Conventional machining methods typically use larger tools to machine at lower speeds. In general, larger tools are not designed to perform more complex machining. In order to process with a micro tool, a conventional machine tool must be operated at a low speed, and the micro tool is brittle and easy to break. Larger tools have a higher resilience to the force of the chips due to their greater mass. Conversely, smaller tools are more susceptible to breakage due to greater brittleness. Poor chip removal is one of the main causes of tool damage. In fact, microtools that are damaged by poor chip removal are more than microtools that are damaged by unreasonable cutting parameters. To minimize the possibility of tool damage, the chips must be quickly removed from the cutting zone. Microtools require high spindle speeds during machining, and even higher spindle speeds for fast chip evacuation. Definition of tool size and machining speed: Micro-tools include milling cutters and drills with a diameter of 0.250" (6.35mm) or less. These small-diameter tools are essential for complex and fine machining, and high-speed spindles are used for optimum machining results. There is no exact definition and absolute parameters for high-speed cutting, but one available reference definition is that the spindle speed is above 25000r/min, which can be called high-speed cutting. The three related factors to improve the machining efficiency of micro-tools include the optimization design and application of micro-tools. Low viscosity coolant and high speed cutting technology.
(1) Design of micro tools
Miniature tools that simply scale down the geometry of larger diameter tools are often difficult to achieve efficient feed and achieve satisfactory machining accuracy. As the tool diameter decreases and the spindle speed increases, the tool requirements also change. Conventional tool designs with machine clamps are not suitable for the machining requirements of micro tools. This is mainly because the requirement for increasing the speed of the tool is not limited to the reduction of the tool diameter. The increased speed requires a better balance of the tool and a larger chip space to ensure smooth chip removal and prevent built-up edge. The use of micro-tools for efficient high-speed machining requires specialized optimization of the tool. The correct geometry of the micro-tools, combined with the high-speed spindle machine and reasonable cooling, completely eliminates the need for secondary machining to remove burrs.
(2) Optimization of cooling method
When using high-speed machining with micro-tools, a lot of cutting heat is generated, so some measures are needed to cool down. While high-speed cutting has certain advantages in reducing heat of cutting, high-speed cutting techniques alone are not sufficient to completely solve the cooling problem, so an effective cooling system is still required for some processes.
The cooling system eliminates heat of cutting and also lubricates the tool for fast cutting on the workpiece surface. Trying to cut a piece of cold butter with a cooled knife is quite difficult because the knife is not lubricated when it is cut through the butter surface. But if the knife is heated, it melts a little butter, which lubricates the knife, making it easy to cut butter. The same principle is used for high speed cutting with tools. Microtools require a lubricant that is lower in viscosity than water because of the need to allow coolant to reach the cutting edge of a high speed rotating tool. The emulsion-based coolant has a higher viscosity than the water-based coolant and is therefore not suitable as a lubricant for high-speed machining of micro-tools.
The micro-spray cooling system used in processing can use alcohol (ethanol) as a cooling liquid, which is ideal for cooling lubrication of non-ferrous metals and certain plastic materials. However, the use of oil-based coolants in the processing of steel-based materials, that is, the advantages of alcohol coolants is not suitable for the processing of steel materials, because cemented carbide tools may cause instantaneous discharge on the steel surface, if exposed to ethanol-based cooling A relatively high dynamic potential can be generated in the liquid. Previous 1 2 3Next page
Commonly used spray coolants are usually petroleum-based products, and these coolants need to be properly recycled after use, at an additional cost. Alcohol is evaporated after use, so there is no need to dispose of it or recycle it. Although alcohol is flammable, its low volatilization point makes it a very effective cooling lubricant for high speed machining. Because alcohol is a natural compound, it is environmentally friendly, free of waste, and requires no cleaning, so there is no associated cost. In addition, the use of alcohol as a cooling lubricant does not leave any oil stains on the workpiece, thereby avoiding the secondary operation of degreasing the workpiece, and the cost of these processes is quite high.
