<0.2mm is called foil. According to the thickness of the metal foil is divided into thick foil, single-zero foil and double-zero foil. Among them, the thickness of thick foil is <0.2mm-≥0.1mm, the thickness of single-zero foil is <0.1mm-≥0.09mm, the thickness of double-zero foil is ≤0.001mm, and the thickness of the thinnest foil that can be industrially rolled at present is 0.0045mm.Nowadays, aluminium foil has the largest production, which accounts for almost more than 85% of the world's total production of foils, and China is the largest producer and exporter of aluminium foils in the world. The output in 2020 reaches 4,050kt, which is about 65% of the global total, and the export volume accounts for 30% of the output, which reaches 1,215kt.

Titanium foil is difficult to produce, high price, low production, it is estimated that the world's production in 2020 will not exceed 20 tonnes, the main producer is the United States, and the use is not wide, the aircraft skin insulation material is one of its high-end applications. As we all know, when the aircraft flying in the air, its outer metal skin will be due to intense friction with the air and other reasons for heat heating, in order to heat is not transmitted to the internal, must be set up to protect the thermal insulation layer (Figure 1). It consists of four layers of insulation boards welded together, with a layer of thinner flat sheet sandwiched in between. Figure 2 is the heat insulation plate parts diagram, is made of {{30}}.08mm TB2 alloy foil, TB2 is a -type titanium alloy, Ti{{10}}Mo-5V-8Cr-3Al alloy (mass %): Al2.5-3.5, Mo4.7-5.7, V4.7-5.7, Cr7.5-8.5, Fe0.30, C0.05, N0.04, H0.015. O0.15, other impurities individual 0.1, total 0.4, the rest Ti.

The United States, France and other super-plastic forming process to process this titanium foil heat insulation spanner, however, this process can be processed out of high-quality insulation board, but the production cycle is long, and the workpiece for a long time in a high-temperature state, will be absorbed more or less oxygen, titanium above 649 degree no longer has the ability to oxidation, will absorb more oxygen and become brittle, so that the mechanical properties of the overall decline. In addition, superplastic forming is suitable for the preparation of simple shape of the workpiece, for the complex workpiece shown in Figure 2 is very difficult to superplastic forming, because the processing of the mould is never easy.

As the heat insulation plate is diffusion welding, therefore, should be precise and strict control of oxygen content, so it is best to weld in a vacuum furnace, but this needs to be added to the expensive equipment, increasing the investment, but also increase the operational difficulties. For this reason, Beijing Institute of Aeronautical Technology Cheng Xiuquan, etc. proposed the use of semi-dipole mould with the use of envelope protection process successfully prepared qualified low-cost, high quality and high efficiency of the titanium foil aircraft heat insulation plate, the effect is good, and get the high praise of the user.

Production, first of all, the TB2 alloy foil placed in the envelope, in the thermoforming before the removal of oxygen in the envelope, can be removed by conventional vacuuming method, suction will be sealed after the envelope. The use of sleeve technology should pay attention to the following matters: carefully clean up the titanium sheet and sleeve surface oil and debris, be sure to dry and clean; strict selection of sleeve material, no leakage at high temperatures, itself does not emit any gas, should also be selected as much as possible to use high-temperature strength of the lower material, in order to reduce the resistance to deformation, to improve the life of the mould, to ensure that the dimensional accuracy of the workpiece requirements; sleeve should be coated with a layer of thin and uniform stop welding flux, so as to avoid sleeve And titanium foil welded together, but the stop welding agent at high temperatures can not emit any harmful gases, can not contain water, glue and other substances.

Will be prepared in 750 degree forming package, the pressure should not be too high, preheating 1min-2min, holding pressure 20s-30s, remove the package, to be cooled down to take out the workpiece, the surface of the workpiece is almost as bright as the original foil. Measurement results show that the oxygen content of the surface layer <200ppm, no change in the thickness of the oxide layer. It can be seen that the sleeve not only protects the workpiece from contamination, but also bears most of the uneven deformation, which greatly improves the uniformity of the deformation of the workpiece, and the measured thickness of the deformed workpiece is 0.067mm-0.072mm, which is completely within the deviation range of the thickness of the original foil.