OBRABOTKAMETALLOV Vol. 27 No. 1 2025 technology To evaluate the effectiveness of the NMA described above in the composition of oil-based MWFs, laboratory testswere conducted todetermine the empirical frictioncoefficient under conditions approximating the drilling process. References [20, 21] describe various methods for determining the friction coefficient of lubricants, noting that it is not always possible to assess the actual friction coefficient using a particular machining method, due to the inherent characteristics of each method. Furthermore, the widely used four-ball machine methodology for determining the friction coefficient does not allow for reproducing the friction process occurring, for example, in the contact zone between the cutting tool and the workpiece during drilling. Experimental evaluation of the effectiveness of the developed oil-based MWF with NMA as a friction modifier, as well as evaluation of its tribological properties, was conducted using the “cone spinning on the cone” method for determining the friction coefficient, performed on a radial drilling machine2Co522. The experimental stand functioned as a tribometer, allowing for the determination of the empirical friction coefficient approximating the drilling process. A spiral drill bit made of steel B6Mo5 with a modified cutting edge geometry was used as an indenter (Fig. 2). This provided friction between the indenter (drill bit) and the conical surface of the counterbody (workpiece). During the research process, a three-component dynamometer M-30-3-6k was mounted on the machine table to register both axial force and torque. The workpiece, made of corrosion-resistant steel 0.12 C-18 Cr-10Ni-Ti with a previously drilled hole, was fixed on the dynamometer using a flange and a three-jaw chuck. The indenter was a spiral drill bit with a diameter D = 10 mm and a point angle of 2φ = 118°, made of high-speed steel 6 W-5 Mo-4 Cr-2 V, featuring rounded cutting edges (see Fig. 2). Axial force and torque values were recorded using the three-component dynamometer M-30-36k. The signal from the dynamometer was transmitted to a personal computer through an amplifier and analog-to-digital converter for subsequent generation of dependence diagram. Fig. 6 illustrates the general view of the experimental stand. A protective screen was used to prevent the measuring equipment from being splashed with MWF during the research process. The laboratory testing procedure was as follows: the counterbody 4 was fixed on the dynamometer using a three-jaw chuck and a flange. The indenter 1 was fixed in the machine spindle using a chuck. After starting the machine and subsequent feeding the tested modified MWF through slot 2 into the contact zone, the axial load on the counterbody was gradually increased to the required value P0, followed by measuring the friction torque. The spindle speed was 500 rpm with an axial load on the indenter of P0 = 2,000 N. To compare effectiveness, the following MWF compositions were used: vegetable oil (sunflower oil), industrial oil I-20A, vegetable oil (sunflower oil) with NMA, and industrial oil I-20A with NMA, at a constant MWF supply rate of 0.5 l/min. Fig. 3 presents the results of experimental studies to determine the empirical friction coefficient, using the methodology described above. During friction between a rotating indenter (drill bit) and a stationary counterbody, using the friction torque Mfr is more effective than using the friction force. The force of resistance to the movement of the indenter (drill bit’s) relative to the counterbody surface is a distributed force, directed opposite to the velocity vector of the body under consideration. Fig. 2. Geometry of the cutting edge of a modified drill (indenter): 1 – counterbody (workpiece); 2 – indenter (spiral drill); 3 – circular groove for supplying to the cutting zone; 4 – throughhole for removing MWF
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