CNC machining

  CNC machining(图1)

  As a representative of advanced productivity in modern manufacturing, CNC machining plays an extremely important role in machinery, aerospace and mold industries. Since the 1990s, countries in Europe, the United States and Japan have been competing to develop and apply a new generation of high-speed CNC machine tools, accelerating the pace of high-speed development of machine tools. In the high-speed spindle unit, the motor spindle speed is 15000~100000r/min, the fast moving speed of the high-speed and high-acceleration/deceleration moving parts is 60~120m/min, the cutting feed rate is as high as 60m/min, and the feed rate of the high-speed machining center It can reach 80m/min, and the empty running speed can reach about 100m/min. The HyperMach machine tool of the American CINCINNATI company has a maximum feed rate of 60m/min, a fast rate of 100m/min, and a spindle speed of 60,000r/min. In terms of machining accuracy, in the past 10 years, the machining accuracy of ordinary CNC machine tools has increased from 10 μm to 5 μm, and the precision machining center has increased from 3 to 5 μm to 1 to 1.5 μm, and the ultra-precision machining accuracy has begun to enter the nano level ( 0.01 μm). The development and application of a new generation of high-speed CNC machine tools, especially high-speed machining centers, is closely related to ultra-high-speed cutting. 

  1. Differences in the cutting level of machining centers at home and abroad

  At present, the cutting speed of turning and milling in advanced countries has reached more than 5000-8000m/min; the rotation speed of the machine tool spindle is more than 30000r/min (some as high as 100,000 r/min). For example: when milling planes, the cutting speed in foreign countries is generally greater than 1000-2000m/min, while the domestic cutting speed is only equivalent to 1/12-1/15 of that in foreign countries, that is, 12-15 hours of work done in China is equivalent to 1 work done abroad. Hour. According to the survey, the actual cutting time of many machining centers is less than 55% of the working time. Therefore, how to improve processing efficiency and reduce scrap rate has become a common problem discussed by many enterprises. A survey of the cutting efficiency of domestic CNC machining centers found that there are many problems such as low tool accuracy, large blade runout, low processing finish, and unmatched process equipment. 

  2. Ways to improve cutting efficiency

  (1) Reasonable selection of cutting amount

  At present, new cutting processes such as dry cutting and hard cutting represented by high-speed cutting have shown many advantages and strong vitality, and have become the main way for manufacturing technology to improve processing efficiency and quality and reduce costs. 

  Practice has proved that when the cutting speed is increased by 10 times and the feed rate is increased by 20 times, far beyond the traditional cutting "forbidden zone", the cutting mechanism has undergone fundamental changes. As a result, the metal removal rate per unit power is increased by 30% to 40%, the cutting force is reduced by 30%, the cutting life of the tool is increased by 70%, the cutting heat left on the workpiece is greatly reduced, and the cutting vibration almost disappears. ; Machining has undergone an essential leap. According to the current situation of machine tools, in order to give full play to the high-speed machining capabilities of advanced tools, high-speed machining is required to increase the volume of material to be removed per unit time (material removal rate Q). 

  While choosing a reasonable cutting amount, try to choose a fine-pitch cutter (the number of cutter teeth per inch diameter of the cutter is ≥ 3), increase the feed per tooth, improve productivity and tool life. The relevant experimental research shows that: when the linear speed is 165m/min and the feed per tooth is 0.04mm, the feed speed is 341m/min, and the tool life is 30 pieces. If the cutting speed is increased to 350 m/min, the feed per tooth is 0.18 mm, and the feed speed reaches 2785 m/min, which is 817% of the original processing efficiency, and the tool life is increased to 117 pieces. 

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