Automobile pull rod ball head assembly assembling detection method

Abstract

The application discloses a kind of automobile pull rod ball head assembly assembly detection methods, belong to pull rod ball head detection technical field, solve the ball head pull rod assembly in dissimilar metal galvanic couple, roll riveting residual tensile stress and polyurethane ball seat and the micro gap between shell, under the dry-wet alternation of chlorine salt, form corrosion environment induced pitting crack, final inspection cannot be identified due to obstruction, resolution and detection limitations, crack penetrates shell after serving for several years, causing sealing plate failure and ball head pull-off, resulting in vehicle steering out-of-control accident.The application comprises the following steps: S1, in the polyurethane ball seat press-fitting process, synchronous acquisition servo press press-fitting force signal and ram displacement signal.The application synchronously acquires ball seat press-fitting force-displacement and roll riveting torque-feeding data, respectively extracts gap geometry and residual stress deviation parameters, fuses into corrosion fatigue risk index and outlier determination, identifies high-risk workpieces prone to fatigue cracks under chlorine salt conditions, and avoids the flow of ball head assemblies into real vehicles that are missed in the final inspection blind area.

Description

Technical Field

[0001] This invention relates to the field of tie rod ball joint testing technology, and more particularly to an assembly testing method for automotive tie rod ball joint assemblies. Background Technology

[0002] The ball joint tie rod assembly adopts a bottom-loaded, top-closed structure. Its automated assembly relies on a high-precision rotary indexing plate, on which accompanying fixtures are evenly distributed. Each station operates in an orderly manner with specialized equipment. A vibratory feeder transports the ball joint housing, which is grasped by a robotic arm and rotated 180 degrees before being precisely placed into the accompanying fixture for centering and clamping. The robotic arm then grasps the ball joint pin, and with the aid of an end effector and force sensor, inserts the pin through the large opening and exits through the small opening of the housing. The vibratory feeder transports a polyurethane ball seat, which is placed into the housing by the robotic arm. A servo electric cylinder drives the pressure head to complete the pressing and briefly maintain pressure. Next, the vibratory feeder transports a metal sealing plate, which is placed into the housing by a suction cup robotic arm. A low-pressure cylinder drives the pressure head for pre-pressing and fixing. Finally, a riveting machine is used, employing upper mold positioning and planetary rotation and radial feed of rollers to complete the riveting of the large opening of the housing. The system monitors the roller feed and riveting torque to control quality. After assembly, the torque sensor detects the swing torque and starting torque of the ball head pin, and the industrial camera, together with the algorithm, completes the visual final inspection. Defective products are diverted by the robot, and qualified finished products are unloaded by the robot to the discharge conveyor belt. The entire production data is recorded by the system and bound with traceability codes to ensure assembly accuracy and product consistency.

[0003] In the automated assembly of ball joint rods employing an inverted shell, bottom loading of the ball pin, top pressing of the polyurethane ball seat, and roll riveting of the metal end plate, the metal end plate, made of austenitic stainless steel or chrome-plated carbon steel with high-potential passivation, and the shell, made of phosphated ordinary carbon steel, forms a dissimilar metal galvanic couple at the tight contact interface, with the shell as the anode and the end plate as the cathode. Simultaneously, the concentric extrusion of the rollers and the superposition of multiple contact pressures during the riveting process introduce a residual tensile stress field along the axial direction at the inner root of the shell end. Furthermore, due to manufacturing tolerances and riveting springback, a closed annular gap with a width between 25 and 100 micrometers and a sufficient depth-to-width ratio is naturally generated between the upper surface of the polyurethane ball seat, the lower plane of the end plate, and the inner cylindrical surface of the shell. Additionally, because the outer surface of the riveted rod has a smooth and regular rolled edge shape, the multi-angle industrial camera experiences a significant impact on the inner root due to the rolled edge at the end. Due to physical obstruction and resolution depth limitations, microscopic corrosion or early short cracks cannot be captured. The online detection of oscillating torque shows a qualified value because the crack has not yet extended to the point of affecting the preload of the polyurethane ball joint. The airtightness test also passes smoothly because the crack has not yet penetrated the wall thickness. Even with the introduction of non-destructive testing methods such as eddy current testing or phased array ultrasonic testing, it is difficult to achieve reliable identification at the production line level due to the complex curvature of the end face, the economic efficiency of the cycle time, and the insufficient signal-to-noise ratio of micron-level cracks. As a result, this latent defect may only be exposed after hundreds of hours of accelerated corrosion by neutral salt spray and superimposed alternating load durability bench testing. Once a ball joint assembly with such defects has been in service in a high-chlorine environment in a real vehicle for several years until the crack penetrates the wall thickness of the housing and causes the sealing plate to fail, the ball joint will be pulled out of the housing, the vehicle will instantly lose steering control, and cause the highest level of driving safety failure accident.

[0004] Therefore, an assembly and testing method for automotive tie rod ball joint assemblies is proposed to solve or alleviate the above problems. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing an assembly and testing method for automotive tie rod ball joint assemblies.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for assembling and inspecting automotive tie rod ball joint assemblies includes the following steps: S1. During the polyurethane ball seat pressing process, the pressing force signal and the pressure head displacement signal of the servo press are collected synchronously. The pressing force signal is filtered to eliminate periodic interference. A continuous and differentiable pressing force fitting function is established for the filtered pressing force and displacement data, and the first and second derivatives of the fitting function are calculated. S2. Based on the fitting function of the pressing force and its first and second derivatives, identify the inflection point of the pressing curve, record the inflection point force and inflection point displacement, obtain the pressing end force, calculate the force attenuation rate during the pressure holding stage, obtain the ball seat rebound displacement, and calculate the effective compression of the ball seat. S3. Based on the relative deviation of the effective compression of the ball seat and the relative deviation of the force attenuation rate during the pressure holding stage, the gap risk index is synthesized according to the first preset weight. The gap risk index characterizes the degree to which the geometric dimensions of the occluded gap deviate from the ideal range. S4. During the riveting process, the output torque of the riveting motor and the radial feed displacement of the roller are collected synchronously. The torque signal is filtered and smoothed, and a torque fitting function is established for the smoothed torque and displacement data. S5. Based on the torque fitting function, calculate the riveting torque slope, the riveting endpoint torque, and the riveting end torque increment ratio; S6. The riveting torque slope, riveting end torque and riveting end torque increment ratio are compared with the corresponding nominal values ​​to obtain normalized values. The residual stress risk index is synthesized according to the second preset weight. The residual stress risk index characterizes the degree to which the residual tensile stress level introduced by the riveting process at the root of the inner side of the shell opening deviates from the normal range. S7. The gap risk index and the residual stress risk index are fused according to the preset fusion model to obtain the corrosion fatigue latent risk index. The standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces is calculated. When the standardized deviation score exceeds the preset threshold, the workpiece under inspection is determined to have corrosion fatigue latent defect risk.

