Sheet metal parts are important parts of aircraft body and automobile body, in order to shorten the production cycle of sheet metal parts, finite element method is used to evaluate the manufacturability of parts in the initial stage of part design. In order to improve the calculation efficiency of the existing finite element method of sheet metal forming and ensure the simulation accuracy, based on the theory of one-step quick forming finite element method, multistep quick forming finite element method was studied. The influence of loading path and deformation history in sheet metal forming process is considered by introducing intermediate configuration. The structure of intermediate configuration is the key of multi-step quick forming finite element method, the intermediate configuration is decoupled into two independent processes of bending deformation and tensile deformation, which were calculated. In the bending deformation stage, the slip constraint surface is calculated according to the position relationship between the sheet and the die without considering the material flow. At the stage of tensile deformation, the material flow is restricted to the slip constraint plane, and the intermediate configuration is obtained through stress balance iteration and node modification. Taking a typical sheet metal part as an example to simulate the forming, and comparing with the existing commercial finite element software in calculation accuracy and efficiency, the feasibility and effectiveness of the algorithm are verified. The results show that the proposed algorithm can quickly construct reasonable intermediate configuration and accurately predict the formability and thickness distribution of parts.

Titanium alloy hollow lattice has excellent mechanical properties and physical functions, which is a typical load-function integration structure, and has good application prospects in future aircraft. The superplastic tensile elongation of TA15 and TA32 titanium alloys was measured by uniaxial tensile method at different temperatures and strain rates, the maximum elongation reached 1450% and 950% respectively. The diffusion bonding tests of TA15 and TA32 titanium alloys were carried out at different temperatures and pressures. According to the superplastic tensile and diffusion bonding tests, the optimal process parameters of superplastic forming and diffusion bonding were determined as 920 ℃/1.5–2.0 MPa/2 h. The hollow lattice structure of TA15 and TA32 titanium alloys with different configurations and geometric parameters were formed by superplastic forming/diffusion bonding (SPF/DB) process at optimal craft. The mechanical properties of titanium alloy hollow lattice were measured by flat compression and three-point bending method, the maximum strength reached 23.83 MPa and 596 MPa respectively. The influence of geometric parameters on the flat compression and bending properties of titanium alloy hollow lattice was studied by means of finite element analysis and experimental analysis. The thermal insulation performance of titanium alloy hollow lattice structure was studied by measuring the temperature difference between the cold and hot surfaces by single-side heating method. At 400 ℃/1 h, the thermal insulation temperature difference reached 276.3 – 310 ℃.

Spark plasma diffusion bonding (SPDB) is a new diffusion bonding technology with high efficiency, green and energy saving, which is based on the principle of pulse current promoting plastic deformation and atomic diffusion in the process of spark plasma sintering, and combines temperature field–force field–electric field. Spark plasma diffusion bonding is suitable for the bonding of dissimilar metal materials, refractory metals and high-temperature ceramic materials, and has great application potential in aerospace, nuclear power, high-end medical equipment and other fields. This paper briefly introduces the basic principle and equipment composition of spark plasma diffusion bonding technology, and the action mechanism of pulse current on interface atomic diffusion bonding and interface phase formation. The basic principle and equipment composition of spark plasma diffusion welding technology are briefly described. The mechanism of atomic diffusion and phase formation at the interface is summarized by pulsed current. The research status at home and abroad on the application of spark plasma diffusion welding to materials is introduced in detail. Finally, the future trend of spark plasma diffusion welding technology is prospected, and the development direction and suggestions are given according to the development status and issue of this technology.

Superplastic forming technology is an advanced forming technology that makes use of the superplastic large deformation ability of materials to manufacture thin-walled complex components. In the process of superplastic forming and superplastic forming/diffusion bonding, there are many process parameter variables and high requirements for parameter synchronization control, which are generally carried out on special superplastic forming machine. It is more convenient to control key parameters such as blank temperature, tool and die temperature, deformation zone, deformation speed, deformation stress, etc. The traditional superplastic forming machine is far from meeting the needs of scientific research and production due to its unidirectional pressing, insufficient functional integration and low degree of automation. Therefore, this paper focuses on three new functions of superplastic forming equipment, including multi-directional loading, “gas–liquid” coupling control and automatic feeding and unloading. With the integration and deep integration of advanced manufacturing technology and information technology, superplastic forming machine will further develop towards the direction of large-scale, clean, automatic, multi-energy field compounding and specialization, and will further improve the production efficiency and application scope of superplastic forming technology.

In view of the technical difficulties in the preparation of NiAl alloy sheets and the secondary forming of the complex thin-walled components, a new integrated process of forming and in-situ reaction is proposed to manufacture NiAl alloy thin shell parts. First, the Ni foils and Al foils are alternately stacked in the mold and plastic forming is performed under the action of solid granules medium, then the formed Ni/Al laminated thin shell parts continue to stay in the mold and are heated under the pressure of the solid granules medium, leading to the in-situ reaction of Ni/Al layers into the NiAl alloy. Finally, the NiAl thin shells are manufactured. The microstructure of the component was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and the high temperature mechanical properties were tested. The results show that the NiAl alloy conical shell is composed of single NiAl phase, and the coarse crystal layer and fine crystal layer are alternately distributed in the thickness direction, which is a typical bimodal structure without holes and other defects. The component hardness is 317HV and the distrbution is uniform, the tensile strength is 71 MPa at 1000 ℃, and the elongation can reach 74%.

