"One small step for the gear, one big step for China." One of the fundamental reasons why the manufacturing technology of China's major equipment power plant has always been controlled by people is that the gear manufacturing technology is backward. Large-scale high-precision bevel gears are mainly used in large ships, locomotives, mining metallurgy, energy exploitation and national defense military equipment, and are the core components of advanced power plants. For a long time, its processing technology and equipment have been monopolized by western developed countries. Previously, China's annual import of high-precision and large-size gears required 200-300 million US dollars, and the unit price exceeded 300,000 yuan, which was expensive and the supply cycle was long, which restricted the development of China's equipment manufacturing industry.
At present, there are several methods to process straight bevel gears: straight bevel gear planer; Double cutterhead straight bevel gear milling machine; Straight bevel gear broaching and milling machine; Generally required straight bevel gears can also be machined by generating method with ordinary milling machine and indexing head.
Straight bevel gear planer is a machine tool for rough and finish machining straight bevel gears by generating method with paired planers.
Double-cutter-head straight bevel gear milling machine adopts two cutter heads with staggered cutter teeth, and milling the left and right tooth surfaces in the same tooth slot by generating method. Due to the relative movement between the milling cutter head and the workpiece in the toothless length direction, the bottom of the milled tooth slot is round, and the cutting module and tooth width are limited.
Straight bevel gear broaching and milling machine is a machine tool that cuts tooth grooves from solid wheel blank in one rotation of large diameter broaching and milling gear disc by molding method. Because the cutter is complex and expensive, and each workpiece needs a special cutter head, it is only suitable for mass production.
Conical hob for quasi-involute bevel gear milling machine, a machine tool for continuous indexing and tooth cutting according to generating method. When cutting teeth, taper hob uses large end cutting first, and then uses small diameter end cutting. In order to ensure the consistent cutting speed in the whole cutting process, the machine tool controls the speed of the hob through a stepless speed change device. When cutting teeth, the shaking table, hob and workpiece all do continuous rotary motion to process the workpiece, and the shaking table reciprocates once. The vibration table and the rotation of the workpiece generate generating motion through the differential mechanism, so that the workpiece can obtain the tooth profile curve with the same height along the tooth length.
The above is the processing method of removing materials layer by layer with mechanical tools to meet the accuracy requirements. Because cutting with a tool, the hardness of the material cannot be too great during processing, that is, the hardened material cannot be processed; Difficult-to-cut materials (such as stainless steel and titanium alloy). ) is also a difficult problem in current production. And because of mechanical vibration, it is difficult to improve the accuracy of machining straight bevel gears at one time. Precision straight bevel gears also need rough machining, quenching and grinding. Large gear planer is difficult to manufacture and still needs to be imported at present.
Accuracy parameters of straight bevel gear planer
Main parameters, contents, international advanced domestic advanced domestic general domestic backward evaluation methods and explanations.
(1) refer to JB4 176-86 for machining accuracy.
1, accuracy level 6 level 6 level 7 level 8.
2. Surface roughness Ra (micron) 1.6 1.63.2 > 3.2.
(2) Whether there is a numerical control system
(3) noise DB (a) ≤ 80 80 ~ 83 83 ~ 85 > 85
This paper introduces the patented technology of WEDM and the machine tool for machining straight bevel gears.
(Invention patent number: 2008 10 123589.9)
Machining straight bevel gear with numerical control WEDM;
WEDM, sometimes called WEDM. Its basic working principle is that the continuous moving thin metal wire (called electrode wire) is used as the electrode to carry out pulse spark discharge on the workpiece to generate instantaneous high temperature, so that the workpiece material is partially melted or vaporized, and the metal is removed and cut into shape. This is a non-contact macro processing method with little processing power. WEDM is mainly used to process all kinds of complicated and precise workpieces, such as punches, female dies, male dies, fixed plates and discharging plates of blanking dies, forming tools, templates, metal electrodes for EDM, all kinds of tiny holes, grooves and arbitrary curves. It has the outstanding advantages of small machining allowance, high machining precision, short production cycle and low manufacturing cost, and has been widely used in production. At present,
According to the different running speeds of electrode wires, WEDM machines are usually divided into two categories:
One is HS-WEDM. The wire electrode moves back and forth at a high speed, with a general wire speed of 8 ~12m/s. The wire electrode can be reused and the machining speed is fast. However, the fast wire electrode will easily cause the wire electrode to shake and produce stripes when reversing, which will reduce the machining quality. It is the main model produced and used in China and the original WEDM processing method in China. At present, on the basis of high-speed wire-cutting machine tool, multi-cutting technology and frequency converter are adopted, and the wire-cutting speed is changed when the corresponding electrical machining parameters are adopted, which effectively improves the machining surface quality and machining accuracy of high-speed wire-cutting EDM machine tool, and becomes a new medium-sized wire-cutting machine tool with machining accuracy of 0.006mm and surface quality of Ra 1.0 micron. ..
