However, in the late18th century, with the development of steam engines and other machines, cutting tools developed rapidly. 1783, René of France first made a milling cutter. 1792, taps and dies made in Maudslay, UK. The earliest document about the invention of twist drill was recorded in 1822, but it was not produced as a commodity until 1864.
At that time, the cutting tool was integral high-carbon tool steel, and the allowable cutting speed was about 5 meters per minute. 1868, the alloy tool steel containing tungsten was specially made in Muscher, England. 1898, American Taylor and White invented high-speed steel. 1923, Germany Schroeder invented cemented carbide.
When alloy tool steel is used, the cutting speed of the tool is increased to about 8m/min, which is more than doubled when high speed steel is used, and more than doubled when cemented carbide is used, and the surface quality and dimensional accuracy of the machined workpiece are also greatly improved.
Due to the high price of high speed steel and cemented carbide, the cutting tool adopts welding and mechanical clamping structure. From 1949 to 1950, the United States began to use indexable inserts on turning tools, and soon it was applied to milling cutters and other tools. 1938, Germany's Degussai Company obtained a patent for ceramic tools. 1972, General Electric Company produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride blades. These non-metallic tool materials can make the tool cut at a higher speed.
1969, sandvik Iron and Steel Works, Sweden obtained the patent for producing titanium carbide coated cemented carbide blades by chemical vapor deposition. From 65438 to 0972, Bonsa and Ragulin in the United States developed the physical vapor deposition method, which coated a hard layer of titanium carbide or titanium nitride on the surface of cemented carbide or high-speed steel tools. The surface coating method combines the high strength and toughness of the matrix material with the high hardness and wear resistance of the surface layer, thus making this composite material have better cutting performance.
According to the form of the machined surface of the workpiece, tools can be divided into five categories. Tools for processing various external surfaces, including turning tools, planers, milling cutters, broaches and files on the external surfaces; Hole processing tools, including drills, reamers, boring tools, reamers and broaches for inner surfaces; Thread processing tools, including taps, dies, automatic thread cutting heads, thread turning tools and thread milling cutters; Gear machining tools, including hob, gear shaper cutter, gear shaving cutter, bevel gear machining tool, etc. Cutting tools, including sawtooth circular saw, band saw, bow saw, cutting turning tool and saw blade milling cutter, etc. In addition, there are combined cutters.
According to the cutting motion mode and the corresponding blade shape, tools can be divided into three categories. General tools, such as turning tools, planers, milling cutters (excluding shaping turning tools, shaping planers and shaping milling cutters), boring cutters, drill bits, reamers, reamers and saws, etc. Forming tools, the blade shape of which is the same as or almost the same as the cross-sectional shape of the workpiece to be processed, such as forming turning tools, forming planers, forming milling cutters, broaches, conical reamers and various thread processing tools; Generating cutter is used for machining gear tooth surface or similar workpiece, such as hob, gear shaper cutter, gear shaving cutter, bevel gear planer, bevel gear milling cutter and so on.
The structure of various tools consists of a clamping part and a working part. The clamping part and the working part of the integral structure tool are both made on the tool body; The working part (tooth or blade) of the insert-tooth structure cutter is embedded in the cutter body.
There are two types of clamping parts of tools: holes and handles. A holed cutter is sleeved on the spindle or spindle of a machine tool through an inner hole, and transmits torque through a shaft key or an end key, such as a cylindrical milling cutter and a nested face milling cutter.
There are usually three kinds of tools with handles: rectangular handles, cylindrical handles and conical handles. Turning tools, planers, etc. Usually rectangular handle; The tapered handle bears axial thrust through taper and transmits torque through friction; Cylindrical handle is generally suitable for smaller twist drills, end mills and other tools. When cutting, torque is transmitted by friction generated during clamping. The handles of many tools with handles are made of low-alloy steel, while the working parts are made of high-speed steel by butt welding.
The working part of the tool is the part that generates and processes chips, including the blade, the structure that breaks or rolls chips, the space for removing or storing chips, the channel of cutting fluid and other structural elements. The working part of some tools is cutting part, such as turning tool, planer, boring tool and milling cutter. The working part of some tools includes cutting part and calibration part, such as drill, reamer, internal surface broach and tap. The function of the cutting part is to chip with the blade, and the function of the calibration part is to make the machined surface smooth and guide the tool.
There are three types of working parts of tools: integral, welded and mechanically clamped. The whole structure is to make a cutting edge on the cutter body; The welding structure is that the blade is brazed to the steel cutter body; There are two kinds of mechanical clamping structures, one is to clamp the blade on the cutter body, and the other is to clamp the brazed cutter head on the cutter body. Carbide tools are generally made into welding structure or mechanical clamping structure; Porcelain cutters all adopt mechanical clamping structure.
