Compared with general‐purpose devices, optical devices have much tighter quality requirements with respect to transparency, refractive index, birefringence, and stability. However, compared with low packing pressure, the distribution of refractive index variation becomes much more uniform, with a maximum variation of –2.5 × 10−3, whose absolute value is less than a half of that under low packing pressure. Measurements were made on refractive index changes with hydrostatic pressures between 1 bar and 1 kbar using the helium yellow line. Get the latest public health information from CDC: https://www.coronavirus.gov. Volume and temperature coefficients of polarizability were evaluated for the cubic crystals and glasses. Previously, we have performed a preliminary investigation of injection‐molding process for high‐precision polymer lens manufacturing. For the lenses in this study, the temperature gradient in the radial direction must have brought about uneven shrinkage, which means that the material at the radial location further away from lens center shrinks faster than that at locations closer to the center. Intelligent Optimization of Mold Design and Process Parameters in Injection Molding.
A. J. Richard, K. T. McCrickard, and P. B. Fleming, J. Chem. Baak .
Find NCBI SARS-CoV-2 literature, sequence, and clinical content: https://www.ncbi.nlm.nih.gov/sars-cov-2/. On the other hand, in recent years, because of its attractive features of low weight and ability to be manufactured in high volume, polymers have been receiving considerable attention as materials for precision optical components used in digital cameras, cellular phones with cameras, DVD recorders, and various sensor cameras for automotive applications.1. Schematic of the measuring system. Differently, in the transverse direction the variation of refractive index shows good symmetry with respect to the axis parallel to the flow direction, with the maximum value of refractive index variation in the center of the lenses. Simultaneous Control of Birefringence and Warpage for Thermoplastic Optical Lenses Fabricated Using Microinjection Molding.
This cooling rate difference of the injected material at different radial locations produced the melt temperature gradient in the radial direction. An interferometer for measuring change in index of refraction with pressure is described. This results in a shift of the interference … Instead of further decreasing, the refractive index variation increases when the point of interest is over the center of the lenses. The investigation provided us with in‐depth understanding of the packing phase in injection molding. J Res Natl Bur Stand A Phys Chem. To date extensive investigations in refractive index of optics made from polymer or polymer composites have been performed. Interferometer‐based systems have been used to measure the refractive index or its variation.9-14 Other methods including return loss2 and Abbé refractometer4,15 have also been used.
In this case, the packing phase was very effective in that a high pressure was applied to the melt already filled in the mold cavity, thus capable of compensating the shrinkage within the cavity. Bur. J Res Natl Bur Stand A Phys Chem. Learn more. As the packing pressure is elevated, the wavefront exhibits clear axial symmetry with respect to the flow direction, with the wavefront decreasing from center to the edge. The specific volume can be expressed by the two‐domain modified Tait model, In the finite element simulation, the three stages of the injection‐molding process were analyzed, namely filling, packing, and cooling.
When the packing pressure is high, such as 120 MPa used in this research, the polarizability may no longer be considered negligible, which somewhat weakened the original assumption used in the modeling process.
However, glasses are less suitable for mass production. The refractive index of benzene shows no effect due solely to temperature within the experimental error. In this way, we obtain the variation with pressure of the electronic static dielectric constant ∊∞.
Wavefront measurement of plastic lenses for mobile-phone applications. One is the simplification of the polymer flow in the Moldflow simulation, as well as the limitation of simulating continuation of cooling after demolding. Sci. USA.gov. Natl. However, the opposite was observed in the present study (see Figs.
The gate location for the molded lenses is at the right side of the image, i.e., the flow direction is from right to left. Proper control of refractive index and its variation is essential for the performance of optical devices. Along the flow direction starting from the gate to the opposite side, the applied packing pressure should be the highest, decreasing gradually toward the outer areas. | The authors acknowledge the assistant by Robert Miller in mold fabrication at The Ohio State University, and the helpful discussion on simulation with Prof. Lih‐Sheng Turng at University of Wisconsin‐Madison. eCollection 2019.
For the lenses fabricated under high packing pressure, one can see relatively large difference of refractive index variation between the two directions. To obtain accurate density results, finer meshes as compared to coarse element sizes used in conventional analysis were adopted. 1964 Sep-Oct;68A(5):489-498. doi: 10.6028/jres.068A.046.
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