A simple and novel combination of ultra-precision diamond ball-end milling and micro injection molding technique is described to produce precise microlens arrays out of polycarbonate (PC), polymethylmethacrylate (PMMA) as well as polystyrene (PS). The microlens arrays consist of 100 lenses in a 10 9 10 array with a lens radius of 273 lm, a lens diameter of 300 lm and a lens depth of 45 lm. Pitch between the lenses is fixed at 800 lm. The injection molding parameters were optimized to get precise microlens geometries with low surface roughness. The results show a precise diamond milled mold insert and injection molded microlens arrays with minor deviations in radius and surface roughness of the microlenses, particularly for microlens arrays out of PMMA.
The strength and fracture toughness o f Al-Zn-M g-Cu-Ti(-Sn) alloys were investigated by performing tensile and plane strain fracture toughness (KIC) tests. Detailed observations with optical, scanning electron and transmission electron microscopy were conducted to analyze microstructure andfracture surfaces o f the alloys. The results revealed that addition o f Sn refined the solution-aging grain size o f matrix and reduced coarsening rate o f precipitate during aging. Narrower precipitation free zones and more discontinuous distribution o f grain boundary precipitates were observed to be displayed in the Sn-containing alloy. Small size second phase particles M g fin were observed to form in the Sn-containing alloy and distribute in the fin e dimples offracture surface. These features o f microstructure were believed to impart higher strength and fracture toughness o f the Sn-containing alloy on overaging.
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