Segmented Screw Fastener Thread Design for Die Life
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Solution Overview
Problem
Conventional threaded screw fasteners with enhanced pull-out and back-out resistance characteristics are difficult to manufacture due to rapid wear of cutting dies, limiting the quantity and efficiency of fastener production.
Innovation Solution
A threaded screw fastener design featuring a shank with both conventional and anti-back-out thread formations, where the anti-back-out threads have a more inclined front flank surface and a nearly vertical rear flank surface, allowing for equal thread spacing and reduced stress on the cutting die, thereby improving manufacturability without compromising installation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional buttress-type threads with significantly inclined forward flank surfaces are used to enhance pull-out and back-out resistance, then pull-out resistance is improved, but manufacturing difficulty increases and cutting die life decreases
Solution Approach 1:
The thread formation is divided into two distinct segments: conventional threads near the tip for easy installation, and anti-back-out threads near the head for enhanced pull-out resistance. This segmentation allows each segment to be optimized for its specific function while using appropriate cutting parameters, thereby improving overall performance without excessive manufacturing difficulty
Solution Approach 2:
Different thread geometries are applied to different locations along the shank. The conventional threads at the distal end have standard flank angles for easy installation, while the anti-back-out threads at the proximal end have modified flank angles (nearly vertical rear flank, 30-60 degree front flank) to maximize pull-out resistance. This local differentiation optimizes both installation and holding characteristics
2Reliability
If threads with inclined rear flank surfaces are used to improve anti-back-out characteristics, then back-out resistance is enhanced, but cutting die wear increases
Solution Approach 1:
The thread formation is segmented into conventional threads for initial installation and anti-back-out threads for final securing. Only the anti-back-out threads use the aggressive geometry with nearly vertical rear flanks, limiting the wear-inducing cutting parameters to a smaller portion of the total thread length while still achieving the desired anti-back-out effect
Solution Approach 2:
The thread geometry parameters are changed specifically in the anti-back-out region: the rear flank angle is modified to be nearly vertical (0-8 degrees) and the front flank angle is increased to 30-60 degrees. These parameter changes are localized to the proximal threads, allowing enhanced anti-back-out characteristics without requiring the entire thread formation to use wear-intensive cutting parameters
3Strength
If anti-back-out thread formation with modified flank angles is implemented, then pull-out resistance is enhanced, but installation characteristics may be adversely impacted
Solution Approach 1:
The thread system is segmented into two functional zones: conventional threads at the tip that facilitate easy installation with standard torque, and anti-back-out threads near the head that provide enhanced pull-out resistance. This segmentation ensures that installation characteristics are maintained by the conventional threads while the anti-back-out threads provide the strength enhancement
Solution Approach 2:
The anti-back-out thread geometry with modified flank angles is applied locally only to the proximal portion of the shank near the head, while the distal portion retains conventional thread geometry. This local application of modified geometry provides enhanced pull-out resistance at the critical anchoring zone without adversely affecting the overall installation characteristics
Data Source
AI summary
A fastener with multiple thread characteristics includes a shank and head. The shank has a penetrating tip distal most from the head. The shank includes a first, conventional thread formation formed therein adjacent the penetrating tip and a second, anti-back-out thread formation adjacent the conventional thread formation, between the conventional thread formation and the head.