Improved design of high precision gear hob profile
First, the question is raised: The design of the main drive turbine gear of a main steam turbine gear unit requires that the accuracy of the gear manufacturing process be improved to 5 precision in GB 10095-88. At the same time, it must be ensured that 45% of the tooth height direction is in the middle of the tooth height and 80% in the tooth length direction. Contact accuracy requirements for contact at the mating end. The gear contact accuracy, especially the contact accuracy in the tooth height direction, mainly depends on the gear tooth profile accuracy, and the tooth profile accuracy of the hobbing gear is mainly ensured by the hob tooth profile accuracy. Based on many factors, in order to achieve the above accuracy requirements, the peak-to-valley shape of the gear teeth of the old unit is geared, the contact area of ​​the tooth tip and the tooth root contact is incorrect, and the proportion of the contact area is seriously insufficient. The main drive gear is still modified by the tooth tip and it is expected that the hobbing tooth shape is a toothed profile design with a slight convex and smooth edge involute. According to the product gear design, the tooth profile accuracy, the tooth tip modification amount, JB 3227 -83 AAA grade hob tooth profile accuracy 3 tolerances, improved design hob tooth profile line, from the original semi-cubic parabola trim edge involute linear tooth profile to tooth top, root root trimming, tooth height A slightly concave trimming involute in the concave tooth profile line (as shown in Figure 1). Second, the solution to the problem: 1. Improve the design of the hob tooth profile line. The original semi-cubic parabola trimming involute linear tooth profile is changed to the tooth top, the tooth root trimming edge, and the tooth height is slightly concave in the trimming involute. Profile line (as shown in Figure 1). 2 Problem Solving The design idea is: The tooth profile accuracy in the middle of one part of the concave tooth tooth height is equivalent to the AAA precision requirement in JB 3227-83. The median value of the tooth top and root root trimming is equivalent to the gear tooth. Shape repair margin. In order to ensure that the tooth shape of the middle part of the tooth height meets the involute tooth shape requirement, the middle half of the tooth shape of the full tooth height is controlled to be as small as possible, so that the middle contact of the hobbing gear tooth height direction is as A little wider. Design gear trimming requirements: M42 large gear is 0.042, M4.5 large gear is 0.036, root modification is zero. 5-stage gear tooth profile accuracy: M7 large gear is Dff=0.024, M4.5 large gear is Dff=0.013, M4.5 small gear is Dff=0.008. JB 3227-83 AAA grade hob tooth profile accuracy: M7: dff = 0.006; M4.5: dff = 0.005. In order to ensure that the hobbing gear tooth shape is smooth and no abrupt change and the tooth shape is slightly convex. The tool profile design proposes three technical requirements: The concave amount of the hob tooth profile is qualified in the range of A and B curves, but the "0" point should be the most concave, and the tooth root concave amount should be larger than the tooth top concave amount. The complete tooth shape should be a concave curve with several curved curves connected smoothly and without sharp points. The “0†point is the machining detection hob tooth profile reference point with a tolerance of ±0.10. In order to eliminate the concave point between the concave curve and the hob tooth tip and the root arc, the shape curve is allowed to extend as a tangent and is tangent to the arc curve. 3 The application of the concave line adopts the old unit M4.5 and the material is M35 high cobalt high speed steel hob. It is modified according to the design principle of the concave tooth profile line. After the modification, the hob precision and the tooth profile line are all achieved. Design requirements. A pair of left and right rotary knives were used to roll a pair of simulated large and small gears of 34CrNiMo on the RFW10S precision gear hobbing machine. The tooth shape is obviously convex, the convex amount is 0.005~0.006, and the tooth edge trimming amount is 0.03, which meets the requirements of the product gear tooth shape design precision. The pair of gear pairs roll up to reach the middle of the tooth height about 30%~ 35% contact. This design solves the problem of linear contact between the top and the top of the old unit. Although it does not meet the 45% design contact requirements, it can fully assist the increase to the tooth height by using the micro-research process under the premise of ensuring the accuracy of the single item of the gear. Third, the conclusion: 1. The successful application of the new design of the indented indented line in the manufacture of the test hob and the product-specific hob proves that it can fully meet the requirements of the hob manufacturing process. The hob manufacturing precision can fully meet the manufacturing precision requirements. 2. The tooth shape of this new type of hob is obviously different from that of the linear hob, which realizes the ideal idea of ​​the slight convexity in the middle of the tooth height, completely eliminating the peak-tooth shape. The hobbing test and the official product gear meshing contact area have a significant improvement over the older unit gears. The problem that the top of the tooth, the linear contact contact area of ​​the tooth root is incorrect, and the proportion of the contact area is seriously insufficient is eliminated, and the design contact precision requirement of the desired tooth height middle contact is realized. Completely solved the key problem of the long-term attack of the old unit near the tooth top and the tooth surface of the tooth root.
Figure 1 Schematic diagram of the concave line in the M4.5 gear