A method for optimizing superplastic forming process parameters

Abstract

This invention discloses a method for optimizing superplastic forming process parameters, belonging to the field of profile processing technology, and solves the problems of unreasonable superplastic forming parameters and poor forming quality. This invention locks the optimal superplastic deformation window of the material through isothermal unidirectional superplastic fundamental performance testing, defines the initial safe value ranges for four core process parameters including forming temperature and strain rate, constructs a correlation mapping model between process parameters and forming quality, mechanical properties, and processing efficiency, obtains a preliminary parameter set through multi-objective global optimization, and iteratively corrects the model through orthogonal verification experiments and measured data, finally outputting the optimal process parameters. This invention improves the accuracy of parameter optimization, reduces profile forming defects, increases product qualification rate, and is adaptable to superplastic forming processing of various types of profiles.

Description

Technical Field

[0001] This invention relates to the field of profile processing and production, and in particular to a method for optimizing superplastic forming process parameters. Background Technology

[0002] Currently, superplastic forming technology, with its advantage of enabling materials to achieve maximum plastic deformation under specific conditions, has been widely used in the profile processing field, especially suitable for the integrated forming of complex cross-section profiles and thin-walled profiles. It can effectively reduce processing steps, lower production costs, and simultaneously improve the forming accuracy and mechanical properties of profiles. However, the determination of superplastic forming process parameters (such as forming temperature, strain rate, holding time, and forming pressure) currently relies heavily on experience or single-variable experiments, lacking systematic optimization methods, leading to unreasonable parameter combinations.

[0003] In existing technologies, either the coupling effect between various process parameters is not considered, and only individual parameters are adjusted, failing to achieve optimal overall process performance; or the optimization methods are too simplistic, failing to construct a scientific optimization model that combines the characteristics of the profile material and the requirements of the forming structure. This results in poor stability of the optimized parameters in practical applications, easily leading to defects such as uneven wall thickness, wrinkling, cracking, and excessive dimensional deviations in the formed profiles, affecting the quality and pass rate of profile products, and making it difficult to meet the high-precision and high-consistency processing requirements of high-end profiles in aerospace, rail transportation, and other fields. In addition, existing optimization methods are not specifically designed for the structural characteristics of the profiles (such as cross-sectional shape and wall thickness), resulting in poor versatility and inability to adapt to the processing requirements of commonly used superplastic profile materials such as different grades of aluminum alloys and titanium alloys.

[0004] Meanwhile, existing optimization schemes generally suffer from long optimization cycles and high testing costs, making it impossible to achieve rapid and accurate optimization of process parameters and difficult to form a closed-loop iterative optimization system. This seriously restricts the large-scale promotion and application of superplastic forming technology in the field of profile processing. Summary of the Invention

[0005] Therefore, to address the aforementioned problems, this invention proposes a method for optimizing superplastic forming process parameters. This method solves the technical problems of unreasonable superplastic forming parameters and poor forming quality in profiles.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for optimizing superplastic forming process parameters includes the following steps: S1. Conduct isothermal unidirectional superplasticity basic performance tests on the target metal material to be formed profile. Set no less than 4 sets of increasing temperature gradients and no less than 4 sets of increasing strain rate gradients. For each gradient, complete no less than 3 sets of parallel tensile tests. Obtain the core superplastic deformation data of the material under different temperature and strain rate conditions, such as flow stress and elongation after fracture. Lock the interval corresponding to the peak value of the material's elongation after fracture as the optimal superplastic deformation window. S2. Combining the cross-sectional structural characteristics of the profile to be formed, the wall thickness design parameters of 0.5mm-10mm, the forming dimensional accuracy requirements and the mechanical properties of the finished product, the initial safe range of values ​​for the four core process parameters of superplastic forming is defined. The basic threshold of the forming temperature range is determined by the formulas Tmin=T0+0.1T0 and Tmax=T0+0.8T0, where T0 is the melting point thermodynamic absolute temperature of the target material. S3. Based on the coupling characteristics of each process parameter within the initial safe value range, construct a correlation mapping model between process parameters and profile forming quality, mechanical properties of formed parts, and forming efficiency. S4. Taking the standard of profile forming accuracy, the mechanical properties of formed parts meeting the design threshold, and the optimal forming efficiency as the collaborative optimization objectives, multi-objective global optimization is carried out in combination with the constructed correlation mapping model to obtain the preliminary optimized process parameter set; S5. Based on the preliminary optimized process parameter group, design an orthogonal verification experiment, complete the superplastic forming trial production of profiles, and collect the actual forming quality test data and mechanical property test data of each group of trial parts; S6. Use the measured data obtained from the verification experiment to iteratively correct the correlation mapping model, repeat the global optimization and experimental verification process until the preset optimization termination condition is met, and finally output the optimal superplastic forming process parameters that are suitable for the target profile.

