Feifei Xu

Glass-ceramic optical components are extensively employed in advanced optical systems. The high-hardness and low-fracture toughness of glass-ceramics make it prone to cracks and subsurface damage during conventional cutting. The laser-assisted diamond cutting method can significantly improve the nano-cutting performance of glass-ceramics by locally heating and softening the material. However, its dynamic removal mechanisms remain unclear. The coupling mechanisms between the laser thermal field and the mechanical response of the material require further investigation. This study aims to reveal the dynamic removal mechanisms of glass-ceramics under laser-assisted nanoscale cutting conditions through numerical simulations and systematic experiments. It includes a systematic analysis of the effects of laser heating on chip morphology, temperature fields, stress fields, and cutting forces using a laser-assisted nano-cutting model. Additionally, through nanoscale taper cutting experiments, this study quantifies the enhancement effect of laser power on the critical depth of no observed surface cracks (NOSC). Finally, subsurface integrity results elucidate the mechanisms through which laser assistance inhibits crack propagation. The findings will provide theoretical support for optimizing laser-assisted cutting parameters and achieving high-quality machining of glass-ceramics.

Overcut or poor surface quality will easily during thin floor milling due to its low rigidity. Machining with the assistance of mobile support device is an important and frontier manufacturing method for milling the thin floor of a pocket on the thin-walled workpiece. Existed mobile support devices that provide positive contact pressure can effectively avoid the poor surface quality which caused by the vibro-impact vibration between the workpiece and the milling cutter but not the overcut. Besides, inappropriate support element will lead to surface damage to the backside of the floor. This paper proposes a new supporting method to overcome the aforementioned problems encountered during milling the thin floor of a pocket on the thin-walled workpiece. The method utilizes a directionally controllable high-pressure air jet to provide adaptive support for thin-walled workpiece and the air jet support synchronously follow the motion of the milling cutter. Specifically, when milling with a high level of axial depth of cut, the direction of the high-pressure air jet is controlled to flow away from the floor to generate a sucking pressure, which applies a pulling force on the floor to counteract the axial milling force and thus inhibits overcut behavior. On the other hand, when milling with a low level of axial depth of cut, the direction of the high-pressure air jet is controlled to flow toward the floor to generate a positive pressure, which applies a push force to prevent cutter-workpiece impact vibration and thereby improve surface quality of the machined surface. An experimental platform is constructed to verify the feasibility of proposed method. Milling experiments under conditions of no air jet support, air jet support with positive pressure and air jet support with sucking pressure are conducted based on the built platform. Force signals, surface roughness and part accuracy are compared and the critical depth of cut for the transition from vibro-impact vibration behavior to overcut behavior is revealed. The results indicate that the high-pressure air jet with controllable flow direction is effective to suppress the vibro-impact vibration and overcut behaviors during thin floor milling process. It also successfully avoids damage of the backside of the floor caused by the rigid support element, improving both machining accuracy and surface quality. The findings validate the feasibility of the proposed method. The developed method expands the applicability of current milling processes with mobile support devices assistance and provides some valuable insights for the design and optimization of air jet support with controllable flow direction.

Purpose: The microcutting performance of the ¹⁰B/Al composite is significantly poor because of the existence of hard boron particles. The effects of cutting parameters, including uncut chip thickness and cutting speed, on the material removal mechanism and surface generation are investigated to improve the surface quality. Design/methodology/approach: The 2D finite element model, which includes a rigid cutting tool, a reinforced phase, a matrix and a dense layer, is established. The effects of uncut chip thickness on material removal mechanism and surface generation are analyzed from a probabilistic perspective. The relationship between the uncut chip thickness and the probability in which the machined surface will have a better surface quality is constructed. A Gaussian distribution formula is applied to describe the machined surface quality. Findings: Two representative particle-removal modes, namely, cutting-through and pulling-out modes, are observed. For cutting-through mode, when the relative cutting location is small, better surface quality is obtained. For pulling-out mode, the quality of the machined surface gradually improves because the further increase of the relative cutting location reduces the height of the generated pit and scratches. The microcutting at high cutting speed tends to suppress the scratch phenomenon. The best surface quality will be obtained at small uncut chip thickness and high cutting speed. Originality/value: The surface quality generated in microcutting of the ¹⁰B/Al composite can be improved by optimizing the cutting parameters and controlling the particle-removal modes based on the proposed Gaussian distribution formula.

The side flow of material in nano cutting is one of the most important factors that deteriorate the machined surface quality. The effects of the crystallographic orientation, feed, and the cutting tool geometry, including tool edge radius, rake angle and inclination angle, on the side flow are investigated employing molecular dynamics simulation. The results show that the stagnation region is formed in front of tool edge and it is characterized by the stagnation radius R s and stagnation height h s . The side flow is formed because the material at or under the stagnation region is extruded by the tool edge to flow to the side of the tool edge. Higher stagnation height would increase the size of the side flow. The anisotropic nature of the material which partly determines the stagnation region also influences the side flow due to the different deformation mechanism under the action of the tool edge. At different cutting directions, the size of the side flow has a great difference which would finally affect the machined surface quality. The cutting directions of {100} < 011>, {110} < 001>, and {110} < 1-10 > are beneficial to obtain a better surface quality with small side flow. Besides that, the side flow could be suppressed by reducing the feed and optimizing the cutting tool geometry. Cutting tool with small edge radius, large positive rake angle, and inclination angle would decrease the side flow and consequently improve the machined surface quality.

The material characteristics such as size effect are one of the most important factors that could not be neglected in cutting the material at nanoscale. The effects of anisotropic nature of single crystal materials in nano-cutting are investigated employing the molecular dynamics simulation. Results show that the size effect of the plastic deformation is based on different plastic carriers, such as the twin, stacking faults, and dislocations. The minimum uncut chip thickness is dependent on cutting direction, where even a negative value is obtained when the cutting direction is {110}. It also determines the material deformation and removal mechanism (e.g., shearing, extruding, and rubbing mechanism) with a decrease in uncut chip thickness. When material is deformed by shearing, the primary shearing zone expands from the stagnation point or the tip of stagnation zone. When a material is deformed by extruding and rubbing, the primary deformation zone almost parallels to the cutting direction and expands from the bottom of the cutting edge merging with the tertiary deformation zone. The generated surface quality relates to the crystallographic orientation and the minimum uncut chip thickness. The cutting directions of {110}, {110}, and {111}, whose minimum uncut chip thickness is relatively small, have better surface qualities compared to the other cutting direction.