Papers by Author: Bei Zhi Li

Abstract: In order to reconcile the contradiction between the ceramic grinding efficiency and surface integrity, high-speed grinding with diamond grinding wheel is supposed to be a solution. In this paper, first of all, a normal grinding force model is proposed based on the consideration of the material property and the grinding process parameters. It can be seen that an elevated grinding wheel velocity in combination of a higher workpiece speed can increase the machining rate while maintaining the desired surface integrity. After a series of grinding tests, a comprehensive measurement has been done to study the surface damage by the surface roughness, the microscope profile and the X-ray diffraction. In particular, the effect of the grinding parameters on the ground surface are analyzed and reported.

Abstract: In this paper, an adaptive edge detection method (Canny operator and Otsu threshold selection based adaptive edge detection method - COAED) is proposed. The COAED method combines a new hybrid filter with Canny operator to avoid the conflict of Canny operator between noise removing and edge locating, and uses Otsu threshold selection method to determine Dual-threshold of Canny operator adaptively. The new hybrid filter firstly judges whether the pixel is polluted by impulse noise, and then uses a corresponding filter to process the current pixel. A median filter is used if the pixel is thought to be impulse noise; otherwise an improved mean filter is selected to weaken the Gaussian noise. After the image is smoothed by the hybrid filter, a Canny operator with small Gaussian variance is used to extract edge. Because only part of Gaussian noise remains, Canny operator with small Gaussian variance can suppress the noise and preserve the edge effectively. Using the gauge image polluted by hybrid noise as experiment object, the performance of COAED method is evaluated qualitatively and quantitatively. Experimental results show that the COAED method is superior to Canny operator.

Abstract: Simulation of FEM based grinding process has a lot of advantages in comparison with analytical models. In this paper, firstly, a simulation model of single grit high speed grinding for DIN-41Cr4 and Ti6Al4V by commercial software DEFORM 3D has been described. And then, grinding experiments and microscope observations of the single grit high speed scratch tests on both materials have been carried out. The end results show that the wheel velocity has a positive influence on the strain rate. Additionally, the temperature lag effect will be much more significant under high-strain-rate process condition. In other words, it is the theoretic element of temperature decrease phenomenon on the wheel-workpiece contact area during high speed grinding. Furthermore, it is found that the high strain rate also optimizes the chip formation performance, which makes it possible to machine difficult-to-cut materials, titanium alloy for example, with high efficiency.

Abstract: The existing research shows that high-speed grinding is the main way to machining the common materials and difficult-to-machine materials efficiently and critically. However, the research on mechanism and high-speed characteristics of high-speed cylindrical grinding is few searched. Based on three-dimensional simulation software DEFORM-3D, the simulation model of high speed cylindrical grinding with single grit was established, and the relevant experiment of 3D simulation for high speed cylindrical grinding process was processed. In this paper, the impact of the grinding parameters, such as wheel speed and depth of cut on the grinding force and grinding temperature is explored through analyzing the variation of strain rate, grinding force and temperature, and found that the increasing strain rate can lead to the increase in grinding force and temperature. According to the simulation experiment results, the control model of grinding temperature for prediction of grinding temperature and optimization of grinding parameters, is analyzed and developed in the end. The engineering experiment, conducted on the high speed cylindrical grinder and measured grinding temperature with thermal infrared imager, has been carried out in this study. Engineering and simulation experiments results show good match, for grinding temperature would decline with the increasing wheel speed when the grinding depth keeps constant, and thus can reduce grinding burn, improve the surface quality of workpiece.

Abstract: With FEM software of AdvantEdge, a model was created to analyze cutting force and thermal in the high-speed milling process, this model included a complete milling process of cutter radius. Combined with experiments validation, in high-speed milling, the normal force is greater than the tangential force and result in greater residual stress of that direction, which indicates that mechanical force play an essential part on the formation of residual stress. When the speed is over certain scope, the cutting force decreases, but the cutting temperature has been rising. In Roughing, by limiting the range of high-speed the residual tensile stress impact can be reduced. While in finishing, as the feed rate reducing the residual tensile stress will decrease greatly, improving the surface quality of thin-walled parts.