Recessed Spring Washer Flow Drill Screw Torque Stability
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Solution Overview
Problem
Existing fastening techniques, such as flow-drill screwing, face issues with torque fall-off, especially in thick materials and dissimilar material combinations, where the torque relaxation after assembly and curing can compromise the joint's integrity, particularly in polymer-based substrates and after paint processes.
Innovation Solution
A screw design incorporating a recessed spring washer with a defined spring rate, which is integrally formed or separate, and a flow-hole-forming tip, that provides a clamping load and maintains torque through thermal expansion and contraction, preventing torque fall-off and enhancing sealing by a flange extending at least 90° from the longitudinal axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a flow-drill screw is used in thick materials or dissimilar materials, then the joining capability is improved, but torque fall-off occurs after assembly and curing
Solution Approach 1:
The recessed spring washer is designed with dynamic elastic properties to continuously adapt to thermal expansion and contraction of the workpieces. The washer's spring rate is specifically engineered to maintain optimal clamping force across temperature variations, transforming the static fastening system into a dynamic one that self-adjusts to environmental changes.
Solution Approach 2:
The invention changes the physical parameters of the fastening system by introducing a compliant element with specific elastic properties. The recessed spring washer's material composition and geometric dimensions are optimized to provide the desired spring rate, fundamentally altering how the joint responds to thermal stresses compared to rigid fastening systems.
2Strength
If adhesive is used in conjunction with flow-drill screw, then the joining strength is improved, but torque fall-off concern increases
Solution Approach 1:
The recessed spring washer acts as a pre-configured cushioning element that anticipates and compensates for torque relaxation before it occurs. By maintaining constant clamping pressure through its elastic recovery, the washer prevents the adhesive joint from experiencing torque fall-off, thereby protecting the bonded interface throughout the service life of the assembly.
3Reliability
If the flange extends at least 90° from the longitudinal axis, then the sealing capability is improved, but the device complexity increases
Solution Approach 1:
The recessed spring washer integrates multiple functions into a single component: it provides sealing through its extended flange geometry, maintains clamping force through its spring properties, and distributes load across the joint interface. This merging of sealing, fastening, and compensation functions into one element avoids the need for separate sealing components, thereby reducing overall assembly complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The screw effectively prevents torque fall-off and maintains a consistent clamping load across thermal changes, ensuring the joint's stability and integrity in various materials like aluminum and polymer composites, facilitating high-volume, single-sided joining of composites and metals.
Implementation Method 1
The recessed spring washer defines a spring rate sufficient to prevent torque fall-off
Implementation Method 2
maintains torque through thermal expansion and contraction
Data Source
AI summary
A screw for use in joining workpieces, for example automotive body parts, is provided that includes a head portion, an externally threaded shank extending from the head portion, a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank, and a recessed spring washer disposed under the head portion. The recessed spring washer is configured to apply a clamping load to joined workpieces as they expand and contract.