The blade is an important part of the aero-engine. The main function of the blade is to cooperate with the engine cavity to form a continuous change of the air or gas cross-section and direction. Cooperate with the main shaft or the turbine disk to realize the high-temperature compression and easy gas flow of the gas generator, and at the same time ensure the gas. The high speed flow is converted into the required aircraft power. The functional mission and working characteristics of the blade in the engine determine the complexity of blade machining. The leading process uses advanced manufacturing processes. The difficulty in blade manufacturing lies in the fact that it is a thin-walled part with poor rigidity and is more sensitive to the overall rigidity of the tool-clamp-workpiece system. The relevant engineering personnel of AVIC Shenyang Liming Aero Engine (Group) Co., Ltd. pointed out in an interview with the metal processing online reporter that the modern engine blade machining is developing towards high-efficiency CNC machining.
1. Common materials for engine blades
The development trend of aviation blade materials is high performance (light weight, high strength, high modulus, high toughness, high temperature resistance, oxidation resistance and corrosion resistance) and low cost. Blade materials from aluminum alloys, stainless steels, titanium alloys to high-temperature alloys and new composite materials are constantly evolving as engine performance requirements continue to increase.
2. Characteristics of machine tool tools for aeronautical hair blade processing
The quality of the blade body profile directly affects the blade's working performance. Conventional blade processing methods are time consuming and labor intensive, and accuracy is difficult to guarantee. High-performance CNC milling machines are increasingly used in blade machining, with imported machine tools accounting for a significant proportion. The characteristics of this type of machine are as follows:
(1) Multi-axis linkage Generally, 4-axis or 5-axis linkage is realized, or more shaft control is realized on the basis of 5-axis linkage and composite machining linkage control is realized.
(2) High-speed spindle The high-efficiency CNC machining of the blade places high demands on the spindle of the high-performance CNC machine tool. The high-speed spindle is combined with the high-performance tool system to achieve efficient cutting of the blade.
(3) High dynamic response feed system In addition to the high spindle speed required under high-speed machining conditions, high requirements are also placed on the feed shaft speed and acceleration and deceleration to ensure the machine has a fast response capability.
(4) High rigidity and high precision The spindle system, feed system and machine tool structure should have good static stiffness, dynamic stiffness and thermal stability.
(5) Intelligent Machine control intelligence and intelligent process.
At present, the blade processing tool is mainly made of cemented carbide tools. Compared with foreign companies, domestic high-end products of machine tool enterprises have gaps with foreign companies in terms of technology level and industrialization. Domestic machine tool companies want to make breakthroughs in the aerospace field, but also need to strengthen technological innovation, improve product quality stability, further improve the technical service system, and enhance core competitiveness.
3. High efficiency cutting strategy for airborne blades
The material, structure and process characteristics of the airfare blade put forward higher requirements on processing quality, efficiency and cost. High-efficiency cutting is to make a detailed analysis of the "machine tool-part-tool-clamp" process system characteristics, the path of the tool, the numerical control programming, the cutting amount, etc. in the process of CNC machining, the tool type, tool structure and clamping scheme. Machining schemes such as tool axis inclination and cutting parameters such as cutting depth, cutting speed and feed rate are fully optimized to achieve high quality, high efficiency, low cost and green CNC machining.
(1) Reasonable selection of tools High-efficiency tools involve tool materials, tool coating technology, tool structure design and optimization, and tool matching technology. The choice of tool must be adapted to the condition of the equipment, and must also take into account the characteristics of the blade and difficult to machine materials, while also achieving efficient cutting. Choosing the right tool material is key, and the choice of the tool's reasonable geometry is the key. Under the conditions allowed by the process characteristics, the tool with a large radius of the tool tip is used for high-speed milling. Proper selection of tools that match the blade material and processing conditions during processing.
(2) Scientific selection of cutting amount Scientific selection of cutting amount is very important in blade processing. In the efficient milling of blades, the cutting depth, spindle speed, and feed per tooth are scientifically given according to the effective diameter of the tool. The feedrate is calculated based on the feed per tooth and the spindle speed. When machining with a ball end mill, if the axial milling depth is less than the tool radius, the effective diameter will be less than the nominal diameter of the milling cutter, and the effective speed will be less than the nominal speed. This will also occur when using a circular cutter with a shallow depth of cut. Happening. When optimizing the machining parameters, the effective milling speed should be selected.
(3) Reasonable development of the machining plan, optimization of the path of the blade to select the roughing of the blade profile, in order to remove a large margin, and leave a uniform machining allowance for the finishing, coarse milling should ensure a higher Material removal rate. For example, the five-axis linkage blade machining center has a wide-line machining function, and the cylindrical end mill is used for milling the blade. The milling trajectory is a wide elliptical arc (see Figure 1), compared to the milling of the ball-end knives. For the same peak height or surface quality for milling, the resulting tool path is much larger. Therefore, this processing has high processing efficiency. In actual machining, a rotary machining method that moves from one end to the Other end in the longitudinal direction of the blade, that is, a spiral milling method, has high machining efficiency and machining accuracy.
The finishing of the blade profile is to obtain high shape and positional accuracy, and at the same time to achieve a certain level of surface roughness. Taking titanium alloy blades as an example, in order to reduce the springback effect of titanium alloy material processing and the influence of tool wear on machining accuracy during large-area machining, the tool must ensure sharpness and avoid the same tool to be processed for a long time, causing the blade to be profiled. The level of processing accuracy is inconsistent, which is beneficial to improve the final finishing of the profile. The machining center tool magazine function is applied in the machining, and the automatic tool change is realized according to the tool life to improve the automation degree of the machining process. Using the online measurement function, the measurement program is programmed to realize effective control of the part processing process and complete processing without intervention.
4. Air navigation blade processing case
A blade blade shoulder arc is machined on a five-axis linkage device. There are two kinds of CNC machining schemes (see Figure 2 and Figure 3): 1 Using the imported ball-end tool, the spiral milling method is used to complete the rough and fine machining of the parts, and the effect is very good. 2 All use of domestic end milling cutter processing, using end knife, side edge segmentation processing method.
Comparison of schemes: Both schemes fully consider the process of CNC machining and the overall process route. The machining routes of rough milling, semi-finishing milling and finishing milling are adopted, and the cutting tools and cutting parameters are preferred, from the process method and the machining process. Controlled the deformation of the blade profile CNC machining, the effect is remarkable, achieving high-speed, high-efficiency, high-quality CNC machining without margin. The difference between the two schemes is that the first scheme uses the imported ball-end tool to process, the tool cost is high, and the machining precision is high; the second scheme uses the domestic end mill to process, the tool cost is lower, and the surface roughness value of the part is greatly reduced. The metal removal rate is high and the tool life is also ideal.
5 Conclusion
High-efficiency cutting technology for aeroplane blades is a technically complex system engineering. We should fully optimize the process elements such as blank status, tool geometry, clamping method, path and cutting amount. Adopting process measures that effectively reduce the deformation of the process, eliminating the adverse effects of various process conditions on the deformation. While improving the rigidity of the system, choose a new high-efficiency tool that matches the mechanical, chemical and physical properties of the part. Select a high-precision dynamic balance tool holder to adjust the tool overhang and reduce the vibration source. Cutting tests are also carried out on the tools used to machine the parts, optimizing the amount of cutting, increasing the metal removal rate, and ultimately achieving high quality, high efficiency, low cost and green and efficient processing.
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