Materials Science Forum Vols. 532-533

Abstract: Utilizing gas as the dielectric instead of dielectric liquid has enabled the development of dry wire electrical discharge machining (WEDM) technology for finishing cut. This paper studies on the surface quality of tool steel with WEDM method, which is conducted in gas to improve the accuracy of finishing cut, and compares the surface quality in atmosphere and in water. Experiment results showed that Low-Speed WEDM in atmosphere offers advantages such as better straightness, lower surface roughness and shorter gap length, but WEDM in atmosphere has poorer material removal rate than conventional WEDM in water. It was also found the removal rate in atmosphere can be improved by increasing the wire winding speed.

Abstract: Based on the 3D FE model of conventional spinning, the influence of curvature radius of roller-trace on the conventional spinning process has been studied. It is found that when the curvature radius of roller-trace is smaller, the maximum of thinning rate and hoop compressive stress increases dramatically with the increasing of the radius, and curvature radius does little effect on the forming process when it is up to a critical value. To obtain a more reasonable selection criterion of curvature radius of roller-trace, a new index named flange width has been put forward， which represents the comprehensive effect of workpiece diameter and mandrel diameter in the forming process of conventional spinning. Further research has been done and the selection criterion of curvature radius is obtained: the smaller the flange width is or the larger the workpiece thickness or the entry tangential angle is, the larger the range of reasonable curvature radius is.

Abstract: The composite materials, 3Y-TZP added with TiN or/and Al2O3 particles, were fabricated by hot-pressing techniques. The effect of TiN and Al2O3 on the low temperature degradation of 3Y-TZP was investigated. It is shown that both TiN and Al2O3 can inhibit t-m transformation of 3Y-TZP and prevent the transformation from propagating into the specimen interiors when aged at a low temperature. The inhibition to the low temperature degradation of 3Y-TZP by Al2O3 is more sensitive to the aged temperature than by TiN. Compared with Al2O3, TiN is more available to inhibit t-m transformation on aged surfaces. The degradation resistance of 3Y-TZP codoped by TiN and Al2O3 is stronger than that of 3Y-TZP dispersed only by TiN or Al2O3.

Abstract: The present study was undertaken to examine the effects of metal coatings on the surfaces of diamond crystals embedded in two kinds of bond matrix. Diamonds with or without coatings were incorporated into two matrices for hot-pressing, thereby forming four kinds of diamond composites. The transverse rupture strength (TRS) of the composites was measured to assess the bending strength of the composites. SEM and EDS were used to analyze the fractured surfaces of the composites. It was found that the TRS of the composites containing coated diamonds increased in both bond matrices. But the coatings in the bond matrix without rare earth increased TRS a little more than the case with rare earth due to a different failure mechanism of metal coatings.

Abstract: Ceramic coating materials own some advantages, for example high-rigidity, good abradability and good performance under high temperature. At the same time, ceramic coating materials are also difficult-to-machine materials. High machining precision and efficiency can be obtained in grinding WC-Co coating by cup wheel. The affection of grinding temperature is very important for grinding processing. But there is no research on grinding temperature of WC-Co coating by cup wheel. So in this paper, grinding temperature by cup wheel is researched on theory, the new concept, which is effectiveness width of arc moving heat source, is presented, and theoretical formula of grinding temperature is also built. Then experimental research on grinding temperature of WC-Co coating by cup wheel is done by use of thermocouple temperature measurement technology. The experimental results show the validity and effectivity of the theoretical formula. The affection of grinding parameters to grinding temperature is researched also.

Abstract: According to the principle producing the cutting track of cutter, to study the influence of the cutting track of cutter on the process of high speed ball-end milling, the single-factor models for evaluating the cutting track of cutter are established. Adopting four kinds of the typical cutting track of cutter, the experiment of high speed ball-end milling is processed. The model of multi-ply fuzzy comprehensive evaluation for the cutting track of cutter is established, fuzzy comprehensive evaluation for the cutting track of high speed ball-end milling cutter is accomplished by the application of fuzzy mathematics theory. Results show that the cutting contact curve of cutter affects directly the process of high speed ball-end milling, fuzzy and uncertain properties exist in the evaluation for the cutting track of cutter. The optimum cutting track can be selected by multi-ply fuzzy comprehensive evaluation for the cutting track of high speed ball-end milling cutter.

Abstract: The experimental results for silicon carbide (SiC) wheel with fine grit size grinding of silicon carbide (Si3N4) revealed that the grinding parameters affect not only the ground silicon nitride surface roughness, but also the degree of surface damage. There exists complex non-linear relationship between the grinding parameters and surface quality. Better surface roughness doesn’t surely mean less surface damage. A method of prediction of grinding quality based on support vector regression is then presented according to the condition of small samples. The result shows the prediction accuracy based on this method is obviously higher than neural network, which provides an effective way for optimizing the grinding parameters to ensure the grinding quality as well as grinding efficiency while grinding of silicon carbide using conventional abrasive.

Abstract: In Polishing Process based on Vibration of Liquid (PVL), abrasive particles driven by polishing liquid will brush and etch workpiece to achieve material removal. Because the liquid is vibrated in ultrasonic frequency, polishing process will be greatly affected by cavitation phenomenon. The critical thermal conditions and high-speed liquid jet produced by bubble dynamics may damage workpiece. A refined Dissipative Particle Dynamics method is applied to study the effect of acoustic cavitation on PVL. Validity of the numerical simulation is tested according to experimental results.

Abstract: A new deposition method is described using EDM to deposit tool electrode material on workpiece in air. Then by exchanging the polarities the deposited material can be removed selectively, thus micro structure can be fabricated. First, the EDD realized conditions are predicted. Then with ordinary brass, steel and tungsten electrodes and high-speed steel workpiece, EDD experiments are carried out to obtain micro structure in air. With continuous deposition strategy of single cylinder, a HIT character type array made up of 15 micro cylinders is deposited. And micro three-dimensional spiral structure can be obtained with brass electrode using feed of only z axis. The 19-circle micro spiral structure is 0.19mm in external diameter, 0.1mm in wire diameter and 3.39mm in height. Measurements show that deposited material has obvious delaminating structure and is corrosion resistant, whose components depend on those of the tool electrode material.

Abstract: Present modeling algorithm for large-sized revolving parts’ camber can not ensure the smoothness, so a new modeling algorithm based on NURBS Curve was proposed in this study. In detail, the new modeling algorithm is as following: Firstly transfer these discrete points, which are measured along the part’s axial lead by equal distant, into a weighting unity sequence. Secondly filter this sequence by wavelet de-noising algorithm. Thirdly replace the discrete points’ amplitudes by the corresponding weights of filtered sequence, thus yield a group of new discrete points. Lastly calculate the control vertexes and weighting factors by local rational interpolation algorithm, and construct a spatial NURBS Curve through the new discrete points to obtain the model of large-sized revolving parts’ camber. It was experimentally confirmed that this model can represent drilling stem’s camber smoothly and improve its pressure straightening precision.