Key Engineering Materials Vols. 447-448

Abstract: This study employed the Anodic Aluminum Oxide (AAO) method twice for AAO processing to prepare neatly-arranged aluminum oxide film micro nano porous structure, and conducted experiments by adjusting different condition parameters (current, voltage, and temperature). The experimental results showed that voltage would directly affect the pore space and surface roughness of the aluminum oxide film. In addition, after anodic treatment, the positive and negative surfaces demonstrated varying degrees of roughness under the same conditions. In this study, the experiment of surface roughness impact on cell proliferation demonstrated that cell proliferation was better when surface roughness was in the range of 0.4 nm < Ra < 1.2 nm.

Abstract: This paper presents a glass molding press (GMP) method to fabricate microgroove array and micropyramid array on the glass plate by replicating the shape of the mold to the glass surface. The differences between microgroove forming and micropyramid forming were investigated by experiments and finite element method (FEM) simulations. Microgroove arrays and micropyramid arrays were generated on the flat glass plate in the GMP process by using an electroless-plated Nickel Phosphorus (Ni-P) mold, on which the microstructures are fabricated by micro cutting. Furthermore, FEM simulations were used to trace the stress distribution and the strain distribution during the glass deformation, which illustrates the glass material flow in the microgrooves and the micropyramids on the mold during pressing. By comparing the processes between microgroove forming and micropyramid forming, the differences between them observed in the experiments were explained by the simulation results. Finally, some techniques to improve the forming accuracy were proposed.

Abstract: The solar concentrator is the primary means of solving the contradiction between cost and photoelectric conversion efficiency. The design and fabrication of concentrator are the key techniques to accelerate the application of photovoltaic systems. A novel type of composite concentrator is designed, including two mirrors and one planar lens. The primary mirror focuses the sunlight on the secondary condenser, which is one multi-segmented cone mirror to produce homogenization on the solar cell. The selection strategy of structure parameters is analyzed by the numerical calculation methods. The concentration ratio and homogenization on the receiving surface are also obtained using the optical simulation method. The designed mirrors are fabricated by the ultra-precision turning method, and then assembled according to the location parameters designed. The proposed methods are proved to be satisfied with the solar application efficiently by the experiments.

Abstract: In this study, the authors employ a multi-point die-support structure to hold the punch plate of a stamping die in order to intercept useless force from the slide of a press machine. The developed multi-point support structure has 12 support cells (support units) between the punch plate and the slide of the press machine; the cells are metal cylinders working as springs. The support unit has a ball contact at the interface of the punch plate, and the interface freely for rotates and slides horizontally. The support unit has strain gauges on the side surface, and we can determine the bearing load at each unit, as well as elastic deformation. We can observe the bearing load distribution and then relocate the support units to better distribute the supporting points. The authors discuss the relocation of support units and demonstrate the efficiency of the proposed structure for reducing the jolt of a stamping die set. The range of jolt between the punch plate and the die plate of the experimental die is 0.711mm with normal support for piercing a 30mm-diameter hole on a 1.2mm-thick JSC980Y sheet. However, it is 0.355mm with the proposed die-support structure after several relocations of the support units.

Abstract: Porosity graded composite component can be found in applications such as fuel cells, filters or bio-scaffolds or implants. In this paper, two materials powder injection moulding is applied to manufacture bi-layer ceramic components with graded porosity. Ceramic spinel, AR7820, is selected to form the denser layer while the porous layer consists of AR7820 with starch or graphite pore former and spinel AR7845. The pore formers have proven to be feasible in producing porous structure in individual component. Porous layer with graphite and starch pore formers sintered at 1600oC has a porosity of 36% and 37% respectively. However delamination of the layers occurs when they are shaped together with AR7820. This is because the pore formers altered the shrinkage behaviour of the base material which resulted in discrepancies in the shrinkages between the two layers. On the other hand, defect free porosity graded composite component with good and continuous bonding between the layers was obtained when AR7845 is combined with AR7820.

