Fluid jet polishing (FJP) is a versatile method used for polishing small and complex components. The unstable removal function which is caused by the pulsation of turbulent jet is one of the main limitations for FJP. In this paper, this problem is addressed by a novel shear thickening FJP method. The shear thickening fluid (STF) is employed for preparing the polishing slurry instead of conventional Newtonian fluid. The principle of shear thickening FJP is present based on analyzing the behavior of STF under the special shear rate distribution. Then the influence of the shear thickening behavior on the material removal rate and the surface roughness of UBK7 components is investigated. The performance of the shear thickening FJP is verified detail by experiments. It is found that the shear thickening behavior would be beneficial to the surface accuracy of workpiece, owing to its ability of reducing the turbulence intensity in the boundary layers of fluid jet. Compared with normal FJP, the surface roughness of polished parts could be improved more than 40% in shear thickening FJP, while maintaining the material removal rate.
The slurry of fluid jet polishing mainly consists of deionized water and abrasives. Material removal is mostly regarded as plastic removal by the strike of the abrasives on the workpiece surface. Since jet pressure is relatively low, which result in a low material removal rate and bring a limitation of applying to this processing method. To improve the material removal rate of glass (Fused Silica, UBK7, K9, etc.), alkaline slurry was used to enhance chemical effects during polishing. Firstly, the material removal of conventional neutral slurry (pH≈7) and the new alkaline slurry (pH≈10, 11, 12, 13) were compared and the results showed that alkaline slurry brought an obvious increase in material removal rate. Then, four kinds of slurry of different alkalinity (pH≈10, 11, 12, 13) were used in polishing experiments to make clear the influence of alkaline intensity on the material removal rate. It was found that a larger material removal rate would be obtained with a higher pH slurry. Finally, the surface roughness which were made by slurry with different alkalinity were also compared, the results reached as that slurry with higher pH could bring lower surface roughness. It could be drawn from this study that enhance the chemical effects in fluid jet polishing could be an effective way to enlarge the material removal rate and improve the processing performance.
In order to find out the law how the nozzle height influences the removal function in FJP, a mathematical model of the nozzle-rotating removal function is proposed and its correctness has been verified by experiment. Moreover, another model which is able to predict the surfaces processed by different removal functions is established in this paper. The calculation results show the profile of nozzle-rotating removal functions change from W-shaped to single peak Gaussian shaped as the nozzle height increases. Besides, when the removal functions are Gaussian shaped, the best surface roughness is obtained when the removal function is the widest and shallowest one. Which has theoretical significance for the optimization of the process parameters in actual processing.
The current study presents a detailed theoretical analysis on the performance of aerostatic journal bearings. The dimensionless Reynolds equation is derived and discretized by the finite difference method. An iterative procedure is adopted to get the air film pressure distribution. The bearing characteristics such as load capacity, stiffness and air flow rate under various bearing operating and geometric parameters are investigated. The numerical results show that the journal rotation plays an important role on the bearing characteristics, and the rotating speeds must be taken into consideration. The proposed method provides a valuable approach for analyzing the performance of aerostatic journal bearings, and can be used for the bearing optimizing design.