| In the past, the cutting of spiral bevel gear has been carried on the special gear milling machine or gear grinding machine, and by adjusting machining parameters to modify the tooth contact pattern which is under the influence of each parameter coupling. The geometric characteristics and the meshing process of spiral bevel gear whose processing parameters inter coupling and influence the tooth contact conditions comprehensively are complex so trial cuts are conducted repeatedly and the contact condition are closely observed in the rolling test. It is quiet difficult to gain a set of processing parameters which can ensure the quality of good contact. Along with the rapid development of the high speed cutting technology and its application in machining center, the cutting of spiral bevel gear on machining center has become a reality and can solve some difficult problems which can’t complete on special machine tool in machining big bevel gears. However, the existing tooth surface modification technology and tooth contact analysis is limited to special milling tooth machine, therefore it is urgent to establish a set of tooth surface modification theory based on machining center cutting spiral bevel gears. Basing on efficiently forming bull wheel, this paper puts forward a theory of quantitative modification of pinion tooth surface on conjugate, and preciously meshes the target pinion tooth surface modified with high precision basing on the theory, then carries on tooth contact analysis, exploring the impact on tooth surface meshing performance by the change of the modification coefficient.Main content of this article:1 The tooth surface equation of the gear based on the gear forming processing is set up. According to the principle of gear engagement, the theoretical tooth surface equation of complete conjugate for the pinion in the analysis of the gear pair meshing coordinate system is deduced.2 By using the principle of the rotating projection to mesh the pinion tooth surface, the relationship between the three-dimensional tooth surface coordinates and the two-dimensional grid coordinates is established and then the discrete point data of small tooth surface is solved. On the basis of grid data, the deviation between the target pinion tooth surface and complete conjugate tooth surface is built by applying differential curve surface equation and modification calculating of full conjugate small tooth surface is performed, then the grid discrete point data of modified small tooth surface is obtained.3 The discrete points of the modified tooth surface of the pinion is matched preciously by using the double cubic NURBS surface fitting method and the digital gear tooth surface equation of pinion is obtained, then the precision of fitted tooth surface is analyzed. Tooth contact analysis(TCA) between theoretical tooth surface of bull gear and digital gear tooth surface of the pinion is conducted. The gear transmission error and the contact pattern is obtained. Then the feasibility of the modification design on full conjugate tooth surface of the pinion is verified. The influence on the result of TCA by the tooth profile drum modification coefficient and tooth length drum modification coefficient is explored.4 By importing tooth pastry data got by calculating to 3d software, the change of contact area before and after modification is observed and the feasibility of theoretical modification is analyzed. Taking a pair of gears with small round teeth 8, and big wheel teeth 37 as an example, the pinion modification is calculated and the discrete points are obtained using the modification theory of this paper proposed, and it is imported into 3d software to generate entity. Then programs are made to machine the pinion on the machining center for processing experiment and the rolling test of the gear is conducted, observing tooth contact zone and TCA results are basically identical, which has proved the validity of the modification theory proposed in this paper. |
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