The geometric parameters of the cutting part of the tool have great influence on cutting efficiency and machining quality. Increasing the rake angle can reduce the plastic deformation when the rake face squeezes the cutting layer, reduce the friction resistance of the chip flowing forward, and thus reduce the cutting force and cutting heat. However, increasing the rake angle will reduce the strength of the cutting edge and reduce the heat dissipation of the cutter head.
When choosing the angle of tool, we need to consider the influence of many factors, such as workpiece material, tool material, machining performance (rough machining and finish machining) and so on. And we must make a reasonable choice according to the specific situation. Generally speaking, the tool angle refers to the marking angle used in manufacturing and measurement. Due to the different installation position of the tool and the change of cutting direction, the actual working angle and scoring angle are different, but this difference is usually very small.
The materials used to make tools must have high high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertia, and good manufacturability (cutting, forging and heat treatment, etc.). ), and it is not easy to deform.
Generally, materials have high hardness and wear resistance; When the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower its bending strength and impact toughness. Because of its high bending strength, impact toughness and good machinability, high speed steel is still the most widely used tool material in modern times, followed by cemented carbide.
Polycrystalline cubic boron nitride is suitable for cutting hardened steel and hard cast iron with high hardness. Polycrystalline diamond is suitable for cutting nonferrous metals, alloys, plastics and FRP. Carbon tool steel and alloy tool steel are only used as tools such as files, dies and taps.
The cemented carbide indexable insert has been coated with titanium carbide, titanium nitride, alumina hard layer or composite hard layer by chemical vapor deposition. The developing physical vapor deposition method can be used not only for cemented carbide tools, but also for high-speed steel tools, such as drills, hobs, taps and milling cutters. As a barrier to chemical diffusion and heat conduction, hard coating slows down the wear speed of tools, and the life of coated blades is more than 1 ~ 3 times longer than that of uncoated blades.
Because parts work in high temperature, high pressure, high speed and corrosive fluid media, more and more difficult-to-machine materials are used, and the automation level of cutting and the requirements for machining accuracy are getting higher and higher. In order to adapt to this situation, the development direction of tools will be to develop and apply new tool materials; Further develop the vapor deposition coating technology of tools, and deposit a layer with higher hardness on the matrix with high toughness and high strength to better solve the contradiction between hardness and strength of tool materials; Further develop the structure of the rotary cutting machine; Improve tool manufacturing accuracy, reduce product quality differences, and optimize tool use.
The cutting performance of the coating is obviously better than that of TiN coating. Tool life for processing Inconel 178 Although PVD coating shows many advantages, some coatings such as Al2O3 and diamond tend to adopt CVD coating technology. Al2O3 is a coating with strong heat resistance and oxidation resistance, which can isolate the tool body from the heat generated by cutting. Through CVD coating technology, the advantages of various coatings can be integrated to achieve the best cutting effect and meet the needs of cutting.
For example. TiN has the characteristics of low friction, which can reduce the loss of coating structure, TiCN can reduce the wear of wing, TiC coating has high hardness, and Al2O3 coating has excellent heat insulation effect. Compared with cemented carbide tools, coated cemented carbide tools have been greatly improved in strength, hardness and wear resistance. Turning workpieces with hardness of HRC45~55, low-cost coated cemented carbide can realize high-speed turning. In recent years, some manufacturers have greatly improved the performance of coating tools by improving coating materials. For example, some manufacturers in the United States and Japan use Swiss AlTiN coating material and new patented coating technology to produce coated blades with hardness as high as HV4500~4900, which can cut die steel with hardness of HRC47~58 at a speed of 498.56m/min. When the turning temperature is as high as 1500 ~ 1600℃, the hardness does not decrease and it does not oxidize. The life of the blade is four times that of the general coated blade, the cost is only 30%, and the adhesion is good. With the continuous improvement of the composition, structure and pressing technology of ceramic materials, especially the progress of nanotechnology, it is possible to toughen ceramic tools. In the near future, ceramics may cause the third cutting revolution after high-speed steel and cemented carbide.
Ceramic tools have the advantages of high hardness (HRA9 1~95), high strength (bending strength is 750~ 1000MPa), good wear resistance, good chemical stability, good anti-adhesion performance, low friction coefficient and low price. Moreover, the ceramic tool also has high high temperature hardness, reaching HRA80 at 1200℃. During normal cutting, the durability of the ceramic tool is extremely high, and the cutting speed is 2-5 times higher than that of cemented carbide. It is especially suitable for processing high-hardness materials, finishing and high-speed machining, and can cut all kinds of hardened steel and hardened cast iron with hardness reaching HRC65. Commonly used are: alumina-based ceramics, silicon nitride-based ceramics, cermets and whisker toughened ceramics.
