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Because large plastic deformation occurs in hydroforming bellows there is a residual stress distributing in the metal after forming, which is complex and not easy to be measured. The existence of residual stress might have an effect on the corrosive property and bulking performance of bellows. A finite element model was established to simulate the forming residual stress of the nickel alloy multi-layer bellow. The distribution of residual stress was calculated out and validated by cosα X-ray diffraction measurement. Thus the forming mechanics and the effects of layer number and forming pressure on the residual stress in the hydroforming bellow were both discussed in detail based on the established model. It was shown that the calculated residual stress had the same trend with the experimental results. The axial and circumferential residual stresses at the outer surface of the peak were both compressive. There existed the maximal Von Mises stress at the inner surface of the peak of the bellow. At this position the radial and axial residual stresses were both tensile. When applying multi-layer bellows and less forming pressure a lower forming residual stress could be obtained because of the narrow plastic strain region during forming.

To overcome the problem of welding distortion on conventional multiple segment structures, and the problem of requiring large-scale forming equipment and severe thinning occurs in high-pressure hydroforming process, a novel less-loading hydroforming process is proposed for manufacturing large-size hollow components in this paper. The geometrical relationship of the tube blank during less-loading hydroforming process is firstly discussed. Then, experiment and numerical simulation are conducted to investigate the forming behavior of a large-size tubular component of aluminum alloy 5A06 with rectangular cross-section. It is found that the needed internal pressure, die closing force, and axial force for the less-loading hydroforming are significantly reduced, which are about 1/22, 1/8 and 1/28 of those required in high-pressure hydroforming, respectively. During the less-loading hydroforming process, the tube blank is firstly deformed by bending to fill the die corners, and then deformed by circumferential compression. Moreover, the compression deformation characteristics make the thickness increase. However, a too large circumferential compression and/or an insufficient supporting pressure will cause a wrinkle defect. These results provide insights for less-loading and approaching uniform manufacturing of large-size hollow components.

The uniaxial tensile test of the 5A06-O aluminium–magnesium (Al–Mg) alloy sheet was performed in the temperature range of 20–300 °C to obtain the true stress–true strain curves at different temperatures and strain rates. The constitutive model of 5A06-O Al–Mg alloy sheet with the temperature range from 150 to 300°C was established. Based on the test results, a unique finite element simulation platform for warm hydroforming of 5A06-O Al–Mg alloy was set up using the general finite element software MSC.Marc to simulate warm hydroforming of classic specimen, and a coupled thermo-mechanical finite element model for warm hydroforming of cylindrical cup was built up. Combined with the experiment, the influence of the temperature field distribution and loading conditions on the sheet formability was studied. The results show that the non-isothermal temperature distribution conditions can significantly improve the forming performance of the material. As the temperature increases, the impact of the punching speed on the forming becomes particularly obvious; the optimal values of the fluid pressure and blank holder force required for forming are reduced.

Forming process of the metal bellows is very sensitive to the fluctuation of material parameters. In this state, revealing the influence of material parameters on deformation behaviors is important for desirable dimension and mechanical performance. In this paper, the effects of the material parameters of 316L stainless steel on the bellow hydroforming process are studied by finite element analysis and Taguchi method. The most important factor influencing the final shape of convolution of the metal bellows is found out. Two multi-linear regressions between the quality responses and the material parameters are extracted and evaluated by simulated and experimental results. Based on the regression equations, response surfaces of the quality characteristic and the reasonable factor region for required forming quality are obtained. Further, the relationship between the internal pressure and the material parameters is built to guarantee the shape of the bellows. The method is applied in the scenario when the material is changed to AISI 304 steel, and a satisfying prediction profile is achieved.

Liquid impact forming (LIF), a composite forming technology of metal thin-walled tubes based on tube hydroforming (THF) and stamping forming, is introduced to increase the forming efficiency and decrease the cost. In this paper, a finite element model was established to study the forming characteristics of composite tubes under different mold cavities and clamping speeds. Then, the effects of different loading parameters on the bulging height, fillet radius and wall thickness distribution of composite tubes were analyzed systematically. Furthermore, the main factors affecting the formability of the tube were investigated based on response surface method (RSM), with the wall thickness variance, bulging height and fillet radius of the tube designed as targets, the mold side length, clamping speed and initial internal pressure selected as variables, the optimal loading parameters were obtained. At last, experiments of composite tubes based on the optimized loading parameters were conducted. The results showed that the deviation between the experimental results and the numerical simulation was within 5%, which verified the accuracy and reliability of the parameter optimization results.

Finite element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the yield surface shape used in mechanical modeling. The yield surface mainly depends on the number of input variables used to define the yield surface. The present paper's aim is to compare the constitutive models to fit the hardening laws. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tubular samples were collected by conducting uniaxial tensile tests and tube bulge test. The best fitted constitutive hardening model was utilized on both Hills 1948 and Hills 1990 yield criteria and the accuracy of the simulations was predicted. Thickness and strain distributions, as well as the geometry of the bulged specimen, were taken as comparison parameters. Experimental validation was performed on all the available predicted data and was observed to be best for the Hills 1990 yield criteria.

Abstract The objective of this study is to improve the bulging and minimize the thinning ratio to enhance manufacturing of components in Industries. Tube hydroforming is an advanced manufacturing technology used for making intricate and complex tubular parts which required less cycle time. This research focuses on hydroforming process, formability and process parameters design to replace the conventional tube bending, welding and cutting operations. The prediction of parameters is done by applying numerical and experimental approach. During experimentation the pressurized fluid is used to deform the tubes in a plastic deformation. In this study, two types of grade materials are used such as AISI304 and AISI409L of 57.15 mm external diameter with 1.5 mm thickness in the form of electric resistance welded tubes to measure stain path, thinning and bulge height. However, it is observed that the internal pressure and L/D ratio are effective parameters in both numerical analysis and experimentation. In axial feed condition, it is observed that 16.3% thinning in weld region and 44.6% thinning in base metal region, whereas, in fixed feed condition, it is observed that 7.7% thinning in weld region and 18.6%thinning in base metal region for L/D = 1 and L/D = 3 respectively. The numerical analysis with experimental results shows a very good match. It is seen that the axial feed leads to better formability with fixed feed condition because in axial feed condition material supplies towards the center of the bulge tube. The feasibility of the hydroforming process for manufacturing of AISI304 and AISI409L grade material as per the requirements of the industries is also checked. The maximum bulging is observed in L/D = 2 by comparing with the other ratios. This process can be effectively used for AISI304 grade material because the formability is better than AISI409L. Article highlights The strain path measured and predicted at necking point for ERW tube in both weld and base metal. Thinning is measured during bulging of tube under the axial and fixed feed condition. For L/D = 1 ratio observed strain distribution in unidirectional and L/D = 2, 3 observed in plane strain and bidirectional respectively.

