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Creep age forming (CAF) is an advanced forming technology that combines creep deformation and age hardening processes. When compared with the conventional forming technologies including roll bending and shot-peen forming, CAF has many advantages of low residual stress, excellent dimensional stability, good service performance and short production cycle. It is an optimal technique for precise manufacturing for shape and properties of large-scale complicated thin-walled components of light-weight and high strength aluminum alloys in the aviation and aerospace industries. Nevertheless, CAF has an inevitable disadvantage that a large amount of springback occurs after unloading, which brings a challenge on the accurate shape forming and property tailoring of components. Therefore, how to achieve accurate prediction and control of springback has always been a bottleneck hindering the development of CAF to more industrial applications. After the factors of affecting springback and measures of reducing springback are summarized from the internal and external aspects, constitutive models for predicting springback and springback compensation methods for CAF of aluminum alloy panel components are reviewed. Then, a review of research progresses on tool design for CAF is presented. Finally, in view of the key issue that it is difficult to predict and control the shape and properties of components during CAF, the technical challenges are discussed and future development trends of CAF are prospected.

Creep age forming techniques have been widely used in aerospace industries. In this study, we investigated the effect of aging temperature (143 °C–163 °C) on the creep behavior of Al-Li-S4 aluminum alloy and their mechanical properties at room temperature. The mechanical properties were tested by tensile testing, and the microstructural evolution at different aging temperatures was examined by transmission electron microscopy. Results show that the creep strains and the room-temperature mechanical properties after creep aging increase with the aging temperature. As the aging temperature increases, the creep strain increases from 0.018% at 143 °C to 0.058% at 153 °C, and then to 0.094% at 163 °C. Within 25 h aging, the number of creep steps increases and the duration time of the same steps is shortened with the growth of aging temperatures. Therefore, the increase in aging temperatures accelerates the progress of the entire creep. Two main strengthening precipitates θ′ (Al2Cu) and T1 (Al2CuLi) phases were characterized. This work indicates that the creep strain and mechanical properties of Al-Li-S4 alloys can be improved by controlling aging temperatures.

Creep age forming (CAF) process is a novel metal forming method with major benefits including improved mechanical properties and cost reduction for aviation industry applications. CAF happens due to creep phenomenon and stress-release during the artificial aging of heat-treatable aluminum alloys. In this work, the creep age forming of 7075 Aluminum alloy at 120, 150 and 180 °C for 6, 24 and 48 h was done; tensile and hardness tests were used to characterize the samples. Results on spring-back revealed that it was influenced by time and temperature; by increasing the time and temperature, it was reduced from 54.1 to 39.51. Mechanical property evaluation also showed that by increasing the time, the strength and hardness could be enhanced due to microstructural evolution and precipitation during the CAF process. According to the mechanical and CAF results, two samples were selected as the optimum ones and their work hardening behavior and fracture surfaces were investigated

The effect of forming pin arrangement on formed shape accuracy with sparse multi-point flexible (SMPF) tool has been experimentally and numerically investigated for creep age forming (CAF) process. An analytical method has been introduced to predict shape, stress and strain distributions of blanks loaded by SMPF tool with different pin configurations. Experiments and FE simulations of loading and CAF processes by SMPF tool with various pin number/interval conditions have been performed and the formed shapes after loading and CAF have been quantitatively analysed. The results show that increasing pin numbers in SMPF tool decreases shape errors and stress variations in the loaded blank, leading to lower deflections of the formed blank after CAF. With increasing pin numbers, the formed shape approaches the shape formed with corresponding surface tool. The shape error percentage in loaded blanks is significantly enlarged after CAF with SMPF tool, from 3% to more than 20% for singly-curved tool shapes with aluminium alloy 6082, and detailed value varies with tool shapes. Stresses in loaded blanks directly affect CAFed shapes and it has been found for the first time that there is a same stress discrepancy level between loaded blanks with SMPF tool and corresponding surface tool to achieve a particular shape accuracy after CAF with different tool shapes. It is proposed that the stress discrepancy parameter in loaded blanks can be used as a new and more efficient design criterion for pin arrangement in SMPF tool for CAF process. In addition, an asymmetric pin pattern, which reduces half of pins in SMPF tool and increases efficiency, has been proposed and its effectiveness for CAF process has been tested and discussed.