The red hardness of alumina-based ceramic tools is higher than that of cemented carbide, and the cutting edge will not produce plastic deformation at high speed, but its strength and toughness are very low. In order to improve its toughness and impact resistance, ZrO or a mixture of TiC and TiN can be added, and another method is to add pure metal or silicon carbide whiskers. Silicon nitride-based ceramics not only have high red hardness, but also have good toughness. Compared with alumina-based ceramics, its disadvantage is that high temperature diffusion is easy to occur when processing steel, which aggravates tool wear. Silicon nitride-based ceramics are mainly used for intermittent turning and milling gray cast iron. Cermet is a kind of material with carbide as matrix, in which TiC is the main hard phase (0.5~2? M) is a tool similar to cemented carbide, but it has low affinity, good friction and good wear resistance. It can withstand higher cutting temperature than traditional cemented carbide, but it lacks impact resistance, toughness in strong cutting and strength at low speed and large feed.
In recent years, through a lot of research, improvement and new manufacturing technology, its bending strength and toughness have been greatly improved. For example, the new cermet NX2525 developed by Japan's Mitsubishi Metal Company and the new cermet blade CT series and coated cermet blade series developed by Sweden's sandvik Company have grain structure diameters as small as 1? M below, the bending strength and wear resistance are much higher than those of ordinary cermets, which greatly broadens its application scope. Cubic boron nitride (CBN) CBN is second only to diamond in hardness and wear resistance, and has excellent high-temperature hardness. Compared with ceramics, its heat resistance and chemical stability are slightly worse, but its impact strength and crushing resistance are better. It is widely used for cutting hardened steel (HRC≥50), pearlite gray cast iron, chilled cast iron and superalloy, and its cutting speed can be increased by one order of magnitude compared with cemented carbide tools.
The composite polycrystalline cubic boron nitride (PCBN) tool with high CBN content has high hardness, good wear resistance, high compressive strength and good impact toughness, but its disadvantages are poor thermal stability and low chemical inertia. It is suitable for cutting heat-resistant alloys, cast iron and iron-based sintered metals. The content of CBN particles in PCBN tool is low, and the hardness is low when ceramic is used as binder, but it makes up for the shortcomings of the former material, such as poor thermal stability and low chemical inertia, and is suitable for cutting hardened steel.
Residual stress of ceramic and PCBN tools in cutting hardened steel When cutting gray cast iron and hardened steel, ceramic tools or CBN tools can be selected. Therefore, it is necessary to carry out cost-benefit and processing quality analysis to determine which one to choose. Fig. 3 shows the tool surface wear after processing gray cast iron with Al2O3, Si3N4 and CBN tools. The cutting performance of PCBN tool material is better than that of Al2O3 and Si3N4. However, the cost of Al2O3 ceramics is lower than that of PCBN materials when dry cutting hardened steel. Ceramic knives have good thermochemical stability, but they are not as tough and hard as PCBN knives. When the cutting hardness is lower than HRC60 and the feed rate is small, ceramic tools are a better choice. PCBN tool is suitable for cutting workpieces with hardness higher than HRC60, especially for automatic machining and high precision machining.
In addition, under the same flank wear, the residual stress on the workpiece surface after PCBN tool cutting is relatively stable than that of ceramic tool. When using PCBN tool to dry cut hardened steel, the following principles should be followed: when the rigidity of the machine tool allows, choose a larger cutting depth as much as possible, so that the heat generated in the cutting area can partially soften the metal at the front edge of the cutting edge, which can effectively reduce the wear of PCBN tool. In addition, when using PCBN tool for small cutting depth, it should also be considered that the heat in the cutting area can not spread too late, and the cutting area can also produce obvious metal softening effect, which can reduce the wear of the cutting edge.
