The development of knives plays an important role in the history of human progress. As early as the 28th to 20th centuries BC, brass and copper cones, drills, knives and other copper tools appeared in China. In the late Warring States period (3rd century BC), copper knives were made due to the mastery of carburizing technology. The drill bits and saws of that time were somewhat similar to modern flat drills and saws.
However, the rapid development of knives came in the late 18th century with the development of machines such as steam engines. In 1783, René of France first produced a milling cutter. In 1792, Maudsley in England produced taps and dies. The earliest documented record of the invention of the twist drill was in 1822, but it was not produced as a commercial product until 1864.
The cutting tools at that time were made of solid high-carbon tool steel, and the allowed cutting speed was about 5 meters/minute. In 1868, the British Muschet made alloy tool steel containing tungsten. In 1898, Taylor and... White invented high-speed steel. In 1923, Schlueter of Germany invented cemented carbide.
When alloy tool steel is used, the cutting speed of the tool is increased to about 8 m/min. When high-speed steel is used, the cutting speed is increased by more than twice. When carbide is used, the cutting speed is increased again compared to high-speed steel. More than twice that, the surface quality and dimensional accuracy of the cut workpiece are also greatly improved.
Due to the high price of high-speed steel and cemented carbide, the cutting tools have welding and mechanical clamping structures. Between 1949 and 1950, the United States began to use indexable inserts on turning tools, and soon they were used on milling cutters and other cutting tools. In 1938, the German company Degussa obtained a patent for ceramic knives. In 1972, General Electric Company of the United States produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride blades. These non-metallic tool materials allow the tool to cut at higher speeds.
In 1969, Sweden's Sandvik Steel Works obtained a patent for using chemical vapor deposition to produce titanium carbide-coated carbide blades. In 1972, Bonsa and Lagolan of the United States developed a physical vapor deposition method to coat the surface of cemented carbide or high-speed steel tools with a hard layer of titanium carbide or titanium nitride. The surface coating method combines the high strength and toughness of the base material with the high hardness and wear resistance of the surface layer, giving the composite material better cutting performance.
Tools can be divided into five categories according to the form of the workpiece's machined surface. Tools for processing various external surfaces, including turning tools, planers, milling cutters, external surface broaches and files, etc.; hole processing tools, including drill bits, reamers, boring tools, reamers and internal surface broaches, etc.; thread processing Tools, including taps, dies, automatic opening and closing thread cutting heads, thread turning tools and thread milling cutters; gear processing tools, including hobs, gear shaper cutters, shaving cutters, bevel gear processing tools, etc.; cutting tools, including inserts Toothed circular saw blades, band saws, hack saws, cut-off turning tools, saw blade milling cutters and more. In addition, there are combination knives.
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 formed turning tools, forming planers and forming milling cutters), boring tools, drill bits, reamers, reamers and saws; forming tools, the cutting edges of such tools Have the same or nearly the same shape as the cross section of the workpiece to be processed, such as forming turning tools, forming planers, forming milling cutters, broaches, cone reamers and various thread processing tools, etc.; generating tools use the generating method to process gears Tooth surfaces or similar workpieces, such as hobs, gear shapers, gear shaving cutters, bevel gear planers and bevel gear milling cutters, etc.
The structure of various cutting tools consists of a clamping part and a working part. The clamping part and the working part of the overall structure tool are both mounted on the tool body; the working part (the teeth or blade) of the tool with the toothed structure is mounted on the tool body.
There are two types of tool clamping parts: those with holes and those with handles. Tools with holes rely on the inner hole to be mounted on the spindle or spindle of the machine tool, and use axial keys or end keys to transmit torsional torque, such as cylindrical milling cutters, sleeve-type face milling cutters, etc.
