Molding Die Edge Design for Junction Box Bus-Bar Windows
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Solution Overview
Problem
The existing techniques for forming windows in electric junction boxes to expose bus-bars result in edge abrasion due to the flow of molten resin, especially when the window edge is angled, leading to potential damage and reduced mechanical strength of the molding die.
Innovation Solution
The window edge is designed with a first edge along a virtual line angled with respect to the bus-bars and a second edge formed as a rectangular triangle, preventing the formation of acute edges on the die, which would otherwise be abraded by the resin flow, and broadening the raised portions to enhance mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the window edge is formed at an angle with respect to the bus-bar extending direction to support bus-bars in a cantilever fashion, then the positioning accuracy and vibration absorption are improved, but the die edge strength is deteriorated and abrasion occurs during molding
Solution Approach 1:
The die edge is modified from a sharp angle to a rounded curvature with a specified radius. This curvature eliminates the stress concentration point that caused abrasion during molding, while still maintaining the angled configuration needed for cantilever support of bus-bars. The rounded edge distributes the molten resin flow pressure more evenly, preventing die wear.
Solution Approach 2:
The die structure is designed with different local characteristics: the edge portion has a rounded curvature to resist abrasion, while the interior maintaining portions preserve the angled configuration for proper bus-bar positioning. This local differentiation allows the die to simultaneously achieve both positioning accuracy and edge strength.
2Manufacturing precision
If the window edge is formed at an angle to align with terminal positions, then the electrical connection precision is improved, but the die edge becomes vulnerable to abrasion from molten resin flow
Solution Approach 1:
The angled window edge that provides precise terminal alignment is modified with a rounded curvature at its termination. This curvature protects the edge from direct contact with molten resin flow, preventing abrasion while maintaining the angled orientation needed for accurate terminal positioning and electrical connection.
Solution Approach 2:
The potential harm of molten resin flowing against the die edge is converted into a beneficial design feature. The rounded edge design allows the resin to flow smoothly around it, transforming what would be a harmful abrasive force into a controlled flow pattern that actually helps distribute resin evenly and reduces stress concentration.
Data Source
AI summary
An electric junction box, comprises a plurality of bus-bars spaced apart from each other, and a case made of a resin, covering the plurality of bus-bars and including a window for exposing a portion of the plurality of bus-bars, wherein the window has a first edge located at respective exposed portions of the plurality of bus-bars and a second edge located between the respective exposed portions of the plurality of bus-bars; and the first edge is formed along a virtual line that is at an angle with respect to an extending direction of the bus-bars, and the second edge is formed with a depressed area having a shape of a rectangular triangle whose slope is the virtual line.