Stress-relaxation age forming (SRAF) of a component (820 × 300 × 3 \({\mathrm{mm}}^{3}\)) with complex and large curvatures has been simulated and a corresponding SRAF test of an Al–Mg–Si alloy, AA6082-T6, has been carried out in this study. An FE model is established to simulate the stress-relaxation ageing (SRA) behaviour of AA6082-T6 during SRAF at various stress levels, ranging from elastic to plastic regions, and a unified constitutive model for SRA of the material has been implemented in the finite element (FE) software ABAQUS via the user-defined subroutine CREEP. An optimised tool surface was determined from the FE simulation through springback predication and compensation and was used for manufacturing test. A good agreement of the formed shape has been achieved between the FE simulation and the SRAF test, with a maximum shape error below 4 mm, satisfying the industrial requirement. The hardness results from the formed plate showed an insignificant change of strength during SRAF, and are in good agreement with the simulation. The effects of the initial plastic strain and creep strain generated during loading and stress-relaxation stages on the formed shape have also been analysed.

Creep age forming (CAF) has been developed to manufacture large complex components in aerospace industry. However, crystalline textures in initial material for CAF process may influence the creep ageing behavior, leading to low precision of formed component. In-planer anisotropy in creep-ageing behavior of a textured Al-Cu-Mg alloy was investigated. The total creep deformation decreased with the increase of the angles between the applied stress and rolling direction. The creep deformation of samples with loading direction parallel to rolling direction is 2.33, 2.07 and 1.62 times greater than that perpendicular to the rolling direction, under 120 MPa, 150 MPa and 180 MPa, respectively. A strong dependence of the anisotropy in creep deformation on the initial textures was suggested, according to the equivalent slid system numbers. With the rise of the external stress, the creep deformation of three different orientation samples increases but the anisotropy of those declines. However, the stress exponent difference among the three orientation samples may be related to the equivalent Schmid factor changes. Although the anisotropy of the mechanical properties in creep aged samples with various orientations is less than 5%, the in-planar anisotropy values of creep deformation under different creep age forming conditions are larger than 30%. It indicated that creep-ageing anisotropy of the studied alloy sheet cannot be ignored in their CAF applications. Keywords: Creep age forming, Creep-ageing anisotropy, Texture, Al–Cu–Mg alloy

Forming features of a 435 mm × 293.7 mm integrally-stiffened panel of AA2219, creep-age formed under a single curvature bending radius of 1160 mm at 165 ˚C for 8 h, have been experimentally and numerically investigated. A finite element model has been developed to simulate springback behaviour and mechanical properties of the stiffened plate in creep age forming process. The simulation results indicate that the final shape of the panel depends on creep and plastic deformations. Furthermore, creep age forming experiment of the plate has been carried out. The relative error of springback between the simulation and experimental values is up to 11%, whilst average yield strength error is 3.2%. In addition, both simulated and experimental results show that the degree of strength anisotropy is not obvious on the skin, but it is significant for the ribs.

Creep age forming of an Al-Cu-Li alloy (AA2050-T34) with an asymmetric tension/compression creep-ageing behaviour has been experimentally and numerically investigated in this study. Creep age forming experiments of plates with different thicknesses have been carried out to form doubly curved shapes using a recently developed sparse multi-point flexible forming tool. Corresponding FE model for creep age forming, incorporating the material model that describes the stress-strain relation and asymmetric creep-ageing behaviour of the alloy, has been developed through PAM-STAMP. The flexible forming tool can generate various tool shapes for creep age forming and is ideal for innovative trials. Stress concentration was found in some forming pin areas of the loaded plate. With larger initial loaded plastic strain and higher creep strain generated in these local areas, bumps may occur in formed shapes after creep age forming under certain circumstances. It is shown that the FE model is able to predict the formed shape accurately for thicker plates and can be used for tool set-up optimisation.

