Self-piercing riveting system, rivet and self-piercing riveting method

Abstract

The invention discloses a self-piercing riveting system, a rivet and a self-piercing riveting method, and relates to the technical field of riveting, the self-piercing riveting system comprises the rivet, a female die, a blank holder, a punch, an ultrasonic assembly and a control device, the rivet is provided with a head and a leg, the leg is provided with a micro-texture structure, the female die is used for bearing a to-be-riveted metal plate, and the punch is used for punching the to-be-riveted metal plate. The blank holder is used for being matched with the female die to clamp a metal plate to be riveted, the punch is movably arranged in the blank holder and used for pressing a rivet arranged in the blank holder, the ultrasonic assembly is arranged on the punch and used for providing ultrasonic waves acting on the metal plate to be riveted, and the control device is electrically connected with the ultrasonic assembly. According to the self-piercing riveting system, not only can a macroscopic interlocking structure be formed between the rivet and the metal plate, but also a microscopic interlocking structure can be formed between the rivet and the metal plate, so that the connection strength between the rivet and the metal plate is improved, and a microscopic gap between the rivet and the metal plate is reduced.

Description

Technical Field

[0001] This application relates to the field of riveting technology, and in particular to a self-piercing riveting system, rivet, and self-piercing riveting method. Background Technology

[0002] Self-piercing riveting (SPR) is a commonly used sheet metal joining technique. Specifically, the rivet penetrates the upper sheet metal and expands in the lower sheet metal to form an interlocking structure, thereby achieving the connection between the upper and lower sheet metal.

[0003] However, in traditional self-piercing riveting processes, the rivet and metal sheet typically only form a macroscopic interlocking structure, leading to the following problems: 1. Low connection strength: When the interlocking structure is subjected to tensile force, the rivet is prone to dislodgement, resulting in low peel strength; 2. Microscopic gaps exist between the rivet and metal sheet. In service environments requiring long-term vibration, these gaps provide space for relative movement between the rivet and metal sheet, causing fretting wear and resulting in rivet loosening; 3. Microscopic gaps exist between the rivet and metal sheet. In service environments with corrosive media, these gaps provide space for the penetration of corrosive media, affecting the reliability of the rivet; 4. When the metal sheet uses high-strength materials or special structural materials with high deformation resistance, the connection quality is unstable because the metal sheet is not easily deformed. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a self-piercing riveting system, a rivet, and a self-piercing riveting method, which can form a microscopic interlocking structure between the rivet and the metal sheet, thereby improving the connection strength between the rivet and the metal sheet and reducing the microscopic gap between the rivet and the metal sheet.

[0005] The self-piercing riveting system according to a first aspect embodiment of this application includes: A rivet having a head and legs, wherein at least one of the inner and outer surfaces of the legs is provided with a microtextured structure; A die, the die being used to support the metal sheet to be riveted; A pressure ring, which is used to cooperate with the die to clamp the metal sheet to be riveted; A punch is movably disposed within the pressure ring and is used to press down the rivet disposed within the pressure ring to rivet the metal plates to be riveted. An ultrasonic component is disposed on the punch and is used to provide ultrasonic waves acting on the metal sheet to be riveted. A control device, which is electrically connected to the ultrasonic component.

[0006] The self-piercing riveting system according to the embodiments of this application has at least the following beneficial effects: when performing self-piercing riveting on at least two layers of metal sheets, ultrasonic waves acting on the metal sheets are provided by an ultrasonic component. Based on the friction reduction effect of ultrasonic vibration, the resistance of the rivet penetrating the metal sheet can be reduced. In particular, since the legs of the rivet in the self-piercing riveting system of this application are provided with micro-textured structures, the metal sheet undergoes plastic flow under the action of ultrasonic waves and fills the legs of the rivet which are provided with micro-textured structures. This allows the rivet and the metal sheet to form not only a macroscopic interlocking structure but also a microscopic interlocking structure, thereby improving the connection strength between the rivet and the metal sheet and reducing the microscopic gap between the rivet and the metal sheet.

[0007] According to some embodiments of this application, the microtexture structure includes a plurality of spaced grooves, the cross-section of which is arc-shaped.

[0008] According to some embodiments of this application, the depth of the groove is 10 μm to 50 μm.

[0009] According to some embodiments of this application, the width of the groove opening is 1.5 to 3 times the depth of the groove.

[0010] According to some embodiments of this application, the spacing between two adjacent grooves is 2 to 4 times the width of the groove opening.

