A control method and control device for a high-strength bolt processing apparatus

Abstract

The application discloses a control method and a control device of high-strength bolt processing equipment, and is applied to cold upsetting forming of a bolt with a large length-diameter ratio. The method synchronously collects a main punch servo motor current value and a micro-strain signal of a clamping mold side wall; when it is determined that the current value growth rate is greater than a preset threshold value and the micro-strain signal has a step rise, it is determined that a stress counterattack critical point is reached; at this time, the main punch feeding is kept, and a breathing pulse instruction is sent to a clamping oil cylinder, so that the clamping pressure is suddenly dropped in a very short time to break the friction force balance, and then the overload clamping state is immediately restored, and the micro-slippage of the rod part is actively induced to release the internal stress; finally, the slippage is obtained as an additional compensation value and is superimposed into the remaining feeding stroke of the main punch. The scheme can overcome the anti-slippage and pressure release contradiction caused by the traditional rigid dead lock, and then can effectively block the micro-crack initiation and accurately ensure the bolt forming size.

Description

Technical Field

[0001] This invention relates to the field of fastener processing and control technology, specifically to a control method and control device for high-strength bolt processing equipment. Background Technology

[0002] High-strength bolts with large length-to-diameter ratios (such as high-strength alloy steel fasteners of grade 10.9 and above) are indispensable in many high-end manufacturing fields, and cold heading is their core manufacturing process. In this process, the equipment typically uses a clamping die to apply a continuous radial clamping force to the bolt shank, while simultaneously controlling the main punch to provide extremely high axial pressure to violently extrude the end of the bar stock, causing it to undergo plastic deformation and thus upset to form the head. To prevent the slender shank from slipping or bending under the enormous axial upsetting pressure, a constant and extremely high overload clamping force must be maintained throughout the entire extrusion cycle to achieve rigid locking of the shank.

[0003] However, due to the high hardness and severe work hardening tendency of high-strength materials, when the main punch extrudes the head at high speed, the volumetric flow rate of the material in all directions often cannot keep up with the axial extrusion speed of the punch. This contradiction between stress hardening and the lag in volumetric flow can instantly generate a huge axial back stress. Under the state of rigid locking throughout the process, this back stress has nowhere to be released in the stress concentration area at the junction of the rod and the head, which can easily induce micro-cracks inside the material, forming hidden defects. At the same time, the tightly clamped rod will also produce tiny serpentine twists in the die cavity due to the axial extrusion of internal stress, resulting in serious deviations in the straightness of the final product.

[0004] To alleviate this destructive internal stress, simply reducing the clamping force throughout the entire cycle or using flexible clamps will cause the slender rod to lose its restraint and bend directly in the early stages of stamping. If the rod is allowed to slide freely under pressure, the feeding length of the main punch will become uncontrollable, resulting in insufficient thickness of the bolt head or an overall short length after forming.

[0005] Therefore, how to resolve the contradiction between anti-slip clamping and internal stress release in order to effectively prevent the generation of microcracks and ensure the accuracy of the final molded dimensions is an urgent technical problem to be solved. Summary of the Invention

[0006] In order to solve at least one of the technical defects mentioned in the background art, the present invention aims to provide a control method and control device for high-strength bolt processing equipment.

[0007] A first aspect of the present invention provides a control method for a high-strength bolt processing equipment, the method comprising:

[0008] The real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall are collected simultaneously during the cold heading process.

[0009] Within a set continuous time window, when it is determined that the growth rate of the real-time current value is greater than the preset hardening retardation threshold, and a step increase in the micro-strain signal is detected simultaneously, it is determined that the current rod material has reached the stress backlash critical point.

[0010] When the stress backlash critical point is reached, the main punch continues to feed and sends a breathing pulse command to the servo proportional valve of the clamping cylinder, so that the clamping pressure drops sharply to the set ratio of the initial rated pressure within the preset pulse release time to break the friction balance. Then, it immediately returns to the preset overload clamping pressure to actively induce the rod to produce a backward micro-slippage to release the internal stress.

[0011] The displacement sensor obtains the actual backward slippage of the rod during the execution of the breathing pulse command. This backward slippage is then added as an additional compensation value to the remaining target feed stroke of the main punch, and the main punch is controlled to complete the final cold heading according to the compensated total stroke.

[0012] A second aspect of the present invention provides a control device for a high-strength bolt processing equipment, the device comprising:

[0013] The signal acquisition module is used to synchronously acquire the real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall during the cold heading process.

[0014] The critical determination module is used to determine that the current rod material has reached the stress backlash critical point when the growth rate of the real-time current value is greater than the preset hardening retardation threshold and the micro-strain signal is simultaneously detected to have a step increase within a set continuous time window.

