Self-Piercing Riveting Barrier Layer for Crack-Resistant Joints
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Solution Overview
Problem
Self-piercing riveting technologies face challenges in forming durable joints between sheets with different mechanical properties, such as aluminum and steel, due to stress concentrations and coating damage, leading to failures like cracking and damage to pre-coatings.
Innovation Solution
Incorporating a barrier layer between the bottom sheet and the die in the self-piercing riveting system, which can be made of cold-formed or dual-phase steel, to reduce stress concentrations and optimize joint formation by adjusting the setting force based on the barrier's thickness and yield strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If self-piercing riveting is used to fasten sheets with different mechanical properties (e.g., aluminum and steel), then joining capability is improved, but joint integrity deteriorates due to cracking of the less ductile layer
Solution Approach 1:
A barrier layer made of more ductile material (e.g., aluminum) is introduced between the less ductile sheet (e.g., steel) and the die. This intermediary layer absorbs and redistributes the forming stresses, preventing stress concentrations that would otherwise cause cracking in the less ductile sheet. The barrier layer acts as a stress buffer, allowing the riveting process to proceed without compromising joint integrity.
2Reliability
If pre-coated sheets are used in self-piercing riveting, then corrosion resistance is improved, but coating integrity deteriorates due to damage during button formation
Solution Approach 1:
The barrier layer serves as a protective intermediary between the die and the pre-coated sheet. During the button formation process, the barrier layer absorbs the mechanical stresses and prevents direct contact between the die and the coating, thereby preventing coating damage while allowing the riveting process to complete successfully. This preserves both the corrosion resistance benefits of the coating and the structural integrity of the joint.
3Strength
If high setting force is applied during riveting, then joint strength is improved, but stress concentrations increase causing cracking
Solution Approach 1:
The barrier layer distributes the high setting forces applied during riveting across a wider area, preventing localized stress concentrations that would cause cracking. The more ductile barrier material deforms plastically, absorbing peak stresses and redistributing them uniformly, thereby enabling high joint strength to be achieved without exceeding the stress tolerance of the less ductile sheet.
4Reliability
If barrier layer is added to reduce stress concentrations, then joint integrity is improved, but device complexity increases
Solution Approach 1:
The barrier layer is designed as a disposable, inexpensive component that is consumed during the riveting process. It is a simple sheet of ductile material that requires no complex installation or removal procedures - it remains embedded in the joint as part of the final assembly. This approach adds minimal complexity while effectively solving the stress concentration problem.
Data Source
AI summary
A self-piercing riveting (SPR) system includes a top sheet and a bottom sheet. The top sheet is layered above the bottom sheet and are disposed between a die and a blank holder. The SPR system further includes a barrier disposed between the bottom sheet and the die, wherein the barrier is configured to reduce stress concentrations during formation of a joint between the top sheet and the bottom sheet. The barrier may has a thickness between 0.8 mm and 1.0 mm and is made from a cold formed or a dual phase steel alloy.