Showing papers on "Hydroforming published in 2012"

New Developments of Hydroforming in China

Abstract: This paper reviews the recent developments of hydroforming technology in China. Limited corner radius, ring hoop tension test and tube bulging test were introduced on fundamentals of hydroforming. New hydroforming and hydro-bending process of ultra-thin tubes were investigated. Ultra-thin Y-shaped parts and complex section components were manufactured and applied in aerospace and aviation industry. Applications of tube hydroforming in automotive industry in China are also presented, including the hydroforming machines and production lines, typical automotive parts and potential market. New sheet hydroforming process with controllable radial pressure was proposed to increase the formability of sheets metals. Warm tube and sheet hydroforming were analyzed and discussed. [doi:10.2320/matertrans.MF201122]

Experimental and numerical investigation of localized thinning in hydroforming of micro-tubes

Abstract: An experimental program has been carried out for hydroforming of stainless steel micro-tubes. Under careful control, it was found that failure takes place randomly, which is significantly different from observations of failure in hydroforming of macro-tubes, where failure loads and locations are predictable. This occurs because wall thinning of micro-tubes in forming processes is non-uniform, i.e. localized necking takes place randomly. To investigate the localized thinning mechanism, an integrated crystal plasticity finite element (CPFE) modeling system has been developed. In this paper, a simplified plane strain CPFE model is presented and used to investigate the localized thinning and failure features in hydroforming of micro-tubes. The crystal plasticity equations were implemented in the ABAQUS/Explicit FE code through a user-defined material subroutine, VUMAT. Single crystal, three-grain and polycrystal FE models were generated to study the localized thinning/necking mechanism and the effect of differing adjacent grain orientations, as well as the number of grains across the smallest specimen dimension, on the necking features. It has been confirmed from the analyses that the localized thinning observed in hydroforming of micro-tubes is significantly affected by the microstructure and grain orientations of the material.

An investigation of the optimal load paths for the hydroforming of T-shaped tubes

Abstract: This paper proposes a new method to design the optimal load curves for hydroforming T-shaped tubular parts. In order to assess the mathematical models, a combination of design of experiment and finite element simulation was used. The optimum set of loading variables was obtained by embedding the mathematical models for tube formability indicators into a simulated annealing algorithm. The adequacy of the optimum results was evaluated by genetic algorithm. Using this method, the effect of all loading paths was considered in hydroforming of T-shaped tubes. Eliminating of variables with lower effect could simplify the problem and help designers to study the effect of other parameters such as geometrical conditions and loading parameters. Applying the optimal load paths obtained with the proposed method caused an improvement in the thickness distribution in the part as well as a decrease in maximum pressure.

Experimental and numerical investigation of the hydroforming behavior of paperboard

Abstract: The material behavior of two different types of paperboard was characterized in tensile tests and in a new test device called paperboard bulge test. A particularly adapted hydroforming process was used to produce three-dimensional paperboard structures. Furthermore, an online measurement device to describe the mold-filling behavior is introduced. The experimental results were compared to the results obtained with an FEA investigation. The investigations showed the possibilities of the new forming process, as well as the advantages of FEA methods used to pre-define the process parameters.

The effect of tube dimensions on optimized pressure and force loading paths in tube hydroforming process

Abstract: The precise control of internal pressure and axial force loading paths significantly affects the final product quality. In this study, the effect of tube dimensions on the pressure and force loading paths in tube hydroforming process is investigated by using simulated annealing optimization method linked to a commercial finite element code. The optimized loading paths, obtained for different tube geometries with a constant expansion ratio, are then compared. The effects of initial diameter and wall thickness on shape conformation, optimal internal pressure and axial force (or feed) are discussed on the basis of optimal loading paths. Several guidelines in prediction and determination of tube hydroforming parameters are obtained by optimization analysis.

Study on experimental approaches of forming limit curve for tube hydroforming.

