As we all know, precision machining in the aerospace industry has very high requirements for materials. Of course, it is to meet the particularity of aerospace equipment, and more importantly, because of the environmental impact of aerospace. Due to the special environmental impact, the general materials on the market cannot meet the needs of this environment, and some special materials will inevitably be needed to replace them. Today I would like to introduce to you a more commonly used material, which is titanium alloy. It is especially common in aerospace. Why is this material used so often? That has something to do with its characteristics.
Titanium alloy has a small specific gravity, which determines its small mass, high strength and thermal strength, hardness and high-temperature resistance, and a series of excellent physical and mechanical properties such as resistance to seawater and acid and alkali corrosion, which determines its excellent physical and mechanical properties no matter what environment it is in. All can be used. In addition, the deformation coefficient is very small, so it has been widely used in aerospace, aviation, shipbuilding, petroleum, chemical, and other industries.
Precisely because titanium alloy has the above differences from ordinary materials, it also determines that it is very difficult to process in precision processing. Many machining factories are unwilling to process this material and do not know how to process it. . Due to the small deformation coefficient of titanium alloy, high cutting temperature, large tooltip stress, and severe work hardening, the tool is prone to wear and chipping during cutting, and the cutting quality is difficult to guarantee. So how to do cutting processing?
When cutting titanium alloy, the cutting force is not large, the work hardening is not serious, and it is easy to obtain a better surface finish. However, the thermal conductivity of titanium alloy is small, the cutting temperature is high, the tool wear is large, and the tool durability is low. The tool should be selected from titanium alloys. Tungsten cobalt carbide tools have a small chemical affinity, high thermal conductivity, high strength, and small grain sizes, such as YG8, YG3, and others tools. During the turning process of titanium alloy, chip breaking is a difficult problem, especially when processing pure titanium. In order to achieve the purpose of chip breaking, the cutting part can be sharpened into a fully arc-shaped chip groove, which is shallow in the front deep in the back, and narrow in the front. The rear width makes it easy for the chips to be discharged outward so that the chips will not wrap around the surface of the workpiece and cause scratches on the surface of the workpiece.
The cutting deformation coefficient of titanium alloy is small, the contact area between the tool and chips is small, and the cutting temperature is high. In order to reduce the generation of cutting heat, the rake angle of the turning tool should not be too large. The rake angle of the carbide turning tool is generally 5-8 degrees. Due to the high hardness of titanium alloy, in order to increase the impact strength of the turning tool, the clearance angle of the turning tool should not be too large, generally 5°, in order to strengthen the strength of the tooltip, improve heat dissipation conditions, and improve the impact resistance of the tool. , a negative edge inclination angle with a large absolute value is adopted.
Controlling a reasonable cutting speed, not too fast, and using titanium alloy special cutting fluid for cooling during processing can effectively improve the durability of the tool and select a reasonable feed rate.
Drilling is also commonly used. Drilling titanium alloys is difficult, and burnt tools and drill breakage often occur during the processing. The main reasons are poor sharpening of the drill bit, untimely chip removal, poor cooling, and poor rigidity of the processing system. Depending on the diameter of the drill bit, grind the chisel edge to a narrow width, generally 0.5mm, in order to reduce the axial force and vibration caused by resistance. At the same time, at a distance of 5-8mm from the tip of the drill bit, grind the edge of the drill bit narrower, leaving about 0.5mm, which is beneficial to the chip removal of the drill bit. The geometry must be sharpened correctly, and the two cutting edges must be symmetrical. This can prevent the drill bit from cutting only one edge, and the cutting force is all concentrated on one side, causing premature wear of the drill bit and even chipping due to slippage. Always keep the blade sharp. When the blade becomes dull, stop drilling immediately and re-sharpen the drill bit. If you continue to forcefully cut with a dull drill bit, the drill bit will soon be burned and annealed due to friction and high temperature, causing the drill bit to be scrapped. At the same time, the hardened layer of the workpiece is thickened, which increases the difficulty of re-drilling in the future and the number of drill grinding times. According to the drilling depth requirements, the length of the drill bit should be shortened as much as possible, and the thickness of the drill core should be increased to increase rigidity and prevent edge chipping due to vibration during drilling. The practice has proven that a φ15 drill bit with a length of 150 mm has a longer life than a drill bit with a length of 195 mm. Therefore, the selection of length is also very important.
Judging from the above two common processing methods, titanium alloy processing is relatively difficult, but with good processing, good precision parts can still be processed, such as titanium alloy parts for aerospace equipment.
