Large-sized potassium dihydrogen phosphate(KDP)crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project.Restricted by the size,previous studies have been aimed mainly at the ...Large-sized potassium dihydrogen phosphate(KDP)crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project.Restricted by the size,previous studies have been aimed mainly at the removal principle and surface roughness of small-sized KDP crystals,with less research on flatness.Due to its low surface damage and high machining efficiency,water dissolution ultraprecision continuous polishing(WDUCP)has become a good technique for processing large-sized KDP crystals.In this technique,the trajectory uniformity of water droplets can directly affect the surface quality,such as flatness and roughness.Specifically,uneven trajectory distribution of water droplets on the surface of KDP crystals derived from the mode of motion obviously affects the surface quality.In this study,the material removal mechanism of WDUCP was introduced.A simulation of the trajectory of water droplets on KDP crystals under different eccentricity modes of motion was then performed.Meanwhile,the coefficient of variation(CV)was utilized to evaluate the trajectory uniformity.Furthermore,to verify the reliability of the simulation,some experimental tests were also conducted by employing a large continuous polisher.The results showed that the CV varied from 0.67 to 2.02 under the certain eccentricity mode of motion and varied from 0.48 to 0.65 under the uncertain eccentricity mode of motion.The CV of uncertain eccentricity is always smaller than that of certain eccentricity.Hence,the uniformity of trajectory was better under uncertain eccentricity.Under the mode of motion of uncertain eccentricity,the initial surface texture of the100 mm×100 mm×10 mm KDP crystal did achieve uniform planarization.The surface root mean square roughness was reduced to 2.182 nm,and the flatness was reduced to 22.013μm.Therefore,the feasibility and validity of WDUCP for large-sized KDP crystal were verified.展开更多
Additive manufacturing(AM)is a reliable technique for constructing highly complex metallic parts.Direct energy deposition(DED)is one of the most common technologies used for AM-printed metal alloys.However,issues such...Additive manufacturing(AM)is a reliable technique for constructing highly complex metallic parts.Direct energy deposition(DED)is one of the most common technologies used for AM-printed metal alloys.However,issues such as weak binding,poor accuracy,and rough surfaces still affect the final products.These limitations in the metal-feed DED process indicate that post-processing techniques are required to achieve high quality in terms of both mechanical properties and surface finish.Conventional contact-based post-processing methods have several drawbacks,including difficulties in accessing complex shapes,environmental impact,high time consumption and cost,and health risks for operators.To address these problems and improve surface quality,a laser polishing process has been proposed.By melting or ablating the material with a laser,the laser-polishing process enables the smoothing of the initial topography.It should be noted that there are currently no reviews focusing specifically on laser polishing as a surface treatment technology for the DED process.Therefore,this review presents a unique examination of the mechanisms and primary user-set parameters for both continuous wave(CW)and pulsed laser polishing.The objective is to demonstrate the capabilities of each process and the benefits of using them for the surfaces of DED metal parts.Additionally,existing knowledge and technology gaps are identified,and future research directions are discussed.展开更多
We provide some sharp criteria for studying the ergodicity and asymptotic stability of general Feller semigroups on Polish metric spaces. As an application, the 2D Navier-Stokes equations with degenerate stochastic fo...We provide some sharp criteria for studying the ergodicity and asymptotic stability of general Feller semigroups on Polish metric spaces. As an application, the 2D Navier-Stokes equations with degenerate stochastic forcing will be simply revisited.展开更多
基金funded by the National Natural Science Foundation of China(Grant No.51135002)Science Fund for Creative Research Groups of NSFC(Grant No.51621064)。
文摘Large-sized potassium dihydrogen phosphate(KDP)crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project.Restricted by the size,previous studies have been aimed mainly at the removal principle and surface roughness of small-sized KDP crystals,with less research on flatness.Due to its low surface damage and high machining efficiency,water dissolution ultraprecision continuous polishing(WDUCP)has become a good technique for processing large-sized KDP crystals.In this technique,the trajectory uniformity of water droplets can directly affect the surface quality,such as flatness and roughness.Specifically,uneven trajectory distribution of water droplets on the surface of KDP crystals derived from the mode of motion obviously affects the surface quality.In this study,the material removal mechanism of WDUCP was introduced.A simulation of the trajectory of water droplets on KDP crystals under different eccentricity modes of motion was then performed.Meanwhile,the coefficient of variation(CV)was utilized to evaluate the trajectory uniformity.Furthermore,to verify the reliability of the simulation,some experimental tests were also conducted by employing a large continuous polisher.The results showed that the CV varied from 0.67 to 2.02 under the certain eccentricity mode of motion and varied from 0.48 to 0.65 under the uncertain eccentricity mode of motion.The CV of uncertain eccentricity is always smaller than that of certain eccentricity.Hence,the uniformity of trajectory was better under uncertain eccentricity.Under the mode of motion of uncertain eccentricity,the initial surface texture of the100 mm×100 mm×10 mm KDP crystal did achieve uniform planarization.The surface root mean square roughness was reduced to 2.182 nm,and the flatness was reduced to 22.013μm.Therefore,the feasibility and validity of WDUCP for large-sized KDP crystal were verified.
基金supported by National Key Research and Development Program of China(Grant No.2022YFB4600901).
文摘Additive manufacturing(AM)is a reliable technique for constructing highly complex metallic parts.Direct energy deposition(DED)is one of the most common technologies used for AM-printed metal alloys.However,issues such as weak binding,poor accuracy,and rough surfaces still affect the final products.These limitations in the metal-feed DED process indicate that post-processing techniques are required to achieve high quality in terms of both mechanical properties and surface finish.Conventional contact-based post-processing methods have several drawbacks,including difficulties in accessing complex shapes,environmental impact,high time consumption and cost,and health risks for operators.To address these problems and improve surface quality,a laser polishing process has been proposed.By melting or ablating the material with a laser,the laser-polishing process enables the smoothing of the initial topography.It should be noted that there are currently no reviews focusing specifically on laser polishing as a surface treatment technology for the DED process.Therefore,this review presents a unique examination of the mechanisms and primary user-set parameters for both continuous wave(CW)and pulsed laser polishing.The objective is to demonstrate the capabilities of each process and the benefits of using them for the surfaces of DED metal parts.Additionally,existing knowledge and technology gaps are identified,and future research directions are discussed.
基金supported by the Financial Support from Key Laboratory of Random Complex Structures and Data Science,Academy of Mathematics and Systems Science,Chinese Academy of Sciences(Grant Nos.2008DP173182 and Y129161ZZ1)National Natural Science Foundation of China(Grant Nos.11021161 and 11201456)National Program on Key Basic Research Project of China(973 Program)(Grant No.2011CB808000)
文摘We provide some sharp criteria for studying the ergodicity and asymptotic stability of general Feller semigroups on Polish metric spaces. As an application, the 2D Navier-Stokes equations with degenerate stochastic forcing will be simply revisited.
