Ceramic materials have good high temperature resistance, corrosion resistance, high strength and high hardness, and are excellent high-performance materials. With the development of ceramic materials science, more and more preparation technologies have been introduced, and the properties of ceramic materials have been gradually improved. Ceramic materials can be used in high-tech fields such as space exploration and aerospace.
The atoms of ceramic materials are combined through covalent bonds and ionic bonds, while the atoms of metal materials are combined through metallic bonds, so ceramic materials and metal materials have completely different properties. Ceramic materials have great resistance to deformation under shear stress at room temperature and have high hardness. Since ceramic crystals are composed of cations and anions and the chemical bonds between them, the chemical bonds are directional, the atomic packing density is low, and the atomic spacing is large, making the ceramics very brittle and causing many defects during processing, so it is typical Difficult to process materials. It is very important to develop efficient and low-cost processing technology.
1. Turning and grinding processing technology of ceramic materials
Ceramic materials are extremely brittle, and it seems difficult to connect ceramics with turning. However, indentation experiments on ceramic materials show that ductile machining of ceramic materials can still be achieved if appropriate diamond tool angles and cutting parameters are selected. Relevant experiments also show that ceramic materials can be processed using superhard tool materials. Li Xiangfan's experiments on ultra-precision turning of ceramic materials show that W-Co carbide can be used to process ceramic parts. Hara Akio of Japan used polycrystalline diamond tools to turn Al2O3 and Si3N4 ceramics. At present, diamond tools are mainly used for turning ceramic materials. Single crystal diamond tools are superior to polycrystalline diamond tools in terms of sharpening performance. They are all micro-cutting, with low removal rate, and the processing quality and accuracy are difficult to guarantee, and further research is needed.
Grinding can meet the processing requirements of hard metals, so it can also become the main processing method of ceramic materials, and its accuracy and efficiency are relatively moderate. Diamond grinding wheels are generally used to grind ceramic materials. When the diamond grinding wheel grinds materials, the abrasive grains cut into the workpiece. The ceramic surface material in front of the cutting edge of the abrasive grains is squeezed. When the pressure value exceeds the endurance limit of the ceramic material, it is crushed and formed into debris. . At the same time, when the abrasive grains cut the workpiece, due to the action of compressive stress and frictional heat, the material under the abrasive grains will produce local plastic flow and form a deformation layer. When the abrasive grains are cut out, the deformation layer will disappear from the workpiece due to the disappearance of the stress. Break away to form chips. Looking at ceramics from the chip formation mechanism
The method of material removal is still brittle. A large number of processing defects remain on the surface after grinding, so deep processing becomesNecessary process. In order to reduce the cost of deep processing, the concept of ductile domain grinding has been proposed in recent years. The main goal of ductile domain grinding is to improve the grinding surface quality, and adopt technologies such as adjusting the arrangement of abrasive grains and precision dressing to achieve efficient and precise processing of ceramic materials. The grinding of ceramic materials also has problems such as grinding wheel wear and clogging and low processing efficiency. These problems require further research.
2. Special processing technology of ceramic materials
Ultrasonic processing is to apply ultrasonic vibration to the processing tool or the material being processed, add liquid abrasive or paste abrasive between the tool and the workpiece, and press the tool against the workpiece with a small pressure. During processing, due to the ultrasonic vibration between the tool and the workpiece, the abrasive particles suspended in the working fluid are forced to continuously hit and polish the surface to be processed at a very high speed and acceleration, coupled with the cavitation and overpressure effects in the processing area, This results in a material removal effect. Ultrasonic processing is more suitable for the brittleness of the surface of ceramic materials. The surface quality processed by this method is better and it is easy to realize processing automation. Its disadvantages are low processing efficiency and low tool life.
Laser processing of ceramic materials uses a laser beam with extremely high energy density to irradiate the surface of the ceramic material. The light energy is absorbed by the ceramic surface, and part of the light energy is converted into heat energy, causing the local temperature to rapidly increase, causing melting and even vaporization to form pits. . As energy continues to be absorbed, the vapor in the pits expands rapidly, ejecting the molten material at high speed and generating a highly directional shock wave, so that the material is eroded under the action of high temperature, melting, vaporization and impact. Laser processing is efficient and environmentally friendly, but the temperature gradient on the surface of the light spot can easily form micro-cracks on the surface of ceramic materials, and laser equipment is expensive and the use cost is high.
Electrical discharge machining mainly removes materials through high-temperature melting and vaporization generated by discharge between electrodes. EDM is suitable for processing conductive materials. Because ceramic materials are electrical insulators, special processes must be adopted. One high-voltage EDM method involves placing an insulating ceramic material workpiece between a pointed electrode and a flat electrode. A high DC or AC voltage is applied between the two electrodes, causing the medium near the sharp electrode to be broken down, causing glow discharge erosion. Another processing method is to press a thin metal mesh on the thin ceramic workpiece as an auxiliary electrode. The auxiliary electrode and the tool electrode are connected to the positive and negative electrodes of the pulse power supply respectively, and placed in the oil working fluid. When the pulse voltage is applied to Between the two poles, spark discharge is generated between the tool and the auxiliary electrode; when the electric spark passes through the auxiliary electrode on the workpiece, due to the gasification, injection or sputtering of the metal materialThese functions make the surface of ceramic parts conductive and processing can continue. Another processing method is to coat the surface of ceramics with conductive materials for EDM processing. Electric discharge machining still faces problems such as low processing efficiency and difficulty in ensuring the quality of the machined surface, which require further research.
3. Special processing auxiliary turning and grinding technology
The efficiency of turning and grinding processing is relatively high, but its requirements for tools are very high, and the surface quality of ceramic materials is difficult to guarantee, and it is also difficult to process formed ceramic parts. In order to improve the processing accuracy and processing range of ceramic materials, the introduction of special processing technology in turning and grinding will achieve higher processing efficiency and surface quality at the same time.
Ultrasonic grinding is to apply ultrasonic frequency vibration to the tool or workpiece while grinding, making full use of the high-frequency vibration and cavitation of ultrasonic waves to remove materials. The ultrasonic grinding method is more suitable for the processing of ceramic materials. The processing efficiency gradually increases as the brittleness of the material increases. Ultrasonic grinding technology can significantly reduce the grinding temperature, increase the service life of the grinding wheel, and improve the processing accuracy and surface quality.
Laser-assisted turning technology irradiates laser light onto the ceramic material near the tool. During the turning process of the ceramic material, the shear area of the material is softened by the high temperature generated by the laser, which reduces the cutting resistance of the ceramic material and increases the processing ductility of the ceramic material. Thus, efficient ductile processing of ceramic materials is achieved.
Online electrolytic grinding technology introduces electrolysis technology into the grinding process, and uses a continuous limited amount of electrolysis to erode the metal bond on the surface of the grinding wheel, thereby dressing the grinding wheel to achieve the purpose of continuously exposing micro-powder abrasive grains. Online electrolysis technology is the result of research by the Japan Institute of Physics and Chemistry, and the processing of ceramic materials can reach the level of ultra-precision processing.
4. Cost trend
With the continuous breakthroughs and advancements in ceramic material processing technology, production efficiency has improved significantly, and ceramic processing costs have also been continuously reduced.
5.Conclusion
The wide application of ceramic materials in high-tech fields has promoted the research on their processing technology. Ceramic materials have high hardness and brittleness, so it is difficult to process using traditional turning and grinding technology. However, special processing technology is efficient and low-cost, so the method of combining traditional turning and grinding technology with special processing technology will be the most popular method for ceramic processing in the future. Trends in technology research.
