Two-Step Rivet Swaging for Low-Ductility Sheet Joining
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Solution Overview
Problem
Self-piercing rivets are ineffective for joining low ductility materials like Ultra High Strength Steel, magnesium, 7000 series aluminium, cast aluminium, and carbon fibre due to difficulty in penetration and flaring without causing material cracks, leading to weak joints prone to failure under dynamic loads.
Innovation Solution
A method and apparatus that pierce and swage the rivet into the workpiece in two separate operations using a punch and die assembly, with a die changing mechanism to provide a rivet receiving surface, allowing for controlled flaring without requiring high forces, and a rivet design with features like ribs or a knurled band to increase engagement and control insertion depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rivet with very high hardness is used to penetrate Ultra High Strength Steel, then penetration capability is improved, but the rivet becomes brittle and cracks during insertion
Solution Approach 1:
The rivet insertion process is divided into two separate steps: first penetration, then flaring. This segmentation allows each step to be optimized independently - the rivet can be hard enough to penetrate UHSS without being excessively brittle, and the flaring step provides the necessary engagement without requiring extreme hardness.
Solution Approach 2:
The penetration action is performed first to create the hole through the UHSS workpiece. Only after successful penetration is the flaring action applied to create engagement. This preliminary sequencing ensures the rivet is in position before attempting to deform it, preventing crack propagation.
2Productivity
If traditional self-piercing rivet method is used on low ductility materials, then insertion speed is maintained, but material cracks and joint weakness occur
Solution Approach 1:
The single-step self-piercing process is segmented into two distinct operations: penetration and flaring. This allows control over material deformation - the penetration creates the hole without excessive force, and the subsequent flaring provides controlled engagement, preventing cracks in low ductility materials while maintaining efficiency.
Solution Approach 2:
The system dynamically adapts the die configuration between steps. The die is modified or changed to provide a rivet receiving surface with appropriate geometry for the flaring operation, optimizing the engagement process for low ductility materials without compromising the penetration step.
3Device complexity
If rivet flaring is performed in a single step with penetration, then process complexity is reduced, but control over flaring is insufficient causing material damage
Solution Approach 1:
The flaring operation is separated from penetration and performed as a distinct second step. This segmentation provides sufficient control over the flaring process to prevent material damage in low ductility materials, while the overall apparatus remains relatively simple through the use of a modifiable die rather than completely separate equipment.
Solution Approach 2:
The die is dynamically modified or changed to provide the appropriate receiving surface for the flaring operation. This dynamic adaptation enables precise control over the flaring process without requiring a completely separate complex apparatus, balancing control needs with device simplicity.
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 secure joining of low ductility materials without causing damage, reducing the risk of joint failure under dynamic loads and allowing for efficient assembly in tight spaces with reduced apparatus size and weight.
Implementation Method 1
A shank of the rivet passes through the upper sheet of material and then flares outwardly as it travels into the lower sheet of material and approaches the die. Outward flaring of the shank may be referred to as upsetting the rivet.
Data Source
AI summary
A method of inserting a rivet into a workpiece using a rivet insertion apparatus, the method comprising, during a first rivet insertion step, using a punch and die to drive the rivet into the workpiece such that a slug of workpiece material is removed from the workpiece and travels into a bore provided in the die, modifying or changing the die to provide a rivet receiving die surface, then during a second rivet insertion step, using the punch to drive the rivet further into the workpiece such that a shank of the rivet is upset by the rivet receiving die surface.