[0011] According to some embodiments of this application, the self-piercing riveting system further includes a pressure sensor disposed on the punch and capable of acting on the rivet, and the pressure sensor is electrically connected to the control device.

[0012] A rivet according to a second aspect of this application is applied to a self-piercing riveting system according to the first aspect of this application described above.

[0013] The self-piercing riveting method according to a third aspect of this application, applied to the self-piercing riveting system according to the first aspect of this application, includes the following steps: Preparation stage: Stack the metal sheets to be riveted and fix them on the die. Place the rivet at the preset position on the top of the stacked metal sheets to be riveted, with the legs of the rivet facing down. Insertion phase: The punch descends and pushes the rivet through the upper metal plate at a constant speed. During this process, the ultrasonic component is controlled by the control device to provide ultrasonic waves with a first preset frequency and a first preset amplitude to reduce the insertion resistance of the rivet. Expansion and Interlocking Stage: The punch continues to descend to push the rivet deeper into the lower metal sheet. During this process, the ultrasonic component is controlled by the control device to provide ultrasonic waves with a second preset frequency and a second preset amplitude, wherein the second preset frequency is higher than the first preset frequency and the second preset amplitude is higher than the first preset amplitude, so that the part of the metal sheet that contacts the leg of the rivet generates plastic flow and fills the microtexture structure of the leg of the rivet. Pressure holding stage: The punch stops descending and applies a preset pressure to the rivet within a preset time. During this process, the ultrasonic component is shut down by the control device. Retraction phase: The plunger retracts, and the retraction speed of the plunger is less than the downward speed of the plunger.

[0014] According to some embodiments of this application, the first preset frequency is 22kHz to 35kHz, the first preset amplitude is 3μm to 12μm, the second preset frequency is 30kHz to 55kHz, and the second preset amplitude is 10μm to 32μm.

[0015] According to some embodiments of this application, the second preset amplitude is 0.4 to 0.8 times the depth of the groove.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a structural schematic diagram of a self-piercing riveting system according to an embodiment of this application when riveting metal sheets; Figure 2 This is a schematic diagram of the structure of a rivet according to an embodiment of this application; Figure 3 yes Figure 2 Enlarged view of a portion of point A in the middle; Figure 4 yes Figure 2 Enlarged view of a portion of point B in the middle; Figure 5 This is a cross-sectional schematic diagram of a partial structure of a rivet leg according to an embodiment of this application.

[0018] Figure label: Metal sheet a; Rivet 100, head 110, leg 120, groove 121; Die 200; 300mm pressure ring; Punch 400; Ultrasonic component 500. Detailed Implementation

[0019] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] In the description of this application, it should be understood that if directional descriptions are involved, such as up, down, front, back, left, right, etc., indicating the directional or positional relationship based on the directional or positional relationship shown in the accompanying drawings, it is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0021] In the description of this application, if words such as several, greater than, less than, exceeding, above, below, or within appear, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the number itself, and "above," "below," "within," etc. are understood to include the number itself.

[0022] In the description of this application, the use of terms such as "first" and "second" is for the purpose of distinguishing technical features only, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0023] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0024] Reference Figures 1 to 5 The self-piercing riveting system according to a first aspect embodiment of the present application includes a rivet 100, a die 200, a pressure ring 300, a punch 400, an ultrasonic component 500, and a control device.

[0025] Specifically, the rivet 100 has a head 110 and a leg 120. At least one of the inner and outer surfaces of the leg 120 is provided with a microtextured structure. The die 200 is used to support the metal sheet a to be riveted. The pressure ring 300 is used to cooperate with the die 200 to clamp the metal sheet a to be riveted. The punch 400 is movably disposed in the pressure ring 300. The punch 400 is used to press down the rivet 100 disposed in the pressure ring 300 to rivet the metal sheet a to be riveted. The ultrasonic component 500 is disposed in the punch 400. The ultrasonic component 500 is used to provide ultrasonic waves acting on the metal sheet a to be riveted. The control device is electrically connected to the ultrasonic component 500.

[0026] When performing self-piercing riveting on at least two layers of metal sheet a, ultrasonic waves acting on the metal sheet a are provided by ultrasonic component 500. Based on the friction reduction effect of ultrasonic vibration, the resistance of rivet 100 piercing into metal sheet a can be reduced. Since the leg 120 of rivet 100 in the self-piercing riveting system of this application is provided with a micro-textured structure, the metal sheet a undergoes plastic flow under the action of ultrasonic waves and fills the leg 120 of rivet 100 with a micro-textured structure. This allows the rivet 100 and the metal sheet a to form not only a macroscopic interlocking structure but also a microscopic interlocking structure, thereby improving the connection strength between rivet 100 and metal sheet a and reducing the microscopic gap between rivet 100 and metal sheet a.