[0007] Further: In the isothermal unidirectional superplasticity basic performance test of method S1, four sets of increasing temperature gradients T1, T2, T3, T4 and four sets of increasing strain rate gradients e1, e2, e3, e4 are set. The average value of all parallel test data is taken as the final superplastic deformation basic data. The temperature and strain rate range corresponding to the peak elongation after fracture of the material is locked as the optimal superplastic deformation window.

[0008] In method S2, the initial safe value range of the four core process parameters includes the forming temperature range, strain rate range, holding time range, and forming pressure range. The final value of the forming temperature range must simultaneously meet the basic threshold requirements and the optimal superplastic deformation window range. The range of the interval correction coefficients A1 and A2 is 0.1-0.8, and A1 < A2.

[0009] In the correlation mapping model of method S3, the comprehensive evaluation coefficient M of profile forming quality is calculated using the following formula: M=(B1*D1+B2*D2+B3*D3) / (B1+B2+B3) In the formula, D1 is the wall thickness uniformity deviation value of the profile forming part, D2 is the outline dimension accuracy deviation value of the profile forming part, D3 is the form and position tolerance deviation value of the profile forming part, B1, B2, and B3 are the preset weight coefficients corresponding to D1, D2, and D3, respectively, and the value range of B1, B2, and B3 is 0.1-0.7, and B1+B2+B3=1.

[0010] In the correlation mapping model of method S3, the comprehensive evaluation coefficient N of the mechanical properties of the profile forming part is calculated simultaneously using the following formula: N=(C1*E1+C2*E2+C3*E3) / (C1+C2+C3) In the formula, E1 is the measured tensile strength of the profile forming part, E2 is the measured yield strength of the profile forming part, E3 is the measured elongation after fracture of the profile forming part, C1, C2, and C3 are the preset weighting coefficients corresponding to E1, E2, and E3, respectively, and the values ​​of C1, C2, and C3 are all in the range of 0.1-0.7, and C1+C2+C3=1.

[0011] In method S4, the comprehensive objective function F for multi-objective global optimization is determined by the following formula: F = K1*M + K2*N + K3*S S=(t1+t2+t3) / t0 In the formula, S is the processing efficiency coefficient of superplastic forming of profile, t1 is the heating and holding time before profile forming, t2 is the pressure holding forming time of profile, t3 is the cooling and unloading time after profile forming, t0 is the preset standard total forming time, K1, K2, and K3 are the preset weight coefficients corresponding to M, N, and S, respectively, and the values ​​of K1, K2, and K3 are all in the range of 0.1-0.7, and K1+K2+K3=1. The minimum value of F is the core optimization objective in the optimization process.

[0012] In method S6, the correction coefficient K of the association mapping model is determined by the following formula: K = (Mactual / Mpre-defined + Nactual / Npre-defined) / 2 In the formula, M is the measured value of the comprehensive evaluation coefficient of forming quality obtained from the verification test, Mpre is the predicted value of the comprehensive evaluation coefficient of forming quality output by the correlation mapping model, N is the measured value of the comprehensive evaluation coefficient of mechanical properties obtained from the verification test, Npre is the predicted value of the comprehensive evaluation coefficient of mechanical properties output by the correlation mapping model, and the corrected output value of the correlation mapping model is multiplied by the correction coefficient K.

[0013] In method S6, the optimization termination condition is determined by the following formula: |Fbefore - Fpresent| / Fbefore ≤ R In the formula, Ffront is the comprehensive objective function value of the previous iteration, Fcurrent is the comprehensive objective function value of the current iteration, R is the preset maximum allowable rate of change, and the value of R ranges from 0.1% to 1%; or the number of iterations reaches the preset maximum number of iterations X, and the value of X ranges from 5 to 30.

