A hybrid method for crackless and high-efficiency ultraprecision chamfering of KDP crystal

Abstract

To enhance the optical performance of the optics used in inertial confinement fusion (ICF), the edges of the large-sized KDP crystal need to be removed to form chamfered faces with high surface quality (RMS <5 nm). Fly cutting with single point diamond tool has been widely used to process potassium dihydrogen phosphate (KDP) to achieve extremely high surface quality. However, the depth of cut (DOC) of fly cutting is usually several microns, which results in very low machining efficiency for the chamfering of KDP crystal as the amount of materials to be removed is in the order of millimeter. To overcome this problem, this paper proposes a hybrid machining method by combining precision grinding with fly cutting to achieve crackless and high-efficiency ultraprecision chamfering of KDP crystal. In addition, a combined machine tool has been developed, and experiments have been carried out to determine the optimal machining procedures and verify the effectiveness of the proposed method. Experimental results show that the machining efficiency can be improved by nearly five times using the proposed method to produce the same machined surface quality as that of the traditional fly cutting process.