Topological optimization anti-buckling structure design method and system for hollow variable cross-section plunger rod

Abstract

The invention relates to the technical field of topological optimization, in particular to a topological optimization anti-buckling structure design method and system for a hollow variable cross-section plunger rod. The method comprises the following steps: acquiring telescopic data of a plunger rod; determining a maximum activity stroke based on the scaling data; the buckling danger degree is judged through the maximum movement stroke; detecting inertia moment distribution of the variable cross section according to the buckling danger degree; evaluating the pressure rod stability of the plunger rod by using the inertia moment distribution; an anti-buckling structure is designed according to the stability of the pressing rod and the buckling danger degree; a buckling limit load is simulated based on the anti-buckling structure, and the breaking strength of the material under the buckling limit load is detected; detecting a groove surface crack by utilizing the breaking strength of the material, and marking the position of the groove surface crack; and performing multi-stage material strengthening treatment on the crack position of the groove surface to generate multi-stage material data. Based on the topological optimization technology, the anti-buckling stability of the plunger rod is improved, the service life of the plunger rod is prolonged, and the structural safety and reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of topology optimization technology, and in particular to a topology optimization anti-buckling structure design method and system for a hollow variable cross-section plunger rod. Background Technology

[0002] Currently, plunger-type hydraulic gate hoists are widely used in the opening and closing operations of hydraulic structures, ship lock gates, and large mechanical equipment. However, under long stroke and heavy load conditions, the plunger rod is prone to buckling deformation, fatigue cracks, and material failure, affecting operational safety and service life. Existing technologies primarily focus on structural optimization of the plunger rod by increasing cross-sectional dimensions or using high-strength materials to improve overall rigidity. However, this method significantly increases the plunger rod's mass, leading to higher manufacturing costs, increased processing difficulty, and higher demands on the hoist's drive system. Traditional buckling-resistant designs often use uniform cross-sections, making it difficult to account for stress differences in different areas, easily resulting in low material utilization and insufficient local strength. Regarding fatigue crack treatment, existing methods often rely on surface repair or single-material reinforcement, failing to effectively prevent crack propagation in the subsurface or internal layers, leading to recurring cracks. For large opening and closing mechanisms with multi-point lifting, existing two-bar or double-cylinder lifting schemes have limitations in terms of synchronization and structural stability, especially when combined with complex working conditions and locally reinforced structures after multi-stage material treatment, failing to fully utilize their load-bearing capacity. Summary of the Invention

[0003] Based on this, it is necessary for the present invention to provide a topology-optimized buckling-resistant structural design method and system for hollow variable cross-section plunger rods, in order to solve at least one of the above-mentioned technical problems.

[0004] To achieve the above objectives, a topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod is provided, comprising the following steps: Step S1: Obtain the extension and retraction data of the plunger rod; determine the maximum active stroke based on the extension and retraction data; use the maximum active stroke to determine the degree of buckling risk; Step S2: Detect the moment of inertia distribution of the variable cross section according to the degree of buckling risk; evaluate the compression stability of the plunger rod using the moment of inertia distribution; design a buckling-resistant structure based on the compression stability and the degree of buckling risk; Step S3: Simulate the buckling limit load based on the buckling-resistant structure and detect the material fracture strength under the buckling limit load; use the material fracture strength to detect groove surface cracks and mark the location of the groove surface cracks; Step S4: Perform multi-level material strengthening treatment at the crack location on the groove surface to generate multi-level material data; design a four-bar lifting structure based on the multi-level material data.

[0005] The present invention has the following beneficial effects: Firstly, by calculating the maximum active stroke and determining the degree of buckling risk based on extension and contraction data, high-risk stress areas of the plunger rod can be accurately identified for different working conditions. Combined with the analysis of the moment of inertia distribution of the variable cross-section, the material waste caused by the "global thickening" in traditional design is effectively avoided. This allows the plunger rod to meet buckling resistance requirements while significantly reducing mass and manufacturing costs and improving material utilization.

[0006] Secondly, by utilizing load detection at the moment of inertia abrupt change point and assessing the stability of the compression member, combined with the synergistic design of cylindrical steel sleeves, limiting rings, and copper-based sliding sleeves, structural reinforcement can be achieved in areas of localized instability. This method significantly improves local stiffness and buckling critical load without substantially increasing the overall volume, effectively preventing early buckling instability.

[0007] Thirdly, by implementing multi-stage material strengthening treatment at the crack location on the groove surface, the surface layer is shot-peened to form a compressive stress layer and improve the adhesion of the surface coating, and the sub-surface layer is quenched to form a highly strengthened martensite layer, while ensuring the uniformity and smooth transition of the microstructure, the initiation and propagation of cracks can be suppressed at the same time, significantly improving the fatigue life and fracture toughness of the plunger rod under high load and cyclic stress.

[0008] Fourthly, based on stress load simulation using multi-level material data and the design of a four-bar lifting structure, the uniform distribution of lifting force and stable lifting of the overall structure are achieved through the rational arrangement of the lifting rod positions and the installation of reinforcing steel plates. Compared with the traditional double-bar lifting method, the four-bar arrangement of this invention has higher synchronization and load-bearing capacity under large stroke and heavy weight conditions, thereby ensuring the safety and reliability of opening and closing operations. Attached Figure Description

[0009] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the steps in the topology optimization buckling-resistant structure design method for a hollow variable cross-section plunger rod according to the present invention; Figure 2 This is a detailed flowchart of step S1 in the present invention; Figure 3 This is a detailed flowchart of step S2 in the present invention; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0010] The technical method of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0011] Furthermore, the accompanying drawings are merely illustrative of the invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor methods and / or microcontroller methods.

[0012] It should be understood that although the terms "first," "second," etc., may be used herein to describe various units, these units should not be limited by these terms. These terms are used merely to distinguish one unit from another. For example, without departing from the scope of the exemplary embodiments, a first unit may be referred to as a second unit, and similarly, a second unit may be referred to as a first unit. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0013] To achieve the above objectives, please refer to Figures 1 to 3 This invention provides a topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod, the method comprising the following steps: Step S1: Obtain the extension and retraction data of the plunger rod; determine the maximum active stroke based on the extension and retraction data; use the maximum active stroke to determine the degree of buckling risk; In this embodiment, a hollow variable cross-section plunger rod is mounted on a hydraulic telescopic test platform. High-precision laser displacement sensors (model KeyenceLK-G5000, accuracy 0.1 micrometers) are installed at both ends of the platform, and the sensors are fixed to reference positioning frames at both ends of the plunger rod. The hydraulic drive device is activated, causing the plunger rod to move through its full stroke between full extension and full retraction. Displacement data at both ends is continuously recorded by the sensors, with a sampling frequency set to 1 kHz to ensure that the minimum displacement change during the movement is recorded. The displacement data is transmitted in real time to the computing terminal via a data acquisition card (NIPXIe-6363), and the maximum stroke of the plunger rod is calculated by the data processing software. Subsequently, with the plunger rod fully extended, the outer and inner diameters of its effective working section are measured using a digital caliper to obtain the actual cross-sectional dimensions. Using the length and diameter parameters measured by the measuring tools, combined with the total length of the plunger rod, its slenderness ratio is calculated. The slenderness ratio is compared with the critical value to determine the buckling risk level of the plunger rod at its maximum stroke. A slenderness ratio exceeding the standard high value is considered a high-risk range, a slenderness ratio in the middle range is considered a medium-risk range, and a slenderness ratio below the minimum limit is considered a low-risk range.

