Friction Stir Rivet Mandrel Design for Dissimilar Material Joining
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Solution Overview
Problem
Friction stir riveting technologies face challenges in joining dissimilar materials and preventing the undesirable displacement of softened material sideways into the joint between workpieces, leading to potential detachment of displaced material.
Innovation Solution
A friction stir rivet with a mandrel and body configuration that includes a mechanical interface to inhibit rotational and translational motion, featuring a mandrel head with a substantially pointed surface to reduce material displacement, allowing for effective joining of workpieces without preexisting holes and minimizing the creation of detachable slugs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If friction stir riveting is used to join workpieces, then the workpieces can be joined without preexisting holes, but softened material tends to displace sideways into the joint between workpieces
Solution Approach 1:
The rivet is divided into two separate components: a body portion that remains in the workpiece and a mandrel portion that is driven through. This segmentation allows the mandrel to control material flow during insertion while the body provides the final anchoring function, thereby preventing sideways displacement of softened material.
Solution Approach 2:
The mandrel acts as an intermediary tool that temporarily controls the material flow during the riveting process. As the mandrel is driven through the softened material, it mediates the material displacement by constraining it within the rivet body, preventing unwanted sideways flow into the joint interface.
2Adaptability or versatility
If friction stir riveting is used to join dissimilar materials, then joining versatility is improved, but material flow control becomes more difficult
Solution Approach 1:
The riveting process utilizes dynamic conditions where the mandrel rotates during insertion to generate frictional heat and soften the dissimilar materials. The rotation speed and insertion rate are dynamically adjusted to control the material flow characteristics, enabling versatile joining of dissimilar materials while maintaining precise material flow control.
Solution Approach 2:
The process controls material flow by changing parameters such as rotation speed, insertion rate, and mandrel geometry. These parameter changes allow adaptation to different material combinations while maintaining control over material displacement, enabling the joining of dissimilar materials with varying thermal and mechanical properties.
3Strength
If the mandrel head is enlarged to upset the body end, then mechanical anchoring is improved, but the risk of creating detachable slugs increases
Solution Approach 1:
The mandrel head is designed with a pointed surface that performs preliminary action by piercing through the workpieces before the upset operation. This preliminary piercing action creates a controlled path for material flow and prevents the formation of detachable slugs during the subsequent upset and anchoring process.
Solution Approach 2:
Instead of expanding the mandrel head outward which could create detachable slugs, the process inverts the approach by using the pointed surface to pierce inward first, then using the upset operation to create anchoring features that lock the rivet in place, thereby improving reliability while maintaining strong mechanical anchoring.
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 solution enables robust joining of dissimilar materials by controlling material flow and attachment, reducing the likelihood of material displacement and detachment, thus enhancing joint stability and minimizing clearance issues.
Implementation Method 1
the mandrel is rotated about its rotational axis. The rivet is driven toward and into the workpieces such that resultant frictional heating between the rivet and the workpieces causes the materials of the workpieces to soften
Implementation Method 2
Further rotation of the mandrel is stopped, allowing the workpieces and mandrel to cool below the process temperature, thereby permitting the softened workpieces to harden
Implementation Method 3
the workpieces are held together by the fluidly bonded materials of the workpieces, the differential thermal contraction of the workpieces and the rivet, and the mechanical loading between the mandrel and the body
Data Source
AI summary
A method of joining workpieces includes rotating a friction stir rivet via a mandrel and driving the rivet into the workpieces causing frictional heating between the rivet and the workpieces and causing the materials of the workpieces to soften, thereby providing a fiction stirred displaceable path for the rivet to traverse, and driving the rivet along the displaceable path until the rivet mandrel pierces through the workpieces and a cap of the rivet is seated against the workpieces. Subsequent to seating the cap, further rotation of the mandrel is stopped and the workpieces are allowed to cool and harden. An axial load is then applied to the mandrel sufficient to provide mechanical loading between the rivet body and the workpieces. A resultant volume of displaced material from the workpieces is fixedly attached to the workpieces, thereby avoiding the creation of a potentially detachable slug of the displaced material.