Riveting control method based on technological process curve

Abstract

The invention provides a riveting control method based on a technological process curve, and the method comprises the steps: collecting at least one piece of technological physical quantity data reflecting the riveting feeding process in real time at a rivet leg expansion and locking stage in the riveting feeding process of a rivet, and constructing a corresponding technological process curve; based on different types of physical quantity characteristics related to the rivet forming end point and the connector head height in the technological process curve, at least one stop criterion used for judging the riveting forming end point is constructed, the stop criteria are monitored, and each stop criterion comprises an activation condition and a stop judgment condition; after any activation condition is met, judging a corresponding judgment stopping condition; and when any stop judgment condition is met, it is judged that the current riveting process reaches the forming end point state, and the riveting feeding process is controlled to stop. According to the invention, the head height consistency can be realized only through tail-stage control, the control complexity is obviously reduced, the connection quality is improved, and under-connection and over-damage are prevented.

Description

Technical Field

[0001] This disclosure relates to the field of metal plastic joining technology, and in particular to a riveting control method based on process curves. Background Technology

[0002] In the manufacturing of lightweight alloy structural components, mechanical joining processes such as flat die self-piercing friction riveting (F-SPR) are widely used due to their high connection quality and high degree of automation. In mass continuous production, these processes generally employ a control mode based on preset fixed parameters (such as displacement and force).

[0003] However, in large-scale riveting processes, fixed process parameters are difficult to adapt to the dynamically changing actual forming process due to inherent factors such as fluctuations in material properties, changes in equipment status, and slight differences in the dimensions of connecting components. This often leads to insufficient connection forming or overfeeding, resulting in insufficient connection strength or workpiece damage, seriously affecting product consistency and incurring additional costs.

[0004] Therefore, for flat die F-SPR and joining processes with similar process characteristics, there is an urgent need for a method that can sense the joining status in real time during the forming process and dynamically adjust the control strategy to achieve high precision and high stability control of the joining endpoint quality (especially the head height). Summary of the Invention

[0005] This disclosure provides a riveting control method based on a process curve. In the mass production of lightweight alloy components for mechanical connections (such as riveting and rotary friction connections), due to factors such as material property dispersion and equipment condition fluctuations, traditional control methods based on fixed displacement, pressure, or energy thresholds are difficult to continuously match the actual forming process, easily leading to under-forming or over-forming of the connection, resulting in insufficient joint performance consistency, decreased sealing reliability, and increased rework rate.

[0006] In a first aspect, embodiments of this disclosure provide a riveting control method based on a process curve, applied to a process of connecting plates by rotating and feeding a rivet. The method includes: during the rivet leg expansion and locking stage of the riveting feed process, real-time acquisition of at least one process physical quantity data reflecting the riveting feed process, and construction of a corresponding process curve; based on different types of physical quantity characteristics in the process curve related to the rivet forming endpoint and the joint head height, construction of at least one stop criterion for determining the riveting forming endpoint, and monitoring of the stop criterion, wherein each stop criterion includes: The activation condition is used to define the process stage at which the stop criterion takes effect, thereby initiating monitoring of the forming process; and the stop judgment condition is used to determine, after the activation condition is met, whether the current riveting forming state has reached the forming endpoint corresponding to the preset head height threshold range based on real-time data of the process curve, so as to determine whether to terminate the riveting feed; after any of the activation conditions is met, the corresponding stop judgment condition is executed; when any stop judgment condition is met, it is determined that the current riveting process has reached the forming endpoint state, and the riveting feed process is controlled to stop, so as to obtain a riveted joint that meets the preset head height threshold range.

[0007] In some embodiments, the different types of physical quantity characteristics include at least one of the following: a combination of characteristics based on riveting feed displacement and riveting pressure; a combination of characteristics based on riveting feed displacement and riveting torque; a characteristic based on the rate of change of riveting pressure; and a combination of characteristics based on riveting feed displacement, riveting pressure, and time.

[0008] In some embodiments, the plurality of stop criteria include a displacement compensation criterion, which is set based on a characteristic combination of riveting feed displacement, riveting pressure, and time, and includes corresponding activation conditions and stop judgment conditions, wherein: the activation condition is: the riveting feed displacement during the riveting feed process reaches the main feed displacement value; the stop judgment condition includes: after satisfying the activation condition, entering the compensation riveting feed stage; in the compensation riveting feed stage, determining whether at least one of the first to third sub-conditions is satisfied; when at least one of the first to third sub-conditions is satisfied, issuing a stop signal to terminate the riveting feed process, wherein the first sub-condition is that the cumulative feed displacement since the start of the compensation riveting feed stage reaches a preset holding pressure feed displacement, the second sub-condition is that the real-time riveting pressure reaches a preset maximum holding pressure output value, and the third sub-condition is that the duration of the compensation riveting feed stage reaches a preset holding pressure time.

[0009] In some embodiments, the plurality of stop criteria include pressure threshold criteria, which are set based on a characteristic combination of riveting feed displacement and riveting pressure, and include corresponding activation conditions and stop judgment conditions, wherein: the activation condition is: the riveting feed displacement during the riveting feed process reaches the pressure stop start displacement; if it is determined that the real-time riveting pressure signal exceeds the preset pressure threshold, a stop signal is issued to terminate the riveting feed process.

[0010] In some embodiments, the plurality of stop criteria include a torque threshold criterion, which is set based on a characteristic combination of riveting feed displacement and riveting torque, and includes a corresponding activation condition and a stop judgment condition, wherein: the activation condition is: the riveting feed displacement during the riveting feed process reaches the torque stop start displacement; the stop judgment condition is: after the activation condition is met, if it is determined that the real-time riveting torque signal exceeds a preset torque threshold, a stop signal is issued to terminate the riveting feed process.

[0011] In some embodiments, the plurality of stop criteria include a pressure change rate inflection point criterion, which is set based on the characteristics of the riveting pressure change rate and includes corresponding activation conditions and stop judgment conditions, wherein: the activation condition is: the riveting pressure signal reaches the inflection point stop starting pressure; the stop judgment condition is: after the activation condition is met, the riveting pressure rise rate is calculated; if the riveting pressure rise rate exceeds a preset rate threshold, a riveting pressure inflection point is detected, and the current riveting pressure value is recorded as the inflection point pressure value; if the inflection point pressure value has been recorded, and it is determined that the real-time riveting pressure signal exceeds the sum of the inflection point pressure value and a preset compensation pressure value, a stop signal is issued to terminate the riveting feed process.

[0012] In some embodiments, at least one process physical quantity data reflecting the riveting process is collected in real time, and a corresponding process curve is constructed, including: real-time collection of riveting feed displacement, riveting pressure and riveting torque; constructing functional relationships between the riveting feed displacement, riveting pressure and riveting torque and time and with the riveting feed displacement, respectively, to form the process curve.

[0013] In some embodiments, the method further includes: if the riveting feed displacement reaches the riveting feed reference value and none of the multiple stop criteria are triggered, then control the continued feeding of the positive compensation displacement.