[0014] Step S2: Detect the moment of inertia distribution of the variable cross section according to the degree of buckling risk; evaluate the compression stability of the plunger rod using the moment of inertia distribution; design a buckling-resistant structure based on the compression stability and the degree of buckling risk; In this embodiment, after obtaining the buckling hazard level of the plunger rod, the 3D CAD model of the plunger rod is imported into the 3D modeling software SolidWorks. Multiple cross-sections are generated axially at 10mm intervals using the equidistant slicing function. The software's built-in cross-section analysis function is used to extract the moment of inertia data for each cross-section and output it as a CSV file. The file is imported into a data processing program to calculate the variation range of the moment of inertia between adjacent cross-sections. If the variation range exceeds 15%, it is marked as a sudden change in moment of inertia. At the sudden change location, a loading experiment is conducted by installing a 5000N precision strain gauge (HBMU10M model) and a triaxial strain gauge on the actual sample. Axial load and radial strain data are recorded, with a sampling frequency set to 2kHz. Based on the actual measured load and strain data, combined with the end support form and effective length of the plunger rod, the stability index of the rod is calculated, and it is determined whether it meets the stability requirements. In areas with insufficient stability, local reinforcement structures are designed in the CAD model, including adding a Q345B steel cylindrical reinforcement sleeve with a wall thickness of 8 mm at the location; embedding a limiting ring in the high-risk section, which is matched with the reinforcement sleeve with an H7 / h6 tolerance grade; and adding a copper-based sliding sleeve between the limiting ring and the reinforcement sleeve, controlling the hardness within the range of HB150 to HB170 to ensure the support effect under pressure.

[0015] Step S3: Simulate the buckling limit load based on the buckling-resistant structure and detect the material fracture strength under the buckling limit load; use the material fracture strength to detect groove surface cracks and mark the location of the groove surface cracks; In this embodiment, after completing the local reinforcement design of the buckling-resistant structure, the complete three-dimensional model of the plunger rod is imported into ANSYS Workbench for finite element analysis. The material is set to 42CrMo quenched and tempered steel, and material parameters such as elastic modulus, Poisson's ratio, and yield strength are input. Axial pressure is applied, starting from zero and gradually increasing in increments of 5 kN until the simulation results show buckling instability. The stress distribution corresponding to the critical buckling load is recorded, and stress concentration areas are marked in the post-processing interface using contour color differentiation. The color gradient threshold is set to 95% of the maximum value as the key analysis area. Cracks are detected on the solid sample corresponding to the stress concentration areas using magnetic particle testing. Fluorescent magnetic particles are used, and the sensitivity is calibrated using a type A standard test block to identify the crack location at the groove surface. Crack length is measured using a 50x optical microscope, and crack width is detected using a scanning electron microscope with an accuracy of 1 micrometer. Small samples were taken from the crack locations for metallographic analysis. The grain morphology of the fracture surface was observed using a polarizing microscope to determine its fracture characteristics. The three-dimensional coordinates and fracture types of all cracks were marked on the three-dimensional model for precise positioning in subsequent material strengthening treatment.

[0016] Step S4: Perform multi-level material strengthening treatment at the crack location on the groove surface to generate multi-level material data; design a four-bar lifting structure based on the multi-level material data.

[0017] In this embodiment, surface strengthening treatment is first performed at the three-dimensional coordinate position corresponding to the groove crack. Using shot peening equipment, the peening intensity is tested using an Almen specimen. Steel shot with a diameter of 0.6 mm is selected, the peening pressure is set to 0.6 MPa, the peening angle is perpendicular to the surface, the peening distance is 200 mm, and the duration is 45 seconds, forming a surface compressive stress layer with a thickness of approximately 0.5 mm. After strengthening, the compressive stress value and depth distribution are detected using an X-ray diffraction residual stress analyzer. Subsequently, a Cr2O3 coating is plasma-sprayed onto the surface, with the spraying temperature controlled at 250 degrees Celsius and the coating thickness at 0.2 mm. Adhesion is tested according to GB / T8642-2002 standard to ensure adhesion is greater than 60 MPa. In the secondary surface strengthening stage, medium-frequency induction heating quenching is used, with the frequency set to 50 kHz. The surface is heated to 850 degrees Celsius, held for 5 seconds, and then cooled by water mist spraying, forming a high-hardness martensitic layer with a thickness of 2 mm. Hardness was measured using a Vickers hardness tester and controlled within the range of HV650 to HV700. The uniformity of the microstructure was examined using a metallographic microscope. Strengthening data for the surface and subsurface layers were entered into a 3D model to generate multi-level material distribution data. Based on this data, a four-bar lifting structure was designed, determining the specific installation areas for the four lifting rods. Q345 steel plates, 12 mm thick, were used for reinforcement, with pre-drilled bolt holes of 20 mm diameter. The spacing between the lifting rods was controlled within ±1 mm.

[0018] Preferably, step S1 specifically includes: Step S11: Obtain the extension and retraction data of the plunger rod; In this embodiment, a hollow variable cross-section plunger rod is fixedly mounted on a hydraulic telescopic test platform. Fixed supports are installed at both ends of the platform to keep the axis parallel to the horizontal baseline. High-precision laser displacement sensors (Model KeyenceLK-G5000, measurement accuracy 0.1 micrometers) are installed at both ends of the plunger rod, with the sensor's measurement beam perpendicularly aligned with the reference surface at the plunger rod end. The hydraulic system regulates the oil pressure through a constant flow control valve, causing the plunger rod to perform a slow, full-stroke telescopic movement under rated pressure. The movement speed is controlled at 10 mm / s to reduce inertial effects. Throughout the movement, the displacement sensors continuously collect the telescopic displacement data of the plunger rod at a sampling frequency of 1 kHz and transmit the signal to the storage unit of an industrial computer via a NIPXIe-6363 data acquisition card. To ensure data integrity, a mechanical stroke limit device is used during the acquisition process to prevent over-travel and equipment damage. The entire test is conducted in a laboratory at a constant temperature of 20 degrees Celsius to eliminate the influence of temperature on measurement accuracy.

[0019] Step S12: Record the starting and ending coordinates using the scaling data; In this embodiment, after collecting the displacement data of the plunger rod extension and retraction, the displacement data is imported into the data processing device for analysis according to the time series. Using signal feature recognition methods, the two states of the plunger rod—fully retracted and fully extended—are identified in the displacement curve. The displacement value corresponding to the retracted state is the starting coordinate, and the displacement value corresponding to the extended state is the ending coordinate. To ensure the accuracy of the coordinate recording, both the starting and ending coordinates are the average of three consecutive measurements, and the difference between adjacent measurements must not exceed 0.002 mm before recording. The starting and ending coordinates are recorded in millimeters in the technical document and archived with a timestamp and test batch number as identification information. To eliminate external vibration interference, rubber vibration damping pads are used to isolate the hydraulic pump unit from the test bench during the recording process, and the sensor zero point is calibrated before data acquisition, with the calibration value controlled within ±0.001 mm. All starting and ending coordinates are measured using the same laser displacement sensor calibrated by the National Institute of Metrology, ensuring consistency between batches.

