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In tube hydroforming process, due to friction condition, uniform wall thickness and sharp corners may not be achieved. Use of ultrasonic vibration can improve the contact conditions at the tube-die interface. The current work studies the effect of applying ultrasonic vibration on wall thickness and corner filling of hydroformed tubes. In order to understand the process an analytical model based on geometric relationships and stress-strain states has been established. The wall thickness and corner radius of hydroformed tube can be obtained by solving the model. By comparing the results of the FEM models of tube in two cases of ultrasonic hydroforming (internal pressure along with the oscillations of the die) and conventional hydroforming (internal pressure only), the effects of vibration on wall thickness and corner filling are investigated. The results indicate superimposing ultrasonic vibrations to the process will increase corner filling ratio of the tube significantly, and more uniform tube wall thickness will be achieved.

Tube Hydroforming Process (THF) is heavily affected by the pressure-displacement diagram, and adjustment of the raw tube. Three common defects of the process are bursting, buckling and wrinkling. In this work, the leading conditions to wrinkling defect have been studied. Proper criteria are required to predict wrinkling condition, and to quantify wrinkling when subjected to various pressure-displacement diagrams. A variety of criteria have been presented by researchers, most of which are suitable to a specific geometry. In current work, two criteria are considered namely, the strain difference and the radius velocity. At first an accurate FEM (Finite Element Model) model of the process have been established and validated. Then based on a number of experiments with different diagram, the process have been simulated and analyzed. According to experiments imbalances between pressure and displacement, improper sitting of tube in the die, poor vacation of the tube and the existence of external tiny particle inside the die, are the reason of wrinkling criterion in the tube. The Response Surface Method (RSM) has been used to model the responses from the finite element analysis. The behavior of the process has been predicted using this model.

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The use of tube hydroforming process to produce integrated parts is growing in various industries. In this research, the hydroforming process has been used to convert the circular cross-section of the tube into a square one. In this process, due to the high hydrostatic pressure of the fluid, the friction in the contact area between the tube and the die surface increases significantly. High friction prevents the metal flowing of the tube material on the die surface and therefore it becomes very difficult to completely form the tube inside the die and obtain sharp corners. In this research, in order to improve the tube formability, applying ultrasonic vibrations to the hydroforming die has been used, which causes a temporary gap to be created in the contact surface of the tube and the die, and therefore the amount of friction is reduced and the tube material can slide more easily. By developing a 3D finite element model, the ultrasonic tube hydroforming process was evaluated. Modal analysis was used to evaluate the different shape modes of the die. The effects of ultrasonic vibrations on the deformation process have been evaluated using two variables: corner radius of square die and average wall thickness. An ultrasonic hydroforming setup was designed to form the annealed copper tube and was stimulated using selected resonance frequencies. The results of the finite element model were validated with the deformed tube in the experimental test. After confirming the results, the numerical model was used to evaluate the process parameters.