Thread-Forming Screw With Segmented Pre-Thread
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Solution Overview
Problem
Existing thread-forming screws require high torque for insertion into fastening bases, which can lead to material hardening and increased manufacturing costs, and pose challenges in handling and straightening wooden parts due to brittle properties.
Innovation Solution
A thread-forming screw with a pre-thread section featuring a cross-sectional geometry that deviates from cylindrical, incorporating chip pockets and segmented pre-thread segments, reducing the torque required for thread formation and allowing for non-hardened material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a pre-thread section is added to form a pre-thread in the borehole wall, then the pull-out force resistance is improved and torque requirement is reduced, but the screw core geometry becomes complex and manufacturing difficulty increases
Solution Approach 1:
The pre-thread is divided into multiple pre-thread segments distributed over the circumference instead of a continuous pre-thread. This segmentation simplifies the screw core geometry while still achieving the function of forming a pre-thread in the borehole wall, reducing manufacturing complexity while maintaining pull-out force resistance
Solution Approach 2:
The screw core has different geometries at different circumferential positions: some areas have pre-thread segments while others have chip pockets. This local differentiation allows the screw to perform multiple functions (thread formation and chip removal) with a relatively simple overall structure, balancing manufacturing ease with functional performance
2Strength
If hardened steel material is used to withstand high insertion torque, then the screw strength is improved, but the material cost increases and handling becomes more difficult
Solution Approach 1:
The pre-thread segments perform the preliminary action of forming a pre-thread in the borehole wall before the main thread engages. This preliminary thread formation reduces the torque required for insertion, allowing the use of non-hardened or lightly hardened materials that are easier to handle and less expensive while still withstanding the reduced insertion torque
Solution Approach 2:
The invention changes the operational parameters by reducing the insertion torque requirement through pre-thread formation. This parameter change allows transitioning from hardened steel materials (designed for high torque) to non-hardened or lightly hardened materials (easier to handle and manufacture), achieving the same functional outcome with different material properties
3Object-generated harmful factors
If chip pockets are introduced into the screw core, then chip absorption capability is improved, but the screw core cross-sectional geometry deviates from cylindrical and manufacturing complexity increases
Solution Approach 1:
The screw core cross-section is segmented into multiple regions: pre-thread segments and chip pockets distributed over the circumference. This segmentation allows chip pockets to be integrated into the core structure without requiring a completely non-cylindrical geometry, simplifying manufacturing while providing effective chip absorption capability
Solution Approach 2:
The invention merges the functions of thread formation and chip removal into a single integrated screw core structure. The pre-thread segments and chip pockets are combined in the screw core design, allowing both functions to be achieved with a unified geometry that is easier to manufacture than separate components
Data Source
Figure 1~2
Figure 3~4
AI summary
The screw (1) has threads (5, 9) formed at screw cores (4, 8) for fastening the screw to an attachment surface. A pre-thread section (7) of the thread (5) is attached to a main thread section. The core (8) has a cross section geometry in the pre-thread section with respect to its longitudinal extension. The thread (9) is formed by individual pre-thread segments (G1, G3), where the segments are separated from each other by a splinter recess provided between a lateral surface of the pre-thread section and the core (8) of the pre-thread section. The screw is made from steel of the type 20MnB4.