The Design Of Ultra-hard Micro Mills And Processing Research For Milling Micro Structures On Lif Crystal

Inertial confinement fusion (ICF) can produce high-quality and low-cost energyand has become a hot research topic nowadays. LiF (Lithium Fluoride) crystal iswidely used as optical window in ICF related experiments for its excellenttransmissivity and wide wave band for transmission. The stair-shape fusion target is antypical example, it can hardly be manufactured by other manufacture methods for itsstrict demands for dimentional accuracy and surface quality, while micro milling hasits decided advantage. However, LiF is a kind of soft brittle crystal and ductile modecutting poses a challenge to the selection of micro mill geometries and processingparameters. As a result, it’s of great importance to imply the research of micro millsdesign and process parameters optimization when LiF crystal is micro milled.Inicial research of this project has showed that extremely serious diffusive wearexised between WC based micro mills and LiF crystal. The wear mechanisms werestudied. Results showed that WC from the tool basement diffused dramatically to LiFcrystal and reacted with it to produce Li2C2and gas WF, which was the main reason fordiffusive wear. PCD was ultimately selected as the tool material for milling LiF crystaland its chemical inertness was experimental verified.Two types of micro end mills were designed. Their tool geometries wereoptimized by Finite element method (FEM). After optimization, tool type Ⅰ had theradial rake angle, radial clearance angle, axial rake angle and axial clearance angle of-35°,9°,-25°and20°respectively, and tool type Ⅱ had the radial rake angle, radialclearance angle, axial rake angle and axial clearance angle of-60°,12°,-55°and20°respectively. Simulation results showed that the cutting performance of tool type Ⅰwas not so good as the performance of tool type Ⅱ.The process parameters were optimized by both FEM and single-factorexperiments with tool type Ⅱ. Results showed that, as the feed per tooth and spindlespeed increased, the quality of slot surface became better then worse. The best feed pertooth was665nm/z and the best spindle speed was65000r/min. As the depth of cutincreased, the slot surface became worse and it was better to keep the depth of cut below2μm.The orthogonal experiments were done with the tool type Ⅰ, tool type Ⅱ andCBN tool made by NS company respectively. Results showed that, tool type Ⅱpreformed best and could get the best Ra of6.50nm and the average Ra of11.44nm.Tool type Ⅰ behaved worst and CBN tool had the performance between the twoself-made tools. The change law of the crystal surface quality as the processingparameters changed was similar to the result of single-factor experiments. For differenttools, the significance of process parameters’ effect on crystal surface quality wasdifferent totally. The parameters had the least effect on the crystal surface quality cutby tool type Ⅱ. So this tool can realize ductile mode cutting of the crystal within awide parameter range. The sample of stair-shape target made of LiF crystal was milledwith the tool type Ⅱ and the optimized process parameters, and surface roughness aslow as8.40nm Ra could be reached.