Under the development trend of high performance and light weight in the aerospace and automotive fields, aluminum alloys are more and more widely used, the strength of material is getting higher and higher, and the shape of components is becoming more and more complex, a higher challenge is presented to advanced forming manufacturing technology. Hot stamping technology utilizes the good plasticity of the material at high temperature to form a thin-walled and special-shaped complex structure at one time. Meanwhile, it can further control the performance of components, which has become a research hotspot in the academic and engineering circles. Therefore, the research achievements and present situation of the hot stamping technology for aluminum alloy were reviewed, mainly introduced the research progresses of aluminum alloy hot stamping technology principle, typical process method, deformation strengthening mechanism and technical engineering application in recent years. The research status and development trend of hot stamping technology for aluminum alloy represented by 7 series high strength aluminum alloy were discussed and prospected, aiming to provide reference for the development of hot stamping technology for aluminum alloy.

Austenitic stainless steel is widely used in industry, decoration, food, medical machinery and other fields, and has good corrosion resistance and high temperature resistance, etc. However, the oxide scale formed on the surface of austenitic stainless steel causes local cracks in the steel plate and affects the surface quality of steel during the high temperature heating process. Therefore, the high temperature oxidation behavior of austenitic stainless steel was studied, and the evolution processes of the oxide scale on the steel surface under the heating and hot rolling conditions were observed by SEM, EDS and XRD. The results show that when the temperature is 600 ℃,a thin and dense Cr₂O₃ oxide layer is formed on the surface of austenitic stainless steel, and with the increasing of temperature, a uniform double-layer oxide layer gradually formes on the surface of steel and thickens over time. However, when the temperature is 1250 ℃,the upper oxide scale Fe₃O₄ is easy to fall off and layers with the substrate, and the oxide scale with the lower layer and the substrate tightly combined is mainly composed of FeO, Cr₂O₃ and spinel oxide containing Si element. Furthermore, in the rolling process, the surface of the substrate undergoes cyclic oxidation and is destroyed into a broken block structure after the single layer of oxide scale falls off, and the oxide scale is mainly composed of iron oxide, Cr₂O₃ precipitation and FeCr₂O₄.

For 10 steel, a single-pass compression test was carried out on the thermal simulator Gleeble-1500,and the size of sample was Φ10 mm×15 mm. The compression deformation temperatures were 900-1200℃, the strain rates were 0.01-10 s^-1, and the compression amount was 63.2%(the true strain was 1.0). The results show that the stress of 10 steel decreases with the increasing of deformation temperature and increases with the increasing of strain rate during the high-temperature single-pass compression test, and the dynamic recrystallization phenomenon occurres during the thermal deformation of 10 steel. On the basis of this research, the critical strain model of dynamic recrystallization for 10 steel was obtained, according to the true stress-true strain curves, the dynamic recrystallization volume fractions were calculated, and the recrystallization kinetic model of 10 steel was constructed. Furthermore, the dynamic recrystallization grain size model of 10 steel was established, according to the grain sizes measured by the metallographic photos. The average absolute relative error(AARE) was introduced to verify the fitting effect of dynamic recrystallization grain size equation for 10 steel, and the value of AARE was 6.32%, indicating that the fitting effect was good.

The origin, research status at home and abroad and application in the manufacturing industry of clinching technology were introduced, and the three basic forms of clinching joints and their characteristics were introduced. Then, the working principle, main working process and issues needed to be paid attention to in each working stage of clinching technology were expounded. Furthermore, by comparing with traditional riveting technology with rivets and resistance spot welding technology, their advantages in reducing process steps, reducing raw material investment, lightweight material connection, improving fatigue strength, energy conservation and emission reduction, safety and environmental protection, and reducing comprehensive cost were deeply analyzed, meanwhile, the shortcomings and future research and development directions of clinching technology in terms of sheet performance requirements, sheet layer amount requirements, sheet thickness requirements, static strength, etc. were pointed out, which provided theoretical reference and selection basis for the independent application of clinching technology in the manufacturing industry of China.

In order to obtain the reasonable deformation process parameters of warm forming for 7075 high strength aluminum alloy, the stress-strain curve of 7075-T6 aluminum alloy was tested by thermal simulation testing machine Gleeble-3500, and the rheological behavior of 7075-T6 aluminum alloy under the conditions of the deformation temperature of 150-300℃ and the strain rate of 0.01-10 s^-1was studied. Then, the thermal processing map of 7075-T6 aluminum alloy under the strain of 0.3-0.6 was established based on Arrhenius constitutive equation, and the reliability and practicability of the thermal processing map were verified by metallographic microstructure.The results show that 7075-T6 aluminum alloy is highly sensitive to deformation temperature, strain rate and strain amount, and the thermal deformation activation energy Q is 291.151 kJ·mol^-1. The fitting result of the modified Arrhenius constitutive equation is good, and the correlation coefficient r value and the average absolute error AARE are 99.65% and 5.54% respectively, which can better predict the rheological behavior of 7075-T6 aluminum alloy. When the strain is 0.6, the best warm processing safe zone range is the temperature of 250-300℃ and the strain rate of 0.01-0.05 s^-1.

