Semi-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 as they tend to expand excessively during the riveting process, resulting in insufficient material in the undercut region and low obtainable strength, which is a challenge in the automotive industry's trend towards lightweight construction using high-strength metal sheets.
Innovation Solution
A punch rivet design with a ring cutting edge diameter greater than the shank internal diameter, spaced by at least 20% of the radial shank thickness from both the external and internal diameters, and a cutting ring face width less than 10% of the radial shank thickness, along with a shank internal to external diameter ratio less than 0.6, to achieve high rigidity and deformability for effective undercut formation without excessive expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If existing semi-hollow punch rivets (C-rivet, P-rivet) are used for joining high-strength workpieces, then the riveting process can be performed, but the rivets expand excessively during the process resulting in insufficient material in the undercut region and low obtainable strength
Solution Approach 1:
The patent modifies the geometric parameters of the punch rivet by implementing a specific diameter ratio (d3/d1 < 0.6) between the shank internal diameter and external diameter, and by positioning the ring cutting edge at a specific distance (≥20% of radial shank thickness) from both the external and internal diameters. These parameter changes control the expansion behavior during riveting to prevent excessive material displacement while maintaining sufficient undercut formation, thereby resolving the contradiction between obtainable strength and expansion during the process.
2Strength
If the shank internal diameter is increased to maintain sufficient shank internal volume for punch slug reception, then the shank becomes less rigid, but if the shank internal diameter is decreased to increase rigidity, then the shank internal volume becomes insufficient for receiving punch slugs
Solution Approach 1:
The patent establishes an optimal parameter range for the diameter ratio d3/d1 < 0.6, which balances the competing requirements of rigidity and internal volume. This parameter change ensures that the shank maintains sufficient stiffness to penetrate high-strength sheets while retaining adequate internal volume (≥0.5mm³) to receive punch slugs from the metal sheet layer, thereby resolving the contradiction between rigidity and shank internal volume.
3Shape
If the ring cutting edge is positioned closer to the shank external diameter to reduce expansion, then the cutting edge is too close to the surface, but if positioned closer to the internal diameter, then there is insufficient material in the undercut region
Solution Approach 1:
The patent specifies that the ring cutting edge shall be positioned at a distance of at least 20% of the radial shank thickness from both the shank external diameter and the shank internal diameter. This parameter change optimizes the positioning of the cutting edge to control expansion while ensuring sufficient material availability in the undercut region, thereby resolving the contradiction between expansion control and undercut region material.
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 improved punch rivet achieves a high level of rigidity for penetrating high-strength sheets, maintains sufficient shank internal volume for punch slug reception, and ensures a high residual bottom thickness, thereby enhancing the reliability of punch-riveted joints in high-strength materials like steel and aluminum, while preventing excessive expansion.
Implementation Method 1
The improved punch rivet achieves a high level of rigidity for penetrating high-strength sheets
Implementation Method 2
the hollow shank is hereafter radially expanded and is driven radially into the bottom workpiece such that an undercut is formed
Data Source
AI summary
A punch rivet for joining two workpieces, has a head and a shank. The shank is hollow with a shank internal diameter (D3), a shank external diameter (D1) and a shank end face. On the shank end face is a ring cutting edge with diameter (D4) that is smaller than the external diameter (D1) but greater than the internal diameter (D3). The ring cutting edge is radially spaced both from the shank external diameter (D1) and from the shank internal diameter (D3) by at least 20% of the radial shank wall thickness (M5). And the ratio D3/D1 of shank internal diameter D3 to shank external diameter D1 is smaller than 0.6. And the external diameter (D1) merges into an external circumference of the head by a second profile, which defines an underhead radius (R1), and the ratio of R1 to D1 (R1/D1) is smaller than 0.13.