[0014] In some embodiments, the riveting feed reference value is the leg length of the rivet.

[0015] In some embodiments, the riveting feed process includes a flat die self-piercing friction riveting process.

[0016] This disclosure collects process curves during the riveting feed and analyzes the characteristics of multiple physical quantities such as pressure, torque, and displacement at the end of the riveting feed stage to construct a composite stop criterion based on activation and stop judgment conditions. This method initiates endpoint judgment only during the rivet leg expansion and locking stages, eliminating the need for continuous adjustment throughout the entire process. It adapts to fluctuations in material properties and equipment status, accurately identifying key features and triggering stop control at the final forming stage, thereby achieving high-precision and high-consistency control of connection endpoint parameters (such as riveting joint height). This simplifies the control logic while effectively improving connection quality stability and production yield, and reducing the probability of under-forming and excessive damage. Attached Figure Description

[0017] Figure 1 This is a flowchart of a connection control method based on a process curve according to an embodiment of the present disclosure; Figure 2 This is a schematic diagram of the control logic flow for the device to perform the connection forming process in an embodiment of this disclosure; Figure 3 This is a schematic diagram of the stopping logic for stop condition 1 in this embodiment of the present disclosure; Figure 4 This is a schematic diagram of the stopping logic based on the pressure threshold in the embodiments of this disclosure; Figure 5 This is a schematic diagram of the stopping logic for stopping condition 3 based on the torque threshold in this embodiment of the present disclosure; Figure 6 This is a schematic diagram of the stopping logic for stopping condition 4 based on the inflection point of the pressure change rate in this embodiment. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0019] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary 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 enable those skilled in the art to fully understand the scope of this disclosure.

[0020] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0021] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” 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 stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0023] The embodiments described herein can be described with reference to plan views and / or cross-sectional views using the ideal schematic diagrams of this disclosure. Therefore, the example illustrations can be modified according to manufacturing techniques and / or tolerances. Therefore, the embodiments are not limited to those shown in the drawings, but include modifications to configurations formed based on manufacturing processes. Therefore, the areas illustrated in the drawings are schematic in nature, and the shapes of the areas shown in the figures illustrate specific shapes of areas of an element, but are not intended to be limiting.

[0024] Unless otherwise specified, all terms used herein (including technical and scientific terms) 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 this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0025] Unless otherwise specified in this disclosure, the following technical terms shall be interpreted as follows: Double-sided friction riveting is a composite joining process that generates frictional heat through rotational feeding on one side (the rivet side), while the other side (the bottom) is supported and constrained by a die (either a concave or flat die). This causes the rivet and the materials to be joined to undergo plastic deformation under the constraint of the die, ultimately forming a mechanical locking and interface solid-state welding. Its core feature is the synergistic effect of "in-situ frictional heat generation + die-constrained deformation".

[0026] The feed rate refers to the total displacement of the bilateral friction rivet along its own axis during the F-SPR process.

[0027] Head height refers to the vertical height of the head of the double-sided friction rivet above the surface of the upper plate after riveting is completed.

[0028] Back height refers to the vertical height formed by the material deformation protruding from the lower surface of the lower plate (the side in contact with the mold) after riveting is completed.

[0029] Cavity depth refers to the depth of the rivet's inner cavity, the length from the tip of the rivet to the deepest part of the cavity.

[0030] To address the issues of insufficient forming consistency and the tendency for underforming or overforming in the mass joining of lightweight alloy structural components due to fluctuations in material properties, equipment conditions, or connector parameters, this disclosure provides a joining control method based on process curves. This method, based on preset joining process parameters, collects and analyzes process signals such as pressure, torque, and displacement generated during the joining process in real time, extracts characteristic information from the process curves, and judges the joining forming state accordingly. When necessary, it intervenes in the joining process beforehand to improve its controllability.

[0031] The above methods can effectively reduce the probability of incomplete or over-formed connections caused by process fluctuations, improve the consistency and stability of connection forming dimensions (such as rivet height) under mass production conditions, and are suitable for connection scenarios of lightweight alloy structural parts with high connection quality requirements.

[0032] In mass production, for joining processes such as self-piercing riveting (SPR) and rotary friction welding (FEW) that rely on mechanical force to achieve material forming, the consistency of the final quality (such as riveting joint height and weld depth) is crucial to product performance. Due to inherent factors such as material fluctuations and changes in equipment condition, it is difficult to consistently guarantee forming quality by using preset fixed parameters (displacement, force, energy), which can easily lead to defects such as "underforming" or "over-damaging".

[0033] The core of this disclosure lies in the innovative proposal of a universal connection control strategy that does not rely on a single fixed parameter. This method monitors and analyzes the process curves of key physical quantities during the connection process (such as pressure-displacement curves, torque-displacement curves, pressure-time curves, etc.) in real time, and identifies characteristic signals that can reliably characterize that the material has been fully formed and entered a rigid contact state (such as a monotonous and rapid increase in pressure or torque, a specific rate of change inflection point, etc.), and dynamically and adaptively triggers a feed stop command accordingly.

[0034] Specifically, this disclosure designs at least four stop determination conditions that can be activated independently or in combination. The system monitors the relevant process curves in real time during the connection process and issues a stop signal when any of the activation conditions is met, thereby achieving adaptive determination of the forming endpoint.

[0035] The stopping determination conditions include: 1) After reaching the preset basic feed displacement, the system enters the compensation feed stage, and simultaneously monitors the feed displacement, pressure and time parameters during this stage; when any of the following conditions are met: the compensation displacement is completed, the pressure reaches the preset upper limit, or the feed duration reaches the preset time threshold, a stop command is triggered. 2) When the feed displacement reaches the preset displacement, monitor the real-time pressure signal. When the pressure exceeds the preset pressure threshold, trigger a stop command. 3) When the feed displacement reaches the preset displacement, monitor the real-time torque signal. When the torque exceeds the preset torque threshold, trigger a stop command. 4) After the real-time pressure reaches the preset pressure value, identify the characteristic inflection point where the pressure changes from a gradual change to a sharp increase, and trigger a stop command when the pressure exceeds the "inflection point pressure value plus compensation pressure value".

[0036] Users can flexibly select and enable one or more of the above-mentioned stop conditions in the operation interface according to specific process requirements. The conditions are logically ORed, thereby constructing a composite endpoint determination mechanism with high robustness and fault tolerance.

[0037] Furthermore, to address the issue that relying solely on early stopping may lead to insufficient feed, this disclosure introduces a positive compensation mechanism and sets an independent compensation amount parameter. The system uses the feed target corresponding to the basic process parameters as a benchmark. If any stopping condition is not met when the benchmark target is reached, the feed is allowed to continue increasing within a controlled range up to the upper limit of the compensation amount, thereby achieving bidirectional adaptive adjustment for both underforming and overforming deviations.

[0038] In summary, this disclosure provides a general adaptive connection control method and system based on process curve characteristic signals. This method, through the synergistic effect of a configurable multi-condition composite judgment mechanism and a bidirectional intelligent compensation strategy, overcomes the limitations of traditional fixed-parameter control methods, providing a reliable technical solution for large-scale solid-state connection production requiring high-consistency endpoint quality control.

