Topic
Hydroforming
About: Hydroforming is a research topic. Over the lifetime, 2796 publications have been published within this topic receiving 26293 citations. The topic is also known as: Bulge forming.
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TL;DR: In this article, the effect of internal pressure on the variation of shell shape, volume, and wrinkling was analyzed, and the results showed that as the internal pressure increases at the early stage of deformation, the short axis elongates; correspondingly, the volume varies slightly.
Abstract: In order to the study the deformation of die-less hydroforming of ellipsoidal shell under the condition of without restricting the elongation of short axis, experimental research on hydroforming of an ellipsoidal shell with the initial axis length ratio 1.8 was carried out to analyze the effect of internal pressure on the variation of shell shape, volume, and wrinkling. The results show that as the internal pressure increases at the early stage of deformation, the short axis elongates; correspondingly, the volume varies slightly; wrinkling occurs on the equatorial plane when the internal pressure is up to 1.0 MPa, and it becomes severe when the internal pressure is 2.2 MPa; as the internal pressure continuously increases, the long axis begins to shrink rapidly, but the shell volume has a very tiny change within the range of internal pressure 2.2–3.5 MPa; when the internal pressure is 3.8 MPa, the wrinkling is eliminated completely, and the shell volume suddenly increases; when the internal pressure is up to 5.5 MPa, the equatorial plane is no longer shrinking but expanding and the out-of-roundness approaches zero; finally, when the internal pressure is 6.8 MPa, the ellipsoidal shell with the axis length ratio 1.06 is obtained, and the variation of long axis, short axis, and volume are −2.9, 64.6, and 52.7 %, respectively. Simulation was also carried out simultaneously to analyze the stress locus of typical points. It has indicated that the compressive stress in the circumferential direction is the reason of wrinkling occurring; accordingly, the tensile stress in the circumferential direction is the reason of wrinkling disappearing.
14 citations
TL;DR: In this article, a validated finite element model developed by the explicit finite element code LS-DYNA is used to conduct virtual T-shape tube hydroforming experiments and a multi-objective optimization problem considering contact area between the tube and counter punch, maximum thinning ratio, and protrusion height is formulated.
Abstract: The objective of this study is to introduce adaptive support vector regression, whose accuracy and efficiency are illustrated through a numerical example, to determine the Pareto optimal solution set for T-shape tube hydroforming process. A validated finite element model developed by the explicit finite element code LS-DYNA is used to conduct virtual T-shape tube hydroforming experiments. Multi-objective optimization problem considering contact area between the tube and counter punch, maximum thinning ratio, and protrusion height is formulated. Then, the Latin hypercube design is employed to construct the initial support vector regression model, and some extra sampling points are added to reconstruct the support vector regression model to obtain the Pareto optimal solution set during each iteration. Finally, the ideal point is used to obtain a compromise solution from the Pareto optimal solution set for the engineers.
14 citations
TL;DR: In this paper, a new model was developed in which simulated the whole tube instead of considering only its mid-section, judged by the pressure-expansion relations, the model accurately predicted free expansion hydroforming tests results.
Abstract: Free expansion of straight tubes is the simplest test to evaluate tube properties for hydroforming applications and to provide basic understanding of the mechanics of tube hydroforming. A circular cylindrical tube is sealed at both ends and fluid, usually water, is pumped into the tube to increase its internal pressure to bulge and burst the tube. Previous numerical simulations of the free expansion tube test were limited to modeling the mid-section of the tube under various assumptions of deformation path. The simulation results obtained deviated from the experimental results under all simulation conditions considered. A new model is developed in this paper in which the whole tube is simulated instead of considering only its mid-section. Judged by the pressure-expansion relations, the model accurately predicted free expansion hydroforming tests results. Burst predictions were made using the plastic strain criterion, the traditional forming limit diagram and the stress-based forming limit diagram. Detailed discussions concerning the specification of the tube properties in hydroforming and the application of the burst prediction criteria in hydroforming is presented.
14 citations
TL;DR: In this article, the authors presented a virtual thermomechanical fatigue design approach, using a dedicated post processor, which would permit to optimize the design of the fabricated exhaust manifolds, and would lower the development cost and time by limiting both the number of prototype and motor bench tests and, finally, would reduce the risk of failure.
Abstract: The paper deals with the design of stainless steel exhaust manifolds, focusing on the development of high temperature ferritic grades and their forming capabilities related to the new forming processes, like bending and hydroforming. In particular, it is shown along the presentation, how a niobium stabilized 14%Cr grade can be used in replacement of austenitic grades in many situations of complex shaped manifolds thanks to its combined improved formability and its high temperature resistance up to 950°C. Finally, the authors present a “virtual” thermomechanical fatigue design approach, using a dedicated post processor, which would permit to optimize the design of the fabricated exhaust manifolds, and would lower the development cost and time by limiting both the number of prototype and motor bench tests and, finally, would reduce the risk of failure.
14 citations
TL;DR: The introduced process belongs to the category of high speed forming methods and provides typical advantages such as higher achievable strains compared to quasi-static methods using high water pressure and the avoidance of high press forces by application of an “inertia-locked tool” system due to the extremely short process time.
Abstract: The expansion of tubes by direct application of gas detonation waves is an alternative forming method for hollow section workpieces In particular the process can be used for typical hydroforming parts, for example car body or exhaust elements in automotive industry The gas charge of oxygen and hydrogen is both pressure medium and energy source and has the potential to cause high forming velocities The introduced process belongs to the category of high speed forming methods and provides typical advantages such as higher achievable strains compared to quasi-static methods using high water pressure Another advantage of this process is the avoidance of high press forces by application of an “inertia-locked tool” system due to the extremely short process time To develop a controllable process, good knowledge of the interdependencies in the system “medium, workpiece and tool” is essential This can be achieved using simulations in combination with experimental investigations The results are topic of this paper, also including special investigations on the material behavior at high strain rates and temperature gradients
14 citations