Wen Ji Xu

Modeling of Laser Dressing for Metal-Bond Diamond Grinding Wheel

Laser processing of super-abrasive grinding wheel is paying a role in a truing/dressing technique to complement mechanical methods recently. However, normal dressing/truing is difficult owing to the toughness of metal-bond materials and high hardness of diamond abrasive. Both geometric and mathematic models were developed to improve laser processing quality and predict various processing parameters, such as focal offset, and incident power, and power density to perform material removal during laser processing a metal-bond diamond grinding wheel. Various trends of the geometrical features of dressing zone in terms of the varying focal offsets were analyzed. Discussions were also given on dressing-zone geometry control. Experimental studies were carried out using different processing parameters to test the effects of laser poweres on dressing quality. Further grinding-force measurement determined the laser dressing parameters with respect to the wheel surface conditions. The normal force FN reduces up to 20%, while tangential force FT decreases to 7% too.The outcomes were shown well agreement with predicted results.

Gear Finishing and Modification Compound Process by Pulse Electrochemical Finishing with a Moving Cathode

Gears’ surface quality and modification characteristic have an important influence on its working performance. Pulse Electrochemical Finishing (PECF) could get excellent surface topography. In this project, PECF with a scanning cathode is used to finishing the cylinder gear. Tooth profile modification is realized by PECF with an uneven interelectrode gap distribution along the tooth profile and tooth lead modification is realized by PECF with a variable moving velocity of the cathode. The experimental results show that the tooth surface roughness could be decreased from Ra 3.9μm to Ra 0.35μm, which means that the PECF process possesses the finishing ability for the raw surface tooth, and the difference of material removal of PECF with an uneven interelectrode gap distribution could be 46μm and the material removal could be controlled by regulating the moving velocity of the cathode, which means tooth profile and lead modification could be realized by PECF.

Influence of In-Flight Particle Characteristics on the Forming Quality

There are many technical parameters influencing on the coating quality in plasma spray forming which has become an important technology in materials processing. In this study, the relationships between the melting state, in-flight property of particles injected into plasma jet and the forming quality have been investigated. The experimental results show that the temperature field distributions of plasma jet are mainly affected by plasma generator power though CCD imaging and gray-scale processing. The velocity of in-flight particle is directly determined by the flow rate of work gas, and the surface temperature of in-flight particle is obviously affected by assisted gas rate. It is clear that the energy coupling and momentum transferring between plasma and particle have a significant influence on deposition efficiency, porosity, microhardness and microstructure of spray-formed parts, and it also provides a good idea to control the forming quality on-line.

An Experimental Study on 3D Forming of Sheet Metal Using Plasma Arc

For the development of flexible forming using plasma arc (FFUPA), it is extremely necessary to investigate the forming rules of curvilinear scanning and multipath combined scanning. In this paper, the difference between circular scanning and linear scanning and the influence of sheet metal geometry on forming effect have been discussed. In the experiments, circle, ring and rectangle mild steel sheets with thickness of 0.8mm are taken as workpieces and the experimental results show that nonlinear prolonged surface can be obtained by curvilinear scanning and there exists the obvious difference between circular scanning and linear scanning. Afterwards, the reason of the difference mentioned above is concisely analyzed. Finally, some suggestions are presented for the future investigation.

FGM Mould with Fine Veins Rapidly Manufactured by Plasma Spraying

There is the advantage of continuity in organic structure and mechanical property for functionally gradient materials (FGMs), but it is unable to be used in the mould industry for the difficulty of the second machining up to now. In this study, a novel technology of FGM mould with fine veins fabricated by plasma spraying has been developed, which can easily realize the integration of FGM forming and deep machining of the mould. According to applied characteristic of plastic injection mould, WC-12%Co/NiCrAl powders are selected and the reasonable FGM coating has been prepared. Spraying processes have been investigated, such as fabrication of spray mould with fine veins, FGM forming, backing and demoulding, etc. At the same time, the metallography, porosity and microhardness of the spraying layer have been analyzed. The results show that the service performance of the FGM mould is much more excellent than that of the traditional mould, and the life span can also be greatly improved. The research will have a significant influence on the material development in the mould industry.

