A low residual stress stainless steel rail annealing method

Abstract

The application discloses a low-residual-stress stainless steel rail annealing processing method and belongs to the technical field of metal heat treatment. In view of the problems that the existing stainless steel rail annealing process relies on manual experience, single-stress-qualified but finished product out-of-tolerance defects are prone to occurring, overannealing causes processing defects, the stress of the finished product fluctuates greatly, and the qualified rate is low, the application firstly quantizes the residual stress cross-process transmission law, establishes a full-process stress recursive model, fits a process mapping relationship to determine the regulation interval of each annealing process, then inversely deduces the full-process stress threshold chain from the finished product stress threshold, and obtains the globally coordinated optimal annealing reference process through two layers of screening. In production, the stress of the furnace is detected in real time, and when the deviation is out of tolerance, the process is adjusted in each pass in coordination. The model is iteratively corrected in combination with finished product detection to form a control closed loop. The application can reduce process debugging cost, avoid overannealing defects, stably control the residual stress of the finished product, improve the batch qualified rate, and reduce subsequent straightening workload.

Description

Technical Field

[0001] This invention belongs to the field of metal heat treatment technology, specifically relating to a method for annealing stainless steel linear guides with low residual stress. Background Technology

[0002] Conventional machine tool linear guides are mostly made of bearing steel, while stainless steel linear guides, due to their corrosion resistance and non-magnetic properties, are in increasing demand in specialized applications such as food processing, medical equipment, and marine equipment. Residual stress introduced during the processing of stainless steel linear guides is a core factor leading to excessive deformation and affecting the precision retention of equipment. Currently, the industry largely uses multi-pass annealing processes for ordinary steel linear guides to control stress, relying heavily on manual experience for parameter setting, which has many inherent defects. Therefore, this invention urgently needs to solve the following technical problems: There is a lack of quantitative methods for the transmission of residual stress across processes. Process formulation relies on trial and error based on human experience, resulting in high development costs and long cycles. This can easily lead to problems where the stress of a single process is qualified but the finished product is out of tolerance. There is a cognitive bias that "the more thorough the annealing, the better the effect," without considering the adverse effects of annealing, making it impossible to achieve synergy of multiple annealing parameters, and easily leading to processing and performance defects caused by over-annealing; The fixed static process cannot adapt to production fluctuations, the reliance on manual experience for adjustment has poor accuracy, and there is no data feedback and iteration mechanism, resulting in large stress fluctuations and unstable pass rates in finished products. To address this, we propose a low residual stress stainless steel linear guide annealing process. Summary of the Invention

[0003] The purpose of this invention is to provide a method for annealing stainless steel linear guides with low residual stress, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for annealing low residual stress stainless steel linear guides, comprising: Step 1: For the entire stainless steel linear guide production process, classify the processing and annealing processes, define the new residual stress, stress relief rate, and process output residual stress, fit and verify the stress transfer coefficient, establish the recursive formula for residual stress in the whole process, fit the mapping relationship between processing deformation and new residual stress, and annealing parameters and stress relief rate, determine the single-pass annealing control range, and summarize it into the whole process control boundary set. Step 2: Using the residual stress threshold of the finished product as the control target, the allowable stress threshold chain of the whole process is obtained by reverse recursion. The stress elimination rate of each annealing is used as the optimization variable. The optimal elimination rate combination is obtained through two layers of screening: stress threshold and local optimal critical point. The corresponding process parameters are matched to generate the synergistic annealing benchmark process, and the expected residual stress of the benchmark finished product is calculated. Step 3: During the production process, for each workpiece entering the furnace for annealing, the actual process output residual stress is detected, and the residual stress deviation is calculated. If the deviation causes the finished product to exceed the tolerance, the stress relief rate is adjusted step by step from the current annealing. The corresponding process parameters are matched and annealing is performed. After the finished product is inspected, the model parameters are corrected in reverse to form a control closed loop, so as to stably control the residual stress of the finished product within the threshold.

[0005] Preferably, the specific process for establishing the recursive formula for residual stress throughout the entire process is as follows: The production process is sorted and classified into processing and annealing processes. Independent serial numbers are assigned to the two types of processes, and a unified serial number is assigned to all processes in the entire process. The physical meanings of newly added residual stress, stress relief rate, process output residual stress, and finished product residual stress threshold are defined. Process and detection parameters that affect residual stress during production are collected. By tracking the stress data of multiple batches of normally produced workpieces through each process, a structured stress dataset is formed. Based on the stress samples of adjacent processes, a basic linear model is fitted to solve for the stress transfer coefficient between adjacent processes and complete the accuracy verification. By combining the basic model of the process mechanism of added stress during processing and stress relief during annealing, a recursive formula for residual stress throughout the entire process is established, clarifying the calculation rules for processing processes that have no stress relief effect and annealing processes that have no added processing stress.

[0006] Preferably, the specific process for fitting the mapping relationship between processing deformation, newly added residual stress, annealing parameters, and stress relief rate is as follows: The expected residual stress at the inlet of each annealing stage is calculated using the recursive formula for residual stress throughout the entire process. Using multiple sets of detection data on the cross-sectional change rate of a single machining process and the corresponding newly added residual stress as the object, the least squares polynomial fitting method is used to obtain the mapping relationship between machining deformation and newly added residual stress. For each annealing step, independent gradient process tests were conducted, and process levels covering the entire control range were set to test the stress relief rate, workpiece mechanical properties and subsequent processing performance under different processes. Using multiple sets of test data on single-pass annealing process parameters and corresponding stress relief rates as the object, the least squares method was used to fit and obtain the mapping relationship between annealing parameters and stress relief rates.

