Ya Li Hou

Model and Simulation of Slurry Velocity and Hydrodynamic Pressure in Abrasive Jet Finishing with Grinding Wheel as Restraint

The models for three-dimensional velocity and hydrodynamic pressure of abrasive fluid in contact zone between wheel and workpiece on abrasive jet finishing with wheel as restraint were presented based on Navier-Stokes equation and continuous formulae. The emulational results shown that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and workpiece and the maximum pressure was generated just in the minimum clearance region in which higher fluid pressure gradient occur. It can also be concluded the pressure distribution was uniform in the direction of width of wheel except at the edge of wheel because of the side-leakage. The velocity in the x direction was dominant and the side-leakage in the y direction existed. The velocity in the z direction was smaller than the others because of the assumption of laminar flow. The smaller the gap distance is, the larger the velocity in the x direction. The magnitude of the velocity is also proportional to the surface velocity of the wheel.

Application of Lubrication Theory to Near-Dry Green Grinding – Feasibility Analysis

This paper describes an investigation about the grinding fluid optimization supply based on lubrication theory. The models for three-dimensional hydrodynamic flow pressure in contact zone between wheel and work are presented based on Navier-Stokes equation and continuous formulae. It is well known that hydrodynamic fluid pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Moreover, conventional methods of delivering grinding fluid, i.e. flood delivery via a shoe or jet delivery tangential to the wheel via a nozzle, have been proved that they can not fully penetrate this boundary layer and thus, the majority of the cutting fluid is deflected away from the grinding zone. Therefore, in this paper, a new delivery method of grinding fluid, the minimum quantity lubricant (MQL)-near-dry green grinding is presented and analyzed for it not only reduces hydrodynamic lift force but also reduces grinding fluid cost to achieve green manufacturing. Experiments have been carried out to validate the performance of the MQL supply compared with conventional flood cooling. The experimental results have shown that the theoretical model is in agreement with experimental results and the model can well forecast hydrodynamic pressure distribution at contact zone between and workpiece and the MQL supply in grinding is feasible. Experiments have also been carried out to evaluate the performance of the MQL technology compared with conventional flood cooling. Experimental data indicate that the proposed method does not negatively affect to the surface integrity and the process validity has been verified.

Investigation into the Mechanical Properties of Nanometric Zirconia Dental Ceramics

This study was focused on the testing and assessment of the mechanical properties of nanometric zirconia dental ceramics. The density and the apparent porosity of specimens were tested with the Archimedes drainage method. The length variation of the specimens before and after sintering was measured with a vernier caliper, and the linear contraction was tested. An X-ray diffractometer was used for the specimen phase analysis. SEM was used to observe the section micrograph of the specimens. A universal mechanical testing machine was used to test the three-point flexural strength and the fracture toughness. A microhardness tester was used to test the Vickers hardness of the test specimens. Results indicates that the flexural strength of the test specimens ≥ 890MPa, the fracture toughness ≥6Mpa.m1/2, the Vickers hardness ≥ 1240MPa, the linear contraction ≥ 21%, and the apparent porosity ≥ 0.32%. Fully satisfying the requirements in oral medicine, the ceramic is an ideal material for biological joints and dental prosthesis.

Expanding of College Students’ Scientific Quality and Innovation with the Carrier of Research Program

In order to meet the demands of high-quality talents raised by the nation, guide and inspire the college students’ hard thinking so as to get more fruits and improve their personal refinement, continuously promote the standard, systematic, and scientific construction of scientific innovation of our students, create a good atmosphere for the students’ participation into the scientific research and practice, and to cultivate high-quality comprehensive talents with innovation capability, in accordance with the reality of our college, we propose that taking the research program as the carrier, the students take part in the instructors’ scientific program. Meanwhile, the instructors are responsible for the scientific innovation activities of the students, and give evaluations in terms of working attitude, scientific quality, innovation capability, working effect. After several years’ exploration, a satisfied result is achieved.

Investigation into High-Speed/Super-High Speed Grinding

Abrasive machining is a widely employed finishing process for different-to-cut materials such as metals, ceramics, glass, rocks, etc to achieve close tolerances and good dimensional accuracy and surface integrity. High speed and super-high speed abrasive machining technologies are newest developed advanced machining processes to satisfy super-hardness and difficult-to-machining materials machined. In the present paper, high-speed/super-high speed abrasive machining technologies relate to ultra high speed grinding, quick-point grinding, high efficiency deep-cut grinding were analyzed. The efficiency and parameters range of these abrasive machining processes were compared. The key technologies and the newest development and current states of high speed and super-high speed abrasive machining were investigated. It is concluded that high speed and super-high speed abrasive machining are a promising technology in the future.

Investigation into the Grindability and Surface Integrity of the Nickel Base Superalloy Using Liquid Nitrogen Jet Grinding

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, planning, 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 grind ability and surface integrity of the nickel base super alloy resulting from the application of cryogenic cooling.

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.

An Investigation into Integrate the Surface Hardening with the Grinding Precision Finishing

The grinding hardening is a new surface heat treatment technology using grinding heat in which induce martensitic phase transformation in the surface layers of annealed or tempered steels to achieve surface strengthening processes and integrate the surface hardening process with the grinding precision machining. In the paper, a thermal model to describe this process has been presented from the thermal partition modeling and has been used to predict subsurface time–temperature profiles in the dry cylindrical grinding crankshaft using cubic boron nitride (CBN) wheels. The grinding hardening experiment was carried out in precision cylindrical grinder M1420E, using work-piece material 42CrMo4 and CBN grinding wheel under dry grinding condition. The experimental results showed the theoretical model is agreement with experimental results and the model can well forecast the grinding hardening depths.

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.

Power Spectral Density Analysis 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 precision machining, in which inject slurry of abrasive and liquid solvent to grinding zone between grinding wheel and work surface under no depth of cut 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 machining. The micro removal machining with grinding wheel as restraint, not only to attain higher surface form accuracy but also to can efficiently acquire defect-free finishing surface with Ra0.15~1.6