DEVICE FOR STUDYING CUTTING TOOL WEAR

M. F. POLETIKA, V. A. NAUMOV

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

In studying the wear of a cutting tool, a number of difficulties are encountered:

1. After each experiment it is necessary to remove the cutter and carry out the intended set of measurements. This takes a great deal of time; moreover, it is difficult to set the cutter in exactly the same position in which it was before the test, which may lead to a change in the nature of the wear, i.e., to a change in the experimental conditions.

2. Measuring—or still more, recording on paper tape—the wear profile of a tool without removing the cutter from the machine is very difficult, or even impossible.

In order to eliminate the difficulties listed above, a special research method has been developed in the metal-cutting laboratory of TPI. Its essence is as follows. Replica impressions are cast from the worn surface of the cutting tool with the aid of Wood’s alloy. Wood’s alloy (cerrobend) has a low melting point (68–98°C), does not shrink upon cooling, and copies very well even the finest scratches on the surface under investigation. The impression is an inverse copy of the surface being studied.

Then, on an instrument specially designed and manufactured in the metal-cutting laboratory, the wear profile is recorded on paper tape at strictly specified vertical and horizontal magnifications.

Existing profilographs could not be used for this purpose, since they had either an insufficiently large working travel of the sensor stylus at the required small probing force, or a large working travel of the sensor stylus but, at the same time, a very large probing force and an unacceptable form of the tip.

In the method and instrument developed, the above-mentioned shortcomings and difficulties have been eliminated. In addition, the impressions obtained can be stored for a fairly long time and make it possible to study the nature of wear in greater detail, using various instruments, means, and methods of comparison.

Technical characteristics of the profilograph

1. Vertical magnification . . . . 100, 200, 400, 1000.
2. Horizontal magnification, constant over all ranges . . . . 100.

1. Length of travel of the measuring table — 20 mm.
2. Working travel of the sensor probe — 0.8 mm.
3. Maximum travel of the sensor probe — 2.5 mm.
4. Speed of movement of the measuring table — 1.15 mm/min.
5. Measuring force — ≈ 0.5 g.
6. Error of vertical magnification:
   a) with sensor travel of 0.8 mm — ±3%,
   b) with sensor travel of 0.5 mm — ±2%.
7. Error of horizontal magnification — ±1%.
8. Mains voltage — 127/220 V.

Brief Description of the Setup

The setup for recording profilograms from impressions of the front or rear faces of cutting tools (Fig. 1) consists of a differential inductive sensor 1 with a mechanism for forced displacement of the measuring table 2 and an electric self-recording instrument 8 of type BV-662 from the Kalibr plant.

A measuring table 2 is mounted on plate 3, capable of movement in two mutually perpendicular directions by means of micrometer screws. One of these screws 4, by means of a gear pair, is engaged with the output shaft of reduction gear 5. Mounted on the reduction gear is a phase-sensitive two-winding electric motor 2ASM-100 b with a control panel.

Fig. 1

Power to the electric motor is supplied from the selsyn panel of the self-recording instrument at a voltage of 127 V.

The differential sensor is constructed as follows (Fig. 2). Two cup-shaped cores 2 made of Armco iron, containing inductive coils 3 inside, are press-fitted into a housing of nonmagnetic material 1. The cores are closed by plate 4 made of Armco iron. From above

the brass cover 5 and rod 6 for installing the sensor in the bracket are fastened. From below, in bracket 9, an armature 7 made of a nonmagnetic material (celluloid) is mounted on needle bearings. Two precisely ground disks 8 made of Armco iron are glued to the armature, and a stylus 10 is attached to one of the ends; it is a corundum needle with a very small radius of curvature.

When the position of the stylus changes, the armature rotates about point O, and the gap between the armature disks and the coil cores changes—

Fig. 2

which causes an induction emf in the coils. The signal is fed to a recording instrument and, in the corresponding devices, is converted into a trace on paper tape.

The assembled sensor is mounted on bracket 10 and stand 12 of the measuring table (Fig. 1). With the apparatus switched on, the test specimen is placed on the measuring table (it is shown in Fig. 1), and the stylus of the sensor armature is brought up to it. By means of nut 11, the stylus is adjusted so that the pen of the recorder is positioned approximately in the middle of the paper tape; recording is then carried out.

Tests have shown stable and reliable operation of the apparatus and linearity of the characteristics within the working range of displacement of the armature stylus. In investigating the wear of complex tools (drills, milling cutters, slotting cutters, etc.), the value of the method described increases substantially because of its simplicity and accessibility.