[0007] Preferably, in step S1, during the polyurethane ball seat pressing process, the pressing force signal and the pressure head displacement signal of the servo press are simultaneously acquired, the pressing force signal is filtered to eliminate periodic interference, a continuously differentiable pressing force fitting function is established for the filtered pressing force and displacement data, and the first and second derivatives of the fitting function are calculated. Specifically, this includes the following steps: The timing data of the pressing force signal and the displacement signal of the press head of the servo press are synchronously collected at a sampling frequency of not less than 1000 Hz to form a set of data points with one-to-one correspondence between force and displacement. A second-order notch filter with a center frequency of 50 Hz was used to filter the pressing force signal to eliminate power frequency interference and obtain the filtered force sequence. For the set of force-displacement data points composed of the filtered force sequence and displacement sequence, a local weighted regression method is used to establish a fitting function for the pressing force. At each displacement point, data points within a neighborhood window centered on that displacement point with a half-width of 0.1 mm to 0.3 mm are selected. A Gaussian kernel function is used to assign fitting weights to each data point that decay with distance. A third-order polynomial is fitted within the window. The constant term of the polynomial is taken as the fitting value of the pressing force at that displacement point, the coefficient of the first term is taken as the instantaneous slope of the pressing curve at that displacement point, and twice the coefficient of the second term is taken as the rate of change of the slope of the pressing curve at that displacement point. Local weighted regression fitting is performed on all displacement points one by one to obtain the fitting function of the press-fitting force that is continuously differentiable throughout the entire stroke, as well as its first-order derivative function and second-order derivative function.

[0008] Preferably, S2, the basic pressing force fitting function and its first and second derivatives, identify the inflection point position of the pressing curve, record the inflection point force and inflection point displacement, obtain the pressing end force, calculate the force attenuation rate during the pressure holding stage, obtain the ball seat rebound displacement, and calculate the effective compression of the ball seat, specifically including the following steps: Within the search interval of 0.5 mm before the press-fitting start position to the press-fitting end position, the absolute value of the rate of change of the slope of the press-fitting curve at each displacement point is traversed to find the displacement point that obtains a local maximum value as a candidate inflection point. When the absolute value of the rate of change of the slope at the candidate inflection point is greater than or equal to the preset inflection point judgment threshold, the candidate inflection point is confirmed as the press-fitting inflection point, and the inflection point displacement and the corresponding inflection point force are recorded. The maximum value of the monotonically increasing segment of displacement during the pressing process is taken as the pressing end displacement, and the pressing end force corresponding to this pressing end displacement is obtained according to the pressing force fitting function. During the pressure holding stage, in which the displacement remains constant after the pressure head reaches the end point, the average value of the pressure force at the last few sampling points of the pressure holding stage is taken as the pressure holding end force. The force attenuation rate of the pressure holding stage is calculated, which is the difference between the pressure holding end force and the pressure holding end force divided by the pressure holding end force and then multiplied by 100%. After the pressure head retracts, the ball seat rebound displacement is obtained by measuring the difference between the actual height of the upper surface of the sealing plate and the theoretical nominal height, or by measuring the difference between the critical displacement when the pressure head and the ball seat disengage during the unloading process of the servo press and the displacement at the end of the pressing. Calculate the effective compression of the ball seat, which is the nominal total compression of the ball seat minus the rebound displacement of the ball seat. The nominal total compression of the ball seat is the difference between the original free height of the ball seat and the nominal height after assembly.

[0009] Preferably, step S3 involves synthesizing a gap risk index based on the relative deviation of the effective compression of the ball seat and the relative deviation of the force attenuation rate during the pressure holding stage, according to a first preset weight. The gap risk index characterizes the degree to which the geometric dimensions of the occluded gap deviate from the ideal range, specifically including the following steps: Obtain the nominal effective compression, which is the statistical average of the effective compression of the ball seat in historical qualified batches; The relative deviation of effective compression is calculated as the absolute value of the difference between the effective compression of the ball seat and the nominal effective compression, divided by the nominal effective compression. Obtain the nominal force decay rate, which is the statistical average of the force decay rate during the pressure holding stage in historical qualified batches; The relative deviation of the force attenuation rate is calculated by dividing the absolute value of the difference between the force attenuation rate and the nominal force attenuation rate during the pressure holding stage by the nominal force attenuation rate. The gap risk index is obtained by weighting the relative deviation of effective compression and the relative deviation of force attenuation rate according to the first preset weight. The first preset weight includes a first weight and a second weight. The value of the first weight ranges from 0.6 to 0.7, and the value of the second weight ranges from 0.3 to 0.4. The sum of the first weight and the second weight is equal to 1.

[0010] Preferably, in step S4, during the riveting closing process, the output torque of the riveting motor and the radial feed displacement of the roller are simultaneously acquired, the torque signal is filtered and smoothed, and a torque fitting function is established for the smoothed torque and displacement data. Specifically, this includes the following steps: At the riveting finishing station, the output torque signal of the riveting motor and the radial feed displacement signal of the roller are synchronously collected at a sampling frequency of not less than 500 Hz, forming a set of data points with one-to-one correspondence between torque and displacement. The zero displacement point is the position when the roller just contacts the edge of the housing. A second-order Butterworth low-pass filter with a cutoff frequency of 10 to 20 Hz is used to filter the torque signal, and a combination of forward and reverse filtering is used to achieve zero-phase characteristics and obtain a smooth torque sequence. The smoothed set of torque and displacement data points is fitted globally by least squares using a second-order polynomial to obtain the torque fitting function. The second-order polynomial has a constant term, a first-order term, and a second-order term. Calculate the fitting coefficient of determination. When the fitting coefficient of determination is less than 0.9, mark the workpiece as an abnormal workpiece in the riveting process.

[0011] Preferably, step S5, calculating the riveting torque slope, the riveting endpoint torque, and the riveting endpoint torque increment ratio based on the torque fitting function, specifically includes the following steps: The range of 30% to 80% of the total radial feed stroke of the roller is selected as the stable range of plastic flow. The fitted torque values ​​at the beginning and end of this range are calculated. The difference between the torque value at the end and the torque value at the beginning is divided by the length of the range, and the quotient is used as the riveting torque slope. Take the radial feed amount when the roller feeds to the target endpoint set in the process, and calculate the fitted torque value corresponding to the feed amount at the endpoint according to the torque fitting function, which is used as the end torque of the riveting endpoint. Take the position at 80% of the total radial feed stroke of the roller, calculate the corresponding fitting torque value based on the torque fitting function, divide the difference between the end torque of the riveting and the torque value at the 80% position by the end torque of the riveting, and multiply by 100%. The resulting percentage is used as the torque increment ratio of the end riveting stage.