Laser shock hydraulic microforming (LSHM) is a new microforming that combines the advantages of laser shock microforming and impact hydroforming. LSHM uses monopulse laser to drive the rubber layer for squeezing liquid medium to form metal foils. The size effect and forming mechanism under this process will surely introduce new features, and they were explored in terms of maximum bulge height, surface topography, thickness distribution, microhardness, microstructure, and elastic recovery. When N=t/d (thickness/grain size)>1, the N value decreases, the maximum bulge height and thickness thinning increase, and the roughening of surface topography is not obvious. When N 4.3, this case accords with inverse Hall−Petch tendency because twin nucleation is dominant. When N 1 due to the increase in the scale of grain atoms. The increase in laser power density can appropriately reduce the elastic recovery ratio because of grain refinement.

Even though fiber metal laminates (FMLs) were developed many years ago, existing forming approaches are not well qualified to produce intricate and small thin geometry. There are great difficulties in the deep drawing procedure, even for low forming depth. These difficulties are mainly related to the fiber layers limited elongation compared to the metals, and the process parameter selection during the deep drawing, which needs to be chosen very carefully. This research presents a numerical and experimental study on the influence of the hydroforming process parameters on FML hemispherical dome. The Aluminum 2024-T3 and prepreg glass fiber were used to produce the FML blanks. The parameters covered in this investigation were cavity pressure (CP), blank holder force (BHF), die entrance radius (DR), blank holder gap (BHG), and punch speed (PS). Taguchi’s design of experiments determined the effects of the input parameters on wrinkling and thinning. Results indicated that the BHG has the most significant impact on thinning and wrinkling. Optimization was conducted, and the optimum selected process parameter values were 80 kN for BHF, 15 MPa for CP, 8 mm for DR, 1.1 mm for BHG, and 30 mm/min for PS. Results revealed that FML cups formed by the optimized parameters could improve the utilization of the FMLs in mass production.

International audience; During tube hydroforming process, the friction conditions between the tube and the die have a great importance on the material plastic flow and the distribution of residual stresses of the final component. Indeed, a three-dimensional finite element model of a tube hydroforming process in the case of square section die has been performed, using dynamic and static approaches, to study the effect of the friction conditions on both plastic flow and residual stresses induced by the process. First, a comparative study between numerical and experimental results has been carried out to validate the finite element model. After that, various coefficients of friction were considered to study their effect on the thinning phenomenon and the residual stresses distribution. Different points have been retained from this study. The thinning is located in the transition zone cited between the straight wall and the corner zones of hydroformed tube due to the die–tube contact conditions changes during the process. In addition, it is clear that both die–tube friction conditions and the tube bending effects, which occurs respectively in the tube straight wall and corner zones, are the principal causes of the obtained residual stresses distribution along the tube cross-section.

Nickel-based superalloy thin-walled components have been used in aerospace equipments requiring high reliability and durability at high-temperature condition. To overcome the problem of severe thinning occurs in conventional one-step hydroforming, this paper proposes an innovative multi-step hydroforming process for manufacturing complex T-shaped tubular parts of nickel-based superalloy. The appropriate process parameters in every step for preventing undesirable wrinkling and splitting defects, including internal pressure, axial feeding length, axial feeding ratio, and retreating displacement of middle punch, have been determined through a detailed numerical simulation investigation. The results show that manufacturing of a GH4169 T-shaped tubular part with expanded diameter can be successfully implemented using a four-step hydroforming. Moreover, the four-step hydroforming process, as well as the forming defects and the thickness distribution of several typical sections on the hydroformed GH4169 T-shaped tubular part, are all discussed. Finally, the complex GH4169 T-shaped tubular part with a thickness more than 3 mm can be obtained successfully after the top of the side branch is removed. These results provide insights for the manufacturing of T-shaped tubular part with expanded diameter, and contribute to the development of superalloy tube forming process at room temperature.

The assembled camshaft is a recently developed split assembly technology that enables the realization of lightweight cars and improves engine performance. Residual shaft–cam contact pressure is affected by camshaft elastic recovery and affects connection quality. This study investigated a cam with an isometric–trilateral profile for tube hydroforming with a hollow shaft via experiments and finite element analysis. A novel, indirect residual contact pressure measurement method is herein proposed. Hydraulic parameter effects on residual contact pressure and elastic recovery were analyzed using the theory of plastic mechanics. For hydraulic pressure below 85 MPa, increasing hydraulic parameters increased residual contact pressure nearly linearly while decreasing elastic recovery.

Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming, the stress concentration and defects such as wrinkling and fracture may easily occur. It is a key to reveal the deformation behaviors in order to obtain a sound product. Based on the ABAQUS platform, a 3D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment. The stress and strain distributions, wall thickness variations and bellow profiles of each layer in the whole process, including bulging, folding and springback stages, are studied. Then deformation behaviors of bellows under different forming conditions are discussed. It is found that the wall thinning degrees of different layer vary after hydroforming, and is the largest for the inner layer and smallest for the outer layer. At folding stage, the wall thinning degree of the crown point increases lineally, and the difference among layers increases as the process going. The displacements of the crown point decrease from the inner layer to the outer layer. After springback, the U-shaped cross section changes to a tongue shape, the change of convolution pitch is much larger than the change of convolution height, and the springback values of the inner layer are smaller than the outer layer. An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase. With changing of process parameters, bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback. This research is helpful for precision forming of multi-layered bellows.

