Abstract
Freeform surfaces are featured with superior optical and physical properties and are widely adopted in advanced optical systems. Slow tool servo (STS) ultra-precision machining is an enabling manufacturing technology for fabrication of non-rotationally symmetric surfaces. This work presents a theoretical and experimental study of surface topography generation in STS machining of freeform surfaces. To achieve the nanometric surface topography, a systematic approach for tool path generation was investigated, including tool path planning, tool geometry selection, and tool radius compensation. The tool radius compensation is performed only in one direction to ensure no high frequency motion is imposed on the non-dynamic axis. The development of the surface generation simulation allows the prediction of the surface topography under various tool and machining variables. Furthermore, it provides an important means for better understanding the surface generation mechanism without the need for costly trial and error tests. Machining and measurement experiments of a sinusoidal grid and microlens array sample validated the proposed tool path generation and demonstrated the effectiveness of the STS machining process to fabricate freeform surfaces with nanometric topography. The measurement results also show a uniform topography distribution over the entire surface and agree well with the simulated results.
Highlights
Owing to the superior optical and physical properties, freeform surfaces are an important catalyst in the development of high-value-added photonics and telecommunication products, such as laser beam printers and scanners, head mounted displays, progressive lens molds, fiber optic connectors, and advanced automotive lighting systems [1,2,3,4]
The machined microlens array surface was measured for both curve conformity and surface roughness and 34.5 nm Ra was achieved over 0.7 mm scanning length
The measurement results indicate the machined topography of the structured freeform surface is less than 10 nm and uniformly distributed
Summary
Owing to the superior optical and physical properties, freeform surfaces are an important catalyst in the development of high-value-added photonics and telecommunication products, such as laser beam printers and scanners, head mounted displays, progressive lens molds, fiber optic connectors, and advanced automotive lighting systems [1,2,3,4]. With the technical evolution in advanced manufacturing, ultra-precision machining technologies have been developed for the deterministic fabrication of high precision freeform surfaces including tool servo turning, ultra-precision raster milling, ultra-precision grinding and polishing [6,7,8,9]. Materials 2018, 11, 2566 slow tool servo (STS) machining provides an important means for generating optical freeform surfaces without the need for any subsequent processing. It has the advantages of simpler setup, faster cycle times and better machining accuracy over other techniques. Yi and Li [7] proposed an innovative diamond tool trajectory that allows the entire 5 × 5 microlens array to be fabricated in a single operation using STS machining. Yin et al [10]
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