Plastic Thread-Forming Screw Profile for Low Insertion Torque
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Solution Overview
Problem
Existing screws designed for plastic materials face high mechanical loads and high insertion torque due to larger pitch and smaller flank angles, leading to potential damage to the component.
Innovation Solution
A screw design with a changing thread profile contour that includes a forming area and a bearing area, where the forming profile contour is larger than the bearing profile contour, allowing for low insertion torque and reduced mechanical load while ensuring high pullout values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a larger pitch and smaller flank angle are realized for the screw, then the insertion torque is reduced, but the mechanical load on the plastic component increases
Solution Approach 1:
The thread is divided into two distinct functional zones: a forming area with larger thread profile (extending 3× mean thread radius from the end) that creates the female thread in the plastic, and a bearing area with smaller thread profile (extending 2/3 to 5/3 of mean thread radius) that provides mechanical support. This segmentation allows the forming area to accommodate material springback with lower stresses while the bearing area carries the mechanical load.
Solution Approach 2:
Different regions of the thread are given different geometric properties optimized for their specific function. The forming area has a larger thread profile contour with flank angles suited for material deformation, while the bearing area has a smaller thread profile contour optimized for load bearing. This local differentiation resolves the contradiction by allowing low insertion torque in the forming region while maintaining high strength in the bearing region.
2Ease of operation
If the forming area thread profile is enlarged to accommodate material springback, then insertion torque is reduced, but the thread profile becomes proportionally larger requiring more material removal
Solution Approach 1:
The thread is divided into two distinct functional zones: a forming area with larger thread profile (extending 3× mean thread radius from the end) that creates the female thread in the plastic, and a bearing area with smaller thread profile (extending 2/3 to 5/3 of mean thread radius) that provides mechanical support. This segmentation allows the forming area to accommodate material springback with lower stresses while the bearing area carries the mechanical load.
Solution Approach 2:
The thread profile contour is varied along the axial length of the screw. The forming area uses a larger profile contour parameter set that accommodates material springback, while the bearing area transitions to a smaller profile contour parameter set that minimizes material removal. This parameter change along the thread length resolves the contradiction between accommodating springback and minimizing material loss.
3Strength
If the bearing area is made sufficiently long to achieve basic holding function, then pullout strength is improved, but the transition area from forming to bearing area increases
Solution Approach 1:
The forming area, extending 3 times the mean thread radius from the screw end, performs the preliminary action of creating the female thread in the plastic component before the bearing area engages. This extended forming zone ensures complete thread formation and springback accommodation before the bearing area begins its load-bearing function, minimizing the transition region while ensuring proper thread establishment.
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 achieves low insertion torque and minimal material damage by compensating for springback in the female thread, enabling high pullout strength without excessive stress on the plastic component.
Implementation Method 1
compensating for material springback
Implementation Method 2
reduced friction during insertion
Data Source
AI summary
The invention relates to a screw (IO) in order to cut a mating thread in a plastic article, comprising a lower threaded part (F) and an upper threaded part (T), the lower threaded part having a larger diameter and its tip covering a larger surface than the upper threaded part.