The other is low-speed LS-WEDM, in which the electrode wire moves at a low speed in one direction, and the linear speed is generally lower than 0.2m/s, and the electrode wire is no longer used after discharge, so it works smoothly, evenly and with little jitter, and the machined surface quality can reach Ra0.2μm and the machining accuracy can reach 0.002mm.
The control of electrode wire trajectory is controlled by digital program, and advanced digital automatic control technology is adopted to drive the machine tool to automatically complete machining according to the NC machining program pre-programmed according to the geometric parameters of the workpiece before machining. At present, WEDM machine tools are generally numerically controlled.
The following introduces the basic structure and machine parameters of WEDM machine tool for machining straight bevel gears.
Firstly, the machined gear blank is installed on the rotary center of the numerical control turntable. Tilt and adjust the rotating central shaft (adjust the silk thread for large machine tools) so that the included angle between the silk thread and the axis of the numerical control turntable is the cone angle of the straight bevel gear. Adjust the position of the silk thread, so that one end of the silk thread (molybdenum wire or copper wire) takes the center of the straight bevel gear as the fixed point (that is, the revolving spherical center of the bevel gear), and the other end takes the base circle on the big end of the tooth surface of the straight bevel gear as the feeding base point. At this time, the silk thread span between the two nozzles is the radius of the rotary spherical center of the straight bevel gear, and the servo motor is started to lock the turntable and the silk thread feed screw. Start the numerical control system to make the rotation angle of the numerical control turntable advance and retreat with the thread at the big end of the straight bevel gear tooth surface, and write a program according to the design equivalent modulus of the straight bevel gear to realize the linkage of rotation and advance and retreat. When the electrode wire is at the tooth tip, the numerical control turntable rotates, but the electrode wire does not move, which is the tooth tip of the straight bevel gear. After turning the central angle of the tooth tip, the electrode wire at the big end is fed correspondingly with the rotation of the workpiece, that is, the tooth-shaped part is machined. When the electrode wire reaches the tooth root, the workpiece continues to rotate, and the tooth root part is machined at this time; When turning the center angle of the tooth root, the electrode wire retreats to process the other half tooth profile of the same tooth, and when it reaches the tooth top, it completes the processing of a tooth. Next, treat all the teeth in turn. Under the control of the numerical control system, the electrode wire generates the tooth profile according to the standard involute of the big-end equivalent gear. The standard straight bevel gear is machined by high-frequency discharge of silk thread to produce electric spark to corrode the gap produced by the workpiece. When the silk thread is parallel to the center line of the numerical control turntable, that is, the included angle is zero, the electrode silk thread advances and retreats in parallel along the center direction of the gear, and the gear synthesized by numerical control is a standard spur gear. This machine tool can accurately process the teeth of rotary parts, such as the teeth of precision indexing toothed disc and the teeth of high-speed steel circular saw blade.
The control part of the machine tool is drawn by computer programming software and generates program code instructions, which are integrated by driving module, high frequency power amplifier and silk thread control system. The machine tool consists of a numerical control tiltable precision turntable, a take-up mechanism, a bobbin feeding and lifting table, and a cutting fluid supply, recovery and filtration system. Precision grating ruler is installed on the workbench to display the positioning and travel data of silk thread directly. The upper and lower wire racks are installed on the linear guide rail, which is driven by the motor to lift. The distance between the two wire racks is displayed by the grating ruler, which is convenient for adjusting the span between the two water nozzles.
Main models and parameters of fast (medium) wire feeding machine
TypeNo. Maximum Machining Diameter Maximum Machining Modulus Range Maximum Machining Modulus Maximum Workpiece Taper Distance Maximum Workpiece Tooth Number Range Best Machining Precision Best Surface Roughness Maximum Machining Efficiency Main Engine Overall Size Net Weight
YDK7760 600mm is not limited to 305mm and is not limited to Class 41.0 μ m180mm2/min1.4×1.8×1.8m.
YDK77 120 1200mm is not limited to 605mm, and it is not limited to class 41.0μ m180mm2/min2.4× 2.6× 2.4m5.5t.
