Key Engineering Materials Vols. 304-305

Abstract: Block electrode discharge grinding is an effective approach to produce micro rods. However, it is difficult to fabricate the rods into desired miniature and precision. To solve this problem, the tangential feeding method is proposed to control the finish size of micro rods. With this method, the micro rod is first fed in its radial direction, and then in the tangential direction for an enough distance. The wear of the block electrode decreases gradually from the start to the end, and the wear in the end can be neglected. Experiments indicate that the large capacitance or voltage can obtain high machining speed, while the small ones can gain thin micro rods. Based on this result, the policy of delaminating grinding is adopted to gain enough thin micro rods at a high machining speed. The Φ5µm micro rods can be ground with this method. SEM results show that the relative error of the size control is less than 10%.

Abstract: PCD tools, especially curve edge PCD compound tools are used widely in machining nonferrous and non-metal materials with high efficiency and precision because of their excellent cutting properties. But high quality grinding of PCD tools is the uppermost obstacle in application because there are great difficulties to profile and sharpen edge in grinding, especially for milling cutter and drill with curve edge. This paper studied technology of wire EDG curve edge PCD compound tools by wire electrical discharge grinding machine with five-axis CNC system. The grinding quality was evaluated by scanning electron microscope (SEM) and roughometer. Three steps processing technique (roughing, finishing and fine finishing) and optimal process parameters of wire EDG PCD tools were recommended after considering synthetically the surface quality, precision and machining efficiency. The results met the requirement of high surface quality, precision and efficiency. This paper also applied successfully the optimal technology to grind a PCD milling cutter with outer and inner blade by electrical discharge grinding machine with five-axis CNC system. By the optimal parameters, the process yielded high precision of ±4.3µm and low roughness of 0.30µm. Experiment results have great practical significance to the high precise and efficient wire EDG of PCD tools.

Abstract: According to the composition of nano ceramics, the paper firstly analyses mechanism of^nano ceramics materials surface machining in ultra precision grinding processes and gives a new critical grinding depth formulation. Then many grinding experiments have been done between the nano ceramics and the common ceramics in the same grinding parameters and grinding methods. Atomic force microscopy (AFM) images show that nano ceramics have outstanding machining performance. Its grinding processes is plastic material cutting like metal cutting, and nicks are clear and brittleness desquamated pits existing in common ceramics grinding surface have not found in nano ceramics grinding surface. Then, according to analyze microcosmic surface quality by AFM, the conclusion is that the nano ceramics surface quality is better than the common ceramics after grinding processes. Concretely, its surface roughness Ra tower above one or two degree than the common ceramics, and there is no crackle, no nick, and no obvious cutting defect. The research results provide experimental and theoretical guides for selection of grinding parameters and grinding methods.

Abstract: It is an effective method to enhance the engineering ceramic grinding efficiency using the organic grinding fluid added with the long chain alcohol. In the cutting-grinding experiment, the ceramic grinding efficiency was 2.4 times higher than the common grinding fluids. The microstructural analysis and the hardness testing performed for the liquid-solid interface using the Raman Spectrum technology and the nano impression technology found that there were abnormal peaks in the Raman Spectrum of the liquid-solid interface between the ceramics and the organic grinding fluid and the presence of abnormal peaks was familiar with the changing rules of surface hardness. The effect might change the grinding mode of the diamond grain micro-blade in the grinding process, thus to affect the grinding efficiency and the machining quality. It is a research direction to be further discussed.

Abstract: The fuzzy allowable intervals of the deflection, the vibration frequency and the fatigue strength of the shaft fixing grinding wheel are proposed in present paper based fuzzy set theory. According to fuzzy probability theory, the fuzzy reliability model of the rigidity, the fuzzy reliability model of the vibration and the fuzzy reliability model of the fatigue for the shaft fixing grinding wheel in internal grinding are given. The method is put into real example.

Abstract: The hierarchy model for grindability evaluation of ceramics was set up. All influence factors of ceramic grindability can be considered together by application of analytic hierarchy process (AHP) approach. Material property parameters and grinding parameters were selected as evaluating factors to have a comprehensive estimation of ceramic grindability. Saaty 1-9 scales were applied to make comparison matrix by pairwise comparison of factors. Then weights of factors were calculated. The grindabilities of ceramics were evaluated by comparison of comprehensive values of grindability. SiC, Al2O3, Si3N4 and ZrO2 were evaluated with AHP approach as an example. Five influence factors, including hardness, fracture toughness, elastic modulus, grinding force and material removal rates, were selected for evaluation. Grindabilities of four ceramics, ranking form easy to difficult, are SiC, Al2O3, ZrO2 and Si3N4. The research shows that AHP approach is a reasonable and effective evaluation method for grindability of ceramics.

Abstract: Predicting the precision of grinding process, especially correlating surface functionality generation to grinding conditions, would be of great significance to improve grinding accuracy of the end precision product. Huang developed a very promising revolutionary spectral data analysis technique based on the Hilbert transform. The concrete methods of the EMD, the local Hilbert spectrum are introduced. An artificial neural network (ANN) based on back propagation is developed to predict surface roughness Ra. An accelerometer is employed as in-process surface recognition sensor during grinding process to collect the vibration as input neurons. Changing the grinding condition, training and testing within the artificial neural networks to retrieve the weightings, the experimental results show that the proposed ANN surface recognition model is economical, efficient and the model has a high accuracy rate for predicting surface roughness.

Abstract: The crack extension course and ductile removal mechanism of nano ZrO2 ceramics were analyzed in this paper. On the basis of contrast tests with or without ultrasonic vibration, the influences of critical ductile grinding depth on grinding forces and surface quality were studied by dynamometer, SEM and AFM in different grinding condition. The reason for the increase of the critical grinding depth was discussed based on the analysis of grinding force and ultrasonic vibration course. At last, the formation mechanism of surface topography observed by AFM in ductile domain was analyzed. The research indicated that ultrasonic machining could obtain nano finished surface with high efficient.

Abstract: Visible waviness on the ball bearing’s outer ring groove, which processed by groove grinder, results in a lower precision of post processing. To reduce the waviness, some experiments are conducted to analyze the property of grinder structure. Accord to analysis result, a modification scheme is provided. In scheme an equilibrant device is designed on the grinding wheel shaft, and rotation of grinding wheel shaft with equilibrant device is simulated with the MSC.visualNastran software.