Thread-Forming Screw Rib Structure for Thin Sheet Metal Holding Force
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Solution Overview
Problem
Thread-forming screws face challenges in achieving sufficient holding force and resistance to overdriving in thin sheet metals, where the material is too thin to ensure a strong connection.
Innovation Solution
A screw design with a continuously threaded shank and a front forming portion featuring a rib that intersects the screw thread, forming a partial counter thread, which displaces sheet metal material to create a screw-in collar, increasing the holding force by providing more engagement space for the screw thread.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a smooth thread-free portion is used to widen the bore, then the bore formation is facilitated, but the holding force and resistance to overdriving are insufficient in thin sheet metal
Solution Approach 1:
The screw shank is segmented into a thread-free forming portion at the front end and a threaded portion extending rearward. The forming portion creates the bore through friction heat and material displacement, while the threaded portion provides thread formation and engagement. This segmentation allows each portion to perform its specific function optimally, resolving the contradiction between ease of bore formation and sufficient holding force.
Solution Approach 2:
The invention extends the threaded portion rearward along the screw shank, utilizing the longitudinal dimension to increase the length of thread engagement in the sheet metal. This dimensional extension provides sufficient holding force and resistance to overdriving while maintaining the smooth forming portion at the front for efficient bore creation.
2Strength
If the threaded portion is extended to increase holding force, then the connection strength improves, but the bore formation capability is reduced
Solution Approach 1:
The screw shank is divided into distinct functional zones: a smooth thread-free forming portion for bore creation through friction heat and material displacement, and a threaded portion for thread formation and engagement. This segmentation enables the forming portion to widen the bore effectively while the threaded portion provides sufficient holding force through extended thread engagement.
3Length of stationary object
If a long thread-free portion is provided, then the bore widening is achieved, but the thread engagement length is reduced
Solution Approach 1:
The screw shank is segmented into a thread-free forming portion and a threaded portion. The forming portion has sufficient length to create and widen the bore through friction heat and material displacement, while the threaded portion extends rearward to provide adequate thread engagement length for holding force and resistance to overdriving.
Solution Approach 2:
The threaded portion is extended along the longitudinal dimension of the screw shank, maximizing the available length for thread engagement within the constraints of the overall screw length. This dimensional optimization ensures sufficient holding force while maintaining an appropriate thread-free forming portion.
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 screw-in collar enhances the holding force and resistance to overwinding by allowing more thread engagement, particularly in thin sheet metals, ensuring a secure connection with a longer passage protrusion and improved torque resistance.
Implementation Method 1
The bore is produced by the friction heat that is created in the rotation of the screw and softens the sheet metal.
Data Source
AI summary
A thread-forming screw which is provided in particular for thin, perforated sheet metal contains a threaded shank which below the screw head is initially configured so as to be cylindrical and then continues to a conical forming portion. The screw shank within the forming portion has a rib forming an incomplete counter thread.