Device for Instantaneously Stopping the Cutting Process During Drilling

D. V. Kozhevnikov, Yu. V. Shchepetilnikov

(Presented by the scientific seminar of the Department of Machine Tools and Metal Cutting)

To study the process of built-up-edge formation, devices are used that make it possible to stop the cutting process instantaneously.

The devices described in the literature [1, 2, 3], however, proved unsuitable for studying the process of built-up-edge formation during drilling in the case of internal cooling, when a chuck for supplying coolant to the rotating drill is mounted on the machine spindle.

Below a device is described (Fig. 2) that makes it possible to stop the cutting process instantaneously during drilling under conditions in which coolant is supplied directly into the cutting zone.

Fig. 1.

It consists of a stationary body 3, carrying a fork 9, in which a lever 10 is mounted, and of a rotating part 4, supported by a radial-thrust bearing 1. On top, on the rotating part, which is made so as to prevent coolant from entering the device, a bushing 5 for installing specimens 6 and a stop plate 8 are fastened. To reduce the moment of inertia, the rotating part is made as light as possible, and its rotation is carried out in two roller bearings 2, which, if necessary, make it possible to freely remove the entire rotating part 4 from

housing 3. The fundamental difference between this device and existing ones is that, after the rotary part of the device 4 is released, as a result of the rapid withdrawal of lever 10 from contact with stop bar 8, the rotary part of the device is driven by the drill itself, located under the chip. The absence in the device of a removable support or a key to be cut through necessitates switching off the mechanical feed simultaneously with releasing the rotary part of the device.

The reliability of the device was evaluated on a 2A150 vertical drilling machine as a function of cutting speed, from the standpoint of the time required to accelerate the rotary part to the rotational speed of the machine spindle. The tests were conducted according to the scheme shown in Fig. 1. On the rotary part of the device 1, a contact 2 was installed, consisting of a flat spring plate.

Fig. 1. Device for the instantaneous interruption of the cutting process during drilling.

View A

Fig. 2

The fork 3 of lever 4 and screw 5, which at the moment of fixation of the rotary part is in contact with the spring plate 2, are insulated.

from the body of the fixture and connected to the vibrators H135 1.5 of the loop oscillograph H102. The other end of the measuring circuit was closed to the body of the fixture. The signal to the oscillograph vibrators was supplied from two 1.3 V cells through potentiometers P, only when the contacts of lever 3 and screw 5 with stop plate 6 and spring plate 2 were closed. At the moment lever 4 is withdrawn, the signal supplied to vibrator 1 is interrupted, and, as a result of the rotation of the rotary part that has begun, the signal supplied to vibrator 2 is also interrupted. In Fig. 3

Fig. 3

oscillograms of the instant at which the contacts open are presented for two spindle speeds. The film travel speed in this case was 1000 mm/sec, and the pulse frequency of the time marker was 1000 Hz. As can be seen from Fig. 3, the rotation of the rotary part of the fixture begins after its release even at a speed of 1170 rpm with a delay of no more than 0.0003 sec.

Such rapid action of the fixture is ensured by the elastic-deformation forces of the loaded elements of the fixture, directed in the direction of rotation of the drill. Thanks to this, the fixture can be used to obtain chip “roots” at sufficiently high spindle speeds.

REFERENCES

1. Oxford. On drilling metals. Mashinostroenie, No. 11, Moscow, 1955.
2. D. V. Kozhevnikov. A fixture for instantaneous stopping of the drilling process. Advanced scientific-technical and production experience of TsITEIN, topic 11, No. 61—20/5, Moscow, 1961.
3. Yu. P. Kholmogortsev. High-Productivity Drilling. Chelyabinsk, 1963.