Handled knives usually have three types: rectangular handle, cylindrical handle and conical handle. Turning tools, planers, etc. generally have rectangular shanks; conical shanks rely on taper to withstand axial thrust and transmit torque with the help of friction; cylindrical shanks are generally suitable for smaller twist drills, end mills and other tools, and use clamping during cutting. The friction generated transmits a torsional moment. The handle of many shank knives is made of low alloy steel, and the working part is made of high-speed steel butt welded together.
The working part of the tool is the part that generates and processes chips, including the blade, the structure that breaks or rolls up the chips, the space for chip removal or storage, and the channels for cutting fluid and other structural elements. The working part of some tools is the cutting part, such as turning tools, planers, boring tools and milling cutters; the working part of some tools includes the cutting part and the calibration part, such as drills, reamers, reamers, internal surface drawing tools, etc. Knives and taps etc. The function of the cutting part is to remove chips with the blade, and the function of the calibration part is to smooth the cut surface and guide the tool.
The structure of the working part of the tool includes three types: integral type, welding type and mechanical clamping type. The overall structure is to make a cutting edge on the cutter body; the welding structure is to braze the blade to the steel cutter body; there are two mechanical clamping structures, one is to clamp the blade on the cutter body, and the other is to clamp the blade to the cutter body. The brazed cutter head is clamped to the cutter body. Carbide cutting tools are generally made of welded structures or mechanical clamping structures; porcelain cutting tools all use mechanical clamping structures.
The geometric parameters of the cutting part of the tool have a great influence on the cutting efficiency and processing quality. Increasing the rake angle can reduce the plastic deformation when the rake face squeezes the cutting layer, and reduces the frictional resistance of chips flowing through the front, thereby reducing cutting force and cutting heat. However, increasing the rake angle will also reduce the strength of the cutting edge and reduce the heat dissipation volume of the tool head.
When selecting the angle of the tool, you need to consider the influence of many factors, such as workpiece material, tool material, processing properties (roughing, finishing), etc., and you must make a reasonable choice based on the specific situation. Generally speaking, the tool angle refers to the marked angle used for manufacturing and measurement. During actual work, due to the different installation positions of the tool and changes in the cutting motion direction, the actual working angle is different from the marked angle, but the difference is usually very small. .
The materials used to make cutting tools must have high high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertness, good processability (cutting, forging and heat treatment, etc.), and Not easily deformed.
Usually when the hardness of the material is high, the wear resistance is also high; when the flexural strength is high, the impact toughness is also high. But the harder the material, the lower its flexural strength and impact toughness. High-speed steel is still the most widely used tool material in modern times due to its high bending strength, impact toughness, and good machinability, followed by cemented carbide.
Polycrystalline cubic boron nitride is suitable for cutting high-hardness hardened steel and hard cast iron; polycrystalline diamond is suitable for cutting iron-free metals, alloys, plastics, fiberglass, etc.; carbon tool steel and alloy tool steels are now used only for tools such as files, dies and taps.
Carbide indexable inserts are now coated with titanium carbide, titanium nitride, aluminum oxide hard layer or composite hard layer using chemical vapor deposition method. The developing physical vapor deposition method can be used not only for carbide cutting tools, but also for high-speed steel cutting tools, such as drill bits, hobs, taps and milling cutters. The hard coating acts as a barrier that hinders chemical diffusion and heat conduction, slowing down the wear rate of the tool during cutting. The life of the coated blade is approximately 1 to 3 times longer than that of the uncoated blade.
As parts that work under high temperature, high pressure, high speed, and corrosive fluid media are used in more and more difficult-to-machine materials, the automation level of cutting processing and the requirements for processing accuracy are getting higher and higher. Come higher and higher.
In order to adapt to this situation, the development direction of cutting tools will be to develop and apply new cutting tool materials; further develop the vapor deposition coating technology of cutting tools to deposit higher hardness coatings on high toughness and high strength substrates to better solve the problem. The contradiction between the hardness and strength of tool materials; further developing the structure of indexable tools; improving the manufacturing accuracy of tools, reducing the difference in product quality, and optimizing the use of tools.