Laser shock hydroforming is a novel microforming method that adopts laser energy as the driving force and liquid as the medium to transmit pressure. The method combines the advantages of laser shock forming and micro hydroforming. Previous research has demonstrated that this method can deform thin sheets into complex shapes at high strain rates. We know that the formability of materials is improved at high strain rates, but experimental analysis on this method alone cannot examine the deformation process. Therefore, this study first conducted free- and die-forming experiments of laser shock hydroforming to characterise the features of the deformation process and understand the factors that may contribute formability enhancement. Experimental results were discussed to uncover the formability of thin sheets under different conditions, including the laser energy and the effect of the die. Then, a numerical model was established considering fluid–solid interaction. The deformation process, sheet velocity, contact stress and strain rate were investigated through numerical means, and these indicators explain the mechanism of formability improvement in this method. Furthermore, the numerical results indicate a positive phenomenon—pressure equalisation—which might be due to the reflection of pressure off the rigid side wall of the liquid chamber.

Sealing performance of standard rubber gaskets in the radial contact seal structure are observed through the experiment. A kind of profiled rubber gasket is proposed to replace the standard gasket. Leakage experiment and numerical simulation are carried out to study the sealing performance and failure mode of the profiled gasket. Several equations are presented to help analyze the failure reason. Results show that sealing performance of the profiled rubber gasket is more reliable than that of the standard rubber gasket. The failure reason of the profiled rubber gasket is that the friction force between the gasket external face and tube wall cannot balance the tube internal pressure. Dimension precision of the metal compressive ring has a great effect on the failure pressure.

In the present study, the mechanical model of section element in tube bulging area was established through the stress conditions of hydraulic bulging. Based on the mechanical model, the equivalent stress and equivalent strain equations of the section element in the bulging area were derived, respectively. Combined with the experimental data, the equivalent stress and strain of the section element in the bulging area were fitted by polynomial, and the plastic hardening model of thin-walled tube under pulsating loading was obtained. In order to verify the model precision, the plastic hardening models obtained from pulsating hydroforming and non-pulsating hydroforming were taken as the material model by finite element simulation respectively. The experimental results were compared with the simulation results which showed that as a pulsating hydraulic loading material parameters, the model established in this paper had higher precision.

Tube hydroforming (THF) is a process that makes use of fluid means to form the tubular samples into desired form. In the present work, two materials SS 304 and AA-1100 tube samples were heat-treated at various temperatures, viz., as-received, 150 °C, 200 °C and 250 °C to know their effect on the formability. Heat-treated samples were tested for the mechanical properties using universal testing machine, and the obtained results were utilized for carrying out the numerical simulations of THF process. Simulations were performed at various L/D ratios to attain various strain paths with different heat treatment temperature results. The effects of the aforementioned parameters on bulge height, internal pressure and FLD were investigated. The obtained results from both the materials through numerical simulations were validated by the analytical model. The simulation results were observed to be in good agreement with the analytical model.

Pulsating tube hydroforming with axial feeding is an effective method to improve the forming performance of thin-walled tube. A beneficial wrinkle can make the tube wall thickness more uniform and create a greater bulging height during forming process. The method of expressing the degree of wrinkle with geometrical and mechanical criteria is applied to distinguish the wrinkle types, and thus, the wrinkles can be divided into beneficial ones and harmful ones based on the deformation wrinkle features with different forming parameters. The wrinkling behavior in tube pulsating hydroforming with axial feeding was investigated in this article by experimental study, numerical simulation and theoretical analysis. The results showed that loading parameters had great influence on formability and wrinkling behaviors and that the beneficial wrinkles could be identified and used effectively by controlling the relation of wrinkling degree and forming parameters. Furthermore, the evolution processes of wrinkling behaviors in tube-bulging experiment were observed, the characteristics of wrinkling in every stage were analyzed and the relationship between wrinkling degree and forming parameters was established in the experiment.

Magnesium alloys have been known as the next generation material for lightweight body structures. Pulsating hydroforming is an effective method to improve magnesium alloy sheet forming performance, and the formed parts are characterized by lightweight, high-specific strength and stiffness. The deformation performance of magnesium alloy sheet AZ31B with a thickness of 0.6 mm under pulsating hydroforming has been investigated by means of experimental study, numerical simulation and theoretical analysis. The results show that under the same maximum hydraulic pressure, compared with simple linear loading, the magnesium alloy forming parts with pulsating hydraulic loading not only have better wall thickness uniformity and larger bulging height but also can delay the occurrence of fracture, improve the forming performance and ultimate the forming ability of magnesium alloy sheet. A new evaluation index is proposed to simplify the comprehensive forming performance of magnesium alloy parts with different amplitudes and frequencies more accurately, which can also be applied to determine the optimal forming parameters of magnesium alloy sheet AZ31B in the pulsating loading condition.

Due to the high requirements of drawing equipment and process, it is relatively rare in the field of aluminum alloy sheet forming to introduce soft or sticky fluid medias as soft mold into the course of hydroforming with a non-isothermal condition that maintaining the temperature of high pressure liquid differs to the ones of molds. Consequently, in this paper, the material stress-strain curve in the temperature range is obtained by the bidirectional tensile hot bulging test which contains compress to sheet’s thickness, and can best meet the characteristics of non-isothermal hydroforming in mechanics compared with unidirectional hot stretching. Based on analysis of stress-strain of 6061-T6 aluminum alloy, its constitutive equation on the basis of an original model of processing hardening rate is established for finite elements numerical simulation, and a highly accurate setting range of forming temperature can be confirmed to provide guidance for practical manufacturing accordingly. Result of the study suggests, by applying the constitutive model mentioned above, simulation on non-isothermal hydroforming can reach a desirable effect; The non-isothermal condition set reasonably causes an enhance to the junction of straight wall and round corner, and a deduce of thickness reduction rate simultaneously, limit height increases as a result. Besides, the fluency of blank located in the flange improves to a great extent when its temperature is well set. The position of the 1 mm wall thickness constant line of the workpiece is further reduced, so that the forming quality of the workpiece is remarkably improved.

