The vertical surface is a common and typical characteristic structure among Nomex honeycomb core components. However, the conventional high-speed milling and ultrasonic cutting struggle to meet the high-quality machining requirements of a vertical surface. In this study, an ultrasonic trepanning method is proposed and a special ultrasonic trepanning tool is developed, aiming to improve the machining quality of the vertical surface. The trepanning quality of the vertical surface is further studied from the aspects of dimensional error and trepanning incision quality. Based on the kinematic characteristics of ultrasonic trepanning, a theoretical model of dimensional error in trepanning is established. Meanwhile, the influence of ultrasonic vibration on the trepanning process is analyzed, and the result shows that ultrasonic vibration significantly improves the equivalent elastic constant of the honeycomb core material. The theoretical model is proposed to predict the trepanning dimensional error, which is verified by experiment. The effectiveness of the ultrasonic vibration on the incision quality is verified by several experiments, and the quantitative analysis results demonstrate that ultrasonic vibration significantly improves the trepanning quality of the vertical surface.
GH4068 superalloy is a new type of nickel-based superalloy in the aerospace field. It is an important alloy material for the manufacture of aircraft tubular components and aero-engine hot-end components. These components need to be machined with good surface quality to meet their use requirements. New hybrid machining processes can improve the quality of surface finish compared to conventional machines. In this paper, ultrasonic assisted turning (UAT) technology was applied to the machining of GH4068 superalloy. The experimental system of UAT was established. Experiments of UAT and conventional turning (CT) of GH4068 superalloy were carried out to study the effects of cutting speed, feed speed, cutting depth and vibration amplitude on cutting force and surface roughness. The surface morphology of the workpiece and chip were observed. The experimental results show that Fx and Fy can be reduced by a maximum of 44% and 63%, respectively, and the surface roughness can be reduced by a maximum of 31% after adding ultrasonic vibration. Compared with CT, the UAT has a better machining quality, a more obvious chip-breaking effect, and a smaller chip bending radius, which guides the high-quality processing of the GH4068 superalloy.
Carbon fiber-reinforced plastic/titanium alloy (CFRP/Ti) stacks are widely used in the aerospace field based on their high strength to weight ratio and heat resistance. High-quality bolt hole assembly is critical for the safety of the aerospace industry. Reaming is a crucial process in precision machining and is extensively used to improve the quality of bolt holes. Due to the different properties of the material, machining with conventional reaming (CR) presents some challenges, such as tolerance variations across the hole group and difficulty in controlling thrust. In this paper, ultrasonic vibration is applied to the reaming process. A geometrical model of ultrasonic vibration reaming (UVR) was established to analyze its kinematic law. UVR experiments on CFRP/Ti stacks were carried out to study the influence of different ultrasonic amplitudes on reaming thrust and the influence of tool speed on thrust, dimensional accuracy, and surface roughness under optimal ultrasonic amplitude. The average thrust forces in UVR decreased by over 57% (Ti) and 40% (CFRP), respectively, compared to CR. The roughness of CFRP is reduced by 20% with UVR and 28% for titanium alloys. The surface topography of the holes is significantly improved by UVR. This work guides the manufacture of high-quality bolt holes for CFRP/Ti stacks.
Ultrasonic cutting is an advanced technology for processing Nomex honeycomb materials. The disc cutter is one of the most commonly used tools, whose wear and breakage state have an important impact on the honeycomb material machining process. Currently, the disc cutter lacks systematic characterization methods, and its tool wear laws are not yet clear. This paper conducts a wear experiment of the disc cutter in an ultrasonic cutting Nomex honeycomb core and proposes the attributes of cutting edge rounding (CER), flank wear VB, diameter reduction, and cutting edge breakage width to characterize the tool wear and breakage forms quantitatively. Moreover, the tool wear and breakage forms of the disc cutter are categorized, and the variation laws of the disc cutter wear and breakage characteristics are studied. The experimental study reveals that the wear forms of the disc cutter are mainly cutting edge dulling and flank wear. The CER and flank wear VB increase with increasing cutting length, and the wear mechanism is mainly abrasive wear. The breakage forms are mainly chipping and cracking breakage. The diameter reduction changed slowly, and the cutting edge breakage width tended to increase. The surface quality of the honeycomb gradually deteriorates with the increase of tool wear and breakage. The experimental results are important to study the tool wear mechanism of ultrasonic cutting of the Nomex honeycomb core with the disc cutter as well as tool design and manufacture.
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