Internal grinding method and internal grinding machine

Details Internal grinding method and internal grinding machine Internal grinding method and internal grinding machine

2000-03-02

2003-09-09

Rose, Robert A. (Department: 3723)

Abrading

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

With indicating

C451S021000, C451S051000

Reexamination Certificate

active

06616508

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an internal grinding method for grinding an inner surface of a work having a straight-line generatrix shape while oscillating a grindstone relative to the work, and an internal grinding machine useful in carrying out this method.
2. Description of the Related Art
Internal grinding of a cylindrical small part such as a rolling bearing inner ring is performed by moving (oscillating) a grindstone forward and backward within a work along an axis of a X-axis slide table while carrying out intermittent in-process measurement. When an inner surface of a small work
2
is ground, a dimensional restriction does not allow a grindstone
1
attached at an end of a wheel spindle
4
and an in-process gauge
3
to keep simultaneous contact with a ground surface of the work
2
. As shown in
FIGS. 6 and 7
, the grindstone
1
and the in-process gauge
3
are therefore oscillated synchronizedly so as to perform size measurement on the work
2
by inserting the in-process gauge
3
into the work
2
when the grindstone
1
moves backward.
By this method, conventionally, grinding is generally finished when intermittently measured value reaches over a predetermined target-size value. In this case, however, the grinding cannot be always finished at a real target size. Accordingly, the dimensional accuracy is restricted. With regard to this aspect, in order to improve the dimensional accuracy, there have been proposed a method and a device in which predictive control is performed. On the basis of the intermittently measured in-process signal, the measuring device is retreated and the feeding of a grindstone is stopped on the basis of the predictive control signal (Japanese Patent Examined Publication No. Sho. 53-14797). In this method, the measuring device retreats just before the target size and terminates its size measuring operation. The grindstone is retreated from the work when the predicted size gets the target-size.
In the above-mentioned method and device, grinding is finished (the grindstone is retreated, from the work) at an arbitrary position in an oscillation stroke in accordance with the predictive target size signal. As a result, the contact position between the work and the grindstone is not fixed when grinding is terminated, which causes difference in diameter in the inner surface of the work. For such a reason, there is a disadvantage that the generatrix shape of the work deteriorates.
In order to solve the foregoing problem, there has been proposed a method in which an predictive operation for the work size is carried out with intermittently measured data by an intermittent in-process measuring device, and the oscillation speed or the remaining number of oscillation after the predictive operation is controlled so that a grindstone comes to a forward end of its oscillation just when the work size comes into a certain range of its target size (Japanese Patent Unexamined Publication No. Hei. 4-310368). In this method, a grindstone always stops grinding in full contact in axial direction, so that not only the dimensional accuracy of the work but also the generatrix shape accuracy and the cylindrical accuracy are improved.
In actual grinding work, the wheel spindle
4
is bent by normal grinding force as shown in
FIGS. 8 and 9
. As a result, when the oscillation of the grindstone
1
is backward, the forward end of the grindstone
1
grinds the surface of the work
2
locally. Specifically, in the above-mentioned grinding method accompanied with intermittent measurement, grinding width Wb becomes about ½ of whole length Wf of the work when the grindstone moves backward, as shown in FIG.
8
. In the conventional method, however, the wheel spindle
4
is oscillated in parallel with the moving direction of the X-axis slide table which performs trueing of the grindstone, so that the normal grinding force is not reduced in proportion to the reduction of the grinding width (Wf→Wb) when the grindstone moves backward. As a result, the normal grinding force per unit grinding width becomes excessive so that the grindstone
1
machines the work
2
at its forward edge
1
a
sharply. When the generatrix shape of the work deteriorates on a large scale in the process of grinding, the deterioration affects the dimensional accuracy of the work when the grinding is terminated. It is therefore necessary to keep the generatrix shape of the work properly during machining.
The above-mentioned conventional methods are not intended to improve the work shape on the way of grinding, but to correct the work generatrix shape, which has deteriorated in the machining cycle, just before finishing gringing, without lowering the dimensional accuracy. For example, in the foregoing grinding control method in Japanese Patent Unexamined Publication No. Hei. 4-310368, the grindstone always stop grinding at a forward end of an oscillation stroke, but deterioration of the generatrix shape of a work caused by sharp grinding at the forward end of the grindstone during its oscillating operation cannot be removed completely when grinding is terminated. In addition to the deterioration of the work shape, in the conventional methods, there is a problem of local abrasion of the grindstone due to large grinding resistance produced locally when the grindstone moves backward, so that the life of the grindstone is shortened.
Therefore, the applicant of the present invention has therefore disclosed a grindstone oscillation method in which a grindstone was oscillated in a direction inclined relative to the forward/backward moving direction of a X-axis slide table which performs trueing of the grindstone. In order to realize this method, the applicant developed an internal grinding machine shown in
FIG. 10
(Japanese Patent Unexamined Publication No. Hei. 5-285808). This configuration will be described with reference to
FIGS. 10 and 11
.
An X-axis slide table
7
and a work head-stock (not shown) which holds a work
2
in opposition to the moving direction of the table
7
are mounted on a bed of a grinding machine. Further, an in-process measuring device
9
having an in-process gauge
3
is provided in the vicinity of the head-stock. An oscillation unit
6
is mounted on the X-axis slide table
7
through a vertical pivot shaft
115
which can be inclined relative to the table
7
. In addition, a table
116
which reciprocates along a guide portion
6
a
is mounted on the oscillation unit
6
. A wheel spindle device
5
which can be inclined relative to the table
116
is mounted on the table
116
. In the illustrated example, the wheel spindle device
5
which can be moved around a pivot
114
(see
FIG. 10
) provided on the working table
116
, which is independent of the motion of the oscillation unit
6
relative to the X-axis slide table
7
. In this connection, this pivotal structure may be replaced so that arcuate irregular engagement portions each having an appropriate radius around the pivot shaft
115
of the oscillation unit
6
is formed on the upper surface of the table
116
and the lower surface of the wheel spindle device
5
respectively, and the wheel spindle device
5
can be tilted relative to the working table
116
along these arcuate engagement portions. Four piezoelectric force transducer
117
for detecting normal grinding force are mounted between the wheel spindle device
5
and the table
116
. The normal grinding force applied to the grindstone
1
in grinding operation is sum of the values detected by the four force transducers
117
.
An arcuate groove
118
with the pivot shaft
115
as a center thereof is formed in the upper surface of a rear end of the oscillation unit
6
. Through this arcuate groove
118
, a clamp bolt
119
for fixing the oscillation unit is screwed into the X-axis slide table
7
from the upper surface of the oscillation unit
6
. A hydraulic cylinder (not shown) is mounted on the X-axis slide table
7
. A piston rod
120
of the hydraulic cylinder is engaged with a head portion o

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