Hydroforming（or Internal high pressure forming） is an advanced manufacturing technology for manufacturing hollow monolithic components. It is a kind of pipe material used as a blank material, and oil is used as a pressure transmitting medium. When an ultrahigh pressure is applied inside the pipe, axial thrust is applied to both ends of the pipe blank. Make up the feed.

Due to the combined action of the two external forces, the tube blank is plastically deformed, and finally adheres to the inner wall of the cavity, so that the tube blank becomes a modern plastic processing technique with three-dimensional shaped parts. According to the forming characteristics of the tube blank, the parts are divided into a forming zone and a feeding zone. The forming zone is the portion of the tube blank that undergoes a plastic deformation diameter change; the feed zone is the portion that feeds the forming zone.

When the inner high pressure is formed, the pipe end seal is formed by the punch and the die to form a rigid seal, so the mold is easy to wear at this place, and the wear block is usually used in the mold seal section to improve the die life. After the parts are formed, the subsequent processes such as slotting and punching are completed by the auxiliary hydraulic cylinders in the mold. Then the oil is relieved, the axial punch returns, and the hydraulic machine slides up, and the parts can be taken out.

The Hydroforming（or Internal high pressure forming） process is mainly divided into three stages: (1) Initial filling stage The tube blank is placed in the cavity and clamped, and the axial punches at both ends are horizontally advanced to form a seal. The air inside the tube is discharged by prefilling the liquid. (2) Forming stage At the same time as the tube blank is pressurized and bulged, the punch advances the feeding inward according to the set loading curve, and the tube blank is basically pressed against the mold under the combined action of the internal pressure and the axial feeding. Most of the area except the transition R angle has been formed at this stage. (3) Shaping stage The internal pressure is increased to make the transition R angle completely fit the cavity, and the workpiece is finished. The main technical parameters of the Hydroforming（or Internal high pressure forming） are initial yield pressure, cracking pressure, forming pressure, axial feed force, clamping force and feeding amount. (1) Initial yield pressure The pressure required for the tube blank to plastically deform. (2) Cracking pressure The pressure at which the billet is cracked. (3) Plastic pressure In the later shaping stage, the pressure required to ensure the complete formation of the part. (4) Axial feed force The basis for the selection of the axial propulsion cylinder is determined by three parts: the force to ensure plastic deformation of the tube blank, the high pressure reaction force of the punch and the friction force. (5) Clamping force The force required to close the mold during the forming process is the main basis for the selection of the hydraulic press. (6) Feeding amount Determine the important parameters of the horizontal cylinder stroke. Due to the influence of the loading path and the frictional force, the feeding amount cannot be completely sent to the forming zone, and the wall thickness of the forming zone is to be thinned, and the actual feeding amount is usually 60% to 80% of the ideal feeding amount.

Compared with the traditional thin plate stamping and welding process, the Hydroforming（or Internal high pressure forming） is processed with the pipe as the processing object, and has the following characteristics:

1) The Hydroforming（or Internal high pressure forming） process can reduce development and manufacturing costs, reduce body weight, and improve material utilization. Internal high-pressure forming parts usually only need one pair of molds, and thin-plate stamping often requires three or more processes, and tooling development and subsequent manufacturing costs will be greatly improved. The number of processes is reduced and the amount of process waste is reduced accordingly. In the case of meeting the requirements of the parts, the hollow parts of the inner high pressure forming can achieve weight loss of 20% to 30% and material utilization rate by 30% to 50% compared with the stamped and welded assembly.

2) The Hydroforming（or Internal high pressure forming） process can improve the machining accuracy of parts and the safety performance of the body. For parts with complex shapes, the internal high-pressure forming can realize one-time forming, which avoids the accumulated error of the parts in the multi-order machining process, thereby improving the precision of the parts. The Hydroforming（or Internal high pressure forming） is a cold working process, and the strength of the part can be greatly improved by the work hardening in the deformation process, and the integrity of the original tube blank is good, and the overall rigidity can be ensured, so that it can be used in the load-bearing structural parts of the automobile body. The safety of the body.

3) Due to the high pressure required for Hydroforming（or Internal high pressure forming）, the tonnage of the clamping press is also large, usually above 3500t. The high pressure generating source and electrical control system are relatively complicated, and the equipment manufacturing cost is also high. In addition, because the part forming quality and wall thickness distribution are closely related to the loading path, the cost of research and development and trial production is high. These factors have limited the development and popularization of the Hydroforming（or Internal high pressure forming） process to a certain extent. Hydroforming（or Internal high pressure forming） production line Based on the Hydroforming（or Internal high pressure forming） process, the Hydroforming（or Internal high pressure forming） production line can be mainly divided into four major modules: clamping press, forming die, high pressure generating system and electrical control system. In recent years, due to the process of high pressure forming technology in pipe parts And the cost advantage has been rapidly promoted in the automotive industry. In order to further promote the lightweight design of the car, more hollow components will be developed on the body. As the UHP forming parts are gradually applied to various positions of the vehicle body, it may subvert people's understanding of the car shape and the body.