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ZCCCT-Efficient NC Machining of Titanium Alloy Aviation Structural Parts

Date:2020/03/06


Titanium alloys are more and more widely used in the aviation industry due to their high strength, good mechanical properties and strong corrosion resistance. With the increasing proportion of titanium alloys in aircraft, the impact of numerical control of titanium alloy aerospace structural parts processing efficiency on aviation manufacturing companies is also increasing. Titanium alloy is a difficult-to-machine material. Its relative machinability is 0.15 to 0.25, and the processing efficiency is only 10% of aluminum alloy. Therefore, the low processing efficiency of titanium alloy aerospace structural parts severely restricts the mass production of modern aircraft. Achieving efficient machining of titanium alloy aerospace structural parts has become a common concern for aerospace manufacturing enterprises, CNC equipment manufacturers and tool manufacturers.

Cutting performance of titanium alloy.
Titanium alloy has the characteristics of good mechanical properties, strong corrosion resistance and small specific gravity. However, in machining, the cutting performance of titanium alloy is very poor, mainly in the following aspects:(1) High cutting force. Titanium alloy materials have high strength and large cutting resistance during cutting, which results in a large amount of cutting heat at the cutting edge;(2) Low thermal conductivity. Titanium alloy has low thermal diffusivity, and a large amount of cutting heat is concentrated in the cutting area;(3) The blade tip stress is heavy. Titanium alloy has low plasticity, and the chips generated by machining are very easy to bend, resulting in a short contact length between the chips and the rake surface, so the unit area of the cutting edge has an increased force, causing stress concentration at the tip;(4) High friction. Titanium alloy has a small elastic modulus, which causes increased friction between the rake face and the flank face;(5) High chemical activity. At high cutting temperatures, titanium can easily react with gases such as hydrogen, oxygen, and nitrogen in the air to form a hard layer on the surface and accelerate tool wear.
Efficient processing equipment for titanium alloy.
In order to meet the efficient processing of titanium alloy structural parts, the new titanium alloy processing equipment shows the following developing trends:(1) High torque. Titanium alloy has high strength and high cutting force during machining. One of the obvious characteristics of titanium alloy processing machine tools is the large spindle torque and swing angle torque.(2) Application of electric spindle. High-power, high-torque electric spindles have been applied to titanium alloy processing.(3) Horizontal machining center is used for titanium alloy processing. The horizontal machining center is convenient for chip removal, which is conducive to improving processing efficiency and processing quality. The interchangeable workbench is easy to realize multi-station processing and set up flexible production lines to improve equipment utilization.(4) High-pressure internal cooling. During the machining of titanium alloy, the cutting heat is concentrated at the tip, which is easy to cause tool wear or damage. High-pressure internal cooling can accurately spray the cutting area to take away the cutting heat.
Titanium alloy efficient machining cutting tool.
The cutting workability of titanium alloy is poor, and the cutting speed of traditional processing methods generally doesn’t exceed 60m / min. The rough machining of titanium alloys mainly uses the method of large depth of cut, low speed and low feed to obtain the maximum metal removal rate. PVD coated carbide cutting tools are used for finishing for high-speed milling with small cutting width and large cutting depth to obtain efficient cutting. Therefore, titanium alloy machining tools mainly focus on how to avoid chattering, reduce cutting force, and reduce cutting temperature during strong cutting:(1) Titanium alloy face milling:When face milling titanium alloy parts, milling with small depth of cut and large feed is used to obtain efficient processing. The principle of high-feed milling is to reduce the tool's main deflection angle, so that the tool can still maintain a small chip thickness under high feeds, so as to reduce the cutting force at high feeds and achieve low cutting speed, a large feed is obtained, increasing the metal removal rate per unit depth of cut. At the same time, the cutting force part is vertically upward, the tangential force is small, and the power consumed is also small. This processing method does not require high power and rigidity of the machine tool, and is widely used.(2) Titanium alloy cavity processing: Slot cavity is a main feature of titanium alloy aerospace structural parts. The material removal rate is high and the workload is large. Therefore, slot cavity processing is the key to the efficient processing of titanium alloy parts. Strong cutting with large cutting depth, low speed and low feed to obtain maximum metal removal rate is an effective method for roughing titanium alloys. At present, the powerful milling tools for rough machining titanium alloys are widely used with the highest efficiency of corn milling cutters.(3) Fillet processing technology: In order to reduce the weight of the aircraft, the fillet at the corner of the groove of the aircraft structure is usually small, and a milling cutter with a smaller diameter is required for processing. Due to the abrupt cutting amount at the fillet, the cutting force varies greatly. In the case of abrupt cutting force, the tool easily generates vibration and even chipping, which results in severe tool wear and low machining efficiency. Plunge milling is the best way to solve the corner processing efficiency. The plunge milling process has less vibration than conventional milling, and the cutting method has a high efficiency in removing the corner allowance. Inserting and milling at the corners by inserting and milling tools with different diameters can remove most of the remaining margin of the corners, and then use the end mill to remove the residue generated by inserting and milling, which can greatly improve the processing efficiency.(4) Precision side milling technology:When finishing the side wall, the interruption of milling is used to achieve the purpose of high-speed cutting to improve the surface quality and processing efficiency of the part. When finishing the side, due to the small cutting width, the cutting time for each revolution of the cutter teeth is very short, that is, the cooling time is very long. In the case of sufficient cooling, the cutting temperature can be effectively controlled, so the cutting speed can be greatly increased to improve the processing efficiency.High-speed cutting and finishing of titanium alloys can greatly improve machining efficiency and precision.(5) Simulation optimization technology:The cutting allowance of titanium alloy structural parts will change continuously during rough machining. The NC program compiled by the current CAM software can only set fixed cutting parameters. In order to avoid the impact of the local program on the tool and the machine due to the excessive cutting amount, the general method is to reduce the overall cutting parameters to ensure tool life and part quality Therefore, the processing efficiency is extremely low. Vericut's simulation optimization technology can solve this problem well. The cutting parameter optimization library is set by Vericut software, and the software is used for simulation. The actual machining allowances and cutting conditions are guessed through the simulation, and the cutting parameters in the program are optimized according to the machining allowances and cutting conditions. Not only extends the tool life, guarantees the quality of the parts, but also improves the processing efficiency.

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