Gear grinding machine and gear grinding method

Details Gear grinding machine and gear grinding method Gear grinding machine and gear grinding method

2000-12-08

2003-05-13

Hail, III, Joseph J. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

With indicating

C451S005000, C451S009000, C451S010000, C451S180000

Reexamination Certificate

active

06561869

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a grinding machine and a grinding method for grinding the tooth flanks of a gear-like workpiece as a stock material with a gear-shaped grinding stone engageable with the particular tooth flanks in the process of manufacturing a gear-like product having internal teeth or external teeth.
2. Description of the Related Art
A method for grinding the tooth flanks of the internal teeth, such as a wire cut method or an electric discharge machining, is well known in the process of manufacturing a product having internal teeth such as an internal gear, a ring gear or an internal spline. The problem of the prior art, however, is that a long machining time is required and therefore volume production is difficult with small equipment. Another problem is a high price due to a high cost caused by an increased size of the machining equipment for volume production.
In the grinding machine or the grinding method for grinding the tooth flanks of a gear-like object to be machined (workpiece), having internal or external teeth, with a grinding stone engageable with the particular gear flanks, a contact pressure of a predetermined magnitude is required to be generated in the machining section in which the tooth flanks of the gear-shaped grinding stone and the tooth flanks of the gear-like workpiece to be ground are in contact with each other. A conventional grinding method is known as a technique meeting this requirement, in which a gear-shaped grinding stone and a gear-like workpiece in mesh with each other are rotated simultaneously in complete synchronism with each other. However, the mechanism for synchronously rotating the grinding stone and the workpiece requires a high accuracy, and therefore the machining equipment cost is very high. Thus, this method is not economical from the viewpoint of the machining cost.
In a comparatively simple conventional method described in Japanese Unexamined Patent Publication (Kokai) No. 34-1650, on the other hand, a gear-shaped grinding stone is rotated thereby to cause the free running of a gear-like workpiece in mesh with the grinding stone, while the driven workpiece is braked thereby to exert a resistance (rotational resistance) of a predetermined magnitude on the rotation of the workpiece. The contact pressure required for grinding is thus generated in the machining section, thereby grinding the tooth flanks of the workpiece.
The prior art using the free-running method described in the patent publication cited above, however, cannot successfully meet the unavoidable deterioration with age including the reduced sharpness of the grinding stone and the reduced rotational resistance to the gear-like workpiece caused by the wear of the brake. Also, the prior art, which never intends to control the magnitude of the rotational resistance with high accuracy, harbors a problem that the tooth flanks of the workpiece cannot always be finished with high accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to cope with the problem of the prior art described above and to provide an improved internal tooth grinding machine which can grind the internal teeth at high speed with small machining equipment while at the same time making possible volume production with high accuracy at low cost.
Another object of the invention is to provide a grinding machine constituting a simple, inexpensive machining means employing the free-running method as in the prior art described above, wherein a sufficiently high machining accuracy can be maintained in keeping with the deterioration with age including the reduced sharpness of the grinding stone and the reduced rotational resistance due to the brake wear, thus making it always possible to grind a gear-like workpiece with high accuracy on the one hand and a novel method of grinding a gear-like workpiece on the grinding machine on the other hand.
In order to achieve the objects described above, according to one aspect of this invention, there is provided an internal tooth grinding machine for grinding the tooth flanks of the internal teeth of a workpiece having a circular outer periphery and a gear-shaped inner periphery in such a manner that the workpiece is caused to engage with a grinding stone having external teeth formed on the outer periphery thereof, and one of the grinding stone and the workpiece is rotated with the other run free, while at the same time reciprocating one of the grinding stone and the workpiece relatively to the other in an axial direction, the internal tooth grinding machine comprising:
at least two rollers located on the outer periphery of the workpiece for holding the workpiece at a machining position by holding the workpiece in collaboration with the grinding stone located on the inner periphery of the workpiece;
a plurality of bearings for rotatably supporting the rollers, respectively;
a block for supporting the bearings; and
a roller support unit for pressing the workpiece against the grinding stone through the blocks and the rollers.
The internal tooth grinding machine according to the invention basically operates in such a manner that one of the gear-shaped grinding stone and the workpiece having internal teeth is rotated while the other, in mesh, is run free thereby to grind the tooth flanks of the workpiece. In the case where only the contact points of the tooth flanks, formed by free running, are ground, the force is concentrated only on the narrow contact points between the external tooth flanks of the grinding stone and the internal tooth flanks of the workpiece. In that case, only the slight slip between the tooth flanks of the grinding stone and the workpiece contributes to the grinding work and, therefore, high-speed, high-accuracy grinding would be impossible. In the internal tooth grinding machine according to the invention, on the other hand, not only one of the grinding stone and the workpiece is run free but also both are reciprocated relatively to each other in the axial direction at the same time, and therefore all the parts of the gear profile including the tips and bottoms of the workpiece can be ground at high speed with high accuracy. The effect of the reciprocal motion is strengthened by the fact that a force is exerted on the contact surface between the grinding stone and the workpiece due to the free running. In other words, the free running and the reciprocal motion have a multiplier effect.
In the internal tooth grinding machine according to the invention, a workpiece with a circular outer periphery is supported rotatably by at least two rollers. Therefore, the outer periphery of the workpiece and the parts of the grinding machine supporting the workpiece are prevented from wearing. As a result, the machining accuracy and the durability of the grinding machine are further improved.
An alternative method for running the workpiece or the grinding stone freely while at the same time reciprocating them relatively to each other along the rotational axis consists in rotating the grinding stone with a grinding stone support unit while at the same time causing the same grinding support unit to drive the grinding stone to reciprocate along the axial direction. Still another method is to drive the rollers in the rotational direction by a rotation drive unit while running the workpiece and the grinding stone freely. Preferably, however, the grinding stone rotatably supported by the grinding stone support unit is preferably reciprocated in the axial direction.
The internal tooth grinding machine according to the invention, which usually employs at least two rollers, desirably comprises three or more rollers for stabilizing the supported condition of the workpiece leading to a further improved the workpiece machining accuracy and the durability of the grinding machine. Further, in the case where the machine comprises three or more rollers, at least one block supporting a roller is separated from the other blocks supporting rollers, so that the former is movable relative to the latter i

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