Study On Precision Slicing And Grinding Processes Of KDP Crystal

KDP(Potassium dihydrogen phosphate, KH2PO4) crystal has big electro-optic and non-linear optical coefficient, high laser damage threshold, low optical absorption coefficient, high optical uniformity and proper transparent wave band. It is the only material that can be used in ICF as laser frequency conversion part and electro-optic switch. However, it is well-known that KDP crystal is one of most difficult to machine materials because it is soft, fragile, hygroscopic and anisotropic. Slicing, single point diamond cutting, grinding and MRF polishing are usual methods in KDP crystal mahining. Currently, domestic precision machining methods such as single point diamond cutting and MRF polishing have disadvantages as follows:small scale waveness, round edge and low efficiency. Besides, big size crystal slicing is in lack of effective method, the currently adoped band saw slicing has problems such as big kerf loss, edge chipping and accidental breaking of big size crystal. Exploration and research on precision slicing and grinding processes of KDP crystal are of important practical meaning and application value to solve the current technical difficulties that restrict our machining of KDP crystal.Firstly in this paper, based on the current problems in big size KDP crystal slicing with steel band saw and diamond plated band saw, we experimentally studied low stress slicing method for KDP crystal with diamond wiresaw which mainly focused on the influence of technical parameter on Ra, flatness, parallelism and subsurface damage. Comparison and analysis of the influence of different technical methods on surface quality and subsurface damage of sliced KDP crystal were made and material removal mechanism and damage mode for low stress wiresaw slicing of KDP crystal were discussed. Finally, the maximum subsurface damage of KDP crystal low stress wiresaw slicing and the material needed to be removed for next step machining processes were provided; a method for real time deviation correction during low stress diamond wiresaw precision slicing was developed and the low stress precision slicing of KDP crystal with 390mm slicing width and 5mm thickness was achieved.In order to obtain the influence of anisotropy on surface and subsurface damage and its depth, single point scratching test was done to study the development of surface and subsurface cracks and the depth of SSD (subsurface damage) of different crystal orientation. Single diamond grit grinding test was done to study the influence of different grinding mode, depth of cut and grit speed on the material removal mode of KDP crystal, which can provide theoretical basis for technical parameter experiment, surface profile and subsurface damage analysis of the next step fixed abrasive machining (slicing/grinding).Precision grinding process of KDP crystal was explored which included the theoretical analysis and experimental research of influence of grinding mode, wheel performance and grinding parameter on surface quality, subsurface damage, grinding force and temperature. The comparison of rotary ultrasonic grinding and traditional grinding was carried out concentrating on workpiece machining quality (Ra, surface profile and subsurface damage etc.). The influence of material anisotropy on machining was analyzed and the material removal mechanism of KDP crystal grinding was discussed. The work establishes good foundation for future efficient and low damage surface precision grinding of anisotropic material such as KDP crystal.