Muhammad Helmi Nur Widiyarto

Experimental investigation of the machined surface waviness, vibrations and cutting forces in peripheral milling

Abstract. This paper presents an experimental investigation on the intrinsic relationship among the machined surface waviness, vibrations of both the spindle head and workpiece, and cutting forces in peripheral milling. A series of well designed cutting tests were carried out with different helical end mills under different cutting parameters on a vertical machining centre. The 3D cutting forces were recorded by a Kistler dynamometer, and the vibrations of the spindle head and workpiece were monitored by accelerometers during the cutting process. The surface topography and surface waviness were measured by a Form Talysurf PGI after the cutting process. All of the recorded signals were carefully analyzed and compared to each other. The results demonstrate that the amplitude of the surface waviness is correlated to the amplitude of the vibrations or chatter of both the spindle head and the workpiece, and the surface waviness is dominant at the spindle frequency, regardless of chatter occurrence in the cutting process.

Evaluating the structural dynamics of a vertical milling machine

Many CNC machine tools are used in general-purpose machining environments, resulting in a wide variety of machining conditions being present at the cutting tool. The requirement for guide-way to bearing clearances and limited mass of the structural elements results in a limited stiffness between the cutter and workpiece. This, coupled with the inertial effect of the structural element masses and drive-system, can lead to complex vibration modes that are affected by the axis positions and machine tool configuration. Therefore, the study of the dynamic behaviour of the machme is important in determining the response of the machines structure to an external force. In this paper, the results and the setup of an experimental modal analysis performed on a vertical milling mache at the Ultra Precision Engineering Centre of the University of Huddersfield are presented. Ths work will be used as the foundation to carry out further activities into the modelling and correction of vibration-induced machining errors on CNC machine tools.

Structural analysis and characterisation technique applied to a CNC vertical machining centre

There is a requirement for improved 3D surface characterisation and reduced tool wear, when modern computer numerical-controlled (CNC) machine tools are operating at high cutting velocities, spindle speeds and feed-rates. This research project investigates vibration-induced errors on a CNC vertical machining centre under dynamic conditions. A model of the machine structural dynamics is constructed using the Finite Element Method (FEM) for the comprehensive analytical investigation of the machine vibration behaviour. The analytical model is then validated against the measured results obtained from an experimental modal analysis (EMA) investigation. A correlation analysis of the simulated and experimental modal analysis results is undertaken in order to improve the accuracy of the model and minimise modelling practice errors. The resulting optimised model will need further sensitivity analysis utilising parametric structural analysis and characterisation techniques in order to identify a potential for vibration reduction using passive methods.