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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.

In this study, the hydroforming process parameters of a bi-layered X-type tube are designed and optimized by exploring the response surface methodology. First, UG software is used for model setup of the bi-layered X-type tube and mold, which is imported into DYNAFORM software for further numerical simulation and calculation of the hydroforming process. The main parameters of the loading path are selected as experimental factors for the methodology. The maximum thinning ratio of the inner and outer tubes, the maximum clearance between bi-layers, and the limit fillet radius of the top branch tube are used as test evaluation indicators. In accordance with effective evaluation indexes, perturbation plots, optimization evaluation criteria, and contour graphs, the relationship among the main influencing factors is analyzed and the process parameters of the optimal loading path are screened. Finally, a comparison between experimental results and simulation is made and shows that the error is within 6%, which indicates that the optimization method of the hydroforming process parameter in a bi-layered X-type tube has high feasibility.

Growth and advancement in modern technologies and requirement of miniaturized parts in various field of manufacturing has attracted several micro fabrication processes. Advancements in micro manufacturing has grown tremendously and development in micro metallic parts are very much welcomed due to the high demand of micro parts by manufacturing industries for their ability to withstand difficult working conditions. With the miniaturization of parts and process, the so-called size effects influence the micro manufacturing process. Different categories of size effects, their nature of involvement during downscaling and their effects are discussed in this article. Influence of size effects based on materials used, process conditions, downscaling and other parameters affecting the production of micro parts especially focusing on micro hydroforming process and micro deep drawing process are studied through literature and discussed in detail.

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.

A new generation of fluid pressure forming technology has been developed for the three typical structures of tubes, sheets, and shells, and hard-to-deform material components that are urgently needed for aerospace, aircraft, automobile, and high-speed train industries. In this paper, an overall review is introduced on the state of the art in fundamentals and processes for lower-pressure hydroforming of tubular components, double-sided pressure hydroforming of sheet components, die-less hydroforming of ellipsoidal shells, and dual hardening hot medium forming of hard-to-deform materials. Particular attention is paid to deformation behavior, stress state adjustment, defect prevention, and typical applications. In addition, future development directions of fluid pressure forming technology are discussed, including hyper lower-loading forming for ultra-large non-uniform components, precision forming for intermetallic compound and high-entropy alloy components, intelligent process and equipment, and precise finite element simulation of inhomogeneous and strong anisotropic thin shells.

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.

Biconvex tube is prone to problems such as severe wall thickness reduction or wrinkling in hydroforming due to the big diameter-thickness ratio and large expansion ratio. In this paper, the segmented dies were employed to manufacture the biconvex tube, and the forming performance of the part under different loading paths was simulated by ABAQUS/Explicit software, then the corresponding results were obtained. The influence of loading path–related factors on the formability of the biconvex tube was analyzed by the response surface method. Based on the optimization evaluation criteria, the predicted loading path was determined to be linear loading, and the maximum axial feeding was 13 mm and the maximum internal pressure was 89 MPa.

Tube Hydroforming is one of the most effective manufacturing processes used in modern times since it satisfies the current robust requirements of the manufacturing industry. It finds enormous applications in the automobile and aerospace sectors owing to the inherent advantages over conventional forming processes, like consumption of less material with no compromise on the part strength. Complex geometries can be developed with high accuracy in less number of manufacturing stages, which would, in turn, reduce the overall manufacturing cost. Such an ability of this process to fabricate products with high strength-to-weight ratios at economical costs make it energy-efficient and it does push a step further towards sustainable and modern innovative manufacturing. This paper presents the development of a detailed nonlinear finite element model for the tube hydroforming process that uses Abaqus/Explicit as a computational tool. Elastic-plastic material constitutive behavior is defined using a flow-stress equation, and the Arbitrary Lagrangian-Eulerian technique (ALE) is used to determine the material flow. Input parameters like applied pressure, initial tube thickness, and die-corner radius are considered against output parameters like formed tube thickness, final part dimensions, and stress concentration. The developed model is validated with a previously published literature by Rakesh A. Shinde et al. (2016), and the results are found to agree for the case of percentage of thickness reduction. Following the work done by Rakesh A. Shinde et al., three different numerical cases are created with different die corner radii and tube thicknesses, for 3 different internal pressure values, viz., 41 MPa, 43 MPa, and 45 MPa. The results obtained in the paper are first replicated, and the research is further extended for different loading/unloading rates and peak load holding times (loading paths). Results indicate the sufficiency of only lower loads to produce the required formability. Accordingly, simulations are also performed for cases of lower pressures. Results show that accurate part dimensions at much lower stress concentrations could be obtained at lower values of pressure. The presented work also looks into the optimisation of the process using a well-established DOE technique – Response Surface Methodology. Accordingly, a multi-objective optimisation is performed, considering 20 simulations for the cases of three parameters and three levels. The significant influencing parameter is also identified.

