Fabrication of aspheric surface using ultraprecision cutting and BMG molding

A new process to replicate an aspheric lens is presented in this study. A mold of oxygen free copper (OFC) is fabricated using ultraprecision machining, which is a popular material for machining due to its good machinability. But OFC has a very low hardness of 1.606 GPa, it is not suitable for the subsequent molding process. Then, this OFC mold (known as the first mold) is used to hot emboss on Mg58Cu31Y11 amorphous alloy to form a secondary mold which is one kind of metallic glass. The hardness of the secondary mold is as high as 3.445 GPa, whereas the glass transition temperature (Tg) of the Mg58Cu31Y11 metallic glass is as low as 413 K (140 °C), at which the Mg58Cu31Y11 metallic glass shows a good glass-forming ability (GFA). In order to perform superplastic microforming, the working temperature must be close to the glass temperature around 413 K. Therefore, in this study, the temperatures of the hot embossing experiments to fabricate the secondary mold are set at 423 K (150 °C). It shows experimentally that the working temperature is dependent on the applied stress level. Since the Mg58Cu31Y11 metallic glass has superplastic property at the supercooled liquid region, it can be easily formed by the master die. This embossing process on the Mg58Cu31Y11 metallic glass makes molding process faster and more diverse applications. Next, the secondary mold is used to emboss on polymethylmethacrylate (PMMA) sheets for replication process. The Mg58Cu31Y11 metallic glass is not only a good material for hot embossing process to fabricate micro-structure directly, but also an excellent fast-molding material for hot embossing process. It is expected that the machining processes described in this paper could be applied to the related fields to fabricate precision components required of micro, sub-micro, or nano order of dimensional accuracy.