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Research Papers

Fabrication of Plano-Concave Plastic Lens by Novel Injection Molding Using Carbide-Bonded Graphene-Coated Silica Molds

[+] Author and Article Information
Xiaohua Liu

School of Mechanical Engineering,
Beijing Institute of Technology,
No. 5, Zhongguancun South Street,
Haidian District, Beijing 100081, China;
Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: liuxh89@126.com

Lin Zhang

Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: zhou.1879@buckeyemail.osu.edu

Wenchen Zhou

Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: zhang.5265@buckeyemail.osu.edu

Tianfeng Zhou

School of Mechanical Engineering,
Beijing Institute of Technology,
No. 5, Zhongguancun South Street,
Haidian District, Beijing 100081, China
e-mail: zhoutf@bit.edu.cn

Jianfeng Yu

Nanomaterial Innovation Ltd.,
1109 Millcreek Lane,
Columbus, OH 43220-4949
e-mail: dendrions@yahoo.com

L. James Lee

Department of Chemical and Biomolecular Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: lee.31@osu.edu

Allen Y. Yi

Department of Integrated Systems Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: yi.71@osu.edu

1Corresponding author.

Manuscript received September 20, 2018; final manuscript received May 28, 2019; published online June 21, 2019. Assoc. Editor: Martine Dubé.

J. Manuf. Sci. Eng 141(8), 081011 (Jun 21, 2019) (7 pages) Paper No: MANU-18-1677; doi: 10.1115/1.4043980 History: Received September 20, 2018; Accepted May 29, 2019

Injection molding of plastic optical lenses prevails over many other techniques in both efficiency and cost; however, polymer shrinkage during cooling, high level of uneven residual stresses, and refractive index variations have limited its potential use for high precision lens fabrication. In this research, we adopted a newly developed strong graphene network to both plano and convex fused silica mold surfaces and proposed a novel injection molding with graphene-coated fused silica molds. This advanced injection molding process was implemented in the molding of polymer-based plano-concave lenses resulting in reduced polymer shrinkage. In addition, internal residual stresses and refractive index variations were also analyzed and discussed in detail. Meanwhile, as a comparison of conventional injection mold material, aluminum mold inserts with the same shape and size were also diamond machined and then employed to mold the same plano-concave lenses. Finally, a simulation model using moldex3d was utilized to interpret stress distributions of both graphene and aluminum molds and then validated by experiments. The comparison between graphene-coated mold and aluminum mold reveals that the novel injection molding with carbide-bonded graphene-coated fused silica mold inserts is capable of molding high-quality optical lenses with much less shrinkage and residual stresses with a more uniform refractive index distribution.

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References

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Figures

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Fig. 1

(a) Preparation of carbide-bonded graphene-coated fused silica molds, (b) graphene-coated fused silica plano and convex mold inserts, and (c) aluminum plano and convex mold inserts

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Fig. 2

The schematic showing the process of injection molding with graphene-coated fused silica molds: (a) preparation, (b) injection molding, and (c) demolding

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Fig. 3

Sketch of the SHS-based wavefront measuring system. 1: Laser, 2: polarizer pair, 3: plastic plano-concave lens in index matching liquid, 4: telescope lens assembly, 5: microlens array, and 6: CCD camera.

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Fig. 4

A meshed FEM model of plastic plano-concave lens in moldex3d

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Fig. 5

Photograph of a plastic plano-concave lens (showing with gate, runner, and sprue) by injection molding

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Fig. 6

Sketch of the injection molded plano-concave lens showing two directions for observation

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Fig. 7

Central cross-sectional contours comparison among graphene-coated fused silica mold, aluminum mold and their molded lens in both (clockwise) (a) parallel direction and (b) transverse direction. Comparison of sag between graphene-coated fused silica and aluminum molds and their lenses in both (c) parallel direction and (d) transverse direction.

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Fig. 8

The normalized residual stress distributions of the molded plastic plano-concave lenses by (clockwise) (a) and (c) graphene-coated fused silica molds and (b) and (d) aluminum molds. (a) and (b) are measured results under a plain polariscope and (c) and (d) are simulated results by FEM software moldex3d.

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Fig. 9

The measured and simulated residual stress intensity comparison of the molded plastic plano-concave lenses by graphene-coated fused silica molds and aluminum molds

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Fig. 10

The wavefront variation in injection molded plastic plano-concave PMMA lenses by (a) graphene-coated fused silica molds and (b) aluminum molds

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Fig. 11

Refractive index variation comparison of the plastic plano-concave lens between graphene-coated mold and aluminum mold in both parallel and transverse directions

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