Abstract: This paper proposes a set of experimental approaches to establish the forming limit curve (FLC) in different forming modes for tube hydroforming. In tension–compression strain state, analytical models are constructed to determine the linear strain paths at the pole of the hydroformed tube, and a self-designed free hydroforming apparatus with axial feeding and internal pressure are used to carry out the bulge tests. In plane strain state, the difference is that both ends of the tube are fixed with different punches. In tension–tension strain state, a novel hydroforming apparatus are designed. The novel device requires the simultaneous application of lateral compression force and internal pressure to control the material flow under tension–tension strain states. The linear strain paths for the right hand side of FLC by finite element method simulation are calculated. The linear strain paths in different strain states are verified and the FLC of roll-formed QSTE340 seamed tube is constructed through the proposed experimental approaches. Comparison between simulation and experimental results for hydroforming process of front crossmember shows that the experimental FLC is accurate and valid for tube hydroforming.

Analytic Prediction of the Process Parameters for Form-Fit Joining by Die-Less Hydroforming

Abstract: The Commission of the European Communities aims for a reduction of new car CO2 emissions of 120 grams per kilometer in 2012. As a result of the omnipresent efforts of the automotive industry to hit these tighter emission standards innovative lightweight strategies, e.g. the use of lightweight materials are developed. This entails new joining techniques that are appropriated to the new lightweight materials. The die-less hydroforming process is a joining method for tubular joints which meets the new demands of lightweight strategies. Since there is no need for any additional connection elements or filling material, it is an interesting alternative to conventional welding and riveting processes. The present paper describes the basic principle of the die-less hydroforming joining technology with a special focus on form-fit connections. An analytical model, based on the membrane theory with an additional local consideration of bending stresses is developed. This analytic approach can be used to calculate the working fluid pressure, required to bulge the tube material into the groove of the outer joining partner. Taking into account the material parameters as well as the groove and tube geometry, this model allows a reliable process design. Additionally, validation of the model by experimental investigations will be provided.

A hybrid-constrained MOGA and local search method to optimize the load path for tube hydroforming

Abstract: The production of a tubular hydroformed part often requires a combination of internal pressure and axial force at the tube ends to fully form the tube to its specified geometry. A successful hydroforming process requires not only achieving a part that conforms to the design specifications, but also ensures that the part has a reasonably uniform thickness distribution and is free of defects, such as wrinkles, severe thinning, or fractures. The load path design (pressure vs. end feed history) largely determines the robustness of the process and the quality of the finished parts. In this paper, a hybrid constrained optimization method was proposed to solve this type of multi-objective problem by coupling a multi-objective genetic algorithm and a local search. The load path design procedure was developed by considering five objectives: four formability objectives (i.e., to minimize the risk of wrinkling, global and local thinning, and fracture) and a geometric objective (to minimize the corner radius). A Kriging predictor was used to accelerate the computation of genetic operations and generate new feasible solutions. Finite element simulations of the hydroforming process were also used after each generation to accurately evaluate the objectives of the offspring, and solutions with rank 1 were retained throughout all generations. Once the Pareto solutions were obtained by multi-objective genetic algorithm, a local search was carried out in the regions of interest with the assistance of visualization. This optimization method was applied to the hydroforming of a straight tube to create a part with an expanded region with a square cross section; the optimum load path produced a very safe part with a corner radius of only 9.115 mm and a maximum thinning of only 23.9%.

Optimizitation of the pressure path in sheet metal hydroforming

Abstract: Fluid pressure is the most important parameter in hydroforming deep drawing process. In this manuscript, we present the results obtained from FE modelling using genetic algorithm to determine the optimum fluid pressure for the production of a two-stepped workpiece in the deep drawing hydroforming process. It is suggested that a two-stepped workpiece can be manufactured in a single step which is a significant advantage compared to conventional sheet forming processes. It is also shown that the lowest pressure point in the optimization curve occurs at the step height, which has the potential to allow for a more accurate pressure path selection procedure at shorter times while reducing the number of trials.

