Abrading – Abrading process – Gear or worm abrading
Reexamination Certificate
2003-02-27
2004-06-22
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Gear or worm abrading
C451S010000, C451S011000
Reexamination Certificate
active
06752695
ABSTRACT:
TECHNICAL FIELD
The invention concerns a process for the modification of tooth traces and/or for the correction of tooth trace deviations of a gear by the continuous generation grinding of the tooth flanks of the gear in accordance with the generalities of the patent claim 1.
BACKGROUND OF THE INVENTION
With respect to load capacity and noise development, modern high capacity gear drive units are subjected to ever more stringent requirements. In many cases, in order to fulfill these requirements, the grinding of gears no longer provides them with a truly involute tooth flank form, but with a purposely modified flank geometry. These modifications are designed such that under operating conditions they have a positive influence on the loading and quiet running of the gear drive. The resulting demand made on a modern gear flank grinding machine is that the flank modifications specified by the gear designer can be programmed as simply as possible and generated with high precision. The same requirement prevails for the input and execution of the correction of machine and setting related flank geometry deviations after gear tooth inspection on a gear measuring machine.
Due to the mostly differing functions of the left and right tooth flanks, e.g. as working or non-working flank, different tooth trace contours are frequently desired on the left and right flanks. A more pronounced crowning, for example, can be demanded for the non-working flank than for the working flank. Similarly after gear measurement, the tooth trace corrections to be undertaken across the face width on the left and right flanks frequently do not have the same contour. A further demand made of a modern gear grinding machine, therefore, is that the desired flank modifications and corrections of flank geometry deviations can be entered separately for the left and right flanks.
A known process for the manufacture of gears is the double flank continuous generation grinding with a cylindrical grinding worm. In this process, during the grinding stroke the two flanks of the thread of the grinding worm engage with the two gear flanks simultaneously at two points of contact lying opposite each other in the normal plane. If here the grinding stroke of the grinding worm takes place parallel to the gear axis at a constant coupling ratio between grinding worm and gear rotations, the tooth traces produced on the gear's left and right flanks are straight and mutually parallel. For the modification of tooth traces, these straight lines are usually used as reference. The modification can thus be defined as the deviation off a non-modified tooth trace across the face width of the gear.
DE 197 06 867.7 shows one of the possible methods of producing tooth trace modifications by continuous tooth flank generation grinding. With this method the grinding worm employed is adapted according to the gear modification desired. That is to say that flank geometry of the grinding worm is modified in the lead direction of the grinding worm thread, such that by axial shifting of the grinding worm during the grinding stroke, i.e. during passage through the workpiece tooth space, the desired tooth trace modification is formed by conjugate reproduction of the modified flank form of the grinding worm on the workpiece tooth flank. This process is expensive, however, as for every modification the appropriate matching grinding worm geometry must be produced beforehand, and reproduced with every dressing operation.
In another more widespread method, to which the present invention is also related, supplementary motions of a magnitude corresponding to the desired modifications are purposefully superimposed on that relative motion between grinding worm and gear needed to grind non-modified tooth flanks. These supplementary motions are produced by NC axes of the machine which are suitable for the purpose. By altering the centre distance between grinding worm and gear, and by tangentially shifting the grinding worm, it is possible to shift the tooth space width and respectively the angular position of both tooth flanks, i.e. the tooth space centre, in the direction of rotation of the gear. The latter can also be achieved by means of a suitable supplementary rotation of the gear relative to the grinding worm within the generative coupling incorporated between the two elements.
This method affords a greater flexibility. Also of advantage is that the same NC machine axes can be used for the modifications as are used for the continuous generation grinding of the gear. Additional resources for the adaptation of the grinding worm thread geometry are dispensed with. In practice however, cases are also to be encountered which make combined use of both of the methods described above.
The method last described has the disadvantage, however, that the supplementary motions of the NC axes which produce the modifications of the tooth traces are effective on both tooth flanks simultaneously, because the grinding worm is in contact with both flanks of the gear at once. Therefore the tooth traces of the left and right flanks cannot be altered independently of each other. Hence the requirement initially mentioned, namely that the desired flank modifications and corrections of flank geometry deviations can be entered for the left and right flanks separately, is not fulfilled.
For example, by altering the centre distance between grinding worm and gear in a circular arc relationship across the face width, this process produces crowning of equal magnitude on both flanks. Moreover in the case of helical gears, the apex points are mutually offset in the longitudinal direction by an amount equal to the offset of the points of contact of the grinding worm thread on the left and right flanks. Likewise rotary displacements between the grinding worm and the gear within the generative coupling during passage through the tooth space produce directional changes of the tooth traces of equal magnitude on both workpiece tooth flanks, but of opposite algebraic sign. The same applies for axial displacements of the grinding worm relative to the gear.
For simple, frequently occurring form elements of tooth trace modification such as crowning, end relief and helix angle alterations on both flanks, this method may suffice. For more intricate form elements and higher standards, however, it is inflexible, and its implementation is complicated, untransparent, and tedious and exacting for the setter or operator, so that the risk of error is increased.
SUMMARY OF THE INVENTION
The objective of the invention is therefore to create a process which obviates the above-mentioned disadvantages.
This objective is achieved with a process having the characteristics of patent claim 1.
In the process according to the invention, tooth trace modifications and/or corrections of tooth trace deviations are defined separately for the left and the right flank. From these separate sided entries for modifications and/or deviation corrections, supplementary motions of the NC axes of a tooth flank grinding machine are calculated and performed during the grinding stroke. These supplementary motions cause supplementary displacements between the grinding worm and the gear in various directions of motion. Thus the desired left and right hand tooth trace modifications and/or tooth trace corrections are realized on the gear in one and the same grinding stroke.
Therein motions in a first direction of motion take effect on the left and right flank symmetrically with the same algebraic sign, e.g. a radial infeed of the grinding worm. Motions in a second direction of motion take effect on the left and right flank symmetrically, but with opposite algebraic signs, e.g. a relative rotation between grinding worm and gear within the generative coupling, or an appropriate linear displacement of grinding worm and gear relative to each other.
The process according to the invention permits in an efficient manner modified tooth trace contours as well as corrections of tooth trace deviations to be realized in a single common grinding stroke,
Browdy and Neimark , P.L.L.C.
Morgan Eileen P.
Reishauer AG
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