Advanced Materials Research Vols. 311-313

Abstract: In order to turning the skirt of middle-convex and varying ellipse piston, this paper proposes a Variable Cross-section Helix Turning Trajectory (VCHTT) algorithm. it divide the turning trajectory of the piston skirt into transversal and helix, then obtain the coordinates of ellipse transversal cutter-contact points on the basis of centric polar radius arc interpolation (CPRAI) algorithm, and uses line surface intersection method to obtain the coordinates of helix cutter-contact points on the middle-convex and varying ellipse piston skirt. At last，merge two coordinates matrices to obtain the final coordinate surface of cutter-contact points of turning tool. With comparison, it finds that the VCHTT algorithm improves the interpolation accuracy by 0.04um than other methods.

Abstract: In order to reduce production cost of making H₂, one of the key points was to reduce Pt loading in Pt/C catalytic electrode. In our study, a new type of Pt/C membrane electrodes, PtCu-LaO_x/C (abbr. PCL) and LaO_x-PtCu/C (abbr. LPC) double-layer structure, in which Pt nanometer particles homogeneously dispersed on the surface of carbonaceous substrates were manufactured by Ion Beam Sputtering (IBS) technology. The hydrogen evolution polarization curves of these double-layer membrane electrodes were tested by three-electrode system, and the optimal sample was selected by the calculation results of their exchange current density (i₀) and decomposition voltage (E_d). It was found that PCL with Pt loading less than 0.05mg/cm² (the electrode area) whose decomposition voltage and exchange current density was -0.204(V vs SCE) and 147.0μA/cm2 respectively in balanced condition.

Abstract: Brake piston is a huge demand non straight wall cavity part for the typical automotive industry; the traditional processing method is machine processing, or preforming by cold extrusion, and then machining. In this paper, the combined cold precision forging method of cold extrusion and spinning was proposed, which might improve the overall performance of parts and reduce costs. The rigid plastic finite element model of cold extrusion and spinning was established to simulate the forming process. The results showed that the combined cold precision forging method was available to manufacture non-straight wall cavity piston.

Abstract: Abstract：This paper analyses the causes and effective estimation method of nonlinear error; By machine tool motion solution, established a five-axis machine tool BV100 motion transformation mathematical models, combined with linear interpolation principle established the error compensation and nonlinear motion error model of the machine tool .by VB language, developed nonlinear error compensation function of special post process; and through the impeller cutting experiment validate the processor is correct and practical.

Abstract: By using the mesocarbon microbead (MCMB) and graphite as raw material, the tubular cathode green bodies of a direct ethanol fuel cell（DEFC）are shaped by the gelcasting technology and the tubular cathode is prepared by spraying the diffusion layer and the Pt/C catalyst layer after the sintering process. Through the tubular cathode physical performance and electrical property test, the advantages and disadvantages of cathode tube performance are studied at different graphite proportion. The results showed that with the increase of graphite, the ratio porosity of cathode tube support body increases at first and then decreases. However, the density has a converse trend. While the maximum porosity of the cathode tube is more than 0.5 and the corresponding density is 0.95g/cm3. Strength test showed that the cathode tube strength is better with the graphite ratio from 0 to 40 percent and can meet the actual needs. Electrical property tests showed that the cathode tube has higher current density with the graphite ratio of 40 and 50 percent.

Abstract: Analytical model is a valuable tool for the design process and performance optimization of fuel cell systems. In this paper, two-dimensional mathematical models of the tubular cathode in a direct ethanol fuel cell (DEFC), which include models of catalyst layer，support body, diffusion layer and gas flow, are developed to describe not only the electrochemical kinetics on the tubular cathode, but also multi-component transfer process in the tubular cathode. The model of spherical agglomerate is used in the catalyst layer, and the effect of ethanol penetration on oxygen reaction of the tubular cathode is also considered. Based on the model, Comsol Miphysics is used to simulate the concentration distribution of components and the current density distribution. Additional, the influence of diffusion layer and catalyst layer in the tubular cathode and the cell operating conditions on the performance of DEFC are analyzed. The results show that the mass transfer resistance exists in the diffusion layer, and the gas concentration decreases inside the battery. It is further showed that electrochemical reactions mainly happen in the catalyst layer, and oxygen concentration decrease rapidly at this time, while the water concentration can be increased.

Abstract: The welding processing of Mg-rare earth alloy NZ30K was studied using laser-TIG hybrid welding. For comparison the NZ30K alloy was also welded by the gas tungsten arc (TIG) and laser beam respectively. The microstructure of the welded joints had been analyzed. The hybrid welding method could refine the grains in the fusion and improve the tensile strength of the welded joints obviously. The arc plasma and the laser-induced plasma during welding were recorded by a high speed camera and the area of the plasma was calculated through image processing technology. Among the three welding processes the plasma area of the hybrid welding is the largest, but not a simple addition of the TIG welding and laser welding. The results show that Mg-rare earth alloy NZ30K can be well joined using the laser-TIG hybrid welding method.

Abstract: The cutting temperature is a key factor which directly affects thermal distortion, the machined part’s dimensional accuracy, as well as the tool wear in machining process. Aiming to effectively remove the cutting heat yields in machining process, the cutting tool with heat pipe cooling has been developed in recent years. This research focuses on developing a clear understanding of the temperature distribution in end mill embedded with heat pipe. Mathematical model is developed based on the heat transfer theory and the metal-cutting theory. 3-D finite element models are set up. The thermal boundary conditions are properly set, and contrasts of the temperature field in end mill with and without embedded heat pipes by numerical simulations are given.

Abstract: Microstructures and mechanical properties of welded Ti-6Al-4V alloy lap joints are discussed under different parameter conditions of laser welding. The results reveal that the fusion zone consists mainly of acicular α＇martensite. The shear strength of the lap joint reaches a maximum of 836MPa at a laser power of 4kW and welding speed of 2.3m/min. When the laser power is 4kW and the welding speed is 2.1m/min, microstructures of weld joint become coarse and the shear strength falls to 736MPa. The microhardness value in the weld zone is the highest and it gradually reduces from the weld center to base metal due to the difference of microstructure. When the weld heat input is constant, larger laser power has resulted in growth of the grain and the decrease of shear strength and microhardness of lap joints.

Abstract: Aiming at improving the interpolation efficiency without lowering the machining accuracy, the velocity look-ahead algorithm in the numerical control (NC) system is introduced. Firstly, the machining path’s transferring vector angle model is established, and then the conditions of direct transfer for the adjacent paths are also discussed. Secondly, based on the linear acceleration/deceleration control, the velocity look-ahead algorithm is put forward which can find the approximate-optimal velocity adaptively according to the maximum number of the look-ahead blocks and the geometric properties of the machining path. Finally, the acceleration/deceleration control in the consecutive micro-path can be realized, therefore, the high-speed and smooth transfer of feed-speed among machining path blocks can be achieved.