Key Engineering Materials Vol. 416

Abstract: This paper presented a new technique, which was the online wear evaluation of wheel in grinding WC-Co coating by using wavelet packet decomposition. Based on the measurement method, theory of online wear evaluation of wheel was introduced. The selection principle of characteristic signals was brought up, and the grinding acceleration signal was the best choice among many characteristic signals. The time domain signal analysis method of wavelet packet decomposition was analyzed. Lastly, experiments on the wear of wheel were performed, and experimental results showed the validity of the method.

Abstract: A new dressing device for dense type diamond grinding wheel, whose elliptic vibration was prompted by single longitudinal vibration, was designed using a local resonance method. It was employed to dress the metallic bond super-abrasive grinding wheel and the dressing force characteristics were analyzed. The results indicate that the thrust force decreased to 1/7-1/10 of that of conventional method, and the main cutting force decreased by 70%. Compared to other dressing parameters, the dressing force in elliptic ultrasonic vibration was more sensitive to grinding speed. Thrust force and main cutting force increased rapidly when rotation speed beyond 72rpm. But when the ultrasonic power was higher than 50W, dressing force decreased very slowly. It was observed that the new dressing method is contribute to better surface finish such as more even surface, less crush abrasives, more uniform abrasive abscission and so on than the conventional method.

Abstract: Combining the advantages of rheological behavior of magnetorheological fluid (MRF) and flexibility adjustability of rubber gasbag, a magnetorheological flexible gasbag polishing technique applied to free-form mould is proposed. With the development of robotic gasbag polishing technique, the flexibility of rubber gasbag can be adjusted by three methods of changing its internal pressure controlled through a pressure control unit, its own material property and structural parameter, and the rheological behavior of MRF inside of it in response to the application of an alterable magnetic field. Effect of rheological behavior to the flexibility of rubber gasbag and surface quality of mould is the single most important focus in this paper. The magnetorheological flexible gasbag polishing system is established and rheological behavior of MRF with magnetic field is described. Through polishing experiment focusing on the relationship between the surface roughness and current around electromagnetic coil, it can be obtained that magnetorheological flexible gasbag polishing technique is effective to improve surface quality when increasing current around coil in certain extent.

Abstract: Surface phase structure has an important effect on the surface machining quality. The surface phase transition characteristics of ZrO2 and ZTA ceramics under different machining methods were tested by X-ray diffraction in the paper. Through the qualitative and quantitative phase analyses, the influences of several different precision machining methods on the phase transitions in the machined surface were studied. Research results show that there are more transitions from tetragonal phase ZrO2 to monoclinic phase ZrO2 in the high speed grinding surface; because of the high-frequency vibration of lapping tool in ultrasonic lapping, the stress condition in the grinding area can be improved and the stable tetragonal phase ZrO2 in the ultrasonic lapped surface is easy to get. The research conclusions have important significance on analyzing the surface residual stress and improving the surface machining quality of engineering ceramics.

Abstract: Brittle materials are popularly used as engineering materials for excellent properties. But the properties of brittle materials are different and special, and cause to different surface formation mechanism during the grinding process. In the study, surface roughnesses after grinding with different mesh size diamond wheels were measured. Combined with scanned surface topographies, the relation between the surface roughness and the properties of these brittle materials was discussed. It could be found that the material properties led to the different surface characteristics of brittle materials.

Abstract: An attempt has been made to investigate the new generational manufacturing technology for multi-layer diamond tools by brazing. A kind of new multi-layer brazed diamond core drills with random grains distribution was made by mixing diamond particles with brazing alloy powders. And a preliminary machining performance experiment was carried out through drilling granite. The testing results show the typical topography of the multi-layer brazed diamond core drills after drilling granite, just like that of multi-layer sintered ones, is that diamond grits drag long tails. Different from multi-layer sintered diamond core drills, no grit pull-outs can be seen during the whole drilling process because of chemical metallurgical effect between diamond grit and brazing alloy, the same as monolayer brazed diamond core drills. The main drawback to this kind of multi-layer brazed diamond tools is each individual particle is not subjected to the same drilling force throughout the drilling operation because of random grain distribution. This leads to premature fracture of the leading particles. Similarly, because large gaps between particles exist, the bond is being exposed to the workpiece, which leads to erosion of the bond. The overall performance is lower tool lives and slower drilling speeds. Therefore, ideally, diamond particles should be evenly distributed throughout the bond, which means they are all subject to the same drilling forces and the multi-layer brazed diamond tool is operated at its optimum efficiency.