[0012] Preferably, step S6 involves comparing the riveting torque slope, the riveting endpoint torque, and the riveting end segment torque increment ratio with their corresponding nominal values ​​to obtain normalized values, and then synthesizing these values ​​according to a second preset weight to obtain a residual stress risk index. The residual stress risk index characterizes the degree to which the residual tensile stress level introduced by the riveting process at the root of the shell's inner side deviates from the normal range. Specifically, this includes the following steps: Obtain the nominal riveting torque slope, the nominal riveting end torque, and the nominal riveting end torque increment ratio. All three are statistical averages of the corresponding characteristic parameters in historical qualified batches. Divide the riveting torque slope by the nominal riveting torque slope to obtain the normalized torque slope value. Divide the end torque of the riveting roll by the nominal end torque of the riveting roll to obtain the normalized value of the end torque. Divide the final riveting torque increment ratio by the nominal final riveting torque increment ratio to obtain the normalized value of the final increment ratio. The residual stress risk index is obtained by weighting the normalized values ​​of the moment slope, the end moment, and the final increment ratio according to the second preset weight. The second preset weight includes the third weight, the fourth weight, and the fifth weight. The third weight is greater than the fourth weight and the fifth weight, and the sum of the third weight, the fourth weight, and the fifth weight is equal to 1.

[0013] Preferably, step S7 involves fusing the gap risk index and the residual stress risk index according to a preset fusion model to obtain a corrosion fatigue latent risk index, calculating the standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces, and determining that the workpiece under inspection has a corrosion fatigue latent defect risk when the standardized deviation score exceeds a preset threshold. This specifically includes the following steps: Obtain the nonlinear coupling coefficient and the linear combination weight. The nonlinear coupling coefficient has a value range of 0.5 to 0.8, and the linear combination weight includes a sixth weight and a seventh weight, the sum of which is equal to 1. The corrosion fatigue latent risk index is calculated according to the preset fusion model. The preset fusion model is: the corrosion fatigue latent risk index is equal to the product of the nonlinear coupling coefficient and the crevice risk index and the residual stress risk index, plus 1 minus the sum of the product of the difference of the nonlinear coupling coefficient and the sixth weight and the crevice risk index plus the product of the seventh weight and the residual stress risk index. Obtain a benchmark sample set of corrosion fatigue latent risk index for historical qualified workpieces. The benchmark sample set consists of the corrosion fatigue latent risk index of several qualified workpieces produced during the stable operation of the production line and verified by accelerated corrosion fatigue bench durability test. Calculate the mean and standard deviation of the benchmark sample set. The standardized deviation score of the workpiece to be inspected is calculated as the difference between the corrosion fatigue potential risk index of the workpiece to be inspected and the mean of the benchmark sample set, divided by the standard deviation of the benchmark sample set. Set low-risk and high-risk thresholds. When the standardized deviation score is less than or equal to the low-risk threshold, the workpiece is judged as low-risk and released normally. When the standardized deviation score is greater than the low-risk threshold but less than or equal to the high-risk threshold, the workpiece is judged as medium-risk warning workpiece and undergoes sampling bench verification. When the standardized deviation score is greater than the high-risk threshold, the workpiece is judged as high-risk workpiece and rejected.

[0014] Preferably, step S7, fusing the gap risk index and the residual stress risk index according to a preset fusion model to obtain a corrosion fatigue latent risk index, calculating the standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces, and determining that the workpiece under inspection has a corrosion fatigue latent defect risk when the standardized deviation score exceeds a preset threshold, further includes the following steps: For workpieces that are determined to be low-risk and pass subsequent bench verification, the mean and variance are updated using an exponentially weighted moving average method, with the smoothing factor ranging from 0.01 to 0.05. The mean is updated by multiplying the smoothing factor by the corrosion fatigue latent risk index of the qualified workpiece, plus 1 minus the difference of the smoothing factor multiplied by the old mean. The variance update method is as follows: the new variance is equal to the smoothing factor multiplied by the square of the difference between the corrosion fatigue potential risk index of the qualified workpiece and the new mean, plus 1 minus the difference of the smoothing factor multiplied by the old variance.

[0015] The present invention has the following beneficial effects: This invention simultaneously collects force-displacement data during the press-fitting process of polyurethane ball joints, extracts the effective compression amount and holding pressure attenuation rate, quantifies the geometric deviation of the 25–100 μm annular closed gap, and simultaneously collects torque-feed displacement data during the riveting process, extracts the torque slope, endpoint torque, and final segment increment ratio, quantifies the deviation of the axial residual tensile stress at the root of the joint, and fuses the above two types of parameters into a corrosion fatigue risk index through a nonlinear model. Based on the distribution of historical qualified workpieces, outlier determination is performed, thereby identifying workpieces that are prone to forming a high-chlorine strong acid corrosion environment in the annular gap and inducing fatigue crack initiation under alternating wet and dry chloride salt conditions before leaving the factory. This prevents ball joint assemblies with such defects from entering the actual vehicle due to physical obstruction of the rolled edge and insensitivity to non-penetrating cracks during the final inspection of the production line. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of the present invention; Figure 2 This is the pressure-displacement curve of the polyurethane ball seat press-fitting according to the present invention; Figure 3 The first / second derivative of the press-fit curve of this invention; Figure 4 This is the force decay curve during the pressure holding stage of the present invention; Figure 5 This is the riveting closing torque-feed curve of the present invention; Figure 6 This is the force decay curve during the pressure holding stage of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first," "second," and "third" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] An assembly inspection method for automotive tie rod ball joint assemblies, such as... Figure 1 As shown, it includes the following steps: S1. During the polyurethane ball seat pressing process, the pressing force signal and the pressure head displacement signal of the servo press are collected synchronously. The pressing force signal is filtered to eliminate periodic interference. A continuous and differentiable pressing force fitting function is established for the filtered pressing force and displacement data, and the first and second derivatives of the fitting function are calculated. S1.1 Synchronously acquire the timing data of the pressing force signal and the pressure head displacement signal of the servo press at a sampling frequency of not less than 1000 Hz to form a set of data points with one-to-one correspondence between force and displacement; S1.2. A second-order notch filter with a center frequency of 50 Hz is used to filter the pressing force signal to eliminate power frequency interference and obtain the filtered force sequence. S1.3. For the set of force-displacement data points composed of the filtered force sequence and displacement sequence, a local weighted regression method is used to establish a fitting function for the pressing force. At each displacement point, data points are selected within a neighborhood window centered on that displacement point with a half-width of 0.1 mm to 0.3 mm. A Gaussian kernel function is used to assign fitting weights to each data point that decrease with distance. A third-order polynomial is fitted within the window. The constant term of the polynomial is taken as the fitting value of the pressing force at that displacement point, the coefficient of the first term is taken as the instantaneous slope of the pressing curve at that displacement point, and twice the coefficient of the second term is taken as the rate of change of the slope of the pressing curve at that displacement point. S1.4 Perform local weighted regression fitting on all displacement points one by one to obtain the fitting function of the press-fitting force that is continuously differentiable throughout the entire stroke, as well as its first-order derivative function and second-order derivative function; Based on the above steps, the pressing force signal and press head displacement signal of the servo press are collected. After notch filtering to eliminate power frequency interference, a continuously differentiable pressing force fitting function is established through local weighted regression, as detailed below. Figure 2 The pressure-displacement curve of the polyurethane ball seat is shown below; Meanwhile, based on the above S1-S1.4, the extracted pressing curve fitting function and inflection point force and endpoint force directly reflect the initial fit tightness between the ball seat and the shell. By comparing with the statistical results of historical qualified batches, the algorithm can determine that there is an abnormality in the size or hardness of the ball seat material when the inflection point force or endpoint force exceeds the normal distribution range.

