In mechanical processing, hole processing accounts for about 1/3 of the total processing. Hole machining is semi-closed cutting, so chip removal, heat transfer, and cutting fluid pouring are all difficult, and the machining is more difficult. With the progress of science and technology, in mechanical product parts, the requirements for hole accuracy and surface roughness are increasing, and the processing of precision holes often becomes the key to production and needs to be solved urgently.
Hole processing technology should not only study the machine tools and tools (so-called hardware) used in processing, but also study how to effectively use the application technology of these equipment (so-called software).
Definition and classification of holes
What is a hole? According to the national standard GB1800-1979: The hole mainly refers to the cylindrical inner surface. It can be seen from this that the broad sense of pore refers to the containment surface. Holes can usually be classified as follows:
(1) Divided by shape. There are cylindrical holes, conical holes, drum holes, polygonal holes, spline holes and other special-shaped holes as well as special-shaped holes (such as curved holes). Among them, cylindrical holes are the most widely used.
(2) Divided by form. There are through holes and blind holes (not through holes); deep holes (refer to holes whose depth L to hole diameter D exceeds 5, L/D is abbreviated as depth-to-diameter ratio or length-to-diameter ratio; L/D=5～20 is general Deep holes, L/D﹥20～30 are medium-deep holes, L/D﹥30～100 are called special deep holes) and shallow holes.
(3) According to the size of the aperture. There are large holes (D﹥100mm), ordinary holes (D=10～100mm), small holes (D=1～10mm) and micro holes (D<1mm holes).
(4) According to the processing mechanism. There are mechanical processing, special processing, electromechanical composite processing and so on. Although there are many special processing methods, due to the relatively expensive equipment and low processing efficiency, traditional mechanical processing will still be the main method of hole processing no matter it is now or in the foreseeable future.
(5) According to processing accuracy. There are coarse holes (such as holes after drilling and rough boring), semi-precision holes (such as reaming, coarse reaming, semi-fine boring holes) and precision holes (such as fine reaming, fine drawing, fine grinding, honing, and grinding的孔) etc. Precision holes usually refer to holes with tolerance levels above IT7～IT6 and surface roughness Ra<0.8～0.4m. Its geometric shape accuracy (such as roundness, cylindricity, axis straightness, etc.) is generally specified in its dimensional tolerance Within the range of 1/2 to 1/3 of the belt.
With the rapid development of aerospace, automobiles, high-speed trains, wind power, electronics, home appliances, energy, molds, hydraulics, machine tools and precision machinery and other equipment manufacturing industries and the upgrading of products, the application of precision holes is increasing. For example, various valve holes and high-pressure cylinders widely used in hydraulic systems are some typical precision holes. Hole machining is more difficult due to its own characteristics, and precision hole machining is even more difficult.
Features of hole processing
Hole processing is a relatively complicated process, and the problems of chip removal, cooling, lubrication, and guidance must be properly solved during processing. The main features of hole processing are:
(1) Due to the constraints of the aperture size, length and shape of the workpiece to be processed, the cutting tools are relatively slender and have poor rigidity, and most of them are cantilevered clamping methods. Machining is likely to cause tool deflection and vibration.
(2) Chip removal is difficult. To improve the chip holding and chip evacuation conditions, it is necessary to increase the chip groove, but this will reduce the strength and rigidity of the tool.
(3) The cutting fluid is difficult to introduce into the cutting area, the friction between the chips, the tool and the workpiece hole wall is very large, and the cutting temperature is high, especially when processing deep holes. Therefore, the cutting fluid has a special and important role in hole machining. The reasonable selection and correct use of cutting fluid have a great impact on the quality of hole machining, tool life and cutting efficiency.
