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Spherical metal shell constructions are widely utilized as storage containers in the chemical industry or as characteristic symbols in large urban centers. Traditional manufacturing methods for these shells typically involve deep drawing or spinning hemispherical halves, which are subsequently welded together. These conventional methods suffer from low productivity and limited economic viability due to the requirement for large dies and machinery. In contrast, spherical metal parts produced using Die-less HydroForming (DHF) offer high dimensional accuracy, reduced costs, and shortened production times compared to traditional technologies. The DHF process entails defining the blank profile, initial bending formation, sealing the blank profile by welding, and applying increasing fluid pressure to deform the outer shell. The determination of the initial blank shape is crucial as it significantly impacts product quality. Initial blanks for fabricating spherical parts using DHF can take various forms, but are primarily categorized into two development types: meridional and latitudinal. Despite extensive research on the initial blank structure for forming spherical metal products, a critical gap remains: the lack of comparative studies on the post-forming product quality of different blank types. This paper directly addresses this void, employing numerical simulation and experimental validation to comprehensively assess how these two initial blank types influence product quality, specifically by analyzing thickness variation and dimensional accuracy. Spherical metal products with a diameter of 400 mm, made from SUS304 stainless steel, were used for comparing post-forming quality. The research results indicate that latitudinal blanks achieve a dimensional accuracy deviation of 2.3%, an average thinning rate of 9%, and a shorter weld seam length, thereby reducing manufacturing time and enhancing productivity.

Feeding path and movable die designs are crucial to implement bellows manufacturing with an appropriate hydraulic pressure and make the products satisfy the required geometrical and dimensional specifications. In this paper, a tube hydroforming process combined with movable die designs is developed to obtain an appropriate forming range of the internal pressure and increase the thickness uniformity in the formed product. Two kinds of feeding types are proposed to discuss the effects of the feeding path and die design on the convolution heights and thickness uniformity in the formed bellows. A finite element simulation software “DEFORM” is used to analyze the plastic deformation of the tube within the die cavity using the proposed feeding types for three different shape bellows. Allowable forming ranges of internal pressures for sound products with required tolerances in geometry and dimensions using different feeding types are also investigated. Finally, tube hydroforming experiments of three-convolution bellows are conducted and experimental thickness distributions and convolution heights of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.

For large curved thin-walled parts, the introduction of double-layer sheet hydroforming process can obviously inhibit the defects, such as wrinkling and cracking. In this paper, 6061-T6 thin-walled semi-ellipsoidal parts are taken as the research object. Firstly, the coefficient fitting method of Fields-Backofen constitutive equation at high temperature is optimized. Secondly, the influence of upper sheet with different strength and liquid chamber loading path on the formability of parts is analyzed. At the same time, the pre-bulging process with a pressure value of 6 MPa was selected to improve the wall thickness reduction rate of the punch contact area. Through the response surface method, the interaction among the circumferential pressure, the friction coefficient between the sheets, and the thickness of the upper sheet was studied. The optimal process parameters of the part forming were predicted by the existing data, and the prediction accuracy was verified by numerical simulation. On the basis of the optimal process parameters, it is found that the parts have good forming performance at 150 °C, and the simulation results are verified by experiments.

Deep drawing of aviation aluminum parts is a difficult problem in the manufacturing field of aviation sheet metal parts. In this paper, a deep parabolic 2A11-O aluminum sheet part was taken as the target to studies the problem of difficult coordination between wrinkling and fracture in the one-pass forming process of rubber bladder hydroforming. Material performance testing showed that 2A11-O aluminum sheet has a significant Bauschinger effect. The Chaboche hardening model was used to construct a plastic material model, and finite element simulation was used to simulate the forming process, providing guidance for the design of forming processes. Due to the narrow forming window of 2A11-O aluminum sheet, the forming results are highly sensitive to the loading path and lubrication state. After careful experimental study, the forming process of the part with rubber bladder hydroforming was successfully realized by designing the loading curve in sections and lubricating the surface of the sheet in sections. The design ideas and lubrication methods used in this study can provide reference for the exploration of the same type of technology.

The tube hydroforming technology is a rapid-forming technique in multi-way tube integrated and lightweight manufacturing. The forming performance of the multi-way tube under this technology was comprehensively analyzed and summarized in this paper. Firstly, the influencing factors, such as axial feed loading path and internal pressure, forming friction, and die transition fillet, in the process of multi-way tube forming were analyzed and summarized. Secondly, the optimization method of the multi-way tube forming performance in hydroforming was analyzed. Finally, the reduction of hydraulic expansion costs and the development of new hydroforming technologies were expounded.