High-performance aluminum alloy is light, has high strength, but is very difficult to be formed. In the forming process of aluminum alloy parts with special-shaped bottom, there are defects such as poor fittability accuracy, instability, and cracking at the complex bottom, and the forming accuracy is an important performance index to characterize the forming quality. In this paper, a precision warm hydroforming scheme of pre-bulging and deep drawing is designed, and a method of applying independent circumferential pressure on the periphery of the flange in the later stage of pre-bulging is proposed to maintain the shape of the bottom and improve the fittability accuracy. The effects of temperature difference and independent circumferential pressure on the wall thickness and fittability of the part are studied. At the same time, response surface method is used to study the interaction among pre-bulging pressure, liquid chamber pressure, and circumferential pressure, and the optimal forming conditions are obtained after optimization and compared with the test piece. The results show that independent circumferential pressure can significantly improve the ability of the bottom of the pre-bulged part to maintain the acquired shape, and the temperature difference can effectively improve the plasticity of the sheet, the depth of drawing, and the quality of the part. After optimization by response surface method, the minimum wall thickness of the part is 0.8013 mm and the fittability is 94.2%. The forming quality parameters of the test piece are in good agreement with the numerical simulation parts, which indicates that this simulation can effectively predict forming situation of the part, and provides scientific guidance for precision forming of complex-shaped bottom parts.

By combining the advantages of sheet hydroforming and multi-layer sheet deep drawing in wrinkling suppression, double-layer sheets hydroforming process was proposed. Different from the multi-layer sheet deep drawing, the two sheets are not bonded together, the upper sheet is introduced to eliminate the wrinkling defects occurred in the formed lower sheet. Therefore, how to determine the appropriate upper sheet is the key point in this process. Based on this, some investigations in selecting the appropriate upper sheet have been down, but the selection principle for the appropriate upper sheet is still ambiguous. To make clear this, in this paper, a semi-ellipsoid curved sheet part made of 2198 Al-Li alloy with an axial length ratio of 0.9 was chosen as the target part, by changing the thickness of the upper sheet (5A06-O aluminum alloy); the primary and secondary order of the anti-wrinkle ability and interfacial friction stress in suppressing the wrinkle defects were investigated and the selection principle for appropriate upper sheet is obtained.

Although fiber metal laminates (FMLs) were invented a few decades ago, large-scale manufacturing, especially the forming process of small and complex-shaped products, has not been matured yet. The forming difficulty comes with the limited strain rate of the fiber layers compared to the metallic layers. As a result, the conventional approaches to form FML parts are not very suitable. Understanding the material behavior during the forming process is critical to find a new technique for relatively intricate and smaller FML parts. The blank holder gap (BHG) is one of the effective parameters to control the material flow in the deep drawing process, but in the case of the FMLs, the situation is completely different due to the laminate constituent. The compression of the fiberglass and thermo-plastique resin to the blank holder force (BHF) is not the same as the metals. The resin acts like a rubber, which decreases the thickness of the laminate and affects the friction between the laminate layers, especially when forming semi-cured laminates, which makes it hard to define an ideal BHF. This paper presents the results of numerical and experimental investigation of the effect of the BHG on the hydromechanical deep drawing (HDD) of a cylindrical cup made with 2/1 Glare sheets. It is found that the optimized BHF and cavity pressure (CP) with a BHG of 1.1 mm, smaller than the laminate’s initial thickness of 1.2 mm, resulted in a good part with a significant depth improvement of 35 mm. Results also exhibited that FML parts manufactured by considering the BHG can enhance its applications and lead to a reduction of time and effort spent in mass production.

Plastic injection forming (PIF) is an alternative sheet metal forming method for complex geometrical parts with dimensions in low tolerance. This method is a combination of injection molding and hydroforming in which a molten polymer material has been injected over a sheet metal via a plastic injection molding machine. In this study, aluminum sheets 1.5 mm thick were shaped by PIF at various injection pressures, melt temperatures and injection speed. The effects of these parameters on the formability of the sheet metal were investigated using the experimental design technique. The thinning rate, flange radius and the hardness values of the shaped sheets were considered in the experimental study. Injection pressure was found to be the most effective parameter and melt temperature was the second degree effective parameter for the thinning rate. The usability of the PIF process in industrial applications as an alternative method was emphasized by comparing PIF with conventional hydroforming by means of the finite element method (Ls-Dyna). A 2.07 % deviation was observed between the FE results for hydroforming and the experimental results for PIF.

In this study, the cup part of fiber metal laminates (FMLs) was formed by a method which combines the semi-cured preparation and hydroforming processes. The FMLs in this research were produced by using glass woven fiber prepreg and aluminum 2024-T3. The process parameters were designed by Taguchi method, and the optimized parameters (3 mm pre-bulging height, 15 MPa cavity pressure, 4 MPa pre-bulging pressure and 1.15 mm clearance between blank holder and die) were obtained by range analysis. The part without defect can be obtained using the optimized parameters. The thinning rate of each layer, stress-strain distribution, and the failure modes were analyzed with experiments and numerical simulations. The results show that the middle layer has a great influence on the thinning, stress-strain distribution, and fracture modes in different directions. Numerical simulation can be used for predicting the thinning rate and fracture location. Small-size FML parts can be fabricated directly using the semi-cured hydroforming process, which can improve the production efficiency and expand applications of FMLs.