Advanced forming technologies have been evolving at a rapid pace with the products applicability in the industrial fields of aerospace and automobile especially for the materials like aluminum and titanium alloys (light weight) and ultra-high strength steels. Innovative forming methods like hydroforming (tube and sheet) have been proposed for industries throughout the world. The ever-increasing needs of the automotive industry have made hydroforming technology an impetus one for the development and innovations. In this paper, the review on various developments towards lightweight materials for different applications is presented. The influencing process parameters considering the different characteristics of the tube and sheet hydroforming process have also been presented. General ideas and mechanical improvements in sheet and tube hydroforming are given late innovative work exercises. This review will help researchers and industrialists about the history, state of the art in hydroforming technologies of the lightweight materials.

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.

In the present study, the Johnson-Cook damage model is proposed as a comprehensive damage criterion to predict all types of probable failures in tube hydroforming process. Also, the Johnson-Cook material model is used to predict the profile of hydroformed tubes and their dimensions. The validity of numerical results was verified using experimental results obtained in this study. Moreover, because of the importance of friction force in this process, existing between the tube and die, the friction coefficient is determined using the ring compression test, separately. The comparison of experimental and numerical results shows that Johnson-Cook damage model can predict all of the possible failures in tube hydroforming process correctly, both in terms of location and loading conditions. And this model does not predict any failure if, the tube is hydroformed perfectly. Additionally, it was cleared that the Johnson-Cook material model is a proper model to predict the profile of hydroformed tubes with remarkable accuracy. Also, it was found that the loading path and creation of a proper wrinkling have a determinative and vital role in the prosperity of the process.

In this work, a hydroforming analysis of an exhaust pipe clamp adaptor made of galvalume steel was performed. Deformation and failure of galvalume exhaust pipe connectors and its coatings via the hydroforming process were studied. An explicit type (LsDyna) numerical analysis approach was adapted for the development of the hydroforming process. Pressure rate, unconstraint length, residual stress, strain hardening, and spring-back effects were considered in the analysis. The failure of tubular parts was evaluated via a forming limit diagram (FLD) according to Hill- Swift criteria. The hydroforming process was developed according to three models, which are found in the safety forming region of FLD studies. Minimum thickness values obtained from the experiments were compared with finite element analysis (FEM). The maximum percentage thinning ratio in the tubular section was more than 18 - % at 65 MPa internal pressure. The relationship between thickness reduction at plastically work hardening regions and residual stress was discussed. The deformation characteristics of the produced connector headers were also analyzed by scanning electron microscopy (SEM) and micro Vickers hardening measurements. The FEM analysis and FLD examination indicated that the failure did not occur in hydroformed specimens, whereas damage was observed at coated’ plastic work regions through microscopical investigation.

