Research on the Critical Condition of Brittle-Ductile Transition about Micro-Milling of KDP Crystal and Experimental Verification

다국어 초록 (Multilingual Abstract)

KDP crystal is a kind of brittle material, and improper selection of processing parameter can easily result in brittle domain cuttingof KDP crystal. Determining the critical cutting depth of micro-milling brittle-ductile transition of KDP crystal can guide the selectionof process parameters. The elastic-plastic contact formula of blunt spherical indenter and brittle materials is used to explicate thecontact of micro-cutter edge and brittle materials. Combined with indentation critical load equation, the calculation model ofpredicting the critical cutting depth is established. The critical cutting depth is the function of material properties of the workpiece,the tool material properties and the tool edge radius. The edge radius of CBN flat end milling cutter is measured by atomic forcemicroscopy, and then the critical cutting depth of the KDP crystal material is calculated as 230 nm. By using this milling cutter, microgroovemilling experiments are conducted with different spindle speeds and feeds. The results demonstrate that as the spindle speedincreases, the micro-groove bottom surface gradually transformed from the brittle cutting state to plastic cutting state. The criticalspindle speed is 30000 rpm, and the maximum deformed cutting thickness is 227 nm, which coincides with the result of the theoreticalcalculation model.

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