A novel constitutive model has been proposed in this study that predicts the different stress-relaxation ageing (SRA) behaviour of AA6082-T6 with elastic and plastic loading strains, extending the applications of stress-relaxation age forming (SRAF) from conventional elastically loaded panels to complex-shaped panels under plastically loaded conditions. The particular contributions of loading strain levels in elastic or plastic regions on the evolution of microstructural variables (i.e., inter-particle spacing, dislocation density, and precipitate length), yield strength and stress-relaxation behaviour during SRA process are concurrently modelled. The decreasing creep threshold stress and the increasing dislocation recovery effect from annealing with increasing initial strain in the plastic region have been proposed and introduced in the model. TEM analysis has been performed to quantify the effect of loading strain and ageing time on the evolution of β″ precipitates, and further calibrate the material model. Furthermore, the established model has been implemented into FE simulation to optimise the tool surface design of a train body panel component with complex and large curvatures, and corresponding SRAF tests have been conducted with the optimised tool surface. The maximum shape deviation from the objective shape of a component with a dimension of 820*300*3 mm3 has been controlled within 3 mm, demonstrating the feasibility of the developed material model for SRAF in industrial applications, especially for highly demanded complex-shaped components.

According to retrogression and re-aging treatment (RRA), a novel retrogression and stress-aging treatment (RSA) was put forward for Al-Zn-Mg-Cu alloys. The effect of stress-aging time and external stress on precipitates of pre-retrogressed Al-Zn-Mg-Cu alloy was investigated by transmission electron microscope (TEM). The observation shows that there is a large number of matrix precipitates (MPts) and slightly discontinuous grain boundary precipitates (GBPs) in the pre-retrogressed alloy. The effects of stress-aging time and external stress on precipitates of the retrogressed alloy are significant. With the increase of stress-aging time and external stress, the size of MPts increases and the density of MPts decreases. Meanwhile, the size of GBPs, the distance between GBPs and the width of precipitate free zone (PFZ) increase. Compared with the traditional retrogression and re-aging treatment, the retrogression and stress-aging treatments increase the size of MPts, narrows the width of PFZ and make the GBPs more discontinuous for the studied Al-Zn-Mg-Cu alloy.

Applying pre-deformation to high strength aluminum alloy has significant impacts on shape formation and mechanical properties of component in creep age forming process. The suitable degree of pre-deformation can not only improve forming efficiency, but also attain sound mechanical properties. This paper experimentally investigates the effects of pre-deformation on creep strain, mechanical properties and microstructures of AA2219. The results show that pre-deformation can prolong the duration of primary creep stage and considerably facilitate creep strain. Through mechanical property tests, it is found that pre-stretched AA2219 possesses a high-performance “peak ageing strengthening region” with little fluctuation during creep ageing of 7–13 h. Further examinations by TEM tests indicate that this is due to the fact that the morphology of precipitates in this region remains unchanged without remarkable coarsening. Based on microstructural evolution and ageing strengthening theory, a set of physically-based creep ageing constitutive model is proposed. The developed model takes into account the effect mechanism of pre-deformation and incorporates the coupled interactions of microstructure, yield strength and creep strain. A good agreement between predicted and experimental values is achieved, which verifies the accuracy of the developed model. Hence, it provides the theoretical basis for the prediction of shape and properties in creep age forming of large-scale panel component.

AA6082 is a popular material for automotive body structure because of its good formability and weldability. In this study, stress relaxation and ageing behaviour of AA6082 at T6 condition were investigated through stress relaxation tests with three different initial stresses at 160 °C for 12 h. Interrupted tests for 1, 3, 5 and 12 h and subsequent uniaxial tensile tests were carried out to investigate the effect of ageing time on yield strength of the material. The results show that after 12 h stress relaxation tests with initial stresses of 173, 198, and 225 MPa, the stresses relaxed were respectively 19.4 %, 24.3 %, and 25.6 % of the initial stresses. Minor change of yield strength of the material throughout the ageing time was observed. Moreover, a set of unified constitutive equations was calibrated to model the stress relaxation behaviour of AA6082 during creep age forming process, and related material constants for the AA6082 were determined. A close agreement between experimental data and computed results has been achieved for stress relaxation behaviour of the material. This study helps to understand the stress relaxation behaviors of AA6082 material, and facilitates the CAF applications of AA6082 material in industrial field.