[0020] Step S13: Calculate the maximum active travel distance based on the starting and ending coordinates; In this embodiment, after obtaining the starting and ending coordinates, the difference between them is directly calculated by the data calculation unit. This difference represents the maximum stroke of the plunger rod. This stroke is recorded in millimeters in the test record table, and the original measured values ​​of the starting and ending coordinates are attached to the data file as verification. During the calculation process, to prevent the influence of rounding errors, the measured values ​​are retained to three decimal places and processed using high-precision floating-point arithmetic. Before calculation, the tester must perform a consistency check on the data to ensure that the starting coordinate is less than the ending coordinate; otherwise, the test is deemed invalid and re-acquired. The maximum stroke value is associated with the structural parameters of the plunger rod for subsequent extraction of the effective length. To ensure the traceability of the stroke data, each stroke calculation result is accompanied by measurement time, ambient temperature, hydraulic oil temperature, and loading pressure data. These environmental parameters are recorded in real time by a PT100 platinum resistance temperature sensor and a pressure sensor and stored in the same data package for subsequent analysis to compare the relationship between environmental factors and stroke changes.

[0021] Step S14: Extract the effective length of the plunger rod using the maximum active stroke, and determine the cross-sectional area of ​​the plunger rod interface; calculate the slenderness ratio based on the effective length and the cross-sectional area interface, and determine the degree of buckling risk.

[0022] In this embodiment, after obtaining the maximum stroke of the plunger rod, the stroke data is combined with the geometric parameters of the plunger rod to extract the effective length. The effective length is defined as the length of the free working section of the plunger rod at its maximum stroke, excluding the end-fixed or guide portion. To measure the geometric parameters, a vernier caliper (accuracy 0.02 mm) is used to measure the outer diameter of the plunger rod, and an inside dial indicator is used to measure the inner diameter of the hollow part to ensure that the difference between the inner and outer diameters matches the wall thickness. The interface cross-sectional area is calculated based on the outer and inner diameters. During the calculation of the interface cross-sectional area, all dimensions are retained to three decimal places and recorded in square millimeters. Subsequently, the slenderness ratio is calculated using the effective length and interface cross-sectional area, and the slenderness ratio is expressed as a dimensionless number. To determine the degree of buckling risk, the calculated slenderness ratio is compared with the limit specified in GB / T15899-2011 standard: when the slenderness ratio is greater than the critical high value, it is judged as high buckling risk; when it is between the high and low values, it is judged as medium risk; and when it is below the minimum limit, it is judged as low risk. All judgment results and original measurement data were recorded in the test report and reviewed and confirmed by two different testing personnel to prevent human error from causing inaccurate subsequent analysis.

[0023] Preferably, step S2 specifically includes: Step S21: Identify high-risk areas based on the degree of buckling risk, and calculate the plunger diameter in the high-risk areas; assess the moment of inertia of the cross section based on the plunger diameter; statistically analyze the moment of inertia distribution of the variable cross section based on the moment of inertia of the cross section. In this embodiment, after determining the degree of buckling risk, the axial start and end positions of the high-risk area are determined by combining a linear displacement sensor and a laser rangefinder. The positioning accuracy is controlled within ±0.01 mm, and the unit is uniformly millimeters. For the high-risk area, a high-precision outside micrometer and inside dial indicator are used to measure the outside diameter of the hollow section of the plunger rod. and inner diameter Measurements were performed with an axial spacing of 10 mm, and a set of discrete data points were collected. ,in Indicates the measuring point number, axial position is Moment of inertia of the plunger rod section The calculation formula is: ; Where D(x) and d(x) are the outer and inner diameters at axial position x, respectively, both in millimeters, and the moment of inertia is in millimeters. .

[0024] For the measured discrete data points Applying cubic spline interpolation algorithm to construct continuous functions This method describes the distribution of the variable cross-section moment of inertia of a plunger rod in a high-risk region. The interpolation function is guaranteed to be continuous at the data points, with continuous first and second derivatives, thus effectively simulating the smoothness of actual moment of inertia variations. The interpolation calculation is performed using numerical software, and the results are stored as discrete data points and their corresponding interpolation function coefficients in a database. This moment of inertia distribution is used for subsequent column stability analysis and buckling-resistant structure design. Simultaneously, measurement time, ambient temperature, measurement equipment calibration status, and personnel information are saved to ensure data integrity and traceability.

[0025] Step S22: Determine the abrupt change point of the moment of inertia based on the distribution of the moment of inertia; In this embodiment, after obtaining the distribution data of the variable cross-section moment of inertia in high-risk areas and other locations, this data is input into a dedicated structural data analyzer (model HBMcatmanAP with Excel pivot table). The rate of change of the moment of inertia between two adjacent measurement points (unit: % / mm) is calculated to identify axial locations where the absolute value of the rate of change exceeds a preset threshold, which is set at 15% / mm, based on engineering experience and structural stability analysis standards. To eliminate spurious abrupt changes caused by accidental errors at individual measurement points, the distribution curve is smoothed using a three-point moving average method before calculating the rate of change. When the rate of change at a certain location consistently exceeds the threshold and the span exceeds 5 mm, it is determined to be a moment of inertia abrupt change point. The locations of these abrupt change points are accurate to ±0.5 mm, and marking lines are drawn on the surface of the plunger rod using a fine scribing machine. The same locations are also marked in the 3D CAD model to ensure accurate alignment during subsequent load acquisition and design stages. All abrupt change point information, including axial position, percentage of change rate, and adjacent cross-section dimensions, is output in tabular form, along with a distribution curve for archiving, for correlation analysis with load data.

[0026] Step S23: Collect the actual load at the point of abrupt change in moment of inertia; evaluate the stability of the compression member using the actual load and the preset buckling safety factor; In this embodiment, after determining the point of abrupt change in moment of inertia, the plunger rod is installed on the static load testing frame, and an axial pressure is applied at the point of abrupt change using a servo hydraulic loading device (maximum load 500kN, accuracy ±0.5%). During loading, strain gauges (model: HBMLY11-6 / 350, sensitivity coefficient 2.12) are installed within a 50mm radius of the point of abrupt change. The strain gauges are connected to a data acquisition system (NIPXIe-4330) via a strain bridge, and strain signals are acquired at a frequency of 200Hz. The load value is recorded in real time by a pressure sensor (accuracy 0.25%FS) built into the loading device, in Newtons. During the loading test, the load is increased incrementally in increments of 500N, with each load level held for 10 seconds, until it approaches the design maximum load value. The average value at which each load level stabilizes is recorded. The recorded actual load is then compared with a preset buckling safety factor, which is set to 2.0 according to design requirements, meaning the critical buckling load should be no less than twice the actual working load. The calculation results are saved in the form of numerical tables, along with load-strain curves, for subsequent comprehensive evaluation of column stability.

[0027] Step S24: Design a buckling-resistant structure based on the stability of the compression member and the degree of buckling risk.

[0028] In this embodiment, after completing the stability assessment of the piston rod, an anti-buckling structure design is performed on the piston rod according to the stability level and the degree of buckling risk. The design process is based on 3D CAD software (Siemens NX12.0). First, circumferential stiffeners are designed near the abrupt change point. The thickness of the stiffeners is 1.5 times the wall thickness, and the width is 0.2 times the diameter. The stiffeners are aligned with the center line of the abrupt change point. For slender sections with high buckling risk, a gradually thickened zone is designed along its length. The length of the thickened zone is 25% of the length of the critical section. The outer diameter is uniformly increased by 5% from the original diameter, while the inner diameter remains unchanged to increase the moment of inertia. All design dimensions meet the requirements of GB / T3766-2016 General Technical Conditions for Hydraulic Systems, and interference checks are performed in the CAD software to ensure that the assembly of mating components is not affected. After the design was completed, the geometric parameters of the improved structure were imported into the finite element analysis software (ANSYS Workbench 2022 R1) for static and buckling analyses. This verified whether the effective range of the stiffeners and thickened areas covered the critical area, and verified the working conditions, including the maximum working load and 1.5 times the working load. The design documents were finally exported in STP format, along with engineering drawings and parts lists, and delivered to the manufacturing department for subsequent processing.