[0015] The breathing pressure relief module is used to keep the main punch feeding when the stress backlash critical point is reached, and send a breathing pulse command to the servo proportional valve of the clamping cylinder, so that the clamping pressure drops sharply to a set ratio of the initial rated pressure within a preset pulse pressure relief time to break the friction balance, and then immediately returns to the preset overload clamping pressure to actively induce the rod to produce a backward micro-slippage to release internal stress.

[0016] The closed-loop compensation module is used to obtain the actual backward slippage of the rod during the execution of the breathing pulse command through the displacement sensor, and to add the backward slippage as an additional compensation value to the remaining target feed stroke of the main punch, so as to control the main punch to complete the final cold heading according to the compensated total stroke.

[0017] Compared with existing technologies, this invention can solve the technical contradiction between anti-slip clamping and internal stress release in the cold heading of high-strength bolts with large length-to-diameter ratio. It effectively prevents the initiation of microcracks while ensuring the stability of the rod, and accurately guarantees the final forming size, which can significantly improve the product yield and process stability. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a control method for a high-strength bolt processing equipment disclosed in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the structure of a control device for a high-strength bolt processing equipment disclosed in an embodiment of the present invention;

[0020] Figure 3 This is another schematic diagram of the control device for a high-strength bolt processing equipment disclosed in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] This invention provides a control method for high-strength bolt processing equipment. This method can be applied to the cold heading control of high-strength bolts (e.g., high-strength alloy steel fasteners of grade 10.9 and above) with a length-to-diameter ratio greater than or equal to 5. The method relies on a cold heading machine equipped with a CNC servo hydraulic system. The hardware of this cold heading machine includes: a main punch driven by a main punch servo motor, a clamping die driven by a hydraulic cylinder and a servo proportional valve, a current sensor for collecting the current of the main punch servo motor, a micro-strain sensor attached to the side wall of the clamping die, and a displacement sensor located at the rear end of the clamping mechanism for monitoring the displacement of the rod. The control method of this invention will be described in detail below with reference to specific embodiments.

[0023] Reference Figure 1 As shown, the method includes the following steps:

[0024] S1, synchronously acquires the real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall during the cold heading process;

[0025] In this embodiment, the real-time current value is obtained by a current sensor located on the power supply line of the main punch servo motor, and its magnitude reflects the axial load borne by the main punch when extruding the bolt blank. The micro-strain signal is obtained by a micro-strain sensor (e.g., a resistive strain gauge or a fiber optic strain sensor) attached to the outer wall of the clamping die, which can sensitively reflect the minute elastic deformation of the clamping die sidewall caused by the radial expansion of the rod material.

[0026] In actual cold heading production, the high-speed stamping machinery generates strong vibrations and complex electromagnetic interference, which superimposes on the original acquired signal. If the original signal containing noisy signals is used directly for subsequent critical point determination, it is very easy to cause false triggering or delayed triggering of the criteria.

[0027] Therefore, as an example, after obtaining the real-time current value and the micro-strain signal, the method further includes: using a moving average filtering algorithm to perform noise reduction and smoothing processing on the real-time current value, and using a low-pass filtering algorithm to perform high-frequency mechanical vibration interference filtering processing on the micro-strain signal.

[0028] Specifically, for real-time current values, a moving average filtering algorithm is used for noise reduction and smoothing. Specifically, the control unit establishes a fixed-length data buffer in memory (e.g., storing current values ​​from the last 10 sampling periods). Whenever a new current sample value arrives, the new value is stored at the end of the buffer, and the oldest value at the beginning of the buffer is removed. The arithmetic mean of all current values ​​in the current buffer is calculated, and this average is output as the valid current value for the current moment. As the sampling time progresses, this data window slides forward synchronously, thereby achieving real-time smooth updates to the current signal sequence. It should be understood that this processing method effectively filters out spikes and high-frequency random noise introduced by inverter switching noise or electromagnetic coupling in the current signal, making the current change trend used for subsequent judgment more stable and reliable.

[0029] For micro-strain signals, a low-pass filtering algorithm is used to filter out high-frequency mechanical vibration interference. Because the die is subjected to high-frequency impacts during cold heading, the micro-strain signal often contains vibration components much higher than the actual deformation frequency of the material (e.g., high-frequency components from the rotation of the equipment spindle or the pulsation of the hydraulic pump). The low-pass filtering algorithm sets a cutoff frequency (e.g., 500Hz), allowing only low-frequency signal components below this cutoff frequency to pass through, while filtering out high-frequency mechanical vibration components above this cutoff frequency from the original micro-strain signal. This preserves the deformation signal that truly reflects the stress state of the rod material during extrusion.

[0030] After the above filtering preprocessing, the obtained smooth current signal and pure micro-strain signal are sent to the memory buffer of the control unit.

[0031] S2, within the set continuous time window, when it is determined that the growth rate of the real-time current value is greater than the preset hardening retardation threshold, and the micro-strain signal is simultaneously detected to have a step increase, it is determined that the current rod material has reached the stress backlash critical point.

