Thread-Forming Screw with Sharp Edges Reducing Axial Force
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Solution Overview
Problem
Existing thread-forming screws require large axial forces to initiate thread formation due to incomplete thread formation in the tapered portion, leading to potential slipping issues.
Innovation Solution
A screw design featuring a load-bearing thread portion and a continuously formed, sharp-edged thread-forming thread portion that tapers to the screw tip, allowing full thread formation up to the tip with a specific core hole diameter configuration in the female element for self-forming, reducing the need for excessive axial forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the thread is incompletely formed in the tapered portion with a continuously decreasing diameter and cone angle, then the screw tip can be designed with a simple geometry, but large axial forces are required to start the screw and prevent slipping
Solution Approach 1:
The screw tip is provided with a preliminary formed thread structure before engagement with the workpiece. This pre-formed thread structure allows the screw to initially engage and start threading without requiring excessive axial force, as the thread geometry is already optimized for engagement rather than being continuously tapered from the tip
Solution Approach 2:
The screw features different thread characteristics in different regions: the thread-forming thread portion has a specific cone angle and thread structure optimized for thread formation, while the load-bearing thread portion has a different geometry optimized for strength. This local differentiation allows the tip region to have reduced complexity while maintaining sufficient engagement force
2Ease of operation
If the thread is fully formed with sharp-edged crests up to the screw tip, then thread formation is easier and requires reduced axial forces, but the manufacturing process becomes more complex
Solution Approach 1:
The thread structure is divided into distinct portions: a thread-forming thread portion with a first cone angle and a load-bearing thread portion with a second cone angle. This segmentation allows each portion to be optimized for its specific function - the thread-forming portion for easy engagement and thread creation, and the load-bearing portion for structural strength - while simplifying the overall manufacturing process compared to forming a completely uniform thread to the tip
3Reliability
If the core hole diameter C is larger than the thread diameter A at the screw tip but smaller than the thread diameter B in the transition zone, then secure engagement and gas/liquid tightness are achieved, but the design complexity increases
Solution Approach 1:
The screw features varying thread parameters along its length, with the thread diameter transitioning from A at the tip to B in the transition zone. The core hole diameter C is specifically selected within this range (A < C < B) to optimize both engagement security and gas/liquid tightness. This parameter optimization ensures proper fit and sealing without requiring additional complex features
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
Enables easier initiation and completion of thread formation with reduced axial forces, ensuring secure engagement and gas/liquid tightness in the screw connection.
Implementation Method 1
thread-forming screw (1) which, after having been driven into the component to be screw-connected (5), creates a metric thread (2) in the latter
Data Source
AI summary
A screw for the creation of a metric thread in a female element, includes a load-bearing (metric) thread portion and a forming thread portion which is tapered to the tip of the screw. The flights of the tapered thread portion are sharp-edged and fully formed.