[0039] In this embodiment of the disclosure, the riveting feed process can be divided into multiple consecutive process stages, including: piercing and material filling stage; interface formation and advancement stage; rivet leg expansion and mechanical locking stage; and final forming and pressure holding stage.

[0040] In different stages of the process, the process curves (such as pressure, torque, and displacement) exhibit different characteristics. For example, during the expansion and locking stages of the pin legs, the torque signal begins to rise significantly; during the final forming and holding stages, the pressure curve shows a monotonically increasing trend or a significant inflection point in the rate of change.

[0041] The monitoring strategy disclosed herein is as follows: monitoring is initiated after the riveting feed process enters the leg expansion and locking stage, and the forming endpoint is determined during the final forming and holding pressure stages. By setting activation conditions corresponding to each process stage, different stop criteria are made effective in the corresponding stages, thereby achieving precise identification of the forming endpoint.

[0042] Figure 1This is a flowchart of a connection control method based on process curves according to an embodiment of the present disclosure.

[0043] Firstly, referring to Figure 1 This disclosure provides a riveting control method based on a process curve, applied to a process of connecting plates by rotating and feeding rivets. The method includes: S11. During the rivet leg expansion and locking stage of the riveting feed process, at least one process physical quantity data reflecting the riveting feed process is collected in real time, and a corresponding process curve is constructed. S12. Based on the different types of physical quantity characteristics related to the rivet forming endpoint and the joint head height in the process curve, construct at least one stop criterion for determining the riveting forming endpoint, and monitor the stop criterion. Each stop criterion includes: an activation condition for limiting the process stage at which the stop criterion takes effect, so as to start monitoring the forming process; and a stop judgment condition for determining, after the activation condition is met, whether the current riveting forming state has reached the forming endpoint corresponding to the preset head height threshold range based on the real-time data of the process curve, so as to determine whether to terminate the riveting feed. S13. After any of the activation conditions is met, the corresponding stop judgment condition is determined. S14. When any stop determination condition is met, it is determined that the current riveting process has reached the forming end state, and the riveting feed process is controlled to stop, so as to obtain a riveted joint that meets the preset head height threshold range.

[0044] In this embodiment of the disclosure, the physical quantity signals of each process are continuously collected from the start of the riveting feed process and used to construct the process curve. However, the stop criterion based on the process curve is not continuously effective throughout the entire process, but is controlled by a staged triggering method.

[0045] The various stopping criteria are defined in a hierarchical structure. Each stopping criterion includes: an activation condition for limiting its effective timing, and a stopping condition for determining whether the forming endpoint has been reached after the activation condition is met.

[0046] The activation condition indicates that the current riveting process has entered a specific stage, while the stop judgment condition determines whether the forming endpoint corresponding to a preset head height threshold range has been reached within that stage based on real-time process curve data. By dividing the stop criterion into activation and stop judgment conditions, termination judgments can be avoided in non-target process stages, thereby improving the accuracy and robustness of endpoint determination.

[0047] Specifically, the system only initiates the monitoring and determination of each stop criterion after the riveting feed process enters the riveting leg expansion and locking stage; before this stage, no termination determination or adjustment control based on the process curve is executed. The activation condition of each stop criterion is determined independently, and when the activation condition of any stop criterion is met, real-time monitoring of the stop judgment condition corresponding to that criterion is initiated.

[0048] The various stop criteria are logically ORed, meaning that the termination control of the riveting feed process can be triggered when any stop criterion is met.

[0049] In this embodiment of the disclosure, by analyzing the process curve formed by the rivet during the rotation, friction and feeding of the connecting plate, physical quantity features directly related to the head height of the riveted joint (including but not limited to riveting pressure, riveting torque and riveting feed displacement and their variation characteristics) are extracted and used to construct the stopping criterion, thereby realizing the determination of the rivet forming endpoint.

[0050] Specifically, during the riveting feed process, the system collects at least one process physical quantity data reflecting the riveting forming process in real time and constructs a corresponding process curve. Based on the physical quantity characteristics in the process curve that are directly related to the forming endpoint and the joint height, multiple stopping criteria are constructed. Each stopping criterion includes an activation condition for limiting its effective stage and a stopping judgment condition for determining whether the forming endpoint has been reached. The stopping judgment condition can be set based on the amplitude characteristics, rate of change characteristics, or combination relationships of the physical quantities.

[0051] Finally, when any stopping criterion's stopping condition is met, the system determines that the current riveting process has reached the forming endpoint and controls the riveting feed process to terminate, thereby ensuring that the riveted joint height meets the preset threshold range. Through this control method that determines the endpoint only at the final stage, stable riveting forming quality control can be achieved without continuous adjustment throughout the entire process. In some embodiments, the different types of physical quantity characteristics include at least one of the following: Based on the characteristic combination of riveting feed displacement and riveting pressure; Based on the characteristic combination of riveting feed displacement and riveting torque; Based on the characteristics of the riveting pressure change rate; Based on the characteristic combination of riveting feed displacement, riveting pressure and time.

[0052] In this embodiment of the disclosure, the different types of physical quantity characteristics are mainly manifested as several key combinations or change patterns of physical quantities. Specifically, the different types of physical quantity characteristics may include at least one of the following: (1) Based on the characteristic combination of riveting feed displacement and riveting pressure: For example, after the riveting feed displacement reaches the preset position, it is judged whether the riveting pressure reaches or exceeds the preset threshold. (2) Based on the characteristic combination of riveting feed displacement and riveting torque: For example, after the riveting feed displacement reaches the preset position, it is judged whether the riveting torque reaches or exceeds the preset threshold. (3) Based on the characteristics of the riveting pressure change rate: For example, calculate the rate of change of riveting pressure with time or with feed displacement, and identify its trend or inflection point characteristics. (4) Based on the characteristic combination of riveting feed displacement, riveting pressure and time: For example, after the riveting feed displacement reaches the preset position, a comprehensive constraint judgment is made on the displacement increment, pressure level and duration.

[0053] The aforementioned different types of physical quantity characteristics provide a multi-dimensional physical judgment basis for constructing multiple preset stopping conditions, enabling the system to achieve adaptive endpoint control for different material states, equipment operating conditions, and process fluctuations.

[0054] In some embodiments, the plurality of stopping criteria include a displacement compensation criterion, which is set based on a characteristic combination of riveting feed displacement, riveting pressure, and time, and includes corresponding activation conditions and stopping judgment conditions: The activation condition is: the riveting feed displacement during the riveting feed process reaches the main feed displacement value; The stopping conditions include: After the activation conditions are met, the compensation riveting feed stage begins; During the compensated riveting feed stage, it is determined whether at least one of the first to third sub-conditions is satisfied. When at least one of the first to third sub-conditions is met, a stop signal is issued to terminate the riveting feed process. The first sub-condition is that the cumulative feed displacement since the start of the compensated riveting feed stage reaches the preset pressure-holding feed displacement. The second sub-condition is that the real-time riveting pressure reaches the preset maximum output pressure value for pressure holding. The third sub-condition is that the duration of the compensation riveting feed stage reaches the preset holding time.