In the recent years, the demand for weight reduction in modern vehicle construction has led to an increase in the application of hydroforming processes for production of automotive and aerospace lightweight components. The tube hydroforming measurement site (TH stand), designed and built at Warsaw University of Technology allows both die, and free tube hydroforming processes to be performed, thereby making it possible to obtain information about the material, as well as optimal process parameters [1][2]. The present freshly patented method for metal tube hydroforming is dedicated to short product series or even single products and prototypes [3]. The method is applicable to forming difficult-to-machine materials. The well-known techniques use dies made of plastic or wood, especially to form short product series. The use of moulding sand and properly prepared geometry of casting mould makes possible shaping materials at high temperatures, which could not be done in previous short series solutions, where a plastic or wooden die were used. [1] Sadlowska H., Jasinski C. Morawinski Ł., Strain measurements on the tube hydroforming testing machine, Archives of Metals and Metallurgy Vol. 65 , Issue 1, 2020, pp. 257-263 [2] Sadlowska H., Odksztalcanie sie rur podczas swobodnego rozpeczania hydromechanicznego na stanowisku TH, w: Prace Naukowe Politechniki Warszawskiej. Mechanika, Vol. 267, 2015, ss. 25-30 (in Polish) [3] Patent No. PL424401, Kochanski A., Sadlowska H., Bulletin of the Patent Office of Inventions and Utility Models vol. 17_2019, pp. 11

In recent years, hydroforming has clearly expanded its range of industrial applications due to the growing interest in products which combine high strength with low weight. A current limitation of this technology was its economically justified production volume since the costs of producing tools eliminates the possibility of using hydroforming technology in prototype and single part production. The paper presents a freshly patented solution that allows for single part hydroforming. The new technology combines traditional hydroforming machines with a new approach to tool production. The new rapid die is made quickly and cheaply. The use of materials known from the production of foundry moulds causes the die to deform during hydroforming, but it is a controlled deformation. Thanks to the use of numerical modelling, the deformation of the mould cavity is predicted and taken into account at the design stage. The article presents important issues that need to be considered in the design of this innovative process.

In order to manufacture the double-stepped tube with large expansion ratio, a multistage axial hydro-forging sequence was proposed by combination of hydroforming with movable dies in this paper. The new forming process is divided into four stages. In the second stage, hydro-forging stage, the thickness will be increased and the thinning ratio will be decreased due to the axial compression deformation, then the forming capacity of the tube will be improved. Experiments and finite element simulation were conducted to verify the feasibility of the proposed multistage axial hydro-forging sequence process. Experimental and simulation results showed that double-stepped tube with large expansion ratio can be produced with movable die design. At the same time, a better thickness distribution could be achieved. This investigation demonstrates that multistage axial hydro-forging sequence is a potential forming approach for manufacturing of large-expansion-ratio double-stepped tubes with high reliability. Keywords: Multistage axial hydro-forging sequence, Double-stepped tube, Large expansion ratio, Aluminum alloy

Metal bellows are widely used in piping systems, aerospace, automobile and other industries due to their favourable properties including absorption of expansion, light weight and flexibility. In this paper, the fittability was presented to evaluate the convolution shape precision of the metal bellows. By establishing a finite element model of bellows hydroforming process during the bulging and forming stages, the influence of internal pressure, axial feeding and feeding loading path on the wall thickness variation and fittability of one-convolution bellows was investigated. On that basis, the hydroforming process of multi-convolution bellows was studied, and an experiment was carried out. The results showed that with the increase in internal pressure, the wall thickness of the bellows thinned overall, and the fittability of the root zone of the bellows gradually deteriorated. Some region near the crown zone did not fit the dies well when the internal pressure is small. To improve the fittability of the bellows, the actual axial feeding should be a bit less than the theoretical axial feeding. It is of importance in developing the hydroforming technique and improving the hydroforming quality of bellows.

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.

Producing non-uniformly curved tubes with sharp corners using the common experimental methods in hydroforming process is difficult. A common approach is to increase the internal pressure as high as possible; which may lead to excessive thinning and fracture on the corners of the tubes. To manufacture this type of tubes, the current study has proposed a new hydroforming die to perform such a process by taking two general steps: initial bulging and forming. The proposed die facilitated with two movable bushes is able to produce bended stainless steel tubes with non-uniform curvature and cross-section. To find the optimum pressure and axial feed profiles, finite element simulations were performed, and the results were validated with experiments. The main advantage of this die is that by moving the bushes inside the die cavity, the friction between die and bushes can be reduced considerably while axial feeding is provided properly, leading to produce a tube with a uniform thickness distribution and maximum achievable corner filling.

