Plastic Thread-Forming Screw for Low Torque and High Pullout
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Solution Overview
Problem
Existing screws designed for plastic materials face high mechanical load and low pullout values when attempting to achieve larger pitch and smaller flank angles, leading to potential damage to the component.
Innovation Solution
A screw design with a specific 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 a short transition area and minimal material stress, enabling low insertion torque and high pullout values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a larger pitch and smaller flank angle are realized for the screw, then the thread profile in the forming area can be proportionally larger, but a high load will act on the component
Solution Approach 1:
The thread is divided into two distinct functional areas: a forming area with a larger thread profile contour for material displacement and thread formation, and a bearing area with a smaller thread profile contour for load bearing. This segmentation allows each area to be optimized for its specific function, resolving the contradiction between achieving a proportionally larger thread profile and minimizing mechanical load on the component.
Solution Approach 2:
Different regions of the thread are given different properties: the forming area has a larger pitch and smaller flank angle to effectively form threads in plastic material, while the bearing area has a smaller pitch and larger flank angle to reduce mechanical load and provide load-bearing capacity. This local differentiation of thread properties resolves the contradiction between thread formation effectiveness and component load protection.
2Shape
If the thread profile is proportionally larger, then insertion torque may increase, but pullout values need to be maintained high
Solution Approach 1:
The thread is segmented into a forming area with larger profile for effective thread formation in plastic, and a bearing area with smaller profile that engages after material springback. This segmentation allows the forming area to achieve good thread formation without requiring excessive insertion torque, while the bearing area provides sufficient engagement for high pullout values.
Solution Approach 2:
The forming area performs the preliminary action of displacing and forming the plastic material around the thread. Once this forming action is complete and the material has springback, the bearing area then engages to provide the load-bearing connection. This preliminary formation action reduces the insertion torque required compared to attempting to form and bear load simultaneously with a uniformly large thread profile.
3Productivity
If the transition area from forming area to bearing area is shortened, then insertion efficiency improves, but the bearing area length must be sufficient for basic holding function
Solution Approach 1:
The thread profile parameters (pitch, flank angle) are changed at the transition from forming area to bearing area. This parameter change creates a distinct boundary between the two functional areas, allowing for a short transition zone that maintains insertion efficiency while ensuring the bearing area has sufficient length to provide the required holding function.
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.