Due to the size effect, nano-multilayer films have a melting point depression effect, which has obvious advantages for the joining of temperature-sensitive materials. At the same time, the violent and rapid exothermal reaction between the nano-multilayer films provides a huge heat for the materials joining process. Therefore, when the nanomultilayer film is applied for joining, it can serve in brazing or diffusion bonding as an auxiliary interlayer layer, and on the other hand, it can serve as an independent heat source to provide heat for the SHS joining. The real-time observation of the reaction process of nano-multilayer films is limited by the conditions of single lens shooting speed and measurement accuracy. In addition, the application of molecular dynamics simulation has opened up new ideas for the research of nanomultilayer film reaction mechanism.
The influence of microstructure on the mechanical properties of 6061-T6 aluminum alloy and AZ31 magnesium alloy FSW joints was studied by changing Z-axial force. The results show that, when the Z-axial force is 28kN, the ultimate tensile strength of Al/Mg joints can reach 168MPa. The intermetallic compound layer at the interface is the thinnest, and there are no irregular intermetallic compounds in the severely deformed zone; The mechanical properties of the joints decrease with the increase of Z-axial force. With the increase of Z-axial force, the heat input in the welding process increases, resulting in thickening of intermetallic compound layer at the interface, the irregular structure appears in severely deformed zone and the hole-like defect appears at the upper part of the interface, which reduce the strength of the joints.
Numerical simulation of arc welding and post-weld heat treatment of TC17 titanium alloy plate was carried out, the phase transformation and creep of materials were considered in the model, evolution of temperature field during welding and heat treatment and the distribution of residual stress before and after heat treatment were obtained. Results show that, due to the large heat input, large residual stress is generated after welding, the longitudinal residual tensile stress in the HAZ zone near the welding seam reaches about 650MPa, and it decreases to about 160MPa after heat treatment. Residual stress was measured by blind-hole method and X–ray diffraction. The calculated residual stresses are in good agreement with the measured results of the blind-hole method.
In order to solve the problem of weakening of Al–Li alloy after laser beam welding (LBW) which is applied to a type of civil aircraft fuselage panel, three post–processing methods which were shot peening and heat–treatment + peening were studied. The tensile test, fatigue test and residual stress test were carried out to evaluate and reveal the strengthened effect and mechanism. The results show that fatigue performance is improved significantly but tensile property is reversed. The DFRcutoff values of 0.20mmN and 0.36mmN shot peening are increased by 27.8% and 118.5% compared to original welding state. Better overall performance is presented by heat–treatment of solution and aging + shot penning, which the tensile strength is increased by 32% and the DFR value is increased by 21.9% compared to initial state.
As a special processing technology, explosive welding is widely used in fabrication of various metal clad plate. The clad plate not only has high bonding strength, but also can realize large-area composite of different metals. The cost of noble metal can be effectively reduced. In addition to introducing the basic theory, welding window and experimental technology of explosive welding, new technology and new products of explosive welding were discussed in this paper. Furthermore, the application of explosive welding clad plates in different industry fields and their future development prospects are also described.
Compared with traditional friction stir spot welding, refill friction stir spot welding can produce perfect weld without exit hole, so it has bright future in some cases including termination hole repair of friction stir welds. New research progress of refill friction stir spot welding in the recent years has been reviewed, such as development of welding equipment, study of welding process and forming mechanism, analysis of weld microstructure and mechanical performance, and exploration of dissimilar materials, in addition, several important fields are indicated which include welding robot, keyhole closure process, weld fatigue and bonding between Al with other material.
In the study, friction pull plug welding (FPPW) process of 6–8mm thick 2219–T87 aluminum alloy was discussed. The results show that the structure of the plug and hole, the forming hole and the main welding parameters (axial load, welding speed and feed speed) have important influence on the weld formation. The use of circular arc-shaped plug rod, cylindrical plug hole and stepped tapered bottom hole can improve the flow direction and stress conditions of the base material and eliminate the unwelded defects. The welding speed is 7000r/min, the welding pressure is 20kN, the axial forging force is 20–30kN, and the feeding speed is 1.5mm/s. In the welded joint, the softening in the thermal mechanically affect zone on the base material side is the most obvious, and the hardness value is 79.9HV. Under the optimized parameters, the tensile strength of the welded joint can reach 365MPa, and the elongation is 6%, which is equivalent to 80% of the base metal.
