OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 5 4 3 Results and discussion Using the method described in the last paragraph, we obtained control measurements of the rake (fig. 8, a) and clearance angles (fig. 8, b) for 4 designs of twist drills – one design with a conical sharpening of the flank surface and three designs with a toroidal sharpening of the flank surface with varying the radius of the toroidal generatrix surface Rt (Rt min, 1.25 R, 2.5 R). The initial values of the angles for toroidal sharpening of the flank surface are: rake angle g = 30°, gN = 25°, when moving to a gash gp = 2°, clearance angle a = 8°, aN = 8°, °, at transition to gash ap = 22°. a b Fig. 8. Graphs of the dependence of the rake (a) and clearance (b) angles of various drill designs on the ratio of the length of the main cutting edge at the measurement point from the initial position, to the total length of the main cutting edge Based on the analysis of the graphs, it is found that drills with toroidal sharpening of the flank surfaces have a more uniform decrease in the rake angle from the periphery to the center. The nature of the change in the front and clearance angles of drills with toroidal sharpening of the rear surface is identical to the nature of the change in the geometric parameters of drills with conical sharpening. The rake angle g takes on the greatest values, and the clearance angle a is the smallest at the periphery of the drill. The range of variation of the rake angle decreased from [-18°; 25°] to [2°; 25°], which indicates a decrease in range by 86 %. With a decrease in the radius of the generatrix of the rear toroidal surface, a decrease in the intensity of a decrease in the front angle and an increase in the rear angle are revealed. This tendency makes the change in the sharpening angle of the cutting wedge from the periphery to the center more uniform. The range of changes in the sharpening angle of the cutting wedge decrease from [58°; 77°] to [56°; 68°], which indicates a decrease in range by 56 %. The design of drills with sharpening of the flank surface with a minimum radius of the generatrix has the best distribution of the rake angle and the rake angle has a positive value along almost the entire cutting edge. This will allow the use of such drill designs without additional sharpening in the center with performance indicators comparable to those of drills with sharpening in the center. A graph of the dependence of the sharpening angle of the cutting wedge b on the ratio of the length of the main wedge at the control point, measured from the initial position, to the total length of the main wedge is presented in fig. 9. According to the graph, it is found that the use of drills with sharpening of the flank surface with a minimum radius of the generative provides a uniform angle sharpening of the cutting wedge up to 0.45 of the length of the twist drill, precisely in the zone that is subjected to the most intense loading.
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