Study Of Near Wall Area Micro-cutting Mechanism And Control Method For Softness Abrasive Flow Finishing

During the course of mold manufacture, lots of heteromorphous surfaces are involved,which are of complicated structure and tiny scale, and can be defined as structural surface.Owing to special profile of structural surface, its finishing cannot be realized by traditionalmethods. Aiming at the problem, several fluidic finishing methods are put forward, but thefinishing system structure of these finishing methods is the biggest drawback for increasingmachining precision, so the satisfied finishing results cannot be obtained by these methods.In allusion to the problem, a new no-tool precision finishing method based onsolid-liquid two phase softness abrasive flow (SAF) is brought forward in this paper. Basedon this method, realizable k-ε model is used to describe the flow field of SAF, and therealizable k-ε model is modified by analyzing the motion characteristics of SAF in the nearwall area. The flow characteristic of SAF is numerically simulated by CFD, and based on thesimulation results, observational experiment of particles motion has been carried out. Finally,SAF experimental platform is constructed, and the finishing experiment which oriented tomold structural surface can be realized. Main work of this dissertation is shown as follows:(1) Realizable k-ε model has been chosen to describe SAF compared to standard k-εmodel, because the former model can be better reflect the characteristics of jet flow, free flowand the flow in complex passage. Analyzed the flowing features of SAF in near wall area, anddissipation rate equation of realizable k-ε model is modified based on the analyzing results;the new model can reflect the turbulence dissipation which caused by the finishing in the nearwall area previously, so that the finishing characteristics of SAF can be accurate described bythe model. Based on an analysis of the forces acted on the particles, micro-cutting mechanismof SAF finishing method has been studied.(2) Based on realizable k-ε model, discrete phase model (DPM) is used to establish thekinetic model of SAF, and influencing factors which effect the finishing are simulated. TakingU-shaped restrained flow passage as instance, the variation trends of SAF turbulentparameters and flow passage pressure distribution with different inlet velocities are studied,and motion trails of particles are also simulated. Numerical simulation results derive that pressure decrement of solid phase in flow passage is inversely proportion to inlet velocity, andmotion trails of particles are disorderly and stochastic, which are the sufficient conditions ofSAF finishing. The automobile mold is simulated as a typical structural surface, and SAFdynamic pressure, velocity and turbulent dissipation distribution with different volumefraction are acquired, effectiveness of SAF finishing method has been proved by thesesimulation results.(3) Based on the simulation results, SAF has been mixed with different proportioncutting fluid, dispersing agent and water, and observational experiment of particles has beendesigned. High-speed camera is used to observe the motion trails of solid phase, and velocityvector and vorticity of SAF flow field are obtained by PIV. Particles observational experimentshows that particle motion satisfied requirements of SAF finishing, and feasibility of SAFshould be proved theoretically.(4) Finishing platform which oriented to mold structural surface has been constructed,this platform can make water pump speed governing accurately, so exact transition of SAFflow regime can be realized. Experiment results show that SAF method can improve surfacequality of mold structural surface without change the morphology, and the trace of machiningcan be eliminated. After finishing, Ra of inlet is0.312μm, Ra of outlet is0.556μm and theweight of workpiece reduced0.2g. Experimental results have demonstrated the effectivenessof SAF finishing method.(5) Hardness and size of particles, collision angles between particle and surface, andfinishing time are analyzed based on Preston equation; and the equation has been improved tosuit for SAF finishing. Removal model of SAF finishing is derived based on the improvedequation, and material removal by this finishing method can be obtained.