| Helical gear transmission is widely applied in gear transmission as its meshing performance, large carrying capacity, as well as the advantages of compact structure size, etc. Forming milling is one of the main processing methods of helical gears. Traditionally, the process of helical gear milling is according to its equivalent number of teeth to choose appropriate spur gear cutter. Processing as that resulted in a huge margin for error and has been unable to meet the requirements of gears accuracy from the current rapid development of industry. Therefore, finding new ways to design helical gear form-cutters and implementing automation of the design process via computer is very important and urgent.The milling cutter profiles used to process involutes, transition curves and root curves of gears were solved respectively based on helical surface forming milling theory. The tooth profiles of transitional part and root part are divided into two cases according to the distance of the starting point of the involute and the centre of fillet radius to avoid the discussion of modification coefficient. Calculating according to the engagement of gear and rack to avoid the discussion of uncertainties of the meshed gear as it is the limiting case of gear engagement. This article compares the real tooth profile at end face got from contact optimization with the theoretical tooth face and compares the real tooth profile at normal plane with the theoretical tooth face got through the intersecting line of the tooth surface and the normal plane. Machining errors of several gear key parameters are analyzed in detail and it shows preliminarily that the cutter design in this article is correct. Also it provides grounds for error compensation. This article studies the direct interpolation of cutter curve with cubic spline by performing virtual simulation for it and generates CNC machining in custom-format code. By this way, the interpolation accuracy and efficiency of programming are improved. |
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