[0007] Preferably, the specific process of determining the single-pass annealing control range and summarizing it into a set of control boundaries for the entire process is as follows: All test results of single-pass annealing gradient test are obtained and sorted into an ordered experimental group sequence according to stress relief rate from low to high. The stress relief rate is used as a single variable to iterate from both ends to the middle. The single-pass control range is determined by combining the workpiece performance and processing feedback under different stress relief rates. The verification starts with the lowest stress relief rate experimental group. If stress cracking or deformation exceeding the tolerance occurs in the subsequent processing of the corresponding workpiece, the process is iterated towards a higher stress relief rate until the stress-free type fails to meet the standard, which is then determined as the lower limit of the stress relief rate. The verification begins with the highest stress relief rate experimental group. If the corresponding workpiece has processing defects caused by excessively low hardness, the process iterates towards a lower stress relief rate until both mechanical properties and processing requirements are met, at which point the upper limit of the stress relief rate is determined. The continuous range between the upper and lower limits of single-pass annealing is defined as the stress control interval of single-pass annealing, and all single-pass control intervals are summarized to form the set of stress control boundaries for the entire process of annealing.

[0008] Preferably, the specific process for obtaining the full-process allowable stress threshold chain is as follows: Starting from the final inspection of finished products, calculate the maximum residual stress allowed for each process in reverse order along the production process; The maximum allowable residual stress in the final inspection process of the finished product is equal to the threshold of the residual stress of the finished product as the initial condition for recursion. When it is recursively pushed forward, if the next step is a processing step, the maximum allowable residual stress of the current step is calculated by combining the maximum allowable stress of the next step, the newly added residual stress from processing, and the stress transfer coefficient between steps. If the next step is an annealing process, the maximum allowable residual stress of the current process is calculated by combining the maximum allowable stress of the next process, the stress relief rate of annealing, and the stress transfer coefficient between processes. After recursively covering all processes in the entire process, the maximum allowable residual stress of each process is sorted out according to the production sequence to form a chain of allowable stress thresholds for the entire process.

[0009] The preferred method for obtaining the optimal elimination rate combination is as follows: After completing the calculation of the allowable stress threshold chain, the stress relief rate of each annealing process is used as the optimization variable. The upper and lower limits of the value are determined by combining the stress control boundary set of the whole process annealing. All possible stress relief rate combinations are generated by discretization according to the preset fixed small step size. For each combination, the stress of each process and the stress of the final product are calculated in the forward direction using the full-process residual stress recursive formula. The allowable stress threshold at the corresponding position is compared with the process step by step. Combinations with stress exceeding the threshold in any process are eliminated, and combinations that meet the full-process stress requirements are retained to enter the next round of screening. For each retained combination, determine whether the stress relief rate exceeds the local optimal critical point. That is, the increase in stress in subsequent processing caused by the increase in stress relief rate is greater than the critical value of residual stress reduction. Eliminate combinations that exceed the critical point, and the remaining combinations are feasible process combinations. Among all feasible process combinations, the combination with the lowest residual stress in the finished product is selected as the optimal stress relief rate combination, which is the target value of stress relief rate for each annealing process.

[0010] Preferably, the specific process for generating a synergistic annealing baseline process by matching corresponding process parameters and calculating the expected residual stress of the baseline finished product is as follows: After obtaining the optimal stress relief rate combination, the process control parameters corresponding to the target stress relief rate of each annealing process are matched one by one by combining the annealing parameter-stress relief rate mapping relationship. The matched process parameters are compiled into a full-process collaborative annealing baseline process document to guide annealing operations under normal production conditions. The expected residual stress of the finished product under the collaborative annealing benchmark process is calculated forward using the recursive formula for residual stress throughout the entire process, and is denoted as the expected residual stress of the benchmark finished product.

[0011] Preferably, the specific process for detecting the residual stress output of each workpiece undergoing annealing in the production process and calculating the residual stress deviation is as follows: Before the workpiece enters each annealing process, the actual residual stress output of the workpiece is detected by a non-destructive residual stress detection method. Detection points are selected evenly along the length of the workpiece, and the average value of all detection points is taken as the representative value of the actual stress of the workpiece entering the furnace. The residual stress deviation is calculated by subtracting the actual stress entering the furnace from the expected residual stress at the current annealing inlet obtained by forward derivation of the residual stress formula throughout the entire process under the collaborative annealing benchmark process.

[0012] Preferably, when deviations cause the finished product to exceed tolerances, the stress relief rate is adjusted sequentially from the current annealing stage, and the annealing process is performed to match the corresponding process parameters. The specific process is as follows: If the residual stress deviation is less than or equal to zero, and the furnace inlet stress is determined to be no higher than the reference state, annealing is performed directly according to the parameters set for the synergistic annealing reference process. When the residual stress deviation is greater than zero, the deviation transmission is calculated along the production process based on the stress transmission law to obtain the finished product stress increment. This is then summed with the baseline finished product expected residual stress to obtain the finished product expected stress without adjustment. If the finished product expected stress does not exceed the threshold, the baseline process is still executed. When the expected stress of the finished product exceeds the threshold, the amount of additional stress adjustment that needs to be eliminated is calculated. Starting from the current annealing, the adjustment is carried out step by step. The maximum stress that can be eliminated in the current annealing is calculated with the smaller value between the upper limit of the single-pass control range and the local optimal critical point as the upper limit. If the stress can be eliminated in a single pass, it is adjusted to the target value so that the stress of the finished product meets the standard. If the stress is insufficient in a single pass, the current pass is adjusted to the maximum and the remaining deviation is transferred to the next pass and adjusted according to the same logic until the deviation is offset. After adjustment, match the corresponding process parameters through the annealing parameter-stress relief rate mapping relationship, confirm that the stress relief rate is within the corresponding single-pass control range, and perform annealing according to the matched parameters.

