Journal
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
Volume 134, Issue -, Pages 387-398Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijmecsci.2017.10.025
Keywords
KDP crystal; Micro-milling; Minimum undeformed chip thickness; Size effect; Specific cutting force
Categories
Funding
- Science Challenge Project [JCKY2016212A506-0503]
- National 863 Program [2015AA043301]
- State Key Laboratory of Robotics and System (HIT) [SKLRS201718A]
- Foundation for Innovative Research Groups of the National Natural Science Foundation of China [51521003]
- China Scholarship Council
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Micro-milling is a promising approach to repair the micro-defects on the surface of potassium dihydrogen phosphate (KDP) crystal. However, KDP crystal is difficult to machine due to its properties of soft-brittle and easy deliquescence. This study investigates the minimum undeformed chip thickness hat and the size effect in micro end-milling of KDP crystal by comprehensively analyzing cutting force, specific cutting force and machined surface quality. A model of the chip formation, which is capable of connecting the minimum undeformed chip thickness, the undeformed chip thickness and the periodicity of cutting force together, is developed to predict the value of minimum undeformed chip thickness. The normalized minimum undeformed chip thickness lambda(e) in terms of the ratio of the minimum undeformed chip thickness to the cutting edge radius r(e), is estimated to be 0.43 <= lambda(e) <= 0.48. The significantly non-proportional increase of specific cutting force indicates the existence of size effects when the ratio of feed per tooth to cutting edge radius f(t)/r(e) is less than 0.7. The machined surface quality also reflects severe size effect by the phenomenon that the micro cracks and brittle pits appear on the groove base, and the value of surface roughness R-a is large when the ratio f(t)/r(e) is less than 0.5. Furthermore, the surface quality deteriorates and the brittle cutting appears when the ratio f(t)/r(e) is much larger than 1 which seems similar to macro-milling. The perfect machined surface with almost no ploughing effect and brittle cutting is achieved at a ratio f(t)/r(e) of 0.7. Therefore, a feed per tooth, slightly larger than the minimum undeformed chip thickness but smaller than cutting edge radius, is recommended for micro-milling of KDP crystal or soft-brittle crystal. (C) 2017 Elsevier Ltd. All rights reserved.
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