Notched Self-Drilling Screw Threads for Fast Chip Discharge
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Solution Overview
Problem
Conventional screws experience high screwing resistance and damage due to complete threads, leading to ineffective cutting of workpiece fibers, slow chip discharge, and potential cracking, resulting in loose engagement and reduced screwing speed.
Innovation Solution
The screw features axially spaced thread convolutions with notches and cutting units, allowing for reduced contact area, effective cutting, and efficient chip accommodation, reducing screwing resistance and enhancing engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If complete threads are formed on the screw, then the screwing resistance increases, but the cutting effect deteriorates and thread damage occurs
Solution Approach 1:
The thread convolutions are segmented by introducing notches that divide each thread into multiple cutting units. This segmentation reduces the continuous contact area between the thread and workpiece, lowering screwing resistance while maintaining effective cutting through distributed cutting edges along the thread length
Solution Approach 2:
Different portions of the thread convolution have different functions: the cutting units with sharp edges provide cutting action at the thread crest, while the notched portions provide chip accommodation and reduced contact area. This local differentiation allows simultaneous achievement of effective cutting and reduced screwing resistance
2Area of stationary object
If complete threads are formed on the screw, then the contact area between thread and workpiece increases, but chip discharge space is insufficient
Solution Approach 1:
The thread structure is segmented by notches that create discrete chip accommodation spaces within each thread convolution. These notched portions provide dedicated volume for chip storage without compromising the overall thread engagement area, enabling simultaneous maintenance of contact area and creation of chip discharge pathways
Solution Approach 2:
The notches introduce a radial dimension to chip accommodation by creating inward recesses into the thread body. This transforms the chip storage from a two-dimensional surface contact issue to a three-dimensional volume utilization, providing adequate chip space while preserving thread contact area
3Force
If chips are not discharged efficiently, then screwing resistance increases, but screwing speed decreases
Solution Approach 1:
The notches extract and remove chips from the cutting zone by providing dedicated evacuation pathways. Chips are taken out from between the thread and workpiece through the notched portions, preventing chip accumulation that would increase screwing resistance and slow down the screwing operation
Solution Approach 2:
The knurl portions with troughs accelerate chip discharge by providing low-resistance pathways that enable chips to be rapidly ejected from the workpiece. This rushing through of chips prevents bottlenecks in chip removal, maintaining high screwing speed while keeping screwing resistance low
4Strength
If thread convolutions press chips continuously, then chip accommodation is insufficient, but workpiece cracking occurs
Solution Approach 1:
The continuous thread structure is segmented by notches that create discrete compression zones and relief zones. This segmentation allows localized chip compression in certain areas while providing relief in notched areas, preventing excessive stress concentration that would cause workpiece cracking while maintaining sufficient overall engagement
Solution Approach 2:
The notched portions discard chips from the active cutting zone by providing evacuation pathways, while the knurl portions with troughs recover and accommodate remaining chips in a controlled manner. This discarding and recovering mechanism prevents uncontrolled chip accumulation that would lead to workpiece damage while ensuring adequate chip management for reliable engagement
Data Source
AI summary
A screw includes a shank defining exposed surface sections between spaced-apart thread convolutions, a head and a drill portion disposed at opposite ends of the shank, and at least one knurl portion having troughs recessedly crossing each other within at least one surface section. Each thread convolution has a thread crest formed along a junction of two thread flanks, notches cut into the thread crest, cutting units each situated between every two adjacent notches, and cutting edges each formed around an outer periphery of each notch. Each cutting unit of one thread convolution is aligned with each corresponding notch of another adjacent thread convolution. The cutting units and the cutting edges facilitate a quick cutting effect. Chips are allowed to travel in the notches and the troughs, thereby attaining a quick removal of chips, achieving a suitable accumulation of chips for a tight engagement, and attaining an anti-loosening effect.