Self-Piercing Rivet Die Geometry for Crack-Resistant Closing Heads
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Solution Overview
Problem
Existing punch rivet dies face challenges in producing reliable connections with brittle materials like 7000 series aluminum alloys, often resulting in cracking and reduced service life due to uneven material distribution and excessive compressive stresses, which are exacerbated by the need for additional thermal treatments or complex die designs.
Innovation Solution
A punch rivet die with a cylindrical base body featuring a radially arranged annular demolding section, an adjoining annular channel section, and a centrally located die base, where the demolding slope transitions into an arc-shaped depression with specific radii and angles to facilitate even material flow and reduce mechanical stresses, ensuring uniform expansion and a defined closing head formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a flat surface anvil die is used to ensure an aesthetically pleasing surface, then the surface quality is improved, but the material cannot escape into a cavity leading to excessive compression and stress in the components
Solution Approach 1:
The die cavity is segmented into distinct functional zones: an annular first cavity region for material escape, a second cavity region for rivet expansion, and a flat anvil surface for aesthetic quality. This segmentation allows material to escape laterally in the first region while the second region provides controlled expansion space, preventing excessive compression stresses in the components.
Solution Approach 2:
The invention introduces a lateral dimension for material escape through the annular first cavity region, rather than allowing only vertical compression. Material displaced by the rivet can escape horizontally into the annular cavity, reducing compressive stresses while maintaining the flat anvil surface for aesthetic quality.
2Shape
If an angular die cavity is used, then a closing head can be formed, but the material flow becomes uneven leading to uncoordinated material distribution
Solution Approach 1:
The die cavity uses asymmetric positioning of the annular first cavity region relative to the central second cavity region. The annular region is positioned radially outward from the central expansion zone, creating a controlled asymmetric material flow path that ensures uniform distribution while enabling closing head formation.
Solution Approach 2:
Different regions of the die cavity have different functional qualities: the annular first cavity region provides material escape pathways with specific geometric constraints, while the central second cavity region provides controlled expansion space. This local differentiation ensures uniform material distribution and proper closing head formation.
3Manufacturing precision
If a spherical segment depression is used to support even material flow, then material distribution is improved, but the punch rivet does not spread open sufficiently and may be compressed
Solution Approach 1:
The die cavity is divided into two functional segments: an annular first cavity region for material escape and a central second cavity region for rivet expansion. This segmentation ensures that material flows uniformly into the annular region while the central region provides sufficient space for the rivet to spread open and form the closing head, preventing rivet compression.
4Reliability
If additional thermal treatment is applied to reduce cracking in brittle materials, then connection reliability is improved, but the manufacturing complexity and time increase
Solution Approach 1:
The invention converts the harmful effect of material displacement during rivet setting into a beneficial outcome by providing a controlled annular first cavity region. This region allows material to escape laterally in a controlled manner, preventing negative crack growth in brittle materials without requiring additional thermal treatment processes, thereby maintaining connection reliability while simplifying manufacturing.
Solution Approach 2:
The die cavity geometry is designed in advance with the annular first cavity region to pre-establish controlled material flow paths. This preliminary geometric configuration prevents cracking in brittle materials during the rivet setting process itself, eliminating the need for subsequent thermal treatment and reducing manufacturing complexity.
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 enables the production of reliable punch rivet connections with reduced cracking and extended service life, eliminating the need for thermal treatments by promoting uniform material distribution and controlled expansion, thus enhancing the quality and durability of the joint.
Implementation Method 1
the material of the components displaced by the punch rivet cannot escape into a cavity in the die. As a result, the punch rivet is compressed and expanded more than with conventional punch riveting.
Implementation Method 2
the closing head formed does not evenly enclose the expanded rivet shank
Data Source
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AI summary
The present invention describes a self-piercing rivet die for a rivet gun, by which die a self-piercing rivet connection can be produced in a plurality of components by formation of a closing head. This self-piercing rivet die (1) is characterised by a main body (3) with a top face (8) and a recess (9) which is formed thereon and is arranged rotationally symmetrically relative to a central axis M of the self-piercing rivet die 1. In the cross-section of the self-piercing rivet die (1) the recess (9) has a draft angle (12) of the draft section (10) which merges radially via a step (16) into an arcuate depression (22) of the annular channel section (20), wherein radially inwards the arcuate depression (22) rises in a rectilinear or arcuate or curvilinear manner to the die base (30).