Research On Gas-liquid-solid Three-phase Abrasive Flow Processing Method And Microbubble Enhancement Effect

Monocrystalline silicon,functional crystal,optical glass are information materials and widely used in the field of electronic industry.Surface quality of materials determines the reliabilities and performances of semiconductor equipment.Softness abrasive flow has been successfully used in the processing of complex structural surface.Owing to the restrictions of processing tool and equipment structure,SAF method exhibits low processing efficiency,especially for the above hard-brittle materials.In view of the merits of SAF,it is greatly significant to address the application in the fields of information materials processing.To resolve the above problem,a gas-liquid-solid three phase processing method is proposed.Firstly abrasive flow motion in the near-wall region is analyzed,and turbulence induced by bubbles is modelled;then,particle-wall contact effect,single bubble motion,and abrasive flow motion are modelled,and processing characteristics are analyzed through numerical solution method;finally,observation research is studied through particle image velocimetry,and the effectiveness of the proposed method is validated through comparison processing experiments.The main research contents are conducted as follows.(1)Analyses of abrasive flow optimal motion in the near-wall region are conducted based on fluid layering theory.Fluid turbulence model which can describe the effect of bubbles is studied.Abrasive flow motion is modelled in three respects: abrasive flow motion is modelled based on computational fluid dynamics coupled with discrete element method(CFD-DEM);creating the bubble motion model based on the characteristics of bubble collapse in constrained flow-path;three phase abrasive flow motion is modelled based on computational fluid dynamics coupled with population balance model(CFD-PBM)which can describe the variation of bubble scale.Finally,the processing mechanism of three phase abrasive flow is analyzed based on force analysis of particles.(2)Discrete element model of swirling flow flow-path is created,and the semi-implicit method for pressure-linked equations is adopted to deal with the CFD-DEM model,and the dynamic distribution and evolution law of particle-wall collision in swirling flow field can be obtained.On this basis,the particle-wall collision characteristics in different flow patterns are studied,and the influences of flow-path key scale and fluid viscosity on the particle-wall collision distribution and material removal rate are analyzed.Results show that the inlet diameter will greatly influence the uniformity of particle-wall collision,and an optimal value can be obtained with the increase of inlet diameter.The mechanism for fluid viscosity to affect material removal is different with the variation of abrasive flow patterns,and the uniform processing can be more easily obtained in the low viscosity fluid.(3)The enhancement effects of microbubbles are studied in microscopic and macroscopic views.Three dimensional swirling flow-path is simplified based on the flow-path similarity criterion,and the bubble interface tracking model can be solved by numerical method.The processes of bubble movement,deformation and collapse are obtained,and the relations between jet strength and fluid viscosity can be quantitative analyzed.CFD-PBM coupled model is solved by numerical method,and bubble collapse distributions are described by bubble scale distributions.The influences of fluid viscosity on the bubble collapse distribution,particle turbulence kinetic energy,particle dynamic pressure are studied.Collapse jet can effectively strengthen local particle kinetic energy;Collapse jet can evolve easily in low viscosity fluid;bubble collapse is violently in the initial constrained flow-path.Specific area on the workpiece can be processed through designing the swirling flow-path.(4)Based on the numerical analysis results,validation experiments are conducted.Particle image velocimetry is used to analyze local abrasive flow and macroscopic abrasive swirling flow in the near-wall region.Results show that the scales and directions of turbulence vortices present random distribution;the velocities of particles are increased obviously after bubbles injection,the velocities mainly range from 15.00 m/s to 17.00 m/s,the maximum can reach 20.00 m/s;there are low velocity region,velocity strengthen region and velocity dissipation region in the macroscopic velocity field,which accord with the simulation results.Paint flow display method is adopted to validate the effectiveness of swirling flow.Processing results show that the bubble injection can effectively improve the efficiency,and the average roughness can reach 2.84 nm;three phase abrasive flow method can effectively avoid the deep scratches and surface damages.