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Research Papers

Numerical Simulation and Experimental Study of Residual Stresses in Compression Molding of Precision Glass Optical Components

[+] Author and Article Information
Yang Chen, Lijuan Su

Department of Industrial, Welding and Systems Engineering, The Ohio State University, 210 Baker Systems Building, 1971 Neil Avenue, Columbus, OH 43210

Allen Y. Yi1

Department of Industrial, Welding and Systems Engineering, The Ohio State University, 210 Baker Systems Building, 1971 Neil Avenue, Columbus, OH 43210yi.71@osu.edu

Fritz Klocke, Guido Pongs

 Fraunhofer Institute for Production Technology, Steinbachstraße 17, 52074 Aachen, Germany

1

Corresponding author.

J. Manuf. Sci. Eng 130(5), 051012 (Aug 29, 2008) (9 pages) doi:10.1115/1.2950062 History: Received March 23, 2007; Revised November 08, 2007; Published August 29, 2008

Compression molding of glass optical components is a high volume near net-shape precision fabrication method. Residual stresses incurred during postmolding cooling are an important quality indicator for these components. In this research, residual stresses frozen inside molded glass lenses under different cooling conditions were investigated using both experimental approach and numerical simulation with a commercial finite element method program. In addition, optical birefringence method was also employed to verify the residual stress distribution in molded glass lenses. Specifically, optical retardations caused by the residual stresses in the glass lenses that were molded with different cooling rates were measured using a plane polariscope. The measured residual stresses of the molded glass lenses were compared with numerical simulation as a validation of the modeling approach. Furthermore, a methodology for optimizing annealing process was proposed using the residual stress simulation results.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Conventional abrasive based glass optical lens manufacturing process

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Figure 2

Meshed numerical simulation model in glass molding. (a) The meshed model before molding process. (b) The modeled deformable result.

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Figure 3

Transfer of the simulated stresses to principal stresses for molded glass lenses

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Figure 4

Photoelastic model in a modified dark-field plane polariscope

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Figure 5

Schematic illustration of glass compression molding process

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Figure 6

Time-temperature history of three different glass molding experiments

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Figure 7

The images of three molded glass disks observed under a polariscope: (a) cooling rate=1.24°C∕s, (b) cooling rate=0.43°C∕s, and (c) cooling rate=0.13°C∕s

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Figure 8

Sliced method for birefringence measurement

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Figure 9

Birefringence images of the sliced sample at different angles (top half φ=0deg and bottom half φ=45deg)

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Figure 10

Predicted volume versus temperature curves by structural relaxation model for three different cooling rates

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Figure 11

Simulated residual stress distribution in a molded glass disk using the structural relaxation model, cooling rate q=1.24°C∕s: (a) stress component σxx, (b) stress component σyy, and (c) stress component τxy, and (d) stress component σzz

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Figure 12

Simulated variation of stress component σyy during glass disk cooling from molding to room temperature at two locations (central center Node 26 and central surface Node 1) on three different cooling rates

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Figure 13

(a) Intensity distribution simulated by FEM residual stress results for cooling rate of 1.24°C∕s, (b) the one line intensity distribution from center to edge along the 45deg radius simulated results, and (c) measured results from the molded glass disks with a plane polariscope

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Figure 14

Birefringence intensity distribution of the sliced sample by simulation at different rotational angle: (a) 0deg and (b) 45deg

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Figure 15

Comparison between measured results of the fringe numbers using a polariscope and the simulation results: (a) Point A on the molded glass lens, and (b) Points B, C, and D on the thin sliced glass layer

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Figure 16

(a) Residual stress evaluated by von Mises stress at Node 1 versus annealing rate. (b) Residual stress versus temperature when the faster cooling starts at Nodes 1 and 26.

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