Key Engineering Materials Vols. 407-408

Abstract: Using the tiny-grinding wheel based on the synergistic effect of the electro-magneto- rheological (EMR) fluid, a novel method is presented to machine the three-dimensional (3D) microstructure of hard-brittle materials. Machining experiments of micro-groove were conducted to reveal the machining performances of the tiny-grinding wheel. Experimental results confirm the effectiveness and feasibility of the micro machining technique with the EMR effect-based tiny-grinding wheel. The shape of machined micro groove is found to be an inverted trapezoid, and the material removal mode of normal glass with the micro machining method is the plastic-removal mode. With the increase of the rotation speed of the tool, the material removal rate, width and depth of micro grooves increased first and decreased afterwards. The maximum removal rate, width and depth of micro groove occur at different speeds of the tool.

Abstract: In nanometric cutting process, the actual material removal can take place at atomic level, which makes it difficult or impossible to observe the machining phenomena and measure the cutting parameters in experiments. However, it is crucial to investigate the cutting process in nanoscale. In this study, the molecular dynamics (MD) method is employed to model and simulate the process of cutting monocrystalline copper. The two-body Morse potential and the many-body EAM potential are used for the atoms interaction in the workpiece to study the effect of different potential function on the simulation results. It is found that there are no obvious differences in the chip formation between Morse and EAM potential, but the Morse potential results in higher potential energy and more chips generated in the cutting process.

Abstract: We have developed numerically controlled local wet etching (NC-LWE) as a novel deterministic subaperture figuring and finishing technique, which is suitable for fabricating various optical components and finishing functional materials. In this technique, a chemical reaction between the etchant and the surface of the workpiece removes the surface without causing the degradation of the physical properties of the workpiece material. Furthermore, the processing properties of NC-LWE are insensitive to external disturbances, such as the vibration or thermal deformation of the machine or the workpiece, because of its noncontact removal mechanism. By applying the NC-LWE process using HF/HNO3 mixtures to etch the silicon, we corrected the thickness distribution of the bulk silicon wafer with a diameter of 200 mm and achieved the total thickness variation of less than 0.23 µm within the diameter of 190 mm.

Abstract: Numerically controlled local wet etching is a novel figuring method for fabricating the ultraprecision optical components and/or finishing the functional materials. In this method, localized wet etching area is formed by applying the combination nozzle which consists of a supply part and a suction part of an etchant, and the removal volume at any point on the workpiece surface is determined by the dwelling time of the nozzle. In this paper, we proposed the two-step figuring process, which consists of a rough figuring process by applying a one-dimensional numerically controlled scanning using a large rectangular nozzle and a finishing process by applying two-dimensional numerically controlled scanning using a small circular nozzle, for figuring the plano-aspherical mirror. By applying the two-step figuring process, we fabricated the plano-elliptical neutron focusing mirror with the figure accuracy of less than 0.5 µm and succeeded in achieving the focusing gain of 6.

Abstract: Micro lens array is widely used in photonics and telecommunication products, including back-light module of flat panel display devices and white-light LED illumination. The ultra precision diamond shaping method together with tool servo technique was studied and developed in this research to generate elliptical micro lens array. Each elliptical micro lens has radii in X and Y direction of 1.0 mm and 1.5 mm respectively. A high filling-factor (100 %) elliptical micro lens array with form accuracy better than 0.15μm and surface roughness around 5nm Ra was successfully fabricated.

Abstract: Stainless steel SUS304 is one of the typical difficult-to-cut materials due to strong tendency to adhesion and work hardening. Therefore finished surface becomes rough in machining operations. In this report, precision cutting of SUS 304 is discussed. Surface roughness depends on accuracy of the machine tool, adhesion and roughness of tool flank. We analyzed the factors of surface roughness in turning of SUS304 on an engine lathe. M20 tungsten carbide inserts, coated carbide inserts and cermet inserts were used. Peak-to-valley height of machined surface included approximately 1μm of machine error. Surface profile reflected roughness of tool flank. Polished flank decreased the roughness of finished surface. Adhesion was least in the case of cutting with cermet inserts. We also conducted face turning of SUS304 on an ultra-precision lathe with cermet inserts. Flank of the inserts were polished to 100nmRz. We obtained 50nm of minimum peak-to-valley height and 220nmRz of surface roughness.

Abstract: Polycrystalline diamond (PCD) has been widely used for various cutting tools and die components making use of its hardness and wear resistance properties. The polishing method of a single crystal diamond substrate and SiC using ultraviolet irradiation was newly developed to obtain mirror-finished surfaces. Due to the long polishing time in this method, a better pre-machined surface is required to shorten the total processing time. In this work, the constant-pressure grinding was performed using a cup type metal-bonded diamond wheel and a constant pressure device. After the good constant-pressure grinding, the PCD was finished by the polishing under the ultraviolet irradiation, and the microroughness was reached to be 0.71 nmRa.

Abstract: The existing studies based on 2-dimension cutting model are partial investigations on tool wear. In order to get close to the true cutting conditions, the Lagrangian thermo-viscoplastic cutting simulations were conducted and the tool wears were predicted under different cutting speeds using 3-dimension finite element models. The simulation results indicate that when the cutting speed increases the cutting forces will reduce accordingly while the wear depth will be deeper. As a result, different factors should be considered at the same time when the speed range is selected. This study has shown that the finite element method is a valuable approach to understand the tool wear mechanism in machining and the influences of different cutting speeds.

Abstract: An analytical model of drilling temperature was developed based on the thermal model of orthogonal cutting and equivalent model. In this model, the element of cutting edge of twist drill was acted as an independent cutting process. The effects of drilling parameters on the temperature were also investigated. Tests were conducted with various parameters and temperature was measured by manual thermocouple method. Results indicated that the predicted results were according to the measured ones; the errors were less than 15%. And the laws obtained by analytical model were the same as that obtained by tests.

Abstract: An objective of this study is to develop a new method for the prediction and the avoidance of chatter vibration in milling operation of thin-walled structure by using 3D-CAD and CAE approach. Also, a new identification method for the modal parameters of a vibration system by analyzing radiated sound pressure from vibrated workpiece accelerated by an impulse force is proposed. Then chatter stability lobes are predicted using those modal parameters. Stiffness and modal shapes of the workpiece were obtained using commercial finite element method (FEM) code, and the model was made by 3D-CAD. The damping ratio, which cannot be determined through FEM analysis, was identified from the relationship between the sound pressure radiated from the workpiece and the impulse force. Chatter stability limit was analyzed with the modal parameters obtained through these procedures, and compared with the cutting experiment on the chatter stability limit. The experimental and predicted stability limits are in good agreement. The proposed procedure will help to set the cutting conditions to avoid the chatter.