Thin Sheet Fastening Joint With Undercut Gap for Thermal Stress Relief
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Solution Overview
Problem
Existing methods for connecting functional elements to thin sheets, such as those using punch rivets, often result in material stresses under temperature loads due to differing coefficients of thermal expansion, particularly when steel is used for the functional element and aluminum for the sheet, leading to potential weakening and material displacement.
Innovation Solution
A method involving a functional element with a dome-shaped elevation and a die with a corresponding recess creates a circumferential gap, allowing radial material displacement and reducing thermal stresses, while anti-rotation knobs provide additional protection against twisting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a self-piercing rivet with a hollow cylindrical shank is used to join metal sheets, then a strong mechanical connection is achieved through material displacement and undercut formation, but thermal stresses occur due to different thermal expansion coefficients between steel rivet and aluminum sheet
Solution Approach 1:
The rivet shank is divided into multiple axial sections (first, second, and third shank sections) with different diameters, creating a segmented structure that allows differential thermal expansion in each section, thereby reducing thermal stress while maintaining mechanical connection strength
Solution Approach 2:
Different sections of the rivet shank have different local geometries (varying diameters), where the first shank section has a larger diameter for strong mechanical interlocking, while the second and third sections have smaller diameters to accommodate thermal expansion differences and reduce thermal stress concentration
2Strength
If the rivet shank is deformed to form an undercut connection, then material flow creates a form-fitting connection that enhances bond strength, but this material displacement can cause defects in thin sheet materials
Solution Approach 1:
The setting process uses a dynamic, multi-stage deformation approach where the rivet shank is progressively deformed through different stages (first, second, third shank sections) to control material flow and prevent excessive displacement that could cause defects in thin sheets
Solution Approach 2:
The diameter parameters of different shank sections are specifically designed with precise dimensional relationships, where the first shank section has diameter D1 and subsequent sections have smaller diameters D2 and D3, creating controlled parameter variations that manage material displacement while ensuring adequate connection strength
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 approach enables a stress-free connection under temperature loads, maintaining structural integrity and allowing the use of thin, ductile materials, while the anti-rotation knobs enhance the connection's stability.
Implementation Method 1
a dome-shaped elevation (32) is arranged on this bottom surface (31.2), so that the material of the thin sheet (10) is deformed into this recess (31) of the die (30), so that with radial spreading (G) of the cutting foot (4) outwards, an undercut (5) is created
Implementation Method 2
with radial spreading (G) of the cutting foot (4) outwards, an undercut (5) is created with the formation of a residual base (10.1) in the thin sheet (10)
Data Source
Figure 1~2
Figure 3
AI summary
The invention concerns a method for creating a connection between a functional element (1), having a head portion (2) and a blade (3), and a sheet-like component (10) with a thickness (S), in which the head portion (2) of the functional element (1) is formed with a blade foot (4) which comprises the blade (3) and has a foot length (F) and a prescribed foot diameter (E), the blade foot (4) is pressed by means of a tool (20) acting on the functional element (1) into a depression (31) of a mould (30) by an axial advancing movement while spreading radially to form an undercut (5) in the component (10), without penetrating the component (10), and the depression (31) of the mould (30) is formed with a mould depth (C) and a mould diameter (D). It is provided according to the invention that, to obtain a circumferential gap (7) running around the blade foot (4) at the transition to the head portion (2), the foot length (F) of the blade foot (4) and the mould diameter (D) and the mould depth (C) of the mould (30) are chosen in dependence on the prescribed thickness (S) of the component (10) in accordance with the following: F ≤ 2.2 x S, D ≤ 2 x S + E and C ≤ S.