High-speed cutting is an advanced and developing comprehensive technology. It must combine high-performance high-speed cutting machine tools, tools that are compatible with the workpiece materials, and the best machining technology for the specific machining objects to make full use of high-speed cutting technology. Advantage. Overview Since Dr. Carl Salomon of Germany first proposed the concept of high-speed cutting in the 1930s, after the mechanism and feasibility study in the 1950s, process technology research in the 1970s, high-speed cutting technology research in the 1980s, and high-speed cutting technology in the early 1990s. Cutting technology began to be put into practical use. By the late 1990s, commercial high-speed cutting machine tools have emerged in large numbers. At the beginning of the 21st century, high-speed cutting technology has been widely used in industrialized countries and is becoming the mainstream technology for cutting.
According to the definition of the 1992 International Conference on Production Engineering (CIRP) annual meeting, high-speed cutting usually refers to cutting operations with cutting speeds that exceed 5-10 times the traditional cutting speed. Therefore, depending on the material to be processed and the processing method, the cutting speed range of high-speed cutting is also different. High-speed cutting includes high-speed milling, high-speed turning, high-speed drilling, and high-speed turning, but most applications are high-speed milling. At present, the processed aluminum alloy has reached 2000-7500m/min; the cast iron is 900-5000m/min; the steel is 600-3000m/min; the heat-resistant nickel-based alloy reaches 500m/min; the titanium alloy reaches 150-1000m/min; the fiber reinforcement The plastic is 2000-9000m/min.
High-speed cutting is a system technology. Figure 1 shows various factors affecting high-speed technology. Companies must purchase suitable high-speed cutting machines according to the material and structural characteristics of the products, select the right cutting tools, and use the best cutting technology. To achieve the desired high speed machining results.
Characteristics and application of high-speed cutting Practices have shown that high-speed cutting has the following processing characteristics:
Reduced cutting force
Reduced thermal deformation of the workpiece is beneficial to ensure the size and shape accuracy of the part. The quality of the machined surface is high. The vibration of the process system is reduced. The material removal rate is significantly improved. The processing cost is reduced.
The above characteristics of high-speed cutting reflect the requirements of higher efficiency, quality and cost in its field of application. At the same time, it solves the problem of high-precision precision machining of three-dimensional curved shapes and provides processing for hard materials and thin-walled parts. A new solution.
High-speed cutting is becoming more and more widely used in the aerospace industry, mold industry, electronics industry, automotive industry and other fields. In the aerospace industry, it mainly solves the problems of large parts of material removal, thin-walled parts processing, high-precision, difficult-to-machine materials and processing efficiency, especially high-speed cutting of integral structural parts, which not only guarantees the quality of parts, but also saves many assembly. Work; most of the molds in the mold industry are suitable for high-speed milling technology, high-speed hard cutting can process hardened materials with hardness of 50-60HRC, thus replacing some EDM, reducing the fit grinding process and shortening the mold processing cycle High-speed milling of graphite for high-quality EDM electrodes. The high efficiency of high-speed cutting has made it widely used in electronic printed circuit board drilling and mass production of automobiles. At present, workpiece materials suitable for high-speed cutting are aluminum alloy, titanium alloy, copper alloy, stainless steel "target=_blank> stainless steel, hardened steel, graphite and quartz glass.
High-speed cutting machine tools For high-speed cutting to achieve good application results, high-performance high-speed cutting machine tools, tools that are compatible with the workpiece material, and the best machining technology for the specific machining object must be combined. High-speed cutting machines are essential for high-speed cutting applications.
The spindle speed of high-speed milling machines is generally above 18,000 rpm, and 30,000-60,000 rpm has also been put into practical use in the industry. The power is between ten and tens of kilowatts, and the maximum power is achieved at high speed, but the torque is reduced to the minimum, and the milling is allowed. The knife diameter will also decrease. The high dynamic feed drive linear feed rate is generally 20-40m/min, the linear motor drive speed is 60-120m/min, and the acceleration is 1-2g. The rotary table speed can reach 360rmp, and the rotation acceleration reaches 47°/s2, which basically meets the high-speed five-coordinate linkage processing.