[0013] Preferably, the specific process of reversely correcting the model parameters after finished product inspection to form a control closed loop and stably control the residual stress of the finished product within the threshold is as follows: After the entire process is completed, the residual stress output of the finished product is tested. The tested value is compared with the residual stress threshold of the finished product. If it is not greater than the threshold, the finished product is judged to be qualified in terms of stress. If it is greater than the threshold, it is judged that there is a stress deviation. When stress deviation is determined to exist, trace the source of deviation in reverse along the stress transmission path and correct the parameters of stress transmission coefficient, machining deformation-new residual stress mapping relationship, and annealing parameter-stress relief rate mapping relationship accordingly. The updated model is used for stress calculation and adjustment in subsequent furnaces. Combined with the full-process allowable stress threshold chain, it forms a closed-loop control. Each furnace is executed according to the process of furnace entry detection, deviation calculation, stress adjustment, finished product verification, and model update, so as to stably control the residual stress of the finished product within the allowable range.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) The low residual stress stainless steel linear guide annealing processing method quantifies the transmission law of residual stress between processing and annealing processes, establishes a full-process stress recursion model, and calculates the stress state of each process and finished product without carrying out stress testing for each process. It also eliminates the need to repeatedly try and match process parameters, which can significantly reduce the testing cost in the process development stage and shorten the debugging cycle. It solves the problem of single-pass stress being qualified but finished product stress exceeding the tolerance in traditional processes.

[0015] (2) This low residual stress stainless steel linear guide annealing processing method breaks the traditional misconception that the more thorough the annealing, the better the effect. It avoids the problem of insufficient hardness caused by over-annealing by constraining the local optimal critical point. It matches the synergistic parameters of multiple annealing with the goal of optimal finished product stress, rather than pursuing the lowest single stress. It can simultaneously meet the requirements of stress control, product mechanical properties and subsequent processing, and reduce defects such as sticking, deformation and insufficient hardness caused by over-annealing.

[0016] (3) The low residual stress stainless steel linear guide annealing processing method adopts a production control logic of fixed benchmark process plus dynamic deviation adjustment, detects stress deviation before entering the furnace and adjusts and eliminates deviation in coordination with multiple annealing processes, and iteratively corrects model parameters through finished product inspection results. It can adapt to the fluctuation of raw material and previous processing parameters without relying on worker experience to adjust, can stably control the residual stress of finished products, improve the batch qualification rate, and reduce the workload of subsequent manual straightening. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0018] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1; Please see Figure 1 This invention provides a method for annealing stainless steel linear guides with low residual stress, comprising: Step 1: For the entire stainless steel linear guide production process, classify the processes into machining and annealing processes, define the newly added residual stress, stress relief rate, and process output residual stress, fit and verify the stress transfer coefficient, establish a recursive formula for residual stress throughout the process, fit the mapping relationship between machining deformation and newly added residual stress, and annealing parameters and stress relief rate, determine the single-pass annealing control range, and summarize it into a set of control boundaries for the entire process. The specific process is as follows: The stainless steel linear guide production process is analyzed step by step. Processes such as rolling, drawing, quenching, and straightening that cause additional residual stress in the workpiece are classified as processing processes. A unique serial number is assigned to each processing process along the production sequence. Using the symbol 'i' as the sequence number of the machining process, the additional residual stress on the workpiece after the i-th machining process is denoted as . (This value is calculated by subtracting the residual stress values ​​before and after processing, or by calculating the mapping relationship between processing deformation and newly added residual stress, and is a quantitative characterization value of residual stress).

[0020] The processes of spheroidizing annealing, intermediate stress-relieving annealing, and finished product annealing, which reduce residual stress in the workpiece by heating and holding during the production process, are classified as annealing processes. A unique serial number is assigned to each annealing process along the production sequence. The symbol j is used as the serial number identifier for annealing processes, and the stress relief rate of the j-th annealing process is denoted as . (That is, the ratio of the residual stress eliminated after annealing to the residual stress of the workpiece before annealing. The value is between zero and one. This value is calculated by subtracting the residual stress detection values ​​before and after annealing and then comparing it with the stress before annealing, or by calculating the mapping relationship between annealing process parameters and stress elimination rate.)

[0021] Assign a uniform sequence number to all processes (including processing and annealing processes) along the production sequence, and use the symbol k as the sequence number identifier for any process in the entire process; After the k-th process is completed, the output residual stress carried by the workpiece is denoted as . (This value can be directly measured by conventional non-destructive residual stress detection methods in this field, and is a quantitative characterization of residual stress.)

[0022] Obtain the maximum permissible residual stress threshold of the finished product from the formal product design documents, and denot it as... (This parameter represents the maximum permissible residual stress value for the linear guide rail to prevent deformation from exceeding tolerances during long-term use. It is the ultimate goal of stress control throughout the entire process and serves as a quantitative representation of residual stress.) Collect various process and testing parameters that affect residual stress during each production process, including but not limited to: workpiece deformation, surface hardness, residual stress, processing load, process temperature, and cooling rate.

[0023] Multiple batches of test workpieces were selected under normal production conditions, covering the fluctuation range of material properties and processing parameters in conventional production, to conduct full-process tracking. The residual stress output of the workpiece after each process was detected and recorded. This forms a structured stress dataset covering the entire process; Based on stress sample pairs of all adjacent processes in the dataset, a basic linear fitting model is constructed to solve for the transfer coefficient. The model has the following form: ; in, The stress transfer coefficient between two adjacent processes k and k+1 represents the inherent proportion of residual stress output from process k transferred to process k+1. It takes a value between zero and one and is used to quantify the stress transfer efficiency between processes. It is the fixed intercept term of the basic linear fitting model.

