Fastener Head Undercut Sealing for Watertight Hole-Forming Joints
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Solution Overview
Problem
Existing self-penetrating and thread forming fasteners fail to create an effective seal when used in water-sensitive assemblies like battery boxes due to material displacement during installation, which compromises the watertight integrity of the joint.
Innovation Solution
A multiple zone undercut design in the fastener head, combined with a sealant or crush washer in a secondary undercut area, captures material flow and ensures a proper seal without requiring a through hole in the upper substrate layer, using continuous or discontinuous undercut configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a self-penetrating and thread forming fastener is used to join substrate layers, then the fastener creates its own hole and forms threads through heat generation and material displacement, but the material flow during installation compromises the watertight integrity of the joint
Solution Approach 1:
The fastener head is divided into multiple undercut zones: a first undercut area that is open and receives upflowed material, and a second undercut area that contains the sealant. This segmentation allows material flow to be directed away from the sealant, maintaining watertight integrity while preserving hole formation capability.
Solution Approach 2:
A sealant is introduced as an intermediary substance in the second undercut area to create the watertight seal. The sealant acts as a barrier between the fastener and the environment, preventing water penetration while allowing the fastener to maintain its self-penetrating function.
2Reliability
If sealant is placed in the undercut area of the fastener head, then a waterproof seal can be formed, but the upflowed material from the lower substrate layer displaces the sealant, compromising the seal
Solution Approach 1:
The undercut area is segmented into two distinct zones: the first undercut area that is open and receives the upflowed material, and the second undercut area that contains the sealant. This segmentation creates a protective barrier that prevents material from displacing the sealant while maintaining the waterproof seal.
Solution Approach 2:
The sealant is pre-placed in the second undercut area before the fastening operation. The multiple zone undercut design is prepared in advance to guide material flow away from the sealant, ensuring the sealant remains in its proper position during installation.
3Stability of the object's composition
If a through hole is provided in the upper substrate layer to receive upflowed material, then material displacement of the sealant is prevented, but the assembly complexity increases and the watertight integrity is compromised at the through hole
Solution Approach 1:
The fastener head's multiple zone undercut design serves itself by providing a dedicated receptacle (first undercut area) for the upflowed material. This self-service feature eliminates the need for modifications to the substrate layers, maintaining assembly simplicity while preserving sealant position stability.
4Ease of operation
If the fastener creates heat through rotation and end load to form its own hole, then the installation process is simplified, but the heat and material flow force substrate material away from the screw, preventing proper sealing
Solution Approach 1:
The undercut area is segmented into two functional zones: the first undercut area that is open and receives the heat-softened and upflowed material, and the second undercut area that protects the sealant from material displacement. This segmentation maintains installation simplicity while ensuring sealing effectiveness.
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
The design provides a waterproof seal around the threaded hole without needing a through hole in the upper substrate, ensuring the assembly remains watertight and secure.
Implementation Method 1
These types of fasteners create their own hole in the target substrate by generating heat through rotation speed and the end load applied to the fastener. This heat mixed with the point geometry, which is described in the previously mentioned patents, forces the material to move away from the screw, thereby creating a formed hole.
Data Source
AI summary
A fastener including an elongated shaft extending between first and second shaft ends, with a tip provided at the first shaft end, and a thread region provided between the tip and the second shaft end; and a head with a drive region arranged at the second shaft end. The fastener also incudes a first annular undercut area in an underside surface of the head, where the first annular undercut area is configured and arranged to receive material that has flowed from a substrate during installation of the fastener into the substrate, and a second annular undercut area in the underside surface of the head, where the second annular undercut area is located radially outwardly of the first annular undercut area. Additionally, an annular sealing member is provided within the second annular undercut area, where the annular sealing member makes sealing contact with an upper surface of the substrate.