Asymmetric Self-Tapping Screw Thread for Light Metal Fastening
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Solution Overview
Problem
Existing self-tapping screws face challenges in achieving sufficient strength and favorable material flow when screwing into light metals or alloys, particularly in direct screw connections, where they often result in low failure torque and inadequate pretensioning force.
Innovation Solution
A self-tapping screw with an asymmetric thread design featuring a shank with a thread turn having a load-bearing flank angle of at least 25° and a counter-flank angle of at least 40°, along with a specific thread pitch and core diameter ratio, which provides a larger profile surface area for enhanced flank coverage and pretensioning force, suitable for direct screw connections into light metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional self-tapping screws with smaller flank angles are used, then easier material flow is achieved, but insufficient pretensioning force and low failure torque result
Solution Approach 1:
The patent applies asymmetry by designing the thread flanks with different angles: the load-bearing flank has an angle of 25°-35° while the counter-flank has an angle of 40°-60°. This asymmetric configuration allows the load-bearing flank to provide sufficient pretensioning force and high failure torque, while the counter-flank maintains favorable material flow characteristics during the screwing process into light metals.
Solution Approach 2:
The patent changes the geometric parameters of the thread flanks by specifying precise angle ranges (load-bearing flank: 25°-35°, counter-flank: 40°-60°). This parameter optimization resolves the contradiction by achieving both high strength (failure torque) and ease of operation (material flow) simultaneously through carefully controlled geometric dimensions.
2Strength
If conventional thread designs are used, then simpler manufacturing is achieved, but inadequate pretensioning force results
Solution Approach 1:
The asymmetric thread geometry with differentiated flank angles (25°-35° for load-bearing flank, 40°-60° for counter-flank) generates superior pretensioning force compared to conventional symmetric threads. While the geometry is more complex, it remains manufacturable using standard threading processes, achieving an optimal balance between strength and complexity.
Solution Approach 2:
By optimizing specific geometric parameters (flank angles within defined ranges), the patent achieves adequate pretensioning force without requiring fundamentally new manufacturing methods. The parameter changes are implemented within conventional manufacturing capabilities, resolving the contradiction between strength improvement and manufacturing complexity.
3Strength
If larger flank angles are used, then higher pretensioning force is achieved, but material flow becomes unfavorable
Solution Approach 1:
The asymmetric thread design resolves this contradiction by assigning different functions to different flanks: the load-bearing flank (25°-35°) is optimized for favorable material flow, while the counter-flank (40°-60°) is optimized for generating high pretensioning force. This functional differentiation allows both requirements to be satisfied simultaneously.
Data Source
AI summary
The invention relates to a screw (1), having a shank (3) which is provided with a thread (2) with at least one asymmetrical thread turn (4) with a plurality of windings, wherein the thread has an external diameter (Da), a core diameter (Dk) and a thread pitch (P), wherein the thread turn (4) has thread flanks (7, 8) with a flank angle (phi), wherein the thread flanks (7, 8) have a load-bearing flank (7) and a counter-flank (8) which abut one another directly or indirectly in a thread bottom (9) and at a thread tip (10), and wherein a flank angle (phiL) of the load-bearing flank (7) is smaller than a flank angle (phiG) of the counter-flank (8). The flank angle (phiL) of the load-bearing flank is at least 25°, preferably from 25° to 35°, in particular 30°, and the flank angle (phiG) of the counter-flank is at least 40°, preferably from 40° to 60°, in particular 50°, wherein the flank angle (phi) is from at least 65° to at most 95°. Screws of said type are used, in particular, for direct screw connection in light metal cast components.