Chipless Thread-Forming Screw Shank Segmentation

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Solution Overview

Problem

Existing thread-forming screws are limited in their ability to penetrate unpre-drilled thick metal sheets and produce chips during the process, requiring high press-on force and resulting in material loss and reduced holding force.

Innovation Solution

A thread-forming screw with a tip diameter of 0.25-0.35 mm, a frustoconical section with a 20°-30° point angle, and a thread height defined by the function H=((tan(α/2)+FB)*X+0.2 mm)−RK, allowing chipless penetration of up to 3.1 mm thick steel sheets, and a cylindrical section diameter of 3.0-6.3 mm for optimal screw-in characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If a conventional thread-forming screw is used to penetrate unpre-drilled thick metal sheets, then the screw can form a thread in hard material only in a pre-drilled bore, but it cannot penetrate thick sheets without pre-drilling and is limited to very thin sheets

Engineering Contradiction:

Improvepenetration depthVSAvoidthread formation capability

Core Design Contradiction:

Length of moving objectVSEase of manufacture

Solution Approach 1:

The shank is divided into functionally distinct sections: a frustroconical section (21) for initial penetration and chipless material displacement, and a cylindrical section (25) for thread formation. This segmentation allows each section to be optimized for its specific function, enabling the screw to penetrate thick sheets and form threads effectively

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The frustroconical section performs preliminary action by penetrating the material first, creating a pilot path and displacing material chiplessly before the threading section engages. This preliminary penetration enables the subsequent thread-forming section to operate effectively in thick sheets without pre-drilling

Inventive Principle:

Principle #10Preliminary action

2Length of moving object

If a self-drilling screw is used to penetrate thick sheet metal, then penetration of sheets thicker than 2 mm is possible, but chips are produced which require costly removal and high press-on force must be applied throughout the process

Engineering Contradiction:

Improvepenetration depthVSAvoidchip production

Core Design Contradiction:

Length of moving objectVSObject-generated harmful factors

Solution Approach 1:

By separating the penetration function (frustroconical section) from the thread-forming function (cylindrical section with threads), the screw achieves chipless penetration through controlled material displacement in the frustroconical section, eliminating chip production while maintaining deep penetration capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of drilling away material (self-drilling approach), the frustroconical section displaces material forward in a controlled manner, inverting the traditional drilling mechanism into a chipless displacement mechanism that pushes material ahead of the screw rather than removing it

Inventive Principle:

Principle #13The other way round (Inversion)

3Length of moving object

If a self-drilling screw is used for penetration, then thick sheets can be penetrated, but high press-on force must be applied during the entire setting process

Engineering Contradiction:

Improvepenetration depthVSAvoidpress-on force

Core Design Contradiction:

Length of moving objectVSForce

Solution Approach 1:

The divided shank structure allows the frustroconical section to handle the high-force penetration phase while the cylindrical section handles thread formation, enabling optimized force distribution throughout the setting process and reducing the overall press-on force requirement compared to single-function screws

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The frustroconical section performs preliminary penetration with optimized geometry for force efficiency, creating a path that reduces the force needed for subsequent thread formation, thereby lowering the total press-on force required during the entire setting process

Inventive Principle:

Principle #10Preliminary action

4Length of moving object

If drilling is used for penetration, then thick sheets can be penetrated, but material loss occurs which adversely affects the holding force of the screw

Engineering Contradiction:

Improvepenetration depthVSAvoidmaterial loss

Core Design Contradiction:

Length of moving objectVSLoss of substance

Solution Approach 1:

The screw inverts the drilling approach by displacing material forward rather than removing it, achieving penetration through controlled material movement instead of material removal, thereby eliminating chips and preserving material for optimal holding force

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The frustroconical geometry converts what would normally be harmful chip generation into beneficial controlled material displacement, where the displaced material actually helps form the thread structure and improves rather than harms the holding force

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8596943B2Chipless thread-forming screw

Publication Date: 2013.12.03 HILTI AG

AI summary

A chipless thread-forming screw (10) has a thread-carrying shank (11) provided at its opposite ends with a tip (13) and a head (4), respectively, and having a diameter between 0.25 and 0.35 mm, with the shank (11) having at least one frustroconical section (21) extending from the tip (13) in direction of the head (14) and having, with respect to the thread root (22), a point angle (α) between 200 and 300, and a cylindrical section (25) extending between the frustroconical section (21) and the head (14), and with a starting line (23) of the thread (15) remote from the head (14) being spaced from the tip (13) by a distance (Lt) from 0 to 0.3 mm.