Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
1999-07-20
2001-02-20
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S010000, C451S011000, C451S443000
Reexamination Certificate
active
06190241
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an internally toothed tool for the precision machining of gear-wheels, and a method and dressing wheel for dressing the tool.
BACKGROUND OF THE INVENTION
The invention is based on a method of machining gear wheels, of which the principle is described in U.S. Pat. No. 5,395,189 to Schriefer which may be carried out using an internally toothed tool on a machine as described in U.S. Pat. No. 5,443,338 to Huber et al. It has been found in practice that the machining of corrected teeth with an externally toothed tool with simultaneous movements in three mutually perpendicular axes on a machine without a cradle or the like does not give rise to problems in the case of small widthwise corrections (for example, convexity) whereas machining with an internally toothed tool often produces unsatisfactory results.
The reason is that in the case of an externally toothed workpiece wheel and tool, two convex base bodies perform relative movements. However, in the case of an externally toothed workpiece wheel and an internally toothed tool, a convex and a concave base body are in contact. Therefore, the contact intervals are substantially smaller outside the contact zone and there is a risk of miscutting by secondary cuts or edge contact even with small widthwise corrections during a relative movement between workpiece wheel and tool. Furthermore, the smaller contact intervals lead to increased sensitivity with respect to the position and size of the contact zone. This in turn influences the clockwise and counterclockwise equilibrium of the contact forces and therefore the local instantaneous flank removal which decisively determines the flank quality attainable.
Therefore, mutually orthogonal spatial movements of the contacting base bodies of workpiece wheel and tool are often inadequate, in particular in the case of internally toothed tools.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to improve the method of the type under discussion such that satisfactory results can also be achieved with internally toothed tools. In addition, the tools are to be developed such that they can be used as widely as possible, in particular for preliminary and final honing. Furthermore, it should be possible to adjust the tool according to the machining of the workpieces.
In the contact zone, there is a rotational degree of freedom round the contact normal which is simultaneously appropriately included in the orthogonal three-axis interpolation.
The simultaneous interpolation of (i.e. simultaneous movements along) the three orthogonal axes together with an interpolation of the change in the crossed-axes angle represents the minimum kinematics required. In the case of the movements which can be carried out in shaving and honing machines known to date, more degrees of freedom are provided (e.g. the tilting of the rocker) than is the case here, so that more machine axes have to be controlled therein (which is costly and therefore unwanted).
The method covers two mutually independent kinematic effects. The simultaneous relative displacement of the workpiece wheel relative to the tool in the directions of three orthogonal axes allows substantially free design of the shape of the workpiece wheel and tool base bodies and therefore of flank width corrections (convex, conical, hollow, conical-convex, hollow-convex) and of the instantaneous relative position of the machining zones both on the workpiece wheel and on the tool flanks. Advantageous feed strategies axially, diagonally, transversely or radially to the workpiece wheel axis can be made in succession or merging into one another in this way. The simultaneous rotation round the axis of the crossed-axes angle allows each instantaneous relative contact position of the bodies of the tooth gaps and of the teeth of workpiece wheel and tool to rotate relatively such that no secondary cuts occur and defined contact conditions arise. According to the invention the kinematically acting base body of the tool may be cylindrical, i.e. only convex workpiece wheel flanks of which the kinematically acting base body has identical or greater kinematic convexity than the cylindrical base body of the tool may be produced with this base body.
In this specification “kinematic” and related terms refer to the effective form of a body generated by the combination of its spatial movements and its physical shape.
Alternatively, the tool of the present invention may have a convex base body. Convex, straight and hollow-convex workpiece wheel flanks can therefore be produced, and the size of the contact zone between workpiece wheel and tool flanks may be intentionally influenced.
The present invention also resides in an internally toothed tool, suitable for use in the method set out above, of which the teeth have width corrections which act kinematically differently in the width direction.
Preferably, the tool has a region with a large kinematically acting width correction for preliminary honing, and a region for subsequent final honing, with no or only a small kinematically acting width correction.
The present invention further comtemplates operating with one or more tools in a chuck, the tools having different kinematically acting width corrections. It may be advantageous, for example, to carry out preliminary honing with a cutting-friendly tool with a small contact zone in order to reduce the processing forces and final honing with which the flanks are only smoothed with a large contact zone.
Both preliminary and final honing may be performed with double-flank contact, or the preliminary honing may be performed with single-flank contact, single flank contact being preferably carried out with electronic constraint in this case.
The tool may mesh with the workpiece in a free-running manner during both preliminary honing and final honing. Alternatively, the tool and workpiece may run under constraint during preliminary honing, but mesh in free-running manner during subsequent final honing.
The use of constrained single-flanked contact in the method according to the present invention allows substantially independent free design of the workpiece wheel right-hand and left-hand flank width corrections. The subsequent free-running double-flank contact is brought about by relative displacements of the base bodies and serves only for flank smoothing.
The tool may have two or more axially adjacent identical sets of teeth, which are moved by displacement along the X and/or Y and/or Z axis into the operating position, lying where the axes cross, or away from the crossing position. Alternatively the tool may have two or more axially adjacent different sets of teeth.
In the ideal case, it is possible to displace the individual cylindrically arranged teeth with the X and Z axes of the machine into the intersection or crossing of axes in each case and to increase the internal diameter of the tool by profile displacement to the respective end of the tool life. This is conditional on neither the workpiece wheel itself nor the clamping device colliding with the further teeth located in the axial direction of the tool as these teeth would have to be arranged not on a cylindrical but on a hyperbolic base body for reasons of collision.
However, the present method also allows the base bodies both of the workpiece wheel and of the tool to be conical or conical-convex. It is therefore possible to machine the workpiece wheel in another state of the tool tilted by the X- Y- Z-displacement and A-rotation and therefore to bring the still unused further tool teeth from the collision region.
If a shaft-like workpiece or cluster gear with different teeth is machined in a chuck with several different adjacent tool teeth, machining can also be carried out with adjacent teeth in the tilted tool state to avoid collisions.
The internally toothed tool can basically be dressed with an appropriate dressing tool in the same manner as the machining of a workpiece wheel with the internally toothed tool. It is particularly advantageous if differen
McDowell Robert L.
Morgan Eileen P.
The Gleason Works
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