Abstract: Taking MATLAB as the experimental platform, the detection and recongnition method of steel ball surface defect is put forward. With the method, we could determine whether there are surface defects or not, and identify the types of defects. The process of detection and recognition is as follows: Firstly, two-time wavelet de-noising treatment of the steel ball image is achieved by means of ecomposition, quantization of threshold and recongnition of Sym4 wavelet function, afterward, many collected noise of the steel ball image is reduced effectively. Secondly, the de-noised image is preprocessed and then we can calibrate the boundary of the defects accurately, which is used to extract the characteristic parameters of defects. Thirdly, the types of defects of steel ball are judged, and the process of pattern recognition is reasonablely designed by putting forward the shape parameter F, combined with the characteristic parameters of the defects. Lastly, the feasibility and validity of the detection and recongnition algorithm are verified by lots of analysis about experimental results especially the analysis on the experimental results comparing with the given data.

Abstract: Relative motion of single abrasive is analyzed for the different applied directions of longitudinal ultrasonic vibration, and its locus is simulated in the present paper. The research results show that the locus in two-dimensional ultrasonic vibration is only similar to that in y-direction, and both are close to sinusoid curves. The width of grooves scratched by abrasive grains y-direction (axial direction of grinding wheel) is two times of the vibration amplitude, and the material removal rate increases remarkably. In case of x-direction (tangential direction of grinding wheel) ultrasonic vibration, abrasive grains with periodic force impact material surface with high frequency vibration, which make material fracture removal easy. Therefore, the high efficiency essence of material removal in two-dimensional ultrasonic grinding is revealed in view of locus. In addition, according to the results of grinding experiments, under same conditions good surface quality can be obtained in two-dimensional ultrasonic grinding and material removal rate in common grinding is the lowest. Consequently it is further proved that the method of two-dimensional ultrasonic vibration grinding is an effective one for ceramic materials.

Abstract: Experimental research on grinding characteristics of nano-composites ceramics were carried out using diamond wheel in two-dimensional ultrasonic vibration grinding (TDUVG) and the topography of the scratched grooves were observed with Transmission Electron Microscope. The surface crack, plastic deformation and brittle-ductile transition during chip formation were analyzed. Subsequently, the grinding model of nano-composites ceramics machining in TDUVG was established based on fracture theory of micro-indentation in fracture region and plastic information mechanism of hard-brittle materials. The metamorphic layer can be divided into three regions: brittle-fracture, non-elastic deformation and residual damage region. Ultrasonic grinding process can be divided into three phase: elastic friction and extrusion, crack growth and crack propagation and chip formation.

Abstract: ZTA ceramics is a kind of high performance structural ceramics, and its surface/subsurface damages after machining have great effect on reliability and long-service life of ceramic parts, so it introduces two-dimensional ultrasonic vibration assisted grinding (TUVAG) which is applied in the precision finishing of ZTA ceramic, mathematic motion model of abrasive grain during TUVAG is established, and the special machining path of abrasive grain during TUVAG is analyzed, and the surface/subsurface damages of ZTA ceramics after TUVAG are further discussed. Experimental results prove that TUVAG may make materials removed in a plastic state mostly, the probability of cracks formation and propagation becomes less, and obviously reduce surface damages of ZTA ceramics, and the grinding badness layer of ceramics after TUVAG is shallower than that after diamond grinding at the same grinding parameters.