The evolution law of microstructure and properties for TA15 titanium alloy large forgings during thermal deformation process was studied by process test. The results show that when TA15 titanium alloy undergoes thermal deformation at 950,965 and 980℃, excessive thermal deformation occurs, and the significant recrystallization refinement in the center of forgings is found to form a "double set" structure. Furthermore, the new α-phase structure is about 3-5 μm, which is significantly different from the primary α-phase structure(about 10 μm), resulting in microstructure defects of "center bright line" in the macrostructure of forgings, and the mechanical properties such as strength and plasticity in the microstructure defects region are lower than those in the normal region. Meanwhile, it is found that with the increasing of temperature, the deformation amount decreases to less than 80%, and the generation of microstructure defects is inhibited and the performance of forgings is improved. So by exploring the formation reason of "center bright line" microstruture defects, the process conditions of suppressing microstructure defects are obtained, which provides a basis for the forming of high performance large titanium alloy integral forgings.

Servo press is one of the most important innovations in the field of plastic forming in recent years, and the servo press and forming process based on it can be collectively referred to as servo forming technology. Therefore, the characteristics and current applications of the servo forming technology were introduced briefly, and several new developing trends of the servo forming technology were discussed emphatically, including study of design method for servo press, development of new functional components and energy storage technology, design and optimization of slide motion path, servo forming mechanism and numerical simulation of forming process, servo forming in intelligent manufacturing, etc. In order to realize innovation in the forming process, the transformation from a simple equipment manufacturer to a provider of comprehensive solutions for forming process should be realized by forging equipment manufacturers as soon as possible in china, and the research and development of key core components and the development of servo forming numerical simulation technology and new forming processes should be vigorously developed.

A sequential stacking grouping heuristic (SSGH) algorthms was presented to solve the two-dimensional stacking cutting stock problem and determine the stacking cutting scheme,and the SSGH algorthms sequentially generated the layouts in the cutting stock scheme.For each layout,candidate blank set was formed by selecting the blanks (rectangular pieces) according to the stacking rule,and then the current layout was generated by grouping and nesting the candidate blank set.According to the stacking rule,the usage times of layout was determined,and the generation process of layout was repeated until all the requirements of blanks were met to determine the cutting stock scheme.Each time a layout was generated,the value of blank was corrected by the blank value correction algorithm until the value of blank tended to be reasonable.Furthermore,after many iterations,many different cutting stock schemes were generated,and the one with the lowest total cost was selected as the solution of stacking cutting stock problem.Experimental results show that the SSGH algorthms based on the stacking rule obviously reduces the total cost of two-dimensional stacking cutting stock problem.

In recent years, vibration-assisted plastic forming technology has become an emerging interdisciplinary subject due to the development of vibration utilization engineering in the field of plastic forming, and the coupling of vibration field and plastic force field can produce volume effect of reducing flow stress of material and surface effect of reducing friction at the interface. Therefore, the forming process principles of vibration-assisted drawing, deep drawing, extrusion and rolling, etc. were summarized, and the macroscopic performance, process characteristics and research progress of four typical plastic forming processes were analyzed under the vibration field. On this basis, the research on the mechanism of vibration-assisted plastic forming was summarized around stress superposition effect, vibration softening effect and vibration residual effect, and the interface friction behavior of vibration-assisted plastic forming was also analyzed based on antifriction by vibration and friction model under the vibration field. Finally, the development of vibration-assisted plastic forming technology was prospected.

For the 6061 aluminum alloy plate with the thickness of 60 mm, the change laws of temperature, strain and stress fields of the plate during the rolling deformation process at different reduction rates were studied by Deform simulation analysis technology, and the influences on the core, 1/4 position and the surface of the plate were emphatically analyzed. Then, the texture evolution laws of different positions of the plate were studied by visco-plastic self-consistent (VPSC) finite element method, which provided a new method for the study of deformation behavior and anisotropy in the aluminum alloy rolling process. The results show that during the multi-pass rolling process, the maximum temperature difference between the core and surface area is not prominently affected by the reduction rate of the rolled part, and the maximum temperature difference is 10℃. The accumulative strains at the surface and 1/4 position are always greater than that at the core, the contact between rolled parts and roller causes a large stress on the surface, and it shows obvious uneven stress distribution in the local areas of rolled parts. Three typical textures on β orientation line, that are Copper texture {112}< 11-1>, Brass texture {011}< 21-1> and S texture {123}< 63-4> are formed at the surface, 1/4 position and core of rolled part. With the continuous increasing of rolling reduction rate, the volume fraction of texture increases and the texture strength also increases. Among them, the volume fraction and the strength of S texture show an obvious increasing trend, which further indicates that the strength of S texture is more sensitive to the strain change process than the other two textures.