Developments in Sheet Hydroforming for Complex Industrial Parts

Abstract: Among the various sheet-metal forming processes, hydroforming is one of the nontraditional ones. This process is also called hydromechanical forming, hydraulic forming or hydropunch forming. In hydroforming process, liquid is used as the medium of energy transfer to form the workpiece. The part is formed on a female die, with the liquid under pressure acting in place of a conventional solid punch [1].

Experimental and numerical investigation of an adaptive simulated annealing technique in optimization of warm tube hydroforming

Abstract: Simulated annealing technique – which has attracted significant attention as being suitable for combinatorial optimization problems – has been used in many engineering applications. In current research, this method is used in optimization of a complicated forming process. Warm tube hydroforming is a new technology in the forming of lightweight aluminum and magnesium alloys in automotive, electronics and leisure industries. Owing to the complex nature of this process at high temperatures, and difficulty of obtaining the optimized forming conditions, this process has not received the credit it deserves yet. A new method for optimization of the warm tube hydroforming process is developed by using the simulated annealing algorithm with a novel adaptive annealing schedule. The optimal pressure loading paths are obtained for AA6061 aluminum alloy tubes with different wall thicknesses and corner fillets. The results obtained by simulated annealing technique are verified numerically and experimentally.

Experimental Investigation on Hydromechanical Deep Drawing of Aluminum Alloy with Heated Media

Abstract: Temperature controlled sheet hydroforming is known as the innovative processing of warm/hot sheet hydroforming. Cylindrical cup hydromechanical deep drawing (HMD) at elevated temperature is the typical process for basic research. Warm HMD process was carried out on a warm sheet hydroforming experiment platform to investigate the influences of key processing parameters on formability. The process window of successful forming versus liquid pressure was obtained, which was manifested as a shape of pyramid. The region of successful forming in warm/hot sheet hydroming is a father set of that in cold sheet hydroforming. The microstructure evolution of cups formed by using warm HMD under the effect of temperature was investigated. The grain growth was observed compared with cold HMD. The hardness of hydroformed cup was tested and no apparent reduction of hardness was detected.

The non-hydrostatic response of polymer melts as a pressure medium in sheet metal forming

Abstract: The polymer injection forming process is a recent invention for producing plastic–metal hybrids. It is a combination of injection molding and sheet metal hydroforming process in which polymer melt serves as a pressure medium. This paper presents the experimental investigations on the non-Newtonian nature of thermoplastic melt as pressure medium. The objective of this work is to identify the presence of non-hydrostatic pressure distribution within the cavity and its influence on the final shape of the formed sheet metal component. Experiments are conducted with center-gated injection mold under varying processing conditions. The development of localized cavity pressure during the process is recorded and evaluated against the final shape of formed sheet metal. It has been observed that higher injection rate, higher injection temperature, and higher melt flow index of the processed polymer is necessary for the uniform pressure distribution and subsequently uniform forming of the sheet metal.

An approach to improve thickness uniformity within tailor-welded tube hydroforming.

Abstract: Both experimental and simulation studies were run to investigate the effects of deformation sequence on stress and strain states and thickness distribution during tailor-welded tube hydroforming. The effects of geometrical boundary condition were also studied. Then, an approach to improve thickness uniformity was put forward. Both stress and strain histories indicate that the deformation states of thinner and thicker tubes were obviously different duo to the difference in thickness during tailor-welded tube hydroforming. These induce tensile strain concentrates to happen near weld seam on thinner tube, but compressive strain on thicker tube, which lead to strain mutation around weld seam on tailor-welded tube components. As result, bigger thinning takes place on thinner tube. The difference in thinning ratio between thinner and thicker tubes reaches about 6.6%. By deformation sequence optimization, thickness distribution uniformity can be improved obviously. When deformation sequence altered from thicker tube to thinner tube, the difference in thinning ratio between two segments can be decreased to 1.5%. At last, the effects of geometrical parameters of preform component were analyzed and the suitable parameters were given.