[0027] On the one hand, based on the acoustoplastic effect brought about by ultrasonic vibration, the microtexture structure of the leg 120 of the rivet 100 is filled by the surrounding plastically flowing metal sheet a material, which can form a large number of micro-anchor points distributed throughout the contact interface between the rivet 100 and the metal sheet a. However, when the macroscopic interlocking structure formed by the traditional self-piercing riveting process is subjected to out-of-plane peel load, the stress is concentrated at a limited number of macroscopic contact points, and the rivet 100 is prone to gradual disengagement. Compared with the macroscopic interlocking structure formed by the traditional self-piercing riveting process, the self-piercing riveting system of this application can not only form a macroscopic interlocking structure between the rivet 100 and the metal sheet a, but also a microscopic interlocking structure. Under the synergistic effect of the microscopic and macroscopic interlocking structures, the out-of-plane peel load can be dispersed into a large number of microscopic interface shear and pull-out stresses, thereby significantly improving the peel strength of the rivet 100.

[0028] On the other hand, the acousto-plastic effect brought about by ultrasonic vibration greatly promotes the diffusion and proximity of metal atoms at the contact interface between the rivet 100 and the metal plate a. When the material of the metal plate a fully fills the microtexture structure of the leg 120 of the rivet 100, the rivet 100 and the metal plate a achieve a large-area tight fit at the microscale, greatly reducing the porosity at the contact interface between the rivet 100 and the metal plate a. This state is close to cold welding or solid-state welding, which not only achieves good airtightness and liquid tightness (without the need for additional sealant), but also the dense contact interface between the rivet 100 and the metal plate a can effectively suppress the initiation and development of fretting wear, thereby significantly extending the service life of the rivet 100 in service environments requiring long-term vibration and in service environments with corrosive media.

[0029] In addition, based on the acoustic-plastic effect brought about by ultrasonic vibration, the deformation resistance of high-strength materials such as high-strength steel and magnesium alloys can be significantly reduced, which broadens the applicable material range of self-piercing riveting process and can ensure the connection quality.

[0030] Specifically, the control device is used to control the start and stop of the ultrasonic component 500, and to control the parameters of the ultrasonic waves provided by the ultrasonic component 500, such as frequency and amplitude. The control device can be located inside or outside the punch 400.

[0031] Specifically, the control device includes a timing controller.

[0032] Reference Figure 1 In some of these embodiments, the ultrasonic component 500 is disposed inside the punch 400.

[0033] It should be noted that in some other embodiments, the ultrasonic component 500 may also be disposed outside the punch 400.

[0034] Specifically, the ultrasonic component 500 includes a piezoelectric ceramic transducer and an amplitude transformer. The specific structure and working principle of the ultrasonic component 500 are well-known technologies and will not be described in detail here.

[0035] Reference Figures 2 to 5 In some of the embodiments, the microtexture structure described above includes a plurality of spaced grooves 121, the cross-section of which is arc-shaped, thereby avoiding stress concentration or material filling difficulties caused by sharp edges.

[0036] Specifically, the grooves 121 are evenly spaced, which helps to ensure the consistency of each area of ​​the contact interface between the rivet 100 and the metal plate a.

[0037] Reference Figure 5In some embodiments, the depth d of the groove 121 is 10 μm to 50 μm. This range ensures that the micro-anchors formed at the contact interface between the rivet 100 and the metal sheet a have sufficient effective mechanical engagement depth. If the depth d of the groove 121 is too shallow (d < 10 μm), the anchoring effect is weak; if the depth d of the groove 121 is too deep (d > 50 μm), the filling difficulty increases dramatically, potentially requiring excessive ultrasonic energy, which may lead to material defects.

[0038] Reference Figure 5 In some embodiments, the width w of the groove 121 is 1.5 to 3 times the depth d of the groove 121, i.e., 1.5d ≤ w ≤ 3d. A wider groove 121 facilitates the smooth flow of material into the groove 121 during the initial stage of ultrasonic vibration. The ratio of the width w of the groove 121 to the depth d of the groove 121 must be kept reasonable to ensure sufficient structural strength at the groove 121.

