Dynamometric Installation
Abstract Generated abstract
This paper describes the development of a dynamometric installation for studying cutting forces in deep-hole drilling with single-edge carbide heads. The authors motivate the work by noting the lack of experimental data on how forces are distributed along the cutting edges and present a lathe-based simulation setup that measures tangential, radial, and axial forces, torque, and cutting temperature. The installation uses a specially mounted dynamometer, strain-gauge sensors on the boring bar, and natural-thermocouple temperature measurement, with calibration performed directly on the machine. Initial oscillograms are reported to confirm reliable operation of the system.
Full Text
DYNAMOMETRIC INSTALLATION
D. V. KOZHEVNIKOV, A. V. VODOPYANOV
(Presented by the joint scientific seminar of the departments of machine tools, metal cutting, and mechanical-engineering technology)
The processes currently used in mechanical engineering for machining deep holes are low-productivity and labor-intensive, since they generally involve two operations: drilling and boring. In this case, the boring operation is introduced in order to obtain an accurate hole, which after drilling has drift and misalignment.
Recently, a method for obtaining accurate holes directly after drilling with single-edge carbide heads with external supply of cutting fluid has been introduced into the practice of deep drilling.
The scheme of the action of forces and the arrangement of the guide pads for single-edge carbide heads are shown in Fig. 1. Cutting edges 1 and 2 take up the cutting forces, which can be resolved into components: tangential \(P_z\), radial \(P_y\), and axial \(P_0\). The calculation of typical head designs is carried out on the basis of the condition that the resultant of the tangential and radial forces is located between guides \(a\) and \(b\) [1], [2]; in this case it is assumed that the specific cutting force along the length of the cutting edges does not depend on the cutting conditions or the geometry of the chip-breaking grooves. However, there are no experimental data confirming this proposition.
Fig. 1. Scheme of the action of forces on a single-edge carbide head
To study the cutting forces acting on each section of the cutting edges of single-edge carbide heads, an installation simulating deep drilling was created in the cutting laboratory of TPI.
drilling on the basis of a 1K62 screw-cutting lathe. The modeling was carried out as applied to the drilling of deep holes 35 mm in diameter by face turning of bushings of various diameters, using sulfrezol supplied by the machine-tool pump as the cutting fluid.
The installation makes it possible to measure the tangential, radial, and axial forces and the torque. Simultaneously with the measurement of forces, the temperature is recorded by the natural-thermocouple method.
The design of the installation is shown in Fig. 2. A dynamometer, mounted in housing 1, is installed on the carriage of the 1K62 lathe. The tailstock, with boring bar 6 fixed in it, is rigidly connected to the carriage. Boring bar 6 is fastened in the tailstock by means of a collet chuck. Head 3, with carbide insert 16 fixed in it, is installed in needle bearing 7 and connected to boring bar 6.
Measurement of the tangential and radial forces is carried out by the dynamometer, and measurement of the axial force and torque by means of wire sensors 8 and 9 located directly on the boring bar.
When measuring temperature, one lead of the millivoltmeter is connected to the workpiece by means of a mercury current collector installed on the machine spindle. The second lead is connected to carbide insert 16 through a set of carbide rods 4 insulated from the head by chlorovinyl tubes.
The operating principle and design of the dynamometer were developed on the basis of the universal instrument for measuring cutting forces, UDM-1, created at VNII [3]. The dynamometer consists of housing 1 and bushing 2, secured in the housing by means of four horizontal and four vertical supports. To protect the dynamometer mechanism from sulfrezol and chips, the housing is closed with a cover. All supports are made of heat-treated 65G steel and have a preload somewhat exceeding half the permissible load on a support. The amount of preload is adjusted by screws 10, which are fixed in a definite position by nuts 11.
Bushing 2 is installed coaxially with the spindle axis. One wire strain gauge 5, with a resistance of 100 ohms and a base of 10 mm, is glued to each thin-walled support bushing. The gauges are connected into a bridge circuit differentially in such a way as to ensure the absence of mutual influence of the cutting-force components and the independence of the dynamometer readings from the point of application of the force.
Using the boring bar as the elastic element of the dynamometer for measuring the axial force and torque, without the additional elastic elements currently used for investigating the dynamics of deep drilling, ensures constancy of the stiffness of the system.
Calibration of the dynamometric installation is carried out directly on the machine by means of reference ring-type dynamometers and suspended weights.
Signals from the sensors are recorded with the aid of a UT-4 amplifier and an MPO-2 loop oscillograph.
The oscillograms obtained showed the reliability of operation of the dynamometric installation.
REFERENCES
- N. D. Troitskii. Machining of deep holes. In: Progressive Technology of Machine Building, book 41, Mashgiz, 1956.
- Yu. M. Fridman. Production and Operation of Tools. Experience of Ural Plants, issue 7, Mashgiz, 1955.
- B. N. Mukhin. Instrument for measuring cutting forces in turning. Machines and Tooling, No. 9, 1959.
Fig. 2. Dynamometric installation
Visible designations and dimensions in the drawing: 1–20; section B–B; 75; 196; 200; 186; ⌀125; ⌀20.