In order to promote the application of digital twin technology in the field of aviation forging and promote the intelligent production of aviation forging with high quality, high efficiency and high consistency, by analyzing and comparing the research on digital twin model and intelligent manufacturing architecture by relevant institutions and scholars at home and abroad, the general model of digital twin in manufacturing field was summarized from the perspective of macro intelligent manufacturing. On this basis, the concept of intelligent aviation forging cell based on digital twin was proposed, and it was discussed from three perspectives of connotation, characteristics and components. At the same time, the system architecture of intelligent aviation forging cell based on digital twin was obtained. Finally, the key technologies of digital twin for aviation forging were summarized, and combined with the actual demand, the relavant application of digital twin technology in aviation forging was explored in order to provide reference for engineering application of digital twin technology in the aviation forging field.

The manufacturing process difficulties of thermoforming door ring were studied, and based on the conventional thermoforming scheme, the integration and optimization were conducted to solve the forming wrinkling problem of door ring by using three pressing blocks. Then, the product was optimized by combining with the forming results of CAE analysis, and the rationality and feasibility of the scheme were verified by actual production. Furthermore, the deformation, cracking and deviation of welding line were mainly optimized. The analysis shows that the large flow amount of materials at the corner leads to the deformation of welding line and then cracks, so the welding line should be set in the straight section with small flow amount of material. At the same time, the CAE analysis curve of welding line is reversely output for product matching to achieve the consistency of design and manufacture, and the welding line deviation is controlled within ±3 mm in production validation. In addition, the springback mechanism and precision control method of thermoforming were further studied, and the main causes of deformation for parts are the change of stress-strain fields and thermal expansion and cold contraction caused by metallographic transformation during the cooling process of thermoforming. The CAE analysis shows that reducing the die clearance can reduce the springback of parts. In the processing data, the zoom factor 0.172% is used to compensate the thermal expansion and cold contraction of parts. After the die clearance is reduced, the springback compensation is adjusted, and the accuracy measurement is conducted with the pass rate of 95%.

The low service life of hot forging mold has become one of the key factors for high manufacturing cost of hot forgings.Based on the analysis of the reasons for the low service life of hot forging mold and the problems existing in traditional manufacturing and repair methods,the route diagram of 3D printing manufacturing and remanufacturing technology for hot forging mold was proposed,and the technical connotation and its operation method of each step in the proposed route were illustrated.Then,the key technologies and equipment of the formulation and implementation of 3D printing planning,the smooth processing of mold cavity and the three-dimensional precision measurement,the surface removal and processing of failed mold cavity and the 3D printing remanufacturing of mold cavity surface were studied.Finally,the advancement and practicability of the technology were verified by the example of repair and remanufacturing of hot forging mold for automobile steering knuckle.Compared with the traditional method,the manufacturing and remanufacturing efficiency of hot forging mold are increased by 3.17 times,the cost is reduced by 75%,and the life is increased by 4.47 times.

The stretch-bending process is a kind of forming method which can effectively control the shape precision of bending parts.Theoretical analytical analysis is a research method for studying the process mechanism of stretch-bending and predicting the forming quality of stretch-bending workpieces.There are currently four main methods such as standard load method based on elastoplastic theory,process analysis method based on elastoplastic theory,numerical analysis method based on energy function and difference analysis method based on strain increment theory.Among them,the method 1 gives the forming limit diagram of drawing force and bending moment for workpiece to predict the springback and residual stress distribution of workpiece with different section parameters and materials after unloading.The method 2 focuses on analyzing the stress and strain states of section to calculate the relationship between the springback of workpiece after unloading and the stretch-bending process parameters based on the stretch-bending process.The method 3 and method 4 are both simplified numerical analysis methods and are derived based on functional equations and difference equations respectively to predict the springback and section distortion of parts after stretch-bending.For the current situation that the analytic methods for researching on stretch-bending process were relatively scattered,a more feasible research direction was put forward by analyzing and summarizing the related literature on the study of analytic method for stretch-bending profile.