[0032] In this embodiment, the control unit maintains a set continuous time window in memory (e.g., a time range 50 milliseconds backward from the current moment). Within this time window, the control unit calculates the change in the real-time current value per unit time, i.e., the growth rate of the current value. Simultaneously, the control unit also monitors the amplitude variation of the micro-strain signal within this time window. When the control unit determines that the growth rate of the real-time current value exceeds a preset hardening hindrance threshold, and simultaneously detects a significant step increase in the micro-strain signal from a previous smooth fluctuation state, it determines that the current rod material has officially reached the stress reaction critical point.

[0033] In the above-mentioned determination process, the accuracy of the hardening inhibition threshold directly determines the timeliness and reliability of the critical point determination. If this threshold is set too high, it may trigger the action only after the back stress has already caused internal damage, leading to pressure relief failure; if it is set too low, it may trigger prematurely during the normal extrusion stage, causing unnecessary slippage and affecting the forming dimensions. Considering that the microscopic annealing hardness of high-strength alloy materials of the same grade often varies between different batches, and that the dynamic response characteristics of the cold heading machine will also drift slowly with the equipment status, using a fixed empirical threshold is obviously not suitable for actual production needs.

[0034] Therefore, as an example, this embodiment provides a threshold adaptive calibration method to be performed before the first piece is processed or when changing material batches, specifically by determining the hardening resistance threshold through the following steps.

[0035] S01, before the first piece is processed or when changing material batches, the main punch is controlled to slowly extrude the bolt blank at a constant calibrated speed lower than normal production. During this slow extrusion process, the real-time current value of the main punch servo motor and the actual physical pressure signal of the auxiliary reaction force sensor located at the bottom of the mold cavity are collected simultaneously.

[0036] Specifically, the control unit instructs the main punch to slowly extrude the bolt blank in the die at a constant calibrated speed (e.g., 5% to 10% of the normal speed) far below the normal production speed. The purpose of this slow extrusion is to completely eliminate the dynamic impact inertia and system vibration interference generated during high-speed stamping, making the extrusion process approach a quasi-static loading state, thereby truly reflecting the physical hardening characteristics of the material itself and independent of the dynamic effects of the equipment.

[0037] During this slow extrusion process, the real-time current value of the main punch servo motor and the actual physical pressure signal from the auxiliary reaction force sensor located at the bottom of the die cavity are simultaneously acquired. It should be understood that the auxiliary reaction force sensor directly bears the axial reaction force from the bottom of the billet, and its output signal can very accurately characterize the axial pressure state of the billet in the die cavity. Compared with the method of indirectly estimating the load through current, this physical pressure signal is a more direct reference that is not affected by changes in motor efficiency.

[0038] S02, when the rising slope of the actual physical pressure signal is detected to reach the preset physical saturation inflection point for the first time, the real-time current value growth rate within a set continuous time window before the moment the physical saturation inflection point is reached is extracted, and the product of the real-time current value growth rate and the preset safety buffer coefficient is used as the hardening stagnation threshold.

[0039] Specifically, the control unit continuously monitors the rising slope of the actual physical pressure signal. When the rising slope first reaches a preset physical saturation inflection point, it indicates that the radial volume flow generated by the current billet being squeezed in the mold cavity has completely stopped. The material can no longer flow outwards and can only be forced to extend axially, i.e., it is in a state of absolutely pure axial pressure. At this time, the control unit extracts the real-time current value growth rate within a set continuous time window before reaching the moment of the physical saturation inflection point, multiplies the extracted real-time current value growth rate by a preset safety buffer coefficient (e.g., a value between 0.90 and 0.95), and the resulting product is used as the hardening hindrance threshold specific to the current batch of material and the current equipment state, and is updated and stored in the non-volatile memory of the control unit.

[0040] It should be understood that setting a safety buffer coefficient serves two purposes. First, it provides a reasonable margin for the threshold, ensuring that the subsequent pressure relief action can be triggered before the actual stress reaches its peak under high-speed mass production conditions, thus allowing sufficient time for the servo valve to respond. Second, it can effectively prevent threshold mismatch caused by excessive current due to dynamic additional loads resulting from increased production speed.

[0041] After calibrating the hardening hindrance threshold, the equipment can enter normal high-speed production mode. When performing the joint judgment, in addition to comparing the relationship between the current growth rate and the hardening hindrance threshold, the step rise characteristic of the micro-strain signal must also be examined simultaneously. It should be noted that a simple excessive current growth rate may only be caused by high billet hardness or changes in mold lubrication conditions, and does not necessarily mean a sudden hindrance to material volume flow. Only when the rapid increase in current and the step jump in micro-strain of the mold sidewall occur simultaneously does it indicate a sudden change in the radial expansion force of the rod material within the mold cavity. These two factors together constitute the necessary and sufficient condition for the stress backlash critical point. Through this dual-feature joint judgment, the risk of misjudgment caused by a single signal change can be effectively eliminated, ensuring that the pressure relief control action is triggered only at the most critical stress accumulation moment, thereby minimizing interference with the normal forming cycle while ensuring processing safety.

