Self-Tapping Screw Thread Structure to Reduce Workpiece Cracking
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Solution Overview
Problem
Conventional self-tapping screws experience cracking and reduced structural strength in workpieces due to excessive radial distance between cutting edges and the shank body, leading to insufficient pulling resistance and potential detachment of the self-tapping thread.
Innovation Solution
Incorporation of a supporting unit with spaced-apart teeth and concave surfaces on the screw shank, reducing the radial distance between cutting edges and the shank body, and utilizing projecting portions to engage with connecting grooves for enhanced resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the radial distance between cutting edges and the outer peripheral surface of the shank body is made large, then the cutting ability is improved, but the workpiece is subjected to severe change in shearing force that renders it to crack
Solution Approach 1:
The screw shank is segmented into multiple functional zones: a drilling end section with a first radial distance for initial penetration, and a self-tapping thread section with a second radial distance for thread formation. This segmentation allows different radial distances to serve different functions, preventing workpiece cracking while maintaining cutting ability.
Solution Approach 2:
Different sections of the screw shank are given different local qualities in terms of radial distance. The drilling end section has a larger first radial distance optimized for breaking through the workpiece surface, while the self-tapping thread section has a smaller second radial distance to reduce shearing force changes and prevent cracking during thread formation.
2Object-affected harmful factors
If the radial distance between cutting edges and the outer peripheral surface of the shank body is made smaller to prevent cracking, then the workpiece cracking is reduced, but the depth of the connecting groove is reduced, so that the connecting strength is decreased
Solution Approach 1:
The screw shank is divided into distinct sections with different radial distances. The drilling end section uses a larger first radial distance to create sufficient connecting groove depth for strong connection, while the self-tapping thread section uses a smaller second radial distance to prevent workpiece cracking, thus resolving the contradiction between connection strength and crack prevention.
Solution Approach 2:
The screw shank exhibits local quality variation along its length, with the drilling end section having optimized dimensions for deep groove formation and the self-tapping thread section having optimized dimensions for crack-free operation. This local differentiation allows each section to perform its function optimally without compromising the other.
3Object-affected harmful factors
If the radial distance is reduced to prevent cracking, then cracking is prevented, but the connecting strength between the self-tapping thread and the connecting groove is weak, resulting in insufficient pulling resistance
Solution Approach 1:
The screw structure is segmented into a drilling end section that creates deep connecting grooves for strong anchoring and a self-tapping thread section with reduced radial distance for safe operation. This segmentation ensures that the connecting groove depth is sufficient for reliable connection while the thread formation process does not cause cracking, thereby maintaining both workpiece integrity and pulling resistance.
Solution Approach 2:
Different sections of the screw shank have different local qualities: the drilling end section has larger dimensions optimized for creating deep connecting grooves that provide strong anchoring, while the self-tapping thread section has smaller dimensions optimized for preventing cracking. This local differentiation ensures both workpiece integrity and sufficient pulling resistance.
Data Source
AI summary
A self-tapping screw includes a screw head, a screw shank having a shank body extending from the screw head along an axis, a self-tapping thread extending helically around an outer peripheral surface of the shank body and having a plurality of cutting edges continuously connected to one another and extending outwardly, radially and taperingly from the outer peripheral surface of the shank body, and a supporting unit including a plurality of supporting teeth each disposed between two adjacent ones of the cutting edges, and a plurality of concave surfaces respectively adjacent to the supporting teeth and extending inwardly from the outer peripheral surface of the shank body.