I. Analysis of the Current Status of Cutting Technology at Home and Abroad

 

　　To meet the requirements of modern machining for high efficiency, high precision, and high reliability, surface coatings on cutting tools can effectively extend tool life and provide tools with excellent comprehensive mechanical properties, thereby significantly improving machining efficiency.

 

　　At present, the cutting speeds for turning and milling in advanced countries have reached over 5000–8000 m/min; machine tool spindle speeds are above 30000 r/min (some up to 100,000 r/min). For example, when milling flat surfaces, foreign cutting speeds are generally greater than 1000–2000 m/min, while domestic speeds are only about 1/12–1/15 of those abroad, meaning that 12–15 hours of domestic work is equivalent to 1 hour of foreign work. According to surveys, the theoretical cutting time of many machining centers is less than 55% of the working time. Therefore, how to improve machining efficiency and reduce the scrap rate has become a common issue discussed by many enterprises. To meet the requirements of modern machining for high efficiency, high precision, and high reliability, the manufacturing industries of various countries are paying increasing attention to the development of coating technology and its application in tool manufacturing. A partial survey of cutting efficiency in domestic CNC machining centers found that problems such as low tool precision, large insert runout, low machining brightness, and mismatched process equipment are widespread. After years of development, China's tool coating technology is now at a critical stage: existing technology can no longer meet the ever-increasing requirements of cutting machining, and the coating equipment of major domestic tool factories has reached a period where it must be updated.

 

　　II. Technical Characteristics of High-Speed Cutting

 

　　High-speed cutting technology mainly has the following technical characteristics: First, it can significantly improve production efficiency, mainly because high-speed cutting technology greatly reduces the machining time and auxiliary time in the process, and also improves the degree of automation, thus enhancing production efficiency. Second, it can achieve high machining accuracy: on the one hand, high-speed cutting can reduce cutting forces by at least 30%, minimizing workpiece deformation; on the other hand, the cutting heat generated during machining often has no time to transfer to the workpiece, so thermal deformation can also be controlled within a minimal range. Finally, it can reduce machining energy consumption and save manufacturing resources. Due to the high metal removal rate per unit power, low energy consumption, and short in-process time of workpieces, the utilization rate of energy and equipment is improved, and the proportion of cutting machining in the total resources of the manufacturing system is reduced. This characteristic of high-speed cutting technology well meets the requirements of sustainable development and is of great significance and role in the context of building a resource-saving and environment-friendly society.

 

　　III. Technical Analysis of Improving Cutting Efficiency

 

　　1. Selecting Reasonable Cutting Tools

 

　　In CNC machine tool cutting, there are many types of cutting tools. The role of metal cutting tools is no less than that of Watt's steam engine. To adapt to the characteristics of CNC machine tools—high speed, high efficiency, and high automation—tool materials must have high high-temperature hardness and wear resistance, necessary bending strength, impact toughness, and chemical inertness, good processability (machinability, forging, and heat treatment, etc.), and be resistant to deformation. The tools used are developing toward standardization, generalization, and modularization, mainly including milling tools and hole machining tools. Advanced tools have three major technical features: innovation in materials, coatings, and structures. High-speed cutting tools mainly rely on advances in tool materials and coating technology. High-speed cutting can improve cutting efficiency but is not the only means. Structural innovation of tools is also an effective means to improve cutting efficiency. Currently, high-performance tool materials at home and abroad mainly include: cermets, coated cemented carbide tools, ceramic tools, polycrystalline diamond (PCD), and cubic boron nitride (CBN) tools. The geometric parameters of the cutting part of the tool have a great influence on cutting efficiency and machining quality. In high-speed cutting, the tool rake angle is generally 10° smaller than in conventional cutting, and the clearance angle is 5°–8° larger. To prevent thermal wear at the tool tip, the junction of the main and secondary cutting edges should adopt a rounded or chamfered tool tip (CNC engraving and milling machine) to increase the local tool tip angle, increase the length of the cutting edge near the tool tip and the volume of tool material, thereby improving tool rigidity and reducing the tool breakage rate.

 

　　2. Selecting Reasonable Cutting Speed.

 

　　While selecting reasonable cutting parameters, try to choose fine-tooth cutters (number of teeth per inch of diameter ≥3), increase the feed per tooth, and improve productivity and tool life. Currently, new cutting processes such as dry cutting and hard cutting, represented by high-speed cutting, have become the main ways for manufacturing technology to improve processing efficiency and quality and reduce costs. Feed speed is an important parameter in CNC machine tool cutting parameters, mainly selected based on the machining accuracy and surface roughness requirements of the part, as well as the material properties of the tool and workpiece. The maximum feed speed is limited by the stiffness of the machine tool and the performance of the feed system. In contour machining, the feed rate should be appropriately reduced near corners to overcome the "overshoot" or "undershoot" phenomena at contour corners caused by inertia or process system deformation. Principles for determining feed speed: 1) When the quality requirements of the workpiece can be guaranteed, a higher feed speed can be selected to improve production efficiency. When the linear speed is 165 m/min and the feed per tooth is 0.04 mm, the feed speed is 341 m/min, and the tool life is 30 pieces. If the cutting speed is increased to 350 m/min and the feed per tooth is 0.18 mm (high-speed machining center), the feed speed reaches 2785 m/min, which is 817% of the original machining efficiency, and the tool life increases to 117 pieces. 2) When cutting off, machining deep holes, or using high-speed steel tools, a lower feed speed should be selected, generally in the range of 20–50 mm/min. 3) When machining accuracy and surface roughness requirements are high, the feed speed should be selected smaller, generally in the range of 20–50 mm/min.

