Papers by Author: Yong Bo Wu

Abstract: Carbon fiber reinforced plastic (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. In order for CFRP materials to be used in aircraft structures or machine elements, high quality holes must be created on them efficiently. However, it is difficult for conventional methods such as drilling, helical milling and so on to meet the requirements. Therefore, this study proposes a novel method for creating holes on CFRP products. This method is just performed by tilting the workpiece at a certain angle on the basis of conventional helical milling (CHM) and hence called tilt helical milling (THM). In this paper, the processing principle of the THM is described in detail at first. An experimental apparatus is then constructed by installing a work holding unit produced in house onto a CNC milling machine. Finally, experiments are carried out on the apparatus. The obtained experimental results demonstrated that the THM is capable of creating holes on CFRP with lower burrs and chippings formation compared with those by CHM. By this new method, high quality holes could be obtained with high efficiency compared with conventional methods.

Abstract: Oxygen-free copper (OFC) is a popular material used for molds/dies in injection molding of plastic lens because of its high ductility, strong impact strength and good thermal conductivity. nanoprecision polishing is essential as the final process in its fabrication. For this purpose, a novel polishing method using magnetic compound fluid (MCF) slurry was proposed. In this article, the construction of an experimental rig to realize the proposed method was described at first. Then the effects of process parameters including MCF slurry composition, workpiece oscillation parameter f/A_p-p and clearance Δ between workpiece and MCF carrier on work-surface roughness and material removal were experimentally investigated. As a result, nanoprecision surface finish of OFC was successfully attained by polishing with MCF slurry and the optimum process parameters (f/A_p-p=30 Hz/4mm, Δ=0.6 mm with an MCF slurry (45wt.% of CIP, 12 wt.% of Al₂O₃ grain, 3 wt.% of α-cellulose, 40 wt.% of MF) for obtaining the smoothest work-surface were determined.

Abstract: Inconel 718 has high yield strength, corrosion resistance, heat resistance and fatigue resistance, and possesses a lower thermal conductivity, leading to high grinding force and heavy wheel damage in grinding of this material. Against these problems, ultrasonic assisted grinding (UAG) can be the potential candidate for high efficiency processing of Inconel 718. The current work is, hence, to clarify the fundamental UAG characteristics of Inconel 718 by experimentally investigating the effect of vibration amplitude on grinding force, actual material removal and work-surface roughness under different process parameters such as the wheel rotational speed, wheel depth of cut and vibration amplitude. Summarizing the obtained results revealed that the grinding forces and the actual material removal in UAG are significantly smaller and larger, respectively, than those in conventional grinding. It is also found that ultrasonic vibration can improve the work-surface finish even at deep wheel depth of cut.

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: Based on the regularities of motion of the rigid polyurethane rubber ultrasonic vibration assisted grinding, combined with the kinematic analysis of the general theory and experiments. This paper analyses the variation in position, velocity and acceleration during the manufacture of single abrasive grinding with and without ultrasonic vibration. The impact of rigid polyurethane rubber micro V - groove process introduced by the ultrasonic vibration is explored to verify the feasibility of the ultrasonic vibration assisted grinding of micro-precision machining of hard polyurethane rubber material.

Abstract: Ultrasonic assisted grinding experiments were carried out to evaluate the effects of the ultrasonic vibration (UV) on the face grinding characteristics of nickel based superalloy of Rene77. In experiments, an electroplated cBN grinding wheel was ultrasonically vibrated dominantly along its axis. The experimental results indicated that the X-axis and Y-axis components of grinding forces with UV were smaller by 44.5% and 31.6%, respectively, than those without UV. The usual fractures and debris on the surface of workpiece disappeared and the work-surface roughness Ra was decreased by 42.3% once the UV was applied. The abrasion of the grinding wheel without UV is more serious than that with UV.

Abstract: In this paper, a new machining method is proposed for the high efficiency turning of titanium alloy Ti-6Al-4V in which the cutting tool is ultrasonically vibrated. An experimental setup is constructed by installing an ultrasonic cutting unit onto a NC lathe followed by experimental investigations on the fundamental machining characteristics. The results obtained in the current work showed that (1) the cutting force decreases with the increase in the power supplying level (i.e., the ultrasonic vibration (UV) amplitude), e.g., the cutting force components in X-. Y-and Z-directions were decreased by 48%, 45% and 87%, respectively, once the UV has been applied to the tool at the power supplying level of 50%; (2) the cutting marks with knit pattern are formed on work-surface with UV while the parallel distributed cutting marks are generated without UV, and the surface roughness is decreased by up to 10% when the UV is applied at an appropriate power supplying level; (3) the work-surface straightness is improved by 46% once the UV is applied.

Abstract: Grinding forces characteristics in elliptical ultrasonic assisted grinding (EUAG) of sapphire are investigated experimentally. The EUAG is a new grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The effects of the vibration amplitude and grinding parameters such as the depth of cut, the grinding wheel speed on the grinding forces, grinding force ratio F_n/F_t are clarified. The obtained conclusions are as follows: the grinding forces during EUAG lowers to 50% and grinding forces ratio becomes reduced by 33% compared that during conventional grinding (CG); the grinding forces during EUAG have the less variation rate than those during CG as grinding parameters change; higher grinding wheel speed causes the larger grinding forces in CG, but has little effect on the variation of grinding forces in EUAG. By using EUAG method, the grinding forces and force ratio are greatly decreased, and surface quality is better, meaning that grindability of sapphire material is improved.

Abstract: Ultrasonic assisted turning (UAT) is an efficient cutting technique for difficult-to-cut materials. In order to study the effect of vibration parameters on machining performance, tool-workpiece contact ratio (TWCR) was defined. A finite element model for ultrasonic assisted turning of Ti-6Al-4V was established. Effects of tool vibration frequency, tool vibration amplitude and workpiece cutting speed on cutting force and cutting temperature were analyzed. It is observed that both the increase in the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting forces and cutting temperature. By using the finite element model the appropriate tool vibration frequency, tool vibration amplitude and cutting speed can be obtained.

Abstract: For the final finishing of the substrate surface, Chemo-mechanical polishing (CMP) is often utilized. Those processes are able to offer a great sur-face roughness, but sacrifice profile accuracy. On the other hand, Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of CMP. In order to simultaneously achieve high surface quality and high profile accuracy, CMG process has been applied into machining of large size quartz glass substrates for photomask use. In this paper, based on the characteristics of higher machining efficiency and higher surface quality of ultrasonic vibration machining, a new ultrasonic vibration assisted CMG of silicon wafer hybrid technique is achieved by designing elliptical vibrator with longitudinal mode and bending mode. The experimental results show that under the elliptic ultrasonic vibration assistance, the surface roughness is decreased significantly, the surface quality is improved obviously, and moreover caused little or even doesn’t lead to the surface damage.