Multi-axis linkage CNC milling technology

The five-axis linkage CNC milling process has been widely used in the field of integral blisk manufacturing due to its rapid response, high reliability, good processing flexibility and short production preparation cycle. The United States GE and P·W companies, the British R·R companies, etc., mostly use five-axis CNC milling to process the blisk.

The Northwestern Polytechnical University in China has conducted research on the overall blisk manufacturing technology in 1991, breaking through a number of key technologies, and developed the "special software system for multi-coordinate NC programming of impeller parts", which integrates measurement data preprocessing, surface modeling, Curved surface blanking, tool position calculation, tool position verification and post-processing are integrated. After years of analysis and research, the key process of digital precision manufacturing technology for the integral blisk has been completed, and the combined high-efficiency milling processing of side milling and plunge milling is used to complete the blisk. In addition, its independent research and development of high-efficiency disc milling-plunge milling compound milling center has a significant effect on improving the overall blisk milling efficiency. Meaning, the main milling processing methods and processing samples are shown in Figure 5.

Numerical control milling method and sample of integral blisk

Electrochemical machining technology

Electrochemical machining is a processing method that removes metal materials based on the principle of electrochemical anode dissolution. Its technological advancement (computer-controlled machining process) can ensure machining accuracy and quality, improve machining stability, and reduce production preparation time. Reducing labor intensity is one of the technical ways to solve the problem of overall blisk processing with high quality, high efficiency, low cost, and quick response.

Numerical control electrochemical machining technology combines the technical characteristics of both computer numerical control and electrochemical machining. The tool cathode has no loss and no macro cutting force. It is suitable for processing thin blades and narrow channel blisks, and it uses numerical control technology to realize the creation movement of the profile. , Wide processing range. Therefore, this technology is suitable for processing small-diameter, multi-blade, inter-leaflet channels (1.5~3mm width) and variable cross-section twisted blades.

Developed countries such as the United States and the United Kingdom have conducted in-depth research and application of the blisk CNC electrochemical machining technology. The United States GE company uses the five-axis CNC electrochemical machining method to process the blisk of the advanced engine, and its rough machining, semi-finishing and finishing The process adopts the electrochemical machining method, and the thickness tolerance of the processed blade is 0.10mm, and the tolerance of the profile is 0.10mm [21]. In the processing of the integrated blisk with a crown, Russia adopts a combined process of mechanical profiling EDM and EDM. EDM technology not only improves the processing efficiency, but also removes the surface deterioration layer after EDM and improves the surface quality.

Domestic research on the technology of NC electrochemical machining of integral blisks is still very shallow. Nanjing University of Aeronautics and Astronautics has been researching it since the mid-1980s, and proposed the “straight-blade” cathode NC electrochemical machining and forming or near forming cathode flexible electrochemical machining methods. , A simple linear blade cathode is used for numerical control generating motion, and the forming process of the groove and blade profile of the integral blisk is realized based on the principle of electrochemical anode dissolution, as shown in Figure 6. Because CNC electrochemical machining requires the use of multi-axis CNC electrolytic machine tools, it has high requirements for CNC technology, and it is difficult to master the laws of electrolytic forming. It is currently in the research stage and it is expected to solve the overall blisk machining that cannot be achieved by CNC milling.

Numerical Control Electrochemical Machining Process of Straight Blade Cathode

03

EDM technology

EDM is a special processing method that achieves the purpose of ablating conductive materials through the electric erosion effect produced by the pulse discharge between the two electrodes immersed in the working fluid. In the overall blisk machining process, compared with CNC electrochemical machining and CNC milling processing technology, EDM technology has the following technical advantages:

(1) The processing range is wide, and it can process traditional difficult-to-cut materials, such as high-temperature alloys, hard alloys, and titanium alloys.

(2) There are obvious advantages for the processing of integral blisks with complex structures and narrow passages, which can complete complex feed motions and effectively avoid the interference between the electrode and the workpiece.

(3) There is no macroscopic cutting force during processing, and neither the electrode nor the workpiece will produce macroscopic deformation, and at the same time, no defects such as burrs and tool marks and grooves will occur.

Due to the many advantages mentioned above, EDM has been widely used in the machining of integral blisks with crowns. Shanghai Jiaotong University has conducted in-depth research on the EDM technology of turbine blade discs, and developed special CAD/CAM software, which can complete turbine blade disc modeling, electrode CAD/CAM, tool click trajectory search and other functions, and perform electrical Spark machining obtains a blisk with higher profile accuracy.

Surface polishing and surface treatment technology

After the overall blisk has undergone near-forming and precise forming processing, its surface quality cannot meet its technical requirements. It also needs to go through surface polishing and treatment processes to reduce its surface roughness and improve profile accuracy, thereby increasing the fatigue strength and fatigue strength of the blisk. Service life. At this stage, the domestic blisk surface polishing process is still in the manual polishing stage. Manual polishing is not only labor-intensive and low-efficiency, but also burns easily on the polished surface, and it is difficult to guarantee the accuracy and surface integrity of the blisk, resulting in reduced blisk reliability. At the same time, it is affected by the technical level and proficiency of the workers, and the processing quality is unstable, which seriously affects the performance, safety and reliability of the aero engine and the production cycle. Therefore, it is urgent to conduct in-depth research on the automatic polishing technology of the blisk surface to realize its automatic polishing process. The surface polishing and treatment technologies of the blisk include: abrasive flow polishing technology, numerical control polishing technology, laser shock treatment technology, surface shot peening and finishing technology.