Experimental Research on the Dry Electrostatic Cooling Assisted Machining for Hardened Steel

Dry electrostatic cooling (DESC) assisted machining is one of the green machining technologies that uses ionized air flow as lubricating and cooling medium in the machining process. The influence of discharge parameters on the efficiency of ion transport and ozone concentration in the DESC is experimentally researched. The results show that the efficiency of ion transport increases with the rising of the discharge current and air pressure, but decreases with the rising of the distance from the nozzle and the nozzle diameter. The tungsten electrode is used to obtain high ozone concentration with the nozzle diameter of 2-4mm, air pressure of 0.2-0.4MPa, and the distance from the nozzle within 0.5mm. Experimental research on the DESC assisted machining for hardened steel GCr15 shows that cutting force decreases by 7%-28%, tool wear reduces by 30-50%, and tool life is 1.5-3.3 times more than dry cutting. Better results are achieved when increasing the cutting speed.

Research on Mechanism of Electrochemical Mechanical Finishing

This contribution aims at the mechanism of electrochemical mechanical finishing (ECMF). The change in surface micro-profile of workpiece and its influence on anodic electrochemical dissolution (ECD) as well as the action of the mechanical role were investigated. The results show that the peak-like micro-profile of surface is in favor of improving the ability of ECD. The mechanical role not only scratches the passive film resulted from ECD, but also changes the surface micro-profile of the workpiece. The action of the mechanical role influences the final finished surface quality of the workpiece.

Energy Model in Laser Processing of a Cylindrical Grinding Wheel

Laser processing of abrasive grinding wheels is paying a great role in a truing technique to complement mechanical methods. An energy balance model was adopted that took into account the space modes of laser energy absorbed/scattered by the wheel (circular profile). Both geometric and mathematic models were developed to reveal laser processing mechanism and predict various processing parameters, such as incident position, focal offset, and incident power, to perform material removal during laser processing a cylindrical grinding wheel. Moreover, the incident angle for laser processing of small-vitrified CBN grinding wheels was optimized. Further theoretical analysis and experiments determined the focal position of the incident beam with respect to the wheel profile. Experimental studies were carried out using different processing parameters and grinding wheels to test the effects of laser space properties on processing quality. The experimental results were shown to be in reasonable agreement with predicted results.

Energy-Mode Adjustment in Laser Processing a Small Vitrified CBN Grinding Wheel

A study of the energy-mode adjustment and application was presented to investigate the effects of adjustable methods on energy mode. Three methods of energy-mode adjustment were used: by circular profile itself, by an optical scanning expander and deformable mirror. The circular profile naturally modifies energy density with the changes of incident angle. The optical scanning expander was used to turn a Gaussian beam into a uniform beam. Also a novel technique of deformable mirror was designed to obtain a more controllable energy mode for laser selective processing. Moreover, the models describing energy modes were developed to improve laser-processing performance. An experiment was arranged to simulate single-tip diamond truing and produced a result, as shown in the SEM photo, quite similar to a fine thread. The results were discussed to reveal the mechanism of laser processing.

Fabrication of Superhydrophobic Surfaces on Aluminum Substrates via Electrochemical Etching and Re-Deposition

Superhydrophobic surfaces on metal substrates are often prepared via roughing the surfaces and lowering their surface energy. The superhydrophobic aluminum surface with a water contact angle of 162.5° and rolling angle less than 6° was fabricated via electrochemical etching and re-deposition using the alkalic Na3PO4 electrolyte and then fluorination treating. The surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the surface consists of the micrometer-scale lumps and protrusions, and many nanometer-scale mastoids are filled in these protrusions. These hierarchical micro/nanometer-scale binary structures, which are similar to the micro-structures of lotus leaf surfaces, play an important role in achieving superhydrophobicity. The main components of the binary geometric structures are Al2O3, AlPO4, and H2O. The effects of the processing time and processing voltage on the macro-morphology were also investigated. The macro-rough structures appeared on the edge of the aluminum surface firstly, and then spread gradually to the entire surface.