[0039] Reference Figure 3 and Figure 5 In some embodiments, the distance p between two adjacent grooves 121 is 2 to 4 times the width w of the groove opening of the groove 121, i.e., 2w ≤ p ≤ 4w. The distance p between two adjacent grooves 121 determines the density of micro-anchor points per unit area at the contact interface between the rivet 100 and the metal sheet a. If the micro-anchor points are too dense, the material walls between adjacent grooves 121 may become too thin, leading to shear failure; if the micro-anchor points are too sparse, the advantage of stress dispersion cannot be fully utilized.

[0040] Specifically, the dimensional parameters of the aforementioned microtexture structure are determined based on a combination of microscale plastic forming theory and the attenuation characteristics of ultrasonic energy transmission on the surface. For example, the effective depth of ultrasonic vibration is typically on the order of tens of micrometers, which matches the depth range of the microtexture structure, ensuring that the vibrational energy can effectively act on the material filling process.

[0041] In some embodiments, the self-piercing riveting system also includes a pressure sensor disposed on the punch 400 and capable of acting on the head 110 of the rivet 100. The pressure sensor is electrically connected to a control device. The pressure sensor is used to monitor the riveting pressure and provide feedback to the control device to assist the control device in determining the riveting stage and any unexpected situations.

[0042] The rivet 100 according to an embodiment of this application is applied to the self-piercing riveting system described above.

[0043] The self-piercing riveting method according to an embodiment of this application, applied to the aforementioned self-piercing riveting system, includes the following steps: Preparation stage: Stack the metal sheet a to be riveted and fix it on the die 200. Place the rivet 100 at the preset position on the top of the stacked metal sheet a to be riveted, and make the leg 120 of the rivet 100 face down. During the insertion phase: The punch 400 moves downward and pushes the rivet 100 through the upper metal plate a at a constant speed. During this process, the ultrasonic component 500 is controlled by the control device to provide ultrasonic waves with a first preset frequency and a first preset amplitude to reduce the insertion resistance of the rivet 100. Specifically, the friction reduction effect of ultrasonic vibration is used to reduce the insertion resistance of the rivet 100 and prevent the rivet 100 from twisting or deflecting during the insertion process. Expansion and Interlocking Stage: The punch 400 continues to descend to push the rivet 100 deeper into the lower metal plate a. During this process, the ultrasonic component 500 is controlled by the control device to provide ultrasonic waves with a second preset frequency and a second preset amplitude, wherein the second preset frequency is higher than the first preset frequency and the second preset amplitude is higher than the first preset amplitude, so that the part of the metal plate a in contact with the leg 120 of the rivet 100 generates plastic flow and fills the microtexture structure of the leg 120 of the rivet 100. Specifically, the instantaneous yield stress of the metal plate a is significantly reduced by utilizing the acoustic plastic effect, so that the part of the metal plate a in contact with the leg 120 of the rivet 100 generates plastic flow and fills the microtexture structure of the leg 120 of the rivet 100, thereby forming an interlocking structure at the micro level. Pressure holding stage: The punch 400 stops descending and applies a preset pressure to the rivet 100 within a preset time. During this process, the ultrasonic component 500 is shut down by the control device. Specifically, the rivet 100 and the metal plate a are further compacted under the pressure provided by the punch 400, so that the rivet 100 and the metal plate a are tightly bonded. At the same time, the hardness of the metal plate a is restored, thereby fixing the rivet 100. Retraction phase: The punch 400 retracts, and the retraction speed of the punch 400 is less than the downward speed of the punch 400. Specifically, the retraction speed of the punch 400 is kept low to avoid material elastic rebound or interface damage caused by the punch 400 retracting too quickly.

[0044] In some of these embodiments, the first preset frequency is 22kHz to 35kHz, the first preset amplitude is 3μm to 12μm, the second preset frequency is 30kHz to 55kHz, and the second preset amplitude is 10μm to 32μm.

[0045] In some of these embodiments, the second preset amplitude is 0.4 to 0.8 times the depth d of the groove 121.

[0046] Specifically, the process parameters of the self-piercing riveting method of this application are shown in the following table:

[0047] Specifically, the explanations and technical basis for the table above are as follows: Frequency selection criteria: Insertion stage: The main goal is to reduce friction and prevent rivet 100° deviation. Therefore, a medium to low frequency (22kHz to 35kHz) is used to ensure energy transfer while avoiding premature excessive plastic flow of material.

[0048] Expansion and Interlocking Stage: The main goal is to induce acoustoplastic effects and promote material flow and filling; therefore, mid-to-high frequencies (30kHz–55kHz) are used. The higher the strength and hardness of the material, the higher the required frequency, to activate dislocation motion with more concentrated vibrational energy.

