Linear friction welding technology

Linear friction welding is a solid-phase welding technology. Under the action of welding pressure Pf, one of the weldments makes linear reciprocating motion with a certain amplitude A and frequency f in a straight line direction relative to the other weldment, resulting in friction bonding and shearing. Frictional heat is generated, and the temperature of the friction interface rises. When the friction surface reaches a viscoplastic state, the metal in the weld zone undergoes plastic flow under the action of pressure to form flash. When the temperature and deformation of the friction weld zone reach a certain level, the weldment Align and apply the upsetting pressure Pu, the metal in the weld zone is integrated through mutual diffusion and recrystallization to complete the entire welding process. The process is shown in Figure 4, which mainly includes the following five processes: initial friction stage, Unstable friction stage, stable friction stage, vibration stop stage, upsetting maintenance stage.

The technical advantages of linear friction welding technology in the manufacture of blisks are:

(1) High processing efficiency and low material loss. Compared with CNC milling, linear friction welding can save a lot of precious metals and improve metal utilization; the welding process is fully automated, and human factors are small. The welding control parameters such as pressure, time, frequency and amplitude are simple to control, so Its reliability is high, and the processing time is greatly reduced, and the efficiency is obviously improved.

(2) The welding quality is high, and some welding defects and welding embrittlement related to melting and solidification metallurgy are not produced during the welding process. Due to the short heating time, the heat-affected zone is narrow and the structure is not significantly coarsened. In welding aluminum and titanium alloy materials, it can better reflect its superiority.

(3) Linear friction welding can weld two different materials. Therefore, according to the needs of the overall blisk, in order to further reduce the weight and increase the thrust-to-weight ratio, suitable materials can be selected for welding. At the same time, linear friction welding can repair a single blade, which significantly improves the application rate of the overall blisk and reduces its cost.

Due to the unique process characteristics of linear friction welding, in the field of blisk manufacturing technology, it has gradually replaced electron beam welding. For example, the blisk of EJ200 engine began to use linear friction welding to replace the original electron beam welding technology in 1994. British R·R company has used linear friction welding technology to manufacture a wide-chord fan blisk.

The AVIC Beijing Institute of Aeronautical Manufacturing Engineering and Northwestern Polytechnical University have conducted a large number of studies on the linear friction welding technology of the integral blisk. The Beijing Institute of Aeronautical Manufacturing Engineering has analyzed all stages of its process, including the morphology of the flash in the process. Joint structure, tensile properties and mechanical properties, etc., so as to obtain the process parameters that affect the quality of the welded parts, and provide a lot of theoretical basis for the linear friction welding technology of the integral blisk. Northwestern Polytechnical University independently developed the overall blisk linear friction welding equipment, researched the fuzzy PID control method of the linear friction welding machine force system, formulated the fuzzy control algorithm rules, determined each rule parameter, and established the linear friction welding machine force closed-loop control system In addition, the influence of the elastic deformation of the fixture system on the welding process is analyzed. By establishing the dynamic theoretical model of the linear friction welding process, the effect of the elastic vibration of the fixed fixture on the driving force, mechanical power and output of the linear friction welding machine vibration system is studied. The influence of thermal power provides a reliable basis for the design of linear friction welding equipment.

In short, my country's research on linear friction welding technology is still superficial, and its mechanism, heat generation and heat generation, deformation flow, structure transformation and other technologies still need to be invested in a lot of research. In the 21st century, linear friction welding technology will continue to develop rapidly and be applied It is used in the manufacture of blisks of fighter engines and hollow blades.

Precision forming technology

The domestic precision forming technology in the field of blisk manufacturing mainly includes: CNC milling technology, CNC electrochemical machining technology, and EDM technology. Due to its different technical limitations, each process technology is developing in the direction of high efficiency, low consumption and low cost.