Clip Attachment Wall Structure to Prevent Sink Marks
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Solution Overview
Problem
Resin-molded articles with clip attachment members and ribs on the back surface often develop recessed defects, known as sink marks, at the boundary portions between the clip attachment member and ribs, compromising the strength and aesthetics of the design surface.
Innovation Solution
Incorporating a through-hole penetrating through the attachment wall adjacent to the ribs in the clip attachment member, which prevents excessive resin accumulation and shrinkage, thereby reducing the likelihood of recessed defects while maintaining the structural integrity of the clip attachment member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ribs are formed on the attachment wall to reinforce it, then the strength of the clip attachment member is improved, but sink marks occur on the design surface at the boundary portions between the clip attachment member and ribs
Solution Approach 1:
The patent extracts the problematic boundary portions between the attachment wall and ribs by forming through-holes at these locations. This removes the excess resin that would otherwise accumulate and cause sink marks, while preserving the reinforcing function of the ribs through the attachment wall structure.
Solution Approach 2:
The through-holes create a porous structure at critical locations on the attachment wall, allowing resin to escape during molding and preventing sink mark formation. This porous feature is strategically placed only at boundary portions where sink marks would occur, not throughout the entire structure.
2Manufacturing precision
If ribs are not formed to prevent sink marks, then the design surface quality is improved, but sufficient strength cannot be ensured for the clip attachment member
Solution Approach 1:
Instead of removing the ribs entirely, the patent extracts only the problematic boundary regions by forming through-holes at these locations. This selective removal prevents sink marks while maintaining the rib structure for strength reinforcement.
Solution Approach 2:
The patent applies different structural features to different locations: the attachment wall with ribs provides strength where needed, while through-holes are placed only at boundary portions where sink marks would occur. This local differentiation resolves the contradiction between strength and surface quality.
3Strength
If the attachment wall is made thicker to increase strength, then the strength of the clip attachment member is improved, but resin accumulation and shrinkage increase causing sink marks
Solution Approach 1:
The patent extracts the excess resin that accumulates in thick sections by forming through-holes at boundary portions. This allows the attachment wall to maintain its thickness for strength while preventing the resin accumulation that causes sink marks.
Solution Approach 2:
The through-holes create controlled porous regions in the attachment wall that facilitate resin escape during cooling and solidification, preventing the shrinkage-related sink marks that would otherwise occur in thick-walled sections.
Data Source
AI summary
A resin-molded article is configured so that a body having a design surface and a clip attachment member which is formed on a back surface of the design surface of the body and to which a clip is attachable, the body and the clip attachment member being integrally formed. The clip attachment member includes an attachment wall raised from the back surface, and a rib extending from the attachment wall to the back surface and reinforcing the attachment wall. A through-hole penetrating through the attachment wall is formed at a position adjacent to the rib of the attachment wall.