Bing Heng Lu

Influencing Factors on Dynamic Response of Hydrostatic Guideways

Stiffness and damping of hydrostatic guideways are calculated by small perturbation method based on Reynolds equation in dynamic regime. The hydrostatic guideway is considered as a system which consists of the mass, the spring and the damper. The effects of some main parameters on stiffness, damping and damping ratio are analyzed which include the supply pressure, the film thickness, the pad dimension, the pressure ratio, the lubricating oil volume and the lubricating oil viscosity. The relationships between the settling time of the hydrostatic guideways and these parameters are investigated under a step load. It is shown that the slide block returns to equilibrium without overshooting under a step load, and the amplitude of the block vibration has not a maximum value under a cyclic load, due to the large damping effect( ξ>1). In addition, the settling time can be shorten with the increase of the supply pressure, the film thickness and the lubricating oil volume, and also with the decrease of the pressure ratio and the lubricating oil viscosity. The settling time get the shortest value when recess parameter( α) is 0.55.

Analytical and Experimental Investigation of the Nickel Based Superalloy Using Cryogenic Cooling Grinding

Grinding processes are mainly technique employed widely as a finishing and difficult-to machine such as hardness and brittleness materials machining. However in grinding process, high grinding zone temperature may lead to thermal damage to the work surface, induces micro-cracks and tensile residual stresses at the ground surfaces, which deteriorate surface quality and integrality of the ground surface. The work presented in this paper aims at evaluating the grindability and surface integrity of the nickel base superalloy resulting from the application of cryogenic cooling. Grinding experiments were conducted under three different environments: dry, mineral oil and cryogenic cooling jet. The grindability results have shown that while the cryogenic cooling generates the lowest grinding temperature, no significant differences over the specific grinding force components were observed. As for the ground surface integrity, however, substantial improvements were realized. The novel process not only obviously enhances surface quality and integrality of grinding surface, but also enables retention of the wheel sharpness for a longer period and reduces pollution of grinding fluid to nature.

Analysis of Quadrature Phase-Shift Error Caused by Angular Misalignment in Moiré Linear Encoders

The influence of quadrature phase shift caused by angular misalignment on the measurement accuracy of two moiré linear encoders is analyzed. A mathematical model of quadrature phase-shift error is derived. The model is employed to analyze the quadrature phase-shift error in lateral-moiré-fringe-based and Vernier-moiré-fringe-based linear encoders respectively, and comparisons are carried out. The results show the nonlinearity of the quadrature phase-shift error and the relative insensitivity of the Vernier-moiré-fringe-based linear encoders to the angular misalignment.

Analysis and Measurement of Effective Flow-Rate in Flood Grinding

In the grinding process, grinding fluid is delivered for the purposes of chip flushing, cooling, lubrication and chemical protection of work surface. Due to high speed rotating grinding wheel, the boundary layer of air around the grinding wheel restricts most of the grinding fluid away from the grinding zone. Hence, conventional method of delivering grinding fluid that flood delivery is not believed to fully penetrate this boundary layer and, thus, the majority of the grinding fluid is deflected away from the grinding zone. The flood grinding typically delivers large volumes of grinding fluid was ineffective, especially under high speed grinding conditions. In the paper, a theoretical model is presented for flow of grinding fluid through the grinding zone. The model shows that the flow rate through the contact zone between the wheel and the work surface depends on wheel porosity and wheel speed as well as depends on nozzle volumetric flow rate and fluid jet velocity. Furthermore, the model was tested by a surface grinding machine in order to correlate between experiment and theory. Consequently, the effective flow-rate model was found to give a good description of the experimental results and the model can well forecast the effective flow-rate in flood delivery grinding.

Power Spectral Density and Cross Correlation Function Analysis of Finished Surface by Abrasive Jet with Grinding Wheel as Restraint

The abrasive jet finishing process with wheel as restraint is a kind of compound precision finishing process that combined grinding with abrasive jet machining, in which inject slurry of abrasive and liquid solvent to grinding zone between grinding wheel and work surface under no radial feed condition when workpiece grinding were accomplished. The abrasive particles are driven and energized by the rotating grinding wheel and liquid hydrodynamic pressure and increased slurry speed between grinding wheel and work surface to achieve micro removal finishing.In the paper,the finished surface morphology was studied using Scanning Electron Microscope (SEM) and microscope and microcosmic geometry parameters were measured with TALYSURF5 instrument respectively. According to the metrical results, the surface topographical characteristics were evaluated with correlation function and PSD (Power Spectral Density) of random process about machined surface before and after finishing. The results show that longitudinal geometry parameter values of finishing machining surface were diminished comparing with ground surface,and the mean ripple distance was decreased and, ripple and peak density were increased. Furthermore, the finished surface has little comparability compared to grinding machining surface.The isotropy surface and uniformity veins at parallel and perpendicular machining direction were attained by abrasive jet precision finishing with grinding wheel as restraint and the surface quality is improved obviously.

