Runner design to improve quality of plastic optical lens

Although the layout of multicavity molds is a geometrically balanced design, when the melt flows into the runner, the shear-induced partial changes in material properties will result in intracavity imbalance. This study placed a rectangular flow restrictor within the tertiary runner of a precision o...

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Bibliographic Details
Published in:International journal of advanced manufacturing technology 2013-04, Vol.66 (1-4), p.523-536
Main Author: Tsai, Kuo-Ming
Format: Article
Language:English
Subjects:
Blocking
CAE) and Design
Computer-Aided Engineering (CAD
Design optimization
Engineering
Fluid dynamics
Industrial and Production Engineering
Injection molding
Lenses
Machining
Material properties
Mechanical Engineering
Media Management
Melt temperature
Molds
Original Article
Residual stress
Rheological properties
Temperature distribution
Temperature gradients
Turbulent flow
Warpage
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Summary:Although the layout of multicavity molds is a geometrically balanced design, when the melt flows into the runner, the shear-induced partial changes in material properties will result in intracavity imbalance. This study placed a rectangular flow restrictor within the tertiary runner of a precision optical lens mold to create melt turbulence through flow blocking. Due to polymer rheological characteristics, uniform melt temperature distribution in the runner channel could be obtained, making the temperature distribution inside the cavity more uniform, and reducing the thermal residual stress and warpage of injection molded parts. The optimal runner restrictor design is placing 5 mm away from the secondary runner centerline, making both the depth and the width of the block 3 mm. A relatively uniform melt temperature distribution with a maximum temperature difference of 1.1 °C can be achieved. Injection molds were fabricated according to the optimized restrictor design, and experimental verification was performed. The contour accuracy of a lens parallel to injection direction was improved from 10.44 to 5.03 μm. Therefore, this runner restrictor design can be applied to high-precision optical molds due to the ease of machining and the capability of improving the quality of optical lens.
ISSN:0268-3768
1433-3015
DOI:10.1007/s00170-012-4346-2