Cutters – for shaping – Gear cutting tool – Hob
Patent
1995-06-07
1997-04-22
Howell, Daniel W.
Cutters, for shaping
Gear cutting tool
Hob
409 11, 409 32, 407 29, 407 24, B23F 527
Patent
active
056224591
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a tool for manufacturing crown wheels, whose pressure angle is between a minimum and a maximum value, by means of a machining hobbing process, in which a tool and a workpiece rotate with a constant ratio of the rotational speeds and move with respect to one another in such a way that the tool continuously machines the workpiece, said tool consisting of a disc which can rotate about its axis and on the circumference of which machining elements are disposed whose cutting edges lie in the surface of a profile which extends over the circumference of the disc as substantially helical ribs, the profile having the shape, in each cross-sectional plane perpendicular to the screw direction of the ribs, of a number of profile teeth situated next to one another, said profile shape being based on the base geometry of a pinion which is characteristic for the crown wheel to be manufactured and has involute toothing, and of which the centre of the base circle lies on a circle which lies in a plane perpendicular to the rotational axis of the tool and of which the centre lies on said rotational axis, in such a way that each of the two flanks of each profile tooth is formed by a straight line which is perpendicular to a tangent to the base circle of the characteristic pinion and/or a part of an involute of said base circle, of which the position of the foot on the base circle coincides with the foot of an involute of a tooth of the characteristic pinion on the base circle.
Such a tool is disclosed by the published International Patent Application No. PCT/NL/9100245 of the Applicant.
The tool disclosed by said patent application is satisfactory per se. It is found, however, that the machining times are relatively long. Said machining times are determined by the maximum permissible starting speed which, in the case of a gear wheel milling cutter, is determined by the maximum permissible depth of cut. Too high a starting speed gives rise to excessive wear of the tool.
The object of the present invention is to improve the known tool in such a way that the machining times can be shortened.
This object is achieved according to the invention by means of a tool of the type mentioned in the preamble, which is characterized in that the profile extending over the circumference of the disc has such a shape that a part thereof lies outside the surface of revolution which is formed by rotation of the addendum circle of the characteristic pinion about the rotational axis of the tool, so that the tool has machining elements or machining element parts whose cutting edges lie in the surface of said portion of the profile and can serve for performing a premachining operation when manufacturing a crown wheel.
The invention is based on the insight that it is possible to raise the existing ribs of the profile extending over the circumference of the disc to outside the addendum circle of the characteristic pinion, and to dispose in this region further ribs, in addition to the existing ribs, without this influencing the shape of the active portion of the teeth of the crown wheel to be manufactured.
By virtue of this measure according to the invention, the starting speed can be increased considerably and thus the machining times can be shortened, without this having an adverse effect on the useful life of the tool. It is found that in the case of a milling cutter the starting speed can be increased by approximately a factor of 4 with the depth of cut remaining constant.
A very expedient embodiment of the tool according to the invention is characterized in that, in each cross-sectional plane perpendicular to the screw direction of the ribs, the flank of each profile tooth which is directed towards the profile centre line, which passes through the centre of the base circle of the characteristic pinion and is perpendicular to the rotational axis of the tool, is formed, in the region between the base circle of the characteristic pinion and a first tangent to said base circle, whose point of tangency is situated on the same side
Basstein Augustinus F. H.
Sijtstra Anne L.
Uittenbogaart Gustaaf A.
Crown Gear B.V.
Howell Daniel W.
Tsai Henry W. H.
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