Punch Rivet Cutting Edge Radius Prevents Spreading
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Solution Overview
Problem
Existing punch rivets, such as the C rivet and P rivet, are inadequate for joining high-strength materials as they tend to spread excessively during the punch riveting process, resulting in low material presence and strength in the undercut region of the lower workpiece.
Innovation Solution
A punch rivet with a larger cutting edge radius relative to the shank external diameter, an annular cutting edge diameter smaller than the shank external diameter, and a shank outer chamfer angle less than 42°, which prevents excessive spreading and allows for a sufficient undercut, along with a modified rivet hardness and annular surface size adapted to the piercing force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the punch rivet uses a sharp annular cutting edge with small cutting edge radius (as in C rivet), then the cutting edge can effectively pierce the workpiece, but the rivet spreads excessively during punch riveting, resulting in low material presence in the undercut region
Solution Approach 1:
The patent changes the geometric parameters of the cutting edge by introducing a cutting edge radius (R1) that is at least 0.2 mm, which is significantly larger than conventional sharp edges. This parameter change prevents excessive spreading of the rivet during punch riveting while maintaining sufficient cutting capability, thereby ensuring adequate material presence in the undercut region for high-strength connections
2Strength
If the punch rivet shank external diameter is increased to prevent spreading, then the undercut region strength improves, but the piercing force required increases significantly
Solution Approach 1:
The patent optimizes the ratio between shank external diameter (D1) and cutting edge radius (R1), specifying that R1/D1 should be at least 0.05. This parameter optimization allows the shank to have sufficient diameter to prevent excessive spreading while maintaining a reasonable piercing force requirement. The balanced geometric relationship ensures both undercut strength and piercing feasibility
3Strength
If the punch rivet uses high rivet hardness to join high-strength workpieces (greater than 1,000 MPa), then the piercing capability improves, but the deformability of the shank region decreases, affecting undercut formation
Solution Approach 1:
The patent applies different quality requirements to different regions of the punch rivet. The shank region is designed with specific geometric features (cutting edge radius R1, transition radius R2) that facilitate controlled deformation during punch riveting. This local quality differentiation allows the rivet to achieve both the hardness needed for piercing high-strength workpieces and the deformability required for proper undercut formation
4Measurement precision
If the annular cutting edge diameter is made equal to the shank external diameter, then the cutting edge is maximally effective, but the rivet spreads excessively and material is depleted in the undercut region
Solution Approach 1:
The patent creates an asymmetric geometric relationship where the annular cutting edge diameter (D4) is deliberately made smaller than the shank external diameter (D1). This asymmetric design ensures that the cutting edge is effective for piercing while leaving sufficient material in the shank to prevent excessive spreading and maintain adequate material presence in the undercut region during the punch riveting process
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 joins high-strength workpieces by preventing excessive spreading and ensuring a sufficient undercut, achieving higher strength connections in materials like steel and aluminum, even with high-strength materials exceeding 1,000 MPa.
Implementation Method 1
the upper workpiece being punched through with a specific piercing force
Implementation Method 2
the hollow shank is subsequently radially spread and is driven radially into the lower workpiece, thus forming an undercut
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
The invention relates to a punch rivet (30) for connecting two workpieces (12, 14), with a head (32) and a shank (34), the shank (34) being embodied as a hollow shank having a shank internal diameter (D3), a shank external diameter (D1) and a shank end face, there being embodied at the shank end face an annular cutting edge (50), the diameter (D4) of which is smaller than the shank external diameter (D1), and the shank internal diameter (D3) merging with the annular cutting edge (50) via a cutting edge radius (R2). In this case, the ratio of the cutting edge radius (R2) to the shank external diameter (D1) is greater than 0.3.