Two-Step Injection Molding of Thick Plastic Lenses with Embedded Baffles
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Solution Overview
Problem
The challenge lies in consistently manufacturing thick injection molded plastic lenses with stringent tolerances and surface accuracy, as they tend to shrink during cooling and require expensive equipment and complex control systems, leading to batch-to-batch inconsistency and performance issues.
Innovation Solution
A two-step injection molding process using the same resin, where the first layer is formed with elongated baffles, and a second layer is injected over the first, ensuring proper venting and preventing bubble formation, allowing for improved material flow and cooling in the mold cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thick injection molded plastic lenses are manufactured using conventional single-step injection molding, then the manufacturing process is simple, but the lenses tend to shrink during cooling which reduces dimensional accuracy and surface quality
Solution Approach 1:
The molding process is divided into two separate injection steps: first injecting resin to form a base layer with integrated baffles, then injecting additional resin to complete the thick lens. This segmentation allows each layer to be optimized independently, preventing shrinkage-induced distortion while maintaining manufacturing feasibility.
Solution Approach 2:
The baffles are pre-formed within the first injected resin layer before the second injection occurs. This preliminary structuring ensures proper material flow paths and venting channels are established in advance, preventing defects in the final thick lens while maintaining process simplicity.
2Manufacturing precision
If multi-step injection methods using rotary molds or shuttle molds are used to inject multiple layers, then layer formation is achieved, but the clear boundary surfaces between layers create tolerance issues for thick lenses
Solution Approach 1:
The invention uses the same resin material for both injection steps, eliminating visible boundary lines and creating a homogeneous appearance. This approach maintains the benefits of multi-layer injection (preventing shrinkage distortion) while achieving the surface accuracy and visual continuity required for optical lenses.
3Manufacturing precision
If injection compression methods are used for thick lenses, then dimensional stability is improved, but expensive equipment and elaborate control systems are required leading to batch-to-batch inconsistency
Solution Approach 1:
The process segments the injection into two controlled steps using standard injection molding equipment, achieving dimensional stability through process design rather than complex compression equipment. Each step can be independently optimized while using conventional, cost-effective machinery.
4Temperature
If thicker lenses are manufactured to accommodate LED illumination systems, then heat management is improved, but shrinkage during cooling reduces performance and accuracy
Solution Approach 1:
Dividing the thick lens into two injection layers allows differential cooling and shrinkage compensation. The first layer establishes the base geometry with baffles, while the second layer completes the optical surface, with each layer's shrinkage independently managed during cooling.
Solution Approach 2:
The baffles are formed in the first injection layer before final lens completion. This preliminary structuring ensures proper thermal management pathways are established early, allowing heat dissipation to be built into the lens architecture itself rather than added later.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method ensures consistent dimensional and functional tolerances of thick molded plastic lenses with enhanced batch consistency and surface accuracy, reducing manufacturing costs and complexity while maintaining competitive cycle times.
Implementation Method 1
a first amount of molded resin to form a first layer is injected. In a second shot the first layer is part of the mold cavity and a second shot of the same material is injected over the first layer
Implementation Method 2
They need to be relatively thicker and they can be made by plastic resins since the LEDs do not generate the heat associated with incandescent lights. Thicker injection molded lens are not easy to manufacture because they tend to shrink during the cooling step
Data Source
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AI summary
A thick injection molded lens with embedded layers of the same resin molded using a two step injection process is used in an illumination apparatus having a solid state light source such as an LED. A first layer of the molded Jens includes a first set of elongated baffles of material that are created by corresponding baffles in the mold cavity. The mold cavity baffles are oriented to help the flow of molten material in the cavity. The mold cavity baffles have surfaces that are collinear with the mold flow through a lateral gate. The first set of baffles in the first molded layer help the formation of an unfinished lens of almost equal thickness that contains a first optical surface that can be uniformly cooled in the mold. The first set of baffles in the unfinished lens help to overmold, in a second shot, the same material and to finish the lens. In the second shot, the finished lens further contains a second set of baffles and a second optical surface. The baffles in the mold cavity improve the cooling of the optical surfaces in each first and second shots, help to reduce the shrinkage of the lens, reduce the sink marks and reduce the formation of bubbles in the lens.