In the present era, rapid advancements in science and technology have significantly improved the aviation industry. The aerospace engine, functioning as the power unit for aircraft, is the aircraft's heart. Its design and manufacturing technology play a crucial role in the development of the aviation industry, serving as a key indicator of a country's technological level, military strength, and overall national capabilities. Aerospace engine components, characterized by complex structures, high manufacturing difficulty, and advanced technological content, represent the direction of manufacturing industry development, often referred to as a dazzling gem in the manufacturing sector. Numerical control (CNC) machining technology and equipment originated to meet the demands of aerospace manufacturing and, in the continuous pursuit of high-precision machining, have evolved into foundational key technologies for modern aerospace manufacturing. Both domestic and international aerospace manufacturing industries are the largest users of CNC technology and CNC machine tools, with CNC machine tool manufacturing enterprises accounting for over 80% in aerospace manufacturing enterprises.
The manufacturing of aerospace engine components involves challenging materials, complex shapes, susceptibility to deformation and vibration, and high precision requirements. It represents a country's manufacturing technology prowess and the development level of national defense modernization. Focusing on aerospace engine components such as blades, impellers, casings, and disc shafts, this exploration analyzes the material and structural characteristics, machining methods and features, and machining equipment of these typical components. It summarizes the requirements of aerospace engine component machining for CNC machine tool performance and functionality and provides an outlook on the development trends of aerospace engine manufacturing technology.
Cutting tools play a crucial role in addressing the challenges of machining difficult materials and complex structures in aerospace components. Advanced aerospace products demand components with superior performance, lower costs, and higher environmental friendliness. Machining processes require faster speeds, higher reliability, high repeatability accuracy, and reproducibility. Characteristics such as the difficulty in cutting workpiece materials like aerospace titanium alloys and high-temperature alloys, the complex and thin-walled shapes, high precision dimensional requirements, surface roughness requirements, and large metal removal amounts, pose higher demands on the quality consistency of cutting tools. Modern high-efficiency precision machining requires cutting tools with characteristics such as high precision, high wear resistance, high impact resistance, and high reliability—essentially possessing all the characteristics of high-performance tools.
A clear indication of a high-quality tool solution is the compatibility of the tool's structure, material, and the material of the machined part. Renowned CNC machine tool manufacturers globally spare no effort in developing high-performance CNC machine tools, further focusing on research and development related to high dynamic response, high precision, and high rigidity. High rigidity and high load-bearing capabilities of linear guides ensure smooth continuous movement throughout the entire travel, achieving high geometric accuracy and surface quality of the workpiece and ensuring high processing efficiency. The high rigidity of the machine tool reduces vibrations in the machining system, extending the tool's lifespan. High-performance tooling involves various aspects, including tool material, tool coating technology, tool structure design and optimization, tool matching technology, and tool application.
Blade Machining
Aircraft engine blades are often made of materials such as titanium alloys and high-temperature alloys. These materials have poor cutting performance, stringent dimensional accuracy requirements, and high demands for surface quality. The machining of blades involves various areas, including the airfoil surface machining, blade tenon and tenon teeth machining, damping platform machining, installation plate, and blade crown machining.
The complexity of blade machining lies in the fact that the airfoil section is composed of complex curved surfaces, categorized into straight-line surfaces and non-straight-line surfaces based on forming principles. Straight-line surfaces further divide into expandable and non-expandable. For expandable straight-line surfaces, conventional mechanical machining techniques can be employed. However, for non-expandable straight-line surfaces and free-form surfaces, multi-axis CNC machine tools are required, such as five-axis linked machining centers and five-axis high-speed dragon milling machines.
The root tenon of the blade is processed using a lathe and a plunge-feed powerful grinding machine. The latter possesses the functionality of wheel replacement, equipped with a wheel dressing device, and incorporates online measurement, program adjustment, and automatic compensation functions. Mechanical machining of blades primarily involves milling and grinding, typically utilizing specialized equipment like high-speed blade milling machines. Computer-aided design (CAD) and computer-aided manufacturing (CAM) software generate blade machining programs for blades designed using dedicated blade machining. The blade surfaces are generally forged with a large margin and are polished after numerical control machining. Cutting processing is primarily based on forging blanks, progressing through rough, semi-finish, and finish machining processes, milling the blank to its final dimensions.
Blade machining has consistently been a challenging subject in the CNC machining field, involving complex issues such as blade shaping, machining method selection, toolpath planning, and blade deformation control. Depending on the tool's contact with the blade, blade machining can use point milling and side milling methods.
Point milling allows for more precise processing of the blade's designed surface, with the tool's movement direction aligning closely with the streamline direction, benefiting the aerodynamic performance of the blade. This method is suitable for free-form surface blade machining. However, it has drawbacks such as low processing efficiency, severe tool wear, and increased production costs. Side milling, on the other hand, avoids concentrating the tool-to-workpiece contact at a single point, reducing tool wear, significantly improving the blade's surface roughness, and enhancing processing efficiency.
In China, the commonly used method is segmented side milling, dividing the blade into several segments based on machining features and process requirements, and processing them using side milling. Initially, the outermost segment is machined with a tool's side edge, followed by continuous tool movement to process adjacent segments. In theory, the more segments there are, the shorter the contact line between the blade and the tool, leading to higher processing accuracy. However, frequent tool movements and changing clamping methods limit processing efficiency.
Processing of Disk-Shaft Components
Aerospace engine disk-shaft components include high and low-pressure turbine disks, as well as high and low-pressure compressor disks. The structural composition of disk components generally consists of a rim, web, hub, and sealing teeth. There are dovetail slots on the rim for installing blades, and the web contains small holes that contribute to balancing. Disk components are typically made of materials such as high-temperature alloys and titanium alloys. These materials are challenging to process, with strict requirements for dimensional accuracy, high surface quality, susceptibility to deformation due to thin walls, and elevated demands on machining equipment, tools, and measuring instruments.
The mechanical processing of aerospace engine disk components involves turning, drilling, boring, and grinding, focusing on areas such as the inner and outer circles, front and rear faces, web, serrations, and dovetail slots. Generally, integral forging or welded blanks are chosen and then processed. CNC milling provides flexible, rapid, and highly reliable machining.
As a result, developed countries often employ 5-axis machining centers to mill entire disk assemblies. The key to CNC machining of integral disks lies in the CNC milling of blades. Shaft components primarily refer to fan shafts, compressor shafts, turbine shafts, etc., essential components of the aerospace engine rotor. These shaft components, typically made of high-performance heat-resistant alloy materials, operate at high speeds, rotating tens of thousands of times per minute. They experience complex load conditions, requiring smooth operation, minimal vibration, high fatigue strength, and, consequently, stringent requirements for dimensional precision, geometric tolerances, surface quality, and integrity.
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