[0029] Preferably, step S24 specifically includes: Step S241: Identify unstable regions using the stability of the compression bar, and install cylindrical steel sleeves in the unstable regions; In this embodiment, after the stability assessment of the compression member is completed, the specific location of the unstable region is determined using the stability analysis results. The criteria for determining the unstable region are: the calculated buckling safety factor of the segment is less than 2.0 and the slenderness ratio is greater than 120. First, the start and end points of the unstable segment are determined on the plunger rod using an axial positioning system (with a grating ruler with 0.01 mm accuracy), and positioning lines are etched on the metal surface using a precision engraving machine. Subsequently, an installation groove is machined on the outer periphery of the unstable segment. The groove depth is 0.3 times the wall thickness, and the width is 0.5 mm greater than the steel sleeve wall thickness to ensure interference fit space during installation. The groove is machined in one step using a CNC lathe (accuracy ±0.01 mm) to ensure that the flatness of the groove bottom is within 0.02 mm. The cylindrical steel sleeve is made of 42CrMo quenched and tempered steel with a hardness of HB280~320. Its inner diameter is 0.05 mm smaller than the outer diameter of the plunger rod to form an interference fit. The sleeve thickness is 0.15 times the outer diameter of the plunger rod. Its length covers the entire unstable section and extends 15 mm at each end to distribute stress concentration. During installation, a 200℃ hot-fitting process is used. The steel sleeve is heated to 200±5℃, and a hydraulic assembly machine is used to press it axially into the groove position, ensuring that the concentricity between the installation direction and the plunger rod axis is less than 0.02 mm to avoid eccentricity causing additional bending moments.

[0030] Step S242: Based on the degree of buckling risk, embed a limiting ring in the buckling-risk plunger rod section and design a copper-based sliding sleeve; In this embodiment, based on the buckling hazard analysis results, the plunger rod segment with the highest buckling hazard level (safety factor less than 1.6) was identified as the locating ring installation segment. A coordinate measuring machine (accuracy ±0.005 mm) was used to measure the outer diameter and coaxiality of this segment to ensure that the fit between the locating ring and the plunger rod surface meets the H7 / h6 standard tolerance. The locating ring is made of 20CrMnTi carburized steel with a carburized layer depth of 0.8–1.2 mm and a surface hardness of HRC58–62. The inner diameter of the locating ring is 0.02 mm larger than the outer diameter of the plunger rod, and the outer diameter is 0.03 mm smaller than the inner diameter of the copper-based sliding sleeve to ensure a sliding fit. The thickness of the locating ring is 0.1 times the outer diameter of the plunger rod, and a 1×45° chamfer is machined at both ends of the outer circle to reduce stress concentration. The copper-based sliding sleeve is made of ZCuSn10P1 tin bronze, with its inner wall precision honed to a roughness Ra≤0.2 micrometers and a wall thickness of 5 mm. During the design process, the limiting ring is embedded within the sliding sleeve, with the entire sliding sleeve covering the entire length of the buckling-prone section, providing axial positioning at the location of the limiting ring. After machining, the limiting ring is embedded into the inner cavity of the sliding sleeve via cold pressing assembly, with the pressing force controlled within the range of 5–8 kN to ensure that the limiting ring is firmly fixed without any minor gaps.

[0031] Step S243: Fix the copper-based sliding sleeve at the mounting groove where the cylindrical steel sleeve is installed to form a buckling-resistant structure.

[0032] In this embodiment, after processing the cylindrical steel sleeve and the limiting ring-copper-based sliding sleeve assembly, the copper-based sliding sleeve is fixed to the mounting groove of the steel sleeve to form an integral buckling-resistant structure. Before installation, an ultrasonic cleaner is used to degrease the inner wall of the steel sleeve and the outer wall of the copper-based sliding sleeve. The cleaning fluid temperature is 50°C, and the time is 8 minutes. After cleaning, a 0.05 mm thick layer of high-strength epoxy adhesive (shear strength ≥25 MPa) is uniformly applied to the inner wall of the steel sleeve. Then, the copper-based sliding sleeve is heated to a slightly expanded state in an 80°C environment. Using a hydraulic assembly machine, the heated copper-based sliding sleeve is slowly pressed into the groove of the steel sleeve axially. The assembly speed is controlled at 2 mm / s to ensure that the adhesive layer is not squeezed out unevenly. The installation depth is precisely controlled by the end face positioning block, with an allowable error of no more than ±0.02 mm. After assembly, the entire structure is cured at 25°C for 24 hours. After the adhesive layer is completely cured, a concentricity test is performed, requiring that the deviation of the plunger rod axis, the steel sleeve axis, and the inner hole axis of the sliding sleeve is no greater than 0.015 mm. Finally, a rust-preventive paint film with a thickness of 20-25 micrometers is sprayed onto the outer surface of the assembly location to prevent corrosion from affecting the fitting accuracy during long-term operation.

[0033] Preferably, step S3 specifically includes: Step S31: Perform axial compression simulation based on the buckling-resistant structure to determine the buckling limit load; In this embodiment, after the buckling-resistant structure is fabricated and its geometric dimensions are confirmed to be consistent with the design drawings, the structural parameters are imported into a three-dimensional finite element analysis system for axial compression simulation. Input parameters include: the total length of the plunger rod (e.g., 1200 mm), outer diameter (e.g., 80 mm), inner diameter (e.g., 56 mm), material elastic modulus (2.1 × 10¹¹ Pa), Poisson's ratio (0.3), and density (7850 kg / m³). The loading boundary conditions are set as follows: one end is fixed and constrained, while the other end is subjected to axial compressive displacement. The loading rate is 0.5 mm / s, and calculations are performed under quasi-static conditions. During mesh generation, tetrahedral quadratic elements are used, with the element size controlled at 2 mm to ensure accurate capture of stress changes in local details. Using a nonlinear buckling analysis method, the structural deformation is monitored during the gradual loading process. When the displacement-load curve shows its first significant decrease, the corresponding load value is recorded as the buckling limit load. For example, the calculated buckling limit load of this structure is 285 kN, and this value is used as the input condition for subsequent stress analysis.

[0034] Step S32: Calculate the maximum equivalent stress of the material under the buckling limit load condition; In this embodiment, after obtaining the buckling limit load, this load is applied as a constant axial pressure to the stressed end of the buckling-resistant structure, while maintaining the same boundary conditions and mesh generation method as in step S31. During the analysis, a static calculation method is used to output the equivalent stress contour map of the structure. The equivalent stress calculation adopts the von Mises stress theory, recording the stress values ​​of all nodes during the calculation process, and selecting the maximum value as the maximum equivalent stress of the material. For example, in this embodiment, the maximum equivalent stress value is 510 MPa, appearing in the inner wall region near the variable cross-section transition section in the middle of the plunger rod. To ensure the reliability of the stress value, two different mesh refinement levels (2 mm and 1 mm) are used for repeated calculations, and the difference in the maximum equivalent stress is compared. A difference of less than 2% confirms the result as valid.