A modeling setup based on the cellular automata (CA) method was developed to model the kinetics of static recrystallization (SRX) in hydroformed steel tubes undergoing the annealing process. In addition, the impact of multiaxial deformations on the kinetics of SRX within the hydroformed steel tube was investigated. First, hoop and axial strains developing at the pole of the steel tube during hydroforming were obtained from the digital image correlation measurements. Then, an exact analytical solution was employed to calculate the corresponding hoop and axial stresses at the pole of the bulged tube. Using these biaxial stress–strain curves, the stored energy was calculated for the hydroformed tube specimen. Second, the actual grain topology and crystallographic orientation of grains in the deformed specimen were obtained with the electron backscatter diffraction. Third, the calculated stored energy as well as the microstructural and crystallographic data was incorporated into the CA model as initial conditions to predict the kinetics of SRX in the specimen during annealing. Finally, to assess the accuracy of the CA model, experimental and predicted results were compared in terms of grain topology data including the grain size and aspect ratio distributions, as well as the rate of recrystallization during annealing. A reasonable agreement between the experimental and CA predictions in partial and fully recrystallized specimens was achieved inferring the validity of the developed algorithm and the modeling setup to predict the SRX kinetics during the post-tube hydroforming annealing process.

The microtube hydroforming process is a new type of micro forming technology developed based on the traditional tube hydroforming technology. The micro hollow components with complex shapes can be manufactured with metal micro tubes using micro tube hydroforming process. Although some researches have reported the relative research results such as the design of the experimental equipment etc., the microparts produced with the micro tube hydroforming process has the problems of the non-uniform of wall thickness, low bulge height as well as the high failure rate of the forming process. In the current study, FEM simulation of the micro cross shape tube hydroforming process of the micro SUS304 stainless steel tube with a commercial code was carried out. The availability of the FEM simulation model was verified by comparing the maximum bulge heights obtained in the test and simulation. The influence of the deformation parameters of the micro tube hydroforming process on the deformation behavior of the micro SUS304 stainless steel tube were studied by FEM simulation. The internal pressure loading path, the axial feed loading path and the friction coefficients of 0.05 were conducted. The results show that the more uniform thickness distribution and the bigger bulge height of the cross shape part were obtained with the optimized internal pressure loading path and the axial feed loading path.

In the present work the relationship between deformation and deformation induced surface roughness of 100 micron thick annealed AISI 304 stainless steel was investigated at the meso scale. This work is a continuation of the previous work by the authors where roughness values were determined at the apex of the bulge test samples at micro scale. The apex is believed to be the region of highest stress and strain in a typical bulge process in a circular die. The material was deformed using a biaxial bulge test through hydraulic fluid pressure. The strains on the workpieces were measured with respect to the forming pressure. The surface roughness was measured by scanning the interior (concave) area of bulge with Bruker GTK-17 optical profilometer over an area of 1.3mm x 1mm. The results show linear relationship between roughness and deformation strain, and it establish a similar trend with roughness measured at micro scale.

Tube hydroforming is an advanced metal forming processes, which is widely used to form various tubular parts. Axial feeding is usually used to avoid excessive thinning in hydroforming of a variable-diameter part. However, wrinkling defects are susceptible to occur easily under the axial loading if the wall thickness of the tube is small. A new method was proposed to enhance the expansion ratio and improve the thickness distribution for hydroforming of thin-walled spherical parts using overlapping tubular blanks. A special loading tool was created and AISI 304 stainless steel blanks were used for the experimental research. The effects of blank shapes and normal constraints were studied on wrinkling defects of the overlapping blanks. The results show that wrinkling defects at the inner layer of the overlap are prevented by using curved-edge blanks. Wrinkling defects at the outer layer of the overlap is eliminated by using normal constraints. Finally, a sound thin-walled spherical part was obtained by using an overlapping tubular blank. The maximum expansion ratio is 60% and increased by 30.2% compared with that of conventional hydroforming using a closed cross-sections tube. The maximum thinning ratio was 32.4%, which was decreased by 29.3%. In general, it is feasible to use an overlapping blank to form a variable diameter part. The maximum expansion enhances significantly and the thickness distribution improves apparently.

The different branch diameter of five-way tube affects the design of loading internal pressure in the hydroforming process, where the large-diameter branch is broken more easily than the small-diameter one due to the same ultimate stress of tube material in one-step forming method. Therefore, the first four-way and then five-way of multi-step forming (FFTF) method and the first three-way and then five-way of multi-step forming (FTTF) method were proposed to fabricate the 5A02 aluminum alloy five-way tube with two kinds of branch diameters to avoid the burst of large-diameter branch tube. The finite element simulation of five-way tube hydroforming process shows that the height of small-diameter branch tube is lower and serious wrinkles appear at the large-diameter branch tube in the one-step forming and FFTF method. By optimizing the length of punch, a five-way tube with a big branch height and uniform wall thickness was obtained with the FTTF method. The approach of lengthening the punch in the experiment increased the height of formed branch and reduced the wall thickness reduction rate of five-way tube in FTTF method. Overall, the findings mentioned above can not only offer guide in creating five-way tube with excellent quality, but also be taken as reference to the hydroforming studies on multi-way tube in the future.

Tube hydroforming (THF) technology is widely applied, especially in the automotive and aircraft industries. Material characteristics of tubular workpieces should be evaluated in terms of bending and THF processes. A mathematical model, which combines the assumption of elliptical contour of a bulged wall and the prediction equation of wall thickness, is provided to analyze the THF process and to obtain the strain-stress relationship of tubes. Material characteristics of a DC04-welded tube is obtained by using a self-designed THF test machine. Considering the effects of pre-work hardening, we discuss the material strain-stress relationships of the tube and original sheet blank. An approximate determination method is proposed to obtain the stress-strain curve of the tube by using the curve of the original sheet blank and the hardness of the tube and sheet blank. A suitable constitutive equation with pre-work hardening is applied to the DC04-welded tubes through simulation and experimental methods.

Thermo-hydroforming (THF) process is a single-step process for thermoplastic composite forming, which has a great advantage in terms of the process time and mass production potential as compared to conventional processes. However, with THF processes, wrinkles and deformations are easily generated due to the process characteristics and process parameters. In this study, the matrix material was examined by considering viscoelasticity and changes in formability according to the forming speed. A numerical analysis of the THF composites was performed based on the preferred fiber orientation (PFO) analysis model, which considers the viscoelasticity of the matrix. The deformation change and molding possibility were examined according to various forming speeds. The viscoelastic PFO model showed better analysis efficiency and stability than the primitive PFO model. This analysis will help improve the process of forming thermoplastic composites.

