Study On Formation Mechanism Of Dual-cavity Self-excited Oscillation Abrasive Flow Pulse Characteristics

In view of the fact that there is no effective methods to effectively process the inner surface of the cavity existing in the fields of optical devices,mould,automobile,aerospace and so on,this paper proposes a new polishing method:dual-cavity self-excited oscillation abrasive flow pulse characteristic polishing,which is short for dual-cavity self-excited oscillation abrasive flow polishing,which is based on the self-excited oscillation characteristics of fluid and soft abrasive flow machining.And it is suitable for polishing the inner surface of cavities,pipes and micro holes.In this paper,the numerical simulation and experimental verification of the flow field of the dual-cavity self-excited oscillation abrasive flow polishing technology are studied from the basic principle of the self-excited oscillation pulse characteristics,the material removal mechanism,the factors affecting the self-excited oscillation pulse characteristics and so on.The research contents are as follows:?1?Based on the knowledge of hydrodynamics such as fluid dynamics and fluid resonance theory,the principle of self-excited oscillation pulse characteristics is theoretically explained;the material removal mechanism in the dual-cavity self-excited oscillation abrasive flow polishing is deduced and analyzed,and the material removal model of self-oscillation abrasive flow polishing is determined;the influencing factors of material removal by pulse characteristic polishing method are determined?the velocity of the polishing liquid,the turbulence intensity,the shear force on the inner surface of the flow channel,and the abrasive concentration and grain size?;using the fluid network theory,a similar network model is constructed,the formula expression of the pulse frequency characteristic of the pulse characteristic of the self-excited oscillating abrasive flow is derived,and the structural parameters of the oscillating cavity that affect the intensity of the pulse characteristic are determined;the analysis is selected for numerical simulation.The dynamic model of the abrasive particle flow state is modified,and the turbulence model used in the numerical simulation calculation is modified,and the cavitation model is selected to study the mechanism of the special effect of the low-pressure large-flow self-excited oscillation pulse.?2?The simulation of the self-excited oscillation abrasive flow is carried out by FLUENT.The effectiveness of the self-excited oscillation abrasive flow polishing method is theoretically verified.And the structural parameters of the self-excited oscillation cavity are optimized by simulation.It is determines that when d₂/d₁=1.6,d₃/d₂=1.6,L₁/D₁=0.5,L₂/D₂=0.5,the shock pulse effect is the strongest;it is determined through numerical simulation that d₁=6mm,d₂=9.6 mm,d₃=15.36mm,L₁=40 mm,L₂=50mm,D₁=80 mm,D₂=100mm,?=60°is the optimal structure parameter of self-excited oscillation cavity and runner;the effects of process parameters?inlet speed,inlet pressure,abrasive particle concentration and abrasive particle size?on turbulence intensity and wall shear force are simulated and analyzed.The attenuation of velocity,turbulence intensity and wall shear force are also analyzed.?3?According to the requirements of polishing experiments,dual-cavity self-excited oscillation generators with different structural parameters is designed and manufactured,and the construction of the entire dual-chamber self-excited oscillation abrasive particle polishing experiment platform is completed.The effectiveness of self-excited oscillating abrasive particle flow polishing is confirmed according to pressure fluctuation monitoring experiments,and the polishing results of dual chambers are significantly better than that of single cavity.Through the research and analysis of the inner wall surface polishing experiment of stainless steel pipe,the surface roughness of the inner wall of the stainless steel pipe at the outlet of the lower nozzle is reduced from452nm to 42 nm after 10 hours of processing under the condition of double-chamber self-excited oscillation.On the premise that there is only a single-stage oscillation cavity,the surface roughness of the inner wall of the stainless steel tube at the exit of the lower nozzle is reduced to about 45 nm and it takes 12 hours to achieve it,which verifies the effectiveness and feasibility of the dual-cavity self-oscillation polishing.?4?Through the dual-cavity self-oscillation abrasive flow polishing process experiment,the influence of various process parameters in the material removal model on the processing effect is verified.The influences on the variation value of the roughness obtained from the results of this experiment are,from large to small,the inlet velocity,the inlet pressure,the abrasive grain concentration and the abrasive grain size.