[0055] In this embodiment of the disclosure, a specific example of one of the plurality of preset stopping conditions is a displacement compensation criterion. The displacement compensation criterion is set based on a characteristic combination of riveting feed displacement, riveting pressure, and time. Its design logic is to provide a compensating riveting feed constrained by pressure and time after the main forming is completed, so as to achieve precise control of the endpoint.

[0056] This criterion is configured to execute the following control logic: After the riveting feed displacement reaches the preset main feed displacement value during the riveting feed process, the system enters the compensation riveting feed stage. During the compensation riveting feed stage, the system performs real-time judgment on whether at least one of the first to third sub-conditions is satisfied: The first sub-condition is: the cumulative riveting feed displacement since the start of the compensated riveting feed stage reaches the preset pressure holding feed displacement; The second sub-condition is: the real-time riveting pressure reaches the preset maximum output pressure value for pressure holding; The third sub-condition is: the duration of the compensation riveting feed stage reaches the preset holding time.

[0057] The first to third sub-conditions mentioned above are logically ORed. When at least one of the first to third sub-conditions is satisfied, the system determines that the displacement compensation criterion has been triggered and issues a stop signal, thereby stopping the riveting feed process.

[0058] The displacement compensation criterion can be used to implement a controlled final pressing or shaping process after the main forming stage is completed, so as to improve the consistency of the joint height while ensuring safety.

[0059] In some embodiments, the plurality of preset stop conditions include a pressure threshold criterion, which is set based on a characteristic combination of riveting feed displacement and riveting pressure, and is configured as follows: After the riveting feed displacement reaches the pressure stop start displacement during the riveting feed process, if it is determined that the real-time riveting pressure signal exceeds the preset pressure threshold, a stop signal is issued to terminate the riveting feed process.

[0060] In this disclosure, one specific example of the various stopping criteria is a pressure threshold criterion. The pressure threshold criterion is set based on a characteristic combination of riveting feed displacement and riveting pressure, and is used to determine the connection endpoint by changes in pressure level at the end of the rivet forming stage.

[0061] The pressure threshold criterion is configured to execute the following control logic: The system monitors the riveting feed displacement in real time during the riveting process. When the riveting feed displacement reaches the preset pressure stop initiation displacement, the system begins to compare the real-time riveting pressure signal with the preset pressure threshold. If the real-time riveting pressure signal exceeds the preset pressure threshold, the system determines that the pressure threshold criterion has been triggered and issues a stop signal, thereby controlling the riveting feed process to stop.

[0062] This pressure threshold criterion is applicable to process scenarios where the pressure curve at the end of the riveting process shows a relatively stable or monotonically increasing trend, and can achieve endpoint control while ensuring sufficient connection.

[0063] In some embodiments, the plurality of stopping criteria include a torque threshold criterion, which is set based on a characteristic combination of riveting feed displacement and riveting torque, and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting feed displacement during the riveting feed process reaches the torque stop start displacement; The stop judgment condition is as follows: after the activation condition is met, if it is determined that the real-time riveting torque signal exceeds the preset torque threshold, a stop signal is issued to terminate the riveting feed process.

[0064] In this disclosure, one specific example of the various stopping criteria is a torque threshold criterion. The torque threshold criterion is set based on a characteristic combination of riveting feed displacement and riveting torque, and is used to determine the connection endpoint through torque changes during the rivet's rotational friction and feeding process.

[0065] The torque threshold criterion is configured to execute the following control logic: The system monitors the riveting feed displacement in real time during the riveting process. Once the riveting feed displacement reaches a preset torque-stopping initiation displacement, the system begins comparing the real-time riveting torque signal with a preset torque threshold. If the real-time riveting torque signal exceeds the preset torque threshold, the torque threshold criterion is triggered, and a stop signal is issued, thereby stopping the riveting feed process.

[0066] This criterion is applicable to rotary friction riveting processes where the torque signal shows a significant changing trend at the final stage of forming, and can be used as a supplement to or alternative to the pressure criterion for stopping the process.

[0067] In some embodiments, the plurality of stopping criteria include a pressure change rate inflection point criterion, which is set based on the characteristics of the riveting pressure change rate and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting pressure signal reaches the inflection point to stop the initial pressure. The stopping condition is: After the activation condition is met, the riveting pressure rise rate is calculated. If the rate of increase of the riveting pressure exceeds the preset rate threshold, it is determined that a riveting pressure inflection point has been detected, and the current riveting pressure value is recorded as the inflection point pressure value. If the inflection point pressure value has been recorded, and it is determined that the real-time riveting pressure signal exceeds the sum of the inflection point pressure value and the preset compensation pressure value, a stop signal is issued to terminate the riveting feed process.

[0068] In this disclosure, one specific example of the various stopping criteria is the pressure change rate inflection point criterion. This criterion is based on the characteristics of the riveting pressure change rate and is used to identify the trend change of the pressure curve at the end of the rivet forming stage, thereby determining key control nodes related to the rivet forming endpoint and the joint head height.

[0069] This criterion is configured to execute the following two-phase control logic: Phase 1 (Inflection Point Detection Phase): After the real-time riveting pressure signal reaches a preset inflection point to stop the initial pressure, the system begins to calculate the riveting pressure rise rate. This rise rate can be calculated based on the pressure increment per unit time or the pressure increment per unit feed displacement. If the riveting pressure rise rate exceeds a preset rate threshold, an inflection point in the riveting pressure rise is detected, and the current riveting pressure value is recorded as the inflection point pressure value. This inflection point typically corresponds to the rivet entering its final compaction stage or the material undergoing significant plastic flow.

[0070] Phase Two (Compensation Ceasedown Phase): With the inflection point pressure value already recorded, the system continues to monitor the real-time riveting pressure signal. When it is determined that the real-time riveting pressure signal exceeds the sum of the inflection point pressure value and the preset compensation pressure value, the pressure change rate inflection point criterion is triggered, and a stop signal is issued, thereby controlling the riveting feed process to stop.

[0071] Since different materials typically exhibit a rapid increase in riveting pressure at the end of the connection process, this criterion is based on the trend of pressure change rather than a single fixed pressure threshold. Therefore, it has good adaptability to material strength fluctuations, plate thickness differences, and equipment thermal drift, which helps to improve the consistency and robustness of joint height control.

[0072] In some embodiments, at least one process physical quantity data reflecting the riveting process is collected in real time, and a corresponding process curve is constructed, including: Real-time acquisition of riveting feed displacement, riveting pressure, and riveting torque; The functional relationships between the riveting feed displacement, riveting pressure, and riveting torque as a function of time and as a function of the riveting feed displacement are constructed respectively to form the process curve.