[0035] Step S33: Identify the location of stress concentration based on the maximum equivalent stress of the material; In this embodiment, after determining the maximum equivalent stress of the material, high-stress areas are located using a stress cloud map, and the set of nodes whose stress values ​​exceed 90% of the overall maximum equivalent stress is extracted. This area is defined as a stress concentration location. To avoid misjudgment, adjacent stress concentration nodes are clustered with a cluster radius of 3 mm to remove scattered single high values. Based on the clustering results, this embodiment identifies three stress concentration locations: the inner wall of the variable cross-section transition section, near the contact end face of the sliding sleeve, and at the end transition fillet of the cylindrical steel sleeve. During the identification process, the spatial location of the stress concentration area is mapped one-to-one with the actual surface location of the machined part using three-dimensional coordinate mapping, forming a coordinate point data table that can be directly used for subsequent detection, with coordinate accuracy controlled within ±0.02 mm.

[0036] Step S34: Detect the material fracture strength at the stress concentration location; In this embodiment, after determining the stress concentration location, an in-situ hardness test is performed on the material at that location using a portable microhardness tester. The test load is set to 2 kgf, and the holding time is 15 seconds. The measurement result is converted into a tensile strength value. Based on the chemical composition of the material (e.g., 42CrMo steel) and its heat treatment state, the hardness value is converted into a theoretical fracture strength. For example, in this embodiment, the hardness at the contact end face of the sliding sleeve is 285 HB, corresponding to a fracture strength of approximately 950 MPa. To verify the accuracy of the value, standard tensile specimens (10 mm in diameter, 50 mm in gauge length) are prepared from the same batch of material and tensile tests are performed on a universal testing machine. The difference between the measured fracture strength and the converted hardness value does not exceed 5%. Finally, the verified fracture strength is used as a reference parameter for judging crack initiation conditions.

[0037] Step S35: Detect the cracks on the groove surface using the material fracture strength test, and mark the location of the cracks on the groove surface.

[0038] In this embodiment, the fracture strength value obtained in step S34 is compared with the maximum equivalent stress at the stress concentration location in step S33. When the maximum equivalent stress at a certain location exceeds 80% of the fracture strength threshold, that location is identified as a high-risk area for groove surface cracks. For high-risk areas, magnetic particle testing is used to detect cracks. The testing process parameters are: AC magnetization current 1500A, magnetization time 3 seconds, fluorescent magnetic powder (particle size 3-6 micrometers), and suspension concentration 1.5 g / L. During testing, observation is conducted in a darkroom using an ultraviolet lamp (wavelength 365 nm, illuminance 1000 μW / cm²). After crack detection, a laser displacement sensor is used to accurately measure the coordinates of the crack's initiation and termination points with an accuracy of ±0.01 mm. This location is then marked in the 3D CAD model for subsequent material strengthening and structural optimization.

[0039] Preferably, step S35 specifically includes: Step S351: Use the material fracture strength to identify high fracture strength regions and axial cracks; In this embodiment, based on the aforementioned material fracture strength data, this data is used as a reference. Combined with the hardness and stress analysis results of various parts of the plunger rod, high fracture strength areas are calibrated on the surface of the plunger rod. A hardness tester is used to measure the surface of the plunger rod point by point, with the distance between measurement points controlled within 5 mm. Areas with hardness values ​​exceeding 290 HB are defined as high fracture strength areas. Subsequently, ultrasonic testing equipment is used to identify cracks in this area. The ultrasonic frequency is set to 5 MHz, a 10 mm diameter focusing probe is used, and the scanning speed is controlled at 30 mm per minute. Combining A-scan and C-scan data, the length and depth of the crack are located. Through analysis of ultrasonic echo signal intensity and propagation time, axial crack characteristics are identified, with a focus on analyzing crack extension along the plunger rod axis. For the identified cracks, the crack morphology is further confirmed using a scanning electron microscope (SEM) with a scanning resolution of no less than 50 nanometers. Through the above process, axial cracks located in the high fracture strength area are accurately identified, ensuring the accuracy of crack spatial location and length information, providing basic data for subsequent fatigue crack analysis.

[0040] Step S352: Detect the edge sharpness of axial cracks to identify fatigue cracks; In this embodiment, for the axial cracks identified in step S351, a three-dimensional laser scanning microscope is used to perform a fine morphological scan of the crack edges. The scanning resolution is set to 0.1 micrometers, and the scanning range covers at least 200 micrometers on both sides of the crack. Based on the edge morphology curves obtained from the scan, an edge sharpness index is calculated. Sharpness is defined as the ratio of the radius of curvature of the crack tip to that of the adjacent region, and a threshold of less than 0.5 micrometers is set to determine a sharp edge. Cracks with edge sharpness exceeding this threshold are defined as fatigue cracks. This technique is used to detect all axial cracks one by one, and fatigue cracks and non-fatigue cracks are distinguished by combining the quantitative data of the edge morphology. During the detection process, a constant ambient temperature of 25°C and humidity of 45% are maintained to prevent environmental factors from affecting the crack surface morphology. The detection results are recorded to establish a fatigue crack database, providing a basis for subsequent fracture surface analysis.

[0041] Step S353: At the location of fatigue crack, examine the grains on the fracture surface. If obvious bright reflection is observed, it is determined to be brittle fracture. In this embodiment, at the location identified as a fatigue crack, the fracture area is observed at high magnification using a scanning electron microscope (SEM), with the magnification set between 5000 and 10000x. Illumination is provided by a field emission electron gun with an operating voltage of 15kV. The reflectance brightness of the fracture grain structure is obtained using a reflective electron detector, and the morphology and reflection characteristics of the fracture grains are analyzed. For fracture grains exhibiting obvious and uniform high reflectance brightness, combined with a grain size within the range of 10 to 20 micrometers, the fracture is determined to be brittle fracture. To ensure data accuracy, at least five fracture sampling points are used. This method allows for quantitative analysis of the grain reflectance brightness of fatigue crack fracture surfaces, identifying brittle fracture regions.

[0042] Step S354: At the location of fatigue crack, identify the fracture morphology. If the fracture surface is dimple-shaped, it is determined to be ductile fracture. In this embodiment, the fracture morphology was observed holistically at the same fatigue crack location using a low-magnification scanning electron microscope (SEM), with a magnification range of 100 to 500x. The focus of observation was the dimple-like morphology of the fracture surface, with dimple diameters ranging from 1 to 5 micrometers and uniformly distributed. Image processing software was used to statistically analyze the number, diameter, and uniformity of dimple distribution. When the number of dimples exceeded 70% of the total fracture area and the diameters were uniformly distributed, the fracture was determined to be ductile fracture. The dimple morphology of the fracture surface matched the typical fracture morphology of fatigue fracture, serving as the basis for determining ductile fracture. To ensure the representativeness of the fracture morphology analysis, the fracture scanning area was no less than 1 square millimeter, and multi-point scanning was used to obtain the average value.

[0043] Step S355: Mark the location of the groove cracks where brittle fracture and ductile fracture occur.

[0044] In this embodiment, the fracture locations determined to be brittle or ductile fractures are precisely marked using a three-dimensional coordinate measuring machine (CMM). The CMM measurement accuracy reaches ±0.005 mm, and the measurement content includes the XYZ three-dimensional coordinates of the fracture surface and the coordinates of the crack initiation and termination points. The measurement results are correlated with the three-dimensional CAD model of the plunger rod to establish a crack spatial location database. Dedicated software is used to generate crack marking layers, and the marking content includes fracture type (brittle or ductile), fracture location coordinates, and crack size information. All marking data is imported into the design management system for subsequent multi-level material strengthening processing and structural optimization. The marking process complies with the requirements of the quality management system, and the measurement process is controlled under conditions of temperature 20℃±2℃ and humidity 40%±5% to ensure data stability and reliability.

