Research On NC Machining And Manufacturability Of Plane-generated Double Enveloping Hourglass Worm Pair

' Plane--generated doub1e enve1oping Hourg1ass worm gear drive,as a kind of basic mechanical transmission unit, was inventedunder the background that the mechanica1 industry deve1oped in' the direction of high speed, heavy 1oad and high efficiency. Itmeshes with multip1e teeth, and two contact 1ines exist betweeneach pair of coup1ing gears. Additiona11y, this kind of drivehas great 1ubrication ang1e, that is to say, the ang1e betweenthe tangent direction of the contact 1ines and the re1atives1iding ve1ocity is great. More over, the worm gear pair has thecharacteristics of worm gear drive have such exce11entproperties as heavy 1oad capacity, high efficiency, ease ofbeing lubricated, 1ong service 1 if e, and soon.Traditiona11y, the worm whee1 teeth are machined by dua1generating method to ho1d the contact 1ines between the couplingteeth. It takes 1ong deve1oping time and high cost to deve1opthe worm drive because of the difficulties and 1ong period forthe deve1oping of the hobbing cutter. Therefore, it presents newgenerating method to machine the p1ane--generated doub1eenve1opiflg Hourg1ass worm gear drive us ing NC machi ne too1. Thi sdissertation invo1ves the main aspects of the research, whichachieves the fo11owing positive resu1ts.1. A 5--axes NC machine too1 was mode1ed for the machining ofthe p1ane--generated double enveloping Hourg1ass worm gear drive.By mean of changing the cutter and gearing the axes of the NCMachine tool, the worm and the whee1 can be respective1y machinedusing the same NC machine too1. The worm are ground whi1e theteeth of the whee1 can be finished using genera1cutters--mi 11ers.2. Genera11y, the mating surfaces of the worms are "secondarycutters" for meshing surfaces of the worm whee1s during the2..runn1flg--1n per1od of the worm gear drive. This imp1ies theimportance of high fini shing precision and appropriateroughness for the mating surfaces of the worms. Thisdi ssertation defines the ideal worm and positioning p1anes forthe machining of the worm. It a1so ca1cu1ates the spira1 ang1eof the ideal worms. The definitions and the calculations help to control the inclination angle of the planar cutter, to locate the start point of the planar cutter, to control the turning velocities of the axes of the NC machine tool, and to machine multiple threads of the worms when NC machining is carried out to generate the planar enveloping toroid worm. These key measures gain the high precision of the worm mating surfaces.3. It is hard to mathematically describe the meshing surfaces of the plane-generated double enveloping Hourglass worm gear wheel teeth owing to the existence of non-working areas. A 3D solid model is found to describe this kind of worm wheel teeth by mean of virtual machining. The obtained meshing surfaces of the worm wheel teeth, which can be treated as ideal meshing surfaces, are fitted in Bezier surfaces after discretization by cut planes. Using this information model, editing the NC tool path and extracting the machinability information of the wheel teeth can be easily implemented.4. The evaluation contents and relevant methods are proposed for the manufacturability of plane-generated double enveloping Hourglass worm gear pairs. This kind of worm gear drive is usually applied to transmit power, so that its performances are of great importance for transmission efficiency and service life. Meanwhile, the wheel teeth are generally made of expensive nonferrous metals. It indicates that the performances should be as good as possible while the volume of the wheel should be possibly small. Goal attainment is employed in this dissertation to acquire the satisfying solution in the developing stage of the gearing arrangement. Moreover, according to the principle of computer vision, it calculates the visibility direction of cutter contact (CC) point on the wheel mating surface so to check the cutter interference and to control the cutter angles. While NC programming, the path w...