Papers by Author: Yong Bo Wu

Abstract: Fibre-reinforced polymer (FRP) composites have been widely used in industry. However, the machining of FRP products is difficult, because of very different properties of the fibres and matrix. This paper discusses the development and implementation of a microstructure-based three-dimensional finite element model for the elliptic vibration-assisted (EVA) cutting of unidirectional FRP composites. The results showed that the EVA cutting has a good potential to the machining of FRP composites, featured a much reduced cutting force, better surface integrity and controllable chip size.

Abstract: A kind of zirconia-coated carbonyl-iron-particles (CIPs), which show long-time stability against aqueous, is installed in magnetic compound fluid (MCF) to polish PMMA. Performance (normal polishing force and surface roughness) of zirconia-coated CIP based MCF slurry with different CIP concentrations is investigated. For comparison, the performances of the conventional non-coated CIP (i.e., HQ) based MCF slurry and MRF slurry in which DI-water is employed instead of MF are also examined. In the presence of Al2O3 abrasive particles, the use of zirconia-coated CIP based MCF slurry can not result in better polishing performances compared with conventional HQ CIP based MCF slurry; In the absence of Al2O3 abrasive particles, higher normal polishing force and smoother work-surface were obtained with the zirconia-coated CIP based MCF slurry rather than the MRF slurry; For the zirconia-coated CIP based MCF slurry without abrasive particles, the concentration of zirconia-coated CIP should be less than a certain value (in the current work, 70 wt. %), otherwise MCF slurry shows bad particle dispersion and is easily dried, resulting in the loss of its polishing ability.

Abstract: Ultrasonic vibration assisted processing is well known for the improvement in machined surface quality and processing efficiency due to the reduced forces and tribology-generated heating when grinding hard-brittle materials. We transplanted this philosophy to chemo-mechanical fixed abrasive polishing of optical glass, namely fused silica, in an attempt to improve surface roughness and/or material removal rate. Experiments were conducted to elucidate the fundamental characteristics of chemo-mechanical fixed abrasive polishing of fused silica in the presence and absence of ultrasonic vibration on a setup with an in-house built gadget. The experimental results show that ultrasonic vibration assisted chemo-mechanical fixed abrasive polishing can yield increased material removal rate while maintaining the surface roughness of manufactured optics compared to conventional fixed abrasive polishing without ultrasonic vibration. The mechanism of material removal in fixed abrasive polishing was also delved. We found that the glass material is removed through the synergic effects of chemical and mechanical actions between abrasives and glass and the resultant grinding swarf contains ample Si element as well as Ce element, standing in stark contrast to the polisher that contains abundant Ce element and minor Si element.

Abstract: Ultrasonic-vibration-assisted micro-cutting of Ti-6Al-4V was simulated by finite element analysis software ADVANTEDGE. During the micro-cutting of Ti-6Al-4V the cutting forces were compared between conventional and ultrasonic-vibration-assisted method. In the ultrasonic-vibration-assisted micro-cutting process different frequency and amplitude were applied on the cutting tool. The influences of frequency and amplitude were analyzed. The cutting temperature increases with the increase of the amplitude, and the cutting temperature decreases with the increase of frequency. By using the simulation method the appropriate amplitude and frequency data can be obtained.

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: A theoretical discussion has been presented for the ductile chip formation in grinding of brittle materials. The single abrasive grit was dealt with a top-rounded cutter removing material of varying undeformed chip thickness. The force model in the chip formation zone was established. The stress analysis showed that larger compressive stress and shear stress can be generated in the chip formation zone, which shields the growth of pre-existing flaws in the material by suppressing the stress intensity factor. When the stress intensify factor is smaller than fracture toughness and the resolved shear stress exceeds the critical flow stress of the material, the ductile chip is formed. Experiments of monocrystal silicon grinding were conducted. The results show that the thrust force is much larger than the cutting force, which ensures the larger compressive stress in the chip formation zone and the formation of ductile chip.

