Foreword
With the continuous advancement of science and technology, the demand for high-precision gear market is increasing. Shave-tooth processing is the first developed by the United States's Nyennal Poroch Company in 1926. It was gradually expanded to various departments in the late 1950s. In the current global gear production, it is the most important gear finishing tool. As the development of contemporary industry puts forward stringent requirements for gear noise, mass-produced gears have to further improve accuracy. Shaved teeth can be used as the final process of tooth shape machining to correct radial runout error, pitch error, tooth shape error and tooth orientation error, so the smoothness and contact accuracy of shaved gears will be greatly improved. , while obtaining a finer surface. According to reports, 90% of American high-speed transmission gears are shaved. Shaving teeth can generally improve the accuracy of gears by 1-3, thus placing great hopes on shaving.
First, shave teeth processing principles and methods
1. Shaving tooth processing principle
Shaving gears are hardened grinding gear cutters with serrated flutes along the tooth height. Shaving is the use of shaved gears and gear parts meshing transmission, from the tooth surface of the gear workpiece to cut a small amount of machining allowance for shaving. When the gear workpiece meshes with the shaver, the gear shaft and the tool shaft are not parallel, but they are staggered. Only the gear surface meshes with the shaver, and there is no mechanical connection between the shafts of the two gears. Free spins. This is also a significant difference between shaving and other gear finishing methods and cutting methods.
In the shaving process, gears and shaving cutters in which two shafts are interleaved with each other are rotated on one side by applying pressure on the tooth surfaces, and the tool and gear tooth surfaces are relatively slipped in the tooth height direction and in the axial direction. The edges of many tooth flute grooves on the surface become cutting edges. The top of the sawtooth sipe of the shaving cutter constitutes the tooth face of the cutter, and the tooth grinding is performed with a gear grinder. There is no backlash of the flanks, unlike other cutters (for example, a shaper cutter) with flanks. Therefore, even if the back surface of the gear work piece is held against the back surface of the saw-toothed groove, it will not be excessively cut, and the tooth surface finish can be performed with a machining allowance of 0.02 to 0.05 mm. The cutter pockets on the sides of the shaving cutter teeth are usually parallel to the cutter face or perpendicular to the cutter tooth direction, so that the cutting edges on both sides have positive and negative front legs or zero front corner respectively. When the shaving cutter cuts the workpiece, its tooth flanks and The machined surface of the workpiece is tangential, so when the shaving angle is equal to 0°, this will result in a squeeze phenomenon, so the shaving tooth is a machining process that produces cutting and squeezing in the sliding movement.
2, shaved teeth processing method
The shaving method can be divided into several types according to the direction of movement of the shaving gear or the manner of moving according to the point of engagement. Representative examples include axial shaving, tangential shaving, diagonal shaving and radial shaving. Axial shaving is achieved by the tool or gear along the axis of the gear to move the shaver gear and gear meshing point, and the tooth width of the gear; tangential shave is the tool or gear moves perpendicular to the gear shaft, can be processed The tooth width is limited to the tool's tooth width coverage, but the amount of movement is only a fraction of the ordinary shaved teeth, so the processing time is significantly reduced; diagonal shaved between the two, the tool or gear Tilting in the direction of the axis, the tooth width can be wider than the width of the cutter, the amount of movement of the tool or gear can be between the two; the radial shaving method in the shaving process, the shaving cutter and the gear are Line contact, therefore, has the advantages of high efficiency, high tool durability, high tooth profile accuracy, low surface roughness, and mandatory tooth-to-needle correction capability, and is particularly suitable for machining multiple joint gears and the like.
In addition, the shaving method can be divided into two types: interference gear shave and brake shave gear, in accordance with the pressure necessary for cutting on the gear workpiece and the tooth surface of the cutter. Interference meshing shaved teeth: the tool and the gears are engaged with no backlash, and then the necessary cutting pressure is applied to the tooth surfaces by shortening the center distance; the brake shaving teeth are: the shaft of the passive tool or gear, and the necessary pressure Added to the meshing tooth face, this processing method is usually used for machining only one side tooth face or shaving cutter and gear meshing at any meshing angle, and is usually used for toothing error correction of large gears.
Second, shave teeth concave problem and cause
When shaving, the shaving cutter and workpiece are a pair of helical gears with no backlash. The disc shaver can be seen as a spur gear, and the machined workpiece (shave gear) is clamped on the mandrel during cutting, and is positioned between the two tips on the machine table and is free to rotate. In helical gear meshing, tooth surface contact of the two gears is theoretically point contact. As the gear rotation contact point moves obliquely to the tooth surface, it constantly moves in the tooth height direction and also in the tooth width direction. Therefore, in the case where the degree of overlap is greater than one, when the two pairs of gears mesh at the same time, the two contact points are at different positions in the tooth height direction and the tooth width direction of the adjacent two teeth (this phenomenon is inherent to the drum tooth shaving teeth. The only cause of the error). At the same time, when the shaving cutter and the gear workpiece are meshed, the cutting edge of the cutter forms a tooth surface zigzag cutting groove, the edges and corners of which bite into the gear tooth surface, the tooth surface contact is not a point contact, and the actual engagement state has changed.
Change in the number of tooth-shaped contact points during shaving
The influence of gear manufacturing precision on noise is mainly composed of five major factors including base section error, tooth shape error, ring gear runout, contact accuracy, and tooth surface roughness. The tooth shape error is inseparable from the error produced in the shaving process, and the important problem that cannot be ignored in the shaving process is the tooth profile.
