| Moulds are the important technological equipment during the process of parts forming. The application field of moulds expanded day after day. With the intense market competition the development trend of moulds appeared large scale, complexity and precision. Accordingly the structured surface such as the groove, the groove, the hole and the slot, that existed in moulds, is difficult for contact processing because of size and shape. In order to solve the problem in reality the method of chemical-aid softness abrasive flow polishing was proposed according to the structured surface of moulds.The phase of chemical-aid softness abrasive flow polishing can be divided into chemical polishing and softness abrasive flow polishing. Chemical polishing is easy to operated and free of the restriction of the shape and size. In the same time chemical polishing would remove the mechanical nick layer and the stress layer of parts. The surface of the part after the chemical polishing can be machined by the soft abrasive flow more easily, because bonding capability of the surface atoms can be reduced by chemical reactions. Softness abrasive flow polishing could be regarded as the supplement of chemical polishing. It would remove the unsolved metal oxides on the surface and clean the residual chemical liquid. In order to coordinated the two stages the process and the machining mechanism should be researched. The main content in this paper was as the following.(l)Turbulence characteristics in the process of soft abrasive polishing were researched by the application of numerical simulation. To get detailed information about the turbulence, large eddy simulation and Reynolds-averaged simulation were put into use. The geometry model of numerical simulation was established according to the M shaped flow channel after the analysis of the characteristic of LES and κ-ε model that belonged to Reynolds averaged simulation. Physical parameters in flow channel were gotten by the adoption of Large eddy simulation and κ-ε model in the case of the same initial conditions, boundary conditions and the calculation methods. The results showed that more accurate results could be gotten through large eddy simulation who took more computational workload.On these conditions, physical model entity of the constrained flow channel was constructed. Then the flow field characteristics was observed with the method of PIV, which proved the effectiveness of the method of LES.(2)The analysis of cutting mechanism of soft abrasive flow and the numerical simulation of solid-liquid two-phase flow. Firstly based on erosion theory the main factors to affect the particle motion were analyzed. The machining mechanism of soft abrasive flow were discussed. Secondly the different motion characteristics of the particle in the solid-liquid two-phase flow in a variety of conditions were simulated by the adoption of the combination of LES and SPTM, especially the interaction between the wall and the particles in the near-wall region. The numerical simulation results showed that the velocity of the fluid was the main factor of fluid pulsation. The greater the speed, the more obvious the fluid pulsation. The pulsation of the particles was also influenced by the particle diameter. The larger the diameter of the particle, the larger the inertial force. The particle with large diameter was affected by the pulsation little. The more the volume content, the more the chance of collision among particles. Thus the probability of uncertain movement of particles was bigger. The M shaped flow channel was still in use to validate the feasibility of numerical simulation and make up for the deficiency of the numerical simulation. The movement of particles in the fluid could be gotten through observation experimental system. The experiment showed that on account of the blending effect of turbulence particles deviated from the mainstream direction of movement and collided with the wall surface. Thereby the effective resection of the wall surface could be done by particles.(3)The deployment of the chemical polishing solution and the chemical polishing experiment. Several kinds of chemical polishing liquid were prepared by using different proportion of hydrogen peroxide, oxalic acid, sulfuric acid, urea and other chemical ingredients.1Crl8Ni9,3Cr2Mo,45#and Q235, was used in the chemical polishing experiment. Analytical balance were used to measure the quality of the several steel and mass loss rate could be calculated. The experiment showed that the degree of corrosion of different materials was different in the same chemical polishing solution. At room temperature the surface smoothness of the work piece had a significant improvement after fifteen-minute polishing.(4)Taking45steel for example, the experiment of soft abrasive flow polishing was done by soft abrasive flow precision machining laboratory bench. The law that some factors, such as the velocity of the fluid, the concentration and the size of particles, polishing time, affected the amount of material removed and the surface roughness was researched. The removal rate was calculated after the quality measurement of the test piece by the analytical balance on condition that only one single parameter of soft abrasive flow polishing changed. The TR200handheld roughness instrument was used for measurement. KEYENCE VW-6000dynamic analysis three-dimension display system was used to measure the surface appearance of work piece. The experimental results showed that applying the method of the soft abrasive flow machining on the structured surface finishing of moulds was feasible and valid.(5) The mechanism of softness abrasive flow polishing was analyzed. The mathematical model of the material removal rate was established combining the experiment of soft abrasive flow polishing drawing on the erosion failure model of the multiphase flow transport machinery. |
PDF Full Text Request