Polygonal Core Self-Tapping Screw Reduces Driving Torque
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Solution Overview
Problem
Existing self-boring and self-tapping screws face high driving torque due to friction in thread-free sections and are challenging to produce accurately and economically due to deformation during the rolling process.
Innovation Solution
A self-tapping screw design featuring a polygonal core section in the threaded section, which expands the threaded hole, reducing friction and driving torque, and is manufactured using a rolling process that clamps the screw over the thread, preventing bending and ensuring precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a shaft cutter is added to enlarge the threaded hole, then friction and driving torque are reduced, but the screw deforms during rolling and cannot be produced accurately
Solution Approach 1:
The invention applies a polygonal core cross-section specifically in the threaded section rather than uniformly throughout the shaft. This localized geometric modification creates expansion ribs that enlarge the threaded hole only where needed, reducing friction and driving torque without requiring a shaft cutter that would cause deformation during rolling.
Solution Approach 2:
Instead of adding a separate shaft cutter component to enlarge the hole (as in conventional design), the invention inverts the approach by integrating the hole-enlarging function into the core structure itself through the polygonal cross-section. The corners of the polygonal core act as built-in expansion ribs that perform the enlarging function during screwing, eliminating the need for additional cutting components.
2Ease of operation
If a shaft cutter is used to reduce friction, then driving torque decreases, but production cost increases due to additional manufacturing steps
Solution Approach 1:
The invention merges the functions of the core structure and the hole-enlarging mechanism into a single integrated element. The polygonal core cross-section serves both as the structural core and as the expansion mechanism (replacing the separate shaft cutter). This consolidation allows the screw to be produced in one rolling operation without additional manufacturing steps, reducing production complexity and cost.
Solution Approach 2:
The polygonal core cross-section performs multiple functions simultaneously: it provides structural support as the core, acts as an expansion mechanism to enlarge the threaded hole, and serves as a guide during the rolling process. This multi-functionality eliminates the need for separate components like shaft cutters, simplifying manufacturing while achieving reduced driving torque.
3Ease of operation
If the core section is made polygonal to expand the threaded hole, then friction is reduced, but the screw may deform during rolling
Solution Approach 1:
The polygonal core cross-section is pre-formed during the rolling process itself, before the screw is completed. The rolling dies gradually form the polygonal shape while the screw is being manufactured, ensuring the screw remains straight and stable throughout production. This preliminary formation prevents deformation issues that would occur if the polygonal shape were added later through cutting or other post-processing operations.
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 reduces driving torque and facilitates simple, economical, and precise production of self-tapping screws by minimizing friction and deformation during the rolling process.
Implementation Method 1
The polygonal core section and its corners cause the threaded hole to expand during driving of the screw
Implementation Method 2
the screw is clamped between the roller jaws over the thread, including directly on the polygonal section
Data Source
AI summary
The invention relates to a self-boring and thread-forming tapping screw having a screw shaft with a screw tip at one end and at the other end a force application member for the transmission of a turning moment. The screw shaft includes a threaded section with the screw tip and an adjacent thread-free section of the shaft including the force application member. The threaded section has a shaft core and a self-tapping thread. The threaded section includes a core section axially displaced from the tip and having a polygonal core cross section. Corners of the core cross section define an enveloping circle with an enveloping circle diameter larger than a shaft diameter of the thread-free section.