YDK77200 2000mm, 800mm, 4 grades1.0μ m180mm2/min3.6× 2.6× 2.6m8t.
YDK77300 3000mm is not limited to 800mm, and it is not limited to Grade 41.0μ m180mm2/min5× 3.6× 2.6m9t..
YDK77500 5000mm is not limited to 800mm, and it is not limited to 4 levels, 2.5 microns180mm2/min6.5× 6× 4m12t.
Main models and parameters of WEDM.
TypeNo. Maximum Machining Diameter Maximum Machining Modulus Range Maximum Machining Modulus Maximum Workpiece Taper Distance Maximum Workpiece Tooth Number Range Best Machining Precision Best Surface Roughness Maximum Machining Efficiency Main Engine Overall Size Net Weight
YDK7660 600mm is not limited to 200mm, and it is not limited to grade 4, 0.2 micron, 300mm2/min1.4×1.8×1.8m4t.
YDK76 120 1200mm, 200mm, 4-level 0.2 micron 300mm2/min2.4× 2.6× 2.4m5.5t
Compared with the existing mechanical tool cutting, because there is no macro cutting force, WEDM's method of machining straight bevel gears has the following advantages:
1. During machining, the workpiece has no stress and deformation. Under the control of numerical control instructions, the machining accuracy is high. The teeth are standard involute or function curve, and the surface roughness is good. Micro feed (1μm) and multiple cutting. The machining accuracy can reach 2μm, and the surface roughness is preferably 0.5 μ m.. Precision machine tools can adopt wire cutting structure; For parts with high machining requirements, the structure of middle wire or fast wire is adopted.
2.WEDM is especially beneficial for materials with high strength, toughness and hardness, which are difficult to be machined by mechanical methods. In order to meet the requirements of high precision and long service life, the traditional machining of metal gears needs to leave a certain margin in the tooth profile first, and then it can meet the requirements after quenching and grinding. WEDM can directly process quenched materials. Traditional machining methods are very difficult when encountering bevel gears such as stainless steel, titanium alloy and hard alloy steel. Known as the metal of 2 1 century, "titanium alloy" has been used more and more in the aerospace field because of its low density, high specific strength, high temperature resistance, strong oxidation resistance and stable molecular structure. All kinds of Ni-V-Ti alloy transmission gears for diesel locomotives, positioning transmission gears for various artillery systems in the army and control transmission gears for aerospace vehicles need to be made of titanium alloy, and WEDM is an ideal means to process titanium alloy.
3. It is convenient to manufacture high-precision and ultra-long-stroke machine tools and meet the high-precision machining requirements of special parts. At present, domestic large-scale straight bevel gear processing equipment still depends on imports. Using WEDM technology, because there is no mechanical vibration, high-precision CNC system, CNC turntable and wireframe feed CNC synthesis, the machining trajectory is consistent with the theoretical curve, and high-precision parts can be machined. At present, domestic straight bevel gear planer with diameter > > 800mm has advanced accuracy of 6, and the surface roughness Ra(3.2μm) is generally 8 and Ra(6.3μm). Theoretically, the accuracy of WEDM can exceed Grade 4 (at present, the highest national standard of this index is Grade 4).
4. Machining gears with different modules requires tools with corresponding modules. The tool is complex and expensive, and the wear of the tool seriously affects the machining effect. WEDM tool electrode is simple (copper wire or molybdenum wire), and it can be completed by machining gears with different modules and the same specifications.
5. Low energy consumption and no pollution. The power of small gear planer or milling machine is generally 3 ~ 7.5 kilowatts, and that of large machine tool is tens of kilowatts. WEDM machine tool power is generally less than 2kw；; The working fluid is deionized water or water-based working fluid, which is pollution-free and can be discharged naturally after precipitation.
Revitalize China's equipment manufacturing industry, take the national demand as the innovation orientation, take the development of precision gear and large bevel gear processing machine tools urgently needed by the country as the main direction in the future, and build a world-class large bevel gear machine tool research base through scientific and technological progress and independent innovation.
In a word, the popularization and use of this technology will simplify the manufacturing process of precision straight bevel gears, make them easy to produce, greatly improve the manufacturing accuracy of straight bevel gears, especially change the monopoly position of foreign countries in the localization of large-scale high-precision machine tools, lay a solid foundation for China to truly become a manufacturing power, have broad market prospects, and will certainly bring strong social and economic benefits.