[0025] S2. Based on the fitting function of the pressing force and its first and second derivatives, identify the inflection point of the pressing curve, record the inflection point force and inflection point displacement, obtain the pressing end force, calculate the force attenuation rate during the pressure holding stage, obtain the ball seat rebound displacement, and calculate the effective compression of the ball seat. S2.1 Within the search interval of 0.5 mm before the start and end of the pressing, traverse the absolute value of the rate of change of the slope of the pressing curve at each displacement point, and find the displacement point that obtains a local maximum value as a candidate inflection point. When the absolute value of the rate of change of the slope at the candidate inflection point is greater than or equal to the preset inflection point judgment threshold, the candidate inflection point is confirmed as the pressing inflection point, and the inflection point displacement and the corresponding inflection point force are recorded. S2.2. Take the maximum value of the monotonically increasing segment of displacement during the pressing process as the pressing end displacement, and obtain the pressing end force corresponding to the pressing end displacement according to the pressing force fitting function. S2.3 During the pressure holding stage after the pressure head reaches the end point and the displacement remains unchanged, the average value of the pressure force at the last few sampling points of the pressure holding stage is taken as the pressure holding end force. The force attenuation rate of the pressure holding stage is calculated, which is the difference between the pressure holding end force and the pressure holding end force divided by the pressure holding end force and then multiplied by 100%. S2.4 After the pressure head retracts, the ball seat rebound displacement is obtained by measuring the difference between the actual height of the upper surface of the sealing plate and the theoretical nominal height, or by measuring the difference between the critical displacement when the pressure head and the ball seat disengage during the unloading process of the servo press and the displacement at the end of the pressing. S2.5 Calculate the effective compression of the ball seat. Its value is the nominal total compression of the ball seat minus the rebound displacement of the ball seat. The nominal total compression of the ball seat is the difference between the original free height of the ball seat and the nominal height after assembly, which is given by the product design drawings. Based on the above steps, to demonstrate the first and second derivatives of the pressing force fitting function, please refer to the following... Figure 3 The first / second derivatives of the press-fit curves shown illustrate the decay of the press-fit force over time during the holding phase, after the press head reaches its endpoint and maintains a constant displacement. This is used to obtain the final press-fit force and the final holding force, and to calculate the force decay rate during the holding phase. See details for further information. Figure 4 The force decay curve during the pressure holding stage is shown.

[0026] Meanwhile, based on the above S2-S2.5, the force decay rate during the pressure holding stage is a direct characterization of the viscoelastic properties of polyurethane materials. An abnormally low force decay rate during the pressure holding stage indicates that the ball seat material is too hard or that there is abnormal internal densification. An abnormally high force decay rate during the pressure holding stage indicates that the material is too soft or that there are pores or loose defects inside. Furthermore, although the press-fit force curve mainly reflects the fit between the ball seat and the shell, the profile error of the ball head surface can indirectly change the slope of the press-fit curve after the inflection point by affecting the filling path of the ball seat in the wedge gap. Under normal spherical surface conditions, the force value rises smoothly and repeatably after the inflection point. When the spherical surface profile is out of tolerance, the fluctuation of the force value rise after the inflection point increases significantly. The stability of the inflection point position is also an indirect indicator of the consistency of the ball head surface.

[0027] S3. Based on the relative deviation of the effective compression of the ball seat and the relative deviation of the force attenuation rate during the pressure holding stage, the gap risk index is synthesized according to the first preset weight. The gap risk index characterizes the degree to which the geometric dimensions of the occluded gap deviate from the ideal range. S3.1 Obtain the nominal effective compression amount, which is the statistical average of the effective compression amount of the ball seat in historical qualified batches; S3.2 Calculate the relative deviation of effective compression, which is the absolute value of the difference between the ball seat effective compression and the nominal effective compression divided by the nominal effective compression. S3.3 Obtain the nominal force attenuation rate, which is the statistical average of the force attenuation rate during the pressure holding stage in historical qualified batches; S3.4 Calculate the relative deviation of the force attenuation rate, which is the absolute value of the difference between the force attenuation rate and the nominal force attenuation rate during the pressure holding stage, divided by the nominal force attenuation rate. S3.5. The relative deviation of effective compression and the relative deviation of force attenuation rate are weighted and synthesized according to the first preset weight to obtain the gap risk index. The first preset weight includes a first weight and a second weight. The value of the first weight ranges from 0.6 to 0.7, and the value of the second weight ranges from 0.3 to 0.4. The sum of the first weight and the second weight is equal to 1. The gap risk index is also used to identify the following assembly anomalies: when the pressing inflection point force or the pressing end point force exceeds the statistical distribution range of the corresponding parameters of the historical qualified batches, it is determined that the ball seat material size or hardness is abnormal; when the rate of change of the pressing curve slope exceeds the instantaneous extreme value of the normal fluctuation range at the non-inflection point position, it is determined that foreign objects are stuck in the shell hole; when the fluctuation degree of the pressing force rise in the plastic flow section after the pressing inflection point exceeds the preset fluctuation threshold, it is determined that the spherical profile of the ball head is out of tolerance.

[0028] S4. During the riveting process, the output torque of the riveting motor and the radial feed displacement of the roller are collected synchronously. The torque signal is filtered and smoothed, and a torque fitting function is established for the smoothed torque and displacement data. S4.1 At the riveting finishing station, the output torque signal of the riveting motor and the radial feed displacement signal of the roller are synchronously collected at a sampling frequency of not less than 500 Hz to form a set of data points with one-to-one correspondence between torque and displacement. The zero displacement point is the position when the roller just contacts the edge of the housing. S4.2 A second-order Butterworth low-pass filter with a cutoff frequency of 10 to 20 Hz is used to filter the torque signal, and a combination of forward and reverse filtering is used to achieve zero-phase characteristics and obtain a smooth torque sequence. S4.3. The smoothed set of torque and displacement data points is fitted with a second-order polynomial using least squares global fitting to obtain the torque fitting function. The second-order polynomial has a constant term, a first-order term, and a second-order term. S4.4 Calculate the fitting coefficient of determination. When the fitting coefficient of determination is less than 0.9, mark the workpiece as an abnormal workpiece in the riveting process. Based on the above steps, the output torque of the riveting motor and the radial feed displacement of the roller are collected. After Butterworth low-pass filtering, a second-order polynomial global fitting is used to obtain the torque fitting function, as detailed below. Figure 5 The riveting torque-feed curve is shown.