[0024] The parameters of the basic linear fitting model are solved by the least squares linear fitting method. The fitting process aims to minimize the sum of squared errors between the model calculation values ​​and the actual detection values, and obtains the stress transfer coefficient and fixed intercept term between each pair of adjacent processes.

[0025] The accuracy of the fitted basic linear fitting model is verified. When the model fit meets the accuracy requirements of the process calculation, it is confirmed that the stress transfer coefficient obtained can accurately characterize the residual stress transfer ratio between adjacent processes. Subsequent stress calculations and process optimizations throughout the entire process are all based on this stress transfer coefficient.

[0026] Based on the above-mentioned verified stress transfer coefficients, and considering the process mechanisms of adding residual stress in machining processes and eliminating residual stress in annealing processes, the terms of the basic linear fitting model are physically decomposed to establish a recursive formula for residual stress throughout the entire process: ; In the formula: when the subsequent process is a machining process, there is no residual stress relief effect, and the corresponding stress relief rate is zero; when the subsequent process is an annealing process, there is no new machining residual stress, and the corresponding new residual stress is zero.

[0027] The physical meaning of this formula is: the output residual stress of the next process is equal to the residual stress transmitted from the previous process, plus the residual stress added in this process, and minus the residual stress eliminated by annealing in this process; this formula can be used to calculate the residual stress of all downstream processes from the stress state of the upstream process, without the need for process-by-process testing.

[0028] The expected residual stress at the j-th annealing inlet is denoted as That is, the residual stress output of the previous process in the annealing process is calculated by the recursive formula of residual stress in the whole process; it is used to determine the stress that needs to be eliminated in the annealing process and is a quantitative characterization value of residual stress. The analysis object is composed of multiple sets of detection data, including the cross-sectional change rate (i.e., processing deformation) before and after processing of a single processing step in the tracking test, and the newly added residual stress generated by the processing step itself. The least squares method is used to perform polynomial fitting to obtain the mapping relationship between processing deformation and newly added residual stress. The mapping relationship is used to characterize the correspondence between the degree of deformation of a single processing step and the newly added residual stress. After establishing the mapping relationship between processing deformation and newly added residual stress, the newly added residual stress of a single processing step can be calculated directly by detecting the processing deformation of a single processing step in production, without the need to detect residual stress for each processing step.

[0029] For each annealing process, an independent gradient process test is conducted. Within the parameter adjustment range allowed by the equipment, a gradient process level covering the entire control range is set (that is, for adjustable process parameters such as annealing heating temperature, holding time, and cooling rate, multiple different parameter combinations are set according to an arithmetic gradient to cover the entire adjustable parameter range of the equipment). For each process level, the stress relief rate after a single pass of annealing, the hardness and tensile strength of the workpiece after annealing, and the deformation and cracking of the workpiece in subsequent processing were tested.

[0030] Using the process parameters of single-pass annealing in the above gradient test and the stress relief rate corresponding to the process as the analysis object, the least squares method is used for fitting to obtain the mapping relationship between annealing parameters and stress relief rate; This mapping relationship is used to characterize the correspondence between the process parameters of single-pass annealing and its own stress relief rate. After establishing the mapping relationship between annealing parameters and stress relief rate, the corresponding stress relief rate can be directly calculated through the process parameters set for single-pass annealing in production, without the need to test the stress before and after annealing in each furnace.

[0031] The test results of all single-pass annealing in the gradient test were obtained and organized into an ordered experimental group sequence according to the stress relief rate from low to high. Based on the organized test data, the stress relief rate was used as a single variable to iteratively judge from both ends to the middle. The stress control range of single-pass annealing was determined by the workpiece performance and processing feedback under different stress relief rates. The specific judgment process is as follows: Starting with the experimental group with the lowest stress relief rate in the sequence, mark the stress relief rate corresponding to the current experimental group as the lower limit critical value to be verified. If the workpiece corresponding to the current lower limit verification critical value exhibits stress-induced cracking or deformation exceeding tolerances during subsequent processing, the process moves to an adjacent experimental group with a higher stress relief rate. The stress relief rate corresponding to the adjacent group is then used as the new lower limit verification critical value for repeated verification until the workpiece corresponding to the lower limit verification critical value has no stress-related non-compliance issues during subsequent processing. At this point, the critical value is determined as the lower limit of stress relief rate, which is the minimum stress relief rate required to meet subsequent processing requirements.

[0032] Starting with the experimental group with the highest stress relief rate in the sequence, mark the stress relief rate corresponding to the current experimental group as the upper limit critical value to be verified. If the workpiece corresponding to the current upper limit verification critical value has problems such as cold drawing sticking to the mold or insufficient hardness after quenching due to excessively low hardness, then move to the adjacent experimental group with a lower stress relief rate. Use the stress relief rate corresponding to the adjacent group as the new upper limit verification critical value and repeat the verification until the workpiece corresponding to the upper limit verification critical value meets both mechanical properties and subsequent processing requirements. Then, determine the critical value as the upper limit of stress relief rate, that is, the maximum stress relief rate that does not affect mechanical properties.

[0033] The continuous range between the lower and upper limits of the stress relief rate of the current annealing process is defined as the stress control range of the single-pass annealing process. The stress control ranges of all single-pass annealing processes are summarized to form a set of stress control boundaries for the entire annealing process.