[0049] The insertion and expansion / interlocking stages employ different ultrasonic parameters because the two stages address different physical problems, thus relying on different ultrasonic mechanisms. Specifically, the insertion stage primarily utilizes the friction-reducing (lubricating) effect of ultrasonic vibration to lower interfacial friction and ensure 100% perpendicularity of the rivet. The expansion / interlocking stage, on the other hand, primarily utilizes the acousto-plastic softening effect to significantly reduce material flow stress and promote micro-filling. Parameter design (frequency, amplitude) strictly serves the primary objectives of each stage. In the insertion stage, ultrasonic vibration is mainly used to improve interfacial conditions; in the expansion / interlocking stage, it is primarily used to alter the bulk plastic behavior of the material.

[0050] Amplitude selection criteria: Penetration phase: Low amplitude (3μm~12μm) is used to provide sufficient friction reduction while maintaining the stability of the punch 400.

[0051] Expansion and Interlocking Stage: High amplitude (10μm~32μm) is used. The amplitude A needs to match the depth d (10μm~50μm) of the microtexture structure of the leg 120 of the rivet 100. The amplitude A needs to be slightly smaller than the depth d of the microtexture structure of the leg 120 of the rivet 100 to ensure that the vibration energy can effectively act on the contact interface between the material and the microtexture structure, forcing the material to undergo microscopic plastic flow and fill the groove 121.

[0052] (1) Coupling relationship between vibration displacement and texture geometry: Ultrasonic vibration causes reciprocating displacement on the surface of rivet 100. If the amplitude A is much smaller than the depth d of the groove 121 (e.g., A < 0.3d), the "stroke" of the vibration is insufficient to effectively push the material into the bottom of the groove 121. The material may only accumulate near the opening of the groove 121, resulting in incomplete filling and creating a void at the bottom of the groove 121. If the amplitude A is greater than or equal to the depth d of the groove 121 (A ≥ d), although it can cover the entire groove depth, it will lead to two problems: first, energy is wasted, with some vibration displacement becoming "idle stroke"; second, it may cause excessive forging or even cutting of the material at the edge of the groove 121, destroying the formed micro-interlocking structure, or causing work hardening of the material, which is detrimental to bonding.

[0053] (2) Driving mechanism of material flow: The essence of the material-filled microtexture structure is the micro-upsetting and micro-extrusion process under vibration assistance. The material needs to overcome the friction between itself and the groove wall of the groove 121 and flow into the groove.

[0054] The optimal ratio between amplitude A and the depth d of groove 121 stems from a simplified energy balance consideration: the work done on the material by vibration in one cycle should be sufficient to overcome the plastic deformation work and frictional work required for the material to flow into a characteristic depth (related to d). Based on the balance between effective vibration energy transfer and the material flow driving mechanism, after verification through process experiments and simulations, the ratio of amplitude A to the depth d of groove 121 should be controlled between 0.4 and 0.8 (i.e., A≈0.4d~0.8d). This ratio range ensures that the vibration displacement effectively drives the material to flow into the groove 121, while avoiding energy waste or damage to the already formed structure.

[0055] (3) Compromises in engineering practice: An amplitude A of approximately 0.4d to 0.8d is a validated engineering window. In practical applications, for materials with good flowability (such as soft aluminum alloys), a lower amplitude A (e.g., 0.4d to 0.6d) can be used to fully utilize the material's inherent flowability; for materials that are difficult to deform (such as high-strength steel), a higher amplitude A (e.g., 0.6d to 0.8d) is required to provide a stronger vibration driving force.

[0056] Another reason why the amplitude A is slightly smaller than the depth d of the microtexture structure of the leg 120 of the rivet 100 is to take into account the actual response and thermal management of the vibration system. Slightly smaller amplitude A than the depth d of the microtexture structure of the leg 120 of the rivet 100 ensures effective drive while keeping the system operating in a more stable range, avoiding impacts on the piezoelectric ceramic transducer caused by sudden load changes (such as the instant of complete filling).

[0057] Duration selection criteria: Penetration phase: The duration is mainly determined by the thickness of the metal plate a and the penetration speed. The greater the thickness of the metal plate a and the harder the material, the longer the time required.

[0058] Expansion and Interlocking Phase: The duration must ensure sufficient flow and filling time for the material, which depends on the material's fluidity, thickness, and desired interlocking depth. Thicker, more difficult-to-deform materials require longer ultrasonic treatment times (typically 3–5 seconds).

[0059] Relationship between materials and parameters: Aluminum alloys have good plasticity and low yield strength, so the required vibration energy (frequency and amplitude) is relatively moderate.

