Blind Fastener Stem Interlock for Secure Post-Setting Retention
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Solution Overview
Problem
Existing blind fasteners often result in loose or weak connections after the setting operation, leading to potential noise issues, and the stem may not be securely retained within the body, which can cause reliability concerns.
Innovation Solution
The blind fastener incorporates axially opposed depressions near the stem head to create a form fit between the stem and the body after setting, along with material bulges that provide a force fit, ensuring the stem is securely retained within the body. The geometry of the depressions, including specific radii of curvature and angles, enhances material flow during setting and retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stem is simply inserted into the body without retention features, then the setting process is simple, but the stem becomes loose after setting causing noise and reliability issues
Solution Approach 1:
The stem is segmented into functional zones: a head portion, a shaft portion with circumferential grooves that create material bulges, and a tail portion. The grooves divide the shaft into segments that can independently deform to create interference fits with the body, providing retention without requiring complex additional features.
Solution Approach 2:
The circumferential grooves are pre-formed on the stem shaft before assembly. During the setting process, these pre-formed grooves automatically generate material bulges as the stem is pulled through the body, creating the retention mechanism in advance rather than requiring post-assembly adjustments or complex locking features.
2Stability of the object's composition
If protrusions and depressions are added to the stem for interference fit, then handling and shipping security improves, but the setting process becomes more complex and the stem may strike retention features during setting
Solution Approach 1:
The patent removes the breakneck feature from the stem design, allowing the entire stem to remain in the body after setting. This eliminates the complexity of designing breakneck geometry and the potential for striking retention features during the setting process, while the material bulges provide sufficient retention.
Solution Approach 2:
The stem shaft diameter is varied along its length with circumferential grooves that create localized material bulges. These parameter changes in diameter and geometry create the interference fit effect without requiring separate protrusion-depression retention features, simplifying the setting operation.
3Ease of manufacture
If the stem breaks at a predetermined breaking point during setting, then the broken part can be disposed of, but the remaining stem may not be securely locked into the body
Solution Approach 1:
The stem is designed as a disposable component that is pulled through the body during setting and then broken off. The broken tail portion is disposed of, while the head and shaft portions remain in the body providing permanent retention through the material bulges created by the circumferential grooves.
Solution Approach 2:
The circumferential grooves are pre-formed on the stem to create material bulges during setting. These pre-formed features ensure that when the stem breaks at the tail, the remaining portions are already securely locked into the body through the interference fit, eliminating the need for additional locking mechanisms.
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
This design ensures a secure interlock between the stem and the body, preventing loose connections and noise, with a retention force of between 70 Newtons and 190 Newtons, significantly improving the reliability of the blind fastener.
Implementation Method 1
Blind fasteners generally operate on the principle of radial expansion and/or axial compression of material
Implementation Method 2
Blind fasteners generally operate on the principle of radial expansion and/or axial compression of material
Implementation Method 3
a relatively harder material than that which expands within the hole is used to cause the relatively soft, expanding material to flow radially outwards within the hole
Implementation Method 4
the protrusions and depressions are arranged to provide an interference fit with the unplaced rivet body bore and so help hold the rivet assembly together
Data Source
Figure 1~2B
Figure 3~4
Figure 5
AI summary
Method of setting a blind fastener (10) and blind fastener, comprising: - a body (12) with a hollow shank (16) and a body head (22), - a stem (14) with an elongated cylindrical shaft (32), a weakened portion and a radially enlarged stem head (34), wherein the shaft comprises two diametrically opposed depressions (42) provided between the weakened portion and the stem head, wherein the depressions extend from the underside of the stem head or in a close vicinity of the underside of the stem head, and is adapted to form an interlock with the body, wherein the depressions, in a cross-section, have a V-shape with a inclined flat first surface (44), a second surface (46) comprising a second radius of curvature (R2), the first and second surfaces being connected by an intermediate portion (48) having a first radius of curvature (R1), different from the second radius of curvature (R2).