AGMA - 16FTM03
Worm Screw High-Speed Manufacturing
| Organization: | AGMA |
| Publication Date: | 1 September 2016 |
| Status: | active |
| Page Count: | 15 |
scope:
This paper shows how to produce worm screws when your actual gear hobbing machine configuration has the hob axis perpendicular to the workpiece axis with a swiveling of ± 30 [deg] for the hob head to produce helical gears. As we know, from the perpendicular axis of the work piece, the helix angle of a worm screw is of 90 [deg] ± 30 [deg]. With this type of hobbing machine, it is not possible to produce a worm screw by the two conventional ways: with a worm milling cutter cutting one thread after the other, or using a worm screw hob to produce the multiple threads screw in only one cut pass. To solve the problem, let us think about how a hob meshes with a straight gear. Conceptually, it is like a worm screw meshing with a gear. Now the idea is to think the opposite: the tool is the straight gear and looks like a shaping cutter. The workpiece is the worm screw. Using this concept, all the axis between the work piece and the tool are reversed. The swivel axis of the tool has now to rotate from 90 [deg] minus the worm screw helix angle. That means it has to swivel ± 30 [deg] from the perpendicular between the tool axis and the work piece. Theoretically, with this process your machine can now produce any type of worm screws. The rotation speeds are also reversed. In conventional gear hobbing, the work piece rotation speed is given by the hob rotation divided by the gear tooth number, multiply by the gear's threads number. Now, the cutting speed is given by the rotation of the workpiece. So if a cutting speed of 8.66 [ipm] needs to be reached on a pitch diameter of 0.275 [in], the workpiece rotation will reach 9100 [rpm]! The tool speed will be calculated by dividing the speed of the workpiece by its number of teeth and multiply by the screw number of threads. Everything is reversed. But what is the big advantage? If an axial feed rate of 0.002 [in/piece_revolution
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