Asymmetric Self-Drilling Screw Threads for Chip Evacuation
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Solution Overview
Problem
Conventional screws face challenges in efficiently removing chips during screwing operations, leading to increased screwing resistance, reduced cutting efficiency, and poor pull-out resistance, which can result in the screw being easily pulled out of the workpiece.
Innovation Solution
The screw design incorporates a shank with thread convolutions, ribs, and discharging portions. The thread convolutions have asymmetrically arranged flanks with different vertical distances and flank angles, and the discharging portions feature inclined surfaces and accommodation grooves to guide chips outwards effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional symmetrical thread convolutions are used, then the screw structure is simple, but the cutting efficiency is poor and chips cannot be moved outwards timely
Solution Approach 1:
The patent applies asymmetry by designing thread convolutions with a first thread flank having a first inclined angle and a second thread flank having a second inclined angle, where the angles are different. This asymmetric configuration optimizes chip evacuation by directing chips toward the gap between adjacent thread convolutions, improving cutting efficiency without significantly increasing structural complexity.
Solution Approach 2:
The patent segments the thread convolution into distinct functional portions: a first thread flank for cutting and engaging the workpiece, a second thread flank for chip evacuation, and a gap between adjacent thread convolutions for chip accommodation. This segmentation allows each portion to perform its specific function optimally, enhancing overall cutting efficiency.
2Productivity
If the screw keeps pressing accumulated chips, then the screwing operation continues, but the screwing resistance increases and the workpiece may crack
Solution Approach 1:
The patent extracts chips from the screwing zone by providing gaps between adjacent thread convolutions that serve as chip evacuation paths. These gaps allow chips to be removed from between the thread convolutions and the workpiece surface, preventing chip accumulation and reducing screwing resistance, thereby maintaining higher screwing speeds without causing workpiece cracking.
3Reliability
If conventional thread convolutions are used, then the screw structure is simple, but the pull-out resistance is poor and the screw may be easily pulled out
Solution Approach 1:
The asymmetric thread flank design with different inclined angles creates unequal engagement forces between the screw and workpiece. The first thread flank with its specific inclined angle provides stronger engagement for resisting pull-out forces, while the second thread flank facilitates chip evacuation. This asymmetric configuration enhances pull-out resistance without significantly complicating the screw structure.
Data Source
Figure 1
Figure 2
Figure 3~3B
AI summary
A screw (3) includes a shank (31), a head (32) and a drill portion (33) joined to opposite ends of the shank (31), thread convolutions (34) spiraled on the shank (31), ribs (35) protruding from the shank (31), a discharging portion (36) formed between any two adjacent ribs (35), and cutting portions (37) formed on the thread convolutions (34). Each thread convolution (34) has two thread flanks (341, 342) converging at a thread crest (343) and forms respective thread roots (344, 345) by which different vertical distances are defined. One of the thread flanks (341) includes flank sections (3411, 3412) having different flank angles. Therefore, the thread convolutions (34) are asymmetric. The discharging portion (36) has two inclined surfaces (362) connected to the ribs (35) and an accommodation groove (361) formed therebetween. The cutting portions (37) and ribs (35) serve to cut and cooperate with the asymmetric arrangement to increase the cutting efficiency, thereby reducing screwing resistance, enhancing pull-out resistance whereby the screw (3) is not easily pulled out of a workpiece (4), and removing chips quickly through the discharging portion (36).