[0014] In method S5, the test factors of the orthogonal verification test include four core variables: forming temperature, strain rate, holding time, and forming pressure. Each test factor is set with three levels. All groups of prototypes are completed according to the orthogonal test table. The forming quality test data and mechanical property test data of each group of prototypes are collected simultaneously. After removing abnormal data, the average value of the valid data is taken as the test result.

[0015] The profile includes any one of aluminum alloy complex cross-section profiles, titanium alloy thin-walled profiles, and high-temperature alloy multi-chamber profiles, with the cross-sectional profile dimensions ranging from 50mm to 800mm.

[0016] By adopting the aforementioned technical solution, the beneficial effects of the present invention are: This invention locks the optimal superplastic deformation window of a material through isothermal unidirectional superplasticity fundamental performance testing. Combined with profile cross-sectional structural characteristics and wall thickness design parameters, it defines the initial safe value ranges for four core process parameters: forming temperature, strain rate, holding time, and forming pressure. This provides a scientific quantitative boundary for parameter optimization, solving the problems of existing technologies relying on experience for parameter determination and having unreasonable parameter ranges, thus significantly improving the accuracy of parameter optimization. Furthermore, based on the coupling characteristics of various process parameters within the initial safe value range, a correlation mapping model is constructed between process parameters and profile forming quality, formed part mechanical properties, and forming efficiency. A comprehensive objective function F is built using the forming quality comprehensive evaluation coefficient M, mechanical property comprehensive evaluation coefficient N, and processing efficiency coefficient S. This achieves multi-objective global optimization, ensuring profile forming accuracy meets standards, mechanical properties meet design thresholds, and processing efficiency is optimal. It fully considers the coupling effects between parameters, solving the problem that existing technologies cannot achieve global optimization through single-parameter adjustments. Furthermore, orthogonal verification experiments were conducted to complete the superplastic forming trial production of profiles. Measured data from the prototypes were collected, and the correlation mapping model was iteratively corrected based on the correction coefficient K, forming a closed-loop optimization process of "optimization-verification-correction-re-optimization." This significantly improved the engineering applicability and batch stability of the optimization parameters, effectively reducing forming defects such as uneven wall thickness, wrinkling, cracking, and dimensional deviations in the formed profiles, thus significantly improving the product qualification rate. Furthermore, a fully adaptable optimization method was designed for profiles of different materials and specifications. This method is applicable to the superplastic forming of complex cross-section aluminum alloy profiles, thin-walled titanium alloy profiles, and multi-chamber high-temperature alloy profiles, demonstrating strong versatility. It also significantly shortens the process optimization cycle, reduces experimental R&D costs, and is suitable for large-scale application in the profile processing field. Detailed Implementation

[0017] The present invention will now be further described in conjunction with specific embodiments.

[0018] This embodiment provides a method for optimizing superplastic forming process parameters, including the following methods: S1, Superplasticity Basic Performance Test For the 6061 aluminum alloy target material to be formed into profiles, isothermal unidirectional superplasticity basic performance tests were carried out: four sets of increasing temperature gradients were set: T1=350℃, T2=400℃, T3=450℃, T4=500℃, and four sets of increasing strain rate gradients were set simultaneously: e1=0.0001, e2=0.0005, e3=0.001, e4=0.005. For each combination of temperature and strain rate gradients, three sets of parallel tensile tests were completed. The average value of all parallel test data was taken to obtain the core superplastic deformation data of the material under different conditions, including flow stress and elongation after fracture. Finally, the temperature range of 400℃-480℃ and the strain rate range of 0.0001-0.001 corresponding to the peak elongation after fracture of the material were identified as the optimal superplastic deformation window.

