Chipless Thread-Forming Screw With Dual Crowned Sections
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Solution Overview
Problem
Existing thread-forming screws are limited in their ability to penetrate stacks of metal sheets thicker than 2 mm without cutting, often requiring high contact pressures and resulting in material loss and corrosion issues.
Innovation Solution
A non-cutting thread-forming screw design featuring a first crowned section with a larger radius of curvature, a second crowned section with a smaller radius of curvature, and a conical transition section, allowing the screw to penetrate metal sheets up to 4 mm thick with reduced contact pressure and maintaining load capacity without significant length increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a conventional self-penetrating screw with a single crowned section is used, then it can penetrate thin sheet metal, but it cannot penetrate stacks of metal sheets thicker than 2 mm
Solution Approach 1:
The screw shank is divided into multiple crowned sections (first crowned section with radius R1, second crowned section with radius R2) with different radii of curvature, allowing progressive penetration through different depths of metal sheets. This segmentation enables the screw to handle thicker materials by distributing the forming action across multiple zones along the shank length.
Solution Approach 2:
The invention extends the solution from a single crowned section to multiple crowned sections arranged along the axial dimension of the screw shank. This dimensional extension allows the screw to progressively engage and form threads through thicker material stacks by utilizing the extended axial length to accommodate multiple forming zones.
2Ease of operation
If high contact pressure is applied during screw setting, then penetration into metal sheets is achieved, but material loss occurs and corrosion issues arise
Solution Approach 1:
The invention changes the geometric parameters of the screw shank by introducing multiple crowned sections with different radii of curvature (R1 and R2). This parameter change allows the screw to distribute contact pressure more effectively across the metal sheets, reducing peak pressures that cause material loss and corrosion while maintaining effective penetration capability.
3Length of stationary object
If a self-drilling screw is used to penetrate metal sheets thicker than 2 mm, then penetration is achieved, but chips are produced requiring expensive removal
Solution Approach 1:
Instead of using a cutting approach that removes material (self-drilling screw), the invention uses a thread-forming approach that displaces and redistributes material. The multiple crowned sections on the shank form threads by plastic deformation rather than cutting, completely avoiding chip production and the associated harmful effects of material removal.
4Strength
If the screw shank diameter is increased to maintain load capacity, then load capacity is improved, but the screw becomes significantly longer
Solution Approach 1:
The invention applies different radii of curvature (R1 for first crowned section, R2 for second crowned section) to different local zones of the screw shank. This local differentiation allows optimized material engagement at each depth zone, enabling effective penetration and thread formation in thick material stacks without requiring a proportional increase in overall screw length or shank diameter.
Data Source
Figure 1
AI summary
The present invention relates to a chipless thread-forming screw (10) with a shaft (11) that at least partially carries a thread (15), a tip (13) being arranged at one end of which and a head (14) being arranged at the opposite end. A pointed conical section (21) extends from the tip (13) towards the head (14), with a cylindrical section (25) being arranged between the first pointed conical section (21) and the head (14).To improve such a chipless thread-forming screw, it has a first convex section (22) which adjoins the first pointed conical section (21) in the direction of the head (14) and whose outer surface (12) has a first radius of curvature (R1) in the axial direction, and a second convex section (24) which is arranged between the first convex section (22) and the cylindrical section (25) and whose outer surface (16) has a second radius of curvature (R2) in the axial direction, wherein the first radius of curvature (R1) is not equal to the second radius of curvature (R2).