Analysis and Research on deep hole drilling techno

Analysis and Research on deep hole drilling technology of titanium alloy

Abstract: This paper mainly describes the performance characteristics of titanium alloy, analyzes the main factors of Yingna titanium alloy drilling processing, and puts forward the corresponding measures to improve the deep hole drilling processing of titanium alloy

titanium and titanium alloys have excellent use characteristics, excellent corrosion resistance in the immersion environment of human blood, and good compatibility with human blood and cell tissue. As implants, they do not produce human pollution and allergic reactions. They are recognized by the world as excellent metal materials in the field of biomedicine. Compared with the use of stainless plutonium, drill based alloys and other metal materials, they have greater application advantages, There is a lot of room for development

titanium alloy material has low density (about 4.5kg/M ³)， It has a series of excellent mechanical and physical properties, such as high specific strength and specific fracture toughness, and can resist the corrosion of various acids, alkalis, seawater, atmosphere and other media. It has been more and more widely used in aviation, aerospace, chemical industry, medical devices and other fields. But its processing performance is poor, especially the efficiency of drilling and tapping is very low, which greatly restricts the processing quality and production efficiency of titanium alloy zero in products. In this paper, the specific characteristics of titanium alloy materials and their cutting characteristics in drilling are analyzed, especially the tool materials, tool structures, tool parameters and so on are repeatedly studied and tested, and corresponding measures are taken to better solve the problems existing in the drilling process of titanium alloy

1. Analysis of performance characteristics and processing characteristics of titanium alloy

(1) performance characteristics of titanium alloy

titanium alloy is to add alloy elements to industrial pure titanium to improve the strength of titanium. Titanium alloys can be divided into three types: α Titanium alloy, β Titanium alloy and α+β Titanium alloy. α+β Titanium alloy, such as TC4 (Ti-6A1-4V), which is made of α and β This kind of alloy has stable structure, good high-temperature deformation performance, toughness and plasticity. It can be quenched and aged to strengthen the alloy. It is an important raw material in the aviation industry. The performance characteristics of titanium alloy are as follows:

a) high specific strength. Low density of titanium alloy (4.5kg/M ³)， Light weight, but its specific strength is greater than that of ultra-high strength steel

b) high thermal strength. Titanium alloy has good thermal stability. At 300 ℃ ~ 500 ℃, its strength is about 3 ~ 4 times that of aluminum alloy

c) good corrosion resistance. Titanium alloy can form dense oxide film, and its corrosion resistance is better than that of stainless steel

d) high chemical activity. Titanium has great chemical activity, and has a strong chemical reaction with 0, N, h, C0, carbon dioxide, steam, etc. in the air. It is easy to form tic and tin hardened layers on the surface of titanium alloy, which increases brittleness and decreases plasticity

e) poor thermal conductivity and small elastic modulus. The thermal conductivity of titanium alloy is only 1/4 that of steel and 1/14 that of aluminum

(2) analysis of machining characteristics of titanium alloys

the reason why titanium alloys are difficult to machine is the synthesis of mechanical, chemical and physical properties of titanium alloys. Due to the low thermal conductivity of titanium alloy, which is only 1/4 of steel, 1/14 of aluminum and 1/25 of copper, the heat dissipation is slow, which is not conducive to heat balance. Especially in the process of drilling, the heat dissipation and cooling effect is very poor. High temperature is formed in the cutting area, and the elasticity is large after processing, resulting in increased torque of the drill bit, rapid wear of the cutting edge and reduced durability. At the same time, because the deformation coefficient of titanium alloy is less than or close to L, this is a remarkable feature of titanium alloy processing. Therefore, the path of chip sliding and friction on the front knife is increased, and the tool wear is accelerated. In addition, titanium alloy has high chemical activity. When processed under high temperature and high pressure, it reacts with the tool material to form a solution deposit and diffuse into an alloy, resulting in sticking to the tool, making it difficult to remove the chips, and often causing the bit to be bitten and twist the bit

2. Deep hole drilling of titanium alloy

through the analysis of the processing characteristics of titanium alloy, we understand the factors that affect the drilling of titanium alloy, that is, in the processing process, it is very easy to have problems such as knife burning, drill breaking, rapid tool wear, work hardening, etc., while deep hole drilling of titanium alloy is easier to solve the above problems

