Xi'an Aviation Power Control Technology Co., Ltd. (hereinafter referred to as AVIC West Control) was founded in 1955 and is affiliated to China Aviation Industry Corporation. It is the base for the development, testing and production of China's aviation engine fuel control system, aircraft hydraulics and high-tech mechanical and electrical products. . With advanced digital precision machinery manufacturing, special technology, measurement and testing capabilities and information management tools, there are two design institutes, more than ten professional manufacturing units and related business, production, information technology, international cooperation and other management departments. The digital design and manufacturing system based on PDM enables AVIC Xikong to develop flexible processing capabilities for different products that adapt to the rapid changes in the market.
Since its establishment nearly 60 years ago, AVIC Xikong has developed and produced hundreds of thousands of sets of fuel accessories for more than 150 models of airborne and aerospace engines in China. At the same time, through the implementation of core technology radiation strategy, it has successfully involved in aerospace and land vehicle power control, civil aviation repair, international aviation parts subcontract production and other fields, with Honeywell, Goodrich, United Technologies, Eaton, GE World-renowned aviation companies such as Smith Aerospace and Ai Wei Design Bureau have established long-term and stable cooperative relations.
With the upgrading of engine products in the aerospace industry, the use of titanium alloys is increasing: titanium alloys are an ideal manufacturing material for aircraft engines due to their excellent overall mechanical properties, low density and high corrosion resistance. In the aviation engine fuel control system, titanium alloy has gradually replaced heat-resistant steel, stainless steel and other materials, becoming the material of choice for all kinds of connectors, fasteners and other components. At the same time, the high hardness and high wear resistance of titanium alloys have brought great challenges to the processing, especially the cutting tools. Due to the poor machinability of titanium alloys, the machining problems such as rapid tool wear frequently occur frequently, which seriously affects the machining. Machining accuracy and efficiency. Therefore, AVIC West Control mainly finds suitable cutting parameters and processing techniques by analyzing the cutting performance of titanium alloy materials, selecting reasonable machining tools, and finding the suitable rough machining of titanium alloy shaft parts on CNC lathes. An effective way of finishing.
Titanium alloy processing brings great challenges to the tool
The various properties of titanium make it a powerful material for parts, but many of its properties also affect its machinability. Titanium alloys commonly used in the industry are two-phase titanium alloys, namely (Î±+Î²) titanium alloys. TC4 and TC6 are commonly used in aviation engine fuel accessories, of which TC4 is a typical representative of such alloys. Titanium alloy materials have high hardness, poor cutting performance, and are prone to work hardening, which brings difficulties to cutting. For the parts of materials such as TC4 in titanium alloy, especially the turning process, AVIC West Control has done in-depth research and gained some experience.
Firstly, the elastic modulus of the titanium alloy is small, wherein the elastic modulus of the TC4 is E=110 GPa, which is about half of the steel, and the thermal conductivity is low, so that the workpiece is elastically deformed by the cutting force, and at the same time during the processing. Will produce higher and more concentrated cutting forces. This makes it easy to generate vibrations that cause chattering during cutting and reduce the accuracy of the workpiece, thus improving the rigidity of the machining system.
Secondly, the local high temperature generated by the titanium alloy during the cutting process makes it easy for titanium to absorb oxygen and nitrogen in the atmosphere, thereby forming a hard and brittle outer skin. This causes work hardening of the machined surface, and the work hardening speed is fast, which causes severe scratches on the tool surface and is prone to chipping during the cutting process.
In addition, the physical and chemical properties of the titanium alloy itself make it more compatible with the workpiece during cutting. When the tool is in contact with the workpiece during cutting, the sticking phenomenon is easy to occur, which increases the friction between the tool and the workpiece. The heat of cutting. The resulting large amount of cutting heat cannot be dissipated through the chips in time, greatly reducing the service life of the tool. Therefore, tools for processing titanium alloys must have high heat hardness.
Titanium alloy processing is a systematic project
Among the aero-engine fuel control systems manufactured by AVIC Xikong, titanium alloy parts are mainly small shaft parts, and turning is the main processing method.
The titanium alloy processing here can be regarded as a systematic project, which needs to be considered from various angles such as processing equipment, cutting tools, cutting parameters, and coolant. As far as processing equipment is concerned, titanium alloy processing requires good machine tool processing performance and sufficient cooling. Therefore, the processing equipment selects a CNC lathe with high processing precision, and the spindle vibration during processing is extremely small and the processing stability is good.
The tool materials used for titanium alloy processing have good hardness and wear resistance, excellent heat resistance, high strength and toughness at high temperatures, and certain impact resistance and damage resistance. The knives that meet the above requirements are: ceramic tools, coated carbide tools, cubic boron nitride tools (CBN) and diamond-like tools (PCD). Among them, coated carbide tools are inexpensive, have good thermal conductivity and high hardness, and also excel in red hardness and toughness, although they are better than ceramics, cubic boron nitride tools (CBN), diamond-like tools. Heat resistance and chemical stability are less, but have higher impact and damage resistance than ceramic and diamond-like tools. Therefore, it has become the tool of choice for processing titanium alloys.
