China successfully developed the first 3.35m aluminum-lithium alloy box bottom

According to news from the China Academy of Launch Vehicle Technology on the 6th, recently, the Institute 703 led the joint overall design department to develop China's first "3.35m aluminum-lithium alloy box bottom." The bottom of the box is integrally formed without a single weld, and the material has been upgraded. This marks a major breakthrough in China's launch vehicle tank manufacturing technology and provides important technical support for the development of China's heavy launch vehicle and new generation of manned rockets.

On China’s active rockets, each rocket’s fuel tank has two bottoms. The bottom of each box looks like half a watermelon. The traditional craft is "tailor-welded" by 8 melon petals, 1 top cover and 1 transition ring. There are 10 main welds on the bottom of each box.

According to Wen Tao, deputy director engineer of the 703 Institute of China Academy of Launch Vehicle Technology, a rocket usually has 26 box bottoms, about 260 welds, and a total length of nearly one kilometer. The welding seam destroys the continuity of the material and is the weakest link in the entire bottom of the box. Defects such as pores, deformation and cracks are prone to occur during welding, which affect the reliability and qualification rate of the bottom of the box. After eliminating the weld, the rocket can lose 60 kilograms.

Wen Tao introduced that the "3.35m aluminum-lithium alloy box bottom" adopts the integral spinning forming process, that is, a plate is formed in a single step through a mold in a numerical control program, and is formed in one step. The integral spinning forming has less manufacturing process, short cycle, and high reliability. There is no weld on the whole bottom of the box. The original production cycle of a box bottom took two to three months, but now it can be completed in 15 to 20 days.

Internationally, the bottom of the aluminum-lithium alloy box represents the development direction of the carrier rocket tank. The overall spinning process is the general trend, but its overall formation is very difficult. Currently, only the United States, Japan, and Europe have mastered this technology.

Aluminum-lithium alloy is an advanced lightweight structural material with the advantages of low density and high strength. The use of this material can reduce the weight of the arrow body structure by more than 15% and increase the carrying efficiency by 20%. 703 has passed hundreds of tests and a large number of accurate calculations to overcome the four major technical difficulties of box bottom deformation resistance, forming temperature zone, forming path, deformation amount and pass distribution. The first trial-produced aluminum-lithium alloy box bottom was successful.

Wen Tao said that the successful mastery of the process of "aluminum-lithium alloy box bottom integral spinning forming" will provide important technical support for the development of China's heavy-duty launch vehicle and a new generation of manned rockets. Conquering the "3.35m aluminum-lithium alloy box bottom" forming process is only the first step. In the follow-up, they will continue to trial-produce the "5m aluminum-lithium alloy box bottom" and realize the leap from forming the bottom of the rocket box from having mold to no mold.

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