Standoff Post Compression for Injection Molding Thickness Control
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Solution Overview
Problem
Injection-compression molding processes face complexity and difficulty in controlling part thickness due to mold breathing, which leads to inconsistent cavity volume and increased operational challenges, especially when manufacturing parts with varying thicknesses like ophthalmic lenses.
Innovation Solution
The implementation of a standoff post with an internal compression member that allows slight axial compression beyond a predetermined force value, enabling the cavity to expand without mold opening, and using shims to adjust insert position for varying thicknesses, maintaining constant or varying clamp force above the internal cavity force throughout the molding cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional injection-compression molding with mold breathing is used, then homogeneous part quality and lower residual stress are achieved, but the process complexity and difficulty in controlling part thickness increase
Solution Approach 1:
The invention extracts the compression function from the mold assembly itself and places it on the injection molding machine's platen. By using the machine's existing clamping mechanism to apply compression force directly, the complex mold breathing mechanism is eliminated while maintaining the benefits of compression molding for thickness control and part quality.
Solution Approach 2:
The invention makes the injection molding machine's clamping mechanism serve a dual function: both clamping the mold during injection and applying compression force during the compression stage. This eliminates the need for separate compression mechanisms or complex mold breathing systems, reducing overall process complexity while maintaining precision.
2Manufacturing precision
If mold opening and closing occurs during coining, then cavity pressure decreases and part quality improves, but the thickness of the mold cavity becomes unknown and requires complex shooting algorithms
Solution Approach 1:
The invention uses the injection molding machine's built-in force sensors and control system to monitor and adjust the compression force in real-time. The machine's control system provides feedback on the actual force applied to the platen, eliminating the need for separate shooting algorithms or complex measurement systems while ensuring precise thickness control.
Solution Approach 2:
The invention allows the injection molding machine's own control system to handle the measurement and adjustment of compression force. The machine's existing sensors and algorithms automatically monitor the force applied during compression and adjust parameters to achieve the desired cavity thickness, making the process self-regulating without external complex measurement systems.
3Manufacturing precision
If clamp force is increased to maintain mold closure during coining, then dimensional accuracy improves, but the process becomes more difficult to control and requires larger clamp tonnage
Solution Approach 1:
The invention dynamically adjusts the clamp force during the molding cycle to match the actual needs of the process. Rather than maintaining constant high clamp force throughout, the system modulates the force applied by the platen based on the stage of injection and compression, achieving dimensional accuracy while minimizing the required clamp tonnage at each moment.
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 approach simplifies the molding process by eliminating the need for complex clamp force profiles and convergence calculations, reducing the risk of flash and enabling precise control over cavity thickness, thereby improving dimensional accuracy and reducing operational complexity.
Implementation Method 1
the insert is compressed against the molding material as it cools. This compression helps mold replication by keeping the inserts in intimate contact with the molding material as it shrinks
Implementation Method 2
As the molding material cools and shrinks, force curve 10 is reduced and the mold is able to close back down while maintaining the inserts in intimate contact with the now solidifying mold material
Data Source
AI summary
A hardware configuration and related method for performing a coining-type injection compression operation. The invention is useful in molding lenses since lenses have different thicknesses at various points. The equipment maintains the mold in a closed position during the entire molding cycle. A two part standoff post is designed to provide for slight axial compression during high injection pressure. The standoff post also provides a convenient mounting surface near the parting line to install inserts at various heights.