The initial temper of the material may directly affect the whole creep age forming (CAF) process. In terms of creep deformation and stress relaxation, using the constant-stress creep aging and constant-strain stress relaxation aging tests, the relationship between initial temper and CAF formability is investigated for an Al-Zn-Mg-Cu alloy at 165 °C for 18 h. Three tempers are selected as the initial tempers in CAF, viz., solution, retrogression and re-solution. The CAF formability of this alloy with initial temper of retrogression is the best, and the creep strain of the retrogression tempered specimen after creep aging of 18 h is about 1.21 and 1.34 times than that of the solution and the re-solution tempered specimens, respectively. The calculated stress exponents of this alloy with three initial tempers range from 7.3 to 9.5, indicating that the CAF of this alloy is mainly controlled by the dislocation creep. The various formability for three initial tempers are attributed to different inhibitions of the transgranular precipitates on the dislocation movement. For the retrogression temper, the initial fine and uniformly distributed precipitates are seriously coarsened after 6 h of CAF, which minimally inhibit the dislocation movement. While, for the re-solution temper, the fine precipitates are re-precipitated in the matrix of the alloy, which observably hinder the dislocation movement and lead to the worst formability.

Materials modelling plays an important role for sprinback compensation and tool surface design in creep age forming (CAF). This review aims to provide perspective on the development and trend of materials modelling for CAF of aluminium alloys. Recently proposed unified constitutive equations for creep-ageing behaviour of aluminium alloys during CAF by integrating microstructural evolution and hardening effects are reviewed. The modelling methods and developing trend to quantitively reflect the relationship between the microstructural evolutions and macro creep-ageing behaviour of materials during CAF are discussed.

The process and characteristics of creep age forming technology was introduced. The influence of the creep age forming process on the fatigue performance on aviation aluminum alloy was discussed. Researches from three aspects were reviewed respectively–the fatigue damage mechanism of the creep age forming material, the influence of creep age forming process parameters on the performance of material fatigue, and creep age formed material life prediction mode. The trend of the creep age forming technology and the problems that may exist in its application in the field of aerospace were analysed. Finally, the major research direction was pointed out that fatigue properties of aluminum alloy materials and components based on the creep age forming technology should be studied deeply.

Creep age forming (CAF) of aluminium alloy 7B04 (AA7B04) stiffened plates has been experimentally and numerically investigated in this study. Creep-ageing experiments of AA7B04-T651 were conducted under different tensile stress levels at 140 °C for up to 20 h, and a set of unified constitutive equations was calibrated based on the experimental results of the evolutions of creep strain, yield strength and precipitate size, which was implemented into ABAQUS for CAF process modelling. CAF experiments and corresponding simulations of AA7B04 stiffened plates were then carried out and the effect of stiffener height and die radius on springback and yield strength was studied. It was found that the springback percentage decreases with increasing stiffener height and decreasing forming die radius, and the yield strength is slightly lower in the stiffener than in the skin of the CAFed stiffened plates due to stress effect on ageing progression. A good agreement has been achieved between experimental and corresponding FE results, with maximum deviations of 6.7% and 3.3% respectively for springback and yield strength.

Application of a newly developed flexible forming tool to creep age forming (CAF) process has been investigated in this study. The flexible tool mainly consists of sparsely distributed forming pins, splines and elastomeric sheet. The effect of key factors related to the forming tool on the shape of the formed parts has been studied through various CAF experiments. The key factors investigated in this study include: the interval between forming pins, the arrangement of pins, the accuracy requirement of pin height and the material of splines. It has been found that reducing the interval between pins can efficiently smooth the shape of CAFed plates. The feasibility of asymmetric arrangement of pins has been proven, which can decrease the number of used pins, reduce tool weight, and increase efficiency. The forming results are very sensitive to the pin height, thus the experimental set-up error should be carefully controlled. Additionally, compared with mild steel, spring steel is more suitable as the spline material.