Aiming at the polishing of compressor blade mounting plate, this paper carries out the applied research based on the automatic polishing technology proposed by Beihang University. Combined with the complex surface or structural features of blade mounting plate area, the polishing accuracy and surface roughness can meet the design requirements by the optimization of polishing wheel granularity, polishing process and contact pressure. The test results show that the purpose of replacing manual polishing has been realized, with the surface roughness Ra being less than 0.4μm and material removal amount less than 0.03mm. The polishing efficiency has also been matched with the production cycle of several NC milling machines. The process system is stable during the trial production (200 blades). It is proposed that the polishing technology will be widely used in the development and production of compressor blades.
The relationship between the forming load and the forming process parameters greatly affects the stability of the forming process and the performance of composite stringer preforms. By applying the domestic composite material L-shaped long automatic forming machine to build a mechanical forming load test system, the variation law of forming load was tested and analyzed through the study of molding temperature, molding rate, forming pitch and layup structure, which achieved an empirical formula between process parameters and forming load. The results show that, as the molding temperature gradually increases, the molding rate gradually decreases, on the other hand, the molding pitch gradually increases, which causes the decrease of molding load. When the lamination method is different, the molding load changes as follows: [0°/45°/90°/–45°]ns>[0°/90°]ns>[±45°]ns. Finally, an empirical formula for the relationship between the forming load and the process parameters is obtained, and the molding temperature, the forming rate, and the forming pitch can be practically guided within a certain range.
A method of applying ICP algorithm was researched for the data registration of blade profile point cloud. This method can be used to align the measurement point cloud data of blade profile with its nominal data. First, the matching problem was summarized between measurement data of blade profile and its nominal data. Then the data registration method of blade profile point cloud was described based on the ICP algorithm. Next, the registration process was implemented on the MATLAB platform. Finally, registration examples and comparison experiment were given with respect to the results of CloudCompare software. As a result, the accuracy of this method was proven.
Fiber-reinforced composite materials are increasingly used in the rotorcraft structures to reduce weight and improve efficiency. The rotorcraft industry is constantly in need of higher-performance materials that offer improved mechanical strength and stiffness at a lower weight. This work introduces the composite materials typical application cases and development trends of foreign rotorcraft structures and summarizes the state-of-the-art of civil rotorcraft composite structures, also presents the future technical requirements of higher-performance composites. The overview shows that there exist technical gaps for rotorcraft composite applications between the civil and western. The conclusion shows that higher-performance structural composites, advanced functional composites, structural and functional integrated composite materials, low-cost composite integrated technologies and high-confidence virtual validation technologies of composites will be the future focus.
As an outline control and coordination method commonly used in the development of aircraft in recent years, aircraft template is still not replaceable in current aircraft development for its convenience, low-cost and technological maturity. However, in current digital environment with rapid development of intelligent technology, the design technology relying on 2D drawings has become an important factor that restricts the efficiency and cycle of aircraft development, for which research and development of 3D design technology based on 3D geometric models of parts has become an urgent need for the aviation industry at present. In view of the problem, the 3D design of outline template is studied, which is a large branch of template in sheet metal parts manufacturing. An algorithm of parts’ geometric information extraction and template rapid design is proposed, of which the main parts are as follows: infrastructure feature of sheet metal is defined and its extraction method is proposed. Flange feature are constructed and the geometric attributes required for the template design are calculated. The profile of the outline template are calculated according to the information and data extracted, and the adding are appended. The 3D model of outline template is finally generated. The feasibility and effectiveness of the algorithm are verified by case tests.
To improve the electrical discharge machining (EDM) ablation efficiency of superalloy Inconel718 and enhance the post-ablation surface quality of the superalloy, the multi-channel discharge ablation milling experiments with Inconel718 were performed using a new method of multi-channel discharge ablation. The results show that the number of discharge channels was random in the multi-channel discharge ablation process. In a pulse discharge cycle, with an increase in discharge channels, the voltage waveform decreased stepwise while the current waveform rose stepwise. Compared with EDM ablation, the material removal rate (MRR) of Inconel718 with multi-channel discharge ablation increased by 73.7%, as the total loop current of multi-channel discharge ablation increased. In addition, as the multi-channel discharge dispersed the discharge energy, the surface roughness of the workpiece decreased by 14.6%, surface micro-cracks decreased, and recast layer thickness decreased.
