Self-Tapping Screw Thread Design for Pilot Hole Biting
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Solution Overview
Problem
Conventional self-tapping screws with flat surface-shaped peaks on their external threads have limited initial biting performance and are ineffective in smoothly guiding subsequent threads for internal thread formation, leading to inadequate thread formation and potential damage to the pilot hole.
Innovation Solution
The self-tapping screw features a cylindrical shank with first external threads and a truncated conical shank with second external threads, both having no-thread parts at regular intervals, which reduce initial torque and enhance biting performance without damaging the pilot hole, allowing for smooth plastic forming of internal threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the external thread peak is formed as a flat surface shape to improve initial biting performance, then the biting performance is improved, but the external thread is not raised enough to be referred to as a male thread and cannot guide subsequent external threads smoothly
Solution Approach 1:
The patent applies local quality by differentiating the peak shape of external threads based on their position along the shank. The first external threads (near the end) have a flat surface-shaped peak for improved biting performance, while the second external threads (toward the middle) have a proper male thread peak shape for reliable thread formation and guidance. This localized differentiation resolves the contradiction between initial biting performance and subsequent thread formation quality.
2Device complexity
If only external thread portions at the vertices of the equilateral triangle cross-section are used for plastic forming, then the structure is simplified, but a suitable internal thread cannot be formed by plastic forming
Solution Approach 1:
The patent segments the external threads into two distinct types: first external threads with flat surface peaks for biting, and second external threads with proper male thread peaks for plastic forming. This segmentation allows each type of thread to perform its specific function optimally, resolving the contradiction between structural simplicity and thread formation quality.
3Force
If the external thread with flat surface peak is used, then initial biting performance is improved, but the effect is limited and cannot plastically form a suitable internal thread
Solution Approach 1:
The patent applies preliminary action by using the first external threads with flat surface peaks to initially bite into the pilot hole and create the starting point for thread formation. The second external threads with proper male thread peaks then continue the process to fully form the internal thread. This preliminary action sequence resolves the contradiction between initial biting performance and overall thread formation efficiency.
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 improves initial biting performance, reduces initial torque, and prevents chip production by effectively forming internal threads without damaging the pilot hole, ensuring accurate and efficient thread formation.
Implementation Method 1
plastically forming an internal thread on the inner peripheral surface of a pilot hole
Implementation Method 2
a plurality of no-thread parts at regular intervals in a circumferential direction, whereby both the no-thread parts reduce an initial torque
Data Source
Figure 1~2
Figure 3
Figure 4(A)~4(C)
AI summary
A self-tapping screw according to the present invention includes a head (1) and a shank (2) extending from the head. The shank includes a cylindrical shank (2a) immediately below the head and a truncated conical shank (2b) following an end of the cylindrical shank, the cylindrical shank is provided with a plurality of first external threads (3a), the truncated conical shank is provided with a plurality of second external threads (3b) following the first external threads, and a peak of each of the second external threads is provided with a biting surface (4) having a concave-convex form.