The constitutive modeling and springback simulation for AA2524 sheet in creep age forming (CAF) process were presented. A series of creep aging tests were performed on AA2524 at the temperature of 180–200 °C and under the stress of 140–210 MPa for 16 h. Based on these experimental data, material constitutive equations which can well characterize creep aging behaviors of the tested alloy were developed. The effect of interior stress distributed along the sheet thickness on springback was simulated using FE software MSC. MARC by compiling the established constitutive models into the user subroutine. The simulation results showed that the amount of sheet springback was 61.12% when merely considering tensile stress existing along the sheet thickness; while sheet springback was up to 65.93% when taking both tensile and compressive stresses into account. In addition, an AA2524 rectangular sheet was subjected to CAF experiment in resistance furnace. The springback value of the formed rectangular sheet was 68.2%, which was much closer to 65.93%. This confirms that both tensile and compressive stresses across the sheet thickness should be considered in accurately predicting springback of the sheet after forming, which can be more consistent with experimental results.

a b s t r a c t Creep-age forming (CAF) is one of the relatively new forming techniques that has been proven viable for the production of extra-large integral airframe structures. However, experimental studies on forming stiffened structures under creep-ageing conditions remain scarce. In this work, 200 mm × 48 mm inte- grally stiffened plates of aluminium alloy 2219 have been formed on an end clamp device that has a bending radius of 156 mm and creep-aged at 175 ◦C for 18 h. Three different stiffener designs, namely the beam stiffened, waffle and isogrid plates, are tested alongside the flat plates. Utilisation of PTFE pocket fillers and intermediate sheets to reinforce and protect stiffeners during forming operation is found effec- tive as demonstrated by the defect-free formed parts with smooth curvature. Springback of the plates ranged from 12.2 to 15.7% in the experimental studies for different stiffener designs. Using the CAF mate- rial constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles of the creep-age formed plates. Up to 6.3% differ- ence in springback is observed when forming workpieces with different pre-form age condition alone. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND

Creep-age forming (CAF) is a proven forming technique in the aerospace industry for the production of large integrally stiffened panels. One of the most urgent issues to be addressed in CAF is the development of flexible tooling. Flexible tools already have a long-standing reputation for the economic impact they have brought to the aircraft industry. However, with the rising need to establish comprehensive springback prediction models for CAF, the need for flexible CAF tools is now stronger than ever. In this article, an existing state-of-the-art CAF tool is described followed by the introduction of a novel design concept for flexible tooling. Based on the proposed design method, which utilises mechanical splines and sparsely spaced controlling points, a proof-of-concept prototype is built and characterised using corresponding analytical and finite element models that have been developed. Three parameters that can influence forming surface error: (i) the number of control points, (ii) spaces between control points and (iii) spline thickness are identified and optimised. Finally, an integrated optimisation process for tool offsetting is introduced, and its use is demonstrated. It is confirmed that this design method can be used to make flexible CAF tools with less than ± 1 mm error (defined as vertical difference from prediction) in the forming surface. In addition, this error can eventually be compensated and thus eliminated from CA-formed parts by using the developed optimisation technique. This article provides CAF tool designers confirmed advices for making new flexible CAF tools. Lightweight and flexible CAF tools can now be constructed through the use of mechanical splines and sparse controlling points.

This paper presents a study of anelastic creep recovery during creep-ageing of an aluminium alloy AA7050-TAF. Uniaxial Creep-Ageing and Recovery Test (CART) was used to characterise the influence of anelastic creep strain on total creep deformation for determining the actual amount of springback in creep age forming (CAF) process. CART was performed on aluminium alloy AA7050-TAF at 174°C between the stress levels of 137.5 to 162.5 MPa. A constitutive model was developed for the prediction of the creep-ageing and recovery response of material in creep age forming. A ‘back stress’ variable was used to represent the net effect of the internal stresses of the material which causes anelastic creep recovery. Other microstructural variables were introduced to model complex micro-mechanisms and hardening effects including solid solution hardening, dislocation hardening, and age hardening. It has been found that the permanent strain after creep-ageing depends not only on total creep strain but also on anelastic strain. Simulation results from the constitutive model developed in this study show a good agreement with experimental data.