[0042] S3, when the stress backlash critical point is reached, the main punch continues to feed and sends a breathing pulse command to the servo proportional valve of the clamping cylinder, so that the clamping pressure drops sharply to the set ratio of the initial rated pressure within the preset pulse release time to break the friction balance, and then immediately returns to the preset overload clamping pressure to actively induce the rod to produce a backward micro-slippage to release the internal stress.

[0043] When the critical point of stress backlash is reached, it indicates that the axial backlash stress inside the rod material has accumulated to a dangerous level. If not intervened in time, microcracks will appear at the junction of the rod and the head. To address this, the control unit further executes step S3, initiating active pressure relief and stress release control. That is, without interrupting the continuous feed of the main punch, the control unit actively induces a controllable micro-slippage of the rod by transiently adjusting the clamping conditions, thereby releasing the accumulated internal stress in the form of kinetic energy, rather than allowing it to transform into micro-defects inside the material under a rigid, locked state.

[0044] Specifically, when the stress backlash critical point is reached, the control unit maintains the drive command of the main punch servo motor unchanged, allowing the main punch to continue feeding forward according to the original speed curve. The reason for this setting is that if the main punch feed is stopped while releasing pressure, the rod will experience uncontrollable free rebound under residual stress after losing its clamping constraint, making it impossible to ensure dimensional consistency in subsequent forming. Maintaining continuous main punch feed provides a continuous axial propulsion background for the rod's backward sliding, ensuring that the sliding process takes place within an orderly extrusion field.

[0045] While the main punch continues to feed, the control unit sends a breathing pulse command to the servo proportional valve of the clamping cylinder. This breathing pulse command is a voltage or current control signal with a precise timing waveform. Its waveform characteristics are: first, a very short level transition that instantly increases the valve opening of the servo proportional valve, achieving rapid unloading; then, immediately returning to the original level after a preset time, restoring the valve opening to its initial degree. In response to this breathing pulse command, the pressure in the back pressure chamber of the clamping cylinder drops sharply to a set proportion of the initial rated pressure within a preset pulse release duration.

[0046] The pulse release duration is preferably set to 2 to 5 milliseconds. This duration must be short enough to ensure that the rod only experiences micron-level slippage rather than overall instability and sliding; at the same time, it must be long enough to break the adhesive balance between the rod and the mold under static friction. The set ratio is preferably 60% to 70% of the initial rated pressure. This ratio is sufficient to significantly reduce the peak friction force, allowing the rod to overcome residual friction and begin to move under axial thrust, while preventing complete loss of clamping and rod bending instability.

[0047] At the instant of the sudden pressure drop, the contact interface between the rod and the die, which was previously in a state of static frictional equilibrium, is broken. Because the axial compressive force applied by the main punch is far greater than the frictional force after the sudden drop, the rod is forced to slip slightly backward under the enormous axial thrust. It should be understood that although this slip is only on the micrometer scale, it is sufficient to rapidly release the elastic strain energy accumulated in the interface between the rod and the head, thereby reducing the stress peak to below a safe level and effectively blocking the initiation path of microcracks.

[0048] Furthermore, the breathing pulse command immediately drives the servo proportional valve to restore the clamping pressure to the preset overload clamping pressure with the fastest response speed (e.g., within 1 millisecond). The overload clamping pressure is preferably set to 110% to 120% of the initial rated pressure, a value higher than the constant clamping pressure during normal machining. It should be understood that overload recovery is used to quickly rebuild a stronger clamping constraint than normal after slippage, ensuring that the rod does not experience secondary slippage or bending instability due to stress re-accumulation during the subsequent remaining stroke of the compression process, thereby strictly limiting the slippage behavior to a single pulse cycle.

[0049] It should be noted that the total duration of this breathing pulse action must be controlled within 10 milliseconds, which is much shorter than the duration of the entire cold heading cycle (usually several hundred milliseconds to several seconds), and therefore will not have a perceptible impact on overall production efficiency. At the same time, since the main punch does not stop feeding during the pulse, the contact state between the main punch and the rod is maintained after slippage occurs, avoiding the secondary impact load that may occur when the punch re-contacts the workpiece after separation, ensuring the smoothness and continuity of the loading process.

[0050] Through the coordinated control of respiratory pulse decompression and overload recovery described above, this embodiment can resolve the contradiction between anti-slip clamping and internal stress release in the traditional rigid deadlock mode.

[0051] S4. The actual backward slippage of the rod during the execution of the breathing pulse command is obtained by the displacement sensor. The backward slippage is added as an additional compensation value to the remaining target feed stroke of the main punch, and the main punch is controlled to complete the final cold heading according to the compensated total stroke.

