Hollow Punch Rivet Geometry for High-Strength Sheet Joining
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Solution Overview
Problem
Existing semi-hollow punch rivets, such as the C-rivet and P-rivet, are inadequate for joining high-strength workpieces due to excessive expansion and insufficient material in the undercut region, leading to low obtainable strength and instability during punch riveting, particularly in high-strength metal sheets used in lightweight construction.
Innovation Solution
A punch rivet with a shank internal diameter to external diameter ratio between 0.52 and 0.6, featuring a ring cutting edge with a smaller diameter than the external diameter, and a radial shank thickness greater than 1.1 mm, which reduces radial expansion and maintains sufficient deformability for forming an undercut, while the ring cutting edge merges into the shank internal diameter via a cutting radius and conical surface to enhance stability and deformability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the shank internal diameter is increased to receive the punch slug, then the shank interior volume is sufficient, but the radial shank thickness decreases leading to excessive expansion and insufficient rigidity
Solution Approach 1:
The patent applies parameter changes by optimizing the ratio of shank internal diameter to external diameter within a specific range (0.45 to 0.65). This controlled parameter adjustment ensures the shank has sufficient internal volume to receive the punch slug while maintaining adequate radial thickness (greater than 1.0 mm) to provide the necessary rigidity and resist excessive expansion during the punch riveting process.
2Strength
If the radial shank thickness is increased to provide rigidity and reduce expansion, then the shank can penetrate high-strength sheets, but the shank internal volume decreases making it insufficient to receive the punch slug
Solution Approach 1:
The patent resolves this contradiction by defining an optimal parameter range for the internal-to-external diameter ratio (0.45 to 0.65) and specifying a minimum radial shank thickness greater than 1.0 mm. These parameter specifications ensure that the shank maintains sufficient rigidity to penetrate high-strength metal sheets while simultaneously providing adequate internal volume to accommodate the punch slug during the riveting process.
3Ease of operation
If a sharp ring cutting edge at the shank external diameter is used to pierce the workpiece, then the cutting edge is effective, but the shank expands strongly during punch riveting leaving little material in the undercut region
Solution Approach 1:
The patent applies local quality by positioning the ring cutting edge at a specific location on the shank end face with a diameter smaller than the shank external diameter. This localized feature design ensures effective cutting action during piercing while controlling the expansion behavior during riveting, thereby preserving sufficient material in the undercut region of the bottom workpiece for adequate joint strength.
4Strength
If the punch rivet is designed for high-strength materials (hardness) to pierce high-strength workpieces, then the piercing capability is sufficient, but the deformability in the shank region decreases reducing undercut formation
Solution Approach 1:
The patent applies parameter changes by carefully selecting and coordinating multiple geometric parameters including the internal-to-external diameter ratio (0.45 to 0.65), radial shank thickness (>1.0 mm), and ring cutting edge positioning. These parameter specifications create an optimized balance that allows the shank to maintain sufficient hardness for piercing high-strength materials while retaining adequate deformability to form the necessary undercut in the bottom workpiece.
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 provides a reliable method for joining high-strength workpieces with improved rigidity and residual bottom thickness, reducing material expansion and ensuring a sufficient shank internal volume to accommodate the punch slug, thereby enhancing the strength and stability of the punch-riveted joint in high-strength metal sheets.
Implementation Method 1
the upper workpiece being pierced (perforated) by the hollow shank
Implementation Method 2
A ring cutting edge is realized on the shank end face, the diameter of which is smaller than the shank external diameter
Implementation Method 3
the hollow shank is hereafter radially expanded and is driven radially into the bottom workpiece such that an undercut is formed
Data Source
Figure 1~2
Figure 3~5
Figure 6~8
AI summary
Punch rivet (30) for joining two workpieces (12, 14), said punch rivet having a head (32) and a shank (34), wherein the shank (34) is realized as a hollow shank with a shank internal diameter (D3), a shank external diameter (D1) and a shank end face, wherein on the shank end face a ring cutting edge (50) is realized, the diameter (D4) of which is smaller than the shank external diameter (D1) and the diameter (D4) of which is greater than the shank internal diameter (D3), wherein the ring cutting edge (50) is spaced by at least 20% of the radial shank thickness (M5) of the hollow shank (34) both from the shank external diameter (D1) and from the shank internal diameter (D3). In this case, the ratio D3/D1 of shank internal diameter (D3) to shank external diameter (D1) is smaller than 0.6.