The machine tool spindle and bed should have good rigidity, excellent vibration absorption characteristics and thermal insulation properties. The artificial marble bed has high thermal stability, good vibration absorption performance, and can make the most reasonable machine structure according to needs. Studies have shown that the vibration absorption of artificial marble is about 6 times that of cast iron.
CNC control systems with fast data processing capabilities are a necessary guarantee for high speed machine tools. Figure 2 shows the related technology of the high speed machine tool CNC control system. Front-view technology, large-capacity memory and ETH-ERNET communication are the basis for high data processing speed. NURBS curve interpolation provides short block and smooth interpolation solutions for complex surfaces, and digital drive overcomes the time required for analog control. Hysteresis problem, high resolution feedback technology is the guarantee of high precision machining.
In addition, the safety protection of the machine tool, the number of tool magazines, tool change speed, cooling lubrication, chip removal capacity, etc., are also important issues that must be considered when designing or purchasing high-speed machine tools.
High-speed cutting tool technology High-speed cutting tools not only have higher requirements in terms of durability and reliability than conventional machining, but also have special requirements in terms of tool system safety.
From the perspective of improving durability and reliability, it is necessary to consider: tool base and coating material, tool tip geometry, number of cutting edges and tool bar extension, cutting amount, tooling method, cooling conditions, tool and workpiece material matching;
From the perspective of improving the safety of use, it is necessary to consider the strength and size of the tool system, the clamping method of the tool bar and the machine tool, the blade clamping method, and the tool dynamic balance.
Due to the high-speed cutting high speed and fast feed characteristics, in addition to good wear resistance and high strength and toughness of advanced tool materials, excellent tool coating technology, reasonable geometric parameters and high concentricity of blade accuracy and other factors In addition, special attention must be paid to the influence of other factors on tool durability.
In general, the durability of down-cut milling is higher than that of up-cut milling, while the durability of reciprocating milling is the lowest. Downwardly, the actual reflection of the tool in the feed direction is entered, and the upward movement reflects the tool feeding direction, which has a great influence on the durability. High-speed milling of aluminum alloys usually uses double-edged milling cutters. Excessive cutting edges reduce the chip space and easily cause chip sticking. To avoid the resonant frequency, a three-edged milling cutter can also be used to increase the impact frequency. Aluminum alloy processing is prone to build-up edges, which is very harmful for high speed milling. To reduce the build-up of the built-up edge, the surface of the tool should be smooth; avoid the use of physical vapor deposition (PVD) coated tools, because TiAlN coating is easy to chemically react with aluminum, you can use non-coated tools, fine-grain diamond coating or Diamond-like coated tools; if possible, use oil mist tool internal cooling for cooling lubrication.
High-speed milling tool structure has a great impact on tool durability and safety. Key points include balanced design of tool system; reduced radial and axial runout; control of dynamic balance accuracy; HSK tool holder or similar double is commonly used for machine tool connection Face contact short taper shank; the latest trend of tool clamping is the use of cold-shrink clamping structure (or hot-loading type), using the induction or hot air heating to expand the shank hole during clamping, take out the old tool, and install new The tool is then cooled by air-cooling to the room temperature, and clamped by the interference fit of the tool hole and the outer diameter of the tool. The radial runout of the tool is 4μm, the rigidity is high, the dynamic balance is good, and the clamping force is large. It maintains high clamping reliability at high speeds and is especially suitable for high speed milling at higher speeds.
High-speed cutting technology High-speed cutting technology mainly includes: machining cutting method suitable for high-speed cutting, special CAD/CAM programming strategy, optimized high-speed machining parameters, adequate cooling and lubrication, and environmentally friendly cooling methods.