(3) High-speed cutting technology
The smaller the tool diameter, the higher the spindle speed required to effectively cut the workpiece. When milling, drilling, milling and engraving with micro-tools, high-frequency spindles with a speed range of 6000 to 60,000 r/min are ideal. High-speed cutting technology uses a high-speed, small step, large feed processing strategy. Imagine moving your hand through a burning candle flame. If your hand moves slowly, the flame will have enough time to burn your hand; and if your hand passes quickly, the flame will not be able to burn the skin. The principle of high-speed machining with micro-tools is similar. When the tool moves quickly, the cutting heat is too late to pass into the workpiece and cause various problems.
During the cutting process, the tool continuously cuts the chips away from the workpiece. About 40% of the heat of cutting generated is derived from the frictional heating of each of the flank and the chip, and about 20% is derived from the deformation (bending) of the chip. Therefore, a total of about 60% of the cutting heat is derived from the inside of the chip. High-speed cutting technology attempts to take most of the heat away from the chips for cleaner cutting. The higher machining quality is based on good tool cooling, lower cutting forces and therefore reduced machining vibration.
The high spindle speed reduces the chip load (cut depth) to less than 0.005" (0.13mm). Such a small depth of cut can significantly reduce the cutting force between the tool and the workpiece material. High speed / small cutting force machining Less heat, can reduce tool deviation, and can realize the processing of thin-walled workpieces. With these advantages, high-speed cutting can obtain better surface quality, lower cutting temperature, easy workpiece clamping, and machining accuracy. Higher. Based on the dynamic characteristics of the machine tool for high-speed cutting with micro-tools, the relevant principles of the above-mentioned high-speed cutting technology are completely achievable. Such machines are usually lighter in weight, so the range of motion is larger and better. Sensitivity, flexibility, versatility and high speed. Conventional CNC machines are heavy, so their speed and maneuverability are difficult to achieve at the level of light machine tools, but they can be machined with larger tools. Conventional CNC machine points Like the SUV (pickup), although the power is strong, but the mobility is not enough or can not be parked in a small space. The design and knot of the sports car It is not only powerful, but also has a high level of controllability and sensitivity. The CNC machine for high-speed cutting of micro tools is very similar to the characteristics of sports cars. Just as you can not install a spoiler and paint on the SUV. Racing stripes, and then expect it to be like a sports car, you can not replace a high-speed spindle on a cumbersome conventional CNC machine, it is expected to efficiently complete high-speed machining using micro tools.
When designing a machine, you can choose one of two ideas. You can build a powerful, large machine that can drive large tools for machining with large spindles. Driving large tools requires strong power, which means that large motors with heavier masses must be used. On the other hand, you can also build a lightweight machine for micro tools. Machines designed for high-speed cutting with micro-tools require less cutting force, so the design should focus on speed and sensitivity without the need for large motor drives. In order to achieve high-speed machining of micro-tools, each of the three elements (micro-tools, cooling methods, and high-speed cutting) is equally important. Without any of them, high efficiency, high reliability, and high flexibility are impossible. Processing. Conversely, if the three elements are perfectly combined, you can achieve amazing processing speeds and high levels of processing quality. Its processing advantages are not limited to this, it can completely cancel the subsequent secondary operations such as deburring, degreasing. Previous 1 2 3Next page
Replacing a high-speed spindle on a conventional CNC machine is difficult to expect to meet the high standards required for high-speed cutting. Only machines designed and manufactured for high-speed cutting of micro-tools can meet the demanding requirements of this type of machining. The advantages of high-speed machining with micro-tools include: low cutting force, not easy to damage the tool, low processing temperature, good surface finish, and can eliminate subsequent deburring, oil removal operation and small tool vibration. The spindle speed of up to 60,000r/min makes the machining speed much faster than in the past, and the machining quality of the workpiece is also improved. Today, the variety of workpieces is increasing, and the size of the workpiece is shrinking. The trend toward miniaturization requires that manufacturing processes must undergo changes.