[0073] In this embodiment of the disclosure, to support the parallel determination and independent triggering mechanism of multiple stop criteria, the real-time monitoring of at least one process curve reflecting the changes of process physical quantities during the riveting feed specifically includes: the system real-time acquisition of riveting feed displacement, riveting pressure and riveting torque during the riveting feed process, and constructing functional relationships between the riveting feed displacement, riveting pressure and riveting torque and time and with the riveting feed displacement, respectively, to generate corresponding process curves.

[0074] The process curves may include, but are not limited to: riveting feed displacement-time curve; riveting pressure-riveting feed displacement curve; riveting torque-riveting feed displacement curve; riveting pressure-time curve; and riveting torque-time curve.

[0075] The aforementioned process curves provide the original data source for the aforementioned multiple preset stop conditions, and provide a real-time monitoring data basis for extracting physical quantity features related to the rivet forming endpoint and joint head height.

[0076] In some embodiments, the method further includes: If the riveting feed displacement reaches the riveting feed reference value and none of the aforementioned stop criteria are triggered, then the feed continues to compensate for the positive displacement.

[0077] In practical applications, due to equipment response delays, material performance fluctuations, or sensor signal errors, relying solely on early-triggered stop criteria (negative compensation mechanism) may lead to insufficient riveting feed, thereby affecting the mechanical locking effect and head height stability of the joint.

[0078] Therefore, this disclosure further introduces a positive compensation control strategy, which allows the feed process to continue within a controlled range if the stop criterion is not triggered, so as to achieve compensation and adjustment for insufficient forming.

[0079] In this embodiment of the disclosure, to further ensure sufficient connection and avoid the risk of under-connection, the method further includes a positive compensation control logic. The system presets a riveting feed reference value. During the riveting feed process, when the riveting feed displacement reaches the riveting feed reference value, if none of the multiple preset stop conditions are triggered, the system does not immediately stop the riveting feed process, but instead controls the continued feed of a preset positive compensation displacement.

[0080] The above logic provides additional feed compensation even when the stopping criteria are not met, thus preventing under-compaction or head height deviation caused by material property fluctuations, sensing errors, or process disturbances. This positive compensation logic, together with the aforementioned stopping conditions, constitutes a two-way adaptive adjustment mechanism for the riveting endpoint.

[0081] In some embodiments, the riveting feed reference value is the leg length of the rivet.

[0082] In rotary friction riveting processes, the rivet leg length typically corresponds to the theoretical minimum penetration depth. When the riveting feed displacement reaches the rivet leg length, it usually indicates that the rivet has essentially completed its penetration of the upper sheet material and entered the lower sheet material or the mold constraint area.

[0083] Therefore, using the rivet leg length as the riveting feed reference value can provide a physically meaningful reference position for controlling the riveting endpoint. Based on this, combined with the aforementioned preset stop conditions or positive compensation displacement, the final insertion depth of the rivet can be further finely adjusted, thereby achieving stable control of the joint head height.

[0084] Of course, in other embodiments, the riveting feed reference value can also be set according to the total thickness of the sheet metal, mold structure parameters, or historical process calibration data.

[0085] In some embodiments, the riveting feed process includes a flat die self-piercing friction riveting process.

[0086] In the flat die self-piercing friction riveting process, the rivet induces localized plastic flow in the sheet metal under the action of rotational friction, and forms a mechanically locked structure under the constraint of the flat die. Because this process has high requirements for endpoint control and joint height consistency, the multi-criteria composite control method based on process curves described in this disclosure is significantly applicable to this process.

[0087] In a specific embodiment, this method has been applied to the flat die self-piercing friction riveting process and has effectively improved the head height fluctuation problem under continuous production conditions.

[0088] The adaptive control method based on process curves described in this disclosure is not limited to specific models or structural forms of rotary friction riveting equipment, but is applicable to all riveting processes that form a mechanical locking structure through rivet rotational friction and axial feeding. By real-time analysis of the process physical quantity curves during the riveting feed process and multi-criteria composite judgment, stable control of the connection endpoint and joint height can be achieved.

[0089] Figure 2 This is a schematic diagram of the control logic flow for the connection forming process performed by the device in an embodiment of this disclosure. The flowchart illustrates how, given predetermined multi-segment riveting process parameters, an adaptive stop control method based on process curve characteristic signals is embedded into the conventional riveting feed process to achieve intelligent determination and control of the riveting endpoint.

[0090] (a) Sequential execution of multi-stage process parameters like Figure 2As shown, the riveting feed process can be divided into several sequentially executed process segments (the diagram illustrates a maximum of five segments, but in actual applications, it can be two, three, or more segments). Within each process segment, basic process parameters such as the rotational speed and axial feed speed of the riveting tool can be preset. Specifically, the control flow includes: The system completes the pre-compression action and confirms the mechanical zero point position; The riveting tool is driven to perform rotational friction and axial feed according to the preset parameters of the first process section; After the current process segment is completed, the system will automatically switch to the parameters of the next process segment and continue execution. Complete all process segments in the preset order.

[0091] It should be noted that the selection and optimization of parameters for each process segment are routine process design considerations and not the focus of this disclosure. This disclosure focuses on how to dynamically determine the riveting stop position based on the process curve during the execution of a given multi-segment process.

[0092] (II) Embedding and Triggering Mechanism of Adaptive Stop Control Logic The adaptive stop control logic disclosed herein can be activated at at least one preset stage position during the riveting feed process. After the riveting feed displacement reaches a preset stop initiation displacement (or the pressure reaches a preset stop initiation pressure), the system begins to make real-time determinations on multiple configured preset stop conditions.

[0093] After reaching the stop start position: The riveting feed process continues to be executed according to the predetermined rotation speed and feed speed of the current process section; Meanwhile, the system monitors the process curve signals corresponding to each stop condition in real time, including but not limited to the riveting pressure-displacement curve, the riveting torque-displacement curve, and the riveting pressure-time curve. Based on the real-time collected curve data, it is determined whether multiple preset stop conditions have been triggered.

[0094] The multiple preset stop conditions are logically ORed, meaning that when at least one of the multiple stop conditions is met, the system immediately issues a stop signal to terminate the riveting feed process, thereby completing the riveting.

[0095] Through the above parallel determination mechanism, the system can promptly identify the forming endpoint when different material states or different forming characteristics occur.

[0096] (iii) Compensation control logic when no criterion is triggered In one implementation, when the riveting feed displacement has reached a preset riveting feed reference value (e.g., the length of the rivet leg) and none of the preset stop conditions have been triggered, the system will not stop immediately, but will instead initiate positive compensation feed control logic.

[0097] During the compensation feed phase: The system continues to execute the preset compensation displacement; Meanwhile, the process curve signals corresponding to each stop condition are continuously monitored; If any stop condition is triggered during the compensated feed process, a stop signal will be issued immediately. If the compensation displacement is completed but the stop condition is not triggered, the riveting feed process ends when the compensation displacement is completed.

[0098] Through the above mechanism, the method disclosed herein forms: on the one hand, an early stop control based on multiple criteria for "selective triggering"; on the other hand, a safety fallback control based on the feed reference value and compensation displacement. Together, they constitute a two-way adaptive adjustment mechanism for the riveting endpoint.