The reinforcing skin with variable curvature double surround deep ribs has thin material, low forming limit and large reinforcing rib depth, its traditional rubber forming at one time is not feasible by bulging theory analysis. Therefore, based on the conclusion analysis of equivalent stress nephogram and material thickness change nephogram of reinforcing skin by PAM-STAMP 2 G rubber one-time forming, the design structure of flexible medium tooling for instability suppression and the defect control scheme of multi-pass rubber forming were determined. The combination tooling of the forming die with convex curvature rib shape and the long rubber plates was used for multi-pass rubber aggregated forming, and the combination tooling of the sizing die with concave curvature rib shape and the eyeglass frame rubber block was used for multi-pass rubber forming of buckling correction, which were tested by experiment. The results show that the orderly filling of rubber plates can realize controllable material storage, and the use of hollow flexible rubber block can realize embedded pressure-expansion sizing, which reduces the buckling deformation and springback of reinforcing skin. Thus, the multi-pass rubber forming with rigid and flexible coupling combined tooling structure can improve the height limit of the traditional rubber forming deep rib structure.

Firstly, the hotspot technologies and their global distribution and development trend in various subdivided fields of advanced forging were analyzed based on Patsnap patent big data retrieval platform, and then, the main global R& D entities and companies in each subdivided direction of forging field and their key technology layouts and innovations status were analyzed comparatively by the visualization method.The results indicate that China ranks first in the world in terms of the total number of patents in the advanced forging field, but some advanced forging technologies in Japan, the United States and Germany are still at the leading level in the world.The frontier hotspot technologies in forging mainly focus on high-speed precision forging, forging dies, quality inspection of forgings, continuous forging, forging manipulator, forging digitalization and other technical directions, and its applications are concentrated in the fields of large aerospace die forgings, engine ring forgings, titanium alloy forgings, automobile panels, aluminum alloy wheels, fuel cell plates, highspeed train brake wheels, disks, complex thin shells and wind power engine spindles.

For the two-dimensional irregular graphics nesting problem, a hybrid nesting algorithm(AGAHA) based on heuristic placement strategy and adaptive genetic algorithm was implemented. Firstly, considering the problem that the placement strategy of a single index was easy to fall into the local optimum, a hybrid placement strategy based on no-fit polygon(NFP) was proposed, which comprehensively considered the overall compactness and local compactness of the nesting effect. Then, in order to improve the efficiency of searching for the optimal solution, an adaptive genetic algorithm was used when optimizing the order of graphs. Based on the standard genetic algorithm, the crossover and mutation probabilities were adaptively changed according to changes in population fitness. Finally, the standard test cases in the literature and the cases in the actual production were used to test separately. The results show that the AGAHA algorithm is better than the ordinary genetic algorithm combined with BL algorithm in most cases, and in the actual cases, the results of AGAHA algorithm are better than the result of manual nesting.

Since the motion trajectory of three-dimensional stretch-bending chuck for aluminum profile is generally a space curve, the aluminum profile is stretched and deformed during the stretch-bending process, and the motion trajectory of stretch-bending chuck is difficult to obtain. Therefore, a method for determining the motion trajectory of three-dimensional stretch-bending chuck for aluminum profile was proposed. Firstly, the two ends of inital aluminum profile were divided into fixed end and clamping end, and the coordinate system was established at the fixed end. Secondly, the central axis of product was extracted to discretize into several space points, and each discrete point was taken as the tangent point to make the tangent line of product central axis. Furthermore, the line segment of corresponding length was intercepted along each tangent direction(from the tangent point to the clamping end), the other end of the line segment was the space points through which the chuck motion trajectory passes, and by connecting these points in turn the trajectory of chuck was obtained. Finally, an example was given to verify the proposed method. The results show that within a certain range, with the increasing of the number of discrete points, the springback value decreases rapidly, and then as the number of discrete points continues to increase, the springback value changes little. In the analysis, the middle part is taken as the springback reference standard, and the springback value obtained is closer to the actual result.

In sheet metal bending, springback prediction and control are the key to accurate forming of product. Therefore, for the bending springback problem of free-form surface for SUS430 stainless steel with the thickness of 0.55 mm, the finite element simulation of free-form surface bending for SUS430 stainless steel sheet was carried out by three typical anisotropic yield criteria, such as Hill48, Barlat89 and YLD2000-2 d, and combined with experimental verification, the influence laws of different yield criteria on springback amount of free-form surface bending were studied. The results show that the agreement between the simulation results of YLD2000-2 d yield criterion and the experimental results is the best, which is suitable for the finite element simulation of free-form surface bending for SUS430 stainless steel. Furthermore, there is a certain deviation between the simulation results of Barlatt89 yield criterion and the experimental results, while the difference between the simulation results of Hill48 yield criterion and the experimental results is the biggest. Based on the selection of the YLD2000-2 d yield criterion, the influence laws of the two process parameters of stamping speed and friction coefficient on the springback amount of free-form surface bending was analyzed. Within the range of reasonable process parameters, the higher the stamping speed is, the smaller the springback predicted by the numerical simulation is.

