Alibraheemi M. Providing rational conditions for abrasive cutting of composite carbon pieces on parallel kinematic machines

The object of the study is the process of machining of carbon-carbon pieces with abrasive tool on a parallel kinematic machine. The dissertation is dedicated to the solution of the scientific and applied task of improving the quality of cutting of carbon-carbon composite pieces on the basis of the establishment of regularities of the formation of the surface layer under the influence of an abrasive tool due to ensuring rational conditions of abrasive cutting by a manipulative system of a parallel kinematic machine. A physical model of the interaction was developed and a mathematical description of the thermal phenomena that caused deformation of the instrument was proposed. It is established that excess heat will cause a drastic temperature increase on the periphery of the instrument and, accordingly, will lead to its deformation, resulting in a deterioration in the quality of machined surface, and the width of the cutting will increase. It has been established that with increasing time of machining, the density of sticking of cutting products on the surface of the wheel is increasing, and the removal volume of material decreases. This reduction is due to elastic deformations in the technological system, which increases with the growth of cutting forces. Thus, changing the profile of the abrasive wheel leads to a decrease in the productivity of machining, growth of elastic deformations, changes in the quality of the machined surface. It has been proved that in order to overcome these negative phenomena it is necessary to increase the stiffness, ensuring its rational value when the state of the abrasive wheel is being changed. A new technical solution of parallel manipulator with kinematic redundancy was proposed, an analysis of its kinematics was carried out and the spatial stiffness matrix was established. It has been established that the proposed parallel manipulator possesses with increased stiffness as compared to fully parallel manipulators, and the utility of its application for abrasive machining was shown. The proposed machine essentially changes the stiffness characteristics of the technological system, which allows not only to improve the accuracy of cutting, but also reduce the contact spot and heat dissipation in the cutting zone. Measurements on the manufactured model of the machine experimentally confirmed that the stiffness of the proposed parallel manipulator is 16-28% higher as compared to pentapod manipulator. The economic validation has confirmed, that the use of the proposed technical decisions allows to reduce machining costs by 25–30%.