Study On Fixed Abrasive Polishing Of Soft And Brittle LBO Crystal

All-solid-state laser is widely used in military, industry processing, laser display, medicaltreatment, scientific experiment and other fields. LBO crystal is one of the key materials forall-solid-state laser technology. Fixed abrasive polishing technology can avoid the abrasivescratching, embedding or absorbing the LBO crystal surface, and improve machining efficiencyand surface quality. In this paper, fixed abrasive polishing technology was adopted to polish ofLBO crystal. The pH regulator and pH value of abrasive-free slurry, the matrix hardness andpolishing powder concentration of fixed abrasive pad (FAP), and process parameters, were studiedin order to gain a better surface roughness. The effect of installation manner and processparameters on flatness of fixed abrasive polishing of LBO crystal was investigated. The mainwork and results are as follows,(1) The pH regulator and pH value of abrasive-free slurry were explored. The pH regulatorsof oxalate, acetic acid and citric acid were employed to prepare acidic abrasive-free slurry with pHvalue at4. Deionized water without pH regulator was employed to prepare neutral abrasive-freeslurry with pH value at7. The pH regulators of triethylamine, cyclohexylamine, ethylenediaminewere employed to prepare alkaline abrasive-free slurry with pH value at10. Those abrasive-freeslurries were adopted to polish of LBO crystal. The material removal rate (MRR) of abrasive-freeslurry with acidic, neutral and alkaline gradually reduces, and surface quality gradually enhances.The best pH regulator is ethylenediamine. As the pH value of abrasive-free slurry withethylenediamine increases, the MRR declines firstly and then rises, and surface quality improves.When the optimal abrasive-free slurry with ethylenediamine and pH value at11is adopted topolish of LBO crystal, the MRR is49nm/min and the surface roughness Sa is1.94nm, with somescratches and pits.(2) The matrix hardness and polishing powder concentration of FAP were studied. With thematrix hardness and the polishing powder concentration of FAP increasing, the MRR rises. As thematrix hardness increases, the surface quality slight declines firstly and then improves when theconcentration of the polishing powder (CPP) is100wt%, while the surface quality graduallyimproves when the CPP is150wt%. The surface quality improves with the CPP of FAP increasing.When the optimal FAP with matrix hardness C and CPP150wt%is adopted to polish of LBOcrystal, the MRR is71nm/min and the surface roughness Sa is0.754nm, with few pits.(3) The process parameters of fixed abrasive polishing of LBO crystal were optimized. Theorthogonal experimental method was employed to optimize polishing pressure, rotating speed,rotating speed ratio and slurry flow rate. The MRR of LBO crystal declines with polishingpressure, rotating speed, rotating speed ratio and slurry flow rate increasing. The surface roughness Sa declines with polishing pressure, rotating speed and rotating speed ratio increasing,and it decreases firstly and then rises with increasing slurry flow rate. After comprehensiveoptimization of surface quality and MRR, the process parameters that are polishing pressure14kPa, rotating speed70r/min, rotating speed ratio0.95and slurry flow rate60ml/min. The MRRof the optimal process parameters is93nm/min and the surface roughness Sa is0.184nm, withoutobvious damage.(4) The effect of installation manner and process parameters on flatness of LBO crystal wasinvestigated. The flatness is improved by adopting the loader which can provide uniform loading.The optimal process parameters of flatness are polishing pressure14kPa, slurry flow rate80ml/min, rotating speed ratio (50/50) r/min and swing68~68mm. The PV value of20pointsafter polishing with the optimal process parameters is0.6251wv.And finally, the conclusions of this paper were summarized and the further work of fixedabrasive polishing of LBO crystal was prospected.