[0099] In conclusion, Figure 2 The control flow shown illustrates how the method of this disclosure achieves adaptive and robust control of the riveting endpoint without altering the existing multi-segment riveting process framework. This is achieved by setting a configurable stop start position and introducing parallel stop logic based on the characteristic signals of the process curve. This method effectively reduces the risk of endpoint deviation caused by factors such as material property fluctuations, equipment thermal changes, or processing disturbances, thereby improving the consistency and stability of the riveted joint height.

[0100] In this embodiment of the disclosure, the operator can configure the riveting process through a parameter setting interface for configuring riveting control parameters. This interface is used to configure basic parameters of the multi-segment riveting process and related parameters of multiple stop criteria, thereby achieving adaptive control of the riveting endpoint.

[0101] The parameter setting interface may include: multi-segment process parameter settings, used to set the basic framework parameters of the riveting feed process, including but not limited to the number of riveting segments, feed displacement of each segment, feed speed, rotation speed and compensation displacement, etc.; and adaptive stop criterion parameter settings, used to configure multiple stop conditions and their judgment thresholds based on process curve feature signals.

[0102] Stop criteria parameters may include, but are not limited to: pressure holding feed displacement, pressure holding feed speed, pressure holding time, maximum pressure holding output pressure, pressure stop start position, pressure stop value, torque stop start position, torque stop value, inflection point stop start pressure, inflection point stop change, and inflection point stop compensation pressure.

[0103] During actual operation, the system executes multi-stage feed according to the set process parameters, while simultaneously monitoring the process curve signals corresponding to each stop condition. When at least one of the multiple stop conditions is triggered, the system issues a stop command to terminate the feed process.

[0104] When none of the configured stop conditions are triggered, the system completes the final feed according to the set basic feed displacement and compensation displacement to avoid under-forming.

[0105] Through the above parameter configuration mechanism, the coordinated adjustment of early stop control and positive compensation control at the riveting endpoint can be achieved, thereby improving the consistency and robustness of riveting formation.

[0106] Those skilled in the art should understand that the specific parameter setting interface form, parameter presentation method, and interaction structure can be adjusted according to the system implementation method, and this disclosure is not limited to a specific human-computer interface layout form.

[0107] Figure 3 This is a schematic diagram of the determination process for stop condition 1 in this embodiment of the present disclosure. The figure shows the process curve of pressure changing with feed displacement during the riveting feed process, where the horizontal axis is the riveting feed displacement and the vertical axis is the real-time riveting pressure.

[0108] Stop condition 1 (corresponding to the pressure holding parameter module) is one of the four adaptive stop conditions proposed in this disclosure. It is a compensated feed stage with rigid force and time constraints (setting a pressure holding feed displacement), thus forming a composite control logic with multiple safety boundaries.

[0109] like Figure 3 The pressure-displacement curve shown indicates that the execution of this condition is divided into two stages: Main feed stage: The riveting tool feeds according to preset conventional process parameters until it reaches a preset conventional fixed displacement position. Figure 3 The example in the middle is approximately 4.5mm.

[0110] Compensation feed phase: After reaching the normal fixed displacement position, the system continues to feed at a pressure-holding feed rate, aiming to complete a preset pressure-holding feed displacement. Figure 3 In the example, the pressure-holding feed displacement is approximately 0.7 mm, and the target total displacement is approximately 5.2 mm. During this stage, the system monitors the following three sub-conditions in parallel: (a) Whether the cumulative feed displacement since the beginning of this stage has reached the pressure-holding feed displacement amount; (b) Whether the real-time pressure has reached the preset maximum output pressure for pressure holding ( Figure 3 Example: 17.5KN). (c) Whether the duration of this stage reaches the preset pressure holding time.

[0111] The above sub-conditions are logically ORed, meaning that when any sub-condition is met, the system will issue a stop signal to stop the riveting feed process.

[0112] In this criterion, the preset pressure-holding feed displacement is used to control the displacement compensation at the riveting endpoint, while the maximum pressure-holding output pressure and pressure-holding time are used to limit the force boundary and time boundary in the compensation riveting feed stage to prevent overload or abnormal feed caused by material state fluctuations or equipment limits.

[0113] Figure 3 In the example shown, during the compensated riveting feed stage, the real-time riveting pressure reaches the preset maximum output pressure value before the cumulative compensated displacement, thus triggering a stop by the second sub-condition, and terminating the riveting feed before all compensated feed displacements are completed.

[0114] The pressure-holding displacement can be determined through the following debugging process: First, perform a trial riveting under the preset conventional process parameters. After measuring the head height and confirming the deviation height x, generally set x plus 0.2mm as the displacement.

[0115] It should be noted that the main feed displacement value, holding feed displacement, maximum holding output pressure value and holding time can all be set according to different plate types, thicknesses and process conditions, and this disclosure does not limit their specific values.

[0116] In summary, Stop Condition 1 achieves enhanced safety control of the process endpoint by embedding a compensated feed stage that monitors force and time into the displacement control.

[0117] Figure 4 This is a schematic diagram of the determination process for stop condition 2 based on pressure threshold in this embodiment of the present disclosure. The diagram shows the process curve of real-time riveting pressure changing with riveting feed displacement during the riveting feed process, and marks the pressure stop start position and pressure stop value.

[0118] Stop condition 2 (corresponding to the pressure judgment stop module) is one of the various stop conditions based on the process curve proposed in this disclosure. It realizes the judgment control of the riveting feed endpoint by setting the feed displacement trigger condition and the pressure threshold criterion.

[0119] like Figure 4 As shown, the implementation of stop condition 2 is based on the following two preset parameters: The pressure stop start position is used to define the riveting feed displacement threshold at which the pressure stop logic is activated (e.g., ...). Figure 4 (The example in the middle is about 3.5 mm). This position is usually set after the connector has been inserted into the lower plate to avoid early fluctuation interference. Pressure stop value, a preset pressure threshold used as a stop criterion (e.g., ...). Figure 4 The example in the middle is approximately 16.9 kN.

[0120] During the riveting feed process, the system continuously monitors the riveting feed displacement. When the riveting feed displacement reaches or exceeds the pressure stop start position, the system initiates a threshold judgment on the real-time riveting pressure signal; subsequently, if the real-time riveting pressure signal exceeds the pressure stop value, the system immediately issues a stop signal to control the riveting feed process to stop.

[0121] like Figure 4 As shown, after the stop signal is issued, due to the response time of the control system and mechanical inertia, the real-time riveting pressure may continue to rise and form a brief pressure overshoot. This pressure overshoot is a natural result of the stopping process and is not used as a stopping criterion.

