Analysis of Aerostatic Spindle Bearing Capacity Characteristics Based on a Nonlinear Spring Model

Advanced packaging technology requires increasingly thinner wafers, with wafer thinning being a critical process in advanced packaging. During the grinding of the thinning machine spindle, the edge bearing capacity significantly affects the total thickness variation (TTV) and surface roughness of the thin wafer, making it a key performance indicator. Due to the advantages of high rotational accuracy, frictionless operation, high speed, and high stiffness, aerostatic spindles are widely used in wafer thinning machines. In order to analyze the static bearing capacity characteristics of aerostatic spindles, this paper proposes a 3D finite element analysis model of the force on the rotor of aerostatic spindles using a nonlinear spring instead of an air film. The variation laws of central and edge bearing capacities with displacement were obtained, enabling rapid and accurate analysis of the edge bearing capacity during grinding. It is also applicable to various types of aerostatic bearings, such as orifice and porous types. A 6.2 kW spindle prototype was developed, and an experimental test bench was built. The experimental results indicate that the central bearing capacity is 4080 N at a central displacement of 5 μm; the axial edge bearing capacity reaches 720 N at an axial displacement of 2.5 μm at the grinding wheel edge; and the radial edge bearing capacity reaches 320 N at a radial displacement of 3 μm at the grinding wheel edge. The error between the experimental and calculated results is within 10%. The simplified nonlinear spring model replacing the gas film proposed in this paper can be applied in engineering design.