Barrier Layer in Self-Piercing Riveting for Mixed-Material 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 failure modes like cracking and uneven surfaces.
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 yield strength and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If self-piercing riveting is used to fasten sheets with different mechanical properties (e.g., aluminum and steel), then joining speed and productivity are improved, but the joint integrity deteriorates due to stress concentrations and cracking in the less ductile layer
Solution Approach 1:
A barrier layer is introduced between the bottom sheet and the die to act as an intermediary element. This barrier layer redistributes the stress concentrations that occur during the riveting process, preventing direct stress transfer to the less ductile layer and thereby preventing cracking while maintaining the high-speed self-piercing riveting process
2Reliability
If pre-coating is applied to the sheets (e.g., electrophoretic coating or powder coat), then corrosion resistance is improved, but the coating quality deteriorates due to damage during button formation in the die
Solution Approach 1:
The barrier layer serves as a protective intermediary between the coated bottom sheet and the die during the riveting process. It prevents direct contact and mechanical damage to the coating during button formation, preserving coating integrity while allowing the riveting process to proceed
Solution Approach 2:
The barrier layer is positioned in advance between the bottom sheet and die to provide cushioning protection. This pre-positioned barrier absorbs and distributes the mechanical stresses during button formation, preventing coating damage before it can occur
3Reliability
If a barrier layer is added between the bottom sheet and die, then joint reliability is improved by reducing stress concentrations, but device complexity increases
Solution Approach 1:
The barrier layer is designed as a simple, inexpensive, and easily replaceable component. It can be a thin sheet or pad that is positioned between the bottom sheet and die, performs its stress-distribution function, and then can be quickly removed or replaced between production cycles, minimizing the impact on overall process complexity
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.