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Liquid impact forming (LIF) is a new composite forming technology based on tube hydroforming (THF) technology, which changes the volume of die cavity through impact load and rapidly generates internal pressure to realize tube forming. It does not need external pressure supply source, and it is low cost and high efficiency. In order to study the forming characteristics of the natural bulging area of thin-walled metal tube under different model side lengths and different closing velocities, the change of the cavity volume of thin-walled metal tube under impact hydraulic bulging was first analyzed theoretically, and a mathematical model of internal pressure was established. Then the effects of different loading parameters on the internal pressure, bulging height and wall thickness distribution in the natural bulging area of thin-walled metal tube were studied. Finally, through the comparison of finite element simulation analysis and experiment, it was found that the deviation between the experimental results and the numerical simulation was within 6%, which verified the accuracy and reliability of LIF. It also provides a certain theoretical research and application basis for the development of LIF of metal thin-walled tube. Tube hydroforming technology based on structural lightweight and integration is now widely used in the production of parts and components in aviation, automobile, household appliances and other industries. The technology takes the tube as the blank, bulges the tube into the desired shape under the combined action of liquid pressure and axial load. But it must rely on the high pressure hydraulic power source and the corresponding control system, which has the disadvantages of high manufacturing cost and low forming efficiency. Liquid impact forming is a new tube forming technology developed on the basis of stamping and hydraulic bulging. By changing the volume of tube cavity by impact load, the liquid pressure can be rapidly increased. This process does not require a high-pressure hydraulic power source, has high forming efficiency, and one-time forming, which has great research value. This technology has many applications in aerospace and mechanical engineering, such as automotive subframes and rear axles, etc. And the technique can also be applied to pipeline engineering, especially metal shaped tubes such as tees and special-shaped tubes, etc. [ABSTRACT FROM AUTHOR]

The flow stress, used to describe the plastic deformation behavior of thin-walled tube, is one of the most important parameters to ensure reliable finite element simulation in the tube hydroforming process. In this study, a novel approach of on-line measurement based on digital speckle correlation method is put forward to determine flow stress of thin-walled tube. A simple experimental tooling is developed and free-bulged tests are performed for 304 stainless steel and H62 brass alloy tubes. An analytical approach is proposed according to the membrane theory and the force equilibrium equation. The developed method is validated by means of FE simulations. The results indicate that the present method is acceptable to define the flow stress in the tube hydroforming process. [ABSTRACT FROM AUTHOR]