Interactive approach in improving rigidity of lathe structure

Abstract

During the machining process, the machine tool structural member experiences a different types of forces in its body. These forces must be resisted by the machine structure and in particular the bed and column in a machining center. In case of turning operation, the machine structures undergo bending and twisting in its member, which leads in causing the tool to deflect from its desired position. This results in reduction of set depth of cut at the tool leading to work piece in accuracy, decrease in machine productivity and even cause machine vibrations. Hence it is desired to ensure maximum rigidity at the machine interface for optimum operation. The rigidity is an important factor to evaluate the characteristics of machine tools. One way of decreasing the structural deformations is by increasing the section sizes and or increase wall thicknesses. This causes undesirable increase in weight of the structure and also leads in several trial and error methods for desired optimum operation. In this paper, an alternate method is proposed in which effective deflection at the tool may be decreased by locating shear center of the bed structure near to the machining interface. This helps in minimizing twisting moment and aids in improving rigidity. In this paper, the location of shear center for different geometries having outer section in semi- circular and triangle shape, which defines the cross section of the bed structure, are carried out through analytical method. The shear center locations for these sections are compared with ANSYS for validation. Further, the actual model of the lathe machine is created, wherein the static analysis is carried out to find the distance between the machining interface and shear center. From its analysis part, initially radial force is found for all the section and discussed the importance of these values in machine rigidity.