Creep age forming is often carried out under vacuum or autoclave loading conditions, where a sufficiently high, uniform pressure is required to force the workpiece into close contact with the tool surface. However, many creep age forming tests are performed to evaluate springback by clamping the workpiece to both ends of a cylindrical tool and forcing it to the tool surface, which is different from reality. In this study, a set of mechanistically based unified creep ageing constitutive equations have been incorporated into the commercial finite element code ABAQUS and used to analyse a common creep age forming tester, which employs a cylindrical tool shape. Two loading conditions are investigated: (1) end clamp and (2) uniform pressure. The amount of springback has been predicted, compared and analysed for both loading cases. A method has been introduced to assess the local curvature and springback variations. Good contact was achieved between the workpiece and tool surfaces for the uniform pressure condition (except at the plate end), providing that sufficient pressure was applied. However, for the end clamp condition, contact was limited to the vicinity of the clamps.

A method of springback reduction is presented which involves a combination of solution heat treatment, natural ageing, stretch forming and artificial ageing. A commercial aluminium alloy, 2219-O Hi-Form, is solution heat treated and subjected to two pre-form natural ageing periods of one and seven hours before the stretch forming process. Following the forming process an artificial ageing process combined with creep age forming techniques is used. Springback is assessed following the stretch forming and artificial ageing processes. This process is shown to provide a controlled means of correcting the springback following stretch forming.

A comparative study of the corrosion properties of an AlZnMgCu alloy subjected to simulate age-forming (SAF) and traditional aging was performed. The samples pretreated at 160 °C for 24 h using SAF and traditional aging, were immersed in 3.5 wt% sodium chloride solution for up to 96 h, the process of which was monitored by in situ electrochemical impedance spectroscopy (EIS). Optical profilometry measurement shows that the sample subjected to SAF has deeper pits and larger localized corrosion compared with the traditionally aged sample. EIS results suggest that corrosion rate changes with increasing time of immersion, and age forming makes the AlZnMgCu alloy hard to form effective passive film. The larger precipitate and wider precipitate free zone of the sample subjected to simulate age forming were thought to be responsible for the poor corrosion resistance during the immersion test. Additionally, these results suggest that stress during age-forming increases the grain aspect ratio, which is harmful to intergranular corrosion resistance of the AlZnMgCu alloy.

基于单曲率弯曲蠕变成形装置，针对7475铝合金板材进行了一系列蠕变时效成形实验，测得了不同时效制度和弯曲半径下的回弹量。采用电导率、维氏硬度、金相显微镜、透射电子显微镜和室温拉伸等手段分析了蠕变时效试样的性能与微观组织，并与人工时效试样进行了对比分析。结果表明：回弹量随着弯曲半径的减小、时效时间的延长和时效温度的升高而降低；弯曲蠕变时效试样比人工时效试样具有较高的屈服强度和抗拉强度，延伸率则相反；随着弯曲半径的增大，屈服强度和抗拉强度均呈现出先增后减的规律，在弯曲半径为1200 mm附近存在峰值；弯曲蠕变时效后试样的晶粒尺寸和形状与人工时效试样无明显区别，其析出相则比人工时效试样更为细小和致密。 Based on the single curvature bending creep forming device, a series of creep age forming tests of 7475 aluminum alloy sheets were conducted. The springback of formed samples with different ageing conditions or bending radiuses were measured. Then the properties and microstructures of the creep ageing formed samples were studied by electric conductivity tests, Vickers hardness tests, optical microscopy tests, transmission electron microscopy tests and tensile tests, respectively. And the results were compared with the artificial aged samples. The results show that the springback decreases with the decreasing bending radius, the increasing temperature and ageing time. The yield strength and the tensile strength of the bending creep ageing formed samples are higher than the artificial aged samples, but the elongation is the opposite. As the increasing of the bending radius, both the yield strength and the tensile strength increase first and then decrease, and the peak value appears near the bending radius of 1200 mm. No clear difference exists in the size and shape of grains between the creep aged samples and the artificial aged samples, the size and the particle spacing of the precipitates of creep aged samples are smaller than the artificial aged samples.