[0060] High-strength steel has high yield strength and large deformation resistance, requiring higher frequencies and amplitudes to provide sufficient acousto-plastic softening energy.

[0061] Magnesium alloys have poor plasticity and require relatively conservative frequencies and amplitudes to avoid cracking under vibration. The focus should be on using vibration to improve their limited plasticity.

[0062] Dissimilar materials: The parameters need to be compromised or emphasize the more difficult material to form (usually high-strength steel) to ensure that the interface of both materials can form an effective interlock.

[0063] The timing controller can be programmed to automatically call the corresponding parameter set (as shown in the table above) based on the input material combination and thickness information, so as to achieve intelligent, stable and high-quality riveting.

[0064] Data support: The typical vibration frequency used in ultrasonic machining (USM) is usually greater than or equal to 20 kHz, and the amplitude range is 5 μm to 50 μm. This matches the frequency, micrometer-level amplitude, and microtexture scale set in this application, which in principle confirms the effectiveness and universality of this parameter range in engineering applications.

[0065] Formula reference: (1) Ultrasonic softening item The degree of acoustic softening is measured by a factor called the "ultrasonic softening term". To quantify it, it is directly multiplied by the strength of the slip system. Above. Its expression is: ; In the formula: Ultrasonic intensity is an input variable.

[0066] The acoustic softening coefficient needs to be calibrated experimentally. The calibration value is 0.00216. .

[0067] Acoustic softening index: Used to describe the nonlinear relationship between softening and strength. (The value is...) =1.0 indicates linear softening.

[0068] (2) Calculation of ultrasonic intensity ultrasonic intensity Calculated by the following formula: ; ; In the formula: Sound pressure level.

[0069] ρ: Material density.

[0070] c: Velocity of sound in the material.

[0071] v: The amplitude of the vibration velocity of the particle, which is obtained in the finite element method by nodal displacement and time derivative.

[0072] (3) The complete form of the embedded constitutive model The revised slip strain rate equation (i.e., how the "softening" of the material affects plastic flow) is as follows: ; Key mechanisms: As an intensity attenuation factor, when ultrasound is applied ( )hour, .

[0073] A smaller denominator leads to accelerated slip, which makes it possible to achieve the same decomposed shear stress. Below, slip strain rate A significant increase, macroscopically manifested as a decrease in yield stress and easier occurrence of plastic deformation, i.e., "acoustic softening".

[0074] The optimal duration of high-amplitude ultrasonic vibration during the expansion and interlocking phases This is determined by both the material's acoustic softening properties and the requirements for microtexture filling. Its theoretical basis can be stated as follows: ; in, The time required for a material to completely fill the microtexture without ultrasonic treatment can be determined through experiments or simulations. A(I) is the strain rate amplification factor at a selected ultrasonic intensity I, and is related to the acoustic softening coefficient of the material. And the rate sensitivity index m is related.

[0075] The optimal duration of ultrasound treatment can be determined by the following steps: 1. Benchmark Determination: A riveting experiment was conducted on the target material and rivet 100 without ultrasonic treatment. Metallographic section observation was used to determine the shortest static pressure holding time required for the material to completely fill the microtexture, denoted as [reference needed]. .

[0076] 2. Obtaining the softening coefficient: The acoustic softening coefficient is obtained through standard acoustic plasticity tests of the material (such as ultrasonic-assisted micro-compression tests) or by consulting publicly available acoustic softening performance data for the material. And the strain rate sensitivity index m, and then the strain rate amplification factor A(I) under a specific ultrasonic intensity I is calculated.

[0077] 3. Theoretical calculation: Calculate according to the above formula. .

[0078] 4. Process window verification: Based on, at 0.8 times Up to 1.5 times Process tests are conducted within a specified time frame, with the final process time determined by the criteria of the joint pull-out strength reaching the plateau region and the microstructure filling rate exceeding 95%. This time is typically 2 to 5 seconds.

[0079] Based on the above relationships, the vibration time can be precisely controlled according to the preset ultrasonic power (intensity), ensuring microscopic interlocking is achieved within the shortest effective time, while avoiding thermal effects or interference with the subsequent material hardening and recovery process caused by excessive vibration. The optimal ultrasonic time is usually located between... Within the time window defined by the determined lower limit and the upper limit considering thermal management and process efficiency.

[0080] As examples, two embodiments of this application are listed below: 1. Connection of the same material 1. Set conditions Connected plates: Upper sheet material: AA6061~T6 aluminum alloy, 2.0mm thick.