Commonly used cutting fluid supply methods for hole machining include pouring method and high pressure internal cooling method. The former is the simplest, but the effect of fluid supply is poor and the consumption of cutting fluid is large. The internal cooling method is mostly used for hole processing tools such as oil hole drills, deep hole drills, jet drills, nesting knives and single-edged boring and reamers. It is necessary to make high-pressure internal cooling liquid (oil) channel holes on the tools, and oil and gas The mixture is transported to the cutting area through this channel. This method consumes less cutting fluid, but the tool structure is more complicated. At present, with the advancement of tool manufacturing technology, domestic and foreign tool companies have introduced various new products with high-pressure internal cooling liquid (oil) channel holes, creating conditions for the use of internal cooling. For example, ISCAR company introduced the DR, DZ and DS series of machine-clamped carbide indexable insert shallow hole drills, and the coated carbide single-edged reamer of Germany MAPAL company (cutting speed up to 150-400m/min) , Japan's Mitsubishi carbide small drill bits, etc., they all provide high-pressure cutting fluid channel holes to the jet application area, and the specifications are getting smaller and smaller. According to reports, a small cemented carbide drill produced by a foreign company can have a diameter as small as 3 to 4.5 mm and an oil hole diameter of 0.4 to 0.6 mm.
Current research shows that the cutting fluid is the most effective method of "steam beam" spray cooling, which is almost dry cutting, and the cutting fluid consumption is low, and the processing cost is low. "Vapor" spray cooling is to atomize the cutting fluid with air at a certain pressure (0.3～1MPa), and spray it to the cutting area at a high speed, so that the cutting fluid droplets that are atomized at high temperatures in the area are quickly Vaporize. Because the liquid absorbs a lot of heat when it vaporizes, the temperature in the cutting area can be drastically reduced. At the same time, the cutting fluid can also take away the heat and powder in the cutting area and space, improving the working environment. Practice has proved that when the same amount of cutting fluid is used, the heat absorbed by the "steam beam" spray cooling in the same time is 1000 times that of the pouring method. Therefore, it can not only increase the service life of the tool, but also greatly reduce the consumption of cutting fluid. According to the test of Guhring, Germany, the use of "steam beam" spray cooling on the automobile production line only needs half a cup of oil per shift, and cheap factory regenerated oil can be used. "Steam beam" spray cooling is not only suitable for automatic production lines, but also for general metal cutting.
(4) It is not possible to directly observe the cutting condition of the tool during processing, especially when processing micro holes and deep holes. Therefore, automatic monitoring and control are more important than other processing methods.
(5) Hole dimensional accuracy, geometric shape accuracy, mutual position accuracy and surface roughness are often difficult to control due to the particularity of hole processing, but once the test is successful, it can be maintained more regularly than other processing methods.
The current situation and development trend of hole processing technology
At present, the hole processing in Chinese machinery factories still generally adopts the production mode of general-purpose machine tools and special process equipment. That is, one person, one machine, one tool, or a set of boring molds are still used to complete a process, and the machine tool equipment used has a serious phenomenon of four more and four less, namely: more low-end, high-end and high-flexible CNC machine tools (NC) and machining center (MC) less; more low precision, less high precision; more manual, less automation; more single processes, less machine tools for compound processing. Therefore, the technology level and work efficiency of hole processing in China are low, the processing accuracy is poor, and the flexible structure is lacking. In the past ten years, with the deepening of the technological transformation of Chinese factories and the introduction of advanced technologies, as well as the increase in the application of high-efficiency equipment such as CNC machine tools and machining centers, in a few large state-owned enterprises, the machining accuracy of some precision machine tools has reached or approached foreign advanced However, from a comprehensive point of view, the technological level is still low. Compared with advanced industrial countries, China's existing hole machining accuracy and surface roughness differ by 1 to 2 levels, and the mutual position accuracy of the hole systems differs by 2 to 3 times.
