Ways to Improve Cutting Efficiency of CNC Machining Center

   As a representative of the advanced productivity of 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 competed to develop and apply a new generation of high-speed CNC machine tools, accelerating the pace of high-speed machine tool development. The spindle speed of the motor in the high-speed spindle unit is 15000～100000r/min, the fast traverse speed of the high-speed and high acceleration/deceleration moving parts is 60～120m/min, the cutting feed speed is up to 60m/min, and the feed speed of the high-speed machining center It can reach 80m/min, and the dry running speed can reach about 100m/min. The HyperMach machine tool from CINCINNATI of the United States has a maximum feed rate of 60m/min and a fast speed of 100m/min. The spindle speed has reached 60000r/min. In terms of machining accuracy, in the past 10 years, the machining accuracy of ordinary CNC machine tools has increased from 10μm to 5μm, and the precision machining center has increased from 3～5μm to 1～1.5μm, and the ultra-precision machining accuracy has begun to enter the nanometer level ( 0.01μm). The development and application of a new generation of high-speed CNC machine tools, especially high-speed machining centers, are closely related to ultra-high-speed cutting. 

    1. The difference 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 5000-8000m/min or more; the spindle speed of the machine tool is more than 30,000r/min (some as high as 100,000r/min). For example: when milling a plane, 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 foreign countries, that is, 12-15 hours of work done in China is equivalent to 1 work done in foreign countries. 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 the processing efficiency and reduce the scrap rate has become a common issue for many companies to discuss. An investigation on 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) Reasonably choose 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 a fundamental change. The result is: the metal removal rate per unit power is increased by 30%-40%, the cutting force is reduced by 30%, the cutting life of the tool is increased by 70%, the cutting heat remaining on the workpiece is greatly reduced, and the cutting vibration is almost disappeared. ; An essential leap in cutting has taken place. According to the current situation of machine tools, to give full play to the high-speed machining capabilities of advanced tools, high-speed machining is required to increase the volume of material removed per unit time (material removal rate Q). 

    While choosing a reasonable cutting amount, try to choose a close-tooth cutter (the number of cutter teeth per inch of the cutter diameter is ≥3), increase the feed per tooth, improve productivity and tool life. 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 machining efficiency, and the tool life is increased to 117 pieces. 

    (2) Choose tool materials with good performance 

    In the cutting process of CNC machine tools, the role of metal cutting tools is no less than that of the steam engine invented by Watt. The material used to make the tool must have high high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertness, good manufacturability (cutting, forging, heat treatment, etc.), and not easy to deform. At present, the main tool materials with good performance at home and abroad are: cermet, cemented carbide coated tools, ceramic tools, polycrystalline diamond (PCD) and cubic boron nitride (CBN) tools, etc. They have their own characteristics, and the range of workpiece materials and cutting speeds to which they are adapted is different. CBN is suitable for cutting high-hardness hardened steel and hard cast iron. For example, ceramic tools and CBN tools are mainly used when machining high-hard steel parts (50～67HRC) and chilled cast iron. Among them, ceramic tools can be used for workpieces with a hardness below 60～65HRC. CBN tools are used to cut workpieces above 65HRC; PCD is suitable for cutting non-ferrous metals, alloys, plastics and glass steel, etc. When processing aluminum alloy parts, PCD and diamond film coated tools are mainly used; carbon tools Steel and alloy tool steels are now only used as tools such as files, dies, and taps; carbide-coated tools (such as coated TiN, TiC, TiCN, TiAIN, etc.) have high hardness and a wide range of workpieces suitable for processing. Its anti-oxidation temperature is generally not high, so the increase in cutting speed is also limited. Generally, steel parts can be processed in the range of 400～500m/min. The high temperature hardness of Al2O3 coating is high, and it is wear-resistant when processed in the high-speed range. It has better performance than TiC and TiN coatings. 

    In addition, the geometric parameters of the cutting part of the tool have a great influence on the cutting efficiency and machining quality. The rake angle of the tool during high-speed cutting is generally 10° smaller than that of ordinary cutting, and the clearance angle is 5°-8° larger. In order to prevent thermal wear at the tool tip, the main and secondary cutting edges should be rounded or chamfered to increase the local tool tip angle, increase the length of the cutting edge near the tool tip, and the volume of the tool material. Improve tool rigidity and reduce tool breakage rate. 

    (3) Speed up the development of coating technology

    Since its inception, tool coating technology has played a very important role in the improvement of tool performance and the advancement of processing technology. Coated tools have become a symbol of modern tools, accounting for more than 50% of the tools. At the beginning of the 21st century, the proportion of coated tools will further increase, and it is expected to break through the CBN coating technology technically, so that the excellent performance of CBN can be applied to more tools and cutting processes (including sophisticated and complex tools and forming tools). This will comprehensively improve the cutting level of processing ferrous metals. In addition, the development and application of nano-scale ultra-thin and multi-layer and new coating materials will accelerate, and coating will become the main way to improve tool performance. 

    (4) Choose high-precision blades

    The blade precision is low, the runout is too large, the surface finish of the face milling cutter will be reduced, and even grooves will appear. The runout of the blade on the high-precision CNC machine tool should be controlled within 2～5μm. With the development of CNC machine tools, the surface modification coating treatment of the blade correspondingly appeared (the substrate is high-speed steel, WCo-based cemented carbide, Ti-based cermet), which greatly improves the accuracy of the blade. At the same time, a variety of new indexable insert structures have appeared, such as high-efficiency scraping inserts for turning, complex-shaped front-angle milling cutter inserts, ball-end end milling cutter inserts, and anti-swing high-speed milling cutter inserts. Wait. Indexable inserts have entered a new stage of comprehensive development of materials, coatings and geometries. According to the processing materials and processing procedures, the functions of materials, coatings and geometries can be reasonably combined to develop inserts with the best processing results to meet Different requirements for high-speed, long-life cutting production technology. 