The landing gear device is an important bearing and maneuverable component of the aircraft, which absorbs and dissipates the impact energy formed by the aircraft and the ground during landing and taxiing. With the continuous development of aviation technology and the continuous improvement of customer needs, landing gear products are constantly upgraded. In order to meet the requirements of long life and high reliability of aircraft, more and more new standards, new processes, and new materials are applied; among them, titanium alloys have become a virtue of excellent comprehensive mechanical properties, small density, and strong corrosion resistance. Ideal manufacturing material for landing gear. But at the same time, the characteristics of high hardness and high wear resistance of titanium alloys also bring great challenges to the processing, especially cutting tools. Due to the poor cutting performance of titanium alloys, machining problems such as rapid tool wear and tear frequently occur, which seriously affects Processing accuracy and efficiency. As a leading company in the industry, AVIC Landing Gear Company was also deeply troubled by this problem.
What is the difficulty of processing titanium alloy? We can make a summary based on two charts: First, the elastic modulus of the titanium alloy is low, about 1/2 of that of steel. It is easy to rebound for the surface after removal, and it is easy to produce strong friction with the flank of the tool; Second, the plasticity is low 、 High hardness, small contact area between chips and rake face, large cutting stress at the cutting edge, the cutting edge and cutting edge are easy to wear, usually the cutting speed is about 30m / min; three, chemical activity is large, at high temperature, titanium and Most of the components in the air produce a strong chemical reaction, especially with oxygen and nitrogen, generate a gap solid solution, generate a hard layer with high hardness, and have a strong abrasive effect on the knife; Fourth, the affinity is large, due to the chips and The strong friction between the cutting surfaces, under the action of high cutting temperature and high cutting pressure, the titanium element in the tool material and the workpiece material are compatible with each other, resulting in biting and sticking of the knife, and the tool is prone to bond wear.
Specific examples: A newly developed model landing gear is a tandem structure. The main load-bearing components are made of TC18 titanium alloy. The number of single machines is 18. The structure of the parts is complex, the number is large, the amount of material removal is large, and the blank processing allowance The distribution is uneven, there are many under-pressure parts, there is an α + β phase layer on the surface of the blank, the dislocation is strengthened during the forging process, the surface hardness is high (HRC ﹥ 55), the thickness is 0.1-0.15mm, and the single-piece processing cycle is Around 410h, the processing efficiency is low. In recent years, as the model has been transferred to small batch production, the number of deliveries has increased and the delivery cycle has been shortened. How to shorten the delivery cycle, improve the delivery schedule, and reduce the production cost without changing the existing equipment and personnel? Urgent problems to be solved.
Faced with difficult problems and challenges, the company’s technical experts quickly took action. After research and analysis, we found that TC18 is a high-strength, high alloying α-β two-phase alloy. This material has high strength, good toughness and plasticity, and low thermal conductivity and elastic modulus. The requirements are very high; machining TC18 also requires a large tool rake angle and a sharp edge, but the sharp edge strength is poor, and the oxide layer on the surface of the product increases the possibility of edge collapse. How to keep the cutting edge of the blade sharp and not losing strength is a great test for the treatment of the cutting edge of the blade. Therefore, how to optimize the material of the cutter and improve the cutting parameters of the titanium alloy are the decisive factors for improving the machining efficiency. The conclusion is already obvious-to solve the problem, the key is to make a trade-off between cutting parameters and tool characteristics, and find the most suitable machining tool.
Try hard to find
For this reason, the technical experts of AVIC landing gear explored the cutting parameters through trial cutting and repeated exploration, and finally concluded that the principle of tool selection must be based on the following conditions:
- 1) The material of the tool (according to the material to be processed, the type of processing application, the processing environment and the needs of on-site processing).
- 2) Geometry (divided into the geometry of the shank and the geometry of the cutting edge, which mainly affect the surface quality, chip evacuation effect, cutting edge strength, burr, vibration, etc.)
- 3) Coating (extend tool life, increase cutting speed and feed of the tool, obtain higher production efficiency, and improve the wear resistance of the tool).
- 4) According to the needs of on-site operations, the overall efficiency and processing cost should be coordinated. With full consideration of the performance of the existing machine tools, the use of more conservative cutting parameters can effectively extend the tool life and obtain more reasonable processing efficiency.
The principle of selection is there. It is said that the progress of the matter should be smooth. Unexpectedly, this is not the case: combined with the current status of the company’s CNC equipment, we initially selected a well-known brand indexable carbide coated tool and recommended The cutting parameters are processed. However, the results were not satisfactory-due to the incoming material of the parts being die forgings, the surface has a heat-treated oxide layer, and the balance of the distribution is uneven, the blade wear is serious during processing, and the tool will produce different degrees of wear and tear in less than 2 hours of processing The chipping phenomenon cannot meet the processing needs of mass production. The emergence of this situation has caused the impasse to break into a deadlock.
Since then, AVIC landing gear has tried many products from many brand cutters. After repeated trial cutting verification, Walter’s? 63R1.2 high feed milling cutter (M4002-063-B22-06-02, insert model: SDMT120412-F57 WSP45S) and? 32R8 copy milling cutter (F2231) were finally selected .W.032.Z02.08.L, insert type: RDMT1605M0-D57 WSP45S) as the main cutting tool.
The Walter M4002 milling cutter uses a 4-blade square blade, and the blade coating uses a unique Walter Al2O3 physical coating in the world. The thermal load in this coating process is extremely small, and the optimal internal stress minimizes the possibility of thermal cracking. , So that the toughness of the cutting material is the highest, and the high-temperature alumina coating can effectively prevent the heat from being transferred to the blade, so that the blade has excellent wear resistance; in addition, the perfect smooth rake face design, friction during cutting The low coefficient can reduce the tendency of built-up edge. The unique coating technology combines the wear resistance and toughness to achieve a high degree of process reliability; the cutter body has a variety of interface designs, and the 15 ° main declination angle can be high Under the premise of feed, the best match of depth of cut is achieved. At the same time, according to different workpiece shapes and different processing techniques, M4002 can realize various milling methods such as face milling, ramp milling, helical interpolation milling, plunge milling, etc., especially when the tool has a long overhang, it can effectively reduce the vibration tendency , To meet the needs of efficient processing.
With the full help of Walter technicians, after a large number of indexing tool cutting tests, we finally figured out the process method and optimal cutting parameters of indexable tools for processing titanium alloys, and formulated them according to the part structure and margin distribution Relatively complete process plan and programming method. What is quite shocking is that the processing efficiency has increased by about 40% compared to before! This not only ensures the reliability of parts processing quality and the cost-effectiveness of the production process, but also meets the needs of small batch production and delivery of this model, which greatly promotes the company’s business development.