This article describes various types of titanium alloys, and introduces the processing characteristics of various types of titanium alloys. At the same time, it also summarizes and analyzes the grinding characteristics and processing difficulties, and solves the difficulties in grinding such as burns and wheel adhesion. Method and a possibility of efficient grinding.
Keywords: titanium alloy; characteristics; processing technology
1 Classification of titanium alloys
In 1956, McGovern made a strict distinction between titanium alloys based on the difference in annealing state, and defined different types, which are mainly divided into three categories: α, β, and α + β.
TC4 (Ti-6Al-4V) belongs to α + β phase structure, the largest amount of titanium alloy, and the most complete titanium alloy with performance data. Aluminum and vanadium are the main alloying elements contained in TC4 (Ti-6Al-4V) , Aluminum is an alpha stabilizing element, and vanadium is a beta stabilizing element.
2 Processing technology characteristics
The processing of TC4 titanium alloy is very difficult. The comprehensive process of titanium and titanium alloys is very different from steel, aluminum alloys and many heavy metals in terms of crystal structure, physical properties and chemical properties. The following three factors determine titanium Alloy is a metal that is not easy to process.
- Due to the instability of its chemical composition. TC4 titanium alloy will undergo chemical reaction with oxygen and nitrogen under thermal deformation, and even with some oxygen-containing gas, the reaction will produce oxide scale attached to the workpiece surface, if the temperature is higher, reach 900 ℃ At the above time, scales attached to the surface of the workpiece will produce scales, so that oxygen and nitrogen elements are likely to penetrate into the metal and eventually form a surface getter layer. Higher hardness and lower plasticity are the characteristics of this getter layer.
- The performance of cementite in the metallurgical structure belongs to a complex Fe-C compound. The Vickers hardness can be as high as HV1100, but the impact toughness is almost no.
- Thermal conductivity is not high: If the thermal conductivity of titanium alloy is compared with other alloys such as aluminum alloy, only aluminum alloy is about 1/15, and steel is about 1/5. Compared with aluminum alloy and steel, the thermal conductivity and thermal conductivity of titanium alloy are much lower, only about 1/15 of aluminum alloy, and about 2/7 of steel. The effect on the surface processing quality of some titanium alloy parts is Relatively large.
3 Grinding characteristics
Because titanium alloy has high strength, good thermal stability, high temperature strength, high chemical activity, low thermal conductivity, low elastic modulus and other material characteristics, it is very difficult to grind and is one of the most difficult to process materials, because In this way, its popularization and application range is very limited, because the grinding performance of the titanium alloy is very poor, and there are such problems in the grinding process.
The main grinding characteristics of TC4 titanium alloy are as follows:
- The bonding problem of the grinding wheel is serious. The titanium alloy adheres to the surface of the grinding wheel, and the bonding surface layer is like smoke. The main reason is that the adhesion material falls off during the grinding process. This will cause the abrasive particles to fall off along with the fracture, which will eventually seriously damage the grinding wheel.
- The grinding force is large, and the grinding temperature is high. During the grinding test of single abrasive particles, it was found that when grinding titanium alloys, the larger proportion is the sliding process, and the contact time of the abrasive particles and the workpiece is very short, during which very intense friction and The violent elastic and plastic deformation, then the titanium alloy is ground away into chips, which generates a lot of grinding heat, at this time the grinding temperature can reach up to almost 1500 ℃.
- Grinding will produce layered squeeze chips, the main reason is complex deformation. The band-shaped chips are mostly formed when white corundum grinding wheel (WA60KV) is used to grind 45 steel, and the layer-shaped crushed chips are formed when green silicon carbide grinding wheel (GC46KV) is used to grind titanium alloy.
- Under high temperature conditions, the chemical activity of the TC4 titanium alloy is quite active, and it is easy to combine with oxygen, nitrogen, hydrogen and other elements in the air to form a violent reaction to form brittle and hard such as titanium dioxide, titanium nitride, titanium hydride, etc. Metamorphic layer, which leads to a decrease in the plasticity of TC4.
- During the grinding process of titanium alloys, it is affected by difficult problems, mainly because the grinding heat transferred into the workpiece is difficult to be exported, and the workpiece is easily deformed, burned, and even some cracks appear. Therefore, the surface of the workpiece There will be varying degrees of roughness.
4 Grinding technology innovation
- Inhibition measures to solve grinding burns and cracks
There are some problems when processing TC4 titanium alloy with grinding wheels. The more serious is the adhesion phenomenon. Due to the high speed, the grinding force and temperature are relatively high, which will burn the surface and produce cracks. Ren Jingxin and others have done some experimental research to reduce such burns and cracks during processing. They feel that softer grinding wheels can be used, such as instead of corundum grinding wheels, but silicon carbide or cerium silicon carbide grinding wheels, corundum grinding wheels Resin adhesion, while the former uses ceramic adhesion. Also pay attention to the processing parameters, for example, the speed of the grinding wheel should not be too fast, the experimental analysis should not exceed 20 meters per second, the grinding depth should not be too much, and should not exceed 0.02 millimeters. Within minutes, the grinding fluid must not only dissipate heat well, but also emphasize its lubrication effect, which can effectively suppress the occurrence of sticking phenomenon. If it is dry grinding, the lubricant can be impregnated with solid lubricant Impregnated grinding wheel.
- Titanium alloy grinding wheel bonding phenomenon and its restraining measures
Because in the grinding process of titanium alloy, there will generally be a higher grinding temperature and a larger normal force, so that severe plastic deformation will occur in the titanium alloy in the grinding zone, between the abrasive and the metal The adsorption effect caused by chemical or chemical adsorption; the reason for the transfer of the ground metal to the abrasive particles is the influence of the shear force, which leads to the bonding of the grinding wheel. Finally, the abrasive particles break, and when the grinding force exceeds the binding force between the abrasive particles, the abrasive particles and the bond will peel off from the grinding wheel.
- High-speed and efficient grinding
Human University’s National High-efficiency Grinding Engineering Technology Research Center designed and manufactured ultra-high-speed grinding machine. Some scholars carried out high-speed and efficient grinding of TC4 titanium alloy materials. In the study, the rule that the grinding force per unit area and specific grinding energy are affected by the amount of grinding is analyzed. If the linear velocity vs. of the grinding wheel increases, the grinding force per unit area decreases significantly. However, when the table speed vw and the grinding depth ap increase, the grinding force per unit area increases. If the linear velocity vs. of the grinding wheel increases, the specific grinding energy will increase, but if the table speed vw and the grinding depth ap increase, the specific grinding energy will decrease.