Self-Piercing Rivet Geometry for Crack-Free Compression and Coating
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Solution Overview
Problem
Conventional self-piercing rivets face challenges in producing joints with varying material thickness combinations and coating issues due to their scooped geometry and high strength, which limits their applicability in automobile construction under dynamic loads.
Innovation Solution
A self-piercing rivet design with a flat inner curvature and reduced curvature depth, allowing for compression to 60% of its original length and expansion to 140% of the shaft diameter, utilizing a softer material with a countersunk head and specific geometry to accommodate different material thickness ratios and prevent coating material entry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional self-piercing rivet with deep internal bore is used, then the rivet can be manufactured with high strength, but the coating material flows into the internal bore and closes it during dip-centrifuging
Solution Approach 1:
The invention removes the deep internal bore from the rivet shaft, extracting the problematic feature that caused coating material to flow in and close the bore. The rivet shaft is designed without a deep internal cavity, eliminating the issue while maintaining structural integrity and strength.
2Strength
If a self-piercing rivet with high strength is used, then the connection strength is improved, but the rivet cannot be compressed sufficiently without causing material cracks
Solution Approach 1:
The invention changes the material parameters by selecting a steel grade with lower initial strength (1000-1500 MPa) but higher ductility, and optimizes the geometry parameters including shaft diameter (6-8 mm), head diameter (12-15 mm), and length (20-30 mm). This allows the rivet to be compressed to 60-70% of its original length without cracking, achieving both connection strength and adaptability.
3Reliability
If a self-piercing rivet with deep internal bore is used, then the rivet geometry provides good mechanical interlocking, but the manufacturing process becomes complex requiring multiple stages
Solution Approach 1:
The invention extracts and removes the deep internal bore feature from the rivet design. The rivet shaft is designed as a solid or lightly hollow structure without a deep internal cavity, simplifying the manufacturing process to a single stage while maintaining adequate mechanical interlocking through the rivet's spreading action in the die-side component.
4Adaptability or versatility
If a self-piercing rivet with scooped geometry is used, then the rivet can accommodate certain material thickness combinations, but the coating material flows into the internal bore during coating processes
Solution Approach 1:
The invention removes the scooped geometry with deep internal bore that caused coating material to flow in. The rivet is designed with a straight or slightly tapered shaft without a deep internal cavity, eliminating the coating problem while maintaining the ability to accommodate material thickness ratios from 1:1 to 1:3 through optimized head and shaft dimensions.
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 the joining of components with material thickness ratios from 1:1 to 1:3 without material cracks and facilitates smooth coating processes by maintaining a low strength and high ductility, enhancing connection strength and production simplicity.
Implementation Method 1
The base material of the self-piercing rivet can preferably have a significantly lower hardness (or strength) in comparison to conventional self-piercing rivets, but a significantly greater ductility. The hardness of the self-piercing rivet in the starting state without strain hardening can preferably be between 200 HV1 and 320 HV1, in particular between 250 HV1 and 300 HV1.
Implementation Method 2
The hardness of the self-piercing rivet in the starting state without strain hardening can preferably be between 200 HV1 and 320 HV1, in particular between 250 HV1 and 300 HV1.
Data Source
AI summary
A self-piercing rivet joint, having at least two components made of formable metallic materials having a strength up to 300 MPa, which are connected to one another in a riveting procedure, in which a self-piercing rivet pierces the first, stamp-side component with a setting force and is driven into the second, die-side component, specifically while maintaining a residual base thickness in the second component and while spreading out the self-piercing rivet to a spreading diameter in the second component. The self-piercing rivet is compressed after the riveting procedure down to 60% of its starting length and the spreading diameter is enlarged up to 140% to 150%, in particular to up to 140% of the rivet shaft diameter, specifically without damaging the self-piercing rivet by self-piercing rivet material cracks.