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Abstract Industrial experiments were conducted to investigate the differences in the porosity alleviation between the multi-roll and single-roll reduction modes during continuous casting and develop a simulation model of the porosity closure. The experimental results revealed that heavy reduction and a high solid fraction were beneficial to the porosity alleviation in billets. The simulation results showed that the large plastic strain along the thickness direction (PE22) at the center region caused by the heavy reduction contributed to the porosity closure. The PE22 at the center region of the billet between the single-roll and the multi-roll reduction mode was little different for the same reduction amounts and reduction positions. The reduction efficiency was high at the position of the low solid fraction, which contributed to porosity closure. Since most areas of porosities were formed at the center region of the billet at a high solid fraction, the reduction prior to the formation of the porosities had little effect on the porosity alleviation. The single-roll reduction mode had a better effect on the porosity alleviation than the multi-roll reduction mode because the solid fraction was higher for the single-roll reduction mode. The experimental results are mostly in agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Flexible forming process-polymer powder medium based flexible forming (PPFF) is presented in this research. The metallic bipolar plate (BPP) for a proton exchange membrane (PEM) fuel cell, with a micro-scale flow channel on its surface, is formed using rigid die forming and PPFF process, respectively. Pure copper C1100 (with a thickness of 0.1 mm), annealed at 450 °C for 1 h in vacuum condition, is selected as blank material. The forming experiments are carried out at room temperature in dry friction condition. By comparing the limit forming depth, fracture topography, section wall thickness distribution and surface forming quality of micro-scale flow channels between rigid die forming and PPFF process, it reveals that PPFF process could be developed as a feasible technique to fabricate the bipolar plates of PEM fuel cells. The PPFF process has the following advantages: greater forming depth, more uniform wall thickness distribution, and low cost of the die. [ABSTRACT FROM AUTHOR]

CuSn33 alloy micro parts of different shapes and sizes were successfully fabricated to verify the feasibility of a micro resistance weld moulding (micro-RWM). Cylindrical samples were sintered for 30 min at 600 °C, 650 °C and 700 °C and then cooled to room temperature in a furnace. DSC, metallographic analysis, EDS, XRD and micro-hardness testing were used to characterize the performance of the samples. The samples exhibited the same thermal performance before and after sintering but possessed better microhardness prior to sintering. The microhardness and microstructure of the samples were functions of differences in the sintering mechanism and diameter. The size of micro parts suitable for micro-RWM includes a horizontal size of less than 4 mm and a height of less than 2 mm. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) microelectrodes fitted by multi-layer Cu foil two-dimensional (2D) microstructures can be used in micro-electrical discharge machining (micro-EDM) to machine 3D micro-cavities. Due to the poor diffusion bonding between Cu foil 2D microstructures, the surfaces of micro-cavities often have ridges, which reduce the quality of the machined surface. To solve this problem, the paper proposed a method of using a Sn film as solder between Cu foils to fabricate Cu–Sn composite 3D microelectrodes. First, 50-μm-thick Cu foils coated with Sn on both sides were cut by femtosecond laser to obtain multi-layer 2D microstructures. Second, through transient liquid phase (TLP) bonding, the multi-layer 2D microstructures were laminated and bonded to fit composite 3D microelectrodes. In addition, the paper investigated the influence of the solder layer thickness, bonding time and temperature on the micro-EDM performance of composite 3D microelectrodes. The experimental results show that the composite 3D microelectrode has good micro-EDM performance when the solder layer thickness is 1 μm, the bonding temperature is 800 °C and the bonding time is 15 h. Finally, applying this composite 3D microelectrode in micro-EDM, 3D micro-cavities were processed, and the processing results demonstrated that the ridges on the 3D micro-cavity surfaces were completely eliminated, thereby improving the quality of the machined surface. [ABSTRACT FROM AUTHOR]

A mixture of Sn–Bi eutectic alloy powder, Cu powder and Cu fibre was used as raw material and semifinished micro parts were fabricated via micro-ultrasonic powder moulding (Micro-UPM) in a special semisolid form. The micro parts were obtained after sintering at 750 °C for 10 h and then cooling to room temperature in a furnace. The micro parts were investigated by DSC, metallographic analysis, XRD and tensile tests. The low-melting point Sn–Bi eutectic alloy was completely disappeared after the alloying treated with copper, which resulted in a remarkable increase in the thermal and mechanical properties of the micro parts. [ABSTRACT FROM AUTHOR]

3D micro-electrode which is used in micro-electrical discharge machining (micro-EDM) is difficult to be fabricated. This paper proposes a method of micro-double-staged laminated object manufacturing (micro-DLOM) to fabricate 3D micro-electrode, and verifies its feasibility through the fabrication of 3D micro-electrode. Firstly, under machining parameters of 10 μs pulse width, 40 μs pulse interval, 0.42 A wire cutting current and 80 V voltage, 100 μm-thick Cu foils were cut to obtain multi-layer 2D micro-structures. Then, under the process parameters of 850 °C thermal diffusion temperature, 10 h thermal diffusion time and 100 N forces, multi-layer 2D micro-structures were connected together by vacuum pressure thermal diffusion welding to fit the 3D micro-electrode. Finally, based on the above-mentioned studies, three kinds of 3D micro-electrodes were fabricated by micro-DLOM process and the 3D micro-electrodes were applied in micro-EDM to process 3D micro-structures. Compared with the scanning 3D micro-EDM process, 3D micro-electrode only requires up and down reciprocating method to process 3D micro-structure, which has high processing efficiency. [ABSTRACT FROM AUTHOR]