpiece; 5 - lower workpiece; 6 - support frame; 7 - constant axial pressure; 8 - first rotational speed; 9 - second rotational speed.

[0155] exist Figure 4 In the figure, a is the preparation stage; b is the first stage; c is the second stage; and d is the process completion stage.

[0156] like Figure 4 As shown, this embodiment discloses a constant pressure two-stage single-side friction riveting method for connecting two layers of aluminum alloy plates.

[0157] The connection objects are set as follows: the upper workpiece 4 is a 5083-O aluminum alloy plate with a thickness of 2.0 mm; the lower workpiece 5 is a 6063-T6 aluminum alloy plate with a thickness of 3.0 mm.

[0158] Those skilled in the art should understand that the method disclosed herein is not only applicable to the connection of aluminum alloy plates, but can also be extended to the friction riveting of magnesium alloys, titanium alloys and multi-layer heterogeneous materials, and has wide applicability.

[0159] The riveting equipment uses servo-driven riveting equipment, which can accurately control the axial pressure and rotation speed, and can collect and feedback process signals such as axial feed rate and torque in real time.

[0160] The semi-hollow rivet 2 is formed by cold heading of 40Cr steel and has excellent high-temperature strength and wear resistance; the inner side of the rivet leg is processed with threads.

[0161] First, determine the axial pressure. According to the above axial pressure calculation formula (1), the solid phase welding temperature is set to 400℃, the yield strength of the plate at this temperature is 67.2MPa, and the effective contact area A=28mm 2 , α p =1.1, based on which the constant axial pressure value is calculated to be 2kN.

[0162] Then, the first rotation speed ω1 is determined. Under the condition of dimensionless constant β=2, workpiece thermal conductivity k=200 W / (m·°C), tool contact area A=28 mm 2 , target welding temperature T w 400℃, workpiece initial temperature T0=25℃, dynamic friction coefficient μ=0.42, constant axial pressure F=2000N, total diameter of rivet leg D tool =6mm(effective diameter D e=4mm) and characteristic heat conduction distance L =3mm, according to the speed calculation formula, in order to achieve a balance between heat generation and heat dissipation and maintain the lowest heat dissipation state, the operating speed is set to 4800rpm.

[0163] Next, the second rotational speed ω2 is determined. Under the condition of the dimensionless constant β=2, according to the rotational speed calculation formula, the second rotational speed is set to 2400 rpm.

[0164] Then, the preset energy threshold is determined. 3 , γ e =48, effective volume of the core area V≈84.8mm 3 Under the condition of , the required cumulative total energy is 3.7kJ according to the energy threshold calculation formula.

[0165] Finally, the feed rate switching range is determined. The hot yield strength at a = 1 mm / s and the maximum allowable temperature of 450°C Under the condition of δ=3.5, according to the calculation formula, ∈ is 5, so the switching range is [1mm / s, 5mm / s].

[0166] The switching range is determined based on the thermophysical properties of the lower layer 6063-T6 aluminum alloy plate and belongs to the control range; if the speed switching control is not performed, the feed rate may quickly rise to 9 mm / s, which may cause defects such as cracks and is not a process condition recommended by the method disclosed herein.

[0167] The specific process steps of the embodiment of the present disclosure are as follows:

[0168] Step 1: Preparation Figure 4 a)

[0169] The upper workpiece 4 and the lower workpiece 5 are stacked on the support frame 6, and the driving head 1 clamps the semi-hollow rivet 2 so that the rivet axis is aligned with the predetermined connection position of the workpiece.

[0170] Step 2: Phase 1 ( Figure 4 b)

[0171] Drive head 1 applies a constant downward axial pressure of 2 kN 7 while simultaneously driving rivet 2 at a first rotational speed of 4800 rpm 8. The high-speed rotation generates frictional heat, rapidly heating the material in the contact area between the rivet and the workpiece, causing it to plastically flow and form an initial solid-phase connection at the interface between the upper and lower workpieces.