 

　　IV. Application Experience of High-Efficiency Cutting in Gear Machining Equipment for Construction Machinery

 

　　The application of high-efficiency machining equipment is one of the important ways to realize high-efficiency cutting in construction machinery gear machining, solve machining problems under low-automation production, and improve machining efficiency. The high-efficiency machining equipment used mainly includes CNC form grinding gear machines, high-efficiency CNC hobbing machines, and turning-milling compound centers, etc.

 

　　In the practice of construction machinery gear machining, gear grinding is usually one of the important steps in gear machining. In gear grinding, the generating method is mostly used for gear grinding. However, this traditional grinding method has defects such as low grinding efficiency and complex machining equipment structure, which is not conducive to improving the production efficiency of construction machinery gears. Introducing high-efficiency cutting into the machining process and applying form grinding technology instead of generating grinding can greatly improve gear grinding efficiency, about twice that of generating grinding. However, the disadvantage of using form grinding technology is that problems such as initial burns and grinding cracks have long been unable to be effectively solved. With the development of CNC technology and its application in gear grinding machines, combined with the research and application of high-flow cooling devices, the drawbacks of form grinding for construction machinery gears have been readily solved. Moreover, effective use of CNC form grinding technology in construction machinery gear machining can also achieve tooth profile and lead modification to improve the smoothness of gears during transmission and help significantly improve grinding accuracy.

 

　　CNC hobbing machines have characteristics such as high rigidity, powerful servo functions, and relatively large hob head drive power. Their application in construction machinery gear machining can fully leverage their powerful CNC servo functions and high hobbing speeds to achieve temperature compensation during hobbing, making them efficient machining equipment in gear machining. In practical application of high-efficiency CNC hobbing machines, the hob speed range is relatively wide, about 200–1500 r/min. Compared with the conventional hobbing machine speed range (800–1800 r/min), the hob rotation speed is greatly increased, enabling high-speed hob rotation during machining. At the same time, the high-efficiency CNC hobbing machine adopts seven-axis four-linkage during operation. The generating motion of the spindle and indexing does not require change gears and can be realized only with a mechanical linkage as the carrier. Moreover, the feed system driven by CNC axes can achieve automatic variable speed feed in radial and axial directions and axial cycling. In addition, this machine tool has a high level of intelligence and can accurately calculate the tool shifting amount based on the automatic alignment data of the workpiece, promoting automatic tool shifting during machining and helping to solve the problem of low automation level in gear production and machining. Furthermore, the high-efficiency CNC hobbing machine has high rigidity, and hydraulic automatic clamping of the workpiece can be achieved during gear cutting, reducing vibration during cutting, which helps extend the service life while improving the stability of gear transmission. In the practice of construction machinery gear machining, the cutting force and wear of the hob can be observed through the operation panel. After machining, self-inspection of gear lead and profile errors can also be achieved, helping to improve gear machining quality.

 

　　With the rapid development of CNC technology, CNC equipment has been widely used in construction machinery gear machining, which is of great significance for improving gear machining and cutting efficiency. Among them, the turning-milling compound center realizes the organic unity of turning technology and milling technology, can achieve five-axis linkage on the same equipment, helps complete gear milling, turning processes, and shaft workpiece clamping in one setup, and in gear machining practice, the speed can reach up to 1200 r/min, with very high cutting efficiency.

 

　　In addition, in the practice of construction machinery gear machining, hobbing is the core process technology in gear cutting, accounting for more than 70% of gear cutting. However, in hobbing, conventional hobs are mostly made of high-speed steel, which means that if the cutting speed is greatly increased, problems such as increased hob wear are extremely likely to occur, reducing hob life and increasing machining costs. To address this issue, with the rapid development of coating technology, high-speed steel hob coating technology is widely used in hobbing processes. For example, the application of hob coating treatment technologies such as AlCrN and TiNC in gear machining plays a huge role in improving hob quality and enhancing machining efficiency. The main advantages of coating treatment technology are preventing hob chipping, improving the wear resistance and heat resistance of the hob, and reducing the cutting friction of the hob during cutting. Taking M42 tool material as an example, after TiN coating treatment, the efficiency of the coated hob can be greatly improved, and the cutting speed can reach about 145 r/min. It can be seen that in construction machinery gear machining, increasing the feed rate and comprehensively increasing the hob speed are the most powerful ways to achieve high-efficiency cutting. While cutting speed is increased, chips can be quickly discharged, thereby reducing cutting heat, lowering the cost of cooling in gear machining, and achieving environmental benefits.

 

　　V. Conclusion

 

　　As a very advanced manufacturing technology, high-speed cutting machining has very broad development and application space. It should be said that China's research foundation in this area is still relatively weak. Therefore, on the one hand, we should actively learn and introduce advanced foreign technologies and theories, and do a good job in digestion, absorption, and innovation; on the other hand, we should pay attention to discovering and solving problems in practical work, strive to improve and perfect machining processes and techniques, and accumulate valuable experience and data for technological innovation.

 

　　References:

 

　　[1] Chen Lubang, Wu Wanbin, Yu Hongli, Bai Haifeng. Application of High-Speed Cutting in Flat-Panel Slot Antennas [J]. Manufacturing Technology & Machine Tool, 2012(09).

 

　　[2] Yan Jinhua. Experimental Study on the Effect of High-Speed Cutting on Surface Roughness [J]. Electronic Test, 2013(16).