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Liquid impact forming (LIF), a composite forming technology of metal thin-walled tubes based on tube hydroforming (THF) and stamping forming, is introduced to increase the forming efficiency and decrease the cost. In this paper, a finite element model was established to study the forming characteristics of composite tubes under different mold cavities and clamping speeds. Then, the effects of different loading parameters on the bulging height, fillet radius and wall thickness distribution of composite tubes were analyzed systematically. Furthermore, the main factors affecting the formability of the tube were investigated based on response surface method (RSM), with the wall thickness variance, bulging height and fillet radius of the tube designed as targets, the mold side length, clamping speed and initial internal pressure selected as variables, the optimal loading parameters were obtained. At last, experiments of composite tubes based on the optimized loading parameters were conducted. The results showed that the deviation between the experimental results and the numerical simulation was within 5%, which verified the accuracy and reliability of the parameter optimization results.

Liquid impact forming (LIF) is a new type of composite forming method based on tube hydroforming (THF) and stamping forming. It has high efficiency and low energy consumption, with no need for external pressure source, so LIF has good development prospect and application value in the field of lightweight and integrated manufacturing. In order to investigate LIF technology, the generation mechanism of the internal pressure was analyzed in this paper. Firstly, based on the theory of the liquid volume compression, the change law of the cavity volume of metal thin-walled tubes was analyzed according to size parameters of the tube and dies during the forming process. The mathematical relationship between the internal pressure in the tube cavity and clamping parameters (clamping speed and clamping height) was obtained under the impact load. Then, the theoretical maximum internal pressure Pmax1 was discussed under different die cavities. Furthermore, the relationship between the internal pressure in the tube and the clamping time under different die cavities with a same clamping speed was obtained according to the transient dynamic analysis by ANSYS Workbench. At the same time, the simulated maximum internal pressure Pmax2 and the calculational maximum internal pressure Pmax were acquired under different die cavities. In addition, the LIF experiments were performed using a simple and suitable device to verify the calculational maximum internal pressures under die cavities with different side lengths. Through the comparison of the calculational and experimental maximum internal pressures, it is not difficult to find that the values of both showed a good agreement and the maximum deviation is 10.27%. The research results indicate that the theoretical equation of internal pressure of metal thin-walled tubes based on LIF is reliable, and it will lay a good foundation for further study.

Tube hydroforming is one of the most popular forming technologies in achieving lightweight and integration of tubes and reducing wasting of resources. To better to study the technology, combined with the research progress of scholars at home and abroad, the formability of metal thin-walled tubes under hydraulic bulging is comprehensively and systematically discussed and summarized. In this paper, the forming process and formability of metal thin-walled tubes under spontaneous bulging, hydroforming with radical crushing and liquid impact forming are analyzed in detail, and the development prospects of various forming technologies are expounded respectively. Through the analysis and summary of the formability of tube hydroforming in recent years, it provides a useful reference for the development of tube hydroforming technology.

A double-layered tube is widely used and developed in various fields because of its perfect comprehensive performance and design. With the advent of the era of a double-layered tube, the requirements for double layered tube forming quality, manufacturing cost and forming efficiency are getting higher, so forming methods of a double-layered tube are emerged in an endless stream, the forming methods of a double-layered tube have a great potential in the future. The liquid impact forming technology is a combination of stamping technology and hydroforming technology. Forming a double-layered tube has huge advantages in production cost, quality and efficiency.