This paper presents the research results on mathematical modeling and forming simulation in sheet hydroforming (SHF) process of a hollow spherical part from AISI 1010 steel. The paper used Deform 2D software for the simulation process. The results are intended to evaluate the influence of the process parameters such as forming pressure q (55 MPa, 60 MPa, 65 MPa, 70 MPa), die radius R (9 mm, 12 mm, 15 mm), coefficient of friction f (0.08, 0.10, 0.12, 0.15, 0.2) on the degree of thinning of wall thickness ΔS. Based on the research results allow to determine the reasonable process parameters that improve the degree of thinning of wall thickness in SHF process of a hollow spherical part for the parts of space shape.

The positive displacement motor is currently the most widely used downhole power tool. In order to reduce the cost of drilling and exploration, small boreholes have been used to replace conventional boreholes. The working conditions are complex, so a high-performance positive displacement motor for micro-holes is required. In order to solve the problem of the difficulty in processing the inner spiral surface of the small size and large aspect ratio, the tiny size spiral tube stator is proposed in this paper and the normal temperature and hot state hydroforming of the small size spiral tube is proposed in this paper. The material is 42crmo, and the uniaxial tensile test is carried out at different temperatures. According to the material mechanical properties experiment and the forming process, the finite element model of the hydroformed spiral tube at different temperatures is established. The study found that the suitable tube size is 48mm in outer diameter, 5.5mm in wall thickness, and 1405mm in length. When the processing temperature is 700℃, the hydraulic pressure required for full expansion of the spiral tube is only 70MPa, and the rebound of the spiral tube is very small. The minimum wall thickness is the maximum of 4.31mm, and the maximum wall thickness is the minimum of 5.356mm, and the wall thickness distribution is relatively uniform. The maximum plastic strain of the spiral tube is 0.65, so the damage to the material during the forming process is small, and when the processing temperature is 700℃, the quality of the spiral tube is better.

Stress states on a multi-branch tubular part are the most complicated change in all types of hydroforming process, which result in severe variation of thickness. In this paper, an experimental and numerical research was conducted on a multi-step hydroforming process including intermediate annealing treatment to obtain effect of stress state on the thickness variation of a superalloy GH4169 complex T-shaped tubular part with expanded diameter, which corresponds to a real product used in aerospace industry. The material flow behavior at typical points on hydroformed tube blank was first analyzed. Then, the thickness variation on the hydroformed GH4169 tube blanks was discussed in every step. It is shown that the materials have different flow directions to form the side branch, where the thickness is always thinned during the four-step hydroforming process. Large axial feeding induces a continuous thickening between transition areas and tube ends. The thickness invariant dividing line in the side branch zone moves toward the tube ends with forming going on. However, in the hemisphere zone, it moves slightly towards the center of the side branch. Moreover, the stress states at three typical positions, as well as their effect on the thickness variation, were analyzed based on a sequential correspondence law between stress and strain components. On this basis, the mechanism of thickening in the left transition area, thinning at the top of side branch and thickness variation at the hemispheric pole was revealed. These results are very important for obtaining the thickness distribution of a complex T-shaped tubular part in multi-step hydroforming, and revealing the thickness variation mechanism by using engineering plasticity theory.

Forming complex sheet products using hydrostatic forming technology is currently a focus of the majority of forming processes. However, in order to increase stability during the forming process, it is necessary to identify and analyze the dependency of the forming pressure and the quality of a product on input parameters. For the purpose of modeling the forming pressure, this paper presents empirical research on the product of a cylindrical cup made of various materials, including carbon steel (DC04), copper (CDA260), and stainless steel (SUS 304) with different thicknesses (0.8 mm, 1.0 mm, and 1.2 mm), under a defined range of binder pressures. The regression method is selected to formulate an equation that shows the relationship between the input parameters, including the materials (ultimate strength and yield stress), workpiece thickness, binder pressure and the output parameter, and the formation of fluid pressure. The mathematical equation allows us to determine the extent of the effect of each input on the forming pressure. The experimental results can be used for the easier planning and forecasting of the process and product quality in hydrostatic forming.

Purpose This paper aims to study frictional characteristics of thin-walled tubes in the liquid impact forming (LIF) process. Design/methodology/approach LIF experiments under various impacting velocities were performed on SUS304 stainless steel tubes with various guiding lengths on a custom-designed measurement system to investigate the effects of impacting velocity and guiding length on the coefficient of friction (COF) in the guiding zone. Findings The results indicate that the COF changes dynamically in the guiding zone and decreases with the deformation process. The reduction range of the COF is wider in LIF than in both the conventional and pulsating hydroforming (THF), which may be contributed to the impacting velocities in a short time. Moreover, the COF decreases faster in the first half of the LIF process than in the second half. Under different impacting velocities and guiding lengths, the decreasing rate of the COF in the first half is more sensitive and obvious than that in the second half. Originality/value A method for determining the COF in the guiding zone in LIF is proposed and the frictional characteristics in LIF are studied. Comparing the COF of tubes in conventional THF, pulsating THF and the LIF process is valuable for improving and predicting the tubular formability in various hydraulic environments for industrial production. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0269

Liquid impact forming (LIF) is a new type of composite forming method based on tube hydroforming (THF) and stamping forming. It has high efficiency and low energy consumption, with no need for external pressure source, so LIF has good development prospect and application value in the field of lightweight and integrated manufacturing. In order to investigate LIF technology, the generation mechanism of the internal pressure was analyzed in this paper. Firstly, based on the theory of the liquid volume compression, the change law of the cavity volume of metal thin-walled tubes was analyzed according to size parameters of the tube and dies during the forming process. The mathematical relationship between the internal pressure in the tube cavity and clamping parameters (clamping speed and clamping height) was obtained under the impact load. Then, the theoretical maximum internal pressure Pmax1 was discussed under different die cavities. Furthermore, the relationship between the internal pressure in the tube and the clamping time under different die cavities with a same clamping speed was obtained according to the transient dynamic analysis by ANSYS Workbench. At the same time, the simulated maximum internal pressure Pmax2 and the calculational maximum internal pressure Pmax were acquired under different die cavities. In addition, the LIF experiments were performed using a simple and suitable device to verify the calculational maximum internal pressures under die cavities with different side lengths. Through the comparison of the calculational and experimental maximum internal pressures, it is not difficult to find that the values of both showed a good agreement and the maximum deviation is 10.27%. The research results indicate that the theoretical equation of internal pressure of metal thin-walled tubes based on LIF is reliable, and it will lay a good foundation for further study.

