Composite Brake Disc Hub Casting to Minimize Retained Stresses
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Solution Overview
Problem
Existing composite brake discs face challenges in achieving a lightweight design while maintaining structural integrity and resisting wear and heat, with previous solutions adding complexity through additional connections and materials prone to galvanic corrosion and retained stresses.
Innovation Solution
A brake disc design featuring a rotor made of cast iron with a tubular flange and a hub made of a lighter material, where the hub is cast over the flange in a shrink-fit configuration, with specific wall configurations allowing differential thermal contraction and preventing axial separation, including axially extending teeth, varying radial thickness, and helical screw threads to minimize stresses and prevent separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a composite brake disc uses a lighter hub material (aluminium) to reduce weight, then the weight of the brake disc is reduced, but the hub is prone to galvanic corrosion and retained stresses when connected to the friction ring
Solution Approach 1:
The patent introduces an intermediary layer of molten metal that flows into the interface between the hub and friction ring during casting. This intermediary material fills gaps and creates a metallurgical bond that prevents direct galvanic contact between dissimilar metals while distributing thermal stresses, thereby resolving the corrosion and stress issues without sacrificing the weight advantage of aluminium hub material
Solution Approach 2:
The invention creates a composite structure where the hub, friction ring, and intermediary metal layer form an integrated multi-material assembly. The specific configuration of the friction ring wall encapsulated by the hub, combined with the controlled cooling process, produces a composite joint that leverages the advantages of both aluminium (lightweight) and cast iron (durable, heat-resistant) while mitigating their incompatibilities through the intermediary bonding layer
2Strength
If additional screw connections and retaining rings are added to connect the hub and friction ring, then the connection strength is improved, but the device complexity increases
Solution Approach 1:
The patent merges the connection function into the casting process itself. The molten metal flow during hub formation simultaneously creates the structural connection and provides the bonding interface, eliminating the need for separate fastening components. This consolidation achieves strong mechanical connection while dramatically simplifying the overall assembly by removing multiple discrete parts and assembly steps
Solution Approach 2:
The invention replaces the mechanical fastening system (screws, retaining rings) with a metallurgical bonding system achieved through controlled molten metal flow and encapsulation. This substitution transitions from discrete mechanical elements to an integrated material bond, reducing part count and complexity while maintaining or improving connection strength through the metallurgical interface
3Strength
If the hub is cast over the flange in a shrink-fit configuration, then the connection provides positive resistance to axial separation, but the differential thermal contraction during solidification and cooling may create retained stresses
Solution Approach 1:
The patent controls the thermal parameters during the casting and cooling process. By managing the temperature gradient and cooling rate of the molten metal as it solidifies around the friction ring wall, the process allows controlled differential contraction that develops the desired shrink-fit interference pressure without creating excessive retained stresses. The intermediary metal layer acts as a stress-buffer during this parameter transition
Solution Approach 2:
The invention deliberately utilizes thermal expansion and contraction characteristics of the materials. The hub material and friction ring material have different thermal expansion coefficients, and the controlled cooling process exploits this differential to create the shrink-fit effect. The intermediary metal layer accommodates this differential movement, allowing the hub to contract onto the friction ring with positive axial resistance while managing the stress development through the compliant bonding interface
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
This design achieves a strong, lightweight brake disc with reduced retained stresses and improved resistance to thermal expansion, preventing galvanic corrosion and ensuring secure torque transmission without risk of hub separation, while maintaining structural integrity under rotational and axial forces.
Implementation Method 1
the hub being cast over said flange to encapsulate at least a portion of said wall and being a shrink fit thereon
Data Source
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AI summary
A brake disc for a high performance vehicle comprises a rotor 20 formed of grey cast iron and comprising a friction ring 24 annular about an axis of rotation 26 and, coaxial with the friction ring 24, a tubular flange 28 extending axially from the friction ring 24 to a free end 28a and having a wall 28e with a radially inner face 28c and a radially outer face 28d. A hub 22 formed of aluminium is cast over the flange 28 to encapsulate at least a portion of the wall 28e, with which it has a shrink-fit connection. The encapsulated portion of the wall is made smooth (or otherwise formed with a varying radial dimension, or a screw thread) so as to permit differential thermal contraction, in an axial direction, of the hub 22 relative to the flange 28 as the hub 22 solidifies and cools after its casting. By this means, retained stresses in the hub 22 are minimised.