As we all know, the precision machining in the aerospace industry has high requirements for materials. Of course, one side is to meet the particularity of aerospace equipment, and more importantly because of the environmental impact of aerospace. Because of the special environmental impact, the general materials on the market can certainly not meet the needs of the environment, and some special materials are bound to be substituted. Today I will introduce you to a more commonly used material, that is, titanium alloy, especially in aerospace, it is more common, why is this material used more? That has a certain relationship with its characteristics.
Titanium alloy has a small specific gravity, which determines the small mass, high strength and thermal strength, determines the hardness and high temperature resistance, and is resistant to seawater and acid and alkali corrosion. A series of excellent physical and mechanical properties determine its regardless of the environment. They can all be used. In addition, the deformation coefficient is very small, so it has been widely used in aerospace, aviation, shipbuilding, petroleum, chemical industry and other industries.
Because titanium alloy has the above-mentioned differences from ordinary materials, it is also determined that it has great difficulty in precision machining. Many mechanical processing factories are reluctant to process this material, and do not know how to process this material. . To this end, Xi’an Ruihua Pump Industry has communicated with some titanium alloy processing customers for a long time, and organized some small skills to share with you!
Due to the small deformation coefficient of titanium alloy, high cutting temperature, high tip stress and severe work hardening, the tool is easy to wear and chip during cutting, and the quality of cutting is difficult to guarantee. What about cutting?
When cutting a titanium alloy, the cutting force is not large, the work hardening is not serious, and it is easy to obtain a better surface finish, but the titanium alloy has a small thermal conductivity, high cutting temperature, large tool wear, and low tool durability. The tool should be selected from titanium Tungsten-cobalt cemented carbide tools with small chemical affinity, high thermal conductivity, high strength and small grain size, such as YG8, YG3 and other tools. In the turning process of titanium alloys, chip breaking is a difficult problem in processing, especially the processing of pure titanium. In order to achieve the purpose of chip breaking, the cutting part can be sharpened into a fully curved chip flute, shallow front and deep, narrow front The back 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.
Titanium alloy has a small cutting deformation coefficient, a small contact area between the cutter and the chips, and a high cutting temperature. 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 Because of the high hardness of the titanium alloy, in order to increase the impact strength of the turning tool, the back angle of the turning tool should not be too large, generally 5 °, in order to strengthen the strength of the tip portion, improve the heat dissipation conditions, and improve the impact resistance of the tool Ability, using a negative blade inclination with a larger absolute value.
Control reasonable cutting speed, not too fast, and use titanium alloy special cutting fluid for cooling during processing, which can effectively improve the durability of the tool and select a reasonable feed.
Drilling processing is also relatively common. Titanium alloy drilling is more difficult. Burning knives and broken drills often occur in the processing process. The main reasons are poor grinding of the drill bit, inadequate chip removal, poor cooling and poor rigidity of the process system. Depending on the diameter of the drill bit, narrow the transverse edge, the width is generally 0.5㎜, in order to reduce the axial force and reduce the vibration caused by the resistance. At the same time, the edge of the drill bit is 5-8㎜, and the edge band of the drill bit is narrowed, leaving about 0.5㎜, which is beneficial to the chip removal of the drill bit. The geometric shape must be sharpened correctly, and the two cutting edges must be kept symmetrical, which can prevent the cutting of only one side of the drill bit, and the cutting force is concentrated on one side, so that the drill bit wears prematurely, even causing chipping due to slipping. Always keep the blade sharp. When the blade becomes dull, stop drilling immediately and re-sharpen the drill bit. If the dull drill bit is used to continue cutting, the drill bit will soon be burned and annealed due to friction and high temperature, resulting in the scrap of the drill bit. At the same time, the hardened layer of the workpiece is thickened, which increases the difficulty of re-drilling and the number of times of grinding the drill bit. 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 the rigidity, so as to prevent chipping caused by jitter in the drilling. It has been proved by practice that the drill bit of φ15 has a longer service life than the length of 195. Therefore, the choice of length is also very important.
After the above two common processing, processing of titanium alloy is relatively difficult, but after good processing, it can still produce good precision parts, titanium alloy parts of aerospace equipment.
Tips For Precision Machining Of Titanium Alloy Materials
