High-precision sub-millimeter silicon microspheres are critical components in fields such as micro-bearings, MEMS devices, and optical instruments. However, due to their extremely low mass and small moment of inertia, these microspheres are prone to slippage, rotation stagnation, and uneven wear during traditional concentric V-groove lapping. These issues will severely hinder the convergence of roundness and the control of surface quality. To address these challenges, the work aims to propose a novel dual-eccentric ultra-precision lapping method utilizing a combination of a V-groove and a flat plate. The primary objective is to clarify the effect laws of key process parameters on the lapping mechanism and to achieve high-efficiency, ultra-precision batch machining. Initially, based on the principles of spatial meshing and rigid body kinematics, a geometric kinematic model of the microsphere under a dual-eccentric field was established. To quantitatively evaluate the uniformity of the lapping trajectory, the spherical surface was discretized, and the Standard Deviation (DS) of the trajectory point distribution density was introduced as a key evaluation index. MATLAB simulations were conducted to systematically analyze and compare the trajectory characteristics under concentric, single-eccentric, and dual-eccentric processing modes. The simulation results revealed that the dual-eccentric structure effectively disrupted the periodicity of the sphere's motion, creating a chaotic and ergodic trajectory that covered the entire spherical surface. Comparative analysis determined that the trajectory envelope uniformity was optimal when the upper plate eccentricity was set to 1 mm and the V-groove eccentricity was set to 2 mm. Subsequently, a dedicated experimental platform was constructed, and 0.9 mm silicon microspheres were selected as the processing objects. Single-factor experiments were performed to investigate the specific effects of abrasive concentration, lapping pressure, abrasive particle size, and rotational speeds of the upper and lower plates on three performance indicators: roundness error, surface roughness (Sa), and material removal rate (ηMRR). The experimental results indicate complex non-linear relationships. Specifically, the roundness error and surface roughness exhibited a trend of decreasing first and then increasing with the rise of abrasive concentration, lapping pressure, and rotational speeds. This suggested that while moderate parameter increases enhanced cutting efficiency, excessive pressure or speed induced vibration and motion instability, leading to surface damage and deteriorating roundness. Regarding abrasive particle size, increasing the particle size significantly improved the material removal rate, which was beneficial for rapid roundness convergence during the shaping phase, but it inevitably led to deeper scratches and increased surface roughness. Conversely, smaller particles were essential for achieving a super-smooth surface finish. Additionally, the ηMRR tended to saturate at high abrasive concentrations due to particle interference. Based on these experimental laws, a progressive "roughing, semi-finishing, and finishing" multi-stage lapping process strategy was developed. The roughing stage utilized larger abrasives and higher pressures to quickly correct geometric errors, while the finishing stage employed fine abrasives and lower pressures to remove subsurface damage and improve surface integrity. Verification experiments demonstrated that after applying this optimized multi-stage process, the average roundness of the silicon microsphere converged significantly from an initial 1.849 μm to 0.432 μm, and the surface roughness (Sa) decreased from 23.651 nm to 6.632 nm. In conclusion, the dual-eccentric lapping method can achieve uniform full envelope coverage of the machining trajectory for sub-millimeter silicon microspheres. The proposed stepwise process strategy effectively balances the conflict between machining efficiency and surface quality, providing a viable technical solution for the mass production of high-precision sub-millimeter hard and brittle microspheres.
Key words
silicon microsphere /
dual-eccentric lapping /
kinematic analysis /
uniformity evaluation /
lapping parameters /
processing technology
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Funding
National Natural Science Foundation of China (52305518, 52575238); Science and Technology Planning Project of Sichuan Province (2025ZDZX0028, 2024NSFTD0019)
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