Abstract
As a soft-brittle material, the machined surface quality of potassium dihydrogen phosphate (KDP) crystal is heavily affected by the edge quality of the diamond cutting tool. However, nanoscale micro defects inevitably occur on the freshly sharpened tool edge, and the machining mechanism for KDP crystal remains unclear. Therefore, in this work, three types of tool-edge micro defects are classified according to their cross-sections, including the blunt-edge, crescent-edge, and flat-edge micro defects. Moreover, the smoothed particle hydrodynamics (SPH) method is employed to reveal the material removal mechanism of KDP crystal with consideration of different tool-edge micro defects, and the flat-edge micro defects are subdivided into flat edge A (similar to flank wear) and flat edge B (similar to chamfered edge) on the basis of their effects in machining. The simulation results indicate that the surfaces machined by crescent edge and flat edge A are unsmooth with large-size defects due to the disappearance of hydrostatic pressure beneath the cutting edge. As for the blunt edge and flat edge B, the machined surfaces are smooth with a favorable increment of hydrostatic pressure for processing brittle materials, which indicates that a solution to eliminate the tool-edge micro defects is necessary, e.g., the passivation method. For keeping the cutting edge as sharp as possible in removing the tool-edge micro defects completely by passivation, the effect of tool shank depression angles on the geometries of the passivated cutting edge is investigated, and a high-quality cutting edge with a micro chamfered edge is obtained after passivation at a depression angle of 60° and re-sharpening of the rake face. Finally, the tool cutting performance after passivation is validated through fly-cutting experiments of KDP crystal. The chamfered edge can produce the best defect-free surface with the minimum surface roughness.
Highlights
In diamond turning, except for the high-precision machine tool [1,2], super-stable machining environment [3,4], and material properties [5], the high-quality cutting tool is an important factor that influences the machined surface quality [6,7,8]
A theory of dynamic critical tensile stress was further advanced, which can be regarded as a reference to estimate the effect of tool face orientation on the sharpened cutting edge radius [21]
Montesanti et al [45] reported the procedure of diamond turning KDP crystal, in which tool geometries and tool-edge sharpness were discussed in detail
Summary
Except for the high-precision machine tool [1,2], super-stable machining environment [3,4], and material properties [5], the high-quality cutting tool is an important factor that influences the machined surface quality [6,7,8]. Few studies have focused on the tool-edge micro defects and the possible effect on the machined surface quality. Montesanti et al [45] reported the procedure of diamond turning KDP crystal, in which tool geometries (including tool rake angle and tool nose radius) and tool-edge sharpness were discussed in detail They concluded that the edge quality is one of the least understood aspects in KDP processing. In terms of the literature reviewed above, it can be found that little progress has been made with regard to the tool-edge micro defects and its corresponding elimination method It is a non-negligible factor that influences the machined surface quality, especially for brittle materials.
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