Clinch Nut Selective Hardening for High-Strength Metal Joining
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Solution Overview
Problem
Clinch nuts face challenges when attaching to high-strength metal members, requiring increased compressive strength to avoid deformation, while maintaining manufacturing flexibility for thread formation, which is compromised by the hardness of the metal materials.
Innovation Solution
Selective hardening of clinch fasteners using induction hardening techniques to create zones of varying hardness, allowing for effective piercing and threading without distorting the fastener, enabling use with metals of differing hardness values and strengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hardness and compressive strength of the clinch nut are increased to attach to high-strength metal members, then the piercing and setting forces are sufficient, but the manufacturing flexibility for thread formation is lost
Solution Approach 1:
The clinch nut is selectively hardened in specific zones (pilot portion outer zone and bottom zone) while maintaining softer hardness in the inner zone containing the central bore. This local differentiation allows the hardened zones to provide sufficient strength for piercing and setting high-strength metal members, while the softer inner zone remains suitable for thread formation by roll threading or engagement with thread forming screws.
Solution Approach 2:
The clinch nut is divided into distinct zones with different hardness properties: an outer zone with increased hardness (Rc 40-60) for piercing and setting, and an inner zone with original hardness (Rb 90-30 Rc) for thread formation. This segmentation enables each zone to be optimized for its specific function without compromising the other.
2Force
If the clinch nut is made of high-hardness material to pierce high-strength metal members, then the piercing force is sufficient, but the fastener undergoes unwanted deformation or distortion
Solution Approach 1:
Selective hardening of the outer zone provides the necessary piercing force against high-strength metal members, while the softer inner zone and overall fastener structure maintain sufficient ductility to resist unwanted deformation and distortion during the piercing and setting process.
3Adaptability or versatility
If specialty self-threading screws are provided for use with high-hardness metals, then threading is possible, but the device complexity and variety of fasteners increases
Solution Approach 1:
The selectively hardened clinch nut can be used with standard thread forming screws (such as TAPTITE and TAPTITE 2000 series) across a wide range of metal member hardness values. The inner zone's maintained original hardness allows compatibility with commercially available thread forming screws, eliminating the need for specialty screws and reducing fastener variety complexity.
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 selective hardening process enhances the clinch fastener's compressive strength and resistance to piercing forces, allowing it to be used with high-strength metals like HSLA and UHSLA steel without compromising thread formation capabilities, resulting in a significant strength increase of over 60% while maintaining original hardness for thread rolling screws.
Implementation Method 1
selective hardening of the fastener enables mounting with application of required forces for piercing and/or plastic deformation of the metal member without undesirable deformation or distortion of the fastener
Implementation Method 2
The clinch fastener selectively hardened in accordance with the invention may therefore be used with a variety of metal members of differing strengths and harness values
Data Source
AI summary
A metal clinch fastener has portions thereof selectively hardened to enable use of the fastener with metal members of differing hardness values. The selective hardening of the fastener enables mounting with application of required forces for piercing and/or plastic deformation of the metal member without undesirable deformation or distortion of the fastener. The screw thread region or zone of the fastener has a relatively lesser hardness suitable and may be pre-threaded or later threaded by engagement with a thread forming screw.