Self-Piercing Rivet Button Surface Geometry to Prevent Radial Cracking
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Solution Overview
Problem
High Pressure Die Cast aluminum members exhibit radial cracking during self-piercing riveting, leading to water intrusion and corrosion, and the heat treatment processes required to mitigate this issue are energy-intensive and prone to distortion.
Innovation Solution
A riveted assembly design featuring a differential height surface portion on the second panel member, with raised surface elements that deform to accommodate the self-piercing rivet without radial cracking, and a punch and die system that flares the rivet to secure the panel members, reducing material strain and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If self-piercing riveting is used on high pressure die cast aluminum members, then joining efficiency is improved, but radial cracking occurs on the surface leading to corrosion
Solution Approach 1:
The patent applies local quality by creating a differential height surface portion with raised surface elements at the specific location where the rivet button forms. This localized surface modification allows the material to accommodate the forming process without radial cracking, while the rest of the component maintains its original properties. The raised surface elements provide additional material that can deform plastically during rivet formation, preventing crack propagation.
2Reliability
If heat treatment is applied to increase elongation properties, then cracking is prevented, but energy consumption increases and distortion occurs
Solution Approach 1:
The patent applies preliminary action by modifying the surface geometry before the riveting process. The differential height surface portion with raised elements is created in advance, providing the necessary material reserve and stress distribution characteristics that prevent cracking during subsequent self-piercing riveting. This eliminates the need for post-casting heat treatment to achieve adequate elongation properties.
Solution Approach 2:
The patent replaces the thermal field (heat treatment) with a mechanical field solution (differential height surface portion). Instead of using thermal energy to increase material ductility through heat treatment, the invention uses mechanical surface geometry modification to achieve the same crack prevention effect during the mechanical riveting process.
3Reliability
If heat treatment is used to prevent micro cracking, then corrosion is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent merges the surface preparation function with the casting process itself. The differential height surface portion is integrated into the casting mold design, allowing the protective surface feature to be created during the primary manufacturing operation rather than requiring a separate post-processing step. This eliminates the need for additional heat treatment equipment and process control.
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 solution effectively prevents radial cracking and subsequent corrosion, while reducing the need for extensive heat treatment, thereby minimizing energy consumption and distortion, and enhancing the structural integrity of the riveted assembly.
Implementation Method 1
The rivet has an outwardly flared portion about which a portion of the first panel member and the second panel member are deformed, such that the rivet mechanically connects the first panel member to the second panel member
Data Source
AI summary
A riveted assembly includes a first panel member having a first surface and a second surface opposite to the first surface; a second panel member having a first surface and a second surface opposite to the first surface; and a rivet. The first and second panel members are positioned such that at least a portion of the second surface of the first panel member is in contact with at least a portion of the first surface of the second panel member. The rivet extends into and engages the first surface of the first panel member, and has an outwardly flared portion about which a portion of the first panel member and the second panel member are deformed, such that the rivet mechanically connects the first panel member to the second panel member at a connection region. The second surface of the second panel member has a differential height surface portion at least at the connection region.