(1) selection of drill bit

the drill bit material should meet the following requirements:

a) sufficient hardness. The hardness of the drill bit must be greater than that of the titanium alloy

b) sufficient strength and toughness. Because the bit bears great torsional force and cutting force when machining titanium alloy. Therefore, it must have sufficient strength and toughness

c) sufficient wear resistance. Due to the good toughness of titanium alloy, the cutting edge should be sharp during machining, so the tool material must have enough wear resistance to reduce work hardening

d) the affinity between tool material and titanium alloy is poor. Due to the high chemical activity of titanium alloy, it is required that the affinity between tool material and titanium alloy should be poor, so as to avoid the formation of solution deposition, diffusion and alloy formation, resulting in knife sticking, drill breaking and other phenomena

the cutting tool materials commonly used in the manufacture of titanium alloy drill bits are superhard high-speed steel w6mo5cr4v3a1, w10mo4cr4v3a1 and w6mo5cr4vss inba1, ultra-fine Grain Cemented Carbide and copper bonded cemented carbide YS2, ym051, ym052, ym053, etc. through the test and analysis of drill bits of different materials, the results show that the drill bits made of ultra-fine grain cemented carbide have sharp edges, small wear, and significantly improved efficiency in processing titanium alloy, It is an ideal cutting tool material

(2) characteristics of Ultra-fine Grain Cemented Carbide integral drill

Ultra Fine Grain Cemented Carbide integral drill is made of ultra-fine grain cemented carbide material. The specially designed geometric edge type enables the drill to have self centering function. In addition to the specific requirements for control mode, it has good chip control and chip removal performance during drilling performance

① cutting edge and groove shape

because the drill bit bears a great torque axial resistance when drilling titanium alloy. If the thickness of the drill core is small, the strength of the drill bit is low and the drill bit is easy to break. Ultra fine cemented carbide bits have a breakthrough shape

design. The new shape of "wavy cutting edge" and the structure of "chip removal groove that is not easy to jam" make this product have excellent performance in cutting ordinary steel or tough materials. Drilling material: 45 × copper fire stop, drill diameter φ 12mm, drilling depth 60mm, cutting speed 120m/min, feed rate per revolution 0.25mm/rev, cutting fluid is cooled in water-soluble emulsion. It can be seen from the recorded data that the cutting power of the machine tool has been maintained at about 5kW, and the wavy cutting edge can effectively maintain the sharpness of the edge and reduce energy consumption; The convex arc near the center can improve the rigidity of the tip of the drill bit. When cutting, the small arc on the outside of the groove can make the chips form a curve in a small range and break into small pieces, while the large arc in the center is conducive to the smooth discharge of the chips. The combination of the two greatly improves the chip removal ability of the tool itself

② new drill point design

the top edge of the drill adopts a new centripetal shape design. Because the small vertex angle on the top and the X-shaped horizontal edge have the function of automatic centring and complementary grinding effect, it has a very high centring degree, which helps to reduce the radial swing and the high wear resistance of the material, so it can more effectively ensure the accuracy of processing

(3) working characteristics of being processed

the characteristics of titanium alloy processing are fully considered in the development of medical retention pin NC drilling machine, and the one-time drilling rate is significantly higher than that of standard fried dough twist drill. According to the requirements of the standards of titanium and titanium alloy processing materials for surgical implants - metal materials - pure titanium processing and surgical implants - metal materials - Ti-6A1-4V alloy processing materials, medical TC4 alloy is used, in which φ 0.6 and φ 1.2 the hole is drilled and processed, and the through hole φ The aperture ratio of 0.6 is close to 30 times, which belongs to deep hole drilling, and the aperture is small, the cooling of the cutting area is difficult, the high temperature brought by cutting is very easy to cause work hardening, the durability of the drill bit is poor, and the processing is very difficult

(4) drilling amount

the performance characteristics of titanium alloy require that the speed of drilling titanium alloy should be low and the feed rate should be moderate

(5) cooling and liquid supply mode

due to the high chemical activity of titanium, it is very easy to have a strong chemical reaction with 0, N, h, C0, C02, and whether the tensile testing machine should choose high distribution or common distribution of water. It is easy to form tic and tin hardened layers on the surface of titanium alloy, which increases brittleness and reduces plasticity. We have adopted the method of internal cooling and lubrication in the air mist on the machine tool, using argon as the supply air source, and the working pressure of the air source is 1MPa, The cutting fluid uses machine oil plus extreme pressure additive as the cutting fluid, which is atomized by air oil mist, and then directly sends the cooling mist to the cutting area through the holes in the spindle and tool for cooling and lubrication. Under the joint action of high-pressure protective gas and cutting fluid, the chips are very easy to discharge from the drill bit, and the best cooling and lubrication effect is obtained

3, conclusion

through the analysis of the characteristics of titanium alloy, the problem of too large voltage fluctuation in the drilling process of titanium alloy is emphatically solved, and good results are achieved. The following conclusions are drawn:

(1) ultra fine grain cemented carbide bits are suitable for titanium alloy processing

(2) improving the number and parameters of drill bits can significantly improve the processing efficiency of titanium alloy zero

(3) prepare a coolant suitable for titanium alloy processing for effective cooling, which can prolong the service life of cutting tools and improve processing efficiency. Carry out the stress relaxation test according to en10319