Self-Drilling Screw With Constricted Shank For Coated Panel Fastening
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Solution Overview
Problem
Self-drilling screws face the risk of lifting the upper layer, such as coatings, when screwing into coated panels, leading to unsightly results due to the thread formation before reaching the desired depth.
Innovation Solution
A drilling screw design where the thread begins within a constriction behind the drill bit, with an initial radial distance less than or equal to the hole diameter, ensuring contact with the hole wall at a distance from the surface, and gradually widening, minimizing the risk of surface lifting, and incorporating open spaces for chip removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the thread formation starts at the surface level, then the screwing speed is fast, but the upper layer (coating) is lifted off causing unsightly results
Solution Approach 1:
The drill bit performs preliminary action by creating a hole before the thread formation begins. The hole diameter is specifically designed to be smaller than the final thread outer diameter, allowing the thread to form gradually within the pre-created space, preventing surface lifting while maintaining efficient screwing speed
Solution Approach 2:
The screw structure has different local qualities: the drill bit portion creates a small-diameter hole, while the thread portion gradually expands to the final outer diameter. This local differentiation allows the thread to form progressively within the confined hole space, avoiding coating damage while achieving secure fastening
2Object-affected harmful factors
If the hole diameter is made smaller than the thread outer diameter, then the thread can form progressively without lifting the surface, but the initial contact area is reduced
Solution Approach 1:
The thread outer diameter is designed to increase progressively along the screw length, starting from a smaller diameter at the tip and expanding to the final diameter. This dynamic dimensioning allows initial thread formation in the smaller pre-drilled hole without surface lifting, while providing sufficient contact area in the expanded regions for secure fastening
Data Source
Figure 1~4
AI summary
A drilling screw contains on its front end facing away from the screw head a drill bit having two drilling cutters. At an axial distance from the drilling cutters the screw shank has a constriction, within which the diameter of the screw shank is smaller than the diameter of the hole produced by the drill bit. The constriction is configured such that it has a shoulder running almost transversely to the longitudinal axis and facing the screw head and from which the diameter gradually approaches again the core diameter of the shank. Within this constriction begins the thread, wherein the thread edge initially has a distance from the longitudinal axis of the screw which corresponds roughly to the radius of the hole. The thread edge then runs along a spiral up to the final outer diameter of the thread on the shank.