High-temperature tensile tests were performed on TA15 titanium alloy at strain rates of 0.001 s^–1, 0.005 s^–1, 0.01 s^–1 and temperatures of 880 ℃, 900 ℃, 920 ℃, 940 ℃. The material exhibits excellent superplasticity with elongation exceeding 500% above 920 ℃ and below 0.005 s^–1. The constitutive equations of TA15 titanium alloy and the strain sensitivity index m and material constant K values at different temperatures with strain rate of 0.005 s^–1 were calculated. Finite element simulations were used to analyze the thickness distribution of the double-layered structural component, and pressure–time curves were obtained. At the temperature of 920 ℃, the hollow double layer structural parts with local weight reduction are made by using pre-hollow panels SPF/DB, the minimum wall thickness is 0.31 mm, the diffusion area of the component was analyzed by ultrasonic C-scan, and the results showed that the bonding ratio is higher than 95%.

The SPF/DB process of ultra-thin hollow four-layer structure was investigated by using TA15 titanium alloy hot rolled sheet. Firstly, the superplastic deformation behavior of TA15 titanium alloy in the process temperature range was studied by tensile test, and the corresponding stress–strain curves were obtained. Then, finite element software was used to simulate the design of the four-layer longitudinal reinforcement structure with thin-walled transverse local penetration, and the distribution of wall thickness reduction and stress concentration during the forming process is determined, which provides effective guidance for the subsequent diffusion bonding test. Finally, an ultra-thin hollow fourlayer structure with good vertical ribs and a triangular zone width of only 0.9 mm was successfully prepared. The maximum thinning rate of the panel was 18.6%, the maximum thinning rate of the core plate was 55.1%, and the bonding rate of the diffusion bonding area between the core plate and the panel was 92.1% – 98.5 %. The original microstructure of TA15 sheet for forming is fine, broken and equiaxed, the average grain size is less than 5 μm. After long-term superplastic deformation and thermal exposure, the grain size grows significantly.

Superplastic bulging properties of TA32 titanium alloy sheet under different strain paths were studied by carrying out high temperature gas bulging experiments. Four kind of elliptical dies with different minor-major axis ratios were used to achieve different biaxial tensile strain paths, and the rolling direction and transverse direction of the specimen were parallel to the major-axis direction of the die to analyze the deformation anisotropy. Based on the Barlat' 89 yield criterion under the non-associated flow criterion as well as the strain components, thicknesses and radius of curvature at the apex of the bulging specimens, the equivalent stress–strain curves under different strain paths were determined. The results show that the superplastic bulging properties of TA32 sheet have a remarkable strain path dependence, when the loading path changes from equi-biaxial tension to near plane strain, the ultimate bulging height of the sheet decreases, the thinning rate and peak stress increase, the elongation and formability decrease. Meanwhile, TA32 sheet exhibits significant anisotropy of mechanical properties under high-temperature biaxial tension. When the rolling direction is parallel to the first principal strain direction, the material has lower peak stress and higher plasticity, showing better formability.

Helical milling is a new processing method for assembly hole in aerospace field. Compared with the traditional drilling technology, helical milling has many advantages, such as good processing quality, high drilling efficiency, low tool cost. During the process of helical milling in machining carbon fiber reinforced polymer (CFRP) /titanium alloy (Ti) stacks, due to the huge difference between the two materials, there is a hole diameter deviation between the two layers, which affects the hole making accuracy and becomes an urgent problem to be solved in the application process of helical milling technology. A helical milling test device was built, and the helical milling test of CFRP/Ti stacks was carried out. According to the test results, the causes of the hole diameter deviation between layers of CFRP/Ti were analyzed. The method of restraining the hole diameter deviation between layers was proposed based on changing parameter processing and milling method. Finally, the confirmatory test was carried out and the results show that the hole diameter deviation between layers in helical milling of CFRP/Ti could be effectively reduced by using the variable parameter machining method, which is less than 0.02 mm.

In order to improve the quality of laser drilling, laser drilling experiments of titanium alloy by using the waterjet assisted laser scanning machining method was investigated, the effects of process parameters on the hole diameter and hole taper of titanium alloy were analyzed by response surface methodology. The results show that the impacts of hole diameter are the laser current, pulse frequency and pump voltage in descending order. While the effects of pulse frequency, laser current and pump voltage on hole taper are in descending order. When the optimal laser current is 33.6818 A, pulse frequency is 30.6818 kHz and pump voltage is 12.6818 V, the hole entrance diameter and hole taper are the minimum, the hole exit diameter is the maximum. At the same time, it is found that the hole diameter in waterjet assisted laser machining is larger than that in the air machining, but the hole taper is reduced by 33.2%.

Carbon nanotubes have excellent mechanical properties, but also have high conductivity, high thermal conductivity, flame retardancy and other functional advantages, which are expected to be widely used in many functional directions in the aviation field. In this paper, according to the application requirements of carbon nanotubes in various functional directions in aviation field, the research progress of carbon nanotubes in conductive structures and electromagnetic shielding, in the structural health monitoring of composite materials for aviation, in the electric heating curing of composite materials, in the electric deicing of aircraft wings, and in flame retardant composites are reviewed. The advantages and disadvantages of carbon nanotubes in various functional applications are analyzed. The results show that carbon nanotubes and their macrostructures have great potential in various functional applications, but they still need large-scale, low-cost preparation technology, high-quality stability control technology as a strong support for their functional applications.