Tube hydroforming (THF) is a frequently used manufacturing method in the industry, especially on automotive and aircraft industries. Compared with other manufacturing processes, THF provides parts with better quality and lower production costs. This paper proposes a design approach to estimate the T-shaped THF parameters, such as counter force, axial feed, and internal pressure, through finite element (FE) and artificial neural network (ANN) modeling. A numerical database is built through Taguchi’s L27 orthogonal array of experiments to train the ANN. The micromechanical damage model of Gurson-Tvergaard-Needleman is used with an elastoplastic approach to describe the material behavior. This study aims to find the combinations of THF parameters that maximize the bulge ratio and minimize the thinning ratio and wrinkling. The numerical results obtained by the FE model show good correlation with the results predicted by the ANN.

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 (THF) technology is mostly used in automotive and aerospace industries because of its benefits like high precision, less weight and forming capability of complex shapes. F...

Tube Hydroforming (THF) process is widely used in the aerospace and automotive industries. The success of forming tubular components using the THF process generally depends on many influencing parameters such as geometry, coefficient of friction, loading pathways, material formability, etc. The objective of this study was to determine the effect of the corner radius, coefficient of friction and heat treatment temperature on the bulging of the tubular component using finite element simulations. To address the complexity of parameter selection correctly with different alternatives, the multi-criteria decision-making methods (MCDM) applied in the present work. Two decision models, namely Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) and Performance Selection Index (PSI) methods with entropy weighting criteria were applied for obtaining the best combination of parameters to get a sound quality product. Finally, the proposed ranking was validated by conducting experimental trials and the error was observed to be in limits in comparison with the simulated data. ANOVA was also performed to distinguish the significant parameters and their contribution to the responses. Both the MCDM methods suggested the same favorable and unfavorable alternatives.

Hydroforming processes of metal tubes and sheets are being widely applied in manufacturing because of the increasing demand for lightweight parts in sectors such as the automobile, aerospace, and ship-building industries [...]

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.

Hydroforming is a relatively new technology of forming and profiling. So far, the application of this method has been limited by the costs of die production. The cost of the dies and the long production start-up time made this method economically viable for the production of hundreds of products. The approach change to the tool design for profile shaping techniques has allowed to develop the new hydroforming method perfectly suited to low-volume or even unit production. In traditional solutions, the die is rigid and does not deform during the expansion of the profile. In the newly patented RTH (Rapid Tube Hydroforming) method, the die undergoes controlled deformation during the process. The specificity of the granular materials used for the production of the dies makes modeling the behavior of the die during the expansion of the profile a remarkable problem. This contribution presents considerations on the fuzzy inference method used to model the technological process. As a result, it was possible to more accurately determine the importance of individual die parameters (geometry and material properties), and thus better predict the final shape of the formed profile. The main goal is to understand the effect of shaped profile on the matrix and to recognize the influence of granular material in the matrix under the compaction conditions of the expanded profile on its final geometry.

The hydroforming technology can realize overall forming of large storage tank’s bottom, but the quality is affected by many technological parameters. In view of wrinkling and cracking defects of integral storage tank’s bottom in hydroforming, a multi-objective optimization model is established for process parameters include pre-expansion pressure, hydraulic pressure, blank holder force and fillet radius of blank holder. Based on finite element simulation, the surrogate model between process parameters and quality criteria is established using Kriging technique. NSGA-III is used to determine optimal process parameters when storage tank’s bottom reaches targets include minimum wall thickness variations, minimum fracture trend, minimum flange wrinkle and minimum wrinkle trend. Compared with Particle swarm optimization (PSO) algorithm, NSGA-III algorithm is more suitable to solve this optimization problem. The validity of this method and accuracy of the results are verified by simulation experiments.

