Key Engineering Materials Vols. 315-316

Abstract: During the transferring process of the large die surfaces, there are extensive needs of die surface polishing. Since almost large die surfaces are free-form surfaces, currently, these are almost manually implemented. In order to overcome this barrier, this paper focuses on a new technology of floating polishing, including a) the design of polisher body which has five degrees of freedom and realize the floating polishing while keep the polishing head being indifference equilibrium within the working range, b) normal force of polishing head on die surface analyses and experimental verification by using the slip line field method, and c) establishments of the interference boundaries between dies surface features and polishing head. The research achievements will be used for the development of a portable, state-of-the-art polishing machine and the optimization of the associated polishing process parameters in near future.

Abstract: By adding nano Si3N4 and nano TiC particles into the micro Si3N4 matrix, the Si3N4/TiC nanocomposite ceramics were fabricated via hot pressing technique with Al2O3 and Y2O3 as sintering additives. The thermal shock resistance of Si3N4/TiC nanocomposites were investigated by means of indentation-quenching and quenching-retained strength testing methods. The results revealed that the composite containing 10 wt.% nano Si3N4 particles and 15 wt.% nano TiC nano particles was possessed of the highest thermal shock resistance, with its critical temperature difference being 700~750
. The toughening and strengthening mechanisms by the nano particles addition are deem to be the essential course for the improved thermal shock resistance.

Abstract: Based on the grain movement model of ultrasonic grinding, models representing the grinding force of single abrasive and the material removal rate (MRR) are deduced and verified. Mechanism of high efficiency material removal in work lateral ultrasonic vibration grinding (WLUVG) was analyzed. The MRR of fine-crystalline ZrO2 ceramics in WLUVG and conventional grinding (CG) with diamond wheel were researched experimentally in this work. The effects on the MRR, the surface roughness and microstructure of the process parameters and the size of abrasive are measured. It has been concluded that: (1) the MRR in ultrasonic grinding process is two times as large as that of in CG. (2) any increase in the amount of energy imparted to the workpiece in terms of the average diameter of grains, grinding depth both in with and without ultrasonic grinding, will result in an increase in the MRR and the surfaces roughness. (3) the ultrasonic grinding surface had no spur and build-up edge and its surface roughness was smaller than CG significantly. Surface quality of vibration grinding is superior to that of CG, it is easy for ultrasonic vibration grinding that material removal mechanism is ductile mode grinding.

Abstract: Hermite method and MPM method were studied. Multi-point machining constraints with the cutter tilting forward and backward were derived respectively. So the number of the solutions of the two Multi-point machining methods was doubled than before. To derive some general conclusions about solution areas of Multi-point machining constraints, structure of neighborhood region close to a given point on a surface was used to substitute the surface in the Multi-point machining error calculation. A computational example was also given in the paper. With the theoretical analyses and computational example, it was proved that, for an open and slightly curved surface machining with Multi-points method, without regard to interference, there were four branch areas satisfying Multi-point machining constraints and distributing radically nearby the first tangent contact points respectively on condition that the cutter was tilted forward or backward. And they extended basically in the directions along the principal curvatures at the first tangent contact point.

Abstract: This paper worked on two dimensional ultrasonic grinding system with workpiece adhered to ultrasonic vibration. It analyzed the working locus of abrasive particle under two dimensional ultrasonic grinding (TDUG), and emulated the working course, and gave the key parameters affecting grinding efficiency and grinding locus’s characteristic under different grinding parameters, and brought forward the cutting course between abrasive particle and workpiece under TDUG belongs to an new rotating dynamic contact cutting model. At the same time, it put forward the theoretically critical speed condition under TDUG to obtain the optimum grinding effect, and verified good micro-feature of finished surface under TDUG by the means of grinding tests of nano ZrO2 ceramics.

Abstract: Graphite electrode material has been extensively used for thin-walled electrode manufacturing, due to its typical brittleness, HSM becomes the main process method to obtain higher productivity and good surface finish. According to the structure characteristics of the thin-walled graphite electrode and the problems arising in its high-speed milling, through high-speed milling experiments, researches have been done into the effect of the main cutting parameters on cutting forces, which include cutting speed, feed per tooth, radial cutting depth, axial cutting depth, down or up milling. Finally, cutting parameters optimization strategies of high-speed milling of thin-walled graphite electrode aiming to obtain higher efficiency and high quality are presented as follows: down-cut mode, moderate radial depth of cut and flat endmill should be adopted in high-speed milling of graphite electrode.

Abstract: The tool wear monitoring system based on the image processing and computer vision has better study value and foreground. During the cutting, the cutting tool is always at the movement state, thus, the real-time collected sequence images by CCD sensor are blurred with noise. As a result, we have to confront the problem how to get the high quality images, which is researched by this paper. The paper analyzes the reasons which causing the image blurred, brings forward a degradation function model and finds the degradation of tool wear images dues to the relative movement. According to this function model and combined with the application of fuzzy theory, the restoration algorithm is obtained. The membership function dealing with degraded images of cutting tools is put forward. It turns out that the images restored by this fuzzy restoration algorithm reach our aim.

Abstract: The wear behaviour in the precision interrupted hard part turning SAE8822 case hardened steel by BN250 PCBN cutting tool was studied. Experimental results showed that the main wear mechanism for the PCBN tool was the edge chipping by the fluctuation of cutting forces and cutting temperature. The oxidization and diffusion of the elements between workpiece and PCBN tool decrease the bonded strength between binder and cBN crystal, then lead to the damage of PCBN cutting tool.

Abstract: The wear pattern and mechanism during continuous hard turning GCr15 hardened bearing steel with BZN8200 PCBN cutting tool was studied. Experimental results showed that the main wear pattern is crater wear in rake face and mechanical wear in flank face, the main wear mechanism is made-up with adhesive, oxidization and diffusive wear. The adhesive wear is generated by melt workpiece material flows with binder material of PCBN tool during initial cutting, oxidative wear is derived by cutting temperature and pressure of cutting zone when the flank wear increase after initial cutting, diffusive wear phenomenon is the absolute mechanism with the diffusive effect between workpiece and tool material in final cutting time.

Abstract: In terms of the principle and characteristics, this paper proposes a new method to implement laser shock forming for large region based on the STL model. The method allows the build-up of laser shocking track to be accomplished automatically and therefore resolves the problem of continuous machining in course of the laser shock.