Bistable Rivet Foot Spreading for Low-Ductility Joints
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Solution Overview
Problem
Rivet joints with rivet feet that expand radially during setting are not sufficiently secured in components with low ductility, leading to potential loosening and notching, especially in materials like aluminum die casting.
Innovation Solution
The rivet foot forms a bistable spring portion with two equilibrium states, transitioning from a reduced to an expanded state without significant springback, using the spring buckle effect, and is positioned in a pilot hole with a specific activation contour to secure the rivet element without form-fitting enclosure by the component material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rivet foot is spread radially outward to create form-fitting enclosure by component material, then the rivet element is secured against loosening, but component material with low ductility cannot achieve sufficient enclosure and springback occurs
Solution Approach 1:
The patent changes the geometric parameters of the rivet foot cross-section along its length, creating a specific profile with reduced width at the tip and increased width toward the head. This parameter variation enables the rivet foot to achieve stable spreading engagement with the pilot hole walls without relying on component material ductility or generating springback forces
Solution Approach 2:
The rivet foot is segmented into distinct zones with different cross-sectional characteristics: a reduced cross-section at the tip for initial engagement, a spreading zone with increasing width, and a head portion with maximum width. This segmentation allows each zone to perform its specific function during the setting process, achieving reliable securing without form-fitting enclosure
2Reliability
If the rivet foot tip is form-fittingly enclosed by component material to prevent relative movement, then loosening is prevented, but component material with low ductility is at risk of notching and premature cracking
Solution Approach 1:
The patent modifies the rivet foot cross-sectional parameters to reduce the spreading distance and engagement pressure. The specific profile geometry allows the rivet foot to engage the pilot hole walls with minimal deformation force, preventing notching and cracking in low-ductility materials while still achieving reliable movement prevention
Solution Approach 2:
Instead of deforming the component material to enclose the rivet foot tip, the patent uses the pre-formed pilot hole geometry to contain the spread rivet foot. The pilot hole acts as a mold that defines the final shape and position of the rivet foot, eliminating the need for form-fitting enclosure by component material
3Reliability
If the rivet foot is spread over a spreading distance to create undercut filled with component material, then relative movement is prevented, but the setting process requires high setting force that can damage low ductility materials
Solution Approach 1:
The patent optimizes the cross-sectional parameter distribution along the rivet foot length to reduce the required spreading distance. The gradually increasing width profile allows progressive engagement with the pilot hole walls, distributing the setting force over a longer duration at lower magnitude, thereby preventing damage to low-ductility materials
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 rivet joint effectively secures the rivet element against loosening and maintains the component's integrity without plastic deformation, even in materials with low ductility, ensuring a strong and stable connection.
Implementation Method 1
the rivet foot forms a bistable spring portion with two equilibrium states. A first equilibrium state corresponds to the reduced cross-section, undeformed rivet foot state. When the setting force is applied, the rivet foot changes to the second equilibrium state, in which the rivet foot is spread in the component with an expanded cross-section.
Data Source
AI summary
A riveted joint in which a rivet foot of a rivet element is driven into a component with a setting force, in particular by spreading the rivet foot. The rivet foot has a reduced cross-section in the still undeformed state and has an expanded cross-section in the driven-in state. The rivet foot is designed as a bistable spring portion that has two equilibrium states, namely the undeformed cross-section-reduced state and an expanded spread state. As a result of the setting force being applied, the rivet element changes from the undeformed state to the spread state, in which the rivet foot is spread with an expanded cross-section in the component, in particular without the build-up of a springback force that biases the rivet element towards the undeformed state.