In principle, the high-speed cutting processing method uses layered loop cutting. Direct vertical downward feeding is extremely prone to chipping and should not be used. The milling force of the oblique path feeding mode is gradually increased, so the impact on the tool and the main shaft is smaller than that of the vertical lower cutting tool, and the phenomenon of the lower blade chipping can be significantly reduced. The spiral path feed mode adopts a spiral downward cut, which is most suitable for the high-speed machining of the cavity.
The CAD/CAM programming principle is to maintain a constant tool load as much as possible, minimize the change in the feed rate, and maximize the processing speed of the program. The main methods are as follows: reduce the program block as much as possible, improve the processing speed of the program; add some arc transition segments in the block to minimize the sharp change of speed; roughing is not a simple material removal, so pay attention to ensure this process and The machining allowance in the subsequent process is uniform, and the change of milling load is reduced as much as possible; the stratified down-milling method is adopted; the tangential feeding is performed by continuous spiral and circular trajectory as far as possible to ensure constant cutting conditions; The function of simulation verification provided by the numerical control system is utilized. The parts must be simulated before machining to verify the correctness of the 1 tool position data, 2 whether the various parts of the tool interfere with the parts, and 3 whether the tool and the fixture attachment collide to ensure product quality and operation safety.
The determination of the amount of high-speed milling is mainly based on processing efficiency, surface quality, tool wear and processing costs. When different tools are used to machine different workpiece materials, the processing amount will vary greatly. There is no complete processing data yet. Generally, as the cutting speed increases, the machining efficiency increases, and the tool wear increases. In addition to the higher feed per tooth, the surface roughness of the machine decreases as the cutting speed increases. For tool life, there is an optimum value for each tooth feed and axial depth, and the range of optimum values ​​is relatively narrow. The general selection principle for high speed milling parameters is high cutting speed, medium feed per tooth fz, small axial depth of cut ap and suitably large radial depth of cut ae.
Due to the increased metal removal rate and cutting heat during high-speed milling, the cold-cut media must have the ability to quickly sweep the chips away from the workpiece, reduce the heat of cutting, and increase the lubrication of the cutting interface. Conventional coolant and filling methods are difficult to enter the processing area, but will increase the temperature change of the milling cutter during the cutting and cutting process, resulting in thermal fatigue, reducing tool life and reliability. Modern tool materials, such as cemented carbide, coated tools, ceramics and cermets, CBN, etc., have high red hardness. If thermal fatigue is not solved, no coolant can be used.
On the one hand, the oil mist cooling can reduce the friction between the cutter and the chip-workpiece. On the other hand, the heat transfer effect of the fine oil mist particles when contacting the tool surface is faster than that of the coolant heat conduction. Taking away more heat, it has become the preferred cooling medium for high speed cutting. The nitrogen oil mist cooling medium has achieved good results in high-speed milling of titanium alloy. In addition to the cooling and lubricating effect of air oil mist, the nitrogen oil mist cooling medium also has anti-oxidation wear effect. When the milling speed of 33m/min is compared with air oil mist cooling, the tool durability is increased by 60%, and the milling force can be increased. Reduce by 20%-30%.
Conclusion High-speed cutting is an advanced and developing comprehensive technology. It must combine high-performance high-speed cutting machine tools, tools that are compatible with the workpiece materials, and the best processing technology for the specific processing objects, and fully utilize high-speed cutting technology. The advantages. High-speed cutting tool technology is also a key technology. In order to adapt and promote the development of high-speed cutting technology in China, we should fully realize that tool manufacturing is a high-tech industry and should strengthen basic research, engineering research and applied research in this field. The rapid development of high-speed cutting technology greatly stimulates the demand for high-performance tools. China's tool industry should focus on strengthening the research and development of tool wear resistance, precision and reliability, and improve the competitiveness of tools; In the overall economic benefits brought by high performance, the use of high-performance tools in the application field; providing personalized technical services; according to the current situation in China, it is recommended to focus on the development of coating technology (such as wear-resistant (hard, soft) coating, Composite coatings, nanostructured coatings, etc.), tool quality assurance technology and tool database.
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