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In order to further explore the forming limits of thin-wall tube necking and thickening, and obtain sufficient thickness of the tube in the thickening area, local electric pulse-assisted forming experiments were carried out to study the effects of current intensity and feed speed on the necking and thickening forming of thin-wall tube. The experimental results show that with the increase in current intensity, the temperature in the forming area of the tube increases, and the forming load for necking and thickening decreases. However, with the increase in feed speed, the overall forming load for necking and thickening increases in general, and the smaller feed speed is more conducive to forming. Taking into account the forming efficiency and electrode loss, the corresponding forming process window is obtained for the manufacturing of good parts. That is, during the necking stage, the current intensity shall not be less than 300 A, and the feed speed shall not exceed 10 mm/min. During the thickening stage, the current intensity should not be less than 1400 A, and the feed speed should not exceed 1 mm/min. The target part is finally formed, with an average wall thickness of 5.984 mm in the thickening zone and a thickening rate of 303.2%. [ABSTRACT FROM AUTHOR]

The different branch diameters of five-way tube affect the design of loading internal pressure in the hydroforming process, where the large-diameter branch is broken more easily than the small-diameter one due to the same ultimate stress of tube material in one-step forming method. Therefore, the first four-way and then five-way of multi-step forming (FFTF) method and the first three-way and then five-way of multi-step forming (FTTF) method were proposed to fabricate the 5A02 aluminum alloy five-way tube with two kinds of branch diameters to avoid the burst of large-diameter branch tube. The finite element simulation of five-way tube hydroforming process shows that the height of small-diameter branch tube is lower and serious wrinkles appear at the large-diameter branch tube in the one-step forming and FFTF method. By optimizing the length of punch, a five-way tube with a big branch height and uniform wall thickness was obtained with the FTTF method. The approach of lengthening the punch in the experiment increased the height of formed branch and reduced the wall thickness reduction rate of five-way tube in FTTF method. Overall, the findings mentioned above cannot only offer guide in creating five-way tube with excellent quality, but also be taken as reference to the hydroforming studies on multi-way tube in the future. [ABSTRACT FROM AUTHOR]

A new technology of local electrically assisted necking and thickening forming of 5A02 aluminum alloy tube is developed, to enhance the quality of tube necking and thickening and increase the thickness of the tube wall in thickening area. Advantages of the electroplasticity of pulse current are utilized to guarantee the forming quality of tube necking and thickening. Process parameters such as thickness of the guide block, contact mode of the upper electrode, and the cooling method were studied. The results indicate that the thicker the guide block, the less prone to premature bending and instability in the forming process. The integral electrode is the most stable and the best heat dissipation effect, which avoids the tube from internal buckling. With the increase of the cooling capacity, the average wall thickness increases first and then decreases. According to these results, a process scheme is designed, with which successful experiments have been performed. And the microstructures of the necking and thickening areas were studied by optical microscope. Local electrically assisted necking and thickening technology shows great benefits in tube extrusion forming. [ABSTRACT FROM AUTHOR]

Due to the influence of pressure control precision, the actual pressure in hydroforming process for the tube is usually greater than the design pressure, which causes the fracture of tube. The loading path of T-shaped tube hydroforming process was designed based on the control of limit pressure. First, the limit pressure of tube Pmax was obtained by improving the internal pressure until the tube cracked in the T-shaped tube hydroforming process without the feeding and a theoretical model for predicting instantaneous pressure is developed. Second, the tube bulge height Hmax and the maximum feeding Dmax were explored through manual operation of feeding and pressure in hydroforming machine, in which the overflow pressure is set to Pmax by using an overflow valve; finally, the loading path of internal pressure and feeding was designed using the ladder growth and linear growth in T-shaped tube hydroforming experiment in which the maximum pressure, the maximum feeding, and the overflow pressure (equal to internal pressure) were set to Pmax, Dmax, and Pmax, respectively. The results show that the obtained limit pressure Pmax can avoid the overpressure of the tube and restrain the fracture of the tube through the action of the overflow valve. Meanwhile, the accuracy of the prediction model to figure up Pmax was verified through experiments: the theoretical prediction value of the established model was consistent with the experimental true value. Compared with the T-shaped tube formed by linear loading path, the wall thickness of the formed T-shaped tube by ladder loading path is more evenly distributed without wrinkles and fractures and the height of the formed branch tube close to Hmax. At the same time, it is found that under the differential lubrication tube blank, the time of obtaining a suitable loading path is significantly reduced, and the collocation of ladder mode is simpler and more efficient. [ABSTRACT FROM AUTHOR]

Necking technology was widely used in the airplane pull rod parts. The tube end of airplane pull rod parts made by the traditional technology (such as spinning) was insufficient to thread directly, and it needed to rivet the threaded sleeve, which result in the low joint strength of airplane pull rod parts. Alternatively, a method of necking and thickening for a thin-walled tube using differential temperature extrusion was proposed for the purpose of threading directly. In this work, the effects of temperature and friction during the process of necking and thickening for 5A02 aluminum alloy thin-walled tube were conducted by finite element (FE) simulations and experiments. The simulation results showed that the higher the temperature was and the lower the friction coefficient was, the bigger the thickness of thickening area in the tube end was, which benefited to thread directly. Then, FE simulation was verified to be reliable by experiments. Subsequently, the effect of temperature on the microstructure in the thickening area of the formed workpiece was investigated by the optical microscopy. The microstructural morphology showed the grain size of the thickening area in the formed workpiece coarsened in comparison with the unformed tube when the material was heated at high temperature during the process of necking and thickening of tube. And the higher temperature was, the coarser the grain in the thickening area was. Finally, the reasonable forming temperature and friction was proposed for improving the micro and macro forming quality of the airplane pull rod parts under the necking and thickening process for thin-walled tube. [ABSTRACT FROM AUTHOR]