The cutting performance of the coating is significantly better than that of TiN coating. Tool life in machining Inconel178 Although PVD coatings show many advantages, some coatings such as Al2O3 and diamond prefer 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 also be combined to achieve the best cutting effect and meet the needs of cutting processing.
For example. TiN has low friction properties, which can reduce the loss of the coating structure, TiCN can reduce the wear of the flank surface, the TiC coating has high hardness, and the Al2O3 coating has excellent heat insulation effect, etc. Compared with carbide tools, coated carbide tools have greatly improved in strength, hardness and wear resistance. For turning workpieces with a hardness of HRC45~55, low-cost coated carbide can achieve high-speed turning. In recent years, some manufacturers have applied methods such as improving coating materials to greatly improve the performance of coated cutting tools. For example, some manufacturers in the United States and Japan use Swiss AlTiN coating materials and new coating patented technology to produce coated blades with a hardness as high as HV4500~4900, which can cut mold steel with a hardness of HRC47~58 at a speed of 498.56m/min. When the turning temperature is as high as 1500~1600°C, the hardness does not decrease or oxidize. The blade life is 4 times that of ordinary coated blades, while the cost is only 30, and the adhesion is good. Ceramic materials Ceramic cutting tool materials With the continuous improvement of their composition structure and pressing process, especially the progress of nanotechnology, it is possible to toughen ceramic cutting tools. In the near future, ceramics may lead to cutting problems after high-speed steel and cemented carbide. The third revolution in processing.
Ceramic cutting tools have high hardness (HRA91~95), high strength (bending strength 750~1000MPa), good wear resistance, good chemical stability, good anti-adhesion performance, low friction coefficient and Low price and other advantages. Not only that, ceramic cutting tools also have high high-temperature hardness, reaching HRA80 at 1200°C. During normal cutting, ceramic tools have extremely high durability, and the cutting speed can be 2 to 5 times higher than that of cemented carbide. They are especially suitable for high-hardness material processing, finishing and high-speed processing. They can cut various types of hardened steel and hardened cast iron with a hardness of HRC65. wait. Commonly used ones are: alumina-based ceramics, silicon nitride-based ceramics, cermets and whisker-toughened ceramics.
Alumina-based ceramic tools have higher red hardness than cemented carbide. The cutting edge generally does not produce plastic deformation under high-speed cutting conditions, but its strength and toughness are very low. In order to improve its toughness, To improve impact resistance, ZrO or a mixture of TiC and TiN can usually be added. Another method is to add pure metal or silicon carbide whiskers. In addition to high red hardness, silicon nitride-based ceramics also have good toughness. Compared with alumina-based ceramics, its disadvantage is that it is prone to high temperature diffusion when processing steel, which aggravates tool wear. Silicon nitride-based ceramics are mainly used in Intermittent turning and milling of gray cast iron. Cermet is a kind of carbide-based material, in which TiC is the main hard phase (0.5~2?m). They are combined by Co or Ti binder. It is a tool similar to cemented carbide. But it has low affinity, good friction and good wear resistance. It can withstand higher cutting temperatures than conventional carbide, but lacks the impact resistance of carbide, the toughness during powerful cutting, and the strength during low speed and large feeds.
In recent years, through a lot of research, improvement and adoption of new manufacturing processes, its flexural strength and toughness have been greatly improved, such as the new cermet NX2525 developed by Japan's Mitsubishi Metal Company and Sweden's Sandvi The new cermet blades CT series and coated cermet blade series developed by the company have a grain structure as small as less than 1μm in diameter, and their bending strength and wear resistance are much higher than ordinary cermets, greatly broadening the scope of applications. Its scope of application. Cubic boron nitride (CBN) CBN's hardness and wear resistance are second only to diamond, and it 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 lower. good. It is widely used in the cutting of hardened steel (HRC≥50), pearlitic gray cast iron, chilled cast iron and high-temperature alloys. Compared with carbide tools, its cutting speed can be increased by an order of magnitude.