[0081] Lower layer material: AA6061~T6 aluminum alloy, 2.5mm thick.

[0082] Material properties: density ρ=2700kg / m³, sound velocity c≈5100m / s, yield strength≈276MPa, good plasticity.

[0083] 100 microtexture parameters of the rivet: The rivet 100 has a pre-fabricated microtexture on the leg 120 surface, with a depth of 25μm and a periodic arrangement.

[0084] Ultrasonic vibration system parameters: The piezoelectric ceramic transducer has an output frequency range of 20kHz to 60kHz and an amplitude range of 3μm to 32μm.

[0085] 2. Selection and Calculation of Process Parameters (1) Penetration stage Frequency: Select 25kHz (mid-low frequency, to ensure energy transfer and avoid premature plastic flow).

[0086] Amplitude: Select 8μm (low amplitude, providing friction reduction effect).

[0087] Duration: The time required to pierce through the upper layer of material.

[0088] Assuming a punch with a 400mm diameter descending speed of 10mm / s, the time required to pierce a 2.0mm thick sheet metal is: ; (2) Expansion and Interlocking Stage Frequency: Select 40kHz (mid-to-high frequency, to promote sound plasticity).

[0089] Amplitude: Select 20μm (matching the microtexture depth of 25μm).

[0090] Ultrasonic intensity calculation: According to the formula: ; in: ; The vibration velocity amplitude v can be estimated from the amplitude A and the angular frequency ω: ; Substituting A = 20μm = 2 × 10 -5 m, f = 40 × 10³ Hz: ; but: ; ; Calculation of ultrasonic softening term: Use the formula: ; Aluminum alloy is acceptable ≈0.00216mm² / mW=2.16×10 -6 m² / W, =1.0 (linear softening).

[0091] Substitute: ; That is, the material strength is reduced to about 25.1%, which significantly promotes plastic flow.

[0092] Calculation of optimal ultrasound treatment time: Assume the time required for complete filling of the microtexture without ultrasound. =8s (obtained through experiments).

[0093] The strain rate amplification factor A(I) can be approximated as: ; but: ; Process window verification: Take 0.8 to 1.5 times, that is, 1.61 to 3.02 s.

[0094] Finally, t=2.5s was selected (balancing filling effect and process efficiency).

[0095] (3) Pressure holding stage Holding time: 3s (to further compact the material and restore some of its hardness).

[0096] Holding pressure: Maintain 80% of the peak pressure at 400 pressure on the punch.

[0097] (4) Retreat phase Retraction speed: 2mm / s (to avoid elastic rebound).

[0098] 3. Summary of Process Sequence

[0099] II. Joining dissimilar materials such as high-strength steel and aluminum alloy 1. Set conditions Connected plates: Upper plate: DP780 high-strength steel, 1.5mm thick, ρ≈7800kg / m³, c≈5900m / s, yield strength≈780MPa.

[0100] Lower layer material: AA5052 aluminum alloy, thickness 2.0mm, ρ≈2680kg / m³, c≈5100m / s.

[0101] 100 microtexture parameters of the rivet: The microtexture depth is 35μm (to adapt to the difficult deformation characteristics of high-strength steel).

[0102] Ultrasonic vibration system parameters: piezoelectric ceramic transducer output frequency range: 20~60kHz, amplitude range: 3~32μm.

[0103] 2. Selection and calculation of process parameters (focusing on high-strength steel) (1) Penetration stage (penetrating high-strength steel) Frequency: 28kHz (mid-low frequency).

[0104] Amplitude: 10μm (slightly higher than the aluminum alloy case, due to the high friction coefficient of high-strength steel).

[0105] Duration: Penetration of 1.5mm high-strength steel, speed 8mm / s: ; (2) Expansion and interlocking stage (mainly applied to high-strength steel) Frequency: Select 50kHz (high frequency, activates dislocation motion).

[0106] Amplitude: Select 28μm (matching microtexture depth 35μm).

[0107] Ultrasonic strength calculation (using high-strength steel as an example): v=28×10 -6 ×2π×5×10 4 ≈8.80m / s; ≈7800×8.80×5900≈4.05×10 8 Pa; ≈(4.05×10 8 )² / (7800×5900)≈3.56×10 9 W / m²; Calculation of ultrasonic softening term: High-strength steel It is relatively large, let's assume it's 3.5 × 10⁻⁶. -6 m² / W (requires experimental calibration) =1.0.