[0122] The pressure stop start position and pressure stop value can be set according to factors such as the type and thickness of the materials being connected, the specifications of the connectors, and the equipment status. For example, with all stop conditions closed, a feed rate sufficient to ensure complete riveting is set for trial riveting to obtain a complete pressure-displacement process curve. Observe and record the stable peak or plateau value of the pressure reached at the end of the curve, when the riveting is nearing completion. Subtract a predetermined safety margin (e.g., 0.5 kN to 1.0 kN) from the peak or plateau value, and the result is used as the initial pressure stop value. Subsequently, riveting is performed using this criterion, and the stop value is fine-tuned according to the actual quality of the formed joint (e.g., head height).

[0123] Figure 4 The parameter acquisition method shown is only an exemplary debugging method. This disclosure does not limit the specific value or acquisition method of the pressure stop start position and pressure stop value.

[0124] Figure 5 This is a schematic diagram of the determination process for stop condition 3 based on torque threshold in this embodiment of the present disclosure. The figure shows the process curve of the real-time riveting torque changing with the riveting feed displacement during the riveting feed process, where the horizontal axis is the riveting feed displacement, the vertical axis is the real-time riveting torque, and the torque stop judgment start position and torque stop judgment value are marked.

[0125] Stop condition 3 (corresponding to the torque judgment and stop module) is one of the various stop conditions based on the process curve proposed in this disclosure. It achieves the determination and control of the riveting feed endpoint by monitoring the torque signal output by the drive system during the riveting feed process. This condition aims to capture the significant torque change characteristics that may occur at the final stage of forming when the connecting component and the sheet metal reach rigid contact (such as...). Figure 5 (as shown by the steep rise), and based on this, endpoint control is achieved.

[0126] like Figure 5 As shown, the implementation of stop condition 3 is based on the following two preset parameters: The torque stop start position is used to define the preset feed displacement for enabling the torque stop logic. This position is usually set after the connecting member has been stably driven into the lower plate to ensure that the monitored torque signal can effectively reflect the final state. The torque threshold is used as a stopping criterion.

[0127] During the riveting feed process, the system continuously monitors the riveting feed displacement. When the riveting feed displacement reaches or exceeds the torque stop start position, the system initiates a threshold judgment on the real-time riveting torque signal; subsequently, if the real-time riveting torque signal exceeds the torque stop value, the system immediately issues a stop signal to control the riveting feed process to stop.

[0128] like Figure 5 As shown, after the stop signal is issued, due to the response time of the control system and mechanical inertia, the riveting feed process may continue to generate a short inertial stroke, and the real-time riveting torque may also rise briefly. This process is a natural result of the stopping process and is not used as a stopping criterion.

[0129] The torque stop start position and torque stop value can be set according to factors such as the type and thickness of the materials being connected, the specifications of the connectors, and the equipment status. The torque stop value can be determined by feature recognition: a trial riveting is performed under closed stop conditions to obtain a complete torque-displacement curve; the final segment of the curve is observed to identify the starting point of a significant sharp increase in torque when riveting enters the final stage; the torque value corresponding to this point is selected as the torque stop value, and can be fine-tuned based on the actual riveting effect. This method utilizes the physical characteristic of a sharp increase in the torque change rate at a specific process stage. Figure 5 The torque threshold determination method shown is only an exemplary debugging method. This disclosure does not limit the specific value or acquisition method of the torque stop start position and torque stop value.

[0130] Figure 6 This is a schematic diagram of the stopping logic for stopping condition 4 based on the inflection point of the pressure change rate in this embodiment of the present disclosure. Wherein, Figure 6 The left and middle figures show the process curve of real-time riveting pressure changing with riveting feed displacement during the riveting feed process. The right figure is a partial enlarged schematic diagram of the red rectangle in the left figure. The left and right figures together illustrate the inflection point stopping starting pressure, the inflection point pressure value, and the stopping threshold determined by the inflection point pressure value and the inflection point stopping compensation pressure.

[0131] Stop condition 4 (corresponding to the pressure inflection point judgment and stop module) is one of the various stop conditions based on the process curve proposed in this disclosure. It identifies the characteristic inflection point in the pressure rise process by monitoring the change characteristics of the real-time riveting pressure signal during the riveting process, and judges and controls the riveting feed endpoint based on the inflection point.

[0132] like Figure 6 As shown, the implementation of stop condition 4 is based on the following preset parameters: The inflection point detection threshold is the pressure threshold value used to trigger inflection point detection. When the real-time pressure reaches or exceeds this value, the system starts monitoring the rate of pressure change. This value is usually calibrated through experiments, for example, set to be 2-3 kN lower than the expected inflection point pressure. The inflection point stopping change is a preset pressure rise rate threshold used to determine the inflection point. The system calculates the pressure increment within a unit time (e.g., 10 milliseconds) to obtain the real-time pressure rise rate and compares it with this threshold; this threshold can be determined through trial and error: in the region of rapid pressure rise, the pressure increment within a unit time is calculated, and this increment value is set as the inflection point stopping change. The inflection point stopping compensation pressure is a preset pressure compensation amount used to finely adjust the stopping timing after identifying the inflection point; this value is usually set to a small range (e.g., 0.3 kN to 0.5 kN). In practical applications, a value can be selected within this range first, and then fine-tuned according to the rivet height result to complete the final calibration.

[0133] Its control logic includes the following two stages: Inflection point detection phase: When the real-time pressure reaches the inflection point stopping initiation pressure, the system begins to calculate the pressure rise rate in real time. If this rate exceeds the inflection point stopping change amount, it is determined that a pressure rise inflection point has been detected, and the pressure value at this moment is recorded as the inflection point pressure value.

[0134] Compensation Stop Phase: After detecting the inflection point, the system adds the inflection point pressure value to the inflection point stop compensation pressure, which serves as the dynamic stop threshold. Subsequently, if the real-time pressure exceeds this threshold, the system immediately issues a stop command.

[0135] The inflection point stopping initiation pressure, inflection point stopping change amount, and inflection point stopping compensation pressure can be set according to factors such as the type and thickness of the connected material, the specifications of the connector, and the equipment status. Figure 6 The parameter values ​​and acquisition methods shown are merely illustrative examples, and this disclosure does not limit their specific values ​​or determination methods.

[0136] The adaptive endpoint control method based on process curves disclosed herein is not limited to specific joining processes. The core of this method lies in identifying and utilizing the explicit load change signals caused by rigid contact or full forming at the end of the joining process.

[0137] This method has been successfully applied to mechanically driven solid-state joining processes such as self-piercing riveting and rotary friction unit welding. The fundamental criterion for its applicability is that the process curves (such as pressure-displacement and torque-time curves) of the target process must exhibit significant change characteristics that can be monitored at the end of the forming process (such as monotonically rapid increase, specific rate of change inflection point, etc.).

[0138] Therefore, in principle, any mechanical connection process that meets the above signal characteristics can achieve precise and stable control of its endpoint by applying the control logic of this disclosure.

[0139] Example To enable those skilled in the art to more clearly understand the technical solutions provided by the embodiments of this disclosure, the technical solutions provided by the embodiments of this disclosure will be described in detail below through specific embodiments: In one specific embodiment, two layers of 5-series aluminum alloy plates commonly used in the rail transit field are selected as the connection objects, with a total thickness of 5 mm. A flat die self-piercing friction riveting test is conducted using rivets with a leg length of 4.7 mm and a cavity depth of 5.5 mm.