Abstract: Laser cladding of micro-fluidic channels mold was performed using Nd:YAG laser and synchronous powder feeder. Influences of laser power and powder feed rate on clad layer geometrical dimensions and qualities were investigated. Results show that powder feed rate 1.5-2.5 g/min used obtains micro clad layers which meet geometrical dimensions’ requirement of micro-fluidic channels mold and combination of parameters laser power 400 W and powder feed rate 2.0 g/min achieves micro clad layer with better clad quality. Scanning paths of micro-fluidic channels mold was planned through CAD-CAM software. Using optimum parameters combination, multilayer laser cladding experiment was carried out and a sample of micro-fluidic channels mold was fabricated with expectative structure and hardness. A little milling and polishing makes the sample meet technical requirements, 0.2mm in height and 0.3mm in width. Fabricating a mold takes 15-20 min totally.

Abstract: The finishing process of a metal mold depends on the hand work of experts by using a whetstone tool in many cases. This is because it is difficult to treat the three-dimensional configuration, such as free-form surfaces and convex and concave configurations. To overcome this difficulty, we propose a dynamic magnetic field assisted finishing using magnetic compound fluid (MCF) for three-dimensional configurations. In this paper, we demonstrate the MCF slurry (MCF mixed abrasive and cellulose fiber in) under dynamic magnetic field shows the high form restoration and generates the high normal force compared to that under static magnetic field; resulting in shows the high finishing performance. Moreover, we compare and discuss the surface roughness and form accuracy under both static and dynamic magnetic fields against three-dimensional configuration made of high hardness non-ferrous mold steel HPM75, which is used for plastic injection mold.

Abstract: This paper describes the wear behaviors of a resin bond diamond wheel in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire. 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 our previous work, an experimental apparatus mainly composed of the vibrator was produced and grinding experiments were conducted involving sapphire workpiece. In this paper, further investigations focusing on the wear behaviors of resin bond diamond wheel in EUAG of sapphire were carried out experimentally. The obtained results showed that: (1) the wheel wear process can be divided to three regions according to the variation trend of grinding forces, i.e., an initial region, a steady region, and a deteriorated region; (2) in the initial and steady regions, the grinding forces and the ratio of the normal grinding force to the tangential grinding force in EUAG are much smaller than that in conventional grinding (CG), but in deteriorated region, the grinding forces in EUAG are increased significantly up to be larger than that in CG whereas the grinding forces ratio has few difference between those in EUAG and CG; (3) in all the regions, the work-surface in EUAG is much smoother than that in CG whereas the wheel wear has little influence on the work-surface roughness; (4) the wheel wear in CG is mainly caused by the attrition wear and the macro-fracture and pullout of abrasive grains, while in EUAG by the micro-fracture and cleavage of abrasive grains.

Abstract: This study investigates surface formation characteristics in elliptical ultrasonic assisted grinding (EUAG) of monocrystal sapphire. During EUAG process, the workpiece is imposed to ultrasonically vibrate in two directions, i.e., vertical and parallel to work-surface, by using an elliptical ultrasonic vibrator. In our previous work, the vibrator has been produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body. When two alternating current voltages with a phase difference are applied to the PZT at the same frequency that is close to the resonant frequency of the longitudinal and bending mode of the vibrator, two dimensional ultrasonic vibrations are generated simultaneously, resulting in an elliptical motion on the end face of the vibrator. In this paper, to clarify the work-surface formation characteristics in EUAG of sapphire material, grinding experiments are carried out involving sapphire substrate. In experiments, work-surface roughness is measured, and the ground work-surface morphology is examined by scanning electron microscope (SEM). The experimental results are summarized as: (1) Compared with conventional grinding (CG), the elliptical vibration leads to a decrease of surface roughness up to 25% in EUAG; (2) The surface roughness has a monotonously increasing trend with the increasing wheel depth of cut in both EUAG and CG, but has little variation with the worktable feed rate. As the wheel speed increases, the surface roughness decreases until it reaches a minimum, and then increases in a monotonous trend in both EUAG and CG; (3) The surface quality in EUAG has a significant improvement, and it is prone to achieve the ductile regime grinding of sapphire compared with CG. These indicate that the elliptical ultrasonic assisted grinding is an efficient technique for high performance machining of monocrystal sapphire.