The blade structure and geometric parameters of superhard tools are very important to give full play to the cutting performance of tools. In terms of tool strength, the tip strength of various blade shapes is round, 100 diamond, square, 80 diamond, triangle, 55 diamond and 35 diamond from high to low. After the blade material is selected, the blade shape with the highest strength as possible should be selected. Hard turning blades should also choose as large a radius as possible, and circular and large-radius blades should be used for rough machining, and the radius of the circular blade should be about 0.8 for finishing. About m. The chips of hardened steel are red, soft and banded, brittle, easily broken and not bonded. The cutting surface quality of quenched steel is high, and generally chip agglomeration will not occur, but the cutting force is large, especially the radial cutting force is greater than the main cutting force. Therefore, negative rake angle (GO ≥-5) and large rake angle (AO = 10 ~ 6544) should be adopted for cutting tools. The main deflection angle depends on the rigidity of the machine tool, which is generally 45 ~ 60 to reduce the chatter of the workpiece and tool. Selection of cutting parameters of superhard tool and requirements for process system; The higher the hardness of workpiece material, the lower its cutting speed. The suitable cutting speed range for hard turning finishing of superhard tools is 80 ~ 200m/min, and the commonly used range is 10 ~ 150m/min. The cutting speed should be kept at 80 ~ 100 m/min when cutting high-hardness materials with large depth or intermittent strength. In general, the cutting depth is between 0.1~ 0.3 mm. When machining workpieces with low surface roughness, you can choose a smaller cutting depth, but it should not be too small. The feed speed can usually be selected between 0.05 and 0.25mm/r, and the specific value depends on the surface roughness value and productivity requirements. When the surface roughness ra = 0.3 ~ 0.4? M, hard turning with superhard tools is much more economical than grinding.
There is no special requirement for lathe or turning center to use superhard tools for hard turning except selecting reasonable tools. If the rigidity of lathe or turning center is sufficient and the required precision and surface roughness can be obtained when processing soft workpieces, it can be used for hard cutting. In order to ensure the smooth and continuous turning operation, rigid clamping devices and medium rake angle tools are usually used. If the positioning, support and rotation of the workpiece can be kept quite stable under the action of cutting force, the existing equipment can use superhard tools for hard turning. Application of superhard tools in hard turning; Use superhard tools for hard turning. After more than ten years of development and popularization, this technology has achieved great economic and social benefits. Taking industries such as roller processing as an example, the popularization and application of superhard tools in production are explained below.
Roller Processing Industry Many large roller enterprises in China have used superhard tools to rough, rough and finish all kinds of rollers, such as chilled cast iron and hardened steel, and achieved good benefits. For example, in the rough machining and semi-finish machining of chilled cast iron rolls with hardness of HS60 ~ 80, the cutting speed is increased by three times, and the power and working hours are saved by more than 400 yuan per car 1 roll, and the tool cost is saved by nearly 100 yuan, which has achieved great economic benefits. For example, when our school turns 86CrMoV7 hardened steel roll of HRC 58 ~ 63 with FD22 cermet cutter (Vc=60m/min, f=0.2mm/r, ap=0.8mm), the trajectory of the single-side continuous cutting roll reaches 15000m (the maximum width of the wear zone behind the tool tip is VBmax=0.2mm). Industrial Pump Processing Industry At present, 70% ~ 80% of domestic ballast pump manufacturers have adopted superhard tools.
Slurry pump is widely used in mining, electric power and other industries, and it is an urgently needed product at home and abroad. Its sheath and guard plate are Cr 15Mo3 high hardness iron castings of HRC 63 ~ 67. In the past, because it was difficult for all kinds of tools to turn this material, we had to adopt the process of annealing, softening, rough machining and then quenching. After the superhard tool is used, the first hardening process is successfully realized, which saves annealing and quenching, and saves a lot of man-hours and electricity.
In the automobile processing industry, the processing of crankshaft, camshaft and transmission shaft, the processing of tools and measuring tools, and the maintenance of equipment often encounter the processing problems of hardened workpieces. For example, a domestic locomotive and rolling stock factory needs to process the bearing inner ring for equipment maintenance. The hardness of the bearing inner ring (material GCr 15 steel) is HRC60, and the diameter of the inner ring is F 285 mm The grinding process is adopted, and the grinding allowance is uneven, which requires 2 hours of grinding. It takes only 45 minutes to process an inner ring with superhard tools.
Conclusion: After years of research and exploration, China has made great progress in superhard tools, but superhard tools are not widely used in production. The main reasons are as follows: manufacturers and operators don't know enough about the effect of hard turning with superhard tools, and it is generally believed that hard materials can only be ground; Think the cost of tools is too high. The initial tool cost of hard turning is higher than that of ordinary cemented carbide tools (for example, PCBN is ten times more expensive than ordinary cemented carbide tools), but the cost allocated to each part is lower than that of grinding, which brings much better benefits than ordinary cemented carbide tools; Insufficient research on machining mechanism of superhard tools; The specification of superhard tool machining is not enough to guide production practice. Therefore, in addition to in-depth study of the machining mechanism of superhard tools, it is necessary to strengthen the training of superhard tool machining knowledge, the demonstration of successful experience and strict operating specifications, so that this efficient and clean machining method can be more applied to production practice.