The choice of engraving tools Machining is one of the most widely used machining techniques in modern manufacturing tools. According to statistics, the proportion of foreign cutting processing in the entire manufacturing process is about 80% to 85%, while in China it is as high as 90%. Tools are an indispensable tool in cutting. Whether it is a general machine tool or an advanced CNC machine tool (NC), machining center (MC) and flexible manufacturing system (FMC), tools must be used to complete the cutting process.
The development of tools has a direct impact on productivity and processing quality. Materials, structures and geometries are the three factors that determine the cutting performance of a tool. The performance of the tool material plays a key role. The International Society of Production Engineering (CIRP) pointed out in a research report: "As the tool material is improved, the allowable cutting speed is almost doubled every 10 years." Tool materials have evolved from high-speed steel and cemented carbide to the present. High-performance ceramics, super-hard materials, etc., the heat-resistant temperature has been increased from 500 to 600 ° C to more than 1200 ° C, allowing the cutting speed to exceed 1000 m / min, so that the cutting processing productivity increased by more than 100 times in less than 100 years. Therefore, it can be said that the development of tool materials actually reflects the development history of cutting technology.
During the cutting process, the tool works under strong cutting force and high temperature, and at the same time produces severe friction with the chip and the surface of the workpiece. Therefore, the working conditions are very bad. In order to have good cutting ability, the material must be selected. Tool materials have a significant impact on processing quality, productivity and processing costs. Therefore, the tool material should meet the basic requirements: 1 high hardness and wear resistance. The hardness of the prop material must be higher than the hardness of the workpiece material. Generally, it should be above HRC60 at normal temperature. Under normal circumstances, the higher the hardness of the tool material, the better the wear resistance. 2 high heat resistance. The tool material retains its hardness, strength, toughness and wear resistance at high temperatures. 3 sufficient strength and toughness. The tool material can withstand the cutting forces and the vibrations generated by the cutting to prevent brittle fracture and chipping. 4 good thermal physical properties and thermal shock resistance. It is required that the tool has good thermal conductivity and will not cause cracks in the tool due to large thermal shock. 5 good processability. Tool materials are required to have good processability, including hot workability and machinability. 6 good economy.
Select the tool made of the appropriate tool material according to the workpiece material and machining requirements that need to be cut. With the development of modernization, in order to meet the needs of industry, agriculture and life, a variety of high-hardness and high-strength materials have emerged. In order to meet the cutting requirements, new tool materials are also emerging.
The tool materials commonly used in cutting machining are: carbon tool steel, alloy tool steel, high speed steel, cemented carbide, ceramic, diamond, cubic boron nitride, and the like. Carbon tool steel and alloy tool steel, due to poor heat resistance, should only be used as hand tools. Ceramic, diamond and cubic boron carbide are used only in a small range due to their brittleness, poor processability and high cost. At present, the most commonly used high-speed steel and hard alloy. High-speed steel is called front steel, is a high-alloy tool steel with more alloy elements such as W, Mo, Cr, V, etc., its carbon content is 0.7%~ 1.05%. High-speed steel has high heat resistance and its cutting temperature can reach 600 °C. Compared with carbon tool steel and alloy tool steel, its cutting speed can be doubled. High-speed steel has good toughness and formability and can be used to manufacture almost all kinds of tools. However, high-speed steel also has defects such as wear resistance and poor heat resistance, which has been difficult to meet the increasing cutting tool materials for modern cutting. In order to improve the hardness and heat resistance of high-speed steel by adding new elements to high-speed steel and manufacturing high-speed steel by powder metallurgy. This satisfies the requirements of the basic workpiece for the tool.
Cemented carbide is an alloy made of powder metallurgy with a high hardness and high melting point of metal carbide as a collective, using co, ni as a binder. Its hardness is 74~82HRC and can withstand high temperatures of 800 to 1000. Therefore, the wear resistance and heat resistance are good, and the allowable cutting speed is six times that of high speed steel. However, its strength and toughness are lower than that of high-speed steel, and the craftsmanship is poor. There are mainly scattered types of hard alloys in China: 1"YG type, good toughness but poor wear resistance when cutting tough materials, so it is suitable for processing brittle materials such as cast iron and bronze. 2"YT type, higher hardness than YG, good heat resistance, good wear resistance when cutting tough materials, but poor toughness, generally suitable for processing steel parts. 3"YW class, he has the advantages of the former two, using its tooling skills to process brittle materials and processing tough materials, while also processing high temperature alloys, heat resistant alloys and alloy cast iron materials.
With the advent of high-hardness and difficult-to-machine materials, higher requirements have been placed on tool materials. Many new tool materials have appeared. Ceramics are made of alumina or silicon nitride as the main component. They are pressed and sintered to form a tool material. They have high hardness and high temperature resistance. They are called cutting, but they are brittle and suitable for steel and cast iron. Finishing and semi-finishing of non-ferrous materials. Synthetic diamond is made of graphite catalyst under the action of alloy catalyst. It has high hardness and low friction coefficient with metal, but it is not resistant to high temperature and should not be cut black metal. It is suitable for super-hard finishing of high hardness and wear-resistant materials, non-ferrous metals and non-metals. Cubic boron nitride (CBN) is a synthetic new tool material with cubic boron nitride added to the catalyst under high temperature and high pressure. Its hardness is high, high temperature resistance, and good grinding performance, but the welding performance is poor, and the bending strength is lower than that of hard alloy. Suitable for processing high temperature alloys, hardened steel, chilled cast iron.
Although a variety of new tool materials emerge in an endless stream, carbide tools will still be widely used in cutting for a long time to come. Therefore, it is necessary to research and develop new material preparation technologies to further improve and improve the cutting of cemented carbide tool materials. performance. In order to further improve the comprehensive cutting performance of cemented carbide tool materials, the research hotspots mainly include the following aspects: 1. Refined grains 2. Coated cemented carbide 3. Surface, overall heat treatment and cyclic heat treatment 4. Add rare metals 5. Adding rare earth elements, applying whisker toughening and strengthening, nano-powder composite strengthening technology to comprehensively improve the hardness, toughness and other comprehensive properties of cemented carbide tool materials, is an important direction for the future development of cemented carbide tool materials.
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