Mylokost I. Improving the quality for drilling holes in thin-walled products with orthotropic carbon fibers

The dissertation is devoted to the improvement of the holes quality in the PCM type of carbon fiber and fiberglass by reducing the defects of carbon and fiberglass during their drilling through the development of tools for reverse drilling. The features of carbon and fiberglass machining were analyzed in the paper, and the significant difference of cutting metals and PCM was shown. The influence of the tools geometry to the problem of separation of composite materials during the drilling and to the accuracy and deviations form, the processing temperature of cutting were analyzed. For the first time a scheme of reversing drilling of carbon and fiberglass taking into account the characteristics of the materials that can increase the stability and reduce the probability of defects is proposed. To implement the reverse drilling the reverse drill and a device which provides the reverse of rotational motion of the drill was designed. It was established that the maximum wear h = 0,2 mm for reversing drills with n = 480 rev/min is achieved after cutting of 99 holes, with n = 880 rev/min - 89 holes, the unicast drilling by reverse drill (n = 480 rev/min ) - 49 holes, for stepped drill - 65 holes. Experimentally proved that the increase of main angle in plan leads to increasing of wear and reducing drills stability. It is established that the use of reversible drill holes reduces the deviations from roundness processed by 18% and lowers the temperature in the cutting zone at 2-3 °C compared with step drill. Established that the increasing the plan angle during reverse drilling increases the temperature in the cutting zone on 1-2,5°C. Practical and theoretical results were implemented in production and educational process.