To solve the drawbacks of thinning and poor thickness uniformity in tube hydroforming, a novel method known as axial hydro-forging sequence was developed. In this method, the deformation zones will be subjected to compression deformation throughout the hydro-forging stage to decrease the thinning and improve the thickness distribution compared with the traditional tube hydroforming. To verify the feasibility of this method, experiments and finite element simulations were designed and conducted. Subsequently, the effects of the internal pressure, friction, and reduction on thickness distribution were investigated. The results indicated that the thinning ratio can be decreased significantly by compression deformation. And the thickness of the deformation zone increases with increasing reduction. Furthermore, the thickness uniformity can be improved by a thickness “self-uniformity” in the hydro-forging stage, which was attributed to the von Mises stress distribution. It is demonstrated that the thickness distribution is related to the friction coefficient, but has little dependence on the internal pressure. Experimental and simulation results show that axial hydro-forging sequence is practicable to produce the variable-diameter tube.

The formability of 1 mm thick AA5182 aluminum alloy sheets in deep drawing of square cups by hydroforming was studied. The influence of process parameters (peak pressure, pressure path, and blank holding force) on formability was investigated through numerical simulations and validated with experimental work. The experiments were designed using the Taguchi method. The minimum thickness in the formed cups (at the bottom corners) and the minimum corner radius that can be achieved were considered as the criteria for evaluation of formability. The peak pressure was the most important process parameter affecting thinning and the minimum corner radius that can be achieved. The variation of the pressure path had the least effect on formability. Regression models were developed for prediction of minimum thickness in the cup and the corner radius as a function of peak pressure and blank holding force.

To overcome the problems in forming the variable-diameter tubes by tube hydroforming, such as excessive thinning and high internal pressure, a new approach named axial hydro-forging sequence was proposed. In this approach, the tube was expanded to fill the die cavity firstly and then the thinning ratio was reduced by axial compression deformation produced in axial hydro-forging sequence. To demonstrate the feasibility of this approach, two mechanical conditions were theoretically analyzed in this study include axial hydro-forging condition and deformation sequence. Based on the plastic energy method, a critical wrinkling model for axial hydro-forging sequence was established to calculate the critical wrinkling internal pressure. It was observed that there was a critical wrinkling internal pressure in the axial hydro-forging sequence, and the critical wrinkling internal pressure increased with increasing the tube axial shortening and material strength coefficient, but decreased with the increase of strain hardening coefficient. At the same time, an analytical model based on mechanical analysis was developed to discuss the deformation sequence for different deformation zones. The results showed that the deformation sequence of the three characteristic zones in the process was as follow: maximum diameter zone > transition zone > guide zone, which satisfied the requirement of reducing the thinning ratio. Finally, experiments along with the finite element simulation were performed to validate the analytical model, and effects of key process parameters on tube forming were revealed. As a result, variable-diameter tubes were successfully produced by this approach, which indicated that the axial hydro-forging sequence is a feasible forming approach for the fabrication of tubes with variable diameters.

The automobile exhaust manifold regularly has a multi-valved shape that used to be formed by the combination of stamping and welding. The current study intended to investigate and develop a tube hydro-mechanical forming (THMF) process to form an integral automobile exhaust manifold that has the characters of large deformation and small corner. It included three stages such as pre-forming stage, die-forming stage, and calibration stage. In addition, the non-feasibility of one-step hydroforming process was proved by FE modeling and experimental for the target component. An optimal loading path was obtained through the principle of dichotomy for pre-forming stage and die-forming stage, corresponding to the maximum thinning ratio of 19.7% and 13.27% respectively. The variation of stress and strain states were analyzed for the whole process. As a consequent, the thickness distribution exhibited a V-shaped along axial direction at each stage, while a fluctuated distribution after die-forming was presented along radial direction in the multi-valved area. For the final component, a maximum thinning ratio of 28.53% and the large deformation above 60% obtained from FE modeling kept a reasonable agreement with that achieved from experiments. It showed that THMF has advantages of not only decreasing the internal pressure but also improving the formability of tube.

This work presents an experimental study of aluminum sheet forming. It shows the performances of a steam hydroforming process. The new forming technique is based on both temperature and pressure to make a sheet form. These parameters are linked to the water vaporization process into a cavity covered by the blank. The performances are deduced by comparing the results obtained from the steam tests with those acquired at room temperature. Performances are expressed in terms of forming loads, surface creation, and forming limits. The experimental results show that the use of the steam temperature as a factor could decrease the limit loads necessary for the forming operation and increase the surface creation. On top of improving forming loads and surface creation, increasing steam temperature induces a clear improvement of forming limits.

Aluminum composites have been widely used in a variety of applications requiring high strength levels and low weights. This paper proposes an innovative hydroforming process for the manufacturing of wire-reinforced aluminum tubes. To characterize the proposed hydroforming process for the manufacturing of wire-reinforced tubes (WRTs), a finite element (FE) analysis was conducted with various combinations of wires. The reinforcement effects of the WRT were verified according to the number of reinforcing wires and their diameters. Based on the equivalent plastic strain and tube wall thickness values of the inner tube as derived via the FE analysis, appropriate loading paths for hydroforming experiments were derived according to various combinations of reinforcing wires. Through hydroforming experiments, WRTs without process-induced defects such as insufficient bulging, wire buckling, and tube bursting were successfully obtained. To estimate the mechanical performance of the WRT when under a load, the structural strength was experimentally evaluated through a lateral three-point bending test. The measured structural strength values demonstrate the superior reliability and applicability of the WRT manufactured in this study.

