Driver Bit and Fastener Recess Geometry for Stable Torque Transfer
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Solution Overview
Problem
Conventional fasteners with six-pointed star recesses often fail to engage properly with driver bits due to manufacturing tolerance, leading to torque transmission issues, slippage, and damage to the fastener and driver bit. Additionally, corrosion-resistant coatings can accumulate in the recess, further impairing engagement.
Innovation Solution
The fastener features a screw head with a recess defined by six curved and driven portions arranged alternately around a central axis. These portions include curved, straight, and extension sections that increase the contact area with the driver bit, ensuring proper engagement and torque transmission. The driver bit and punch tool are designed to match this configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional six-pointed star recess is used in the fastener, then the fastener can be manufactured with standard processes, but the recess may not fittingly engage with the driver bit due to manufacturing tolerance, causing torque transmission failure and slippage
Solution Approach 1:
The recess is segmented into multiple functional zones: curved portions for engagement initiation, driven portions for torque transmission, and extension sections for tolerance compensation. Each segment serves a specific function in the engagement process, allowing the recess to adapt to dimensional variations while maintaining reliable connection with the driver bit.
Solution Approach 2:
Different sections of the recess have different geometric properties optimized for specific functions. The curved portions have different curvature radii, the driven portions have specific width and depth, and the extension sections have varying lengths. This local differentiation allows each zone to perform its function optimally while collectively compensating for manufacturing tolerances.
2Reliability
If the outer surface of the fastener is coated with corrosion-resistant material, then the fastener can be used in harsh environments, but the coating accumulates in the recess and adversely affects engagement between the driver bit and recess
Solution Approach 1:
The design extracts the problematic accumulation zones by creating extension sections that extend beyond the main recess body. These extension sections are positioned where coating accumulation would least interfere with driver bit engagement, effectively separating the corrosion protection function from the engagement function.
Solution Approach 2:
The recess design extends in multiple dimensions with varying depths and radii. The extension sections protrude outward from the main recess, creating a three-dimensional structure where coating material can accumulate without blocking the primary engagement path between the driver bit and the driven portions.
3Ease of manufacture
If the recess has a simple six-pointed star shape, then the structure is simple to manufacture, but the contact area with the driver bit is insufficient, leading to torque transmission issues
Solution Approach 1:
The recess is divided into multiple driven portions, each with specific geometric characteristics. These segmented structures increase the total contact area with the driver bit while maintaining a manufacturing process that is an extension of conventional recess formation techniques.
Solution Approach 2:
The recess incorporates curved portions with specific radius of curvature that complement the driver bit geometry. This curvature increases the contact area between the recess and driver bit, improving torque transmission while the overall six-pointed star configuration remains compatible with standard manufacturing processes.
Data Source
AI summary
A fastener includes a screw head and a screw shank. The screw head has a top surface and an inner surrounding surface. The inner surrounding surface has six curved portions and six driven portions disposed in an alternating arrangement. Each of the driven portions has a curved section connected to one of two adjacent curved portions and having a direction of curvature opposite to that of the one of the two adjacent curved portions, a straight section extending along a tangent line of an end of the curved section, and an extension section connected between the straight section and the other one of the two adjacent curved portions.