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 manufacture the large-expansion-ratio double-stepped tube without thinning, a new approach known as multistage axial hydro-forging sequence has been proposed in this study. The whole forming process is divided into five stages. Compared with traditional tube hydroforming, the thickness can be increased by axial compression deformation to reduce the thinning ratio and enhance the forming capacity of the tube in hydro-forging stage and double-stepped hydro-forging stage, respectively. The proposed multistage axial hydro-forging sequence process was implemented by experiments along with the finite element simulation to validate its feasibility. The suitable loading path to prevent defects such as wrinkle and thinning was discussed. The results showed that double-stepped tube with large expansion ratio can be produced successfully with movable dies’ design. There is no thinning in the final tube, particularly in all stepped area, and a better thickness distribution could be achieved. As a result, the proposed multistage axial hydro-forging sequence can be a feasible forming approach for the fabrication of large-expansion-ratio double-stepped tubes with high reliability.

Prediction of failure in sheet metal forming processes accurately is very important for successful production and optimization of parameters. A major problem of conventional strain-based forming limit diagrams (FLDs) is their inability to predict failure accurately in processes such as sheet hydroforming where there is a change in strain path and mode of deformation. In the present work, a stress-based forming limit diagram has been developed for AA 5182 alloy sheets modifying the analytical procedure, proposed by Stoughton, to determine forming limits in stress space from failure strains incorporating anisotropy using Balart’s yield criterion. The developed stress-based FLD has been used to predict failure in sheet hydroforming of square cups. Results are compared with Hill’s quadratic yield criterion. Significant difference has been found in failure prediction between strain-based and stress-based criteria when they are applied to sheet hydroforming. A change in strain path has been observed at the critical corner regions in hydroforming of square cups due to initial drawing and then biaxial stretching during calibration. The experimental validation clearly showed that accuracy in failure prediction can be improved in sheet hydroforming by using a stress-based forming limit diagram.

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.

Purpose Custom-designed metal bellows require alternate ways to produce the die to shorten lead time. The purpose of this study is to explore the possibility of using Additive Manufactured (AM) polymer die as direct rapid tool (RT) for metal bellow hydroforming. Design/methodology/approach Finite element analysis (FEA) was used to simulate bellow forming and to evaluate the compatibility of AM die. Fused deposition modelling (FDM) technique is used to fabricate die with Acrylonitrile Butadiene Styrene (ABS) material. To validate, the width of the metal bellow convolutions obtained from the FEA simulation is compared with convolution formed during the experiment. Findings FDM-made die can be used for a short production run of bellow hydroforming. FEA simulation shows that stress developed in some regions of die is less and these regions have potential for material reduction. Use of RT for this particular application is limited by the die material, forming pressure, width, convolution span and material of bellow. This supports the importance of FEA validation of RT before fabrication to evaluate and redesign die for the successful outcome of the tool. Research limitations/implications The given methodology may be followed to design a RT with minimum material consumption for bellow forming application. Whenever there is a change in bellow design or the die material, simulation has to be done to evaluate the capability of the die. As this study was focused on a short production run for manufacturing one or few bellows, the die life is not a significant factor. Originality/value This paper demonstrates about rapid tooling for metal bellow manufacturing using FDM technique for low volume production. Further, FEA is used to identify low stress regions and redesign the die for material reduction before die manufacturing. AM die can be used for developing customized metal bellow for applications such as defense, aerospace, automobiles, etc.

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.

The basic idea of a solar absorber’s thermal gain increase is the keyhole effect utilization during which the radiation is absorbed by multiple reflections on cavity walls. The lattice of pyramidal or conical cavities on the solar absorber surface can be formed to create a structured surface leading to its overall absorptivity increase and to a reduction of the surface absorptivity dependence on the solar radiation incident beam angle changes caused by the daily and annual solar cycles. This contribution concludes the results of simulations of the effect of cavity geometry, geographical position and absorber orientation on its thermal gain with respect to the technological manufacturability of cavities. Furthermore, the real construction of the absorber with a structured surface using laser welding and parallel hydroforming is briefly described.

