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Frontiers of Mechanical Engineering

ISSN 2095-0233

ISSN 2095-0241(Online)

CN 11-5984/TH

Postal Subscription Code 80-975

2018 Impact Factor: 0.989

Front. Mech. Eng.    2017, Vol. 12 Issue (2) : 181-192    https://doi.org/10.1007/s11465-017-0444-z
RESEARCH ARTICLE
Micro-optical fabrication by ultraprecision diamond machining and precision molding
Hui LI1, Likai LI1,2, Neil J. NAPLES1, Jeffrey W. ROBLEE3, Allen Y. YI1()
1. Department of Integrated System Engineering, The Ohio State University, Columbus, OH 43210, USA
2. Nistica Inc., Bridgewater, NJ 08807, USA
3. Ametek Precitech, Keene, NH 03431, USA
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Abstract

Ultraprecision diamond machining and high volume molding for affordable high precision high performance optical elements are becoming a viable process in optical industry for low cost high quality microoptical component manufacturing. In this process, first high precision microoptical molds are fabricated using ultraprecision single point diamond machining followed by high volume production methods such as compression or injection molding. In the last two decades, there have been steady improvements in ultraprecision machine design and performance, particularly with the introduction of both slow tool and fast tool servo. Today optical molds, including freeform surfaces and microlens arrays, are routinely diamond machined to final finish without post machining polishing. For consumers, compression molding or injection molding provide efficient and high quality optics at extremely low cost. In this paper, first ultraprecision machine design and machining processes such as slow tool and fast too servo are described then both compression molding and injection molding of polymer optics are discussed. To implement precision optical manufacturing by molding, numerical modeling can be included in the future as a critical part of the manufacturing process to ensure high product quality.

Keywords ultraprecision machining      slow tool servo      fast tool servo      compression molding      injection molding      microlens arrays      optical fabrication     
Corresponding Author(s): Allen Y. YI   
Just Accepted Date: 01 April 2017   Online First Date: 24 April 2017    Issue Date: 19 June 2017
 Cite this article:   
Hui LI,Likai LI,Neil J. NAPLES, et al. Micro-optical fabrication by ultraprecision diamond machining and precision molding[J]. Front. Mech. Eng., 2017, 12(2): 181-192.
 URL:  
https://academic.hep.com.cn/fme/EN/10.1007/s11465-017-0444-z
https://academic.hep.com.cn/fme/EN/Y2017/V12/I2/181
Fig.1  End view of an ultraprecision slide showing the linear motor and the slide platform
Fig.2  A lathe configuration for generating freeform optical surfaces with three coordinated axes
Fig.3  (a) Optical layout; (b) a freeform micromirror array machined using slow tool servo process; (c) a Lincoln portrait is formed when the point source irradiance was reflected off the slow tool servo machined micromirror array
Fig.4  (a) High-speed milling with a Professional Instrument airbearing spindle; (b) a press fit chuck and close up view of the micro-milling bit (inset photo)
Fig.5  Microlens array mold fabricated using high speed milling process
Fig.6  A typical precision optical molding process
Fig.7  An off-axis endoscope design using a prism with freeform optical surface
Surface Radius, c −1/mm Thickness/mm Material Semi-aperture, r/mm Conic constant, k/mm
1 2.130 1.900 PMMA 1.021 −0.170
2 −6.113 1.300 PC 0.960 13.318
3 3.027 0.500 ? 0.922 5.456
4 2.276 1.500 PMMA 1.083 −4.373
5 3.030 3.500 ? 1.064 −4.015
Tab.1  The optical prescriptions for the three aspherical lenses
Fig.8  (a) Compression molding assembly; (b) molding process for the 2×2 lens array
Lens Molding temperature/°C Forming load/N Initial thickness/mm Pushing time/min
Lens 1 140 650 2.1 ~30
Lens 2 155 400 1.6 ~20
Lens 3 140 550 2.0 ~15
Tab.2  Compression molding conditions for three lenses
Fig.9  (a) A molded lens array; (b) a quarter of a simulated lens array
Fig.10  (a) Measured and simulated MTF of the assembly module; (b) Captured image of the USAF 1951 target
Fig.11  Sodick microinjection molding machine (Model LD30EH2, Sodick Plustech, www.plustech.com)
Fig.12  Separate plunger and screw design used in the microinjection molding machine (Model LD30EH2, Sodick Plustech, www.plustech.com)
Fig.13  Design of the 24×20-microlens array: (a) Arrangement of microlens array; (b) surface profile of one microlens (in mm)
Fig.14  Tool path generation
Fig.15  (a) A precision machined microinjection mold insert; (b) a mold insert is installed on microinjection molding machine; (c) Wyko scan of a molded microlens array; (d) photos of a complete molded microlens array
Fig.16  (a) Construction and performance of a Shack-Hartmann sensor using an injection molded microlens array; (b) focal plane of the microlens array
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