Hrechuk A. Increasing the efficiency of drilling of products from polymeric fibrous composites with blade drills with diamond inserts

Dissertation for the degree of a candidate of technical sciences (doctor of philosophy) in specialty 05.03.01 "Processes of mechanical processing, machine tools and tools" - V. Bakul Institute for Superhard Materials NAS of Ukraine, Kyiv, 2019. The actual scientific and technical goal of improving the efficiency of drilling holes in CFRP and GFRP parts has been solved by increasing of tool life through using of diamond drill bits and the decreasing of defect treatment by introducing a special drill bit design, the cutting part of which has additional cutting edges and provides cutting on reverse of the drilling. A complex defect criterion (Q) is propoused. It makes possible to determinate the defect of drilled hole at different areas of avoid and stratification, which may have a local character or evenly spread around the hole edge. This is possible due to the first used model of Kolding for predicting the stability of the drill during the processing of parts from carbon fiber. It was established that the drilling of carbon fibers and fiberglass with diamond drillings makes it possible to achieve 8 times the higher stability of the tool compared to carbide drills, and the wear of diamond drills occurs evenly on the back and front surfaces, and the carbide drills are much more intense on the rear surface leading to increase the contact area of back and the treated surfaces, and as a result to increase the defect of the openings. It was shown that reducing the defect of the aperture processing, namely, cutting off the voidness and damaged layer of the hole surface, as well as extending the wear range, which provides defective apertures at Q = 20 % - 25 %,, is due to the cutting processes in the reverse of the drill, using developed diamond drill with a special design with auxiliary cutting edges which are parallel to drill bit axis. It was established that the processing by diamond drillings minimizes the thermodestruction of the hole from 0.50 mm to 0.03 mm in comparison with the carbide drills and is accompanied by a reduction of the treatment temperature by 1.4 times in the processing of carbon sheet ((T = 41 - 49 С) and 3 times in the processing of fiberglass (T = 86 - 90 С). It has been experimentally established that the phenomena of contact interaction between the voidness of the drilled hole and the rotating drill characterize the value of the uncut fibers. The obtained empirical relationships between the signal of acoustic emission and the size of the voidness of the aperture allow to estimate the area of the formed uncut fibers during the process of drilling of carbon fiber and fiberglass. A diamond drill has been developed for efficient processing of holes in fibrous polymer composite materials, which is equipped with two symmetrically-located diamond-carbide plates. Developed practical recommendations for the use of developed diamond drills for the efficient processing of parts from carbon fiber and fiberglass. The pilot-production verification of the results of the dissertation work in the State Enterprise "Antonov" was carried out, namely the application of the developed diamond drill for processing of fiberglass and carbon fiber plastics allowed to increase the tool's stability in 3-5 times, to obtain 2 times lower damages to the surface of the hole and to avoid thermal degradation of the material being processed. in comparison with standard drill bits.