Self-tapping Blind Rivet Mandrel Torque Transfer
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Solution Overview
Problem
Existing self-drilling blind rivets face issues with premature breakage of the mandrel at the predetermined breaking point due to the need to transfer torque for hole formation, especially when the rivet is slightly tilted during drilling.
Innovation Solution
A positive or non-positive fit connection between the mandrel and the rivet shank allows torque to bypass the breaking point, with features like saw-tooth-shaped tips, external gearing, gluing, knurling, and frictional welding to transfer rotational forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque is transferred via the predetermined breaking point at the mandrel to enable hole formation, then the mandrel can rotate to drill the workpiece, but the mandrel breaks prematurely especially when the rivet is slightly tilted during drilling
Solution Approach 1:
The rivet shank acts as an intermediary element that transfers torque from the tool to the mandrel. The positive fit connection between the shank and mandrel creates a torque transfer path that bypasses the predetermined breaking point, allowing the mandrel to rotate without experiencing excessive stress at the breaking point that would cause premature failure
Solution Approach 2:
The torque transfer path is segmented into two parts: (1) tool to rivet shank, and (2) rivet shank to mandrel. This segmentation allows the torque to be applied to the mandrel through the stronger rivet shank rather than directly through the predetermined breaking point, separating the torque application function from the breaking point function
2Power
If a positive fit connection is provided between the mandrel and rivet shank to transfer torque, then larger torques can be applied for hole formation, but the connection complexity increases
Solution Approach 1:
Instead of making the entire mandrel-shank assembly complex, the invention applies local quality by providing the positive fit connection only in the specific region where torque transfer is needed. The saw-tooth-shaped tips and grooves are localized features that enable effective torque transfer without complicating the overall simple structure of the blind rivet system
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 the transfer of larger forces and torques to the tip without mandrel breakage, ensuring reliable hole formation in self-drilling blind rivets.
Implementation Method 1
the tip is performed as a spherical friction surface. It then is serving for the non-cutting drilling by thermic softening of the workpieces by means of the rotation of the friction surface
Implementation Method 2
non-cutting drilling by thermic softening of the workpieces by means of the rotation of the friction surface
Implementation Method 3
a positive fit connection is provided between the mandrel of the rivet and the rivet shank by the feature that the end of the rivet shank on the side of the workpiece is ending as saw-tooth-shaped tips and by the backside of the enlargement of the mandrel of the rivet on the end facing the rivet shank being provided with correspondingly shaped saw-tooth-shaped grooves
Implementation Method 4
the rivet shank at least on the workpiece side with respect to the predetermined breaking point is provided with a knurling and the rivet shank is crimped in the area of this knurling such that in this way a positive fit is provided by the means of which the rotational movement for drilling the tapping tip of the mandrel can be transferred
Implementation Method 5
the back-side of the tapping tip by frictional welding or electric resistance welding can be connected with the rivet shank
Data Source
AI summary
Self-tapping blind rivet (10) having a mandrel (12) carrying a hole-forming tip (16) at its end facing the workpiece, wherein the tip (16) is performed as an apparatus for drilling the rivet's own placing hole, wherein a positive or non-positive connection is provided between the mandrel (12) of the rivet and the rivet shank (18) and, wherein a force application point (26) for a tool is provided at or in the rivet head (20), and a method for placing such a blind rivet.