[0140] Under sheet-level testing conditions, the multi-criteria control method based on process curves described in this disclosure was used for riveting. The results show that the joint height error can be stably controlled within ±0.1 mm, and the joint mechanical properties are consistent. The tensile failure mode is mainly rivet pull-out, and the shear failure mode is mainly rivet shearing, indicating that the joint has formed a stable mechanical locking structure and the connection quality is reliable.

[0141] In the continuous riveting test of large-size plates simulating actual production, under the same process parameters, the temperature rise of the mold caused by continuous processing changed the thermal state of the plate. When using the traditional control method based on fixed parameters, the head height fluctuation increased, and the head height error exceeded ±0.2 mm.

[0142] To address the aforementioned problems, the control method disclosed herein is applied. A stop criterion based on the process curve is used to control the riveting endpoint. The stop criterion includes an activation condition and a stop judgment condition: the activation condition is set after the riveting feed process enters the rivet leg expansion and locking stage (e.g., the feed displacement range after the rivet penetrates the lower plate); after the activation condition is met, a stop judgment is performed based on the real-time pressure signal, and the riveting feed process is terminated when the pressure reaches a preset pressure threshold.

[0143] During the riveting process, the system collects and monitors the pressure-displacement process curve in real time. When the feed displacement reaches the interval corresponding to the activation condition, the monitoring of the pressure criterion is started. When the pressure signal reaches the preset threshold, the system outputs a stop command, thereby realizing adaptive control of the riveting endpoint.

[0144] Using the above control method, in a test of approximately 200 consecutive riveting points, the termination pressure was stabilized within the range of 16.2-16.7 kN, and the head height was stabilized between 2.46-2.57 mm, with a significant improvement in consistency; in the subsequent continuous production of approximately 3000 points, no further head height deviations occurred.

[0145] The above results show that the method disclosed herein can effectively suppress process fluctuations caused by factors such as heat accumulation by identifying and controlling different process stages based on the stopping criteria of the process curve, and achieve high precision and high consistency control of the riveting endpoint.

[0146] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A riveting control method based on a process curve, characterized in that, The method, applied in a process of joining plates by rotating and feeding rivets, includes: During the rivet leg expansion and locking stage of the riveting feed process, at least one process physical quantity data reflecting the riveting feed process is collected in real time, and a corresponding process curve is constructed. Based on the different types of physical quantity characteristics related to the rivet forming endpoint and the joint head height in the process curve, at least one stop criterion is constructed to determine the riveting forming endpoint, and the stop criterion is monitored. Each stop criterion includes: an activation condition, used to limit the process stage at which the stop criterion takes effect, so as to start monitoring of the forming process; and a stop judgment condition, used to determine whether the current riveting forming state has reached the forming endpoint corresponding to the preset head height threshold range based on the real-time data of the process curve after the activation condition is met, so as to determine whether to terminate the riveting feed. Upon satisfaction of any of the activation conditions, the corresponding stop judgment condition is determined. When any stop condition is met, it is determined that the current riveting process has reached the forming end point state, and the riveting feed process is controlled to stop, so as to obtain a riveted joint that meets the preset head height threshold range.

2. The method according to claim 1, characterized in that, The different types of physical quantity characteristics include at least one of the following: Based on the characteristic combination of riveting feed displacement and riveting pressure; Based on the characteristic combination of riveting feed displacement and riveting torque; Based on the characteristic combination of riveting pressure and riveting pressure change rate; Based on the characteristic combination of riveting feed displacement, riveting pressure and time.

3. The method according to claim 1, characterized in that, The multiple stopping criteria include a displacement compensation criterion, which is set based on a characteristic combination of riveting feed displacement, riveting pressure, and time, and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting feed displacement during the riveting feed process reaches the main feed displacement value; The stopping conditions include: After the activation conditions are met, the compensation riveting feed stage begins; During the compensated riveting feed stage, it is determined whether at least one of the first to third sub-conditions is satisfied. When at least one of the first to third sub-conditions is met, a stop signal is issued to terminate the riveting feed process. The first sub-condition is that the cumulative feed displacement since the start of the compensated riveting feed stage reaches the preset pressure-holding feed displacement. The second sub-condition is that the real-time riveting pressure reaches the preset maximum output pressure value for pressure holding. The third sub-condition is that the duration of the compensation riveting feed stage reaches the preset holding time.

4. The method according to claim 1, characterized in that, The multiple stopping criteria include a pressure threshold criterion, which is set based on a characteristic combination of riveting feed displacement and riveting pressure, and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting feed displacement during the riveting feed process reaches the pressure stop start displacement; The stop judgment condition is as follows: after the activation condition is met, if it is determined that the real-time riveting pressure signal exceeds the preset pressure threshold, a stop signal is issued to terminate the riveting feed process.

5. The method according to claim 1, characterized in that, The multiple stopping criteria include a torque threshold criterion, which is set based on a characteristic combination of riveting feed displacement and riveting torque, and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting feed displacement during the riveting feed process reaches the torque stop start displacement; The stop judgment condition is as follows: after the activation condition is met, if it is determined that the real-time riveting torque signal exceeds the preset torque threshold, a stop signal is issued to terminate the riveting feed process.

6. The method according to claim 1, characterized in that, The multiple stopping criteria include a pressure change rate inflection point criterion, which is set based on a characteristic combination of riveting pressure and riveting pressure change rate, and includes corresponding activation conditions and stopping judgment conditions, wherein: The activation condition is: the riveting pressure signal reaches the inflection point to stop the initial pressure. The stopping condition is: After the activation condition is met, the riveting pressure rise rate is calculated. If the rate of increase of the riveting pressure exceeds the preset rate threshold, it is determined that a riveting pressure inflection point has been detected, and the current riveting pressure value is recorded as the inflection point pressure value. If the inflection point pressure value has been recorded, and it is determined that the real-time riveting pressure signal exceeds the sum of the inflection point pressure value and the preset compensation pressure value, a stop signal is issued to terminate the riveting feed process.

7. The method according to any one of claims 1 to 6, characterized in that, Real-time acquisition of at least one process physical quantity data reflecting the riveting forming process, and construction of corresponding process curves, including: Real-time acquisition of riveting feed displacement, riveting pressure, and riveting torque; The functional relationships between the riveting feed displacement, riveting pressure, and riveting torque as a function of time and as a function of the riveting feed displacement are constructed respectively to form the process curve.

8. The method according to claim 7, characterized in that, Also includes: If the riveting feed displacement reaches the riveting feed reference value and none of the aforementioned stop criteria are triggered, then the feed continues to compensate for the positive displacement.

9. The method according to claim 8, characterized in that, The riveting feed reference value is the length of the rivet leg.

10. The method according to any one of claims 1 to 6, characterized in that, The riveting feed process includes a flat die self-piercing friction riveting process.

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