[0029] S5. Based on the torque fitting function, calculate the riveting torque slope, the riveting endpoint torque, and the riveting end torque increment ratio; S5.1 Select the range of 30% to 80% of the total radial feed stroke of the roller as the stable range of plastic flow, calculate the fitting torque values ​​at the beginning and end of the range, divide the difference between the torque value at the end and the torque value at the beginning by the length of the range, and use the quotient as the riveting torque slope. S5.2. Take the radial feed amount when the roller feeds to the target endpoint set in the process, and calculate the fitting torque value corresponding to the feed amount at the endpoint according to the torque fitting function, and use it as the end torque of the riveting endpoint. S5.3. Take the position at 80% of the total radial feed stroke of the roller, calculate the fitting torque value corresponding to this position according to the torque fitting function, divide the difference between the torque at the end of the riveting and the torque value at the 80% position by the torque at the end of the riveting, and multiply by 100%. The resulting percentage is used as the torque increment ratio at the end of the riveting. Meanwhile, based on the above S5-S5.3, the end torque of the riveting is a direct proxy indicator of the locking force of the sealing plate. If the end torque of the riveting is too low, it indicates that the riveting deformation is insufficient or the material resistance is insufficient, and the sealing plate is not effectively locked. If the torque slope is abnormally low, it indicates that the yield strength of the shell material is insufficient, and the locking reaction force provided under the same deformation is lower than the design value.

[0030] S6. The normalized values ​​are obtained by comparing the riveting torque slope, the riveting end torque, and the riveting end torque increment ratio with the corresponding nominal values. The residual stress risk index is synthesized according to the second preset weight. The residual stress risk index characterizes the degree to which the residual tensile stress level introduced by the riveting process at the root of the inner side of the shell opening deviates from the normal range. S6.1 Obtain the nominal riveting torque slope, the nominal riveting end torque, and the nominal riveting end torque increment ratio. All three are statistical averages of the corresponding characteristic parameters in historical qualified batches. S6.2. Divide the riveting torque slope by the nominal riveting torque slope to obtain the normalized value of the torque slope. S6.3. Divide the end torque of the riveting roll by the nominal end torque of the riveting roll to obtain the normalized value of the end torque. S6.4 Divide the final riveting torque increment ratio by the nominal final riveting torque increment ratio to obtain the normalized value of the final increment ratio. S6.5. The normalized values ​​of the torque slope, the end torque, and the end increment ratio are weighted and synthesized according to the second preset weight to obtain the residual stress risk index. The second preset weight includes the third weight, the fourth weight, and the fifth weight. The third weight is greater than the fourth weight and the fifth weight, and the sum of the third weight, the fourth weight, and the fifth weight is equal to 1. The residual stress risk index is also used to identify the following assembly anomalies: when the riveting torque slope or the end torque increment ratio of the riveting process experiences an instantaneous drop exceeding the preset rate of change, it is determined that microcracks have occurred at the edge of the shell closing. When the riveting end torque or the riveting torque slope is lower than the preset lower limit ratio of the corresponding nominal value, it is determined that the sealing plate locking force is insufficient. When the batch average value of the riveting torque slope shows a continuous unidirectional upward trend in a continuous preset number of workpieces and this trend exceeds the normal statistical fluctuation range, it is determined that the roller is excessively worn and triggers the equipment maintenance warning. Based on the above S5-S6.5, the riveting torque slope and the final torque increment ratio are sensitive indicators of the plastic flow state of the material. When the shell undergoes micro-cracking during the riveting process, the formation of the crack releases some stress instantaneously, which is manifested as a local torque drop or a sudden decrease in the slope on the torque curve. If the low-pass filter of S4 retains an appropriate bandwidth, such anomalies can be captured. Furthermore, if the residual stress risk index exceeds a certain critical threshold, corresponding to an extremely high riveting torque slope and end torque, it can be determined that the riveting is under overpressure, in which the probability of micro-cracks in the shell increases sharply.

[0031] S7. The gap risk index and the residual stress risk index are fused according to the preset fusion model to obtain the corrosion fatigue latent risk index. The standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces is calculated. When the standardized deviation score exceeds the preset threshold, the workpiece under inspection is determined to have corrosion fatigue latent defect risk. S7.1 Obtain the nonlinear coupling coefficient and the linear combination weight. The nonlinear coupling coefficient ranges from 0.5 to 0.8. The linear combination weight includes the sixth weight and the seventh weight, and the sum of the two is equal to 1. S7.2 Calculate the corrosion fatigue latent risk index according to the preset fusion model. The preset fusion model is: the corrosion fatigue latent risk index is equal to the product of the nonlinear coupling coefficient and the crevice risk index and the residual stress risk index, plus 1 minus the sum of the product of the difference of the nonlinear coupling coefficient and the sixth weight and the crevice risk index plus the product of the seventh weight and the residual stress risk index. S7.3 Obtain a benchmark sample set of corrosion fatigue latent risk index of historical qualified workpieces. The benchmark sample set consists of the corrosion fatigue latent risk index of several qualified workpieces produced during the stable operation of the production line and verified by accelerated corrosion fatigue bench durability test. Calculate the mean and standard deviation of the benchmark sample set. S7.4 Calculate the standardized deviation score of the workpiece to be inspected. Its value is the difference between the corrosion fatigue potential risk index of the workpiece to be inspected and the mean of the benchmark sample set, divided by the standard deviation of the benchmark sample set. S7.5 Set low-risk and high-risk thresholds. When the standardized deviation score is less than or equal to the low-risk threshold, the workpiece is judged as low-risk and released normally. When the standardized deviation score is greater than the low-risk threshold but less than or equal to the high-risk threshold, the workpiece is judged as medium-risk warning workpiece and sample bench verification is performed. When the standardized deviation score is greater than the high-risk threshold, the workpiece is judged as high-risk workpiece and rejected.

[0032] S7.6 For workpieces that are determined to be low-risk and pass subsequent bench verification, the mean and variance are updated using the exponentially weighted moving average method, with the smoothing factor ranging from 0.01 to 0.05. S7.7 The mean update method is that the new mean is equal to the smoothing factor multiplied by the corrosion fatigue latent risk index of the qualified workpiece, plus 1 minus the difference of the smoothing factor multiplied by the old mean. S7.8 The variance update method is as follows: the new variance is equal to the smoothing factor multiplied by the square of the difference between the corrosion fatigue potential risk index of the qualified workpiece and the new mean, plus 1 minus the difference of the smoothing factor multiplied by the old variance. Based on the above steps, the corrosion fatigue latent risk index is statistically distributed using a benchmark sample set composed of historically qualified workpieces. The standardized deviation score of the current workpiece is then calculated and compared with the low-risk and high-risk thresholds to achieve the final determination. See details below. Figure 6 The force decay curve during the pressure holding stage is shown.

