Theoretical study of influence of prestressed reinforcing elements on stiffness and damping of composite portal structures for metal-cutting small-sized machine tools

Background. In this paper, the authors numerically evaluate the effectiveness of the previously stated technical solution to increase the rigidity of one of the basic units of a small-size milling machine - the gantry. Materials and methods. The investigated portal has dimensions 90x300x450mm and is a molded composite structure with studs in its columns as reinforcing elements. The studs embedded in the composite matrix are in a state of elastic axial tension. The calculations were carried out using finite element modeling method. To investigate the effect of stud preload on the stiffness of the structure, a series of static calculations have been carried out, where the preload value is varied. Results. The simulation results show that the use of preloaded elastically preloaded stud reinforcement results in stiffness gains ranging from tens of percent to 4,7 times, in the longitudinal direction (X axis of the machine) and up to 47% increase in the damping capacity of the structure. It is demonstrated that the increase in rigidity is nonlinearly related to the generated axial force of elastic tension of the studs and can vary in a wide range, which allows approaching and even surpassing the rigidity index of more massive and several times more metal-intensive portal structures of small-sized machines. The obtained increases in rigidity are explained by the authors as a consequence of creating a stressed connection of the portal with the bed, which provides an increase in the friction force and the force of pressing the portal to the base of the machine. The dependence of the portal rigidity on the tension of the studs is revealed and graphically shown, and the function of the dependence of deformations on the tension in analytical form is obtained. Conclusions. The proposed technical solution is promising for the small-sized machine tool industry and allows creating machine units with increased rigidity, damping and reduced metal consumption.