Graphical abstract, Highlights • The mechanical behavior of AA2060 was investigated under HSR deformation and at room temperature. • A novel gripping method was designed to prevent the distortion of strain waves during HSR experiments. • The ductility of AA2060 was enhanced due to the adiabatic softening and inertia effect. • The fracture behavior of AA2060-T8 was changed from brittle to ductile behavior under HSR deformation. • Johnson-Cook constitutive model was modified to predict the dynamic flow behavior of AA2060-T8., Since AA2060-T8 was introduced in the past few years, investigating the mechanical response, fracture mechanisms, and anisotropic behaviour of AA2060-T8 sheets under high strain rate deformation has been crucial. Thus, uniaxial tensile tests were performed under quasi-static, intermediate, and high strain rate conditions using universal testing machines as well as split Hopkinson tensile bars. The experimental results showed that the ductility of AA2060-T8 sheets was improved during high strain rate deformation because of the adiabatic softening and the inertia effect which contribute to slow down the necking development, and these results were verified by the fracture morphologies of high strain rate tensile samples. Furthermore, the strain rate hardening influence of AA2060-T8 was significant. Therefore, the Johnson–Cook constitutive model was modified to consider the effects of both strain and strain rates on the strain hardening coefficient. The results obtained from the improved Johnson–Cook constitutive model are in remarkable accordance with those obtained from experimental work. Thus, the improved Johnson–Cook model can predict the flow behavior of AA2060-T8 sheets at room temperature over a wide range of strain rates. The results of the present study can efficiently be used to develop a new manufacturing route based on impact hydroforming technology (IHF) to manufacture sound thin-walled-complex shape components from AA2060-T8 sheets at room temperature.

Aiming at the problem about misjudging sheet fracture in hydroforming process, the different mechanisms between drawing and hydraulic bulging are analyzed. In this paper, a method to test the forming limit diagram (FLD) based on uniform load in thickness direction is adopted by using laminated plate hydroforming, and the quality of hydroforming process is judged more accurately. By the numerical simulation analysis, the shape of the specimen on five different linear paths is preliminarily determined, and the forming limit diagram of the sheet is obtained under the stretch-compression condition. At the same time, the influence of method of lubrication such as non-lubrication, oil, grease, and thin film on FLD is analyzed. The results show that the first principal strain and the second principal strain increase, and the bulging height decreases with the decrease of friction factor. Among them, the friction factor of thin film is reduced to the lowest. In the process of laminated sheet hydroforming, the thin film lubrication between pieces is more relatively accord with the experimental condition of stretch-compression bulging, and the FLD is more reliable to judge the quality of component formed by hydroforming.

Tube hydroforming (THF) experiments were performed on TP2 copper tubes under different loading velocities and fluid velocities using a self-developed measurement system to investigate dynamic frictional characteristics in the guiding zone. The results show that the coefficient of friction (COF) dynamically changes during forming experiments and decreases with tube deformation. The average descending rate and amplitude of the COF increase with increasing loading velocity. Microscopically, the micro-protrusions on the tubular surface are flattened, and the surface scratches are finer and more uniform, as the loading velocity increases, resulting in a decrease in COF. At the same external loading velocity, the COF increases with increasing fluid velocity and is also extremely sensitive to it. Moreover, improving and predicting the formability of such tubes by accurately adjusting and controlling fluid velocity in THF is valuable and critical for the future.

During hydroforming of Al alloys, cracking often limits the production of specific frames for next-generation transportation vehicles. In this study, microstructural evolution and cracking behavior of an extrusion welded aluminum alloy blank tube were characterized to uncover the failure mechanisms during hydroforming process. Electron back-scattered diffraction, transmission electron microscope, and scanning electron microscope were employed to characterize the grains, textures, and local micro-crack sites. Experimental results demonstrated that grains in the welds region were significantly larger than those in the neighboring regions. Along the weld region, large grains typically with high-misorientation with respect to neighboring grains were identified as the preferred crack nucleation sites. Plastic incompatibility due to preferential yielding in the larger (softer) grains as compared to the surrounding finer (harder) grains is postulated as the origin for local strain localization that leads to cracking in the weld regions during hydroforming.

It is necessary to fabricate individual dies in conventional hydroforming, to produce different tubular parts. This procedure is costly and time-consuming. Tube multi-point hydroforming is a new flexible forming technology which facilitates producing various tubular products by only one die. In this study, a new reconfigurable hydroforming die was designed and fabricated. The main difference of this die with conventional types is substitution of the rigid surface with a set of spaced pins. Different tubular sections could be produced by adjusting the pins position. Due to the low cost of changing the tool into a new die, this process is appropriate for producing small batch numbers of a tubular product. Numerical simulations were employed to determine the effects of pin diameter and polyurethane layer thickness on the characteristics of final products. Increasing the number of pins was found out to improve dimensional accuracy and surface quality. On the other hand, while using a thicker polyurethane layer reduced dimpling, it led to a poor dimensional accuracy. A bulged and a square brass 70/30 tube were produced with an initial thickness of 2 mm. Thereafter, experimental tests were performed to compare distribution of the thickness and variation of dimensions with the numerical results.

Reinforced s-shaped bellows is a kind of typical reinforced metal bellows that can withstand high pressure. Hydroforming process and its simulation technology of reinforced s-shaped bellows were investigated in this paper. The hydroforming technology of reinforced s-shaped bellows is a severe plastic deformation process. Most area of the bellows is in the state of severe plastic yielding with a maximum equivalent plastic strain of 30.6%. At the same time, the wall thickness shows a linear thinning trend from wave trough to peak. The control of hydraulic pressure is a key factor of hydroforming process. The best hydroforming hydraulic pressure is 12 MPa, which is in good agreement with the designed shape. At last, the key factors affecting plastic strain and wall thickness thinning of the hydroforming process were revealed. Plastic strain and wall thickness thinning of the large-pitch bellows in the hydroforming process are obviously higher than those of the small-pitch ones. The waveform parameters directly affect the hydroforming process. However, the influences of initial wall thickness and number of layers of the bellows were not obvious. The maximum thinning rate of the bellows basically maintains around 20%.