Theoretical modeling and analysis of material removal characteristics for KDP crystal in abrasive-free jet processing

Traditional KDP polishing methods, such as magnetorheological finishing (MRF), ion-beam figuring (IBF), and chemical mechanical polishing (CMP), are limited by either hard-to-remove residual particles, unavoidable heating effect, or applicability that is restricted to large-sized KDP. The abrasive-free jet polishing (AFJP) is regarded as a promising polishing method that can circumvent the above issues. KDP AFJP makes use of a thermodynamically and kinetically stable ionic liquid (IL) microemulsion that contains nanometer range water droplets evenly dispersed in the non-aqueous carrier liquid. The sprayed out nanoscale water droplets can remove material through dissolution. In this paper, the normal impinging of a nanoscale water droplet on the KDP surface is investigated. And then a materials removal model is proposed for water droplets. This model considers two major modes, namely deformation of a water droplet in compressing and deformation restoring of a water droplet in slipping process. Finally, KDP AFJP spot experiments were then conducted to validate the model veracity. The proposed model fits well with the simulation and experimental results which further suggest KDP AFJP's feasibility. This proposed model provides a good explanation for KDP AFJP's removal mechanism.