Self-Piercing Fastener Undercut Geometry for High Torque Retention
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Solution Overview
Problem
Self-stamping functional elements used in sheet metal parts face challenges in withstanding high extrusion or tensile forces and torques, requiring improved attachment methods that ensure reliable fastening without pre-punching the workpiece.
Innovation Solution
The functional element features a head part with a contact surface and a limiting section forming an annular space with undercuts, where the inner and outer walls are angled relative to the longitudinal axis, creating a positive connection with the workpiece, and includes ribs and bases for enhanced anti-twist protection and material distribution during fastening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional press-in elements are used without undercuts, then the element can be easily manufactured and installed, but the element cannot withstand high extrusion or tensile forces and torques
Solution Approach 1:
The head part is segmented into functional zones: a contact surface for material distribution, a limiting section with undercut for mechanical interlocking, and a punching section for hole formation. This segmentation allows each zone to perform its specific function optimally, creating strong connections while maintaining manufacturability through standardized geometric features
Solution Approach 2:
The limiting section extends radially outward from the contact surface, creating a three-dimensional undercut structure. This dimensional transition from a flat contact surface to a radially extended limiting section with undercut geometry enables the element to withstand high forces and torques by creating mechanical interlocking in the radial dimension
2Ease of manufacture
If self-piercing elements are used without pre-punched holes, then cost is reduced, but the workpiece must withstand high punching forces during attachment
Solution Approach 1:
The contact surface acts as an intermediary between the punching section and the workpiece material. It distributes the punching forces over a larger area during the self-piercing process, reducing peak stresses on the workpiece while enabling the element to punch its own hole without pre-punching operations
3Reliability
If the element is designed to withstand high forces, then connection reliability is improved, but the element becomes more complex and difficult to manufacture
Solution Approach 1:
The geometry parameters of the limiting section (radial extension distance, undercut angle, wall thickness) are optimized to achieve the required connection reliability. By carefully selecting these parameters, the element attains high force resistance while maintaining compatibility with standard manufacturing processes and tooling
Data Source
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AI summary
The present invention relates to a self-punching functional element (10) designed for punching into a workpiece (36), in particular a sheet metal part, comprising: - a head part (12) forming a flange and - a punching section (18) extending away from the head part and in particular arranged coaxially to a central longitudinal axis (L) of the functional element, with a circumferential punching edge (22), wherein the head part has a contact surface (20) radially surrounding the punching section at least partially on its outer side for bearing against the workpiece and a limiting section (26) radially limiting the contact surface at least partially on its outer side, which extends away from the contact surface in the same direction as the punching section.and wherein an inner wall (28) of the boundary section facing the punching section and an outer wall (24) of the punching section facing the boundary section are arranged at least sectionally obliquely to the longitudinal axis of the functional element, such that the inner wall and the outer wall each form an undercut in at least one plane containing the longitudinal axis.