Multi-material Fastener for Dissimilar Metal Joining
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Solution Overview
Problem
The joining of automotive components made from different materials, such as steel and aluminum, is challenged by thermal expansion differences, leading to distortion and fit issues during thermal processing, as conventional fastening methods fail to accommodate varying coefficients of thermal expansion effectively.
Innovation Solution
A fastener with a plastically deformable head portion, a platform, and a distal end portion featuring elastically deformable locking members, such as tabs or rings, that taper inwardly and are designed to compensate for thermal expansion differences between workpieces, allowing for secure joining while accommodating varying thicknesses and materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fastening methods are used to join dissimilar materials, then the joining process is simple, but thermal expansion differences cause distortion and fit issues during thermal processing
Solution Approach 1:
The fastener utilizes phase change of the material (from solid to softened state during thermal processing) to accommodate thermal expansion differences. The material transitions from a rigid state during assembly to a softened state during thermal processing, allowing it to deform and absorb dimensional changes, then returns to rigid state after cooling, maintaining assembly integrity despite thermal expansion variations between dissimilar materials.
Solution Approach 2:
The fastener is made from a polymer material that combines properties of both rigid structural support and thermal adaptability. This composite material approach allows the single fastener component to simultaneously provide mechanical joining strength while accommodating thermal expansion differences between steel and aluminum parts during thermal processing.
2Manufacturing precision
If mechanical joints are used to restrict part movement during thermal processing, then geometry control is improved, but yielding occurs due to differential thermal expansion
Solution Approach 1:
The fastener material undergoes parameter change from rigid to softened state during thermal processing, allowing it to accommodate thermal expansion without restricting part movement. This eliminates the yielding problem caused by rigid mechanical joints while maintaining geometry control through the material's phase transition behavior.
3Reliability
If adhesive alone is used for joining, then thermal expansion accommodation is improved, but production efficiency decreases due to geometry setting requirements
Solution Approach 1:
The polymer fastener material's phase change property allows it to function as an adaptive mechanical joint that accommodates thermal expansion without requiring separate adhesive applications or geometry setting steps. The material's ability to deform during thermal processing and maintain the joint eliminates the need for additional adhesive curing steps, enabling high-volume production while maintaining thermal expansion accommodation.
4Strength
If rigid fasteners are used to maintain joint stability, then structural integrity is improved, but adaptability to varying joint thicknesses and materials decreases
Solution Approach 1:
The fastener material's phase change from rigid to softened state during thermal processing enables it to adapt to varying joint thicknesses and material combinations. During assembly, the material is rigid enough to maintain joint stability, but during thermal processing it softens to accommodate dimensional variations and thermal expansion differences between dissimilar materials, then returns to rigid state to maintain the adapted configuration.
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 fastener effectively addresses thermal expansion issues by ensuring a secure assembly of dissimilar materials, maintaining geometry and reducing residual stresses, even under high-temperature processing conditions, by using a material like nylon that can deform to fit various joint thicknesses and materials, ensuring a stable bond.
Implementation Method 1
a distal end portion extending from the platform and defining at least one elastically deformable locking member
Implementation Method 2
a plastically deformable head portion
Implementation Method 3
The material and geometry of the fastener may further be configured to compensate for a difference in thermal expansion of the workpieces being joined
Data Source
AI summary
A fastener for use in joining workpieces, for example automotive body parts such as a roof to a body frame member, is provided that includes a plastically deformable head portion, a platform disposed at a bottom of the head portion, and a distal end portion extending from the platform and defining at least one of elastically deformable locking member. The head portion is heat staked to one workpiece, and the elastically deformable locking member engages another workpiece to secure the workpieces together. The platform provides spacing, or a bond gap in one form, between the workpieces, and a material and geometry of the fastener are configured to compensate for a difference in thermal expansion of the workpieces.