How to choose cooling mode for the hottest high-sp

2022-08-14
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How to choose cooling mode for high speed milling

with the application of green manufacturing technology in cutting, it has become a good choice to use compressed air cooling instead of cutting fluid cooling in high-speed milling. However, for specific high-speed milling tasks, which cooling method is more appropriate should be carefully weighed according to different processing purposes and processed materials to obtain the best processing effect. The following are four main process factors that need to be considered when selecting cooling mode

1) hardness of workpiece material of conventional electronic universal material testing machine

if the hardness of workpiece material is 42hrc, compressed air cooling can usually achieve better results. The machining characteristics of high-speed milling high hardness materials are: ① high cutting temperature; ② The chip will become harder than the parent material under the action of cold work hardening. When cutting such materials, if the cutting fluid is used for cooling, the tool may bear the thermal shock caused by intermittent heating and cooling, and the sharp change of temperature is easy to cause the fragmentation of cemented carbide cutting edge. On the contrary, if compressed air is used for cooling, not only the tool temperature can be kept constant, but also the chips can be blown away from the cutting area to avoid additional damage to the tool due to the re cutting effect of high hardness chips

type of workpiece material

if the hardness of workpiece material is 42hrc, the cooling method should be determined according to the type of workpiece material. When high-speed milling viscous materials (such as aluminum, soft stainless steel whose demand for peek in western developed countries is still dominant), cutting fluid cooling is usually required. The cutting fluid can lubricate the tool and make the chips slide upward out of the chip holding groove and separate from the back corner of the tool. In high-speed milling of most die steels (such as P20, H13, S7, nak55, D2, etc.), compressed air cooling may be the right choice. If the workpiece material and the tool are found to adhere during processing, it may indicate the need for cutting fluid; However, it may also indicate the need to choose a different tool coating

tool coating

titanium nitride (TiCN) coating and titanium aluminum nitride (TiAlN) coating are the two most commonly used tool coatings for high-speed milling of die steel. When ball end milling cutter is used to mill workpiece materials with hardness less than 42hrc at cutting speed lower than 245m/min (800sfm) (or circular milling cutter is used to mill the same materials at cutting speed lower than 600sfm), TiCN coating is more appropriate. If the hardness or cutting speed of the processed material is higher than the above cutting parameter range, TiAlN coating is preferred

ticn coating has good adaptability to cutting fluid cooling. Although sharp changes in cutting temperature may still cause the fragmentation of cemented carbide cutting edges, machining within the above cutting parameters generally will not produce cutting temperatures that are sufficient to cause thermal shock hazards

on the contrary, TiAlN coating with good high-temperature cutting performance is not suitable for cutting fluid cooling. When cutting at high temperature, this coating can form a hard and smooth alumina layer on the outer surface of the coating, which is helpful to improve the cutting performance of the tool. (in fact, the high-temperature cutting performance of exalon TiAlN coating developed by millstar company in the United States is more advanced. A solid lubrication layer is added to the outside of this TiAlN coating, which makes it easier for chips to slide away along the cutting edge of the tool.)

the milling of graphite electrode workpiece generally does not have strict requirements for tool coating, and TiAlN coating or diamond coating can be selected. Although these two kinds of coatings can obtain good cutting effect by cooling with compressed air, many processing workshops are still willing to use cutting fluid with the development of mini family, because cutting fluid helps to remove dust generated in processing

surface finish requirements

when high-speed milling is carried out with a ball end milling cutter, cutting fluid cooling may be required to obtain a higher surface finish of the workpiece. Since the cutting speed at the end of the ball end mill is zero, the use of cutting fluid can play a good role in lubrication. When a typical ball end milling cutter is used for micro feed finish milling, the workpiece material located in the low-speed cutting area at the end of the milling cutter may be stuck in the transverse edge (WEB). The residual material in the red hot state is dragged across the workpiece by the tool, and may be welded on the surface of the workpiece, thereby damaging the surface finish of the workpiece. (in order to solve this problem, some machine clip blade milling cutters with spherical contour, such as the Superfinisher blade of millstar company in the United States, can eliminate this horizontal edge by improving the design of the blade.) Cutting fluid can reduce the influence of chip fusion welding and obtain high surface finish by lubricating the tool and workpiece. Based on this consideration, cutting fluid cooling should be adopted even in the machining occasions where TiAlN coated tools are used. Although the tool life may be shortened as a result, sometimes it is necessary to sacrifice part of the tool life in order to meet the surface finish requirements

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