[0034] It should be noted that, unlike the traditional single-pass annealing model where parameters are set independently based on experience, this method quantifies the stress transmission pattern between processes by tracking data from multiple batches of production, and establishes a recursive formula for residual stress throughout the entire process. This allows for the direct calculation of the stress state of each downstream process from the upstream stress, without the need to conduct stress testing for each process. By fitting the two process mapping relationships, the newly added stress and stress relief rate can be directly calculated through the processing deformation and annealing process parameters, which greatly reduces the inspection cost in the production process. By determining the single-channel control range through iteration at both ends, and taking into account both the stress-free processing requirements and the mechanical performance requirements of the workpiece, a reliable feasible domain constraint is provided for subsequent global process optimization. This avoids optimizing process parameters that cannot be implemented, and provides a unified quantitative calculation basis for stress collaborative control throughout the entire process. It can effectively reduce the stress fluctuation problem caused by the reliance on manual experience in traditional processes.

[0035] Step 2: Using the residual stress threshold of the finished product as the control target, the allowable stress threshold chain for the entire process is obtained by reverse recursion. The stress elimination rate of each annealing step is used as the optimization variable. After two layers of screening—stress threshold and local optimal critical point—the optimal elimination rate combination is obtained. The corresponding process parameters are matched to generate a synergistic annealing benchmark process. The expected residual stress of the benchmark finished product is calculated. The specific process is as follows: Starting from the final inspection of the finished product, calculate the maximum allowable residual stress for each process in reverse order along the production flow, and record it as follows: ; The analysis process for the maximum allowable residual stress output for each process is as follows: The initial condition for recursion is that the maximum permissible residual stress output of the final inspection process is equal to the residual stress threshold of the finished product, i.e.: ; n is the unified sequence number of the last process (final inspection of finished products) in the entire process; When recursively calculating backwards, if the next step after the current step is a machining step, the maximum allowable residual stress output of the current step is obtained by modifying the overall residual stress recursive formula. The calculation formula is as follows: ; in, The maximum residual stress allowed for the next machining process. This introduces residual stress for the next machining process. If the next step after the current process is an annealing process, the maximum allowable residual stress output of the current process can be obtained by modifying the recursive formula for residual stress throughout the entire process. The calculation formula is as follows: ; in, The maximum residual stress allowed for the next annealing process is determined. This is the stress relief rate for the next annealing process; Based on the above reverse recursive method, the process is recursively pushed forward until all processes in the entire process are covered, so as to obtain the maximum allowable residual stress output of each process in the entire process. The process is then organized according to the production sequence to form a chain of allowable stress thresholds for the entire process, which serves as a hard constraint for process combination screening.

[0036] After completing the calculation of the allowable stress threshold chain, the stress relief rate of each annealing process is used as the optimization variable. Combined with the set of stress control boundaries for the entire annealing process, the upper and lower limits of the stress relief rate for each annealing process are determined. The stress relief rate values ​​for each annealing process are discretized using a preset fixed small step size, and all possible combinations of stress relief rates are generated through iteration.

[0037] For each generated stress relief rate combination, the residual stress output of all processes in the entire process and the residual stress output of the final product process are first calculated forward using the recursive formula for residual stress throughout the entire process. Then, the residual stress output of each process is compared with the allowable stress threshold at the corresponding position. Specifically: If any process output residual stress exceeds the corresponding threshold, then the combination is discarded. If the stress of all processes meets the threshold requirements, the combination is retained for the next round of screening.

[0038] For combinations that pass the stress threshold screening, determine whether the stress relief rate of each single-pass annealing process exceeds the local optimum critical point, specifically: By combining the stress transfer coefficient with the mapping relationship between processing deformation and newly added residual stress, the stress relief rate of single-pass annealing processes is adjusted one by one. The amount of residual stress reduction brought about by the increase of the stress relief rate by a unit value is calculated, as well as the increase of newly added residual stress caused by the decrease in hardness of subsequent processing processes due to the adjustment. When the increase in residual stress during processing exceeds the amount of residual stress reduction adjusted for the first time, the corresponding stress relief rate is the local optimal critical point for that annealing process.

[0039] If the stress relief rate of any annealing process in the combination exceeds the corresponding local optimum critical point, then the combination is removed. If the stress relief rate of all annealing processes is within the critical point, then this combination is retained as a feasible process combination.

[0040] Among all the remaining feasible process combinations, the combination with the minimum residual stress in the final product process is selected as the optimal stress relief rate combination, which is the target stress relief rate value that each annealing process needs to achieve.

[0041] After obtaining the optimal stress relief rate combination, the process control parameters corresponding to the target stress relief rate of each annealing process are matched one by one according to the annealing parameter-stress relief rate mapping relationship, forming a full-process collaborative annealing benchmark process document to guide annealing operations under normal production conditions.

[0042] The expected residual stress of the finished product under the benchmark annealing process is calculated forward using the recursive formula for residual stress throughout the entire process, and denoted as the expected residual stress of the benchmark finished product. .

[0043] It should be noted that this process breaks away from the traditional debugging logic of trial and error in adjusting parameters from front to back. Instead, it deduces the upper limit of allowable stress for each process step by working backward from the finished product qualification threshold, forming a stress threshold chain for the entire process as a hard constraint. This fundamentally avoids the problem of "single process stress being qualified but finished product stress exceeding tolerance". The logic for judging the local optimal critical point is proposed, which corrects the industry misconception that "the higher the annealing stress relief rate, the better," and avoids the adverse effect of over-annealing leading to insufficient workpiece hardness and increased stress in subsequent processing. The optimal stress relief rate combination obtained through two-layer constraint screening achieves global synergistic optimization for multi-pass annealing, rather than local optimization for a single process. The matched synergistic annealing benchmark process can be directly used in regular production, significantly shortening the process debugging cycle. The calculated benchmark finished product expected stress provides a quantitative comparison benchmark for subsequent dynamic production adjustments.

