Dome Cover Thin Portion Suppresses Weld Marks
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Solution Overview
Problem
The existing methods for manufacturing dome-shaped covers for surveillance cameras using plastic injection molding face challenges in achieving high shape accuracy for the hemispherical optically effective region, leading to degradation in imaging performance due to gate marks and weld marks caused by uneven resin flow.
Innovation Solution
A dome-shaped cover design featuring a recessed thin portion on the cylindrical portion, which regulates resin flow to suppress weld marks, combined with a specialized mold structure including a stripper plate and concave/convex mold pieces to ensure accurate injection and release, allowing for symmetrical or asymmetrical thin portion placement to optimize resin flow and reduce weld mark formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a side gate is arranged at an end of the collar portion to avoid gate marks on the optical surface, then gate marks on the optical surface are eliminated, but weld marks are formed due to uneven resin flow paths
Solution Approach 1:
The patent applies local quality by creating a thin portion at a specific location on the cylindrical portion of the dome-shaped cover. This local thickness variation modifies the resin flow characteristics in that specific region, causing the resin to flow more slowly through the thin portion and thereby preventing weld mark formation at the flow end portion opposite the gate.
Solution Approach 2:
The patent changes the geometric parameter of the cover by forming a thin portion with reduced thickness compared to other regions. This parameter change (thickness) directly affects the resin flow velocity and pressure distribution, enabling control over the flow pattern to eliminate weld marks while maintaining the side gate configuration.
2Productivity
If the dome-shaped cover is manufactured by plastic injection molding with a side gate, then mass production is achieved, but molding irregularities occur due to unequal flow path lengths
Solution Approach 1:
The thin portion is strategically positioned to locally modify resin flow without affecting the overall hemispherical optical surface quality. This localized modification allows the rest of the cover to maintain high shape accuracy required for optical applications while enabling mass production through injection molding.
Solution Approach 2:
The patent uses a mold with a protruding portion that copies the thin portion geometry onto the dome-shaped cover during injection molding. This copying approach enables consistent reproduction of the flow-control feature across mass production while maintaining precision through the mold's precise geometry.
3Duration of action of moving object
If the flow path through the zenith is longer than the circumferential flow path, then resin flow to the flow end portion is delayed, but weld marks are more easily formed due to faster circumferential flow
Solution Approach 1:
The thin portion changes the geometric parameter of the cylindrical portion, increasing the local flow resistance and reducing resin flow velocity through that region. This parameter change equalizes the effective flow path lengths and velocities, preventing the circumferential flow from reaching the end portion too quickly and forming weld marks.
Solution Approach 2:
The thin portion acts as a preliminary anti-action by creating controlled flow resistance before the resin reaches the critical flow end portion. This pre-established resistance prevents the resin from flowing too quickly along the circumferential path, thereby preventing weld mark formation in advance.
Data Source
AI summary
A dome-shaped cover having a high optical performance in which formation of a weld mark is suppressed. The dome cover includes a hemispherical portion, a collar portion, and a cylindrical portion provided between the hemispherical portion and the collar portion, and the cylindrical portion has a thin portion recessed from an outer surface of the cylindrical portion.