Pierce Nut Groove Geometry for High-Strength Sheet Metal
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Solution Overview
Problem
Existing pierce nuts fail to provide sufficient torque resistance and pull-through resistance when used with high-strength sheet metal, leading to increased punching force requirements, tool damage, and alignment errors, as they require substantial metal deformation and are susceptible to fatigue failure.
Innovation Solution
A pierce nut design featuring an abutment surface with an undercut pilot and a countersunk groove without active undercuts, utilizing an inner and outer groove with specific angles and a ridge to facilitate form-fit interlock, reducing sheet deformation and optimizing the punching process for high-strength sheet metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If existing pierce nuts are used with high-strength sheet metal, then torque resistance and pull-through resistance are required, but punching force increases and tool damage risk increases
Solution Approach 1:
The patent changes the geometric parameters of the pierce nut, specifically the groove angle (120-180 degrees) and the removal of active undercuts, to reduce sheet metal deformation during punching. This allows achieving required torque and pull-through resistance with lower punching forces, preventing tool damage while maintaining joint strength.
Solution Approach 2:
Instead of using active undercuts that push metal outward (conventional approach), the patent inverts the approach by creating a groove without active undercuts that allows metal to flow inward and deform into the groove. This reverse approach reduces the punching force required while maintaining the form-fit interlock.
2Strength
If existing pierce nuts deform metal sheet substantially, then form-fit interlock is achieved, but fatigue failure risk increases in thin sections
Solution Approach 1:
The patent changes the groove geometry parameters, specifically setting the groove angle to 120-180 degrees and eliminating active undercuts. This creates a more favorable stress distribution that reduces fatigue loading on thin sections while maintaining adequate form-fit interlock through controlled metal flow into the groove.
Solution Approach 2:
The patent converts the potential harm of metal deformation into a benefit by designing the groove to control deformation in a way that creates a fatigue-resistant joint. The groove geometry guides metal flow to create a interlock that distributes stresses favorably, turning the deformation process into a strength-enhancing feature rather than a fatigue-inducing defect.
3Ease of manufacture
If greater punching force is applied to high-strength sheet metal, then pierce nut attachment is achieved, but alignment errors between pierce nut and punching die increase
Solution Approach 1:
The patent changes the groove angle parameter to 120-180 degrees, which reduces the punching force required for attachment. This lower force requirement improves alignment precision by reducing the likelihood of misalignment between the pierce nut and punching die, while still achieving secure attachment.
4Ease of manufacture
If active undercuts are used in groove design, then metal sheet deformation is facilitated, but punching force and tool wear increase
Solution Approach 1:
The patent inverts the conventional approach by removing active undercuts from the groove design. Instead of using undercuts to force metal deformation, the groove geometry itself (with its specific angle) facilitates metal flow and deformation into the groove, reducing punching force and tool wear while achieving the same form-fit interlock.
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 design enhances joint strength, reduces punching force, minimizes tool damage, and maintains high torque and pull-through resistance, even with high-strength sheet metal, while allowing for compact geometry and improved alignment.
Implementation Method 1
the sheet is plastically deformed and pressed into the groove and beneath the two undercut portions, thereby to achieve a form-fit interlock between the nut and metal sheet
Data Source
Figure 1~3
Figure 4a~5
Figure 6~7
AI summary
A pierce nut (1) for attachment to a plastically deformable metal sheet (4) has an abutment surface (14) adapted to abut against the metal sheet (4), an undercut pilot (11) protruding relatively to the abutment surface (14), and a countersunk groove (16a, 16b) which is formed in the abutment surface (14) and at least partly surrounds the pilot (11). The groove (16a, 16b) is without active undercuts facing the pilot (11). The groove comprises an inner groove (16a) and an outer groove (16b) and a ridge (17) located therebetween.