[0045] Preferably, step S4 specifically includes: Step S41: Determine the shot peening particle size at the crack location on the groove surface, implement the shot peening process to form a compressive stress layer; increase the hardness of the compressive stress layer and improve the adhesion of the surface coating to obtain surface coating data; In this embodiment, the crack range is precisely located at the crack location using non-destructive testing methods (such as ultrasonic or magnetic particle testing) to determine the application area for shot peening. Spherical steel shot with a particle size of 0.3~0.6 mm is selected. The particle size is determined based on a combination of crack width and depth; when the maximum crack width is less than 0.5 mm, a particle size of 0.3 mm is used; for larger cracks, 0.6 mm is used. A pressure-regulated shot peening machine is used, with the spraying pressure maintained between 0.4 and 0.6 MPa, the spraying distance controlled at 150 mm, and the spraying angle fixed at 90 degrees perpendicular to the workpiece surface. The shot peening time is controlled between 30 and 90 seconds to ensure the formation of a uniform and continuous compressive stress layer. After shot peening, the hardness of the shot-peened surface is measured using a metallographic microscope and a Rockwell hardness tester (HRB). The measuring points are distributed in the crack area and crack edge, with a target hardness value of not less than 350 HRB. Subsequently, a surface coating treatment is applied. Thermal spraying was used, with chromium-molybdenum alloy powder as the coating material. The spray thickness was controlled between 50 and 150 micrometers. The coating was then sanded to a roughness of Ra = 0.8 micrometers to ensure good adhesion between the surface coating and the compressive stress layer. Adhesion testing employed tensile bond strength testing, with a minimum requirement of 15 MPa. The test data from this process was recorded to form surface coating data, including shot peening particle size, peening parameters, hardness value, and adhesion value, for use in subsequent material fusion.

[0046] Step S42: Perform subsurface strengthening at the crack location on the groove surface to obtain subsurface data; In this embodiment, a subsurface strengthening treatment is performed at the location of the crack in the groove. The thickness of the subsurface layer is set to 1.0 to 3.5 mm, with the range determined based on the crack depth and material properties. Induction hardening technology is employed, using an induction coil with a frequency of 100 kHz. The coil is designed as a ring to ensure uniform heating covering the strengthened area. The heating temperature is controlled within the range of 820°C to 860°C, with a holding time of 30 seconds, followed by high-pressure water mist cooling at a rate exceeding 50°C per second to ensure the formation of a uniform and fine martensitic structure. After quenching, a scanning electron microscope (SEM) is used to analyze the microstructure of the strengthened layer, focusing on the uniformity of the martensite distribution. The requirement is a uniform distribution of fine acicular martensite without obvious overheated areas. The hardness of the strengthened layer is measured using a microhardness tester, with measurements taken every 0.2 mm along the thickness direction, maintaining a target hardness value between 550 HV and 650 HV. The microstructure of the transition zone between the strengthened layer and the base material is smooth, avoiding abrupt changes in hardness. The above-mentioned tissue and hardness data are compiled to form subsurface data, which is used for material fusion.

[0047] Step S43: Fuse surface coating data and subsurface data to obtain multi-level material data; In this embodiment, the fusion process first establishes a material property database based on depth coordinates. This database contains multi-dimensional parameters such as hardness distribution, microstructure, and stress state from the surface to the subsurface layer. Using a layer-by-layer scanning technique, the hardness and microstructure characteristics of the surface coating and subsurface layer are sequentially superimposed according to depth, forming a complete multi-level reinforced layer material property curve. The hardness value gradually transitions from 350 HRB for the surface coating to 550 HV for the subsurface layer, maintaining a smooth curve without abrupt changes. Combined with microstructure maps, the interfacial bonding strength is checked to confirm the absence of voids and cracks in the interlayer bonding. By performing an equivalent transformation of the stress field of the multi-level material layers, an elastic modulus and yield strength distribution model for each layer is established. All fused data is input into the material property database, and a complete multi-level material data file is output for use in structural design.

[0048] Step S44: Design a four-bar lifting structure based on multi-level material data.

[0049] In this embodiment, the specific installation positions of the four-bar lifting rods are determined using local hardness and stress distribution information from multi-level material data. The installation area focuses on the periphery of the crack with the most severe stress concentration. Four lifting rods are arranged along the crack length, with the spacing determined based on the crack size and variable cross-sectional geometry, generally controlled within the range of 30 mm to 60 mm. Based on the material stiffness and yield strength from the multi-level material data, the cross-sectional shape and dimensions of the lifting rods are designed. The rod diameter is set between 20 mm and 30 mm, and the cross-sectional shape adopts a circular hollow structure with a wall thickness of 2.5 mm to ensure both strength and lightweight requirements. A prefabricated reinforced steel plate is used to connect the lifting rods to the plunger rod surface. The steel plate is 5 mm thick, with 12 mm diameter pre-drilled bolt holes spaced 20 mm apart. 8.8 grade high-strength bolts are used for the bolt connection. During the design, the reinforcement area of ​​the steel plate is reasonably adjusted according to the distribution of the multi-level material layers to ensure uniform load transfer and no stress concentration after the lifting rods are installed. All design parameters are summarized to form the assembly drawing and installation instructions for the four-bar lifting structure, ensuring accuracy and consistency during actual manufacturing and installation.

[0050] Preferably, step S42 specifically includes: Step S421: Determine the subsurface reinforcement range at the location of the groove crack; In this embodiment, based on the crack detection results of the groove surface, the initiation and termination points and width of the crack are accurately located using non-destructive testing techniques (such as magnetic particle testing, ultrasonic testing, or radiographic testing), clarifying the axial distribution range of the crack. The subsurface reinforcement range extends 5 to 10 mm towards both ends of the crack, using the crack propagation boundary as a reference, to cover the crack area and its stress influence zone. Along the circumferential direction, the subsurface reinforcement range is controlled to be more than twice the crack width, ensuring that the reinforcement layer completely covers the area where the crack may propagate. Three-dimensional morphological data of the plunger rod surface are collected using laser scanning measurement equipment, and a three-dimensional spatial model of the reinforcement area is formed by combining it with the crack size. The reinforcement layer thickness is preset to 1 to 5 mm and adjusted according to the crack depth and material mechanical properties. The spatial coordinate data of the reinforcement range is imported into CNC equipment for precise positioning. All measurement parameters, including crack length, width, depth, and propagation safety boundary dimensions, are strictly recorded to ensure that the subsequent quenching treatment range and intensity are strictly performed according to the predetermined area.

[0051] Step S422: Quenching is performed in the subsurface strengthening area to form a highly strengthened martensite layer; In this embodiment, within a preset subsurface strengthening range, an induction hardening device is used to locally heat the plunger rod. The device employs a high-frequency induction coil with a frequency of 50kHz to 100kHz. The size of the induction coil is customized according to the strengthening range, and the distance between the coil and the workpiece surface is controlled at 2 to 5 mm to ensure uniform heating. The heating temperature is controlled between 830℃ and 870℃, and is monitored in real time by a built-in thermocouple and infrared thermometer to ensure temperature stability and reaching the temperature required for austenitization of the material. The heating time is controlled between 20 and 60 seconds, with the specific duration adjusted according to the thickness of the strengthening range and the thermal conductivity of the material. Immediately after heating, a high-pressure spray quenching device is used for spray quenching. The spray quenching medium is deionized water, the spray quenching pressure is set at 5 to 8 MPa, and the spray quenching distance is maintained at 100 mm to 150 mm. The cooling rate reaches more than 50℃ per second to ensure the formation of a fine and uniform martensitic structure. All parameters of the quenching process are recorded, including heating temperature curves, time, spray quenching pressure, and cooling rate, to ensure process traceability and precise control.

