Research And Experiment On Multi-frequency By Ultrasonic Excitated Processing Method

The hard brittle materials such as ceramics have been widely used in many fields because of their high melting point,high hardness,high wear resistance,oxidation resistance and low density,which also brings more difficulties to processing.In order to solve the disadvantages of low efficiency,high cost and poor machining quality in the traditional machining method,this dissertation applied the technology of multi-frequency by ultrasonic excited to the processing of ceramics.The processing method is based on the ultrasonic processing,through the introduction of a free-mass with the low-frequency vibration,and makes high and low frequency vibration together to complete the cutting processing.This dissertation first introduced the motion law and characteristics of multi-frequency by ultrasonic excited processing system.On this basis,the changes of the displacement and velocity of the free-mass,the outlet end of horn and the drill in the collision process were analyzed,and it is found that free-mass plays an important role in the process of accumulation and transfer of energy,which can effectively transfers energy to the drill.The mathematical model of the processing system was established,and based on one-dimensional longitudinal vibration theory and impact vibration theory,the dynamic stress equation of the drill was obtained,which the thickness of free-mass is related to the dynamic stress of the drill,and both of them are positive correlation.Through the indentation fracture mechanics model,the mechanism of material removal was studied,and it is found that the formation velocity,the number and the expansion velocity of the crack increase with the increase of the dynamic stress of the drill.With the motion analysis of the free-mass,the vibration frequency formula of free-mass is obtained,and it is found that the vibration frequency is related to the thickness,and when the vibration range remains unchanged,the higher the thickness,the higher the vibration frequency;and according to the law of conservation of energy,it is found that the average vibration power of the drill can reach 3310 W,which is 15 times higher than mechanical power of the transducer,which shows that high frequency vibration can be converted into low frequency and high power mechanical impact under the action of free-mass.The vibration frequencies of different free-mass were measured by frequency measurement equipment,and the experimental results show that the free-mass is vibrating at different frequencies,and the vibration frequency increases with the increase of thickness;besides the average vibration frequency of free-mass of 4.5 mm in thickness is about 3 times the free-mass of 3.5 mm in the thickness,which the results of the experiment correspond to the theoretical analysis.Based on the spring-mass model,the motion process of free-mass is analyzed,and it is found that the free-mass can greatly improve the vibration energy of the drill;and in order to verify the influence of free-mass on the processing effect,the experiment of processing ceramics was carried out,and the material removal rate under different thickness of free-mass was obtained.The results show that the material removal rate of the free-mass of 4.5 mm can increases by more than 5 times compared with the conventional ultrasonic machining,and the surface damage is avoided;and with the increase of the thickness,the material removal rate increases,and the growth rate is faster and faster,which average growth rate reaches 91(mg/min)/mm.In order to study the change rule and influencing factors of material removal rate,the orthogonal experiment was carried out on three factors of thickness,external diameter and processing time,and it is found that the range of thickness is maximum,which is 77.7 mg/min.The results show that the thickness has the most significant effect on the material removal rate,and the greater the thickness,the higher the material removal rate;the material removal rate increases linearly with the increase of the external diameter;the longer the processing time,the higher the material removal rate,and the faster growth rate.