To overcome the problems in high pressure tube hydroforming (HPTH), such as too high forming pressure, thickness thinning and low productivity, a new forming technology was put forward, named as tube hydro-forging(THFG). In THFG, hollow components were formed by cross-section compression, overturned the traditional idea about conventional tube hydroforming in which the tube was expanded into the desired shape. Compared with HPTH, the role of the internal pressure was translated into the function of supporting and the tube sidewall was subjected to compression deformation throughout the process. These changes permit the THFG process with lots of advantages, such as low required internal pressure, avoiding thickness thinning or crack defect, no need for axial feeding, and so on. In this study, an analytical model based on a rigid, perfectly plastic material model was developed to investigate the possibility and the main influencing factors of the THFG. The analytical solution developed was compared with the experimental results. Experimental results validate that the tube can be formed into the desired shape by cross-section compression under a certain internal pressure supporting. Through the analytical model combining FEM simulation, the critical support pressure was given. The critical support pressure increases gradually as the deformation going on and has great dependence on the materials properties, however has no dependence on the tube thickness. It is also validated that the required pressure in the THFG is much lower than that needed in the traditional tube hydroforming.

Increasing use of hydroforming in automotive applications needs intensive analysis development on all aspects of this comparatively new technology to satisfy an ever-increasing demand by the trade. This paper summarizes a technological review of hydroforming method from its early years to terribly recent dates on numerous topics like material, tribology, equipment, tooling, etc., so that other research worker at completely different components of the globe will use it for additional investigations during this space.

The paper introduces a new tool concept for the hydroforming process, which has two main advantages, namely the increase of the number of drawn parts at a stroke of the forming punch and replacing the use of an expensive hydraulic installation to produce the pressure. According to this new concept the dimensional control can be realized in two ways, by either controlling the fluid volume or the pressure value. The tool concept design of the new hydroforming process is based on the law of the volume constancy. Through experimental work, a simplified concept tool has been tested. Circular parts with circular channels were obtained. FE simulations have been accomplished to predict the best forming conditions for this particular case. In the numerical simulations the working pressure has been modified as a control parameter. The experimental and numerical results validate the new tool concept. At this stage of the multi-channel hydroforming development investigations show that this new die concept could be used in manufacturing different complex sheet metal parts, with small reliefs.

In this paper, an attempt has been made to enhance formability of cryorolled AA5083 alloy sheets (annealed at 275 °C for 15 min) in deep drawing of flat bottom square cup-shaped parts by hydroforming. Numerical simulations based on finite element method have been carried out to study the effect of important process parameters (fluid pressure and sealing force) on formability. The minimum corner radius and the maximum depth that can be achieved without failure and the maximum percentage thinning at the corners have been considered as measures of formability. The results have been compared with conventional deep drawing. The simulation results have also been validated with experimental work in both hydroforming and conventional forming. A process window with optimum combination of peak sealing force and peak pressure has been identified to form the cups up to full depth of the die without failure at die entry or bottom corners. Lubrication between the die and the blank reduced the minimum possible corner radius to nearly 16 mm with thinning less than 6%. In conventional forming only 70% of the full depth could be obtained before failure with 16 mm punch corner radius due to much higher thinning at the corners. This work demonstrates that, by hydroforming, formability of high strength cryorolled Al alloy sheets can be enhanced due to lower thinning and more uniform strain distribution and hence this process route (cryorolling followed by hydroforming) is a potential technique to produce complex parts from lightweight high strength Al alloy sheets due to enhanced formability. Keywords: Aluminum alloy, Cryorolling, Formability, FEM, Deep drawing, Hydroforming

Industry is continuously searching for solutions to increase flexibility and quality in parallel with cost reductions. This paper presents a case study of using set-based design method to develop a gripping system for an innovative three-dimensional bending and forming technology of extruded aluminium profiles. Traditionally, profiles are formed by mandrel-based stretch-bending to improve cross-sectional stability and spring-back, sometimes combined with subsequent calibration e.g. by hydroforming. However, in the highly competitive automotive industry, where light-weighting is high on the agenda, design and process flexibility, tooling cost and dimensional accuracy are important factors to increase value at a reasonable cost. In this paper, a set-based concurrent engineering approach is used to identify, evaluate and prioritize gripping methods to enable three-dimensional bending meeting automotive requirements for dimensional accuracy. The results demonstrate a multitude of options, providing trade-offs between flexibility and function. Further work will be to build a physical demonstrator to validate output from the set-based method used to systematically narrow down the solution space.