[0033] In summary, during the assembly and testing of automotive tie rod ball joint assemblies, the pressing force signal and pressure head displacement signal of the servo press are simultaneously acquired during the polyurethane ball joint pressing process. The pressing force signal is then filtered using a power frequency notch filter to eliminate periodic interference. A continuous and differentiable pressing force fitting function is established from the filtered force and displacement data, and its first and second derivatives are obtained. This lays a continuous and differentiable mathematical foundation for extracting key characteristic parameters reflecting the ball joint compression state and springback behavior from the pressing curve. This transforms the originally discrete and noise-affected raw signal into a continuous function characterizing the entire nonlinear compression process of the polyurethane material, thereby accurately capturing the turning points of the mechanical state and the behavioral characteristics of each stage during the pressing process in subsequent steps.

[0034] Next, this method uses the fitting function of the pressing force and its derivative to find the displacement point within a preset search interval where the absolute value of the rate of change of the slope of the pressing curve reaches a local maximum as the pressing inflection point. This inflection point corresponds to the mechanical state transition of the polyurethane ball seat from the overall elastic compression-dominated stage to the plastic flow wedging stage. Recording the displacement and force value corresponding to this inflection point can reflect the actual state of the initial fit tightness between the ball seat and the shell. At the same time, the maximum value of the monotonically increasing displacement segment during the pressing process is taken as the pressing endpoint displacement and the corresponding pressing endpoint force is obtained. In the holding pressure stage, the holding pressure endpoint force is calculated and the force attenuation rate during the holding pressure stage is obtained. After the press head retracts, the ball is obtained. The ball seat rebound displacement is used to calculate the effective compression of the ball seat. Among these characteristic parameters, the force attenuation rate during the pressure holding stage directly characterizes the viscoelastic relaxation properties of the polyurethane material, thereby indirectly reflecting the hardness of the ball seat material and the uniformity of its internal structure. The effective compression of the ball seat directly determines the size of the axial gap between the upper end face of the ball seat and the lower plane of the sealing plate after assembly. This axial gap is the primary determining parameter for the depth dimension component of the annular occluded gap with a width in the critical range of 25 micrometers to 100 micrometers. Therefore, the accurate extraction of the above characteristic parameters provides a direct quantitative basis for quantitatively describing the degree to which the geometric state of the occluded gap deviates from the ideal design.

[0035] Subsequently, the method uses a weighted average of the relative deviations between the effective compression of the ball seat and its nominal value, and the relative deviations between the force attenuation rate during the pressure holding stage and its nominal value, according to a first preset weight, to obtain a gap risk index. The relative deviation of the effective compression of the ball seat reflects the degree to which the actual compression deviates from the design target, and the relative deviation of the force attenuation rate during the pressure holding stage reflects the degree to which the viscoelastic response of the polyurethane material deviates from the normal state. These two factors, from the perspectives of geometric dimension chain and material mechanical behavior, jointly determine the final width and depth-to-width ratio of the closed gap. The higher the value of the gap risk index, the more the ball seat assembly state deviates from the design ideal value, the stronger the tendency of the closed gap's geometric dimensions to fall into the critical range of 25 micrometers to 100 micrometers that promotes the formation of a corrosive microenvironment, and thus the greater the driving force for the formation of a high-chlorine, strongly acidic local corrosive microenvironment due to the obstruction of oxygen transport and the consumption of oxygen by anodic dissolution in the gap under alternating wet and dry service conditions.

[0036] Meanwhile, this method simultaneously collects the output torque of the riveting motor and the radial feed displacement of the roller during the riveting finishing process. After smoothing the torque signal by low-pass filtering, a second-order polynomial is used to globally fit the torque and displacement data to obtain the torque fitting function. This process eliminates the high-frequency noise interference introduced by friction fluctuations and mechanical vibrations during the riveting process and establishes a continuous analytical expression for the change of torque with radial feed. Thus, it can characterize the evolution law of deformation resistance of the thin-walled metal shell under the centripetal extrusion of the roller during the entire process of plastic flow and gradual inward curling from the perspective of macroscopic deformation mechanics.

[0037] Based on this, the method selects the stable range of plastic flow and calculates the torque increment corresponding to the unit radial feed displacement within this range as the riveting torque slope. This torque slope reflects the work hardening rate and flow resistance of the shell material during the plastic flow stage of edge rolling. The higher the value, the greater the plastic strain energy accumulated by the shell during the riveting deformation process, and the higher the level of residual tensile stress generated by uneven plastic deformation at the root of the closing end. At the same time, the method takes the fitted torque value when the roller feeds to the target endpoint as the riveting endpoint torque. This endpoint torque reflects the total driving torque required to complete all edge rolling closure and is directly related to the degree of pressing of the closing edge against the sealing plate and the final stress state at the root of the closing end. In addition, the method calculates the percentage of the torque increment from the position where the riveting feed reaches the preset percentage of the total feed to the endpoint torque as the final riveting torque increment ratio. This ratio reflects the intensity of the densification deformation after the metal fills the cavity in the final stage of riveting. Its abnormal increase often indicates that the shell material has undergone excessive work hardening and stress concentration in the final stage.

[0038] Subsequently, the method compares the riveting torque slope, the riveting endpoint torque, and the riveting end-stage torque increment ratio with their respective nominal values ​​obtained from historical qualified batches to obtain normalized values. These values ​​are then weighted and synthesized according to a second preset weight to obtain a residual stress risk index. This residual stress risk index integrates information from three dimensions: the degree of work hardening during the plastic flow stage of the riveting deformation process, the total deformation resistance at the final closing moment, and the severity of the final densification deformation. It quantitatively characterizes the extent to which the axial residual tensile stress field introduced by the riveting process at the inner root of the shell taper deviates from the normal fluctuation range. This residual tensile stress field is the mechanical driving force necessary for corrosion fatigue short cracks to propagate along the circumferential and wall thickness directions after initiation from the bottom of the pitting pit. A higher residual stress risk index indicates that the taper root is in a more unfavorable tensile stress state and that the crack propagation rate is faster under subsequent alternating tensile and compressive loads.

[0039] After obtaining the gap risk index, which reflects the tendency of the formation of the geometric microenvironment of the closed gap, and the residual stress risk index, which reflects the degree of deviation of the residual tensile stress level, respectively, this method nonlinearly fuses the two according to a preset fusion model to obtain the corrosion fatigue latent risk index. The fusion model includes both a product term and a linear combination term. The product term is used to capture the interactive enhancement effect produced by the gap risk index and the residual stress risk index when both are high. That is, the acceleration effect of the gap microenvironment and residual tensile stress coupled in the same spatial position on corrosion fatigue failure is much greater than the sum of their individual effects. The linear combination term ensures that when one risk component is in the normal range and the other risk component is abnormal, the corrosion fatigue latent risk index can still respond effectively and will not be missed due to the product becoming zero. The corrosion fatigue latent risk index formed in this way comprehensively reflects the degree of tendency of the workpiece to have corrosion fatigue crack initiation and propagation induced by the coupling of galvanic corrosion, gap acidification and residual tensile stress under the alternating dry and wet service conditions of chloride salt.