Study on Integrated Method of Medical Implant Manufacture Based on Rapid Prototyping Technology

The traditional method to manufacture the medical implant or prosthesis is based on sculpting and on the tissue site,or takes impressions of the entire face about human. The accuracy and efficiency of medical implant or prosthesis produced by conventional method is heavily relied on the skill and experience of both designer and manufacturer. In this paper, an integrated method of medical implant manufacture is approached. This integrated strategy was to establish a system that allows fabrication of facial prosthesis from digital information, and integrates the rapid prototyping with modeling technology of complex three-dimensional geometry from high-resolution non-invasive imaging, reverse engineering and computer aided design. The research results have shown that the integrated method can produce more exact-fit medical implant, that is, the physical model of the implant is more exactly fitted on the skull model. The advantages of this method are that the surgeon can plan and rehearse the surgery in advance, and a less invasive surgical procedure, and less time-consuming reconstructive, and an adequate esthetic can result.

A Measurement System for Step Imprint Lithography

A precision 6-degree-of-freedom measurement system has been developed for simultaneous on-line measurements of imprint lithography stage. To successfully accomplish nanometer-scale pattern transfer from mold to resist film on the wafer, two types of positioning methods, static and dynamic, are used in this system. Two laser interferometers, two optical reflection mirrors and special structure on the stage with 3 elastic tracks are employed in this system to detect the positions and rotations of the stage. Through an algorithm, measurements of pitch, yaw and roll motions can be achieved. This system can realize on-line position detecting. Based on adjusting of PZTs, the detecting precision can reach 10nm and ±3 milli-arcsec, respectively. The measuring range can reach 100mm and ±10 arcsec, respectively.

Research on the Accuracy of Mask Projection Stereo-Lithography

In this research, sub-region curing and mask DPI modification are used to improve the accuracy of MPSL. Because the curing shrinkage at the discrete region does not cause the shrinkage of the entire resin surface, the accuracy of the RP work piece under sub-regional MPSL can be improved effectively. For the optical system error, the accuracy can be improved through the DPI (Dot per Inch) modification. The research results show that accuracy of work piece less than 12mm can be improved through DPI (Dot per Inch) modification. For the work piece above 16mm, the main method which improves the accuracy can adapt sub-region curing procedure. The combination methods of sub-regional exposure and exposure mask DPI modification can significantly improve the dimensional accuracy of parts, and the overall size of the error of parts can be controlled less than 1%.

Innovative Technology Investigation into Cryogenic Cooling Green Grinding Using Liquid Nitrogen Jet

Grinding processes are mainly technique employed widely as a finishing process in a variety of materials, such as metals, hardness and brittleness and ductile materials machining to achieve good dimensional and form accuracy of the product with acceptable surface integrity.However, grinding is associated with high specific energy requirements which may be an order higher than that required in other conventional machining processes such as turning, planing, milling etc. Therefore, in grinding process, high grinding zone temperature may lead to thermal damage to the work surface, induces micro-cracks and tensile residual stresses at the ground surfaces, which deteriorate surface quality and integrality of the ground surface. Therefore, grinding fluids are applied in different forms to control such high temperature, but they are ineffective, especially under high speed grinding conditions where the energy of the fluid is not sufficient to penetrate the boundary layer of air surrounding the wheel. Moreover, the conventional flood supply system demands more resources for operation, maintenance, and disposal, and results in higher environmental and health problems. Therefore, there are critical needs to reduce the use of cutting fluid in grinding process, and cryogenic cooling grinding is a promising solution.The work presented in this paper aims at evaluating the grindability and surface integrity of the nickel base superalloy resulting from the application of cryogenic cooling. KeywordsInnovative technology, Cryogenic cooling, Surface integrity, grinding

Modeling and experimental investigation of useful flow-rate in flood delivery grinding

In the grinding process, grinding fluid is delivered for the purposes of chip flushing, cooling, lubrication and chemical protection of work surface. Due to high speed rotating grinding wheel, the boundary layer of air around the grinding wheel restricts most of the grinding fluid away from the grinding zone. Hence, conventional method of delivering grinding fluid that flood delivery is not believed to fully penetrate this boundary layer and, thus, the majority of the grinding fluid is deflected away from the grinding zone. The flood grinding typically delivers large volumes of grinding fluid was ineffective, especially under high speed grinding conditions. In the paper, a theoretical model is presented for flow of grinding fluid through the grinding zone. The model shows that the flow rate through the contact zone between the wheel and the work surface depends on wheel porosity and wheel speed as well as depends on nozzle position, design, fluid jet velocity. Furthermore, the model was tested by a surface grinding machine in order to correlate between experiment and theory. Consequently, the useful flow-rate model was found to give a good description of the experimental results and the model can well forecast the useful flow-rate in flood delivery grinding.