[0019] S2. Delineation of the initial safe range for core process parameters Based on the cross-sectional structural characteristics of the profile to be formed, the design parameter of 1.2mm wall thickness, the forming dimensional accuracy requirement of ±0.2mm, and the mechanical properties of the finished product, the initial safe range of values ​​for four core process parameters—forming temperature, strain rate, holding time, and forming pressure—is defined: Forming temperature range: The melting point thermodynamic absolute temperature of 6061 aluminum alloy is T0=933K. The basic threshold is calculated using the formulas Tmin=T0+0.1*T0 and Tmax=T0+0.8*T0, resulting in Tmin=933K+0.1*933K=1026.3K and Tmax=933K+0.8*933K=1679.4K. Combining the optimal superplastic deformation window locked by S1, the interval correction coefficients are taken as A1=0.1 and A2=0.8, and A1<A2. Finally, the initial safe value range of forming temperature is determined to be 400℃-480℃, which satisfies both the basic threshold requirement and the optimal superplastic deformation window range. Strain rate range: 0.0001-0.001; Insulation time range: 10min-60min; Forming pressure range: 10MPa-30MPa; S3, Construction of the Association Mapping Model Based on the coupling characteristics of each process parameter within the initial safe value range defined by S2, a correlation mapping model is constructed between process parameters and profile forming quality, mechanical properties of formed parts, and forming efficiency: Calculate the comprehensive evaluation coefficient M for profile forming quality: M=(B1*D1+B2*D2+B3*D3) / (B1+B2+B3) In the formula, D1 is the wall thickness uniformity deviation value of the profile forming part, D2 is the outline dimension accuracy deviation value of the profile forming part, and D3 is the form and position tolerance deviation value of the profile forming part; the weighting coefficients are set to B1=0.5, B2=0.35, B3=0.15, and B1+B2+B3=1. Simultaneously calculate the comprehensive evaluation coefficient N of the mechanical properties of the profiled part using the formula defined in claim 5: N=(C1*E1+C2*E2+C3*E3) / (C1+C2+C3) In the formula, E1 is the measured tensile strength of the profile forming part, E2 is the measured yield strength of the profile forming part, and E3 is the measured elongation after fracture of the profile forming part; the weighting coefficients are set as C1=0.4, C2=0.4, C3=0.2, and C1+C2+C3=1; S4, Multi-objective Global Optimization With the objectives of achieving the required profile forming accuracy, meeting the design threshold for mechanical properties of formed parts, and optimizing forming efficiency as the collaborative optimization goals, and combining the correlation mapping model constructed by S3, a particle swarm optimization algorithm is used to conduct multi-objective global optimization: F = K1*M + K2*N + K3*S S=(t1+t2+t3) / t0 In the formula, S is the processing efficiency coefficient of superplastic forming of profile, t1 is the heating and holding time before profile forming, t2 is the pressure holding time of profile forming, t3 is the cooling and unloading time of profile forming, the preset standard total forming time t0=120min; the weighting coefficients K1=0.5, K2=0.35, K3=0.15 are set; During the optimization process, the minimum value of F was the core optimization objective, and the preliminary optimized process parameter set was finally obtained: forming temperature 450℃, strain rate 0.0005, holding time 30min, forming pressure 20MPa; S5, Orthogonal Verification Experiment Based on the preliminary optimized process parameter group obtained from S4, an orthogonal verification experiment was designed. The experimental factors included four core variables: forming temperature, strain rate, holding time, and forming pressure. Each experimental factor was set with three levels: the three levels for forming temperature were 430℃, 450℃, and 470℃; the three levels for strain rate were 0.0003, 0.0005, and 0.0007; the three levels for holding time were 20 min, 30 min, and 40 min; and the three levels for forming pressure were 15 MPa, 20 MPa, and 25 MPa. The superplastic forming trial production of profiles of all groups was completed according to the nine sets of orthogonal experimental tables. The actual forming quality test data and mechanical property test data of each group of trial pieces were collected simultaneously. After removing abnormal data, the average value of the valid data was taken as the experimental result.

