Plastic Thread Element Geometry for Balanced Screwing Torque
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Solution Overview
Problem
Existing plastic thread elements with self-forming outer threads face issues with uneven torsional loads during screwing, leading to potential failure and a higher screwing-in torque compared to loosening torque, along with limited tolerance between the thread element and component opening.
Innovation Solution
A plastic thread element with an outer thread designed to form a counter-thread by subdividing windings into cutting and inhibition webs, where the cutting web projects radially beyond the inhibition web, distributing torsional loads and ensuring a constant core thickness for symmetric formation, thereby reducing screwing-in torque and enhancing tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cutting edges are provided on individual turns of the threading to form a counter-thread, then the thread element can self-form a thread in the support part, but the screwing-in torque becomes higher than the loosening torque, facilitating loosening and reducing reliability
Solution Approach 1:
The threading is divided into multiple zones with different functions: a first thread zone with cutting edges for forming the counter-thread, and a second thread zone without cutting edges for providing symmetric engagement. This segmentation allows the screwing-in and loosening processes to be controlled differently, ensuring higher screwing-in torque for reliable installation while maintaining controlled loosening characteristics.
Solution Approach 2:
Different portions of the thread element are given different properties: the first thread zone has asymmetric cutting edges for material removal and thread formation, while the second thread zone has symmetric threading for balanced engagement. This local differentiation resolves the contradiction by providing both thread-forming capability and reliable holding strength in appropriate locations.
2Reliability
If cam-shaped radial cutting projections are distributed circumferentially to form counter-thread, then thread formation is achieved, but uneven torsional loads are generated over the screw shaft length, causing thread element failure
Solution Approach 1:
The threading is segmented into a first thread zone with cutting projections for thread formation and a second thread zone without cutting projections for balanced load distribution. This segmentation ensures that the uneven torsional loads are concentrated only in the thread-forming zone, while the second zone provides symmetric engagement that prevents overall thread element failure.
Solution Approach 2:
The cutting projections in the first thread zone perform the thread-forming action preliminarily, creating the counter-thread in the support part before the second thread zone engages. This preliminary action allows the subsequent symmetric threading to engage evenly, distributing torsional loads more uniformly and preventing failure.
3Reliability
If notches are cut from circumferential turns to form cutting edges, then counter-thread formation is achieved, but the screwing-in torque is higher than loosening torque due to cutting edge geometry, facilitating loosening
Solution Approach 1:
The thread element is divided into a first thread zone with notches providing cutting edges for counter-thread formation, and a second thread zone with continuous symmetric threading. This segmentation ensures that the torque imbalance is localized to the thread-forming zone, while the second zone provides balanced engagement that maintains reliable retention.
Solution Approach 2:
The asymmetric notch geometry is applied locally only in the first thread zone where thread formation is required, while the second thread zone maintains symmetric geometry. This local application of asymmetric cutting edges achieves thread formation without compromising the overall retention reliability provided by the symmetric second zone.
4Ease of operation
If the thread element is designed with self-forming outer thread, then ease of installation is improved, but the tolerance between thread element and component opening is limited
Solution Approach 1:
The threading is segmented into a first zone for material removal (thread forming) and a second zone for precise engagement. This segmentation allows the self-forming capability to create the counter-thread while the second zone ensures precise tolerance control during final engagement, combining ease of installation with manufacturing precision.
Data Source
AI summary
A thread element mode of plastic, a connection assembly consisting of a support part made of plastic into which the thread element made of plastic has been screwed by creating a counter-thread, a method for manufacturing the connection as well as a method for manufacturing the thread element. The thread element is characterized by an axial piece on which the circumferential windings of a thread turn are interrupted by at least two chip flutes. The resulting winding areas form a cutting web and an inhibition web, whereby the cutting web extends radially beyond the inhibition web.