[0040] Finally, this method calculates the standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to a benchmark sample set consisting of several qualified workpieces produced during the stable operation of the production line and verified by accelerated corrosion fatigue bench durability tests. When the standardized deviation score exceeds the preset risk judgment threshold, the workpiece under inspection is judged as a workpiece with corrosion fatigue latent defect risk and is intercepted. Thus, before leaving the factory, the method effectively identifies latent defects at the root of the inner side of the seam that have not yet formed through cracks, have not yet affected the torque and airtightness test values, and are physically obscured by the riveting and rolling edge and cannot be directly observed by the vision system.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assembling and inspecting automotive tie rod ball joint assemblies, comprising the following steps: S1. During the polyurethane ball seat pressing process, the pressing force signal and the pressure head displacement signal of the servo press are collected synchronously. The pressing force signal is filtered to eliminate periodic interference. A continuous and differentiable pressing force fitting function is established for the filtered pressing force and displacement data, and the first and second derivatives of the fitting function are calculated. S2. Based on the fitting function of the pressing force and its first and second derivatives, identify the inflection point of the pressing curve, record the inflection point force and inflection point displacement, obtain the pressing end force, calculate the force attenuation rate during the pressure holding stage, obtain the ball seat rebound displacement, and calculate the effective compression of the ball seat. S3. Based on the relative deviation of the effective compression of the ball seat and the relative deviation of the force attenuation rate during the pressure holding stage, the gap risk index is synthesized according to the first preset weight. The gap risk index characterizes the degree to which the geometric dimensions of the occluded gap deviate from the ideal range. S4. During the riveting process, the output torque of the riveting motor and the radial feed displacement of the roller are collected synchronously. The torque signal is filtered and smoothed, and a torque fitting function is established for the smoothed torque and displacement data. S5. Based on the torque fitting function, calculate the riveting torque slope, the riveting endpoint torque, and the riveting end torque increment ratio; S6. The riveting torque slope, riveting end torque and riveting end torque increment ratio are compared with the corresponding nominal values ​​to obtain normalized values. The residual stress risk index is synthesized according to the second preset weight. The residual stress risk index characterizes the degree to which the residual tensile stress level introduced by the riveting process at the root of the inner side of the shell opening deviates from the normal range. S7. The gap risk index and the residual stress risk index are fused according to the preset fusion model to obtain the corrosion fatigue latent risk index. The standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces is calculated. When the standardized deviation score exceeds the preset threshold, the workpiece under inspection is determined to have corrosion fatigue latent defect risk.

2. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, S1. During the polyurethane ball seat pressing process, the pressing force signal and the pressure head displacement signal of the servo press are simultaneously acquired. The pressing force signal is filtered to eliminate periodic interference. A continuous and differentiable pressing force fitting function is established for the filtered pressing force and displacement data, and the first and second derivatives of the fitting function are calculated. Specifically, the steps include the following: The timing data of the pressing force signal and the displacement signal of the press head of the servo press are synchronously collected at a sampling frequency of not less than 1000 Hz to form a set of data points with one-to-one correspondence between force and displacement. A second-order notch filter with a center frequency of 50 Hz was used to filter the pressing force signal to eliminate power frequency interference and obtain the filtered force sequence. For the set of force-displacement data points composed of the filtered force sequence and displacement sequence, a local weighted regression method is used to establish a fitting function for the pressing force. At each displacement point, data points within a neighborhood window centered on that displacement point with a half-width of 0.1 mm to 0.3 mm are selected. A Gaussian kernel function is used to assign fitting weights to each data point that decay with distance. A third-order polynomial is fitted within the window. The constant term of the polynomial is taken as the fitting value of the pressing force at that displacement point, the coefficient of the first term is taken as the instantaneous slope of the pressing curve at that displacement point, and twice the coefficient of the second term is taken as the rate of change of the slope of the pressing curve at that displacement point. Local weighted regression fitting is performed on all displacement points one by one to obtain the fitting function of the press-fitting force that is continuously differentiable throughout the entire stroke, as well as its first-order derivative function and second-order derivative function.

3. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, The steps described in S2, the basic pressure fitting force fitting function and its first and second derivatives, identify the inflection point position of the pressure fitting curve, record the inflection point force and inflection point displacement, obtain the pressure fitting endpoint force, calculate the force attenuation rate during the pressure holding stage, obtain the ball seat rebound displacement, and calculate the effective compression of the ball seat, specifically including the following steps: Within the search interval of 0.5 mm before the press-fitting start position to the press-fitting end position, the absolute value of the rate of change of the slope of the press-fitting curve at each displacement point is traversed to find the displacement point that obtains a local maximum value as a candidate inflection point. When the absolute value of the rate of change of the slope at the candidate inflection point is greater than or equal to the preset inflection point judgment threshold, the candidate inflection point is confirmed as the press-fitting inflection point, and the inflection point displacement and the corresponding inflection point force are recorded. The maximum value of the monotonically increasing segment of displacement during the pressing process is taken as the pressing end displacement, and the pressing end force corresponding to this pressing end displacement is obtained according to the pressing force fitting function. During the pressure holding stage, in which the displacement remains constant after the pressure head reaches the end point, the average value of the pressure force at the last few sampling points of the pressure holding stage is taken as the pressure holding end force. The force attenuation rate of the pressure holding stage is calculated, which is the difference between the pressure holding end force and the pressure holding end force divided by the pressure holding end force and then multiplied by 100%. After the pressure head retracts, the ball seat rebound displacement is obtained by measuring the difference between the actual height of the upper surface of the sealing plate and the theoretical nominal height, or by measuring the difference between the critical displacement when the pressure head and the ball seat disengage during the unloading process of the servo press and the displacement at the end of the pressing. Calculate the effective compression of the ball seat, which is the nominal total compression of the ball seat minus the rebound displacement of the ball seat. The nominal total compression of the ball seat is the difference between the original free height of the ball seat and the nominal height after assembly.

4. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, Step S3 involves synthesizing a gap risk index based on the relative deviation of the effective compression of the ball seat and the relative deviation of the force attenuation rate during the pressure holding stage, according to a first preset weight. The gap risk index characterizes the degree to which the geometric dimensions of the occluded gap deviate from the ideal range, and specifically includes the following steps: Obtain the nominal effective compression, which is the statistical average of the effective compression of the ball seat in historical qualified batches; The relative deviation of effective compression is calculated as the absolute value of the difference between the effective compression of the ball seat and the nominal effective compression, divided by the nominal effective compression. Obtain the nominal force decay rate, which is the statistical average of the force decay rate during the pressure holding stage in historical qualified batches; The relative deviation of the force attenuation rate is calculated by dividing the absolute value of the difference between the force attenuation rate and the nominal force attenuation rate during the pressure holding stage by the nominal force attenuation rate. The gap risk index is obtained by weighting the relative deviation of effective compression and the relative deviation of force attenuation rate according to the first preset weight. The first preset weight includes a first weight and a second weight. The value of the first weight ranges from 0.6 to 0.7, and the value of the second weight ranges from 0.3 to 0.