[0044] Step 3: During the production process, for each batch of workpieces undergoing annealing, the actual residual stress output of the process is detected, and the residual stress deviation is calculated. If the deviation causes the finished product to exceed the tolerance, the stress relief rate is adjusted sequentially from the current annealing stage, and the corresponding process parameters are matched to execute the annealing. After the finished product is inspected, the model parameters are corrected in reverse to form a control closed loop, stabilizing the residual stress of the finished product within the threshold. The specific process is as follows: Before the workpiece enters each annealing process, the actual residual stress output of the workpiece is detected by non-destructive residual stress detection methods (including but not limited to X-ray diffraction, magnetic Barkhausen noise method, and ultrasonic stress detection method). Detection points are evenly selected along the length of the workpiece, and the average value of all detection points is taken as the representative value of the actual stress of the workpiece entering the furnace.

[0045] The residual stress deviation is calculated by subtracting the actual stress entering the furnace from the expected residual stress at the annealing inlet of the process obtained by forward deduction of the residual stress formula of the whole process under the synergistic annealing benchmark process. If the residual stress deviation is less than or equal to zero, it is determined that the stress of the workpiece entering the furnace is not higher than the reference state, and annealing is performed directly according to the parameters set in the collaborative annealing reference process.

[0046] If the residual stress deviation is greater than zero, based on the transmission logic of the residual stress recursive formula for the whole process, the transmission process of the residual stress deviation is calculated step by step along the subsequent production process: when the residual stress deviation passes through the processing process, it is fully transmitted according to the corresponding stress transmission coefficient; when it passes through the annealing process, the residual stress is transmitted according to the stress transmission coefficient multiplied by (1 - the preset benchmark stress elimination rate of the corresponding process in the synergistic annealing benchmark process), and finally the stress increment of the finished product caused by the residual stress deviation is obtained.

[0047] The sum of the stress increment of the finished product and the expected residual stress of the benchmark finished product is used to obtain the expected stress of the finished product without adjusting the process. Compare the expected stress of the finished product with the residual stress threshold of the finished product: if the expected stress of the finished product is less than or equal to the residual stress threshold of the finished product, it is determined that the residual stress deviation will not cause the stress of the finished product to exceed the tolerance, and the synergistic annealing benchmark process shall still be performed. If the expected stress of the finished product is greater than the residual stress threshold, the difference between the expected stress and the residual stress threshold is recorded as the additional residual stress adjustment amount that needs to be eliminated, and stress adjustment is performed step by step. The specific process is as follows: Start adjusting the stress relief rate step by step from the current annealing process.

[0048] Calculate the maximum adjustable stress relief rate for the current annealing process: Take the smaller of the upper limit of the single-pass annealing stress control range corresponding to the current annealing process and the local optimal critical point corresponding to the current annealing process as the maximum allowable stress relief rate for the current annealing. The maximum allowable stress relief rate is compared with the reference stress relief rate corresponding to the current annealing in the synergistic annealing reference process. The difference is multiplied by the stress transfer coefficient that has passed the verification between the current process and the next process and the actual stress entering the furnace obtained in this test, to obtain the maximum residual stress that can be additionally eliminated in the current annealing.

[0049] When the maximum residual stress that can be additionally eliminated by the current annealing is greater than or equal to the amount of residual stress adjustment that needs to be additionally eliminated, the adjusted target stress elimination rate is calculated according to the formula: ; in, To determine the stress relief rate of the current annealing in the baseline annealing process, For the additional residual stress that needs to be eliminated, This is the stress transfer coefficient that has passed verification between the current process and the next process. The actual stress entering the furnace was obtained from this test; Adjust the current annealing stress relief rate to the calculated target stress relief rate. This ensures that the adjusted expected stress of the finished product equals the residual stress threshold of the finished product.

[0050] If the maximum residual stress that can be additionally eliminated by the current annealing is less than the amount of residual stress adjustment that needs to be additionally eliminated, adjust the current annealing stress elimination rate to the maximum allowable value. The remaining uncompensated residual stress deviation is obtained by subtracting the maximum residual stress that can be additionally eliminated by the current annealing from the amount of residual stress adjustment that needs to be eliminated. The remaining unrelieved residual stress deviations are transferred to subsequent adjacent annealing processes. Following the same logic as the current annealing process—"calculate the maximum salient stress → compare the salient stress with the deviation to be relieved → adjust the stress relief rate"—the stress relief rate of each subsequent annealing process is adjusted until all residual stress deviations are offset.

[0051] After the stress relief rate adjustment is completed, the process control parameters corresponding to the stress relief rate of each adjusted annealing process are matched by the established annealing parameter-stress relief rate mapping relationship. This ensures that the adjusted stress relief rate of each annealing process is within its corresponding single-pass annealing stress control range, and the corresponding annealing operation is executed according to the matched process control parameters.

[0052] After all processes are completed, the residual stress output of the finished product is tested. The tested value is compared with the residual stress threshold of the finished product: if the tested value is less than or equal to the residual stress threshold of the finished product, the stress of the finished product is deemed to be qualified; if the tested value is greater than the residual stress threshold of the finished product, stress deviation is deemed to exist.

[0053] If a stress deviation is determined, the source of the deviation is traced back along the stress transmission path. The parameters of the qualified stress transmission coefficient, the mapping relationship between processing deformation and newly added residual stress, and the mapping relationship between annealing parameters and stress relief rate are corrected accordingly. The updated model is then used for stress calculation and adjustment in subsequent furnaces. Combined with the allowable stress threshold chain of the entire process, a closed-loop control is formed.

[0054] The production process is carried out furnace by furnace inspection, deviation calculation, stress adjustment, finished product verification, and model update for each furnace, so as to keep the residual stress of the finished product within the allowable range.

