Papers by Author: Guang Qi Cai

Abstract: According to the analysis in theory, the model of quick-point grinding is different from conventional cylindrical grinding because it is point contact between the grinding wheel and the workpiece due to the point-grinding angles in two directions and the lower grain depth of cut in the process. Especially, the grinding speed has the great effects on the micro-geometry properties and the machining precision of the workpiece surface in the process. Based on the theoretical studies on the surface roughness, the grinding experiments and the measurements of the surface roughness at high grinding speeds were performed in quick-point grinding process. Furthermore, the influencing mechanism of the grinding speed on the ground surface roughness was analyzed. Some conclusions of the grinding parameters influencing precision machining and surface integrity were deduced.

Abstract: On the basis of static analysis, the stiffness model of the parallel grinding machine tool is established from the 3-TPS parallel grinding machine tool newly designed by Northeastern University. By analyzing its stiffness matrix, the optimal objective is given which is the average of the twenty condition numbers of stiffness matrix corresponding to the twenty positions in the margin areas of the workspace. With MATLAB software, the effects are simulated which the structural parameters of the parallel grinding machine tool have on their stiffness, their change laws are gained, and then the stiffness design of the parallel grinding machine tool are conducted based on these laws.

Abstract: It is innovative to combine abrasive jet machining and conventional grinding together in this thesis. And it realizes a new sort of grinding wheel restricted with abrasive jet processing. The three-dimensional mathematical model of hydrodynamic pressure of wedge-like grinding zone between grinding wheel and workpiece on abrasive jet finishing with wheel as restraint was established, and the finite elements simulation analysis for the hydrodynamic pressure was implemented. This paper investigated the liquid hydrodynamic pressure, the regularities of distributing of velocity, influencing factors and the affection for processing technique.

Abstract: The surface integrity finished by abrasive jet with grinding wheel as restraint was experimentally investigated. Experiments were performed with plane grinder M7120 equiped with abrasive jet finishing device and harded workpiece material 45 steel which was ground with the surface roughness values of Ra=0.6μm.The machined surface morphology was studied using Scanning Electron Microscope (SEM) and microscope and microcosmic geometry parameters were measured with TALYSURF5 instrument. The surface hardness for ground and finished surface was measured with HVS-1000 instrument and the phase structure was analyzed by X-ray energy dispersive spectram and residual stresses were measured by PW3208 X-ray diffraction. The Results show that longitudinal geometry parameter values were diminished and ripple was obviously improved comparing with ground surface. Furthermore, the finished surface has condensible residual stresses and high surface hardness comparability compared to grinding machining surface. As a result, life and precision consistency of finished workpiece were improved.

Abstract: The investigation of the experiment method on airflow field around super-high grinding wheel by PIV (Particle Image of Velocity, PIV) instrument was introduced in the paper. The measure system and scheme were designed for the experiment with PIV applied in the super-high speed grinding wheel for the airflow. The processing method of experimental data was discussed and the experiment result validated the feasibility of the experiment method.

Abstract: Quick-point grinding is used to machine the round surface with super abrasive wheel at high grinding speed. Because it is point contact between the grinding wheel and the workpiece due to the point grinding angles in the process, the grinding model is different from the conventional cylindrical grinding in theory. Especially, the edge contact width between the wheel and the workpiece is not always equal to the thickness of the wheel, but rests with the depth of cut and the grinding angles greatly. The depth of cut has the effects on the micro-geometric properties especially the ground surface roughness by means of the variations of the edge contact width, the grinding force and heat in the process. Based on the theoretical studies on the surface roughness, the quick-point grinding experiments and the measures for the surface roughness were performed at different depth of cut. The effective mechanism of the depth of cut on the ground surface roughness was analyzed deeply. Some conclusions to influence surface roughness were also gained.

Abstract: 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$m and finally achieve high efficiency, high precision and low roughness values, furthermore, integrating grinding process and abrasive jet finishing into one features. In the paper, surface topography finished by abrasive jet with grinding wheel as restraint was analyzed and evaluated with power spectral density function. Experiments were performed with plane grinder M7120 and workpiece material 45 steel. The machined surface morphology was studied using Scanning Electron Microscope (SEM) and the microscope and microcosmic geometry parameters were measured with TALYSURF5 instrument. The experimental results show that microcosmic geometry parameter values were diminished comparing with ground surface. Furthermore, the mean ripple peak distancing was decreased and, ripple and peak density were increased. The results indicate that surface qualities by machined with abrasive jet precision finishing were improved obviously.

Abstract: There are lower grinding force and temperature in quick-point grinding process because of the higher grinding speed and the less depth of cut, especially the point contact between the grinding wheel and the workpiece due to the point grinding angles. Thus it can achieve better surface finishing process in grinding cylindrical surface. Since the point grinding model is different from the conventional cylindrical grinding in theory, the surface roughness is in relation to the point-grinding angles greatly besides the grain granularity, depth of cut, grinding speed and axial feeding rate like the conventional cylindrical grinding process. Based on the theoretical studies on the surface roughness in the process, the surface finishing experiments and measures at the various grinding parameters were performed. The experimental results show that the process parameters, such as point-grinding angles, depth of cut, grinding speed and axial feeding rate, must be controlled reasonably for the higher surface finishing demand in quick-point grinding process.

Abstract: Surface microcosmic topography finished by abrasive jet with grinding wheel as restraint was analyzed and evaluated. Generating mechanism of surface morphology finished by abrasive jet with grinding wheel as restraint was investigated and surface topographical characteristics were also evaluated with cross correlation of random process. Experiments were performed with plane grinder M7120 and workpiece material 45# steel which was ground with the surface roughness values of Ra=0.2
0.6m. The machined surface morphology was studied using SEM and microscope and the microcosmic geometry parameters were measured with TALYSURF5 instrument. The experimental results shown that the machined surface change from continuous and parallel micro-groove and plough to randomly discontinuous micro-pit can be observed with machining circles increasing and surface roughness was obviously improved. Furthermore, The finished surface has little comparability compared to grinding machining surface.The isotropy surface and uniformity veins both parallel and perpendicular machining direction were attained by abrasive jet precision finishing with grinding wheel as restraint.

Abstract: The airflow field of super-high speed grinding was analyzed in the paper and the method of computing and analyzing the distribution of the field has been brought forward by applying boundary layer theory. Adopting the method of finite element, the model of airflow field in the 3-D grinding zone has been built up by using software; the solving strategy and the boundary conditions has been defined, where artificial viscosity coefficient in the repetitive and continuous analysis and the method by applying inertia relaxation have been discussed, which helped to revolve stability. The results of simulation was given and analyzed, which can be validated with experiment by using the equipment of PIV (particle image of velocity).