[0052] In step S3, the control unit actively induces a backward micro-slippage of the rod via a breathing pulse command, successfully releasing the accumulated internal stress. However, this active slippage inevitably leads to a loss in the effective extrusion stroke of the main punch. If this loss is not accurately compensated, the final bolt head thickness will be too thin and the overall length too short, thus failing to meet the dimensional accuracy requirements of high-strength bolts. Therefore, under the condition of complex transient interference, this step accurately separates the actual stress-release slippage from the raw signal of the displacement sensor and compensates it in a closed loop to the remaining feed stroke of the main punch.

[0053] However, within the extremely short cycle of the breathing pulse execution (the entire process from the sudden drop in clamping pressure to its recovery to overload clamping pressure), in addition to the active backward slippage of the rod due to the release of internal stress, there is an additional displacement with the same direction but a completely different mechanism: when the die closes rapidly again from the depressurized state to restore overload clamping, the radial closing action between the die and the rod will inevitably produce an axial frictional drag effect. This dragging force will cause the rod to continue to slide slightly backward within the die cavity. Its physical essence is that the radial displacement of the die is converted into the axial dragging motion of the rod through contact friction. If the control unit calculates the total backward displacement based solely on the difference between the readings of the displacement sensor at the moment the pulse command is sent and at the moment the clamping pressure is fully restored (i.e., the traditional end-point minus the start-point method), the pseudo-displacement generated by the frictional drag will be mixed with the actual stress-released slippage, resulting in a significantly larger calculated backward slippage. After adding this larger value as a compensation value to the main punch stroke, it will inevitably lead to overfeeding of the main punch, causing the bolt head thickness to exceed the tolerance, resulting in overcompensated scrap.

[0054] To overcome the aforementioned technical challenges, this invention designs a pseudo-displacement elimination method based on transient displacement step size truncation. Specifically, although true stress-release slip and friction drag have the same displacement direction, their dynamic characteristics are fundamentally different. The former is driven by the instantaneous burst of elastic strain energy accumulated within the material, with extremely high acceleration and rapid velocity decay, resulting in the completion of most of the displacement within a very short time window, and a relatively large absolute value of the corresponding transient displacement step size. The latter is caused by friction drag generated by the radial closing of the mold driven by the hydraulic system, with a relatively gentle speed and a longer duration, and a significantly smaller absolute value of the corresponding transient displacement step size. Based on this physical difference, this embodiment achieves accurate extraction of the true slip amount through the following steps S41-S42.

[0055] S41, During the entire execution cycle from sending the breathing pulse command to the complete recovery of the clamping pressure, the position coordinates of the displacement sensor are continuously recorded according to a preset sampling frequency to construct a displacement trajectory sequence; The difference between two adjacent position coordinates is calculated successively along the time axis of the displacement trajectory sequence, and the calculated sequence difference is used as the corresponding transient displacement step size;

[0056] Specifically, the control unit continuously records the position coordinates of the displacement sensor at a preset high sampling frequency (e.g., set to 10kHz to 20kHz) throughout the entire execution cycle from sending the breathing pulse command to the complete recovery of the clamping pressure. It should be understood that this sampling frequency is much higher than the frequency component of the pulse action itself, and also much higher than the dominant frequency of the mechanical vibration of the device, which is sufficient to capture every subtle movement of the rod during the entire process of decompression, sliding, dragging, and recovery without distortion.

[0057] As the sampling time progresses, the control unit sequentially stores the acquired position coordinates into a circular buffer in memory, thus constructing a high-fidelity displacement trajectory sequence with a time resolution at the microsecond level. Further, the control unit calculates the difference between two adjacent position coordinates along the time axis of this displacement trajectory sequence, using the calculated series of signed differences as the corresponding transient displacement step size. This transient displacement step size actually reflects the instantaneous displacement vector of the rod within each adjacent sampling interval; that is, a positive step size indicates that the rod moves forward, while a negative step size indicates that the rod moves backward.

[0058] It should be understood that during the execution of the breathing pulse, the rod moves backward due to stress release and friction drag, so the corresponding transient displacement step size is negative.

[0059] S42, in the displacement trajectory sequence, find the target position coordinates corresponding to the first drop of the transient displacement step size from greater than the preset intrinsic slip threshold to below the intrinsic slip threshold; calculate the absolute value of the difference between the target position coordinates and the initial position coordinates at the moment the breathing pulse command is sent, and use the absolute value of the difference as the backward slip amount.

[0060] Specifically, the control unit has a preset intrinsic slip threshold, which is a pre-calibrated positive value used to distinguish between displacements caused by active release slip and passive dragging slip. This intrinsic slip threshold can be predetermined in the following ways: during the equipment debugging phase, the breathing pulse action is executed multiple times, and the absolute value of the minimum step size in the active slip segment and the absolute value of the maximum step size in the dragging segment are collected respectively, and the midpoint between the two is taken as the intrinsic slip threshold; or it can be obtained through theoretical calculation combined with experimental correction.

