Abstract
Potassium dihydrogen phosphate (KDP or KH2PO4) crystal is widely used as terminal frequency converters in inertial confinement fusion (ICF). However, KDP crystal is a typical difficult-to-cut optical crystal with the characteristic of soft-brittle. In this work, the relationship between cutting force and processed surface quality in micro ball end-milling of KDP crystal with various depth of cut and spindle speed is studied by carried out the micro-milling experiments. Fast Fourier Transform (FFT) algorithm is used to diagnose the recorded cutting force. The periodic change of cutting force and the cutting force after filtering noises can be got through FFT analysis. Through calculating the correlation coefficients between the static component of thrust force and roughness value Ra of machined grooves, as well as the peak-valley (P-V) value of thrust force and dimensional error of machined grooves, the roughness value Ra and dimensional error of machined grooves would be predicted by monitoring the static component and P-V value of the thrust force, respectively. The relatively large spindle speed helps to reduce the roughness value Ra. The spindle speed with moderate value is recommended to reduce the dimensional error of machined groove because the dimensional error of machined groove will increase when the spindle speed is small enough (causing brittle cutting) or large enough (reducing cutting stability).
Highlights
In inertial confinement fusion (ICF), potassium dihydrogen phosphate (KDP or KH2PO4) crystal is widely used as optical Pockels-cells and terminal frequency converters, due to its large electro-optic coefficient and good quality of growth characteristics [1]
Considering that micro ball end-milling has several principal advantages over other available micro-fabrication technologies such as abilities to fabricate complex 3D geometries with high aspect ratio in a wide variety of metallic and non-metallic materials [2,3,4], it has been widely regarded as a useful method to repair micro-defects, which is generated on the surface of KDP crystal during laser target shooting or machining [5,6]
Chen et al [13,14] revealed that the surface quality is closely related with the cutting parameters and the surface roughness value Ra of machined grooves could be controlled below 20 nm by optimizing the cutting parameters both in micro milling of KDP crystal
Summary
In inertial confinement fusion (ICF), potassium dihydrogen phosphate (KDP or KH2PO4) crystal is widely used as optical Pockels-cells and terminal frequency converters, due to its large electro-optic coefficient and good quality of growth characteristics [1]. Chen et al [13,14] revealed that the surface quality is closely related with the cutting parameters and the surface roughness value Ra of machined grooves could be controlled below 20 nm by optimizing the cutting parameters both in micro milling of KDP crystal. Chen et al [14] found that size effect which is manifested as severe ploughing and rubbing effect is appeared when the undeformed chip thickness is smaller than a certain value in micro milling of KDP crystal. In micro machining of metals, several researchers have studied how cutting parameters influence the cutting force and machined surface quality. In order to find an effective way to monitor the processed surface quality in micro ball end-milling of KDP crystal, the relationship between processed surface quality and cutting force will be researched in detail.
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