[0020] S6. Model Iteration and Optimal Parameter Output The correlation mapping model is iteratively corrected using the measured data obtained from the S5 verification experiment. The global optimization and experimental verification process is repeated until the preset optimization termination condition is met. Model correction: Calculate the correction coefficient K of the association mapping model using the formula defined in claim 7: K = (Mactual / Mpre-defined + Nactual / Npre-defined) / 2 In the formula, M is the measured value of the comprehensive evaluation coefficient of forming quality obtained from the verification test (0.028), Mpre is the predicted value of the comprehensive evaluation coefficient of forming quality output by the correlation mapping model (0.030), N is the measured value of the comprehensive evaluation coefficient of mechanical properties obtained from the verification test (128.6), and Npre is the predicted value of the comprehensive evaluation coefficient of mechanical properties output by the correlation mapping model (132.4); the correction coefficient K is calculated to be 0.94, and the corrected output values ​​of the correlation mapping model are all multiplied by the correction coefficient K; |Fbefore - Fpresent| / Fbefore In the formula, Fbefore is the comprehensive objective function value of the previous iteration, Fnow is the comprehensive objective function value of the current iteration, the maximum allowable rate of change R is preset to 0.5%, and the maximum number of iterations X is preset to 20. When iterating to the 6th time, it was calculated that |Fbefore - Fnow| / Fbefore = 0.32% ≤ R, which satisfies the optimization termination condition. Finally, the optimal superplastic forming process parameters for the target profile were output: forming temperature 445℃, strain rate 0.00045, holding time 28min, forming pressure 18MPa. Using the optimized process parameters of this embodiment, the profile was tested for superplastic forming. The wall thickness uniformity deviation of the formed part was ≤3%, the contour dimension accuracy deviation was ≤0.15mm, and there were no defects such as wrinkling, cracking, or uneven wall thickness. The tensile strength of the formed part was 122MPa, the yield strength was 76MPa, and the elongation after fracture was 14%, which fully met the design requirements. The product qualification rate was increased from 72% in the prior art to 98%, achieving the optimization effect expected by the invention.

[0021] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for optimizing superplastic forming process parameters, characterized in that: Including the following methods: S1. Conduct isothermal unidirectional superplasticity basic performance tests on the target metal material to be formed profile. Set no less than 4 sets of increasing temperature gradients and no less than 4 sets of increasing strain rate gradients. For each gradient, complete no less than 3 sets of parallel tensile tests. Obtain the core superplastic deformation data of the material under different temperature and strain rate conditions, such as flow stress and elongation after fracture. Lock the interval corresponding to the peak value of the material's elongation after fracture as the optimal superplastic deformation window. S2. Combining the cross-sectional structural characteristics of the profile to be formed, the wall thickness design parameters of 0.5mm-10mm, the forming dimensional accuracy requirements and the mechanical properties of the finished product, the initial safe range of values ​​for the four core process parameters of superplastic forming is defined. The basic threshold of the forming temperature range is determined by the formulas Tmin=T0+0.1T0 and Tmax=T0+0.8T0, where T0 is the melting point thermodynamic absolute temperature of the target material. S3. Based on the coupling characteristics of each process parameter within the initial safe value range, construct a correlation mapping model between process parameters and profile forming quality, mechanical properties of formed parts, and forming efficiency. S4. Taking the standard of profile forming accuracy, the mechanical properties of formed parts meeting the design threshold, and the optimal forming efficiency as the collaborative optimization objectives, multi-objective global optimization is carried out in combination with the constructed correlation mapping model to obtain the preliminary optimized process parameter set; S5. Based on the preliminary optimized process parameter group, design an orthogonal verification experiment, complete the superplastic forming trial production of profiles, and collect the actual forming quality test data and mechanical property test data of each group of trial parts; S6. Use the measured data obtained from the verification experiment to iteratively correct the correlation mapping model, repeat the global optimization and experimental verification process until the preset optimization termination condition is met, and finally output the optimal superplastic forming process parameters that are suitable for the target profile.

2. The method for optimizing superplastic forming process parameters according to claim 1, characterized in that: In the isothermal unidirectional superplasticity basic performance test of method S1, four sets of increasing temperature gradients T1, T2, T3, T4 and four sets of increasing strain rate gradients e1, e2, e3, e4 are set. The average value of all parallel test data is taken as the final superplastic deformation basic data. The temperature and strain rate range corresponding to the peak elongation after fracture of the material is locked as the optimal superplastic deformation window.

3. The method for optimizing superplastic forming process parameters according to claim 1, characterized in that: In method S2, the initial safe value range of the four core process parameters includes the forming temperature range, strain rate range, holding time range, and forming pressure range. The final value of the forming temperature range must simultaneously meet the basic threshold requirements and the optimal superplastic deformation window range. The range of the interval correction coefficients A1 and A2 is 0.1-0.8, and A1 < A2.