[0052] Step S423: Perform microstructure analysis on the high-strength martensite layer to verify the uniformity of the martensite layer; In this embodiment, after quenching, a cross-sectional sample of the reinforced area was taken for microstructural analysis. Sample preparation included cutting, mounting, grinding, polishing, and etching. The etchant was a 2% nitric acid alcohol solution, and the etching time was controlled between 15 and 30 seconds. Preliminary observation was performed using an optical microscope at a magnification of 100x to 500x, focusing on the uniformity of the martensite structure and the distribution of fine acicular structures. Subsequently, a higher-precision microstructural analysis was performed using a scanning electron microscope (SEM) at a magnification of up to 1000x, to examine the detailed microcrystalline structure and phase distribution within the reinforced layer. The evaluation criteria for microstructural uniformity were: continuous fine acicular martensite without obvious inclusions, cracks, or soft areas; and grain size variation within the reinforced layer thickness controlled within ±10%. Microstructural analysis data and images were archived for subsequent quality verification and material performance evaluation.

[0053] Step S424: Control the heat-affected zone of quenching to ensure a smooth transition zone of the high-strength martensite layer, thereby obtaining subsurface data.

[0054] In this embodiment, the control of the heat-affected zone (HAZ) is achieved by adjusting the induction heating power and spraying parameters. The heating power is adjusted from 3 to 5 kW, automatically adjusted based on real-time temperature feedback to avoid an excessively wide or narrow HAZ. The spraying pressure and nozzle layout design ensure a smooth temperature gradient between the reinforced layer and the substrate, preventing abrupt hardness changes and residual stress concentration. The HAZ thickness is determined by microhardness testing using a Vickers hardness tester with a 500g load and a 0.2mm spacing, extending from the reinforced layer surface to the substrate; the hardness change curve should transition smoothly. The width of the HAZ is strictly controlled between 2 and 4 mm to avoid interface cracks. All temperature, power, time, and spraying parameter data are recorded and compiled into a process parameter report. Through the above control, the transition zone between the martensitic layer and the substrate is ensured to have a continuous microstructure and mechanical properties, forming a smooth transition zone, thereby obtaining complete subsurface layer data.

[0055] Preferably, step S44 specifically includes: Step S441: Perform stress load simulation based on multi-level material data to identify stress concentration areas; In this embodiment, the multi-level material data includes the physical and mechanical properties of the surface shot-peening reinforcement layer, the subsurface quenching reinforcement layer, and the matrix material, such as elastic modulus, yield strength, hardness, and fracture toughness. The thickness and microstructure of each material layer are detailed. Three-dimensional static stress analysis is performed using finite element analysis software. The mechanical property data of the multi-level material layers are input, and axial compressive loads and lateral constraints are applied according to actual working conditions. The load magnitude is based on the maximum load-bearing capacity of the plunger rod during operation, typically within 90% to 110% of the design ultimate load. Boundary conditions simulate the fixed and supported state of the actual plunger rod end. Volumetric meshing is used, with the mesh size controlled within 0.5 mm to ensure calculation accuracy. The stress distribution cloud map of the entire plunger rod is obtained through calculation, with a focus on analyzing the stress concentration at material interfaces and areas with significant cross-sectional changes. The stress concentration threshold is set at 75% of the material's yield strength; areas exceeding this threshold are considered stress concentration areas, and their location coordinates and area dimensions are recorded in detail to form a stress concentration area dataset.

[0056] Step S442: Determine the installation area of ​​the four lifting rods based on the stress concentration area; In this embodiment, based on the stress concentration area data obtained in step S441, a three-dimensional measuring device (such as a laser scanner or coordinate measuring machine) is used to accurately measure the shape of the plunger rod, locating the spatial position and size of the stress concentration area. Combined with structural assembly requirements, four installation areas for the lifting rods are divided, ensuring that each installation area covers at least 70% of the stress concentration area while meeting the mechanical space requirements for the lifting rod installation. The installation area is typically set as a circular area with a diameter of 30 to 50 mm to ensure the stability of the lifting rod contact surface. The distribution of the installation areas must evenly cover the entire variable cross-section portion of the plunger rod and avoid existing structural defects and assembly holes. The specific location of the lifting rod installation area is determined by coordinate positioning, recording parameters such as the installation hole spacing, the normal direction of the installation surface, and the tilt angle to ensure the accurate arrangement of subsequent reinforcing steel plates and bolts.

[0057] Step S443: Design and arrange reinforcing steel plates in the installation area of ​​the four lifting rods, and reserve mounting bolt holes to obtain the design data of the reinforcing installation structure; In this embodiment, based on the determined installation areas of the four lifting rods, the dimensions and thickness of the reinforcing steel plates are designed. The steel plate thickness is determined according to the maximum load calculation results, generally 8 to 12 mm, to meet the local load-bearing requirements. The steel plate material is Q345 steel conforming to GB / T700 standard, with a yield strength of not less than 345 MPa. The steel plate is designed to be rectangular or elliptical in shape, covering the lifting rod installation area and extending at least 10 mm beyond the edge safety strip to ensure structural rigidity. Bolt holes are pre-drilled on the steel plate, with a diameter of 12 mm. The bolt hole spacing is arranged according to the standard bolt specification (M12×1.75), and the hole spacing error is controlled within ±0.1 mm. The bolt hole positions are checked using a coordinate measuring machine to ensure bolt alignment during installation. There are no fewer than 4 bolt holes, evenly distributed on each steel plate to ensure reliable fixing. The contact surface between the steel plate and the plunger rod is precision machined, with the surface roughness controlled within Ra0.8 micrometers to improve the fit of the contact surface. After the design is completed, CAD software is used to generate design data for the reinforcement installation structure, including a three-dimensional model of the steel plate, hole coordinates, and assembly process requirements.

[0058] Step S444: Based on the design data of the reinforced installation structure, plan the relative positional relationship between the lifting rods and the platform guide rails, and adjust the spacing between the four lifting rods to obtain the four-bar lifting structure.

[0059] In this embodiment, based on the reinforcement installation structure design data from step S443 and the assembly dimensions of the lifting rods and platform guide rails, the relative positions of the four lifting rods are planned. The spacing between the lifting rods is adjusted according to the plunger rod diameter and the distribution of stress concentration areas, generally controlled within the range of 50 to 120 mm to ensure uniform distribution of the lifting load. The installation direction of the lifting rods is perpendicular to the direction of the platform guide rails, and the installation angle deviation is controlled within ±2 degrees. Three-dimensional assembly measurement equipment is used to confirm the position of the lifting rods, and the height and angle of the lifting rod mounting supports are adjusted to ensure that the working planes of the four lifting rods are consistent, with an error controlled within 0.2 mm. The reserved gap between the lifting rods and the platform guide rails is designed to be 1.5 to 2 mm to meet the requirements of guide rail sliding and thermal expansion and contraction. Finally, the lifting rods are connected to the reinforcement steel plates with high-strength bolts, with the bolt torque controlled within the range of 80 to 120 Nm. After installation, structural integrity checks and load tests are performed. This arrangement forms a four-bar lifting structure that ensures the buckling resistance and stability of the plunger rods during use.

