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CNC milling or manual milling is a machining process used to process prismatic parts
CNC milling or manual milling is a machining process used to process prismatic parts

3QMACHINING is a top quality CNC machining manufacturer in DONGGUAN, GUANGDONG, CHINA. We are working our best work for your custom plastic & metal machining parts from design drawing or sample to final shipment with fast delivery and low MOQ. We are using advanced technology and equipment to offer high precision for producing metal and plastic machining parts. In this article, we focus on ultra-high-speed machining of titanium alloy.

Machinability of titanium alloy

Titanium alloy has the characteristics of small specific gravity, high thermal strength, good thermal stability and corrosion resistance, and is widely used in aviation, aerospace, atomic energy and chemical industries. However, the material is difficult to cut, and it has been continuously explored to solve the technical problems of low processing efficiency and poor surface quality of titanium alloys. As advanced manufacturing technology has become more and more widely used in manufacturing, the use of ultra-high-speed cutting technology to cut titanium alloys has shown obvious advantages.

Factors that generally cause poor machinability of difficult-to-machine materials

  • The material contains high hardness particles.
  • High hardness or high hardness at high temperature.
  •  Large work hardening.
  • Poor thermal conductivity and high cutting temperature.
  • The material has high strength, especially high temperature strength.
  • Easy to bond with tools.
  • High chemical activity.

The material to be processed may have poor machinability due to one or more of the above factors.

Machinability analysis of titanium alloy

  • It has a high chemical affinity. Titanium alloy isvery easy to “affinity” with tool materials at high temperatures above 300°C. During cutting, some elements in the tool materials either dissolve in titanium or play a chemical role with titanium.
  • Poor thermal conductivity. Poor thermal conductivity of titanium alloy, low thermal diffusivity, and high cutting temperature. The thermal conductivity of titanium alloy is on average half that of industrial pure titanium, and the thermal conductivity is 1/5 to 1/7 of that of Therefore, under the same cutting conditions, the cutting temperature of titanium alloy is more than one time higher than that of steel.
  • Although the cutting force of titanium alloy is not large, about 75% of that of carbon steel, the contact length between the chip and the cutting tool rake surface is much smaller than that of carbon steel, about half of that of carbon steel. The stress is about 1.5 times that when cutting carbon steel.
  • The work hardening phenomenon of titanium alloy is not very serious, which is about the same as that of low carbon steel.

It can be seen that the main reason for the poor machinability of titanium alloy is due to the extremely high chemical affinity and poor thermal conductivity of titanium alloy. Experiments have shown that the greater the strength of the titanium alloy, the worse the machinability. The more the content of strengthening elements Al, Sn, Zr, Fe, Mo, Cr, etc. in the alloy, the higher the strength of the alloy and the worse the machinability. Impurities of oxygen, nitrogen, carbon, hydrogen, etc. in titanium produce interstitial solid solution, which makes the alloy stronger and has a greater impact on the machinability.

Ultra-high speed machining of titanium alloy

Due to the high chemical affinity of titanium alloys, poor thermal conductivity and high strength, the cutting temperature is greatly increased and tool wear is intensified. Traditional processing methods are difficult to process.

For a long time, we have been exploring ways to improve the machinability of titanium alloys. Reasonable selection of tool materials and tool geometric parameters, reasonable formulation of cutting parameters, and the use of appropriate cutting fluids can all improve the machinability of difficult-to-machine materials to varying degrees. So far, there have been some methods. The commonly used methods include special heat treatment, heating cutting, introducing ultrasonic waves and vibration into the cutting area, etc. However, these methods generally have disadvantages such as low efficiency, high cost, and difficulty in guaranteeing processing quality. Here is an introduction to the advanced manufacturing process technology suitable for titanium alloy processing that can greatly improve production efficiency and product quality,it is ultra-high-speed cutting.

Ultra-high-speed cutting characteristics and scope of application

Ultra-high-speed cutting is a breakthrough in the understanding of traditional cutting. The cutting principle is different from conventional cutting. Ultra-high-speed cutting has its own characteristics and scope of application.