4. The sum of the first weight and the second weight is equal to 1.

5. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, S4, during the riveting closing process, synchronously collects the output torque of the riveting motor and the radial feed displacement of the roller, filters and smooths the torque signal, and establishes a torque fitting function for the smoothed torque and displacement data, specifically including the following steps: At the riveting finishing station, the output torque signal of the riveting motor and the radial feed displacement signal of the roller are synchronously collected at a sampling frequency of not less than 500 Hz, forming a set of data points with one-to-one correspondence between torque and displacement. The zero displacement point is the position when the roller just contacts the edge of the housing. A second-order Butterworth low-pass filter with a cutoff frequency of 10 to 20 Hz is used to filter the torque signal, and a combination of forward and reverse filtering is used to achieve zero-phase characteristics and obtain a smooth torque sequence. The smoothed set of torque and displacement data points is fitted globally by least squares using a second-order polynomial to obtain the torque fitting function. The second-order polynomial has a constant term, a first-order term, and a second-order term. Calculate the fitting coefficient of determination. When the fitting coefficient of determination is less than 0.9, mark the workpiece as an abnormal workpiece in the riveting process.

6. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, S5, based on the torque fitting function, calculates the riveting torque slope, the riveting endpoint torque, and the riveting end segment torque increment ratio, specifically including the following steps: The range of 30% to 80% of the total radial feed stroke of the roller is selected as the stable range of plastic flow. The fitted torque values ​​at the beginning and end of this range are calculated. The difference between the torque value at the end and the torque value at the beginning is divided by the length of the range, and the quotient is used as the riveting torque slope. Take the radial feed amount when the roller feeds to the target endpoint set in the process, and calculate the fitted torque value corresponding to the feed amount at the endpoint according to the torque fitting function, which is used as the end torque of the riveting endpoint. Take the position at 80% of the total radial feed stroke of the roller, calculate the corresponding fitting torque value based on the torque fitting function, divide the difference between the end torque of the riveting and the torque value at the 80% position by the end torque of the riveting, and multiply by 100%. The resulting percentage is used as the torque increment ratio of the end riveting stage.

7. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, Step S6 involves comparing the riveting torque slope, the riveting endpoint torque, and the riveting end segment torque increment ratio with their corresponding nominal values ​​to obtain normalized values. These values ​​are then synthesized using a second preset weight to obtain a residual stress risk index. The residual stress risk index characterizes the degree to which the residual tensile stress level introduced during the riveting process deviates from the normal range at the root of the shell's inner side. Specifically, this includes the following steps: Obtain the nominal riveting torque slope, the nominal riveting end torque, and the nominal riveting end torque increment ratio. All three are statistical averages of the corresponding characteristic parameters in historical qualified batches. Divide the riveting torque slope by the nominal riveting torque slope to obtain the normalized torque slope value. Divide the end torque of the riveting roll by the nominal end torque of the riveting roll to obtain the normalized value of the end torque. Divide the final riveting torque increment ratio by the nominal final riveting torque increment ratio to obtain the normalized value of the final increment ratio. The residual stress risk index is obtained by weighting the normalized values ​​of the moment slope, the end moment, and the final increment ratio according to the second preset weight. The second preset weight includes the third weight, the fourth weight, and the fifth weight. The third weight is greater than the fourth weight and the fifth weight, and the sum of the third weight, the fourth weight, and the fifth weight is equal to 1.

8. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 1, characterized in that, Step S7 involves fusing the gap risk index and the residual stress risk index according to a preset fusion model to obtain a corrosion fatigue latent risk index. The standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces is calculated. When the standardized deviation score exceeds a preset threshold, the workpiece under inspection is determined to have a corrosion fatigue latent defect risk. Specifically, this includes the following steps: Obtain the nonlinear coupling coefficient and the linear combination weight. The nonlinear coupling coefficient has a value range of 0.5 to 0.8, and the linear combination weight includes a sixth weight and a seventh weight, the sum of which is equal to 1. The corrosion fatigue latent risk index is calculated according to the preset fusion model. The preset fusion model is: the corrosion fatigue latent risk index is equal to the product of the nonlinear coupling coefficient and the crevice risk index and the residual stress risk index, plus 1 minus the sum of the product of the difference of the nonlinear coupling coefficient and the sixth weight and the crevice risk index plus the product of the seventh weight and the residual stress risk index. Obtain a benchmark sample set of corrosion fatigue latent risk index for historical qualified workpieces. The benchmark sample set consists of the corrosion fatigue latent risk index of several qualified workpieces produced during the stable operation of the production line and verified by accelerated corrosion fatigue bench durability test. Calculate the mean and standard deviation of the benchmark sample set. The standardized deviation score of the workpiece to be inspected is calculated as the difference between the corrosion fatigue potential risk index of the workpiece to be inspected and the mean of the benchmark sample set, divided by the standard deviation of the benchmark sample set. Set low-risk and high-risk thresholds. When the standardized deviation score is less than or equal to the low-risk threshold, the workpiece is judged as low-risk and released normally. When the standardized deviation score is greater than the low-risk threshold but less than or equal to the high-risk threshold, the workpiece is judged as medium-risk warning workpiece and undergoes sampling bench verification. When the standardized deviation score is greater than the high-risk threshold, the workpiece is judged as high-risk workpiece and rejected.

9. The assembly and inspection method for automotive tie rod ball joint assembly according to claim 8, characterized in that, Preferably, step S7, fusing the gap risk index and the residual stress risk index according to a preset fusion model to obtain a corrosion fatigue latent risk index, calculating the standardized deviation score of the corrosion fatigue latent risk index of the workpiece under inspection relative to the statistical distribution of historical qualified workpieces, and determining that the workpiece under inspection has a corrosion fatigue latent defect risk when the standardized deviation score exceeds a preset threshold, further includes the following steps: For workpieces that are determined to be low-risk and pass subsequent bench verification, the mean and variance are updated using an exponentially weighted moving average method, with the smoothing factor ranging from 0.01 to 0.

05. The mean is updated by multiplying the smoothing factor by the corrosion fatigue latent risk index of the qualified workpiece, plus 1 minus the difference of the smoothing factor multiplied by the old mean. The variance update method is as follows: the new variance is equal to the smoothing factor multiplied by the square of the difference between the corrosion fatigue potential risk index of the qualified workpiece and the new mean, plus 1 minus the difference of the smoothing factor multiplied by the old variance.

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