[0061] After obtaining the transient displacement step sequence, the control unit sequentially determines the absolute value of each transient displacement step along the time axis, starting from the moment the breathing pulse command is sent. It is important to note that the actual stress-relieving slippage speed is extremely fast; the corresponding absolute value of the transient displacement step reaches its peak rapidly after the slippage begins, and then monotonically decreases as the internal stress dissipates rapidly. As the slippage nears its end, the absolute value of the step continues to decrease. Simultaneously, although the absolute value of the frictional drag generated by mold closure is small, its occurrence lags behind the actual slippage because the mold needs to complete its radial closure action first to generate sufficient radial normal pressure to form the axial frictional drag force.

[0062] Furthermore, within the displacement trajectory sequence, the target position coordinates are identified when the transient displacement step length first drops from above a preset intrinsic slip threshold to below the intrinsic slip threshold. This initial drop criterion precisely characterizes the inflection point where the actual stress slip process ends and the mechanical dragging process begins. Specifically: before the inflection point, the absolute value of the transient displacement step length remains consistently above the threshold, corresponding to the rapid stress release phase; after the inflection point, the absolute value of the transient displacement step length first decays below the threshold, and thereafter, the absolute value of the step length remains at a low level below the threshold, corresponding to the slow friction dragging phase when the mold recloses. Therefore, this target position coordinate is the termination position of the actual stress release slip.

[0063] Furthermore, the control unit calculates the absolute value of the difference between the target position coordinates and the initial position coordinates at the moment the breathing pulse command is sent, and uses this absolute value as the backward slip amount. It should be understood that this backward slip amount, because it excludes all pseudo-displacement contributions during the subsequent friction dragging phase, can truly and purely reflect the actual backward distance of the rod caused by stress release.

[0064] As an example, this backward slip is added as an additional compensation value to the remaining target feed stroke of the main punch, including:

[0065] S43, the backward sliding amount is directly accumulated along the feed direction of the main punch to the pre-stored initial feed endpoint coordinates of the main punch to generate dynamic compensation endpoint coordinates, and the main punch servo motor is controlled to drive the main punch to continue to feed forward until the actual position of the main punch reaches the dynamic compensation endpoint coordinates and then the feeding action stops.

[0066] Specifically, the control unit directly adds the backward slip amount along the feed direction of the main punch to the initial feed endpoint coordinates of the main punch, which are pre-stored in the control unit register. Here, the sign of the compensation value represented by the direct addition along the feed direction of the main punch is consistent with the feed direction (both are positive). The essence of the operation is to advance the originally set endpoint position of the main punch forward by a distance equal to the backward slip amount.

[0067] Through the above accumulation operation, the control unit generates a dynamic compensation endpoint coordinate. It should be understood that this dynamic compensation endpoint coordinate is a personalized target position calculated in real time for the actual slip state of the currently processed workpiece, thus enabling piece-by-piece compensation for the dispersion of slip caused by factors such as material batch differences and lubrication fluctuations.

[0068] Furthermore, the control unit uses the dynamically compensated endpoint coordinates as the new target position command and sends it to the servo driver of the main punch servo motor via a high-speed fieldbus (e.g., EtherCAT bus). Upon receiving the new target position command, the servo driver immediately switches to position control mode and drives the main punch to continue feeding forward. During the feeding process, the encoder built into the servo driver provides real-time feedback on the actual position of the main punch, forming a fully closed-loop position control. Once the actual position of the main punch reaches the dynamically compensated endpoint coordinates, the servo driver sends a position interrupt signal to the control unit. The control unit then issues a stop feeding command and maintains this position until the mold opens and the workpiece is demolded, thus completing the final cold heading process.

[0069] By employing the closed-loop compensation method based on transient displacement step length truncation, this invention can accurately recover the stroke lost due to active pressure relief slippage, while simultaneously eliminating pseudo-displacement interference introduced by mold closing friction drag during the compensation process. Therefore, the final formed bolt can avoid microcrack defects caused by unreleased internal stress accumulation, and ensure that its head thickness and total length are strictly within the design tolerance range.

[0070] Reference Figure 2 As shown, this embodiment of the invention also provides a control device 100 for a high-strength bolt processing equipment, the device comprising:

[0071] The signal acquisition module 101 is used to synchronously acquire the real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall during the cold heading process.

[0072] The critical determination module 102 is used to determine that the current rod material has reached the stress backlash critical point when the growth rate of the real-time current value is greater than the preset hardening hindrance threshold and the micro-strain signal is detected to have a step increase within a set continuous time window.

[0073] The breathing pressure relief module 103 is used to keep the main punch continuing to feed when the stress backlash critical point is reached, and send a breathing pulse command to the servo proportional valve of the clamping cylinder, so that the clamping pressure drops sharply to a set ratio of the initial rated pressure within a preset pulse pressure relief time to break the friction balance, and then immediately returns to the preset overload clamping pressure to actively induce the rod to produce a backward micro-slippage to release internal stress.