For the problem of serious stamping springback for aluminum sheet, the solution to reduce the springback of an aluminum alloy automobile skylight reinforcing sheet was studied. Firstly, the process analysis of the part was carried out to determine the preliminary stamping process. Secondly, with the help of synchronous engineering(SE), the serious springback features of part were optimized, and the stamping processes were determined as OP10 blanking, OP20 drawing, OP30 trimming and piercing, OP40 trimming and punching and OP50 trimming and shaping. Then, the whole process simulation was conducted by software Autoform to perform overall and local springback compensations, which made the sizes of the part after springback meet the tolerance requirements. Finally, the die was adjusted based on the sheet inflow amount, and the pressure regulating gasket was used to control the fluidity of sheet and reduce the springback. The final production shows that the combination of SE, springback compensation and adjustment of sheet inflow amount can effectively reduce the springback of aluminum alloy sheet.

The urgent demand of modern industry for lightweight plates was briefly described, the shortcomings of the traditional process for connecting multi-layer lightweight plates were analyzed, and for the plastic deformation connection method of multi-layer plates, the principle, process, advantages and disadvantages of two processes with rivet and without rivet were expounded. Then, the development history, application fields, plastic connection mechanism and material plastic flow behavior for plastic connection process of self-piercing riveting with rivet were mainly discussed, and the process, connection mechanism and connection performance for plastic connection of self-piercing riveting with rivet shapes such as cup shapes, soft and hard cylindrical shape, waist drum shape and pointed screw piercing shape were manly studied. Furthermore, the connection quality and characteristics of flat-anvil cliching, traditional cliching, lock riveted connection of typical shape rivet, spot welding, traditional riveting and adhesive bonding were further summarized, which built the solid foundation for the popularization and application of multi-layer plates with rivet plastic deformation connection method in industrial practice.

For the front door inner panel of a certain type of automobile, in order to solve the crack and dark crack defects of parts in the drawing process, firstly, the production status of die and parts was briefly analyzed, and according to the forming defects, the improvement plan of adding piecrcing knife was put forward. Then, the shape of piercing knife and the piercing height were compared in multiple combinations by finite element simulation, and the optimal piecrcing knife scheme was obtained as the blank holder force of 1200 kN, the piercing kinfe shape of D-type and the piercing height of 15 mm. Finally, the effect of adding piercing knife was verified by stamping test. And there was a certain error of the break width results between the stamping test scheme and the simulation calculation. It is because that there is secondary forming process in stamping test, the recovery and softening of the material in the secondary forming process have a great impact on the stamping test results. This stamping method could be used as the basis for the trend analysis of break width, but it could not be accurately quantitative analysis.

In order to solve the folding defect in the production process of marine connecting rod in a certain factory, the optimization analysis was conducted by software Deform. Since the folding defect of connecting rod was not accurately predicted by the folding angle that comes with the software Deform, the folding probability index was embedded in the software Deform by secondary development to predict the folding defect, and the prediction result was consistent with the actual situation. Then the cause of the folding defect in the fillet transition zone was found by material flow analysis. The influences of fillet radius in blank fillet transition zone, final forging temperature and die pressing speed on the folding probability index were explored, and combined with orthogonal experiments, the optimal process parameters were found and simulated in the software Deform after the secondary development. The simulation result shows that the folding condition is greatly improved. Finally, the factory trial production was carried out. And the shapes of obtained forgings are refined, the folding rejection rate is reduced from 20.97% to 0.91%, and the microstructures and grain sizes reach the production requirements, which verifies the effectiveness of the process optimization and provides a reference for the optimization of similar folding defects.

The traditional synchronous control of hydraulic press needs longer time to reach the steady-state error and can not achieve the high precision synchronous control of hydraulic press. In order to improve the working efficiency of hydraulic press, a synchronous control hydraulic system of hydraulic press with double cylinders was developed, and the control schemes of piston rod in two states for extension and retraction were given. The synchronization error compensation data was transmitted to hydraulic cylinder 2 to complete the dynamic response faster, so as to significantly reduce the displacement difference of hydraulic cylinder 2 and achieve a significant improvement in the synchronization control accuracy. Furthermore, the synchronous control was realized by the error feedback method to achieve the precise control of the synchronous operation process of double hydraulic cylinders, and the PID parameters were adjusted by the genetic algorithm to significantly improve the synchronous control precision of double-cylinder hydraulic system. Compared with the parallel control methods, the error feedback synchronous control method reduced the maximum error by 68.71% and reduced the time required to enter the steady state error by 18.52%. Thus, the precise synchronous control of the hydraulic press could be realized by the synchronous control structure.