Study of the Effect of Material Properties and Sheet Thickness on Formability of Conical Parts in Hydro-Mechanical Deep Drawing Assisted by Radial Pressure

Abstract: Conical parts have a lot of usage in industries. Therefore, it is important to form these parts with high accuracy. In sheet forming processes, producing conical parts is one of the most difficult aspects. The two major problems that occur in the production of conical parts are rupturing and wrinkling. Among the forming processes for producing conical parts, the most capable one is hydroforming deep drawing. In this study, the effects of material properties and initial sheet thickness on forming and thickness reduction of the part were examined by using hydro-mechanical deep drawing assisted by radial pressure. For investigating these two parameters, pure copper and st14 steel are used. In experimental evaluation, sheets with thicknesses of 2.5 mm were used. In the simulation study, the thicknesses of 0.5, 1, and 2 mm were also examined. There is a good agreement between experimental and simulation findings. The results showed that for thinner sheets, the thickness reduction is less, and thus, a more uniform thickness distribution curve was obtained. Also, it was illustrated that for St14 steel sheet the thickness distribution curve will be more uniform compared with that of pure copper sheet.

Modeling of Microchannel Hydroforming Process With Thin Metallic Sheets

Abstract: Micro/mesoscale metal sheet hydroforming (SHF) process is an efficient approach suitablefor mass production to fabricate metal parts with micro/mesochannel features. In conven-tional sheet hydroforming process, the channel’s feature sizes (e.g., the channel width, filletradius, etc.) are much greater than the sheet’s thickness, so that the influence of the filletand the inhomogeneous stress/strain distribution through the thickness direction can beignored. However, the influence becomes increasingly important, because the thickness ofthe sheet and the feature dimensions of the microchannel are in the same magnitude as thefeature sizes of the material and tools reduced to micro/mesoscale. In this paper, an analyt-ical model with consideration of the inhomogeneous stress/strain distribution was devel-oped to predict the channel profile at different pressures in micro/mesohydroformingprocess. Plane-strain deformation behaviors in the section of the workpiece were studied,and the relation function between the pressure and the channel height was established. Viathis function, the channel height could be accurately predicted for a given pressure. Fur-thermore, an experimental setup was prepared, hydroforming experiments using micro-channel dies with various geometric dimensions were conducted, and the channel height ofthe workpieces was measured. It was found that the experimental results matched well withthe simulation results, which confirmed the validity of the analytical model proposed in thisstudy. It is expected that the model will be beneficial in the optimization of the microchan-nel hydroforming process. [DOI: 10.1115/1.4006180]Keywords: sheet hydroforming, micro/mesoscale, analytical model, microchannel

Tailored Profiles Made of Tailor Rolled Strips by Roll Forming – Part 2 of 2

Abstract: The main scope of the presented work is to demonstrate the potential of load optimized tubes with a varying thickness distribution in circumferential direction produced by roll forming. As initial material a so called Tailor Rolled Strip (TRS) sheet metal coil produced by Strip Profile Rolling (SPR) method was used instead of plain sheet. The TRS sheet metal is manufactured in a continuously working process by rolling one or more groves in transverse direction into the sheet metal coil. In this paper, the secondary forming of the TRS sheet metal to TRS tubes is investigated by means of FE-simulations and roll forming experiments. To simulate the manufacturing process of the TRS tube by FEM, an integrated consideration of the process is necessary because of the large local strain hardening in the groves of the initial SPR sheet metal. In experimental roll forming operations welded tubes could be manufactured successfully. The geometrical and material properties of these tubes are analyzed. The reprocessing of TRS tubes by hydroforming is investigated by means of tube bursting tests. It has been found that an additional annealing process is necessary to achieve deformations in the grooved area during the hydroforming process.