Abstract: Microforming is defined as the process of production of metallic micro-parts with sub-millimeter dimension. There is as strong interaction between the scale of the microstructure and the size of the part affecting material flow, the so-called “size effect” in microforming processes. Conventional forming rules cannot be directly applied to the micro-scale forming. To better understand the implications for part geometry and properties, further investigation of the material flow related events is necessary. The aim of this work is to investigate microstructural evolution of pure copper during a micro-extrusion process - for production of micro-pins with diameters varying from 300 to 800µm - by means of optical microscope (OM). Qualitative strain gradient distribution could be observed by those pictures. The results showed that change of micro-pins diameter and die angle affect the microstructure and strain distribution of the final product remarkably, that affect the mechanical properties of the pin formed. Furthermore, microhardness results were consistent with the microstructural observations.

Abstract: In this paper, the sensitivity of T-Shape test to friction conditions was evaluated by observing the extrusion height and load curves throughout the normalized stroke (relative to workpiece diameter). Using the finite element code Deform 2D and assuming plane strain approximation, the effects of changing die geometry to the T-Shape test results were investigated. The sensitivity of the T-Shape test was also improved by introducing the double-sloped T-Shape design. The double-sloped T-Shape test was able to separate the extrusion height curves for shear coefficient of friction 0.0 to 0.4 which was unable to distinguish using the original T-Shape setup.

Abstract: The polypropylene products are injection molded by the dynamic injection molding machine. The performance characteristics of polypropylene products under steady and dynamic injection molding are gained by the DSC indicating methods. Accelerated aging test with hygrothermal test chamber (the aging temperature is 90°C, and the humidity is 95%) is conducted in the study. The regularity for impact strength property of polypropylene is studied during the test in contrast. The change of carbonyl content in the polypropylene products is analyzed both before and after aging by FTIR. The results show that the dynamic injection molding could significantly improve the anti-hygrothermal aging properties of the polypropylene products.

Abstract: This paper presents the experimental investigation of the optimal hot embossing replication to prevent the nanoscale thermal deformation of microstructures replicated from the electroless Ni mold fabricated by the diamond tool-interfered scribing process. The fabricated microstructures have the blazed profile with a period of 2.0 ㎛ and a depth of 0.2 ㎛ and a thermoplastic material PMMA as the replica was used. The hot embossing molding was carried out under the several experimental conditions. In terms of a quality of surface smoothness, profile, sharp blaze edge, surface roughness, peak to valley Ry and optical performance of the replica, the PMMA microstructures replicated under the optimal conditions, were ideally identical with those in the mold in dimension, and it was found that the demolding temperature is the most important factor for replication. From optical testing, diffraction efficiency of the replica was measured, 87.6%, similar to that of the calculated value 89.6%, and the replica molded in other conditions showed the noticeable efficiency drop due to molding error.

Abstract: Feasibility study on producing components with embedded channel by powder injection moulding (PIM) is conducted in this paper. The base plate with open channel was produced by co-injection moulding of polymeric material and ceramic feedstock. The polymeric material acted as the sacrificial material to fill the channel feature. A cover plate was then over-moulded onto the base plate to form green assembly, which was then debinded and sintered. The embedded channel was created when the sacrificial material was removed during the debinding and sintering stage. This process eliminates the need for additional joining process required by conventional manufacturing process which could cause misalignment and leakage under harsh working environment such as high pressure and high temperature. Joining was found between the cover plate and the base plate in over-moulding stage. Temperature and time during solvent debinding played important roles in order to obtain defect free component. Low temperature and short time in solvent debinding resulted in insufficient wax loss which led to various types of defects. A fair good sintered component was obtained under optimal debinding condition at 50 °C for 48 hours. The embedded channel was observed clearly by x-ray inspection without blockage by foreign particles. The shape of the channel was well retained and perfect bonding was formed in the central area of the two plates.