Microstructure Transformation and Refinement Mechanism of Undercooled Cu-Ni-Co Alloy Based on Simulation of Critical Cutting Speed in Ultrasonic Machining

Both Cu60Ni38Co2 and Cu60Ni40 alloy were naturally cooled after rapid solidification from the liquid phase.The transformation law of the microstructure characteristics of the rapidly solidified alloy with the change of undercooling(ΔT)was systematically studied.It is found that the two alloys experience the same transformation process.The refinement structures under different undercoolings were characterized by electron backscatter diffraction(EBSD).The results show that the characteristics of the refinement structure of the two alloys with low undercooling are the same,but the characteristics of the refinement structure with high undercooling are opposite.The transmission electron microscopy(TEM)results of Cu60Ni38Co2 alloy show that the dislocation network density of low undercooled microstructure is lower than that of high undercooled microstructure.By combining EBSD and TEM,it could be confirmed that the dendrite remelting fracture is the reason for the refinement of the low undercooled structure,while the high undercooled structure is refined due to recrystallization.On this basis,in the processing of copper base alloys,there will be serious work hardening phenomenon and machining hard problem of consciousness problems caused by excessive cutting force.A twodimensional orthogonal turning finite element model was established using ABAQUS software to analyze the changes in cutting speed and tool trajectory in copper based alloy ultrasonic elliptical vibration turning.The results show that in copper based alloy ultrasonic elliptical vibration turning,cutting process parameters have a significant impact on cutting force.Choosing reasonable process parameters can effectively reduce cutting force and improve machining quality.

Research on the Characters of the Cutting Force in Vibration Cutting Particle Reinforced Metal Matrix Composites SiC_p/Al

In this paper, turning experiments of machining particle reinforced metal matri x composites(PRMMCs) SiC p/Al with PCD tools have been carried out. The cutting force characteristics in ultrasonic vibration turning compared with that in com mon turning were studied. Through the single factor experiments and multiple fac tor orthogonal experiments, the influences of three kinds of cutting conditions such as cutting velocity, amount of feed and cutting depth on cutting force were analyzed in detail. Meanwhile, according to the experimental data, the empirica l formula of main cutting force in ultrasonic vibration turning was conclude d. According to the test results, the cutting force is direct proportion to cutt ing depth basically according to the relation between cutting force and other fa ctors, which is similar to that of common cutting, so is the feed rate, but the influence is not so big. The influence of cutting speed is larger than that of f eed rate on cutting force because the efficient cutting time increases in vibrat ion cycle with the increase of cutting speed, which causes cutting force to incr ease. The research results indicate: (1) Ultrasonic vibration turning possesses much lower main cutting force than that in common turning when adopting smaller cutting parameters. If using larger cutting parameters, the difference will inco nspicuous. (2) There are remarkable differences of cutting force-cutting veloci ty characteristics in ultrasonic vibration turning from that in common turning m ainly because built-up edge does not emerge in ultrasonic turning unlike common turning in corresponding velocity range. (3) In ultrasonic vibration cutting, t he influence of cutting velocity on cutting force is most obvious among thre e cutting parameters and the influence of feed is smallest. So adopting lower cu tting velocity and larger cutting depth not only can reduce cutting force effect ively but also can ensure cutting efficiency. (4) The conclusions are useful in precision and super precision manufacturing thin-wall pieces.

Effects of process parameters on periodic impact force exerting on cutting tool in ultrasonic vibration-assisted oblique turning

During ultrasonic vibration-assisted machining,the large impact force induced by tool-workpiece reengagement(TWR)is an important factor that affects tool chipping.However,mechanical analysis into process factors that affect the impact force and their influencing mechanisms are insufficient.Herein,a prediction model for the instantaneous cutting force during both TWR and the stable turning process,which depends on the process parameters and material properties,is firstly proposed based on the kinematic and dynamic analysis of ultrasonic vibration-assisted oblique turning(UVAOT).The results calculated using the developed cutting force model agree well with the experimental results presented in the literature.Next,the linear change law of the instantaneous cutting force with cutting time during the actual TWR is clarified using the proposed model.The effect of the UVAOT process parameters on the average impact force during the periodic TWR process is discussed,and the influence mechanism is analyzed from the perspective of mechanics.A positive linear correlation is discovered between the feed speed and average impact force.The ultrasonic amplitude and cutting speed do not significantly affect the average impact force of the new sharp cutting tools.These findings are consistent with the experimental observations of tool chipping and are applicable to select process parameters for reducing tool chipping during UVAOT.