Light-weight performance of load carrying structures can be increased through the use of bifurcations. Stringer sheets make use of this design principle. They consist of a base sheet with stiffening ribs or stringers. In this work the stringers are attached to the flat base sheet via laser welding and afterwards the part receives its targeted 3D shape in a subsequent forming process. While a larger height of the stringers is advantageous in terms of light-weight performance, it can lead to higher compressive stresses in concave areas of the part, causing buckling of the stringers. Previous studies made use of hydroforming for the manufacture of the 3D shaped stringer sheets. During hydroforming a side support to the stringers is given by the pressurized medium. Due to relatively long cycle times, it is not suitable for highly efficient mass production. Hydroforming also has shortcomings in the attainable geometries. This paper presents a new industrial-suited stringer sheet stamping process which is up to 20 times faster than current stringer sheet forming processes based on hydroforming. Furthermore, a numerical model allowing the prediction of stringer buckling is provided. Both, process and numerical model, are experimentally validated.

Pulsating hydroforming and impact hydroforming are two advanced technologies to increase the formability of material compared with other traditional forming technologies. They were systematically investigated from aspects of technical principle, forming mechanism, equipment, and applications. Pulsating hydroforming can improve the forming ability by altering the friction condition of sheet/tube parts or by utilizing the effect of transformation induced plasticity of stainless steels under the pulsating loading. As for impact hydroforming, the strain rate can reach 103–104/s and the instantaneous pressure can be GPa level, which can obviously increase the elongation of hard-to-form material by 20–60%. The effect of flexible liquid and impact impulse was investigated by both experiment and simulation, while the mechanisms were related to the compatible deformation of the second phase, strain decentralization, and defect stabilization. The technologies have been used on the manufacturing of complex, thin-walled components for the fields of aeronautics and aerospace, automobile, nuclear power, etc.

An adaptive, heuristic, nonlinear mathematical model (AHNM) was proposed to optimize the loading path of successful tube hydroforming process through adaptive minimization of the internal pressure and axial load by using Multiple Ridge Regression (Machine learning technique). The AHNM model was implemented, solved, and optimized, and it was found that increasing the number of steps and starting with small increment enables the mathematical model to capture the non-linearity of the real model, which leads to minimizing the system requirements. In this paper Finite Element Modelling (FEM) was developed to verify and test the validity and reality of the implemented loading oaths from the AHNM model for hydroforming of T-shape tube having an elliptical protrusion. The objective function was measured, and the results of minimum thickness, and maximum protrusion height were verified. Besides, the tube was formed with a well wall thickness distribution. Consequently, it is confirmed that developing an adaptive heuristic nonlinear mathematical modelling is effective for obtaining a Loading Path for Hydroforming of a Tube Having an Elliptical Protrusion.

Optimum loading paths for successful tube hydroforming processes have been studied by several researchers. In this paper, an adaptive, heuristic, nonlinear mathematical model (AHNM) was proposed to optimize the loading path of a hydroforming process through adaptive minimization of the internal pressure and axial load of the process. Firstly, Finite Element Analysis (FEA) was used to analyse the hydroforming process where several features of the process were extracted from the FEA for further analyses of the relations among them. To capture these relations and include them in the AHNM, the paper examined several Machine Learning algorithms including Multiple Linear Regression, Multiple Ridge Regression, Decision Tree, and Random Forest. The Multiple Ridge Regression was found to give the highest accuracy to efficiently linear modelling the inputs and outputs of the FEA of the hydroforming process. The AHNM model was implemented, solved, and optimized using several steps of tee protrusion height that create several loading paths. It was found that increasing the number of steps and starting with small increment leads to minimizing the system requirements.