[0172] Step 3: Phase Switching

[0173] During the first stage, after the rivet pierces the upper workpiece 4, the control system monitors the axial feed rate of the rivet in real time; when the rate reaches 2 mm / s, it is determined that the physical state (process stage) switching condition has been met and the speed switching is automatically executed (for the specific switching process, see Figure 5 ).

[0174] Figure 5 It is a schematic diagram of the process of switching from the first stage to the second stage in an embodiment of the present disclosure.

[0175] like Figure 5 As shown, during the first stage of riveting, when the semi-hollow rivet pierces the upper workpiece and enters the lower workpiece, the control system collects the axial feed rate of the rivet in real time. When it is detected that the axial feed rate is in the preset rate range (for example, 2mm / s), the system determines that the riveting process has reached the criterion condition for physical state switching (i.e., process stage switching condition), and then issues a stage switching instruction. The drive head quickly reduces the rivet speed from the first rate of 4800rpm to the second rate of 2400rpm, thereby reducing heat input and avoiding excessive softening of the lower workpiece; after detecting the trigger condition, the speed adjustment is performed immediately, and the switching delay is less than, for example, 0.1s, to avoid the rate rising to the defect risk area (>5mm / s) to ensure a smooth transition between heat input and plastic flow.

[0176] Step 4: Phase 2 ( Figure 4 c)

[0177] Maintaining constant axial pressure 7, the rivet speed is immediately reduced to a second speed of 2400 rpm 9. The rivet is screwed in at this lower speed until the target depth is reached. During this stage, heat input is reduced, the underlying workpiece 5 maintains high rigidity, and plastic metal flow is more stable, effectively suppressing defect initiation.

[0178] Step 5: Process End ( Figure 4 d)

[0179] When the axial feed rate is detected to be close to 0 mm / s, the riveting is determined to be completed. The drive head 1 stops rotating and applying pressure, and quickly returns to the initial position. Finally, a composite connection joint with a smooth surface and dense interior is formed on the workpiece (see Figure 6 ).

[0180] Figure 6 1 is a schematic cross-sectional view of a riveted joint formed in an embodiment of the present disclosure, wherein 10 is a mechanical interlocking connection; 11 is a solid phase connection area.

[0181] like Figure 6As shown in this embodiment, after a two-stage, constant-pressure, single-sided friction riveting process, the resulting composite joint consists of a mechanical interlocking connection 10 and a solid-phase connection zone 11. The rivet legs, in their high-temperature plastic state, penetrate and fill the pre-deformed zone of the underlying workpiece, forming a geometric interlocking structure with the underlying workpiece material, forming a stable mechanical interlocking structure. This structure can withstand shear and tensile loads without relying on additional fasteners or adhesives, providing reliable primary joint strength.

[0182] At the interface between the rivet end and the two workpieces, frictional heat causes the metal in the contact area to reach the solid-phase diffusion temperature range, causing plastic deformation. This promotes diffusion and bonding of metal atoms at the interface, forming a metallurgically bonded solid-phase joint zone. 11 This zone exhibits no visible signs of melting and exhibits a dense and continuous structure, effectively improving joint strength and fatigue life.

[0183] The mechanical interlocking connection 10 and the solid phase connection area 11 work together to significantly improve the overall load-bearing capacity and fatigue resistance of the joint. At the same time, the joint surface is smooth, making it suitable for direct application in structural parts with high requirements for appearance quality.

[0184] Figure 7 1 and 2 are cross-sectional metallographic photographs of the joints according to the embodiments of the present disclosure and the comparative embodiment.

[0185] Figure 7 (a) shows the joint obtained by the single-stage friction riveting process with a constant speed of 4800 rpm. It can be clearly observed that there are obvious cracks and holes in the joint; Figure 7 (b) shows a joint obtained by the constant pressure two-stage process disclosed in the present invention. Its internal structure is uniform and dense, and no macroscopic holes or cracks are found, indicating that the process of the present invention can significantly improve the internal quality of the joint.

[0186] Figure 8 2 are the shear force-displacement curves of the joints of the disclosed embodiment and the comparative embodiment.

