Self-Tapping Screw Thread Structure for Chip Discharge and Low Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing self-tapping screws face issues with increased driving torque due to chip accumulation and poor foreign matter removal, especially when used with long internal screws or screws with adhered foreign materials like paint films.
Innovation Solution
The external screw member features a design with a parallel and tapered threaded portion, incorporating convex portions that gradually increase in diameter and have specific flank angles, allowing for efficient chip discharge and foreign matter removal without excessive torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the length of an internal screw is long, then the number of screw threads to be formed increases, but cutting chips are not discharged well and accumulate in the internal screw, causing screw driving torque to increase abruptly
Solution Approach 1:
The screw thread is divided into two distinct zones: a first zone with a first screw thread and a second zone with a second screw thread. This segmentation allows different portions of the screw to perform different functions - the first zone for initial engagement and chip discharge, and the second zone for forming threads in long internal screws, thereby resolving the chip accumulation problem while maintaining ease of operation.
Solution Approach 2:
Different regions of the screw thread are given different properties. The first zone screw thread has specific geometric characteristics optimized for chip discharge, while the second zone screw thread has characteristics optimized for forming threads in long internal screws. This local differentiation allows the screw to handle both short and long internal screws effectively without excessive torque increase.
2Object-generated harmful factors
If a self-tapping screw is used to remove foreign matter from an internal screw, then foreign matter can be removed, but the spaces between screw threads are narrow causing foreign matter to jam or bite
Solution Approach 1:
The screw thread is segmented into two zones with different geometries. The first zone screw thread is specifically designed with wider spaces between threads to facilitate the discharge of foreign matter such as paint films and spatter, while the second zone is optimized for thread formation. This segmentation enables effective foreign matter removal without jamming.
3Ease of operation
If the contact area between screw thread and prepared hole is made small, then screw driving torque is reduced, but cutting chips are not discharged well
Solution Approach 1:
The screw thread is divided into two zones: the first zone with a first screw thread designed for effective chip discharge, and the second zone with a second screw thread for forming threads in long internal screws. This segmentation allows the screw to maintain low driving torque while effectively discharging chips through the first zone thread configuration.
Data Source
Figure 1A~1E
Figure 2A~2C
Figure 3A~3C
AI summary
A external screw member comprising a head (2), and a shank (3) extending linearly from said head (2), said shank (3) having a parallel threaded portion (31) and a tapered threaded portion (32) formed in order from said head (2) toward a tip end, a screw thread (5) being continuously formed on said parallel threaded portion (31) and said tapered threaded portion (32) at the same pitch, and said screw thread (5) in said tapered threaded portion (32) being configured in a form in which the height of a crest thereof becomes gradually smaller, characterized in that a convex portion (4; 14; 24) protruding more radially outward than the crest of said screw thread (5) is formed in at least one of said parallel threaded portion (31) and said tapered threaded portion (32) over said tapered threaded portion (32) and said parallel threaded portion (31); a screw driving side end face (4d; 14d; 24d) of said convex portion (4; 14; 24) is configured to form an inclined plane which gradually rises from a root position of said end face (4d; 14d; 24d) at the side of the crest of said screw thread (5) toward a crest (4a; 14a; 24a) of said convex portion (4; 14; 24) in a direction (W2) opposite to a screw driving direction (W1) of said screw thread (5) to reach the crest (4a; 14a; 24a) of said convex portion (4; 14; 24).