Age forming is the best forming method of integral panel parts of aircrafts, which have large amount of springback and the springback’s accuracy, is hard to control, so a method which can make an accurate prediction of the springback after forming is needed. This article which is based on creep test data and CPT, fits the creep constitutive equation and obtained the material parameter. The numerical simulation is adopted to process age forming simulation on springback of T-specimen of aluminum 2124, and the simulation result is compared with the test result to do revision of the material parameter; the revised material parameter is applied into the numerical simulation of age forming of the integral panel which is of high strength. Through tests which can confirm the error ranges from -1mm to +1mm, this method’s accuracy is proved.

Creep age-forming (CAF) technology is a new forming method, which combined age hardening and creep forming processes into one. It is mainly used to manufacture wing panels. In this paper, a set of experimental device of creep age forming is developed and the influence of process parameters on the springback of artificially aged 2524 aluminium alloys (AA2524) are investigated. The law of the comprehensive effect of aging time, aging temperature, elastic pre-deformation radius and work-piece thickness, on creep aging springback and mechanical properties of AA2524 is obtained. Based on multiple regression analysis, springback prediction model of process parameters is established and further proven experiments have then been carried out. The result shows that the maximum springback deviation between the experimental results and the prediction ones is within 9.5%. The accuracy of springback prediction model is validated, which provides a theoretical basis for process parameter optimization and springback prediction of CAF.

Age forming technology has some features including high rebound, especially it is difficult to control the precision of rebound. Due to the above-mentioned problems, this technology is difficult to be accepted and used widely. This passage mainly discusses the problem of age forming technology of integral panel with high ribs. Through the basic experiment of T-style 2124aluminium panels, the springback rule was studied, and the springback compensation of the complex mold surface was accomplished by adopting a geometrical compensation algorithm, this mold was used by parts making. The result of experiment is that the error of curved surface of part is less than 1 mm and the steel bar is less than 0.5 mm. It shows that the method is feasible and effective.

About twenty years ago, the process of Creep Age Forming (CAF) was invented, and since then has been developed for the manufacture of heat treatable aluminium alloy panel components particularly, it has been successfully used for aircraft wing panels. Significant research work has been carried out in recent years and process applications have been expanded. This paper contains a review of recent research and development of this novel forming process. It covers process applications in the aircraft industry and scientific research, including the development of forming tools, experimental studies, materials and process modelling and springback prediction. Some potential future applications and challenges for deeper understanding of this novel process are also discussed.

Creep-age-forming of a thick Al-Cu-Li sheet is studied. An industrial stamping press is used to form a double curvature panel at a reduced scale. This forming, which includes several relaxation steps, is modelled using ABAQUS. A material model describing an elasto-viscoplastic behaviour with anisotropy effect has been identified and implemented in ABAQUS using Fortran subroutine. The numerical model is validated by comparing experiments and numerical results in terms of deformed shapes and an improved forming cycle is suggested. This paper is part of the METAFOR project managed by IRT Jules Verne (French Institute in Research and Technology in Advanced Manufacturing Technologies for Composite, Metallic and Hybrid Structures). The authors wish to associate the industrial and academic partners of this project; respectively ACB, STELIA, AIRBUS, CONSTELLIUM, ENSAM.

The age forming technology, characterized by huge spring-backs, has been developed to manufacture large integral wing-skin panel parts, which necessitates devising a method of predicting spring-backs. A 7B04-T7451 aluminum alloy creep test in tension is accomplished at 155 °C, and the creep curves are obtained. The material constants of the mechanism-based creep constitutive equations are determined through experiments. The age forming process and the spring-backs of 7B04 aluminum alloy plates are analyzed using the commercial finite element software ABAQUS. The effects of plate thickness and forming time on spring-backs are researched. The spring-backs decrease with the increase of plate thickness and forming time. The test results verify the reliability of the finite element method (FEM) analysis.

