Self-Drilling Screw Cutting Edge Geometry for Bore Diameter Control
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Solution Overview
Problem
Existing self-drilling screws experience variable bore diameters due to applied press-on force, leading to inconsistent holding values and reduced drilling efficiency at lower forces.
Innovation Solution
A self-drilling screw design featuring a first cutting edge in the radially inner region and a second cutting edge in the radially outer region, both forming conical surfaces with specific acute angles, allowing balanced cutting force distribution and precise borehole diameter control, with optional additional features like a third cross-cutting edge for stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional drilling tip with first and second cutting edges is used, then the drilling tip can penetrate the material, but the bore diameter varies with applied press-on force leading to inconsistent holding values
Solution Approach 1:
The patent modifies the geometric parameters of the cutting edges by defining specific acute angles (α1 and α2) relative to the longitudinal axis, and positioning them at specific radial distances (r1 and r2) from the longitudinal axis. These parameter changes ensure that the cutting edges engage the material symmetrically and consistently, producing boreholes with consistent diameter independent of press-on force variations.
Solution Approach 2:
The patent employs asymmetric positioning of the first and second cutting edges relative to the longitudinal axis, with the first cutting edge at radial distance r1 and the second at radial distance r2. This asymmetric arrangement, combined with specific acute angles, creates a balanced cutting action that stabilizes the bore diameter despite variations in applied pressure.
2Productivity
If a conventional drilling tip design is used, then the structure is simple, but the drilling feed rate decreases at smaller press-on forces
Solution Approach 1:
By optimizing the acute angles (α1, α2) and radial positions (r1, r2) of the cutting edges, the patent enhances the cutting efficiency. The specific geometric parameters allow the cutting edges to engage the material more effectively, reducing the press-on force needed to achieve a given drilling feed rate, thereby improving productivity.
3Power
If the first cutting edge extends to a smaller radius, then thinner chips are produced requiring more cutting power, but if it extends to a larger radius, then thicker chips are produced increasing heat and wear
Solution Approach 1:
The patent defines specific radial distances (r1 for the first cutting edge, r2 for the second cutting edge) from the longitudinal axis, and specific acute angles (α1, α2). These parameter changes optimize the chip thickness to a range that balances cutting power requirements with heat generation and wear, ensuring efficient cutting without excessive thermal load.
Data Source
AI summary
A self-drilling screw (10) has a first cutting edge (21) provided exclusively in a radially inner region of the drilling tip (12), extending at a first acute angle (α1) to the longitudinal axis (L), and a second cutting edge (22) provided in radially outer region of the drilling tip (12) and extending at a second acute angle (α2) to the longitudinal axis (L), with a first enveloping conical circumferential surface (A1) which is defined by the first cutting edge (21) corresponding, with a maximum deviation of +/−10%, to a second enveloping conical circumferential surface (A2) defined by the second cutting edge (22), and with the first acute angle (α1) corresponding, with a maximum deviation of +/−5°, to the second acute angle (α2).