Study on Surface Generation Mechanism of Two-dimensional Ultrasonic Vibration Assisted Grinding of Nano-ceramic
|School||Henan Polytechnic University|
|Keywords||Nano-ceramics Two-dimensional ultrasonic grinding Surface generationmechanism Trajectory Force ratio Acoustic emission monitoring|
Nano-ceramic with high strength, high fracture toughness and dense structure toimprove the machinability of ceramic materials. But the machined surface damagecaused by the inherent brittleness of it is still a problem that precision or ultra-precisionmachining must be resolved. Research shows that the two-dimensional ultrasonicvibration grinding (TUVG) can expand the plastic processing domain of hard and brittlematerials., improve the quality of the machined surface. In order to explore the effect oftwo-dimensional ultrasonic vibration in the nano-ceramic grinding, the paper study thesurface generation mechanism of nano-ceramic in TUVG. The main work can besummarized as follows:1、Based on the kinematic analysis of abrasive in TUVG. Kinematic model of twoadjacent abrasive has been established in the TUVG. Simulation Analysis of trace ofabrasives have been made. The results showed that: the separation characteristics ofTUVG will be strengthen by reducing the wheel radius, increasing ultrasonic amplitudeor improving the ultrasonic vibration frequency. The effect of wheel radius, feed rateand cutting depth on the motion law of single grit on the arc in TUVG have beenanalyzed. The results showed that: In the case of constant spindle speed, reduce wheelradius will shorten the effective contact arc length, reduce notch spacing, increase themaximum un-deformed cutting depth of single grit and increase interference times oftwo adjacent abrasive. The influence degree of workspace speed on abrasive movementtrajectory will increase with the wheel radius decreases. The maximum un-deformedcutting depth of single grit will increase with the work-piece speed increase. Reduce thecutting depth will shorten the effective contact arc length, reduce the maximumun-deformed cutting depth of single grit and increase interference times of two adjacentabrasive.2、Based on the elasticity, Similar model of indention stress field has beenestablished in TUVG. Researched on the effect of force ratio to the indentation stressfield. The results showed that the direction of the maximum principal compressivestress skewed to the front of abrasive with the force ratio increased. Model of themedian crack azimuth under grits has been established in TUVG. The effect of two-dimensional ultrasonic vibration on the direction of median crack has been studied.The results showed that: increase force ratio (or reduce the grinding force ratio) willreduce the median crack azimuth, and conductive to the plastic shear removed ofceramic materials. Based on the momentum theory, Mathematical model of grindingforce ratio of single grit in TUVG on the contact arc have been established. The forceratio on the different position of the contact arc has been analysised. The results showedthat: two-ultrasonic vibration can reduce the grinding force ratio and increase theproportion of shear removal. So reduce the grinding force. The experiment of grindingforce in TUVG has been done to confirm it.3、Based on the kinematic analysis of abrasive in TUVG. Studied the effect oftwo-dimensional ultrasonic on the quality of grinding surface. Mathematical model ofchatter density. The effect of two-dimensional ultrasonic vibration on chatter density ofsingle abrasive has been studied. The results showed that the chatter density in thegrinding surface is proportional to the ultrasonic vibration frequency and inverselyproportional to the work-piece feed rate. Single grain notch model has been establishedto study the effect of two-dimensional ultrasonic vibration on machined surfaceroughness. Two-dimensional ultrasonic vibration reduced the overlap of the sameabrasive notch or increased the degree of interference between adjacent abrasive notch.Thus reducing the machined surface roughness. The result has been verified by theTUVG surface roughness test of nano-zirconia ceramic. Acoustic emission (AE)monitoring testing of the TUVG has been made, to explore the feasibility of AEtechnique in TUVG process monitoring. Experimental results showed that the greater ofthe RMS value, the smaller of the grinding force and the surface roughness under thesame no-spark grinding times. In the case of the other parameters constant, the smallerof the RMS value, the greater of the grinding force and the surface roughness underdifferent no-spark grinding times.