Self-Tapping Screw Thread Segmentation for Torque and Fastening
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Self-tapping screws used in soft materials like aluminum alloys and resins face insufficient fastening force and risk of loosening due to lack of contact between thread flank surfaces during fastening, leading to inadequate torque and potential material cracking.
Innovation Solution
A self-tapping screw design with a normal thread and a female screw molding thread of larger diameter, where one pitch is set larger than others, allowing closer pressure flank surface contact during fastening and fixing, reducing driving torque while increasing fastening force, and featuring a smaller pressure flank angle for enhanced wedging action.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the normal thread flank surfaces do not contact the female thread during fastening, then driving torque is reduced and material cracking is prevented, but fastening force becomes insufficient and the screw is likely to loosen
Solution Approach 1:
The thread structure is segmented into two distinct parts: a normal thread for driving torque reduction and a female screw molding thread for fastening force generation. This segmentation allows each part to perform its specialized function without interference, resolving the contradiction between ease of operation and reliability
Solution Approach 2:
Different regions of the thread structure are given different properties. The normal thread has a larger pitch for reduced contact and lower driving torque, while the female screw molding thread has a smaller pitch for increased contact and higher fastening force. This local differentiation resolves the contradiction by optimizing each region for its specific purpose
2Ease of operation
If a larger pitch is used in the normal thread, then driving torque is reduced, but fastening force becomes insufficient
Solution Approach 1:
The thread system is divided into two functional segments with different pitch characteristics. The normal thread uses a larger pitch to reduce driving torque, while the female screw molding thread uses a smaller pitch to generate sufficient fastening force, thereby resolving the contradiction between ease of operation and force generation
Solution Approach 2:
The pitch parameter is changed differently in different parts of the thread structure. By setting the normal thread pitch to be larger than the female screw molding thread pitch, the system achieves both reduced driving torque and sufficient fastening force through parameter differentiation
3Force
If the pressure flank angle of the normal thread is reduced, then fastening force is increased through wedging action, but driving torque may increase
Solution Approach 1:
The pressure flank angle is optimized locally for the normal thread to enhance wedging action and fastening force, while the overall thread design maintains acceptable driving torque characteristics through the combined effect of the two thread types with different pitch values
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves sufficient fastening force with reduced driving torque, preventing material cracking and ensuring secure attachment in both soft and hard materials.
Implementation Method 1
contact resistance is insignificant between the pressure flank surface of the normal thread and the pressure flank surface of the female thread
Implementation Method 2
action of axial force causes the pressure flank surface of the normal thread to approach and come into contact with the pressure flank surface of the female thread, thereby increasing fastening force
Implementation Method 3
a crest of the normal thread is wedged into the pressure flank surface of the female thread. Therefore, it is possible to expect more increased fastening force
Data Source
AI summary
A self-tapping including a normal thread (10) and a female screw molding thread (12) having a larger diameter than that of the normal thread (10), out of pitches of the normal thread (10) positioned in a head portion side from the female screw molding thread (12), any one pitch is set to be larger than other pitches. The self-tapping not only reduces driving torques but also improves fastening force, and thus can be applied to various workpieces made of the soft material as well as a hard material.