Self-Piercing Fastening Element for High-Strength Materials
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Solution Overview
Problem
Existing fastening methods fail to reliably join high-strength materials without pre-formed holes, as they require excessive forces or two-sided access, and are prone to failure when used with materials exceeding 600-800 MPa tensile strength.
Innovation Solution
A fastening element with a small shaft cross-section and tapered hole-forming portion, driven by a punch, which allows for one-sided joining of high-strength materials with reduced joining forces, featuring a thermally activatable coating and annular grooves for enhanced friction and interlocking, and a compact design for efficient use in the automotive industry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fastening methods are used to join high-strength materials without pre-formed holes, then the joining process can be simplified, but the joining forces become excessive and the fastening element fails
Solution Approach 1:
The patent applies preliminary action by heating the joining area of the high-strength material before fastening. This pre-heating treatment locally reduces the material strength at the joining zone, allowing the fastening element to penetrate and set with significantly lower forces. The heating is performed in advance of the actual fastening operation, creating favorable conditions for subsequent low-force joining.
Solution Approach 2:
The patent changes the physical parameter of the material by applying thermal energy to reduce its strength locally. By controlling the temperature and heating duration, the material transitions from a high-strength state to a more ductile, lower-strength state during the joining process, enabling successful fastening without excessive forces. After joining, the material cools and regains its original strength properties.
2Device complexity
If known joining elements are used with high-strength materials, then the fastening element can be simple in design, but the element fails when penetrating the component completely
Solution Approach 1:
The patent applies parameter changes by modifying the material temperature before fastening. The heating process temporarily alters the mechanical properties of the high-strength material, reducing its flow stress and enabling complete penetration by the fastening element without failure. This parameter change allows simple fastening element designs to successfully join materials that would otherwise be too strong for conventional elements.
3Productivity
If high-strength materials are joined without pre-formed holes, then the manufacturing process can be streamlined, but the joining area requires excessive force that causes deformation
Solution Approach 1:
The patent applies preliminary action by performing localized heating of the joining area before the fastening operation. This pre-treatment reduces the material strength at the specific joining zone, allowing the fastening process to proceed with lower forces that do not cause excessive deformation or require complex tooling, thereby maintaining manufacturing efficiency.
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
Enables reliable joining of components with up to 2000 MPa tensile strength using low joining forces, minimizing deformation and weight, while reducing manufacturing complexity and environmental impact.
Implementation Method 1
The region of the joining area is heat-treated via an electric arc, which is formed between the first component on the one hand and an electrode provided on the joining device on the other hand
Implementation Method 2
the first component is heated in such a way that a strength of the first component in the heat-affected zone is reduced
Data Source
Figure 1~3
Figure 4~5
AI summary
Fastening element (10) for joining at least two components without preformed hole(s) and particularly adapted when at least one of the components is made in a high-strength material, with a setting tool (32) having a punch (34), wherein the fastening element is driven in the components by the punch (34) comprising: - a head (16) at a first axial end - a tapered hole-forming portion (20) at a second axial end opposite to the first axial end, and - a shaft (24) arranged between the tapered hole-forming portion (20) and the head (16) and defining a longitudinal axis (X) of the fastening element between the first and the second axial end (18, 22), wherein the surface of the shaft cross-section is less than or equal 7.1 square millimetres.