Composite polycrystalline cubic boron nitride (PCBN) tools with high CBN content have high hardness, good wear resistance, high compressive strength and good impact toughness. Its disadvantages are poor thermal stability and low chemical inertness. , suitable for cutting of heat-resistant alloys, cast iron and iron-based sintered metals. PCBN tools have a low CBN particle content and use ceramics as the binder. Their hardness is low, but it makes up for the poor thermal stability and low chemical inertness of the previous material. It is suitable for cutting hardened steel.
Residual stress in cutting hardened steel with ceramic and PCBN tools. When cutting gray cast iron and hardened steel, you can choose ceramic tools or CBN tools. For this purpose, a cost-benefit and machining quality analysis should be carried out to determine Which one to choose. Figure 3 shows the flank wear of Al2O3, Si3N4 and CBN tools when processing gray cast iron. The cutting performance of PCBN tool materials is better than that of Al2O3 and Si3N4. But in dry cutting of hardened steel, the cost of Al2O3 ceramics is lower than PCBN materials. Ceramic knives have good thermochemical stability, but are not as tough and hard as PCBN knives. Ceramic tools are a better choice when the cutting hardness is lower than HRC60 and small feed rates are used. PCBN cutting tools are suitable for cutting workpieces with a hardness higher than HRC60, especially in automated processing and high-precision processing.
In addition, under the same flank wear conditions, the residual stress on the workpiece surface after cutting with PCBN tools is also relatively stable than that of ceramic tools. The following principles should also be followed when dry cutting hardened steel with PCBN tools: choose as large a depth of cut as possible under the conditions allowed by the rigidity of the machine tool. In this way, the heat generated in the cutting area will locally soften the metal in the front edge area, which can effectively reduce the wear of PCBN tools. In addition, , when the depth of cut is small, it should also be considered that the thermal conductivity of PCBN tools is poor, so that the heat in the cutting zone has no time to diffuse. The shear zone can also produce obvious metal softening effect, reducing the wear of the cutting edge.
The blade structure and geometric parameters of superhard tools. The reasonable determination of the blade shape and geometric parameters is crucial to giving full play to the cutting performance of the tool. In terms of tool strength, the tool tip strengths of various blade shapes from high to low are: round, 100° rhombus, square, 80° rhombus, triangle, 55° rhombus, 35° rhombus. Once the blade material is selected, a blade shape with the highest possible strength should be selected. Hard turning inserts should also choose the largest possible tip arc radius, and use round and large tip arc radius inserts for rough machining. The tool tip arc radius during finishing is about 0.8?m. Hardened steel chips are red and soft ribbon-shaped, brittle, easy to break, and non-adhesive. The cutting surface of hardened steel has high quality and generally does not produce built-up edges, but the cutting force is large, especially the radial cutting force. It is larger than the main cutting force, so the tool should use a negative rake angle (go≥-5°) and a large relief angle (ao=10°~15°). The main deflection angle depends on the rigidity of the machine tool, and is generally 45°~60° to reduce workpiece and tool chatter. Superhard tool cutting parameters and requirements for process systems Selection of cutting parameters The higher the hardness of the workpiece material, the smaller its cutting speed should be.
The suitable cutting speed range for hard turning finishing using superhard tools is 80-200m/min, and the common range is 10-150m/min; when using large depth of cut or strong intermittent cutting of high-hardness materials, the cutting speed should be maintained at 80-100m /min. Generally, the depth of cut is between 0.1 and 0.3mm. When processing workpieces with low surface roughness, a small cutting depth can be selected, but not too small and appropriate. The feed amount can usually be selected between 0.05 and 0.25mm/r. The specific value depends on the surface roughness value and productivity requirements. When the surface roughness Ra=0.3~0.4?m, it is much more economical to use superhard tools for hard turning than grinding.