The research described in this paper is a study of CAF a 2219 aluminium alloy, which is used for fabricating the isogrid structure for fuel tanks of launch vehicles. The main aim of the research is to develop a small scale CAF test rig, which was designed to analyse the springback behaviour from CAF. The main objective of the experiment was to investigate the potential proposals of creep age forming stiffened structures. Based on the results of the experiment, a potential CAF process for forming 1/3 pieces of an isogrid cylindrical assembly was proposed.

A unified viscoplastic constitutive equation is combined with the Bernoulli-Euler beam equations to create a model to describe autoclave age forming of beam structures used in aerospace structures. Predictions of ‘springback’ based on the model are obtained numerically and compared with experimental data for pure aluminium and 7075 aluminium alloy. Accurate predictions are found between model simulations and experimental observations. Issues related to extensions of the methodology to more complicated geometries are discussed.

In autoclave age forming process (AAF), temperature uniformity in large aluminium panel is one of the most important factors affecting its final shape and performance. In order to predict the temperature field of the panel, a 3D computational fluid dynamics model for autoclave processing of a large aluminium panel is developed and experimental evaluated. A good fitting between the experimental data and calculated results is obtained. During the heating process, the slowest heating points are positioned at the intermediate positions between 15-40% and between 55-70% of the panel length. The panel's peak temperature difference was appeared in the primary stage of soaking process due to the conduction between the panel and mould. It can be concluded that the developed CFD can further used to provide guidance for mould design and processing parameters optimisation.

Two main aspects of the creep age forming of aircraft structures have been studied: (1) to determine if lower wing skin alloys (2024A and 8090) can be creep age formed (artificially aged), and still retain adequate damage tolerance properties, and (2) to assess the creep formability of the new high strength alloy 7449. It has been found that all three alloys are amenable to creep age forming, with usable springback values and satisfactory tensile and damage tolerant properties being achieved. Compared to control samples (T351 for 2024A, T8651 for 8090 and T7951 for 7449), the creep age forming had no detrimental effect on any of the mechanical properties measured. In particular, adequate damage tolerant properties could be achieved after creep age forming even for the 2024A alloy, normally used in the T351 condition.

A method of simulating the age forming of initially flat panels is proposed. It conceptually divides the process into three phases (loading, aging, and unloading) and simulates each phase separately. Some sample simulations are presented for 7075 aluminum alloy based on a simplified version of the general procedure (linear loading and unloading, nonlinear aging). The results of these simulations are used to illustrate several aspects of the predictions. An interesting finding is that the part shape and tool shape are geometrically similar in two important special cases.

The creep age forming process (CAF), also known as the creep forming or age forming process, among other less usual designations ( 1–8 ), is a mechanic-metallurgical forming process applicable to parts manufactured from metallic sheets or plates. It is more suitable for large-contoured parts presenting smooth curvatures ( 9 ), such as aircraft wing skins. Differently from other metal-forming processes that are based on plastic flow, the CAF concept has the advantage of using heat treatment cycles of metals to impose stresses to be released under the effect of temperature and time, by creep mechanisms. CAF simultaneously strengthens the part and changes its shape, resulting in a one-step forming and heat treatment process.

Creep age forming (CAF) is an effective technology to manufacture large aircraft panel components of aluminum alloys. CAF has attracted much attention in the past few years, however, the evolution of microstructure and performances during the process remains unclear.

A unified viscoplastic constitutive equation is combined with Bernoulli/Euler beam equations to create a model of autoclave age forming of beam specimens. Predictions based on the model are obtained numerically and compared with experimental data. Encouraging agreement is found between simulations and observations. Issues related to extensions of the methodology to more complicated geometries are discussed.

A mathematical model of autoclave age forming of aircraft wing panels is developed. The modeling process is illustrated by application to age forming of beam specimens. It is found that a closed form solution can be obtained for a mold in the shape of a circular arc. Closed form solutions are not possible for other mold shapes and a numerical method is, therefore, developed and applied to two noncircular mold shapes. Comparisons of predictions with experimental data obtained by Textron Aerostructures yield good agreement.

A mathematical model of the autoclave age forming of beam specimens is developed based on the assumption of linear viscoelastic response. It is shown that the model is capable of predicting the qualitative features of the age-forming process.