  1. The small temperature rise of the workpiece reduces the thermal deformation of the workpiece.In ultra-high-speed cutting, although a lot of heat is generated, because the chips are cut away from the workpiece at a fast speed, more than 90% of the cutting heat is taken away by the chips, and the heat transferred to the workpiece is very small, and the workpiece accumulates very little heat, so cutting At this time, the temperature of the workpiece will not rise more than 3°C.
  2. Low cutting force.Due to the high cutting speed, the shear deformation zone is narrowed, the shear angle is increased, the deformation coefficient is reduced, and the chip outflow speed is fast, which can reduce the cutting deformation and the cutting force by 30% to 90% lower than the conventional cutting force , The tool durability is increased by 70%, especially suitable for processing thin-walled workpieces with poor rigidity.
  3. High material removal rate and high surface quality.In ultra-high-speed cutting, the feed speed can be increased by 5-10 times as the cutting speed increases, so that the material removal rate per unit time can be increased by 3 to 5 times. In addition, as the cutting speed increases, the chips can be quickly cut away from the workpiece, so the residual stress on the surface is very small. Due to the increase in the temperature of the cutting point, the height of the scale on the surface of the workpiece will be significantly reduced or even disappear completely.

Ultra-high speed cutting titanium alloy

Ultra-high-speed cutting of titanium alloy improves its machining performance under the action of high strain rate response, thereby obtain high machining quality. The speed of ultra-high-speed cutting of titanium alloy is generally controlled in the range of 150-1000m/min. In addition to cutting speed, the key technology for ultra-high-speed cutting of titanium alloy also includes many factors such as tool spindle unit and feed unit manufacturing technology, machine tool support and auxiliary unit manufacturing technology, processing and testing technology. This article focuses on the tool materials that have a great impact on tool durability, machining efficiency and machining quality in the process of ultra-high-speed cutting of titanium alloy, in order to find the best match between the tool and the titanium alloy.

Tool materials for ultra-high-speed cutting.

  • Because the ultra-high-speed cutting speed is several times or even ten times higher than the conventional cutting speed, and the cutting temperature is very high, the ultra-high-speed cutting puts forward higher requirements for tool materials. The tool material should have high heat resistance, thermal shock resistance, good high temperature mechanical properties and high reliability. At present, the tool materials used for ultra-high-speed cutting in the world mainly include: coated cemented carbide, TiC(N)-based cemented carbide, ceramic tools, polycrystalline diamond PCD and cubic boron nitride.
  • Coated carbide cutting tools Coated cutting tools are coated with one or more layers of refractory compounds with good wear resistance on the tough tool body, so that the tool has both high toughness and high hardness and resistance. Grindability, the service life of coated tools is 2 to 5 times longer than that of uncoated tools.
  • Polycrystalline diamond tools Natural diamond tools are brittle in nature and easily break along the physical surface of the crystal, leading to large chippings. In many cases, they have been replaced by polycrystalline diamond (PCD). PCD is made by adding graphite as raw material to catalyst and sintering at high temperature and high pressure. It has good thermal conductivity, abrasion resistance and high hardness.
  • Polycrystalline cubic boron nitride tool Polycrystalline cubic boron nitride (PCBN) is a polycrystalline material obtained by sintering fine cubic boron nitride (CBN) materials together under high temperature and pressure. PCBN tools have the advantages of CBN. , Is also easier to manufacture than CBN, so PCBN has been developed quickly. PCBN has high thermal stability, can withstand cutting temperatures above 1200 ℃, and has high hardness and high wear resistance.

Titanium alloy requirements for tool materials.

According to the processing characteristics of titanium alloy materials, the tool materials are required to have high deformation strength, high hardness, good toughness, good thermal hardness, good wear resistance and good heat dissipation properties.

In addition to the above, because titanium-containing tool materials are easily compatible with titanium alloys at high temperatures, titanium-containing tool materials must not be used.

  • Good thermal conductivity. Due to the high thermal conductivity and thermal diffusivity, the cutting heat is easily dissipated, so the cutting temperature is low. The thermal conductivity of diamond is 1.5-9 times that of cemented carbide.
  • Low thermal expansion coefficient. The thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, which is about 1/10 of that of high-speed steel.
  • Extremely high hardness and wear resistance. The durability of diamond tools when processing high-hardness materials is 10-100 times, even hundreds of times, that of cemented carbide tools

Conclusion

The use of ultra-high-speed cutting titanium alloy, which is difficult to machine, solves the problem of conventional cutting titanium alloy, which not only ensures the processing quality but also greatly improves the productivity, and has a good development prospect. Ultra-high-speed cutting technology is gradually mature for the processing of difficult-to-machine materials.

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