Research On The Performance And Stability Of Variable Orifice And Non-uniform Distribution Aerostatic Spindle

The aerostatic spindle,which is lubricated by gas,has the advantages of high cleanliness,no pollution to the environment,no friction/very low friction,high precision,fast speed and little wear and tear,has increasingly become an important rotating support component in high-end manufacturing industry,especially in the field of high-speed and ultra-high-speed machining.In order to improve the structures and performance of the spindle,in this thesis,we have demonstrated our research in the performance of the non-uniform distribution and variable orifice aerostatic spindle.Moreover,the effects of spindle rotating speed,eccentricity,supply pressure and film thickness on the static dynamic performance and stability are analyzed.It provides reference for structure design and stability analysis of aerostatic spindle.The main work of this paper is summarized as follows:(1)The steady-state Reynolds equation is discretized by the two-order central scheme in Finite Difference Method(FDM)to obtained the gas pressure distribution and bearing capacity of the aerostatic spindle,then,the unsteady Reynolds equation is discretized by two-order central scheme and solved by Linear Perturbation Method.Moreover,the dynamic stiffness coefficient and dynamic damping coefficient of the spindle are obtained.Then the stability threshold is solved to obtain the critical inertia force and critical whirl ratio of the spindle.Based on the programming of MATLAB,the calculation results are compared with the literature content to verify the accuracy of the results.(2)The effects of non-uniform distribution and variable orifice on the static performance and gas pressure distribution of aerostatic spindle are discussed.According to the bearing capacity of different orifice distributions and orifice diameter,six types of orifice distributions and orifice diameter structures were selected as analysis objects.The first three structures are equal orifice diameter,among them,structure 1 is uniform distribution while structure 2 and structure 3 are non-uniform distribution.The last three structures are variable orifice structures,in which structure 4 is uniform distribution of orifices,and structure 5 and structure 6are non-uniform distribution.The results show that whether the orifice distribution is uniform or not,only has little effect on the variation trend of gas pressure along the circumferential direction.When the orifice diameter coefficient is between 0.92～0.95,the bearing capacity of spindle is the largest.(3)The effects of eccentricity,supply pressure,air film thickness and rotating speed on the bearing capacity of different structures aerostatic spindle,analyzed influence of the supply pressure and average film thickness on the dynamic performance and stability threshold of spindle.The results show that the change of spindle structure will not affect the change trend of bearing capacity.Non-uniform distribution and variable orifice structure can improve the bearing capacity of spindle,When the eccentricity is 0.15～0.2,the non-uniform distribution and variable orifice diameter structure has better stability.Based on the program of solving Reynolds equation by MTLAB,the GUI interface is compiled,and the two numerical calculation methods of Finite Element Method(FEM)and FDM are unified into the interface,it is convenient for the adjustment and improvement of the calculation and the output of the calculation results.(4)Analyzed the three kinds of manufacturing errors and journal misalignment on the stability of the aerostatic spindle.the results show that when there is triangular waviness,bearing capacity is the largest,the second is rectangular waviness,and the smallest is sinusoidal waviness.Furthermore,the stability of aerostatic spindle degrades with the increases of the waviness amplitude while the effects of waviness amplitude on spindle stability can be neglected if waviness with large error cycles.When the error amplitude is in the range of 0.075～0.15 um,the spindle is stable.(5)The journal misalignment abates the spindle stability,misalignment in x direction,y direction,x and y direction all result in the increase of critical inertia force and the decrease of critical eddy ratio.The effect of misalignment in the x and y the directions simultaneously on the stability are greater than of in the x or y directions.Journal misalignment should be minimized during spindle assembly.Most of the traditional aerostatic spindle structures are uniform distribution and equal orifice,this paper studied the performance and stability of aerostatic spindle with non-uniform distribution and variable orifice,analyzed the effect of different operating parameters to the bearing capacity,dynamic stiffness coefficient,dynamic damping coefficient and stability threshold of spindle.Moreover,studied the effects of different manufacturing errors and journal misalignment to the spindle,provided a reference for performance analysis and structural optimization of aerostatic spindle.