Papers by Keyword: Ductile Mode

Abstract: Monocrystal sapphire ground surfaces obtained by ductile mode and brittle mode are analyzed in this paper. A two dimension (2D) fractal properties of different ground surfaces are calculated and analyzed by a box-counting fractal method. The results show that the fractal dimension (FD) in parallel grinding direction can imply the material removal mode, especially for the surfaces with a similar roughness Ra obtained in different material removal modes. The ground surface obtained in ductile mode has much higher FD in the parallel direction than that in brittle mode. For the surface with high FD in parallel direction, its profile is more exquisite and surface quality is better. For the surface with a small FD in the parallel direction, a deeper crack and more pronounced defects occur. On the other hand, the profile FD distributions can reflect the anisotropic features of monocrystal sapphire ground surfaces. Therefore, the fractal analysis method has the potential to reveal precisely and comprehensively the ground surface characteristics of monocrystal sapphire.

Abstract: A theoretical analysis for the effect mechanism of elliptic vibration assistance on the cutting of brittle materials is presented in this paper. The crack propagation in the chip formation zone in cutting of brittle materials is examined based on an analysis of the geometry and forces in the cutting region. The cutting model shows that the actual undeformed chip thickness is much decreased with elliptic vibration assistance, and the instantaneous rake angle of the cutting tool edge is also in a larger negative value than those in conventional cutting. These two conditions can ensure the compressive stress is much larger than the shear stress during the cutting process. Then the stress intensify factor is suppressed effectively and the shielding effect on the growth of pre-existing flaws is strengthened in the chip formation zone. The removal of brittle material tends to be in ductile mode without fracture. The characteristic examination of cutting force shows that the ratio of thrust force to cutting force with elliptic vibration is increased compared to that of conventional cutting. This can validate that the larger compressive stress can be generated in the chip formation zone with elliptic vibration assistance. The transition depth to brittle machining of silicon carbide with/without elliptic vibration assistance further supports the presented theory.

Abstract: As the reliable technology, ultrasonic assisted machining is widely used for brittle materials. This paper provides a two-dimensional(2D) ultrasonic vibration assisted machining technology with tool vibration using elliptical vibrator with longitudinal mode and bending mode, and set up the experiment device. Si wafer is taken as the workpiece, and single point cutting experiments for micro groove are investigated. For the further application, the ultrasonic assisted polishing experiment with wheel block is executed. Experimental results indicate that ultrasonic assisted cutting with tool vibration can improve the cutting performance and enhance the ductile removal. And the ultrasonic assisted polishing with whetstone piece makes the better surface roughness and higher material removal rate.

Abstract: There is a demand for high-efficiency and high surface integrity grinding of fused silica. Ductile grinding is an ideal method for producing a mirror finished surface on hard and brittle materials to significantly decrease polishing time. However, the fused silica is still difficult to ductile grind because of its high brittleness. A creep feed taper grinding method was applied to investigate the relationship between maximum grit depth of cut and surface integrity of fused silica. Ductile mode grinding was achieved on fused silica. When the depth of cut exceeds the critical wheel depth of cut, the surface suddenly changes from the ductile mode to the brittle mode. At the same ratio of wheel speed and table speed, the critical wheel depth of cut is noticeably increased by increasing the wheel speed which caused an increase in the temperature at the interface of grains and workpiece. The depth of subsurface damage (SSD) was investigated by polishing the ground surface. The experiment results show that the depth of SSD is deepest in transition mode and stables in brittle mode.

Abstract: Indentations on the three main crystallographic planes (100), (110), and(111) of CaF2 were analyzed. Appropriate material parameters were obtained by experimental load-displacement curves. The results show a value in the range of 70–110 MPa for the initial shear yield strength. The submicron-level orthogonal cutting process of CaF2 had been investigated by the finite element approach, and the effects of tool rake angle on cutting stress and chip formation were investigated. The results indicate that increasing the tool rake angle causes a significant increase in stress and a decrease in chip thickness. The simulation results from the present study show the optimal tool rake angle to the ultra-precision cutting of CaF2 is -20°.

Abstract: Fused silica is an important material for optics of ultraviolet laser transmission. It is difficult to be ground in ductile mode because of a high brittleness. In this paper, ductile mode grinding was achieved by a taper grinding method when the initial surface was a polished surface. However, when the initial surface was an unpolished surface, ductile mode grinding could not be realized because of the existence of surface and subsurface damages. The damages on the ground fused silica surface were repaired by CO2 laser irradiation with optimal laser power and scanning velocity. The optimal parameters were determined by studying the viscosity of fused silica and etching depth of laser irradiated groove. Besides laser processing parameters, surface roughness of laser irradiated surface is also greatly influenced by the initial surface roughness.

Abstract: This paper describes the cutting characteristics of lithium niobate, which is used for surface acoustic wave type micropumps, regarding the formation of micro grooves by direct cutting. Since lithium niobate is a brittle material with a strong crystal orientation dependency, significant differences were observed in the characteristics of the finished surface according to different directions of cutting. The ductile mode cutting of lithium niobate was found to be feasible with cutting depths of approx. 5 μm or less. Also, results of the study show the feasibility of the formation of minute grooves through the cutting of lithium niobate, using milling with an end mill.