Experimental study on rotary ultrasonic machining (RUM) characteristics of Nomex honeycomb composites (NHCs) by circular knife cutting tools

Optimization of Milling Aluminum Alloy 6061-T6 using Modified Johnson-Cook Model

A new criterion to evaluate the machined surface quality of the Nomex® honeycomb materials

Nomex honeycomb core has been widely applied in aerospace industries due to its superior strength and rigidity. However, the machining defects of honeycomb core can deteriorate the bonding strength between honeycomb core and connective face sheet. This paper investigates the tearing defects formatted in milling process of Nomex honeycomb core. Firstly, a cutting force model is proposed to predict the milling forces under various tool entrance angles. Then, finite element simulation for machining honeycomb wall is conducted to reveal the formation mechanism of tearing defects. The accuracy of the model is verified by a group of experiments under different entrance angles and the relative error is below 25% in 1-direction and 20% in 2-direction. It is found that the formation of tearing defects is closely related to the deformation of honeycomb wall and the component of cutting force in direction parallel to wall. The tool entrance angle can be thus optimized based on the reduction of tearing defects. The optimized entrance angle of double wall is among 40° and 70°.

Formation mechanism of tearing defects in machining Nomex honeycomb core

Cracks generated in micro and meso-scales pose a potential threat to the full product. Numerous reports on microscale voids and cracks in Nomex honeycomb composites (NHCs) have focused on the process of co-curing and co-bond. Practically, substantial meso-scale cracks were introduced in the machining without sufficient attention. To fill this gap, the study explored a new phenomenon (i.e., transverse and longitudinal cracks) in meso-scales, with a special focus on formation mechanism and evolution. A meso-scale numerical model of NHCs was developed for the analysis of fracture inducing mechanisms in ultrasonic vibration machining (i.e., multi-source loading conditions). During model establishment and validation, not only the friction model of the cutter and NHCs was amended, but also the cutting force system was evaluated and compensated. Analytical and experimental validation indicated that the cell deformation and the peak value of the cutting force showed a reasonable agreement with the numerical results. Further understanding based on the numerical model can obtain the cracks initiation mechanisms that: (i) Transverse cracks are induced by longitudinal tensile stress, which is generated by tool vibration, while (ii) longitudinal cracks are induced by transverse tensile stress, which is caused by tool feed. The findings of meso-scale cracks not only enhance the significance of curing-induced microcracks and voids, but also provide theoretical guidance for the evolution of macroscopic defects after machining. 

Meso-scale cracks initiation of Nomex honeycomb composites in orthogonal cutting with a straight blade cutter

Simulation and experimental study of ultrasonic cutting for aluminum honeycomb by disc cutter.

Ultrasonic cutting with a disc cutter is an advanced machining method for the high-quality processing of Nomex honeycomb core. The machining quality is influenced by ultrasonic cutting parameters, as well as tool orientations, which are determined by the multi-axis machining requirements and the angle control of the cutting system. However, in existing research, the effect of the disc cutter orientation on the machining quality has not been studied in depth, and practical guidance for the use of disc cutters is lacking. In this work, the inclined ultrasonic cutting process with a disc cutter was analyzed, and cutting experiments with different inclination angles were conducted. The theoretical residual height models of the honeycomb core, as a result of the lead and tilt angles, were established and verified with the results obtained by a linear laser displacement sensor. Research shows that the residual height of the honeycomb core, as a result of the tilt angle, is much larger than that as a result of the lead angle. Furthermore, the tearing of the cell wall on the machined surface was observed, and the effects of the ultrasonic vibration, lead angle, and tilt angle on the tear rate and tear length of the cell wall were studied. Experimental results revealed that ultrasonic vibration can effectively decrease the tearing of the cell wall and improve the machining quality. Changes in the tilt angle have less effect than changes in the lead angle on the tearing of the cell wall. The determination of inclination angles should consider the actual processing requirements for the residual height and the machining quality of the cell wall. This study investigates the influence of the inclination angles of a disc cutter on the machining quality of Nomex honeycomb core in ultrasonic cutting and provides guidelines for machining.

Effects of inclination angles of disc cutter on machining quality of Nomex honeycomb core in ultrasonic cutting

The invention discloses an ultrasonic helical hole milling device which comprises a spindle support, an ultrasonic sleeve, an inner eccentric sleeve, an outer eccentric sleeve, an amplitude-change pole and a transducer located in the ultrasonic sleeve. The amplitude-change pole is connected with a hole forming tool through a spring chuck, and the hole forming tool is a milling cutter or a grinding wheel. The amplitude-change pole is connected with the transducer through an annular flange which is connected with the inner wall of the ultrasonic sleeve through an annular force sensor used for measuring axial and radial force borne by the annular flange. The ultrasonic helical hole milling device further comprises a helical hole-milling rotation driving device connected with the ultrasonic sleeve, a helical hole-milling revolution driving device connected with the outer eccentric sleeve and a feeding system for driving the spindle support to conduct feeding along the axis of the amplitude-change pole. The invention further discloses a machining method for conducting ultrasonic helical hole milling through the ultrasonic helical hole milling device. The ultrasonic helical hole milling device and the machining method have the advantages that the hole forming quality is high, hole forming quality consistency is good, and machining stability is good.

Ultrasonic helical hole milling device and machining method

\n Ultrasonic cutting with a straight blade is an advanced method for cutting Nomex honeycomb cores. However, crushing has generally been observed on the machining surface of the honeycomb core during ultrasonic cutting (UC). In this paper, to avoid crushing, a new blade-inclined ultrasonic cutting (BIUC) method is proposed to decrease the geometric interference between the cutting tool and the honeycomb cores. The cutting geometry systems of UC and BIUC with a straight blade are systematically established to study the effect of the cutting geometry on the machining quality. The crushing degrees caused by the major flank under different tool orientations in UC and BIUC are analyzed. The causes of crushing during the machining of the honeycomb core were revealed from the aspects of machining quality, cutting force, and geometric interference between the major flank and the material. Experiments involving the quantitative analysis of the crushing and cutting forces verify that the BIUC method is able to avoid crushing by controlling the cutting angle. This paper provides a new method for solving the crushing problem in machining honeycomb core with a straight blade.

A Novel Method of Blade-Inclined Ultrasonic Cutting Nomex Honeycomb Core With Straight Blade

The invention discloses an ultrasonic vibration drill hole tail end actuator which comprises a main shaft unit, an ultrasonic knife handle unit and a feeding unit. The ultrasonic vibration drill hole tail end actuator overcomes the defects of a traditional drilling technique, an ultrasonic vibration drilling technique is utilized for conducting drilling on aluminum alloy, titanium alloy, carbon fiber composite materials and other materials difficult to process through robots, especially for conducting drilling on small holes with the diameter being less than 6 mm, and the machining quality and efficiency are improved. A radial wireless transmission mode is adopted for the tail end of a rotor to transmit ultrasonic signals, interference with oil cylinder cutter movement and spindle rotation does not occur, a copper electrode penetrates through a spring rod inner hole to be connected with a knife handle inner copper electrode in cooperation with an elastic pin shaft in the knife assembling process so as to transmit ultrasonic signals, a carbon brush does not need to be replaced, device durability is improved, all power transmission devices are arranged in a main shaft, and a robot can achieve multi-angle drilling. Multiple ultrasonic knife handles can be replaced quickly, and machining efficiency is improved.

Ultrasonic vibration drill hole tail end actuator

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