[0074] The closed-loop compensation module 104 is used to obtain the actual backward slippage of the rod during the execution of the breathing pulse command through the displacement sensor, and to add the backward slippage as an additional compensation value to the remaining target feed stroke of the main punch, so as to control the main punch to complete the final cold heading according to the compensated total stroke.

[0075] As an example, refer to Figure 3 As shown, the device further includes a filtering preprocessing module 105, used after the signal acquisition module acquires the real-time current value and the micro-strain signal:

[0076] The real-time current value is denoised and smoothed using a moving average filtering algorithm, and the micro-strain signal is filtered out for high-frequency mechanical vibration interference using a low-pass filtering algorithm.

[0077] As an example, refer to Figure 3 As shown, the device further includes a threshold calibration module 106, which is used to determine the hardening resistance threshold in the following manner:

[0078] Before processing the first piece or when changing material batches, the main punch is controlled to slowly extrude the bolt blank at a constant calibrated speed lower than normal production. During this slow extrusion process, the real-time current value of the main punch servo motor and the actual physical pressure signal of the auxiliary reaction force sensor located at the bottom of the mold cavity are collected simultaneously.

[0079] When the rising slope of the actual physical pressure signal is detected to reach the preset physical saturation inflection point for the first time, the real-time current value growth rate within a set continuous time window before the moment the physical saturation inflection point is reached is extracted, and the product of the real-time current value growth rate and the preset safety buffer coefficient is used as the hardening stagnation threshold.

[0080] As an example, the closed-loop compensation module 104 is specifically used for:

[0081] During the entire execution cycle from sending the breathing pulse command to the complete recovery of the clamping pressure, the position coordinates of the displacement sensor are continuously recorded at a preset sampling frequency to construct a displacement trajectory sequence; the difference between two adjacent position coordinates is calculated successively along the time axis of the displacement trajectory sequence, and the calculated sequence difference is used as the corresponding transient displacement step size;

[0082] In the displacement trajectory sequence, find the target position coordinates corresponding to the first drop of the transient displacement step size from above the preset intrinsic slip threshold to below the intrinsic slip threshold; calculate the absolute value of the difference between the target position coordinates and the initial position coordinates at the moment the breathing pulse command is sent, and use the absolute value of the difference as the backward slip amount.

[0083] As an example, the closed-loop compensation module 104 is further used for:

[0084] The backward sliding amount is directly accumulated along the feed direction of the main punch to the pre-stored initial feed endpoint coordinates of the main punch to generate dynamic compensation endpoint coordinates. The main punch servo motor is controlled to drive the main punch to continue feeding forward until the actual position of the main punch reaches the dynamic compensation endpoint coordinates and then the feeding action stops.

[0085] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A control method for high-strength bolt processing equipment, applied to the cold heading of bolts with large length-to-diameter ratios, characterized in that, The method includes: S1, synchronously acquiring the real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall during the cold heading process; S2, within a set continuous time window, when it is determined that the growth rate of the real-time current value is greater than the preset hardening stagnation threshold, and the micro-strain signal is simultaneously detected to have a step increase, it is determined that the current rod material has reached the stress backlash critical point; S3, when the stress backlash critical point is reached, the main punch continues to feed, and a breathing pulse command is sent to the servo proportional valve of the clamping cylinder, so that the clamping pressure drops sharply to a set ratio of the initial rated pressure within a preset pulse release time to break the friction balance, and then immediately recovers to the preset overload clamping pressure to actively induce the rod to generate a backward micro-slippage to release internal stress; S4, the actual backward slippage of the rod during the execution of the breathing pulse command is obtained by the displacement sensor, and the backward slippage is added as an additional compensation value to the remaining target feed stroke of the main punch, and the main punch is controlled to complete the final cold heading according to the compensated total stroke; The method of obtaining the actual backward slippage of the lever during the execution of the breathing pulse command by means of a displacement sensor includes: S41, continuously recording the position coordinates of the displacement sensor at a preset sampling frequency throughout the entire execution cycle from sending the breathing pulse command to the complete recovery of the clamping pressure, so as to construct a displacement trajectory sequence; calculating the difference between two adjacent position coordinates along the time axis of the displacement trajectory sequence, and using the calculated sequence difference as the corresponding transient displacement step size; S42, finding the target position coordinates in the displacement trajectory sequence when the transient displacement step size first falls from above a preset intrinsic slippage threshold to below the intrinsic slippage threshold; calculating the absolute value of the difference between the target position coordinates and the initial position coordinates at the moment the breathing pulse command is sent, and using the absolute value of the difference as the backward slippage amount; The backward slip amount is added as an additional compensation value to the remaining target feed stroke of the main punch, including: S43, the backward slip amount is directly accumulated along the feed direction of the main punch to the pre-stored initial feed endpoint coordinates of the main punch to generate dynamic compensation endpoint coordinates, and the main punch servo motor is controlled to drive the main punch to continue to feed forward until the actual position of the main punch reaches the dynamic compensation endpoint coordinates and then the feeding action stops.