1, concave phenomenon mechanism
The overlap factor of shaved gears and shaved gears is generally not an integer, resulting in a change in the number of tooth surfaces that are in contact at the same time. The number of contact points on both sides of the tooth profile also changes when the tooth surface transitions from even tooth contact to single tooth contact (see figure above). When the tooth tip or tooth root comes into engagement, there are two pairs of teeth that are in contact at the same time. When the tooth flank comes into engagement, only one pair of teeth comes into contact. Since the total pressure of the radial feed is approximately constant, the tooth pressure at each contact point reflected in the single-tooth contact area is obviously much greater than that of the two-tooth contact area, and the root is in the double-tooth meshing area. Less metal removal. Around the pitch circle in the single tooth meshing area, the removal of metal is larger. This causes the shading of the shaved tooth profile to occur.
2, cause the tooth concave
The standard tooth razor has various factors in the shave after tooth shaving. The new razor shave is concave in shape, and the shaved razor after many times of reshaping is small and sometimes not concave; shaved The smaller the number of gear teeth, the larger the modulus, the more serious the tooth concave; the greater the intersection angle between the shaver gear and the gear shaft, the worse the shaved tooth profile curve. Hobbing Tooth profile, selection of design parameters related to hobbing, overshoot, shaving cutter, shaving ratio of shaved gear to shaved gear, selection of shaving cutting elements, cutting stroke and smoothing during shaving The ratio of the number of strokes and so on have different degrees of influence on the shaved teeth. Among them, the selection of hobbing tooth profile and shaver blade displacement coefficient, that is, the face meshing angle, are the main influencing factors of shaved teeth. In addition, due to the inconsistent force of the cutting edge of the shaving cutter due to the pre-machining of the hobbing of the hobbing gear, the shaving cutters may have different degrees of wear, and the center portions of the teeth may also be cut off to some extent. The concave.
The presence of the concave phenomenon means that the gear tooth cannot be machined to the correct involute, and that the passive gear or tool rotates at an unsteady speed, which means that there is rotational fluctuations and noise is created. From the shave itself, from its beginning until now, the concave phenomenon has been the cause of shaving problems.
Third, solve the concave method
1, shaved teeth repair
(1) Modification of tooth profile
When a pair of gears meshes, the load changes from the beginning of engagement to the disengagement, and in particular, 1 to 2 pairs of gear teeth work alternately during gear teeth work. The work is not smooth, so it is necessary to perform tooth shape repair on the gear teeth. Shape, through the repair of the top of the tooth, the root of the tooth, so that the meshing of gear teeth from the edge of the smooth transition to the theoretical involute toothed area, thereby improving the quality of meshing. The modification of the gear can be the top of the teeth of a pair of gear teeth, the root trimming of the tooth root, or the top and root trimming of a single gear tooth.
(2) Tooth shape modification
The ideal tooth-to-mesh length of a pair of gears contacts in the full-length direction, but the actual meshing tooth direction is difficult to achieve. In order to achieve a substantially uniform load in the direction of the tooth width and to increase the load-bearing capacity of the gear, it is usually made into a drum shape.
2, shaving cutter design
Shaving with a meshing coefficient of 1.8 to 2 is relatively easy; shaved blades with a meshing coefficient of 1.3 to 1.8 are modified according to the meshing area; Therefore, when designing a shaving cutter, it should be possible to make the shaving cutter and the gear to be shaved at a ratio of 1.8 to 2.
3, Shave the knife shape
The razor modification is to consciously trim the circumscribed part of the razor to compensate for the tooth dent in the shaving process. You can choose to reduce the amount of razor cylindrical grinding method or negative displacement shaving cutter to reduce the workpiece tooth concave. The shaver can be divided into a rack-shaped shaving cutter for machining cylindrical external gears according to its structure, and a disc-shaped shaving cutter, which is mainly used in production. The third is a worm gear shaving cutter. For worm gear finishing. The most commonly used is a disk-shaped shaving cutter with a shape like a gear.
There are three common ways to shave a knife:
The first method is based on the template modification method. The basic principle is to detect the shaved gear tooth concave curve in the first place. According to the detection curve, the modified template is designed and manufactured. The grinding wheel is modified according to the modified template curve, and then repaired. Shaped grinding wheel grinding shaver. However, the determination of the modified template data cannot be solved by theoretical analysis and calculation methods at present. All of them use the method of trial shave by measuring the tooth profile deviation of gears, and then formulating the teeth according to the shape and size of the tooth profile deviation. The shape correction curve is compared and after many repeated grindings, the tooth profile correction curve of the more appropriate shaving cutter is finally determined.
The second is the computer control modification method. The method is to use a special design program to control the grinding wheel on a special grinding machine to achieve the purpose of grinding the shaving cutter.
The third is the random modification method, which uses the anti-cutting principle to install the grinding wheel with a hard surface on the gear position of the shaving gear to replace the workpiece gear for shaving, because the hardness of the dressing wheel is greater than the hardness of the shaving cutter. , so the concave phenomenon will be reflected in the shaver, and then use the shaver to process the gear will reduce or eliminate the concave phenomenon. At present, there has been a method in which a work-piece gear and a shaving cutter in a gear-type diamond trimming wheel replace the shaving process to achieve a shaving cutter shape modification. The process of shaping the process is simple, it is not necessary to remove the shaving cutter separately, the modification time is short, and the operation is easy. When the accuracy of the base wheel is high, the tooth profile accuracy can be up to 5 (GB10095-88) or more. After the wear wheel plating is exhausted, diamond can be replated and the random error in the system processing can be corrected in time. .
Fourth, the conclusion
Although shaver processing has made great progress at present, shaver processing production efficiency is also high. At present, solving the repair of gear teeth from theory and optimization calculation still needs continuous exploration and practice.
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