The subject of research is car exhaust system piping made of chromium–nickel steel of grade AISI304L with a unique, complex shape that was obtained by hydroforming technology. The purpose of the research was to determine the relation between the microstructure features, surface condition, hardness and the stresses on the external surface as determined by the sin2ψ X-ray method. We found that the stresses were tensile and correlated with the steel hardness, i.e. they were greater where the hardness was higher. Moreover, longitudinal stresses showed a relationship with pipe wall thickness, while circumferential stresses did so only partially. According to our data, the greatest value of stress determined in the pipe amounted to 290 MPa, and was close to the yield point of the strain hardened 304L steel. As depicted via XRD and SEM examination, the pipe stress level and hardness were influenced by the transition γ→α’. Furthermore, in the region of higher stress and hardness, the amount of martensite was 10 vol.%. We also noted that the pipe’s outer surface when subjected to friction against the die shows lesser roughness compared to its inner surface upon exposure to water under pressure.

The article presents a newly patented rapid tube hydroforming (RTH) manufacturing method, perfectly suited to single-piece production. The RTH technology significantly complements the scope of hydroforming processes. Due to the unusual granular material of the die tool, in particular moulding sand or mass, the process design requires the use of numerical modelling calculations. This is related to the complexity and the synergistic effect of process parameters on the final shape of the product. The work presents the results of numerical modelling studies of the process, including the behaviour of the die material and the material of the hydroformed profile. The numerical calculations were performed for a wide range of parameters, and can be used in various applications. The significant properties of moulding material used for the RTH tests were determined and one was chosen to build the die in RTH experiments. The results of the numerical modelling were compared with the results of the experiments, which proved their high compatibility. The final conclusions of the analyses indicate that the RTH technology has many possibilities that are worth further development and research.

Manufacturing of irregular bellows with small corner radii and sharp angles is a challenge in tube hydroforming processes. Design of movable dies with an appropriate loading path is an alternative solution to obtain products with required geometrical and dimensional specifications. In this paper, a tube hydroforming process using a novel movable die design is developed to decrease the internal pressure and the maximal thinning ratio in the formed product. Two kinds of feeding types are proposed to make the maximal thinning ratio in the formed bellows as small as possible. A finite element simulation software &ldquo, DEFORM 3D&rdquo, is used to analyze the plastic deformation of the tube within the die cavity using the proposed movable die design. Forming windows for sound products using different feeding types are also investigated. Finally, tube hydroforming experiments of irregular bellows are conducted and experimental thickness distributions of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.

Hydroforming is a manufacturing process that is used to form complex geometries by applying fluid pressure. The punchless hydroforming process is the most popular in the race, considering the absence of any punch that helps in reducing the tooling costs. Based on the part geometries formed, the punchless process can be classified into three categories, namely sheet hydroforming, shell hydroforming and tube hydroforming. Sheet metal hydroforming is a hydroforming process that uses hydrostatic fluid pressure for deforming the blank into a die cavity of the desired shape. Owing to the inert advantages, like lower tooling costs, reduced processing steps, remarkable precision, waste reduction and weight reduction, this process finds extensive use in applications requiring a high strength-to-weight ratio, as in complex automobile parts. The presented work involves the development of a nonlinear 2D finite element model for the sheet hydroforming process of AA5182 (aluminium alloy) using the FE package Abaqus/Explicit and validation of the numerical results using the available literature (Daryl in Logan: a first course in the finite element method. Cengage Learning Products, Canada 2007 [2]). The model is first validated by reproducing the research work carried out by Bharatkumar Modi et al., considering the input parameters, like blank holding force (BHF), sheet thickness and internal pressure, and the corresponding output parameters, like material thickness reduction and die corner radius. The research is further extended by replacing the current blank material AA5182 using cryo-rolled AA5083. The effect of varying BHF, at varying annealing temperature of blank considering varying frictional coefficients, is also studied. This work also investigates the optimisation of the process using a well-established design of experiments (DOE) technique—response surface methodology (RSM).