With the continuous emergence of new materials and new products, the task before us is to solve the processing of hard, brittle, tough, and sticky materials, and solve the problem of precision holes, deep holes, large holes, small holes, and micro holes. Hole machining of heavy parts. Therefore, in the future, hole processing technology should develop in the direction of reliability, long life and high efficiency. Therefore, a new generation of high-performance, high-efficiency, and long-life tool materials (such as fine-grained cemented carbide, coated cemented carbide, powder metallurgy high-speed steel, ceramics, polycrystalline diamond PCD, polycrystalline cubic nitride Boron PCBN, etc.) try to be used on all kinds of hole processing tools. For example, the AQUA twist drill developed by Japan's Fujitsu Company is made of fine-grained cemented carbide and coated with a heat-resistant and friction-resistant lubricating coating. When high-speed wet processing of structural steel and alloy steel (SCM), the cutting speed is 200m /min, the feed rate is 1600mm/min, the processing efficiency is increased by 2.5 times, and the tool life is increased by 2 times; in dry drilling, the cutting speed is 150m/min and the feed rate is 1200mm/min. Japan Daijie has developed a "Bimeng" drill made of polycrystalline diamond (PCD) and cemented carbide as a whole. It is used for wing parts CFRP (carbon fiber reinforced polymer matrix composite material, 2.5mm thick) and When the aluminum alloy (A7075, thickness 2.5mm) laminates are processed, the cutting speed can reach 126m/min, the rotation speed is 10,000r/min, and the feed rate is 500mm/min. Compared with diamond-coated drills, "Bimeng" drills can be reground, so it can greatly extend the tool life and reduce processing costs. At the same time, the establishment of a metal cutting database should be accelerated to optimize the cutting parameters and give full play to the effectiveness of machine tools and tools. Microelectronics technology should also be applied to hole processing technology as soon as possible, and gradually develop in the direction of FMS (flexible manufacturing system) and integrated design and manufacturing CAD (computer aided design) and CAM (computer aided manufacturing). At present, many domestic factories have used microprocessors in production. In addition, we must also pay attention to the development of basic theoretical research, strengthen the research work on the processing technology of large holes, small holes, micro holes, precision holes and difficult-to-machine material holes, adopt new testing methods, explore rules, and continue to innovate. In particular, it is necessary to accelerate the research work on the processing of ultra-micro holes and ultra-precision holes to meet the needs of scientific and technological progress and production development in recent years. At present, in order to further improve the economic benefits of hole processing, it is necessary to organize and vigorously promote a batch of effective advanced tools (such as machine clamped cemented carbide indexable tools, cemented carbide single-edged boring reamer, precision diamond or Cubic boron nitride reamer, single-tube ejector drill, CoroDrill 880 drill bit, etc.) and new processes, such as drilling-boring reaming-diamond or cubic boron nitride reamer instead of traditional drilling-boring (or expansion)-reaming ( (Or grinding)-a new process of grinding (or honing) processing precision valve holes. In recent years, the tool industry has developed a variety of new hole processing tools for automobiles and motorcycles, high-speed trains, aerospace, wind energy and mold industries. They have the characteristics of high efficiency and innovative technology, which have played a role in promoting the progress of hole processing technology in these industries. To an important role. For example, the complete set of hole machining tools for processing aluminum alloy cylinder heads launched by Guhring Company (including composite boring tools for conduit holes and valve seats, step hole boring tools, solid carbide straight groove drills, step drills, countersink drills, etc.); developed by MAPAL company The Mega high-speed drill bit can increase the cutting speed of steel parts to 200m/min, increase the feed rate by about 25%, and shorten the drilling operation time by 60% to 70% without reducing the tool life and drilling quality. ; A rough and fine composite boring tool introduced by the German Vohaote Company. It adopts a modular structure and can complete rough and fine processing of ф3～ф2000mm holes. It is suitable for the processing requirements of various hole shapes. Due to the use of light aluminum structure, the weight of the head is reduced by 60% compared with steel parts, which can meet the processing requirements of various aperture sizes of the casing of wind energy equipment, and the accuracy of the processed holes can reach H7 to H5.
It must be pointed out that developed countries have developed rapidly in hole processing technology, and hole processing methods have also shifted from single mechanical processing to electrical processing, physical processing (laser, ultrasonic), chemical processing and composite processing, and the level of processing accuracy is increasing. The surface roughness value is decreasing day by day, and is developing towards a high degree of automation. Given the gap between us. It is recommended to establish a cross-industry hole processing association to exchange industry information; at the same time, actively introduce foreign new technologies, strengthen the construction of production bases such as hole processing machine tools, hole processing tools and sharpening machine tools, and actively adopt digital display and numerical control equipment to improve manufacturing methods And the flexibility of the means; it is also necessary to strengthen the training of technicians and the education of on-the-job employees, as well as the update of the knowledge of technical personnel, so that our hole processing technology can catch up with the advanced level of foreign countries as soon as possible.
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