To increase the process stability and improve the product quality in the sheet hydroforming with die process, it is crucial for identifying and analyzing the dependence of forming pressure on process parameters. The effects of process parameters (blank holder force, frictional condition) on the forming fluid pressure were thoroughly studied experimentally. The main objective is to establish a relationship between the forming fluid pressure and several factors such as blank holder force and friction between die and sheet. The results demonstrate that the maximum fluid pressure increases with increasing blank holder force and friction. Finally, this relationship aims to support calculations and design data and provide control during the SHF-D process.

Producing conical parts from sheet metal is a highly intricate process that poses significant challenges in the manufacturing industry. To investigate the ductility of an AL-1050 conical part with 12 indentations, the present study employed both experimental and numerical methods, utilizing hydroforming deep drawing with radial pressure (HDDRP). Specifically, the study analyzed the effects of the pressure path, wherein the punch moves towards the die, on the punch force and the distribution of thickness. The study findings indicated an inverse relationship between pressure and cup thickness, with higher pressure resulting in reduced thickness, and the force-displacement curve revealed that the punch force initially increased and then decreased due to an increase in the deformation resistance of the sheet. Additionally, it was observed that when the angle of the conical section was less than 35°, workpiece rupture occurred. To optimize the process parameters, a genetic algorithm–based approach was implemented. The process parameters were fine-tuned by genetic algorithm–based optimization to achieve an optimal outcome.

This study aims to investigate the feasibility of hydroforming (HF) technology coupled with response surface optimization for producing high-quality five-branched AISI 304 stainless steel tubes with different diameters, addressing the shortcomings of traditional manufacturing processes. Conventional techniques often result in issues with multiple consumables, low precision, and subpar performance. The research focuses on finding optimal forming parameters for a more effective process. Initial attempts at a five-branched tube proved unfeasible. Instead, a multi-step forming approach was adopted, starting with the formation of the upper branch tube followed by the two reducing lower branch tubes, a strategy termed “first three, then five”. This method, enhanced by a subsequent solid solution treatment, yielded promising results: the combined height of the upper and lower branches was 141.1 mm, with a maximum thinning rate of 26.67%, reduced to 25.33% after trimming. These outcomes met the product usage requirements. Additionally, the study involved designing and developing dies for manufacturing five-branched tubes with different diameters using servo HF equipment. The effectiveness of the multi-step forming process and parameter combinations was confirmed through experimental validation, aligning closely with the FE simulation results. The maximum thinning rate observed in the experiments was 27.60%, indicating that FE simulation and response surface methodology can effectively guide the production of high-quality parts with superior performance.

During centralizer hydroforming, internal pressure and axial feed critically influence the forming outcome. Insufficient feed causes excessive thinning and cracking, while excessive feed causes thickening and wrinkling. Achieving uniform wall thickness necessitates careful design of the pressure and feed curves. Using max/min wall thickness as objectives and key control points on these curves as variables, the study integrated Non-dominated Sorting Genetic Algorithm (NSGA-II), Multi-Objective Particle Swarm Optimization (MOPSO), Neighborhood Cultivation Genetic Algorithm (NCGA), and Archive-based Micro Genetic Algorithm (AMGA) with LS-DYNA to automatically optimize loading paths. The results demonstrate the following: ① NSGA-II, NCGA, and AMGA successfully generated optimized paths; ② NSGA-II and AMGA produced larger sets of higher-quality Pareto solutions; ③ AMGA required more iterations for satisfactory Pareto sets; ④ MOPSO exhibited a tendency towards premature convergence, yielding inferior results; ⑤ Multi-objective optimization efficiently generated diverse Pareto solutions, expanding the design space for process design.

Abstract Ti–6Al–4 V sheets possess limited formability at room temperature due to low ductility with almost no strain hardening. Pressure pulsation during hydroforming may bring significant improvement as an alternative to the widespread solution hot forming. However, much uncertainty exists on the deformation mechanism and effects of pulsating on difficult-to-form materials. In this study, the effect of pulsating pressure on the hydraulic bulge test was investigated to increase the limited formability of the Ti–6Al–4 V sheet at room temperature. Experimental results of thickness distribution and bulge height obtained from the bulge tests were compared with the finite element simulation results. The results show that the tests with pulsation allow a higher thickness reduction with a slightly more homogenous thickness distribution. Pulsation causes a delay in the material’s failure resulting in a 15.4% increase in the dome height with a 17% increased burst pressure compared to monotonic loading. The underlying microstructural phenomena of increased formability were elaborated using dislocation estimations, fracture surface analysis, and hardness. Test results suggest that pulsation improves formability by 47% in terms of maximum elongation due to stress relaxation.