Metal cutting is the most basic processing method in the manufacturing industry. It is the process of using cutting tools to cut off excess materials of machined parts, so as to obtain qualified parts. The selection of appropriate tool materials plays a vital role in machining efficiency and machining quality. High quality cutting tools should have high hardness and wear resistance, sufficient strength and toughness, high heat resistance, good processability and economy, good thermal conductivity and small expansion coefficient. In all kinds of materials, there may be different performances for the above aspects, which requires the processing personnel to comprehensively analyze the requirements of all aspects and choose the most ideal matching result.
Commonly used tool materials are mainly divided into four categories: tool steel, cemented carbide, ceramics and ultra hard tool materials. Let's see what the characteristics of these four categories are.
Tool steel cutter
Tool steel used to make cutting tools includes carbon tool steel, alloy tool steel and high-speed steel. Its main characteristics are poor heat resistance but high bending strength, low price, and good welding and grinding performance. Forming tools, which are widely used in medium and low speed cutting, are not suitable for high-speed cutting.
Carbon tools belong to special quality non alloy steel, with good machinability and low price. They are used in a large amount in tool steel. Carbon tool steel can obtain high hardness after heat treatment, but when the cutting temperature is higher than 250 to 300 ℃, martensite will decompose and reduce the hardness. In addition, its carbide distribution is uneven, its deformation after quenching is large, it is easy to produce cracks, and its hardenability is poor, and its hardening layer is thin. It is only suitable for low-speed cutting tools, such as files, hand saw blades, etc.
Alloy tool steel is a kind of steel that heats chromium, tungsten, vanadium and other alloy elements on the basis of carbon tool steel to improve its hardenability, toughness, wear resistance and heat resistance. The thermal hardness reaches 325 to 400 degrees Celsius, and the allowable cutting speed is 10 to 15 meters per minute. Therefore, it is mainly used for low-speed machining tools such as taps, dies, etc.
High speed steel is a tool steel with high hardness and wear resistance, which contains more tungsten, molybdenum, chromium, vanadium and other elements. It has good comprehensive properties and is a tool material with the widest range of applications. After heat treatment, the hardness of high-speed steel reaches 62 to 66hrc, the bending strength is 3.3gpa, the heat resistance is about 600 degrees Celsius, and the heat treatment deformation is small, it can be forged, and it is easy to grind out sharp edges. It is commonly used to manufacture forming tools and hole processing tools with complex structures.
Cemented carbide is an alloy material made of hard compounds of refractory metals and bonding metals by powder metallurgy. It is higher than tool steel in hardness, strength, toughness, heat resistance, wear resistance and corrosion resistance. It is one of the most important tool materials today. The cutting speed of cemented carbide tools is 4 to 7 times faster than that of high-speed steel, and the service life is 5 to 80 times higher, but the disadvantage is that they are brittle and cannot be made into integral tools with complex shapes, so they are often made into blades, which are then installed on the tool body or die by welding, bonding, mechanical clamping and other methods.
Ceramic cutting tool
In recent years, with the deepening of the research in the field of high-temperature structural ceramics, the performance of silicon nitride ceramics has been greatly improved, so that silicon oxide ceramic tools have developed rapidly, and become a new tool with faster cutting speed and more wear-resistant than cemented carbide tools. Ceramic cutting tool is a cutting tool material made of alumina or silicon nitride as the matrix, and then a small amount of metal is added, which is sintered at high temperature. It has the characteristics of high hardness, good wear resistance, strong heat resistance, stable chemical properties, low friction coefficient, low strength and toughness, and low thermal conductivity. Therefore, it is suitable for cutting tools for fine machining hard materials at a high speed.
Super hard tool
Ultra hard cutting tools are made of diamond, cubic boron nitride and other materials. They have excellent mechanical and physical properties, and their hardness is much higher than the above three cutting tool materials.
Cubic boron nitride has high hardness, heat resistance and stability, and is inert to iron group elements. Therefore, it is most suitable for making tools for cutting all kinds of hardened hard steel, such as carbon tool steel, alloy tool steel, high-speed steel, as well as all kinds of iron-based, nickel based, cobalt based and other thermally sprayed parts. Diamond tool is the material with the highest hardness in nature. The tool made of it has a wider range of applications and can process all kinds of difficult and non difficult materials. However, natural diamond is expensive and is mainly used in precision machining of non-ferrous metals and non-metallic materials.
With the progress of modern society and the rapid change of science and technology, mechanical material processing has higher and higher requirements for the materials of cutting tools. Therefore, mastering and understanding the use of various cutting tools and the characteristics of materials can better select and correctly use cutting tools and manufacture more accurate parts.