Removal Uniformity in Ring-Pendulum Double-Sided Polishing Based on Pressure Distribution
Objective Ring-pendulum double-sided polishing,a novel type of double-sided polishing process,enables simultaneous processing on the upper and lower surfaces of the components,reducing polishing parallelism errors and enhancing processing efficiency.However,currently,the processing primarily relies on technicians using trial-and-error methods,to accumulate experience for selecting appropriate process parameters.This approach lacks controllability and repeatability,mainly because the prediction of the surface pre-processing is based on the relative speed between the abrasive grain and the component surface,and the number of scribes to calculate the distribution of material removal.This method overlooks the influence of contact surface pressure on the material removal.As a result,discrepancies arise between predicted outcomes and the actual distribution of polished material removal,failing to provide an effective guide for the decision-making on process parameters.Methods We analyze the working principle of the ring-pendulum double-sided polishing equipment,carry out a kinematic analysis of abrasive particles,and obtain the instantaneous relative velocity field distribution between the polishing disc and the component surface.We examine the influence of polishing pressure on the component's processing surface,establish a finite element model of the pressurized cylinder,component,and polishing disc,set constraints according to the pressure loading situation during actual processing,and conduct finite element simulation analysis.Our analysis yields the pressure distribution law on the component surface under both self-weight and pressurized conditions of the upper polishing disc.The data are fitted using the least squares method to construct a pressure distribution model of the contact surface between the ring-pendulum double-sided polishing element and polishing disc.By coupling the instantaneous relative velocity field model of the element and the polishing disc with the pressure model of the contact surface,we derive the instantaneous removal at each point on the component surface according to Preston's equation.The summation of instantaneous removal constructs the prediction model for material removal in ring-pendulum double-sided polishing.Results and Discussions In this study,we select 430 mm×430 mm× 10 mm fused silica elements for practical process experiments.Three components with different initial face types are chosen for processing.The accuracy of the material removal prediction model is verified through three comparative experiments.We investigate the effects of processing pressure and upper disc size on the distribution and uniformity of material removal.Experimental results indicate that larger diameters of the upper polishing disc and lower machining pressures contribute to better uniformity in material removal.Conclusions Guided by the removal distribution prediction model,we apply the derived principles to actual processing.Fused silica samples with an initial surface profile peak-valley(PV)value of 2.09λ(λ＝632.8 nm)and a root mean square(RMS)value of 0.464λ are selected.Through the material removal prediction model(Fig.25),we obtain optimal solutions for process parameters.After processing,the surface PV of the component is reduced to 0.85λ,and the RMS value decreases to 0.137λ(Fig.26).The time required to reduce the component surface PV below λ is cut to 50％of the original duration,achieving rapid convergence of the component surface profile.
large-aperture flat opticsring-pendulum double-sided polishing methodpressure distribution characteristicsremoval uniformitycalculation model for material removal
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