Papers by Author: Guang Qi Cai

Abstract: Grinding experiments for quenched high-speed tool steel by resin bonded CBN (cubic boron nitride) wheel were conducted with a surface grinder. The grinding forces were measured under different grinding parameters. The effects of grinding parameters on grinding forces and grinding force ratio are discussed. Specific grinding energy and heat flux over the grinding zone are computed according to grinding parameters and grinding forces. The effects of grinding parameters on specific grinding energy and heat flux are investigated.

Abstract: In order to investigate that shields have the effect on the thermal equilibrium of CNC machine tool, this paper applies the theory of heat transfer and finite element analysis to analyze the thermal characteristics of CNC lathe CK40A/1000. By ANSYS software, the temperature distributions of spindle engine, headstock and bearing at thermal equilibrium with/without shields are obtained. By analyzing thermal equilibrium patterns and experiments, the temperature of spindle bearings with shields are 3-4 higher than without shields at thermal equilibrium. And shields have less influence on the temperature gradient of tool inner thermal sources.

Abstract: The stiffness model of the parallel machine tool is established by static analysis, the static stiffness analysis is carried out through numerical Simulation and the stiffness distribution is given. On the basis of this, the optimal objective is given which is the average of 729 values of -axis stiffness and -axis stiffness corresponding to 729 positions in the workspace. With MATLAB software, the effects are simulated which the structural parameters of the parallel machine tool have on their stiffness, their change rules are gained, and this provides a basis for the structural design of this type of machine tools.

Abstract: Grinding temperature is the main factor to limit the improvement of grinding efficiency. The main reason of grinding temperature rise is amount of heat transfer into the workpiece in grinding process. How to determine the proportion ratio, which heat transfers into the workpiece, is the main research issue to the precise machining scholars. In this paper, the heat resistance model is used to analyze the proportional coefficient about how much heat transfer into the grinding wheel, and the factors which to influence this coefficient are discussed. The moving heat source method is used to calculate the temperature field caused by single grain heat source, and the heat integral method is used to calculate the heat contains by the grinding chip, and then the heat proportional coefficients transferring into the chip and workpiece are determined respectively.

Abstract: 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.

Abstract: During cylindrical grinding process, the geometric configuration and size of the edge contact area between the grinding wheel and workpiece have the heavy effects on the workpiece surface integrity. In consideration of the differences between the point grinding and the conventional high speed cylindrical grinding, the geometric and mathematic models of the edge contact area in point grinding were established. Based on the models, the numerical simulation for the edge contact area was performed. By means of the point grinding experiment, the effect mechanism of the edge contact area on the ground surface integrity was investigated. These will offer the applied theoretic foundations for optimizing the point grinding angles, depth of cut, wheel and workpiece speed, geometrical configuration and size of CBN wheel and some other grinding parameters in point grinding process.

Abstract: To design a machine tool successfully, its essential parts should be analyzed and evaluated after design but before prototype being made. The spindle assembly is one of the most essential parts of high speed machine tool, so how the dynamic characteristics of the spindle assembly affect the performance of high speed NC machine tool are of great significance and should be studied. This paper’s research is based on a high speed machine tool manufactured by some plant. The finite element analysis model of the spindle assembly of the high speed machine tool was developed by taking the advantage of the spring-damper element to simulate the bearing supports. The modal analysis was made to confirm the dynamic characteristics of the spindle assembly, and the results were compared with the testing ones.

Abstract: With the correlation in stochastic process applied to the experimental results, the surface during grinding and further lapping with abrasive jet finishing (AJF) restricted by grinding wheel was investigated with respect to auto correlation function (ACF) , cross correlation function (CCF) and power spectral density (PSD) analysis. The results indicated that AJF made the surface contour formed periodicity in a small range and removed fluctuation of the surface contour in low frequency greatly. The average spacing of the surface contour decreased and the machined surfaces changed from continuous parallel micro-groove and plough to randomly distributed discontinuous micro-pit with the increase of machining circles. The surface texture became fine and surface roughness was obviously improved. Furthermore, the isotropy surface and uniformity veins both parallel and perpendicular machining direction was attained by the finishing process to improve greatly the wearable capability of the workpiece.

Abstract: Due to the high grinding speed and the less contact length, there is the super high material strain rate in the contact layer during quick-point grinding process. Based on the principle of micro-damages mechanics, it is the impact process between the workpiece and the grits on the wheel in the process. The weakening effects of the super high strain rate caused by the mechanical impact micro-damages and the adiabatic shearing damage can lower the dynamic strength of the material in contact layer and the micro-plastic pile-up deformation on the ground surface in the process. Therefore, it is possible to improve the surface integrity of the workpiece since the materials removal mechanism is changed in quick-point grinding process. In this paper, the impact performances and the model of quick point grinding process were studied. Based on the above, the model of the ground surface roughness related to the plastic pile-up deformation was established. The effects of the strain rate on the ground surface roughness and the materials removal ratio were analyzed. In addition, the grinding experiment was performed to testify such investigations. It is indicated that quick-point grinding is an impact process assuredly during the removing material process.

Abstract: Grinding is a very complex machining process. Single grain grinding methods are useful to study complex grinding action. Very low speed single-grain grinding tests were carried out for 45 steel and 20Cr alloy with 14# ZA grain. The grinding groove width and depth, the grinding force ratio, specific grinding forces, and grain wear and fracture are studied. The plowing decreases with the grinding section area or grinding depth increase. The average tangential force at grain fracture in the experiments is 54.4N; the average normal force at grain fracture is 949.6N. The ratio of tangential-to-normal force varies suddenly when grain fracture.