Touch Fastener Hook Demolding via Curved Head Geometry
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Solution Overview
Problem
Existing touch fastener manufacturing methods face challenges in designing hook shapes that enable demolding from closed cavities while maintaining desired properties such as peel and shear strength, and touch softness.
Innovation Solution
A method involving mold cavity and preform structure shapes that facilitate demolding by using a moldable resin with specific undercut designs and curvature, allowing resin projections to be withdrawn from closed cavities with stems and heads that overhang, and optionally modifying the heads to increase stiffness or deformability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hooking structures are molded with overhanging heads from closed cavities, then manufacturing efficiency is improved, but demolding difficulty increases
Solution Approach 1:
The mold cavity incorporates a curved surface at the distal end of the head portion that curves inward toward the stem. This curvature creates a gradual transition zone that allows the molded hooking structure to be flexed and drawn through the cavity opening without requiring cavity opening, thus enabling easy demolding while maintaining closed-cavity manufacturing efficiency
Solution Approach 2:
The patent specifies that the curved surface extends over a central region of the head portion and that the head portion is undercut on two opposite sides of the stem. These geometric parameter changes create a favorable stress distribution and deformation path during demolding, allowing the structure to be removed intact from closed cavities
2Ease of manufacture
If hook shapes are designed for easy demolding, then manufacturing ease is improved, but fastening strength may deteriorate
Solution Approach 1:
The head portion is segmented with an undercut on two opposite sides of the stem, creating distinct geometric zones. This segmentation allows the curved surface to be positioned strategically to facilitate demolding while the undercut regions maintain structural integrity and fastening capability
Solution Approach 2:
The curved surface at the distal end of the head portion provides a gradual transition that enables easy demolding through controlled flexing, while the overall head geometry maintains sufficient mass and structural rigidity to ensure fastening strength
3Strength
If resin modulus is increased for strength, then peel and shear strength improve, but touch softness deteriorates
Solution Approach 1:
The patent specifies using resin with a modulus of between 100 and 300 ksi, optimizing the balance between strength and softness. This parameter optimization allows the fastener to maintain adequate peel and shear strength while preserving touch softness for comfortable skin contact
Solution Approach 2:
The curved surface geometry at the distal end of the head portion creates localized stress distribution that enhances fastening performance without requiring increased resin modulus throughout the entire structure, thus preserving touch softness
Data Source
Figure 1
Figure 2A~2C
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AI summary
Touch fastener products (120,220,420,520,620,720,820,920,1000), as well as apparatus (100) and methods for manufacturing such products, are described. The methods and apparatus feature certain mold cavity (118) shapes that are designed to facilitate demolding of hammer hook touch fastener elements (122,122''',222,422,522,622,722,822,922,1122) exhibiting desirable fastening properties. Such mold cavity shapes can be combined with particularly soft molding resins to produce useful fastening products.