[0108] Substitute into the above formula: ≈1-3.5×10 -6 ×3.56×10 9 ≈1-12.46; Set to 0 (in practice, it should be limited to a reasonable range; here it indicates that the softening effect is extremely significant, but in actual applications, the strength should be controlled to be no less than 10%).

[0109] Correction: If the limit is minimal =0.1, then the actual effective strength is 10%.

[0110] Calculation of optimal ultrasound treatment time: Assumption (High-strength steel without ultrasonic filling) = 12s.

[0111] A(I) can be estimated as 1 / ≈10 (if) =0.1).

[0112] but: ; Process window: 0.96~1.8s, take t=1.5s.

[0113] (3) Pressure holding stage Holding time: 4s (due to the large springback of high-strength steel).

[0114] Holding pressure: Maintain 85% of peak pressure.

[0115] (4) Retreat phase Retraction speed: 1.5mm / s (slower to prevent interface damage).

[0116] 3. Summary of Process Sequence

[0117] The two embodiments described above demonstrate that the parameter selection method and calculation logic provided in this application can clearly guide the implementation of specific processes and achieve the expected micro-filling and joint performance improvement effects.

[0118] In the description of this specification, the use of terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," and "some examples" indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. 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.

[0119] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A self-piercing riveting system characterized by, The rivet has a head and a leg, at least one of the inner surface and the outer surface of the leg is provided with a micro-texture structure; a concave die for supporting the metal sheet to be riveted; a pressure ring for clamping the metal sheet to be riveted in cooperation with the concave die; a punch movably arranged in the pressure ring, the punch is used to press the rivet arranged in the pressure ring to rivet the metal sheet to be riveted; an ultrasonic assembly arranged in the punch, the ultrasonic assembly is used to provide ultrasonic waves acting on the metal sheet to be riveted; a control device electrically connected with the ultrasonic assembly. The micro-texture structure comprises a plurality of spaced grooves, the cross section of the groove is arc-shaped.

2. The self-piercing rivet system of claim 1, wherein, The depth of the groove is 10-50 microns.

3. The system of claim 2, wherein the punch is configured to be moved in a direction that is substantially perpendicular to the direction of movement of the anvil. The width of the groove notch is 1.5-3 times the depth of the groove.

4. The system of claim 3, wherein the punch is configured to be moved in a direction that is substantially perpendicular to the direction of movement of the anvil. The distance between the two adjacent grooves is 2-4 times the width of the groove notch.

5. The system of claim 4, wherein the punch is configured to be moved in a direction that is substantially perpendicular to the direction of movement of the anvil. The self-piercing riveting system further comprises a pressure sensor arranged in the punch and capable of acting on the rivet, the pressure sensor is electrically connected with the control device.

6. The self-piercing rivet system of claim 1, wherein, The rivet is applied to the self-piercing riveting system.

7. A rivet in a self-piercing riveting system as claimed in any one of claims 1 to 6, characterized in that The self-piercing riveting system of any one of claims 2-5 comprises the following steps:

8. A method of self-piercing riveting, characterized in that Preparation stage: stack and fix the metal sheet to be riveted on the concave die, place the rivet at the top of the stacked metal sheet to be riveted at a predetermined position, and make the leg of the rivet downward; Piercing stage: the punch goes down to push the rivet to pierce the upper metal sheet at a constant speed, in the process, the control device controls the ultrasonic assembly to provide ultrasonic waves with a first predetermined frequency and a first predetermined amplitude to reduce the piercing resistance of the rivet; Expansion and interlocking stage: the punch continues to go down to push the rivet to penetrate into the lower metal sheet, in the process, the control device controls the ultrasonic assembly to provide ultrasonic waves with a second predetermined frequency and a second predetermined amplitude, wherein the second predetermined frequency is higher than the first predetermined frequency, and the second predetermined amplitude is higher than the first predetermined amplitude, so that the part of the metal sheet in contact with the leg of the rivet produces plastic flow and fills the micro-texture structure of the leg of the rivet; Pressure maintaining stage: the punch stops going down and acts on the rivet at a predetermined pressure for a predetermined time, in the process, the control device closes the ultrasonic assembly; Retreat stage: the punch retreats, wherein the retreat speed of the punch is less than the down speed of the punch. The first predetermined frequency is 22-35 kHz, the first predetermined amplitude is 3-12 microns, the second predetermined frequency is 30-55 kHz, and the second predetermined amplitude is 10-32 microns.

9. The method according to claim 8, wherein The second predetermined amplitude is 0.4-0.8 times the depth of the groove.

10. The method of self-piercing riveting according to claim 8, characterized in that ​

Images