The design of the hob in the processing of the hard gear is modified by the shape of the hole (Shanxi Aluminum Factory, Hejin 043300). A hob shaping and rolling test was performed in the laboratory. Analysis and test show that the concave shape of the hob can effectively control the value and direction of the tooth profile error of the medium hard gear, which can ensure the position and width of the gear pair contact belt meet the design and use requirements.
Spur gear ah=Helical gear ah=In the field of vibration and impact load, such as mining, milk steel and other fields, it is most suitable to use medium hardened gear. In recent years, many achievements have been made in the design, manufacture, use and research of medium hardened gears at home and abroad. New tool materials, tool coatings and high-power hobbing machines have been introduced. In the production practice of medium hardened gears, it is found that most of the individual errors of the hobbing gear can reach the accuracy of the grade 7 of GB10095, and only the accuracy of the tooth profile is difficult to achieve. The hobbing tooth shape often appears as "S-shaped or concave", so that the contact area of ​​the gear pair deviates from the pitch circle at the root or the top of the tooth.
Some research institutes and manufacturers abroad have adopted the hob 'concave' trimming technology to solve the project of involute cylindrical gear hobbing tooth shape according to their production situation. Medium hard gear complete manufacturing technology and early fatigue point In the research of eclipse, a more comprehensive theoretical analysis and experiment on the hob shaping technology was given, and the value of hob shaping suitable for China's national conditions was given.
The purpose of the hob 'concave' is to control the direction and shape of the tooth profile error of the hobbing gear, avoiding the "concave" of the gear tooth shape, so that the contact zone width (tooth height direction) and position of the gear pair are reasonable. Improve the bearing capacity of the gear transmission and the smoothness of the meshing. Through analysis and research, the main factors affecting the tooth profile error of the hobbing gear are the cutter cutting tooth profile, the lead groove lead error, and the meshing line error. , hob installation error and tooth surface edge. Solve the hobbing tooth shape and "concave" phenomenon using the hob 'concave' shape modification is most convenient and effective.
1 hobbing gear shape error analysis hobbing tooth profile error is derived from the inherent error of the hobbing method and the relative position and relative motion error of the machine tool-tool-to-workpiece system. The inherent errors of the hobbing method mainly include tooth surface curvature and tooth surface wave. The tooth surface curvature is the envelope error and can be calculated by the following formula.
(1): A rib; R base circle radius; X cutting angle.
The above formula shows that the edge increases as the radius of curvature of the involute increases, that is, the maximum edge appears at the top of the tooth. At this time, the formula (1) can be written as: the number of teeth of the Z-cut gear; the K-knife Number of chip pockets; number of Zr hobs.
This formula shows that the angular angle increases as the modulus m, the pressure angle a, and the number of cutter heads Zr increase, and decreases as the number of gear teeth Z and the number k of the number of the cutter grooves increase. It is the main cause of the toothed topping of the hobbing gear.
The tooth surface waviness is formed by the hobbing axial feed. The value can be expressed by the following formula: AH tooth surface waviness; during the hobbing process, the helical surface parameter error of the hob is transmitted to the workpiece along the mesh line to form a Cut the tooth profile error of the gear. The reference plane error of the hob has a combined effect on the mounting error of the hob, so that the error transmitted to the workpiece increases the component of the mounting runout. Both the helical surface error and the reference surface error of the hob have a sinusoidal variation law, and the hob is turned into a cycle, and the resulting tooth profile error of the cut gear also has a distinct sinusoidal shape, that is, "S shape. According to the calculation formula given by the data, the influence of each single error of the hob on the hobbing gear tooth error is analyzed and found, and the cutting edge groove lead error, the hob base joint limit deviation, the blade tooth profile, the meshing line error and the roll are found. The error of the knife in the reverse direction of the tip of the tooth in the installation and alignment is significant. The cutting edge error is converted into gear tooth shape error one by one. We can easily control the direction of the gear tooth profile error curve with the cutting edge error curve. .
Due to the change of the degree of coincidence during hobbing, some of the left and right cutting edges work simultaneously, and some of the teeth work in a single blade, resulting in an unbalanced axial cutting component. The axial clearance of the drive side gap, the indexing worm and the hob shaft of the indexing worm pair causes the cutting edge to overcut the tooth surface of the workpiece near the pitch circle to form a "concave".
When the hob has pure radial runout, the radial runout phase on the measuring table is consistent at both ends of the hob; when the hob is installed tilted, in addition to the radial runout, there is an axial runout component. Both mounting errors cause a tooth profile error on the gear. Its calculation formula is: it can be seen as a sinusoidal waveform. Since the meshing line error caused by the hob manufacturing error is also a sinusoidal waveform, the hob tooth profile accuracy can be improved by adjusting the hob mounting error. The mounting error of the workpiece also has an effect on the tooth profile: when the number of teeth is small, the eccentricity of the workpiece installation has a significant influence on the tooth profile of the workpiece.
2 The determination of the concave shape in the hob and the purpose of the concave shape in the test hob are: control the tooth shape error direction, so that the gear tooth shape is convex, the contact band of the gear is near the pitch circle and the contact band width is reached. Precision requirements.
The root of the tooth tip is trimmed to accommodate the meshing impact caused by the deformation of the gear in the transmission. According to the calculation analysis and foreign related data, the amount of modification is given as shown in Table 1. Table 1 Modification amount Modulus correction amount The root of the concave tooth in the root of the tooth is trimmed for three m4. 5 hobs The test, the amount of modification is 114m, and the result of rolling the Z=4.5 test piece with three trimming hobs respectively, 1 the amount of hob trimming is too small, no convexity is formed, and the tooth top trimming is not reached. Effect; 2The shape of the hob is small, the tooth profile is convex, the top of the tooth is visible. The 3 hobs are moderately shaped, the tooth profile is convex, and the tooth top trimming and root modification are good.
When the rolling test piece is used for contact fatigue test, the contact belt position and width are in line with the accuracy requirements of GB100957.
3 Conclusion The hob tooth profile error mainly comes from the hobbing tooth surface edge, the hob meshing line error, the tool axis turbulence, the indexing auxiliary side clearance and the hob two-axis table rebound.
The hob shaping curve is given by the amount of concave in the gear, the amount of trimming of the tooth tip, and the amount of deformation of the tooth root, which can eliminate the concave and concave, and can close a certain shape error, so that the gear tooth shape is convex and the gear pair is in contact. The position and width of the belt are controlled, which is very beneficial to the bearing capacity, vibration and noise of the gear transmission.
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