In order to study the forming mechanism and breakthrough precision control technology of counter-roller spinning, the influences of process parameters such as pass thinning ratio, feeding rate, forming angle of roller and radius of inner roller on the roundness, straightness and wall thickness difference of spun part were analyze by the finite element method. The results show that when the pass thinning ratio Ψ_t is 20%-30%, the feeding rate f is 1.5-2.0 mm·r^-1, the forming angle of roller α_ρ is 25°, the radius of inner roller r_ρ内 is 10 mm, the forming accuracy of spun part is the highest. At the same time, the influences of different reduction amounts of inner and outer rollers on forming accuracy were analyzed when the total reduction amount is 9 mm. And the results show that the spun parts have the highest precision when the reduction amount of outer roller is 5 mm and reduction amount of inner roller is 4 mm. Finally, the accuracy of the finite element simulation results is verified by the spinning experiment, and their deviation is less than 15%.

In order to reduce the fluctuation of rotation speed control for volumetric speed regulation system used in hydro-mechanical continuously variable transmission(HMCVT), a control method of PID optimized by genetic algorithm(GA) was designed, and the simulation analysis was carried out by AMESim and MATLAB/Simulink combined software. The results show that after optimization by the control method of PID optimized by GA, the rotation speed reaches overshoot of 0.35% and shows stable state after 0.25 s. Compared with the traditional PID control method, the overshoot is reduced by 18.5%, the required adjustment time is shortened by 0.17 s, and the fluctuation of rotation speed is significantly reduced. Thus, the control method of PID optimized by GA can make the system obtain a shorter adjustment time, achieve more efficient response performance, greatly reduce the overshoot of rotation speed, significantly improve the speed regulation and stability of the system, and obtain better dynamic response performance and rotation speed control precision, which can provide favorable conditions to meet the engineering application.

To improve the drawing quality of vehicle taillight mounting reinforcement, based on dynamic NSGA-II algorithm, a multi-objective optimization method was proposed. Then, aiming at reducing the maximum thinning rate and wrinkling trend function, a multi-objective optimization model was established, and taking four drawbead resistance coefficients and blank holder force as the optimization parameters, the performance parameters of drawn parts under different conditions were obtained based on the finite element method. Furthermore, the dynamic congestion calculation method was introduced into NSGA-II algorithm to maintain the diversity of selected chromosomes and improve the optimization ability of dynamic NSGA-II algorithm, and using the dynamic NSGA-II algorithm to solve the multi-objective optimization model, its Pareto frontier solution was superior to that of traditional NSGA-II algorithm. According to the optimized parameters, ten trial pieces were produced, the mean values of the maximum thinning rate and the maximum thickening rate for trial pieces were less than the mean values of products for manufacturer, and the standard deviations of the maximum thinning rate and the maximum thickening rate of the trial pieces were small. The experimental results show that the production quality and stability are improved after the parameters optimization.

In order to improve the design rationality and production efficiency of forging automatic production line, it is very important to optimize the production time sequence in the design stage. For the design on the automatic production line for crankshaft forging of hot die forging press in an enterprise, based on the overall planning of main engine, target products and robot configuration for the production line, the production time sequence of production line was preliminarily designed, and the bottleneck nodes that limited the improvement of the production beat were found. Then, the action planning of a typical crankshaft product in the production line was realized by the methods of time sequence splitting, time sequence analysis and integration optimization, and the production beat was reduced from 43 s to 20 s, which ensured the high efficiency production of the production line. Professional software simulation results show that on the basis of meeting the functional requirements for the production line, the equipment has no interference, the robot runs smoothly, and the optimized time sequence is more reasonable and efficient.

Spinning for welded joints of the same/dissimilar alloys is an important processing method for the manufacture of aerospace parts. Therefore, the research prospect of spinning for welded joints of the same/dissimilar alloy at home and abroad in recent years were mainly reviewed, the process of spinning for welded joints of the same alloy and the evolution laws of microstructure were summarized, and the influences of different process parameters on forming were explored. The results show that for the same alloy, the process of welding first and then spinning is helpful to reduce the structure inhomogeneity of the welded joints, the mechanical properties of the welded joints are improved to a certain extent, and the difficulty of subsequent forming is reduced. Through analyzing the direction of the spinning deformation force and the mechanisms of action on the microstructure, the defect generation mechanism can be explained effectively, and the forming performance is improved. However, how to prepare blanks of the dissimilar alloy and form high-precision tailor-welded components of the dissimilar alloys and the evolution of the microstructure and mechanical properties for the welded joints in the spinning process needs to be further studied.

Because the tube undergoes a complex multi-pass thermal-mechanical composite processing process during the preparation process,it usually has obvious anisotropy and tension-compression asymmetry,which greatly affects the formability and service performance of tube.Therefore,how to accurately and comprehensively characterize the anisotropy and tension-compression asymmetry of tube and establish the corresponding constitutive model is the premise and foundation of tube forming design and manufacture.However,due to the geometrical features such as curved surface and thin wall of tube,it is difficult to measure and characterize the anisotropy and tensioncompression asymmetry of tube,and the characterization modeling of anisotropy and tension-compression asymmetry for tube has always been a hot and difficult problem in the field of tube forming manufacturing in China and at abroad.Based on the above,the methods of measuring and characterizing anisotropy and tension-compression asymmetry of tube in China and at abroad in recent years were summarized,the relevant modeling methods were reviewed,and the test characterization and the constitutive modeling methods were prospected.