[0055] It should be noted that, unlike the traditional static annealing process which cannot cope with production fluctuations, this process detects the stress deviation of the incoming material in real time before it enters the furnace. Adjustments are only initiated when the deviation will cause the finished product to exceed the tolerance, without making meaningless parameter changes, thus balancing production efficiency and control precision. During adjustment, start from the current furnace annealing and coordinate each pass. Prioritize the adjustment capability of the nearest annealing pass. If the adjustment capability of a single pass is insufficient, coordinate multiple passes to eliminate the difference. The adjustment process must strictly not exceed the allowable range of the process and the local optimal critical point to avoid over-annealing or processing defects caused by stress relief. Finally, the model parameters are corrected in reverse by the finished product inspection results to form a self-optimizing closed loop. The more production batches there are, the higher the model calculation accuracy becomes. This achieves full-process control of "static benchmark process + dynamic deviation adjustment + model self-iteration", which can stably control the residual stress of the finished product within the qualified range, and significantly reduce the stress deviation rate of the finished product and the workload of subsequent straightening.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for annealing low residual stress stainless steel linear guides, characterized in that, include: Step 1: For the entire stainless steel linear guide production process, classify the processing and annealing processes, define the new residual stress, stress relief rate, and process output residual stress, fit and verify the stress transfer coefficient, establish the recursive formula for residual stress in the whole process, fit the mapping relationship between processing deformation and new residual stress, and annealing parameters and stress relief rate, determine the single-pass annealing control range, and summarize it into the whole process control boundary set. Step 2: Using the residual stress threshold of the finished product as the control target, the allowable stress threshold chain of the whole process is obtained by reverse recursion. The stress elimination rate of each annealing is used as the optimization variable. The optimal elimination rate combination is obtained through two layers of screening: stress threshold and local optimal critical point. The corresponding process parameters are matched to generate the synergistic annealing benchmark process, and the expected residual stress of the benchmark finished product is calculated. Step 3: During the production process, for each workpiece entering the furnace for annealing, the actual process output residual stress is detected, and the residual stress deviation is calculated. If the deviation causes the finished product to exceed the tolerance, the stress relief rate is adjusted step by step from the current annealing. The corresponding process parameters are matched and annealing is performed. After the finished product is inspected, the model parameters are corrected in reverse to form a control closed loop, so as to stably control the residual stress of the finished product within the threshold.

2. The annealing method for low residual stress stainless steel linear guides according to claim 1, characterized in that: The specific process for establishing the recursive formula for residual stress throughout the entire process is as follows: The production process is sorted and classified into processing and annealing processes. Independent serial numbers are assigned to the two types of processes, and a unified serial number is assigned to all processes in the entire process. The physical meanings of newly added residual stress, stress relief rate, process output residual stress, and finished product residual stress threshold are defined. Process and detection parameters that affect residual stress during production are collected. By tracking the stress data of multiple batches of normally produced workpieces through each process, a structured stress dataset is formed. Based on the stress samples of adjacent processes, a basic linear model is fitted to solve for the stress transfer coefficient between adjacent processes and complete the accuracy verification. By combining the basic model of the process mechanism of added stress during processing and stress relief during annealing, a recursive formula for residual stress throughout the entire process is established, clarifying the calculation rules for processing processes that have no stress relief effect and annealing processes that have no added processing stress.

3. The annealing method for low residual stress stainless steel linear guides according to claim 2, characterized in that: The specific process of fitting the mapping relationship between machining deformation, newly added residual stress, annealing parameters, and stress relief rate is as follows: The expected residual stress at the inlet of each annealing stage is calculated using the recursive formula for residual stress throughout the entire process. Using multiple sets of detection data on the cross-sectional change rate of a single machining process and the corresponding newly added residual stress as the object, the least squares polynomial fitting method is used to obtain the mapping relationship between machining deformation and newly added residual stress. For each annealing step, independent gradient process tests were conducted, and process levels covering the entire control range were set to test the stress relief rate, workpiece mechanical properties and subsequent processing performance under different processes. Using multiple sets of test data on single-pass annealing process parameters and corresponding stress relief rates as the object, the least squares method was used to fit and obtain the mapping relationship between annealing parameters and stress relief rates.

4. The annealing method for low residual stress stainless steel linear guides according to claim 3, characterized in that: The specific process of determining the single-pass annealing control range and summarizing it into a set of control boundaries for the entire process is as follows: All test results of single-pass annealing gradient test are obtained and sorted into an ordered experimental group sequence according to stress relief rate from low to high. The stress relief rate is used as a single variable to iterate from both ends to the middle. The single-pass control range is determined by combining the workpiece performance and processing feedback under different stress relief rates. The verification starts with the lowest stress relief rate experimental group. If stress cracking or deformation exceeding the tolerance occurs in the subsequent processing of the corresponding workpiece, the process is iterated towards a higher stress relief rate until the stress-free type fails to meet the standard, which is then determined as the lower limit of the stress relief rate. The verification begins with the highest stress relief rate experimental group. If the corresponding workpiece has processing defects caused by excessively low hardness, the process iterates towards a lower stress relief rate until both mechanical properties and processing requirements are met, at which point the upper limit of the stress relief rate is determined. The continuous range between the upper and lower limits of single-pass annealing is defined as the stress control interval of single-pass annealing, and all single-pass control intervals are summarized to form the set of stress control boundaries for the entire process of annealing.

