| Due to the excellent mechanical properties,high temperature resistance,corrosion resistance low thermal expansion coefficient,etc.,carbon fiber reinforced plastics(CFRP)can both be a structural component to bear the load and play a role as a functional material,which makes it be widely used in our country's strategic industry such as missiles,satellites,warship,radar,drilling platform for oil and gas as well as other facilities in our daily life like sports equipment,rail transit and construction.However,as one of the typical hard-to-cut materials,carbon fiber reinforced plastics parts are prone to induce defects as delamination and burr,and severe tool wear has been found as well.In this paper,a study on rotary ultrasonic machining of CFRP is carried out on the problem of hole quality,and the main researches are as follows:Firstly,study on the material removal mechanism and advantages of rotary ultrasonic machining.Through the comparison of machining processes,the materials removal process in rotary ultrasonic machining and conventional grinding is studied,and the mechanism of ultrasonic vibration during the machining process is identified.According to the experimental results and literature research,several kinds of typical defects in machining is summarized.Then,the experimental platform of rotary ultrasonic machining is established,and the drilling tests in both methods of machining are conducted.A new method of defective angle measuring for evaluation of surface ply delamination is proposed.Experimental results in the two drilling methods are compared in several aspects,including the extent of surface ply delamination,surface quality,chip morphology,and tool life.Result shows that compared to the conventional grinding,rotary ultrasonic machining has changed the modes of material removal and destruction,and increased the contact effects between the abrasive and materials,which makes it easier to cut the fiber,gets a better machining quality,has longer tool life as well.Secondly,a study of machining process of CFRP in rotary ultrasonic machining is carried out.The orthogonal experimental method is introduced and then designed and carried out by selecting several processing parameters,which include ultrasonic vibration amplitude,feed rate and spindle speed.After the experiment,effects of processing parameters on the surface quality is analyzed,and the best surface quality with Ra value of 1.187?m and 1.171?m is obtained by optimization of processing parameters.Finally,research on the controlling strategies of interlaminar delamination.Models for critical thrust force and cutting force are developed respectively,and factors causing interlayer delamination is analyzed.Basing on the analysis,some experiments of interlayer delamination controlling strategies are designed and carried out.After the experiments,the influence of different processing parameters on the interlayer delamination is discussed.Result shows that compared with the conventional grinding,the interlayer delamination caused by rotary ultrasonic machining is thinner,and increasing the spindle speed,reducing the feed rate,drilling with a support or using various feedrate can alleviate the extent of delamination.Particularly,drilling with a rigid support and using various feedrate completely eliminates the delamination defects.Through theoretical analysis and experimental researches,the mechanism of ultrasonic vibration in drilling process and the machining parameters of optimal surface quality is obtained in this paper,and delamination controlling strategies have been given as well,which provide a guidance and reference for CFRP drilling technology. |
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