With the increasing of use time for press, the fault problem of press occur frequently, which seriously affects the normal production of the factory. In order to solve this problem, the fault diagnosis of press was conducted by analyzing the vibration signal of press. For crank press JM21-160, the method of simply and accurately extracting the fault characteristics was studied by software Matlab. Based on the experimental data of the actual press, a simple method was proposed to process data by wavelet denoising and time-frequency conversion, which was based on Matlab wavelet toolbox, and the validity of this method was verified by contrast and analysis on the spectrums before and after data denoising. The result shows that this method can simplify and extract data to analyze the frequency characteristics of press fault and has reference value for press vibration signal processing and analysis in the production site.

The high-temperature rheological behaviour and the constitutive model of A356 aluminum alloy play an important role on its stress state, which lays a significant foundation for the finite element simulation of aluminum alloy during the rheological forming process. Therefore, the tensile specimens were prepared from A356 aluminum alloy wheel hub casting billet, the isothermal tensile experiments were conducted by test machine Instron 3369 at the experimental temperature of 300-375℃ and the strain rate of 0.001-0.1 s^-1. The obtained true stress-true strain curves show that the rheological stress of material is significantly affected by thermodynamic conditions such as temperature and strain rate. Based on the true stress-true strain curve, a physical model based on dislocation density theory was established to characterize the rheological stress under different thermodynamic conditions. The predicted value of the model was compared with the experimental data, and the error analysis was carried out. The results show that the established physical model can accurately predict the high-temperature tensile rheological behaviour of A356 aluminum alloy.

In order to change the current situation of multipre processes, low production efficiency and large differences of product performance in curvent production process for an automobile non-standard part, two kinds of automatic cold upsetting schemes were proposed, and the Johnson-Cook constitutive model of 10 B21 steel was established by Deform-3 D. Then, based on the model, the simulated forming of the parts in each station for the two schemes were conducted, and the deformation law, equivalent stress distribution and load situation of the material were analyzed. Furthermore, the process inspection and optimization were carried out, and the final forming scheme was determined, namely, blanking-diameter reducing and inner hole pre-forming-head pre-upsetting-flower head upsetting-head shaping-head final forming-punching, and the process test was completed. Production tests show that the finite element analysis results are accurate, the optimized cold upsetting process is reliable, and the mass production of the non-standard parts can be realized. The obtained parts have complete forming, good surface quality and no problems of scraping, folding, potholes and so on, and the dimensional accuracy meets the production requirements.

For the problems of high manual detection intensity and low efficiency in defect detection of stamping parts at present, a fast detection algorithm(YOLOv4-Mobile) based on the improved YOLOv4(You Only Look Once) model was proposed, which used the improved MobileNetV3 network to replace the CSPDarknet53 network in YOLOv4 structure, and the improved MobileNetV3 network combined a depthwise separable convolution, an inverted residual structure with a linear bottleneck and SE(Squeeze and Excitation) structure. Then, the image of stamping parts collected in the workshop was used to establish the defect data set and enhance the data set, and a set of prior frame parameters corresponding to the defect data set of stamping parts was obtained by K-means clustering algorithm to improve the matching degree of prior frame and feature layer. The test results show that based on the improved YOLOv4 model, the mAP(mean Average Precision) of the fast detection algorithm reaches 89%, which is higher than that of SSD algorithm. Meanwhile, the detection speed reaches 0.15 s per sheet, which is better than the original YOLOv4 algorithm.

Aiming at the non-linear flow problem caused by dead zone of electro-hydraulic servo valve without spool displacement, based on the analysis of the dead zone model of electro-hydraulic servo valve, a compensation model for the dead zone of electro-hydraulic servo valve with differential pressure feedback was designed to achieve the compensation function of dead zone without displacement feedback. Then, the simulation compensation voltage signal was added to the control system of electro-hydraulic servo valve, and the flow rate of proportional flow valve was rapidly compensated by setting the "voltage-flow" slope of the proportional flow valve in different changing stages. According to the difference of the dead zone for electro-hydraulic servo valve under different inlet and outlet differential pressure, the compensation analysis for the dead zone of electro-hydraulic servo valve was carried out. The simulation results show that under the static control characteristics, when the inlet and outlet differential pressure rises from 2 MPa to 6 MPa, the spool displacement decreases by nearly 0.1 mm(maximum), and the flow dead zone shrinks by about 2%. However, under the dynamic control characteristics, the proposed compensation method reduces the dead zone of electro-hydraulic servo valve to 3%, and the compensation method is completely feasible.