[0187] Figure 8 (a) shows the tensile shear performance of the joint in a single-stage constant rotation speed process, with an average peak force of 5718.6 ± 95 N; Figure 8 (b) shows the tensile-shear performance of the joint of the embodiment of the present disclosure, with an average peak force of 7249±217N, an improvement of approximately 26.8% compared to the comparative process. This shows that the disclosed process not only effectively eliminates macroscopic defects within the joint, but also significantly improves the joint's load-bearing capacity and overall mechanical properties.

[0188] It will be appreciated by those skilled in the art that all or some of the steps, systems, and functional modules / units in the methods disclosed above may be implemented as software, firmware, hardware, and appropriate combinations thereof. In hardware implementations, the division between the functional modules / units mentioned in the above description does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed by several physical components in cooperation. Some or all physical components may be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium (or non-transitory medium) and a communication medium (or temporary medium). As is well known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable, and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, it is well known to those skilled in the art that communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0189] Example embodiments have been disclosed herein, and although specific terms are employed, they are used and should be interpreted only in a general illustrative sense and not for purposes of limitation. In some instances, it will be apparent to those skilled in the art that, unless otherwise expressly indicated, features, characteristics, and / or elements described in conjunction with a particular embodiment may be used alone or in combination with features, characteristics, and / or elements described in conjunction with other embodiments. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the present disclosure as set forth in the appended claims.

Claims

1. A unilateral friction riveting method comprising: Clamping the rivet and aligning the rivet axis with the predetermined connection position of the workpieces to be connected; driving the rivet to rotate and press into the workpiece to be connected at a first rotation speed and a preset axial pressure; Based on real-time monitoring of the riveting process, when a preset critical condition is detected, the rotation speed of the rivet is reduced from the first rotation speed to a second rotation speed while maintaining the preset axial pressure; When a preset termination condition is met, the driving of the rivet is stopped.

2. The unilateral friction riveting method according to claim 1, wherein: The preset axial pressure is determined based on the hot yield strength of the material when the solid phase welding temperature is reached and the effective contact area between the rivet and the workpiece.

3. The unilateral friction riveting method according to claim 2, wherein: The first rotational speed is determined based on a heat dissipation rate of the workpieces to be connected; and / or The second rotational speed is determined based on the first rotational speed in accordance with a preset proportional relationship.

4. The unilateral friction riveting method according to any one of claims 1 to 3, wherein: The preset critical conditions include: The accumulated total mechanical work reaches a preset energy threshold and the axial feed rate is within a preset rate range; or The axial feed rate is within the preset rate range.

5. The unilateral friction riveting method according to claim 4, wherein: The preset energy threshold is determined based on the energy absorbed by the materials to be connected.

6. The unilateral friction riveting method according to claim 5, wherein: The preset rate range is a to ∈a, wherein a represents the feed rate when achieving solid phase connection, and ∈ is determined based on the ratio of the hot yield strength of the material at the solid phase welding temperature and the maximum allowable temperature.

7. The unilateral friction riveting method according to claim 5 or 6, wherein: When a preset termination condition is met, stopping driving the rivet comprises: When the axial feed rate reaches or falls below a preset termination threshold, driving of the rivet is stopped.

8. The method according to claim 7, wherein: The preset termination threshold is an axial feed rate less than 0.1 mm / s.

9. The unilateral friction riveting method according to claim 8, wherein: The rivet is a semi-hollow rivet comprising an integrally formed rivet cover and a rivet body. The inner wall, the outer wall or both of the inner wall and the outer wall of the rivet body are formed into a smooth cylindrical surface or a special-shaped structure selected from at least one of a thread, a knurling, an annular groove and an axial groove.

10. A unilateral friction riveting system comprising: a drive head configured to clamp the rivet and provide drive for axial feed motion and rotational motion of the rivet during the riveting process; as well as A support frame configured to secure the workpieces to be connected, Wherein, the unilateral friction riveting system is configured to implement the unilateral friction riveting method according to any one of claims 1 to 9.

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