Modeling and Simulation of the Drivetrain of a Metal Lathe

Vibrations in turning machining are one of the most common sources of problems. Bad quality finishing, decrease of the tool life, dimensional errors, and noise are some of the issues generated by these vibrations. To understand the role of each component, this work presents a model of a metal lathe including its drivetrain, and simulates it during the internal turning operation. The drivetrain is composed by an electric motor connected to the spindle through a pulley and belt transmission. The spindle was modeled as a rotor supported by rolling bearings, while the chuck with jaws and the workpiece were considered to be rigidly attached to the spindle. The interface between the workpiece and the tool was modeled considering their relative displacement and the machining condition, thus generating a set of cutting and drag forces that varies during the operation. The tool holder was modeled by three-node finite volume beam elements that are attached to the turret. The turret was connected to the machine frame through a total joint (configured as prismatic). This model was implemented in the dynamic simulation software MBDyn and a module was developed in C++ to mimic the interaction between workpiece and tool. Different configurations of the machine were tested, such as the diameter of the tool holder and the rotation speed of the spindle, and their influence on the drivetrain is reported.