2. The control method for the high-strength bolt processing equipment according to claim 1, characterized in that, After obtaining the real-time current value and the micro-strain signal, the method further includes: using a moving average filtering algorithm to perform noise reduction and smoothing processing on the real-time current value, and using a low-pass filtering algorithm to perform high-frequency mechanical vibration interference filtering processing on the micro-strain signal.

3. The control method for the high-strength bolt processing equipment according to claim 1, characterized in that, The hardening hindrance threshold is determined as follows: S01, before processing the first piece or when changing material batches, the main punch is controlled to slowly extrude the bolt blank at a constant calibrated speed lower than normal production. During this slow extrusion process, the real-time current value of the main punch servo motor and the actual physical pressure signal of the auxiliary reaction force sensor located at the bottom of the mold cavity are collected simultaneously; S02, when the rising slope of the actual physical pressure signal is detected to reach the preset physical saturation inflection point for the first time, the real-time current value growth rate within a set continuous time window before reaching the physical saturation inflection point is extracted, and the product of the real-time current value growth rate and the preset safety buffer coefficient is used as the hardening hindrance threshold.

4. A control device for a high-strength bolt processing equipment, the device being based on the method of claim 1, characterized in that, The device includes: a signal acquisition module for synchronously acquiring the real-time current value of the main punch servo motor and the micro-strain signal of the clamping die sidewall during cold heading; a critical determination module for determining that the current rod material has reached the stress rebound critical point when, within a set continuous time window, the growth rate of the real-time current value is greater than a preset hardening retardation threshold and a step increase in the micro-strain signal is detected simultaneously; and a breathing and decompression module for maintaining the main punch feed when the stress rebound critical point is reached and providing pressure relief to the servo motor of the clamping cylinder. For example, the valve sends a breathing pulse command, causing the clamping pressure to drop sharply to a set ratio of the initial rated pressure within a preset pulse release time to break the friction balance, and then immediately restores to the preset overload clamping pressure to actively induce the rod to produce a backward micro-slippage to release internal stress; the closed-loop compensation module is used to obtain the actual backward slippage of the rod during the execution of the breathing pulse command through a displacement sensor, and add the backward slippage as an additional compensation value to the remaining target feed stroke of the main punch, and control the main punch to complete the final cold heading according to the compensated total stroke; The device further includes a filtering preprocessing module, which, after the signal acquisition module acquires the real-time current value and the micro-strain signal, performs noise reduction and smoothing processing on the real-time current value using a moving average filtering algorithm, and performs high-frequency mechanical vibration interference filtering processing on the micro-strain signal using a low-pass filtering algorithm. The device further includes a threshold calibration module, which determines the hardening hindrance threshold in the following manner: before processing the first piece or when changing material batches, the main punch is controlled to slowly extrude the bolt blank at a constant calibration speed lower than normal production. During this slow extrusion process, the real-time current value of the main punch servo motor and the actual physical pressure signal of the auxiliary reaction force sensor located at the bottom of the mold cavity are collected simultaneously. When the rising slope of the actual physical pressure signal is detected to reach the preset physical saturation inflection point for the first time, the real-time current value growth rate within a set continuous time window before reaching the physical saturation inflection point is extracted, and the product of the real-time current value growth rate and the preset safety buffer coefficient is used as the hardening hindrance threshold.

5. The control device for the high-strength bolt processing equipment according to claim 4, characterized in that, The closed-loop compensation module is specifically used to: continuously record the position coordinates of the displacement sensor according to a preset sampling frequency during the entire execution cycle from sending the breathing pulse command to the complete recovery of the clamping pressure, so as to construct a displacement trajectory sequence; The difference between two adjacent position coordinates is calculated successively along the time axis of the displacement trajectory sequence, and the calculated sequence difference is used as the corresponding transient displacement step size. In the displacement trajectory sequence, the target position coordinate corresponding to the first drop of the transient displacement step size from above the preset intrinsic slip threshold to below the intrinsic slip threshold is found. The absolute value of the difference between the target position coordinate and the initial position coordinate at the moment the breathing pulse command is sent is calculated, and the absolute value of the difference is used as the backward slip amount.

6. The control device for the high-strength bolt processing equipment according to claim 4, characterized in that, The closed-loop compensation module is further configured to: directly accumulate the backward slip amount along the feed direction of the main punch to the pre-stored initial feed endpoint coordinates of the main punch to generate dynamic compensation endpoint coordinates, control the main punch servo motor to drive the main punch to continue feeding forward until the actual position of the main punch reaches the dynamic compensation endpoint coordinates and then stop the feeding action.

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