Molded Plastic Part with Dynamic Movable Wall for Optical Precision
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Solution Overview
Problem
Conventional injection molding methods for thin-walled plastic parts with complex shapes, such as optical elements, face issues like internal stress, birefringence, and sink formation due to uneven cooling and pressure distribution, leading to deformation and poor precision in molded parts.
Innovation Solution
A novel molding method involving a die with transfer and movable walls, where internal pressure is managed by sliding movable walls and feeding compressed air to form imperfectly transferred convex and concave portions, reducing residual stress and preventing sink formation on transferred surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high injection pressure is used to ensure satisfactory contact with transfer wall surface, then transfer precision is improved, but large internal stress and deformation occur due to rapid cooling
Solution Approach 1:
The die includes a movable wall that can change position during the molding process. The movable wall is positioned to allow controlled expansion of the cavity volume during cooling, enabling dynamic adjustment of pressure distribution to reduce internal stress while maintaining transfer precision on the transferred surface.
Solution Approach 2:
The die has different wall surface characteristics: a transfer wall surface with high precision for optical surfaces and a non-transferred surface with specific properties. The movable wall selectively controls pressure distribution, allowing high pressure at the transfer surface for precision while managing pressure elsewhere to minimize internal stress.
2Stability of the object's composition
If low injection pressure is used to reduce internal stress, then deformation is reduced, but sink formation occurs on the transferred surface
Solution Approach 1:
The movable wall dynamically adjusts cavity volume during the cooling process. By expanding the cavity volume after injection, the system can reduce pressure and prevent sink formation while maintaining sufficient pressure during the critical transfer phase to ensure precision on the transferred surface.
Solution Approach 2:
The movable wall is positioned in advance to create a larger cavity volume before the resin fully solidifies. This preliminary volume expansion prevents sink formation by providing space for the resin to contract during cooling while maintaining surface integrity.
3Productivity
If fast cooling is applied to thin portions, then productivity is improved, but internal stress and deformation increase
Solution Approach 1:
The movable wall enables dynamic control of cavity volume during cooling. By allowing controlled expansion, the system can maintain faster cooling rates for productivity while managing pressure distribution to minimize internal stress and deformation in thin portions.
Solution Approach 2:
The system changes the cavity volume parameter during the cooling process by moving the movable wall. This parameter change allows the thin portions to cool faster while the overall pressure distribution is adjusted to prevent excessive internal stress and deformation.
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 high-dimensional precision and prevents birefringence in molded plastic parts, maintaining the desired shape and reducing internal strain, making them suitable for optical applications without deformation.
Implementation Method 1
feeding compressed air from the imperfect transfer wall surface to the resin to release the resin from the imperfect wall surface by priority
Implementation Method 2
the melted resin in the cavity is cooled to solidify
Implementation Method 3
cooling the resin while controlling the pressure on the resin
Data Source
AI summary
A molded plastic part prepared by injecting a resin in a cavity of a die so that a pressure is generated in the resin in the cavity and at least one transfer wall surface of the cavity is transferred to the resin. The plastic part has at least one transferred surface; at least one imperfectly transferred concave portion on a first surface thereof other than the transferred surface; and at least one imperfectly transferred convex portion on the first surface or a second surface thereof other than the transferred surface. The ratio (a)/(b) of the thickness (a) of the plastic part in a direction perpendicular to the transferred surface to the thickness (b) of the plastic part in a direction parallel to the transferred surface is less than 1.