Enabling Thin-Edged Part Machining of Nomex Honeycomb Composites via Optimizing Variable Angle of Disc Cutters.

Machining Nomex honeycomb composites (NHCs), which are widely-used materials in the aerospace industry, is an imperative process to obtain desired profiles. However, when machining NHCs to obtain a thin-edged surface, some problems can arise due to large cutting forces. To avoid these defects, a method of ultrasonic vibration machining with variable angles of the down milling disc cutter was proposed in this study. The processing principles and motion characteristics of this method were elaborated. A theoretical model of its cutting process was established. The principle of cutting force reduction was qualitatively analyzed based on the model, and an experimental validation was conducted. The results demonstrated that, due to a smaller swing angle in each pass, the proposed method could reduce the fractal dimension of the machined surface by 6.01% compared to 1° with 10° of angle in each pass. And severe machining defects were decreased. Additionally, comparing the process of the fixed 10° angle of ultrasonic vibration machining with the process of a 1° angle in a pass, cutting force can be significantly reduced by 33.5%, demonstrating the effectiveness of the proposed method which improved surface quality by reducing cutting forces.

Building of Longitudinal Ultrasonic Assisted Turning System and Its Cutting Simulation Study on Bulk Metallic Glass.

Bulk metallic glass (BMG) is a new kind of material which is made by rapid condensation of alloy. With excellent properties like high strength, high hardness, corrosion resistance, BMG is increasingly applied in mold manufacturing, weapon equipment and other fields. However, BMG is also one of hard-to-machine materials, which is arduous to be processed precisely and efficiently by the means of conventional cutting. Compared with conventional cutting, ultrasonic machining has a multitude of technological advantages such as reducing the cutting force, extending the tool life, etc. In ultrasonic machining, the ultrasonic electric signal is transformed into high frequency mechanical vibration on the tool, which changes the relationship between the tool and the workpiece in the process of machining. In this study, the longitudinal ultrasonic assisted turning (LUAT) system is established for processing BMG. Its resonant frequency and vibration characteristics are first simulated by modal analysis and harmonic response analysis, and then tested by displacement testing experiments, so that the suitable frequency and the amplitude for BMG turning can be selected and verified. On this basis, the two-dimensional turning finite element model is established to study the effect of ultrasonic vibration on cutting force under different cutting speeds. The research manifest that during the BMG turning, the assistance of longitudinal ultrasonic vibration can significantly reduce the average cutting force as well as the von Mises stress when the turning speed is below the critical turning speed. In addition, the tip of the tool contacts the workpiece discontinuously during cutting process which makes the instantaneous turning force in LUAT more periodic than that in conventional turning (CT).