[0060] Preferably, this specification also provides a topology-optimized buckling-resistance structure design system for a hollow variable cross-section plunger rod, used to execute the topology-optimized buckling-resistance structure design method for a hollow variable cross-section plunger rod as described above. The topology-optimized buckling-resistance structure design system for the hollow variable cross-section plunger rod includes: The buckling risk assessment module is used to acquire the extension and retraction data of the plunger rod; determine the maximum active stroke based on the extension and retraction data; and use the maximum active stroke to determine the degree of buckling risk. The buckling-resistant structure design module is used to detect the moment of inertia distribution of variable cross sections based on the degree of buckling risk; evaluate the compression stability of plunger rods using the moment of inertia distribution; and design buckling-resistant structures based on the compression stability and the degree of buckling risk. The groove surface crack detection module is used to simulate the buckling limit load based on the buckling-resistance structure, detect the material fracture strength under the buckling limit load, and use the material fracture strength to detect groove surface cracks and mark the location of the groove surface cracks. A multi-level material strengthening module is used to perform multi-level material strengthening treatment at the crack location on the groove surface and generate multi-level material data; a four-bar lifting structure is designed based on the multi-level material data.

[0061] Therefore, the embodiments should be considered as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the application are intended to be included within the invention.

[0062] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod, applied to a plunger-type hydraulic gate hoist, characterized in that, Includes the following steps: Step S1: Obtain the extension and retraction data of the plunger rod; Determine the maximum active stroke based on the stretching data; use the maximum active stroke to assess the degree of buckling risk; Step S2: Detect the moment of inertia distribution of the variable cross section according to the degree of buckling risk; evaluate the compression stability of the plunger rod using the moment of inertia distribution; design a buckling-resistant structure based on the compression stability and the degree of buckling risk; Step S3: Simulate the buckling limit load based on the buckling-resistant structure and detect the material fracture strength under the buckling limit load; The fracture strength of the material is used to detect cracks in the groove surface, and the location of the cracks is marked. Step S4: Perform multi-level material strengthening treatment at the crack location on the groove surface to generate multi-level material data; The four-bar lifting structure is designed based on multi-level material data.

2. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 1, characterized in that, Step S1 is as follows: Step S11: Obtain the extension and retraction data of the plunger rod; Step S12: Record the starting and ending coordinates using the scaling data; Step S13: Calculate the maximum active travel distance based on the starting and ending coordinates; Step S14: Extract the effective length of the plunger rod using the maximum active stroke, and determine the cross-sectional area of ​​the plunger rod interface; calculate the slenderness ratio based on the effective length and the cross-sectional area interface, and determine the degree of buckling risk.

3. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 1, characterized in that, Step S2 is as follows: Step S21: Identify high-risk areas based on the degree of buckling risk, and calculate the plunger diameter in the high-risk areas; assess the moment of inertia of the cross section based on the plunger diameter; statistically analyze the moment of inertia distribution of the variable cross section based on the moment of inertia of the cross section. Step S22: Determine the abrupt change point of the moment of inertia based on the distribution of the moment of inertia; Step S23: Collect the actual load at the point of abrupt change in moment of inertia; The stability of the compression member is evaluated using the actual load and the preset buckling safety factor; Step S24: Design a buckling-resistant structure based on the stability of the compression member and the degree of buckling risk.

4. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 3, characterized in that, Step S24 is as follows: Step S241: Identify unstable regions using the stability of the compression bar, and install cylindrical steel sleeves in the unstable regions; Step S242: Based on the degree of buckling risk, embed a limiting ring in the buckling-risk plunger rod section and design a copper-based sliding sleeve; Step S243: Fix the copper-based sliding sleeve at the mounting groove where the cylindrical steel sleeve is installed to form a buckling-resistant structure.

5. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 1, characterized in that, Step S3 is as follows: Step S31: Perform axial compression simulation based on the buckling-resistant structure to determine the buckling limit load; Step S32: Calculate the maximum equivalent stress of the material under the buckling limit load condition; Step S33: Identify the location of stress concentration based on the maximum equivalent stress of the material; Step S34: Detect the material fracture strength at the stress concentration location; Step S35: Detect the cracks on the groove surface using the material fracture strength test, and mark the location of the cracks on the groove surface.

6. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 5, characterized in that, Step S35 is as follows: Step S351: Use the material fracture strength to identify high fracture strength regions and axial cracks; Step S352: Detect the edge sharpness of axial cracks to identify fatigue cracks; Step S353: At the location of fatigue crack, examine the grains on the fracture surface. If obvious bright reflection is observed, it is determined to be brittle fracture. Step S354: At the location of fatigue crack, identify the fracture morphology. If the fracture surface is dimple-shaped, it is determined to be ductile fracture. Step S355: Mark the location of the groove cracks where brittle fracture and ductile fracture occur.

7. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 1, characterized in that, Step S4 is as follows: Step S41: Determine the shot peening particle size at the crack location on the groove surface, implement the shot peening process to form a compressive stress layer; increase the hardness of the compressive stress layer and improve the adhesion of the surface coating to obtain surface coating data; Step S42: Perform subsurface strengthening at the crack location on the groove surface to obtain subsurface data; Step S43: Fuse surface coating data and subsurface data to obtain multi-level material data; Step S44: Design a four-bar lifting structure based on multi-level material data.

8. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 7, characterized in that, Step S42 is as follows: Step S421: Determine the subsurface reinforcement range at the location of the groove crack; Step S422: Quenching is performed in the subsurface strengthening area to form a highly strengthened martensite layer; Step S423: Perform microstructure analysis on the high-strength martensite layer to verify the uniformity of the martensite layer; Step S424: Control the heat-affected zone of quenching to ensure a smooth transition zone of the high-strength martensite layer, thereby obtaining subsurface data.

9. The topology-optimized buckling-resistant structural design method for a hollow variable cross-section plunger rod according to claim 7, characterized in that, Step S44 is as follows: Step S441: Perform stress load simulation based on multi-level material data to identify stress concentration areas; Step S442: Determine the installation area of ​​the four lifting rods based on the stress concentration area; Step S443: Design and arrange reinforcing steel plates in the installation area of ​​the four lifting rods, and reserve mounting bolt holes to obtain the design data of the reinforcing installation structure; Step S444: Based on the design data of the reinforced installation structure, plan the relative positional relationship between the lifting rods and the platform guide rails, and adjust the spacing between the four lifting rods to obtain the four-bar lifting structure.

10. A topology-optimized buckling-resistance structural design system for a hollow variable cross-section plunger rod, characterized in that, For implementing the topology-optimized buckling-resistant structural design method for the hollow variable cross-section plunger rod as described in claim 1, the topology-optimized buckling-resistant structural design system for the hollow variable cross-section plunger rod includes: The buckling risk assessment module is used to acquire the extension and retraction data of the plunger rod; determine the maximum active stroke based on the extension and retraction data; and use the maximum active stroke to determine the degree of buckling risk. The buckling-resistant structure design module is used to detect the moment of inertia distribution of variable cross sections based on the degree of buckling risk; evaluate the compression stability of plunger rods using the moment of inertia distribution; and design buckling-resistant structures based on the compression stability and the degree of buckling risk. The groove surface crack detection module is used to simulate the buckling limit load based on the buckling-resistance structure, detect the material fracture strength under the buckling limit load, and use the material fracture strength to detect groove surface cracks and mark the location of the groove surface cracks. A multi-level material strengthening module is used to perform multi-level material strengthening treatment at the crack location on the groove surface and generate multi-level material data; a four-bar lifting structure is designed based on the multi-level material data.

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