4. The method for optimizing superplastic forming process parameters according to claim 1, characterized in that: In the correlation mapping model of method S3, the comprehensive evaluation coefficient M of profile forming quality is calculated using the following formula: M=(B1*D1+B2*D2+B3*D3) / (B1+B2+B3) In the formula, D1 is the wall thickness uniformity deviation value of the profile forming part, D2 is the outline dimension accuracy deviation value of the profile forming part, D3 is the form and position tolerance deviation value of the profile forming part, B1, B2, and B3 are the preset weight coefficients corresponding to D1, D2, and D3, respectively, and the value range of B1, B2, and B3 is 0.1-0.7, and B1+B2+B3=1.

5. The method for optimizing superplastic forming process parameters according to claim 4, characterized in that: In the correlation mapping model of method S3, the comprehensive evaluation coefficient N of the mechanical properties of the profile forming part is calculated simultaneously using the following formula: N=(C1*E1+C2*E2+C3*E3) / (C1+C2+C3) In the formula, E1 is the measured tensile strength of the profile forming part, E2 is the measured yield strength of the profile forming part, E3 is the measured elongation after fracture of the profile forming part, C1, C2, and C3 are the preset weighting coefficients corresponding to E1, E2, and E3, respectively, and the values ​​of C1, C2, and C3 are all in the range of 0.1-0.7, and C1+C2+C3=1.

6. The method for optimizing superplastic forming process parameters according to claim 5, characterized in that: In method S4, the comprehensive objective function F for multi-objective global optimization is determined by the following formula: F = K1*M + K2*N + K3*S S=(t1+t2+t3) / t0 In the formula, S is the processing efficiency coefficient of superplastic forming of profile, t1 is the heating and holding time before profile forming, t2 is the pressure holding forming time of profile, t3 is the cooling and unloading time after profile forming, t0 is the preset standard total forming time, K1, K2, and K3 are the preset weight coefficients corresponding to M, N, and S, respectively, and the values ​​of K1, K2, and K3 are all in the range of 0.1-0.7, and K1+K2+K3=1. The minimum value of F is the core optimization objective in the optimization process.

7. The method for optimizing superplastic forming process parameters according to claim 6, characterized in that: In method S6, the correction coefficient K of the association mapping model is determined by the following formula: K = (Mactual / Mpre-defined + Nactual / Npre-defined) / 2 In the formula, M is the measured value of the comprehensive evaluation coefficient of forming quality obtained from the verification test, Mpre is the predicted value of the comprehensive evaluation coefficient of forming quality output by the correlation mapping model, N is the measured value of the comprehensive evaluation coefficient of mechanical properties obtained from the verification test, Npre is the predicted value of the comprehensive evaluation coefficient of mechanical properties output by the correlation mapping model, and the corrected output value of the correlation mapping model is multiplied by the correction coefficient K.

8. The method for optimizing superplastic forming process parameters according to claim 6, characterized in that: In method S6, the optimization termination condition is determined by the following formula: |Fbefore - Fpresent| / Fbefore ≤ R In the formula, Ffront is the comprehensive objective function value of the previous iteration, Fcurrent is the comprehensive objective function value of the current iteration, R is the preset maximum allowable rate of change, and the value of R ranges from 0.1% to 1%; or the number of iterations reaches the preset maximum number of iterations X, and the value of X ranges from 5 to 30.

9. The method for optimizing superplastic forming process parameters according to claim 1, characterized in that: In method S5, the test factors of the orthogonal verification test include four core variables: forming temperature, strain rate, holding time, and forming pressure. Each test factor is set with three levels. All groups of prototypes are completed according to the orthogonal test table. The forming quality test data and mechanical property test data of each group of prototypes are collected simultaneously. After removing abnormal data, the average value of the valid data is taken as the test result.

10. The method for optimizing superplastic forming process parameters according to claim 1, characterized in that: The profile includes any one of aluminum alloy complex cross-section profiles, titanium alloy thin-walled profiles, and high-temperature alloy multi-chamber profiles, with the cross-sectional profile dimensions ranging from 50mm to 800mm.