In terms of turning parameters, titanium alloy processing also needs more consideration. If the cutting speed is set, too high cutting speed will cause the cutting heat to rise, the cutting edge of the tool will be overheated, the bonding phenomenon will be serious, the tool wear will be aggravated, the tool life will be shortened, and the surface of the titanium alloy workpiece will be cracked or oxidized. Affect the mechanical properties of the workpiece, so the appropriate lower cutting speed should be selected to ensure the processing cost and ensure the processing quality. Secondly, the cutting depth is set. Because the titanium alloy workpiece must be subjected to preliminary heat treatment before processing, the surface of the workpiece has an oxide layer. To improve the durability of the tool, a relatively large cutting depth should be adopted, and the titanium alloy body can be directly cut into the unoxidized body. The metal layer improves tool life. Another parameter to be considered is the feed amount. The amount of feed does not affect the size of the cutting temperature. Under the premise of ensuring the machining efficiency, it is reasonable to reduce the cutting speed and increase the feed. Cutting method.
In order to ensure the processing quality and improve the durability of the tool, the use of the coolant should also be considered. For example, to fully cool the processing area, the coolant can not only effectively reduce the cutting temperature, but also reduce the sticking of the tool during cutting. Efficiency and extended tool life.
Carbide coated tools improve processing
For rotating parts such as a screw plug part, the maximum outer diameter is Ï†33.8, the material is TC4, and the raw material is Ï†30 bar. The parts are finished in one turning operation (Figure 1). In order to ensure the machining accuracy of the parts, the processing equipment uses the imported CNC lathe, the spindle speed is up to 6000 rpm, the spindle runout is less than 2Î¼m, the spindle vibration is very small during processing, the machining stability is good, the coolant can be sprayed in three directions, and the cooling is sufficient. .
Figure 1 Product parts drawing
For external turning, a well-known brand of carbide coated tools was selected at the beginning, and processed according to the cutting parameters recommended by the manufacturer. Since the incoming material of the part is round bar and the surface has a heat-treated oxide layer, the boundary of the tool is seriously worn during processing, resulting in different degrees of wear and chipping of the tool of 10 to 15 parts (Fig. 2), which cannot be satisfied. Processing needs for mass production.
Figure 2 Tool wear form
After repeated trial and error verification, AVIC West Control finally selected the cemented carbide coating tool at the same price of Walter Company: WNMG080404-NM4 material WSM30 for external rough machining; CCSM09T304-PF4 material WSM30 for external round finishing (pictured 3) This blade is also used for boring.
Figure 3 Carbide coating rough, finishing tool
WNMG080404-NM4 material WSM30 blade is a W-shaped negative blade with 6 effective cutting edges on both sides. NM4 is specially designed for stainless steel and difficult-to-machine materials. It is suitable for medium cutting, with a margin of 0.5~4mm on one side. For 0.16~0.25, you can form perfect chips. The impact resistance of the WSM30 material is very strong, and the blade coating is made of Al2O3 physical coating, which ensures the sharpness of the cutting edge and excellent red hardness, which effectively extends the tool life.
CCMT09T304-PF4 material WSM30 blade is a C-shaped positive blade. PF4 is a finishing groove designed for stainless steel and difficult-to-machine materials. It is suitable for finishing machining with a single-side allowance of less than 1.5mm.
Due to the processing characteristics of the TC4 and the characteristics of the tool material WSM30, a large amount of heat is generated during cutting, and the processing zone temperature can reach 800 Â° C or more, and the high temperature of the tool cutting zone can cause annealing and softening effects on the cutting layer of the workpiece, which can be large. To the extent that the work hardening phenomenon of the parts is eliminated; at the same time, the cemented carbide coated tool is resistant to high temperature and good red hardness, which makes the workpiece easier to cut when roughing the workpiece; the WNMG080404-NM4 blade for rough machining is a convex triangular blade, and the negative blade can For positive and negative use, a total of 6 blades can be used 6 times, which greatly reduces the tool cost during roughing.
Roughing selects low speed and large feed, cutting parameter selection: cutting depth ap=0.8~1.2 mm; feed rate F=0.18~0.4 mm/n; spindle speed S=600~1000rpm. The roughing blade can process 25 to 30 parts with one blade. Finishing and boring machining cutting parameters selection: cutting depth ap=0.2mm; feed rate F=0.1mm/n; spindle speed S=2000rpm, finishing blade can process 45~50 parts, boring When a blade can process 35 to 45 pieces, the surface roughness of the parts after processing can reach Ra0.8, the dimensional accuracy can be controlled within 0.005mm, which satisfies the design requirements of the parts, and the work hardening phenomenon when turning parts is basically eliminated. Increased machining efficiency and tool life.
Figure 4 on-site processing map
The use rate of titanium alloy in the aerospace industry at home and abroad is increasing year by year. However, due to the problems of high processing cost, low processing efficiency and low tool durability, the application level has been greatly hindered. The above analysis of the cutting performance of titanium alloy, reasonable selection of tools and processing parameters, effectively solve the problem of low tool durability when turning titanium alloy parts. Practice has proved that CNC lathes and carbide coated tools are the tools for processing titanium alloys. Walter's products are a more economical choice in turning tool selection.
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