Firstly,the structural characteristics and working principle of radial forging machine were simply introduced.The main progresses in the research and development of hammer driving methods of mechanical drive,hydraulic drive and mechanical-hydraulic hybrid drive for radial forging machine abroad were summarized in the past half century,and the related technical characteristics and product spectrum of the typical products were analyzed and compared.Then,the development and technical status of the radial forging machine in China were introduced in detail.The results show that the hydraulic drive for radial forging machine and its full localization of production lines is the urgent need of forging industry in China.Fault prognostics,health management and intelligent manufacturing are the main theme of the development of hammer driving mode for radial forging machine.Furthermore,the forging limit problem of thin-walled seamless steel pipe and the pursuit of higher stroke rate can promote the evolution of the hammer driving mode of mechanical radial forging machine from the eccentric shaft slider structure to the double blade drive shaft structure.

For the third generation ultra-high strength steel DP980, six kinds of characteristic tensile specimens were designed to obtain different stress states and ultimate strains under different strain paths, and the failure model GISSMO was developed. Then, the simulation calibration of specimen level was completed, and the grid size correction coefficient was obtained based on the benchmarking of unidirectional tensile specimens. Furthermore, the bending damage of cap-shaped beam was calculated by theoretical derivation, and the bending radius was determined. In addition, the quasi static three-point bending experiment and dynamic axial collapse experiment of cap-shaped beam were designed, based on the developed failure model GISSMO, the bending simulation of cap-shaped beam was completed by DYNA to obtain the initial damage value after bending. Finally, the simulation benchmarking was completed by introducing the initial damage. The results show that the simulation results of failure model GISSMO are more consistent with the experimental results after considering initial damage, which indicates that the forming initial damage must be considered when the larger machining initial damage occurs.

Based on the analysis of structural characteristics for three-cylinder crankshaft of 42 CrMo steel, the dressing structure of pre-forgings was optimized by software Deform, the dressing contour was changed from the straight line intersection to the arc transition, and the intersection angle was optimized from 15° to 20° to reduce the stress value of die cavity. Furthermore, the remaining block structure was designed in order to facilitate deformation, mold splitting and subsequent counterweights, the semi-open and semi-closed extrusion barrel structure was designed at the edge of pre-forging die, the pre-forging and final forging deformation amounts were distributed, and the pre-forging and final forging die structures were obtained. Finally, the forming processes of pre-forging and final forging were numerical simulated by Deform-3 D respectively, and the flash values of pre-forgings and final forgings were 15-55 mm and 35-65 mm respectively, which was 5 mm smaller than the measured values. In addition, the pre-forging temperature of forgings was designed to be 1200℃, and the temperature at the end of final forging was over 900°. The production practice shows that the simulation results can assist the structural design of the forging die, the flash of forgings is uniform, the die cavity is filled fully, and the final forgings meet the technical requirements of drawing and acceptance criteria.

In order to study the high temperature hardness of three commonly used hot work die steels and the change laws of wear rate and friction coefficient at 100 and 300℃, the laws for the hardness, friction coefficient and wear rate changing with temperature for three types of hot work die steels were obtained by high temperature hardness test and high temperature friction-wear test. The results show that the hardness gradually decreases with the increasing of temperature. Although the surface nitriding treatment greatly increases the hardness of the material, the hardness decreases more obviously with the increasing of temperature after nitriding treatment. At 300℃, the resistance to deformation of the pin-disk contact surface is reduced, and the friction coefficient between material and plate is less than that at 100℃. At the same time, the pin surface produces a thicker oxide layer at 300℃, and the wear rate is less than that at 100℃. The surface nitriding treatment of the material improves the wear resistance of the material at 100℃, but at 300℃, the wear amount increases instead. Thus, the test results provide reliable basic data support for the selection of mold materials and the improvement of mold wear resistance.

In order to solve the problems such as cracking, wrinkling and springback of aluminum alloy automobile cover panel during stamping production process, for an aluminum alloy automobile side outer panel, the processability of part was analyzed. Then, the process supplementary modeling and sheet shape were quickly designed by software Autoform, and the whole stamping process simulation was carried out on this basis. The simulation results show that the optimization of the original part modeling in synchronous engineering stage can avoid the stamping defects in the design, spheroidizing the fillet in the cracked area and designing a smooth transition in the continuous step modeling can alleviate the cracking risk, setting additional wrinkle absorption modeling and flanging gap in the wrinkle area can alleviate wrinkling, designing stiffeners and adding structural constraints can reduce the springback amount, and avoiding the interference of modeling features can reduce the deformation defects of the stamping surface. Finally, the optimized part is successfully manufactured with good quality, which proves that this method can effectively reduce the time and cost of later stamping die development, improve the quality of product, and provide a good reference for structural improvement of similar parts.