Grinding techniques for fabricating micro-lens array mold made of cemented carbide (Polycrystalline diamond tools and mold surface roughness)

Abstract

A grinding technique was developed to fabricate a micro-lens array (MLA) mold made of cemented carbide with a diameter of 30 μm, a pitch of 35 μm, a diameter expansion rate of 0%, a surface roughness of less than 10 nmRz and 1027 lenses. Grinding tools made of polycrystalline diamond (PCD) and nano-polycrystalline diamond (NPD) with a tip radius of 0.1 mm and formed by laser machining and wet lapping were employed. Grinding was performed by transferring the hemispherical tool profile to the cemented carbide with a hardness of 2650 Hv. When NPD was employed, the tips of diamond particles, which were not aligned in height on the working surface, were worn down and the particles of the lower layer were exposed. A huge number of diamond particles with a size of 50 nm were engaged in the grinding operation. This phenomenon made it possible to fabricate lenses with a surface roughness of less than 10 nmRz and a diameter expansion rate of 2%. In contrast to NPD, removed chips contributed to dressing the working surface of PCD. The sharp cutting edge newly exposed on the working surface caused a negative effect on creating a fine surface and contributed to increasing the actual depth of cut. Accordingly, the formable surface roughness and diameter expansion rate were 15 nmRz and 3%, respectively.

Keywords

• micro-lens array mold
• cemented carbide
• ultraprecision grinding
• polycrystalline diamond
• nano-polycrystalline diamond