In addition to selecting reasonable tools, there are no special requirements for lathes or turning centers when using superhard tools for hard turning. If the lathe or turning center has sufficient stiffness and is processing soft workpieces, If the required accuracy and surface roughness can be obtained, it can be used for hard cutting. In order to ensure smooth and continuous turning operations, a common method is to use rigid clamping devices and medium rake angle tools. If the positioning, support and rotation of the workpiece can remain fairly stable under the action of cutting forces, existing equipment can use superhard tools for hard turning. The application of superhard tools in hard turning uses superhard tools for hard turning. After more than ten years of development, promotion and application, this technology has achieved huge economic and social benefits. The following takes industries such as roll processing as examples to illustrate the promotion and application of superhard cutting tools in production.
In the roll processing industry, many large-scale roll companies in China have used superhard cutting tools to perform raw turning, rough turning and finishing turning of chilled cast iron, hardened steel and other types of rolls, and have achieved good results7 average Improve processing efficiency by 2 to 6 times, saving 50 to 80 processing hours and electricity. For example, when the roll factory of Wuhan Iron and Steel Company rough-turns and semi-fine-turns chilled cast iron rolls with a hardness of HS60 to 80, the cutting speed is increased by three times, with one roll per car, saving more than 400 yuan in electricity, working hours, and cutting tools. The cost was nearly 100 yuan and huge economic benefits were achieved. For example, when our school uses FD22 cermet tools to turn HRC58~63 86CrMoV7 hardened steel rolls (Vc=60m/min, f=0.2mm/r, ap=0.8mm), the single-edge continuous cutting roll path reaches 15000m (tool tip The maximum width of the flank wear zone (VBmax=0.2mm) meets the requirement of turning instead of grinding. In the industrial pump processing industry, currently 70 to 80% of domestic ballast slurry pump manufacturers have adopted superhard cutting tools.
Ballast pumps are widely used in mining, electric power and other industries. They are urgently needed products at home and abroad. Their sheaths and guards are made of Cr15Mo3 high-hard cast iron with HRC63~67. In the past, because it was difficult to turn this material with various tools, we had to use a process of annealing, softening, rough machining, and then quenching. After using super-hard tools, one-time hardening processing was successfully achieved, eliminating the two processes of annealing and then quenching, saving a lot of man-hours and electricity.
In the automotive processing industry, in the processing of crankshafts, camshafts, transmission shafts, cutting tools, measuring tools, and equipment maintenance in automobiles, tractors and other industries, we often encounter difficulties in processing hardened workpieces. For example, a rolling stock factory in my country needs to process the inner ring of the bearing during equipment maintenance. The hardness of the inner ring of the bearing (material GCr15 steel) is HRC60, and the diameter of the inner ring is f285mm. The grinding process is used, and the grinding allowance is uneven. It takes 2 hours to grind; but using super-hard tools first, it only takes 45 minutes to process an inner ring.
Conclusion: After years of research and exploration, my country has made great progress in superhard cutting tools. However, superhard cutting tools are not widely used in production. The main reasons are as follows: production companies and operators do not have enough understanding of the effects of using super-hard tools for hard turning. They generally believe that hard materials can only be ground; they believe that the cost of tools is too high.
The initial tool cost of hard turning is higher than that of ordinary carbide tools (for example, PCBN is more than ten times more expensive than ordinary carbide), but its cost shared on each part is lower than grinding, and the benefits it brings are higher than ordinary carbide tools. Carbide is much better; there is not enough research on the processing mechanism of superhard tools; the specifications for superhard tool processing are not enough to guide production practice. Therefore, in addition to conducting in-depth research on the processing mechanism of superhard tools, it is also necessary to strengthen the training of superhard tool processing knowledge, successful experience demonstrations and strict operating specifications, so that this efficient and clean processing method can be more used in actual production.