5. The annealing method for low residual stress stainless steel linear guides according to claim 4, characterized in that: The specific process for obtaining the full-process allowable stress threshold chain is as follows: Starting from the final inspection of finished products, calculate the maximum residual stress allowed for each process in reverse order along the production process; The maximum allowable residual stress in the final inspection process of the finished product is equal to the threshold of the residual stress of the finished product as the initial condition for recursion. When it is recursively pushed forward, if the next step is a processing step, the maximum allowable residual stress of the current step is calculated by combining the maximum allowable stress of the next step, the newly added residual stress from processing, and the stress transfer coefficient between steps. If the next step is an annealing process, the maximum allowable residual stress of the current process is calculated by combining the maximum allowable stress of the next process, the stress relief rate of annealing, and the stress transfer coefficient between processes. After recursively covering all processes in the entire process, the maximum allowable residual stress of each process is sorted out according to the production sequence to form a chain of allowable stress thresholds for the entire process.

6. The annealing method for low residual stress stainless steel linear guides according to claim 5, characterized in that: The specific process for obtaining the optimal elimination rate combination is as follows: After completing the calculation of the allowable stress threshold chain, the stress relief rate of each annealing process is used as the optimization variable. The upper and lower limits of the value are determined by combining the stress control boundary set of the whole process annealing. All possible stress relief rate combinations are generated by discretization according to the preset fixed small step size. For each combination, the stress of each process and the stress of the final product are calculated in the forward direction using the full-process residual stress recursive formula. The allowable stress threshold at the corresponding position is compared with the process step by step. Combinations with stress exceeding the threshold in any process are eliminated, and combinations that meet the full-process stress requirements are retained to enter the next round of screening. For each retained combination, determine whether the stress relief rate exceeds the local optimal critical point. That is, the increase in stress in subsequent processing caused by the increase in stress relief rate is greater than the critical value of residual stress reduction. Eliminate combinations that exceed the critical point, and the remaining combinations are feasible process combinations. Among all feasible process combinations, the combination with the lowest residual stress in the finished product is selected as the optimal stress relief rate combination, which is the target value of stress relief rate for each annealing process.

7. The annealing method for low residual stress stainless steel linear guides according to claim 6, characterized in that: The specific process for generating a synergistic annealing baseline process by matching corresponding process parameters and calculating the expected residual stress of the baseline finished product is as follows: After obtaining the optimal stress relief rate combination, the process control parameters corresponding to the target stress relief rate of each annealing process are matched one by one by combining the annealing parameter-stress relief rate mapping relationship. The matched process parameters are compiled into a full-process collaborative annealing baseline process document to guide annealing operations under normal production conditions. The expected residual stress of the finished product under the collaborative annealing benchmark process is calculated forward using the recursive formula for residual stress throughout the entire process, and is denoted as the expected residual stress of the benchmark finished product.

8. The annealing method for low residual stress stainless steel linear guides according to claim 7, characterized in that: During the production process, for each batch of workpieces undergoing annealing, the specific process for detecting the residual stress output from the actual process and calculating the residual stress deviation is as follows: Before the workpiece enters each annealing process, the actual residual stress output of the workpiece is detected by a non-destructive residual stress detection method. Detection points are selected evenly along the length of the workpiece, and the average value of all detection points is taken as the representative value of the actual stress of the workpiece entering the furnace. The residual stress deviation is calculated by subtracting the actual stress entering the furnace from the expected residual stress at the current annealing inlet obtained by forward derivation of the residual stress formula throughout the entire process under the collaborative annealing benchmark process.

9. The annealing method for low residual stress stainless steel linear guides according to claim 8, characterized in that: When deviations cause the finished product to exceed tolerances, the stress relief rate is adjusted sequentially from the current annealing stage, and the annealing process is performed to match the corresponding process parameters. The specific process is as follows: If the residual stress deviation is less than or equal to zero, and the furnace inlet stress is determined to be no higher than the reference state, annealing is performed directly according to the parameters set for the synergistic annealing reference process. When the residual stress deviation is greater than zero, the deviation transmission is calculated along the production process based on the stress transmission law to obtain the finished product stress increment. This is then summed with the baseline finished product expected residual stress to obtain the finished product expected stress without adjustment. If the finished product expected stress does not exceed the threshold, the baseline process is still executed. When the expected stress of the finished product exceeds the threshold, the amount of additional stress adjustment that needs to be eliminated is calculated. Starting from the current annealing, the adjustment is carried out step by step. The maximum stress that can be eliminated in the current annealing is calculated with the smaller value between the upper limit of the single-pass control range and the local optimal critical point as the upper limit. If the stress can be eliminated in a single pass, it is adjusted to the target value so that the stress of the finished product meets the standard. If the stress is insufficient in a single pass, the current pass is adjusted to the maximum and the remaining deviation is transferred to the next pass and adjusted according to the same logic until the deviation is offset. After adjustment, match the corresponding process parameters through the annealing parameter-stress relief rate mapping relationship, confirm that the stress relief rate is within the corresponding single-pass control range, and perform annealing according to the matched parameters.

10. The annealing method for low residual stress stainless steel linear guides according to claim 9, characterized in that: The specific process of back-correcting model parameters after finished product inspection to form a control closed loop and stably control the residual stress of the finished product within the threshold is as follows: After the entire process is completed, the residual stress output of the finished product is tested. The tested value is compared with the residual stress threshold of the finished product. If it is not greater than the threshold, the finished product is judged to be qualified in terms of stress. If it is greater than the threshold, it is judged that there is a stress deviation. When stress deviation is determined to exist, trace the source of deviation in reverse along the stress transmission path and correct the parameters of stress transmission coefficient, machining deformation-new residual stress mapping relationship, and annealing parameter-stress relief rate mapping relationship accordingly. The updated model is used for stress calculation and adjustment in subsequent furnaces. Combined with the allowable stress threshold chain of the whole process, a closed-loop control is formed. Each furnace is executed according to the process of furnace entry detection, deviation calculation, stress adjustment, finished product verification, and model update, so as to keep the residual stress of the finished product stably controlled within the allowable range.

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