Investigation Of Hydroforming Equipment Machining Profiled Crosess-section Tube Used In Automobile And Process Parameters

As a near-net shape metal forming technology, tube hydroforming, compared withconventional manufacturing via stamping and welding, has many advantages, such aslightening weight, improving material utilization ratio, stinting energy, reducing operation,potentially economizing tooling costs, improving surface quality, enhancing mechanicalproperties, and so on. In Europe, North America, Japan, and South Korea, it has beenwidely used in the fields of automobile, aeronautics, astronautics, national defence,chemical engineering, medical apparatus, etc. Tube hydroforming is labeled as ablue-blooded process, because it requires high cost of equipment investment and rigorousprocess, which lead it to move forward difficultly in our country. Therefore, the researchon low-cost hydroforming equipments, especially large-tonnage andlarge-operating-platform hydroforming equipments should be strengthened. Correlativematerial preparation and process design guidelines should also be completedsimultaneously. All these works are strategically meaningful for achievingindustrializations of tube hydroforming in our country, where natural resources are poor.The main work and creative harvests in this paper is listed blow:Based on the manufacturing level and working ability of equipment at home, theadvantages and disadvantages of frameworks with beam column and also with sheet frameare introduced briefly, and the feasibility for tube hydroforming equipment to adoptprestress wire-winded framework is confirmed. The solution to improve the resistance ofprestress wire-winded framework to side thrust is also brought forward. Subsequently, theclamping structure of hydroforming machine is optimized, and ultra high pressure sealstructure and hydraulic system is carefully designed. In addition, design, modeling andsimulation of the control system are carded out.Hydroforrning process is heavily influenced by process parameters such as initialoutside diameter and thickness of tube, initial contact length between tube and dies, andfriction conditions. Hence, it is essential to analyze the effect laws. Based on metal plasticdeformation theories, analytical equations are built and the laws are obtained. The equationon relationship between stress and strain under plastic state is built using Levy-Mises'syield criterion. By taking expansion region as instance, variations of stress, strain and tubedimension under different internal hydraulic pressures and axial loads are discussed.Aiming at the problems coming from geometrical nonlinearity, material nonlinearity and boundary condition nonlinearity in tube hydroforming process, nonlinear geometricalequation and constitutive equation of elastoplastic material are derived, and contactalgorithm and friction model used in numerical simulation are also introduced briefly, andsubsequently the dynamic explicit approach used for hydroforming process analysis andthe static implicit FEA used for spring back analysis are analyzed. Instrument panel beamand sub frame are taken as the case to perform the numerical simulation analysis ofhydroforming process. Effect laws of process planning and parameters, such as one-stepforming and multi-step forming, loading paths (internal hydraulic pressure via time andaxial feeding displacement via time), friction conditions, feeding amount, and materialproperties etc., on forming results are also investigated.In order to overcome the disadvantages of conventional optimization methods, thispaper presents a new optimization method to seek optimal hydroforming processparameters, which integrates dynamic explicit FEM into multiple-objective optimizationsolver based on elitist nondomiuated Sorting genetic algorithm (NSGA-â…¡). Using themethod, the feeding amount and loading paths of instrument panel beam hydroformingprocess is optimized. The optimization results obtained by this method are better than theresults obtained by the trial-and-error approach from experience or experimental studies. Inaddition, some pareto results are obtained by running simulation program at a time, andwhich offer a wider choice for process parameter design and designer's decision-making.To validate the accuracy of simulation and optimization results, a series ofexperiments about instrument panel beam are performed. From the experimental results,some laws are obtained, that hydroforming process is influenced by process parameterssuch as loading paths, axial feeding amount, and friction conditions. The results fromexperiments are compared with the results from the FEA simulation and optimization.Finally, design guidelines of process parameter are given.