SPF/DB Surface Mark-off Suppression via Counteracting Gas Pressure
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Solution Overview
Problem
Superplastic forming and diffusion bonding (SPF/DB) processes often result in surface mark-off, which causes cosmetic issues and increases aerodynamic drag in complex metal structures like aircraft exterior assemblies.
Innovation Solution
Applying a forming pressure within a pack and supplying positive gas pressure between the die and the pack to counteract the forming pressure, thereby suppressing surface mark-off during SPF/DB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If superplastic forming and diffusion bonding is used to form complex metal structures, then complex shapes and deep drawn features can be achieved, but surface mark-off occurs causing cosmetic issues and increased aerodynamic drag
Solution Approach 1:
Positive gas pressure is supplied to the die cavity before and during the forming process to counteract the forming pressure and prevent surface mark-off from occurring in the first place. This preliminary counter-action maintains uniform pressure distribution and prevents the pack material from adhering to and marking the die surface.
Solution Approach 2:
A layer of positive gas pressure is introduced as an intermediary between the die surface and the pack material. This gas pressure layer acts as a mediator that transmits forming forces uniformly while preventing direct contact that would cause surface mark-off, thereby protecting the surface finish during the forming process.
2Shape
If forming pressure is applied to expand the pack within the die, then complex shapes can be formed, but surface mark-off is caused on the pack surface
Solution Approach 1:
Positive gas pressure is applied to the die cavity to create a counterbalancing pressure that opposes the forming pressure inside the pack. This counterweight effect prevents the pack material from being forced against the die surface with excessive force, thereby eliminating surface mark-off while still allowing deep drawn features to be formed.
3Manufacturing precision
If positive gas pressure is supplied between the die and the pack to counteract forming pressure, then surface mark-off is suppressed, but process complexity increases
Solution Approach 1:
The positive gas pressure system serves multiple functions simultaneously: it counteracts forming pressure to prevent surface mark-off, maintains uniform pressure distribution during forming, and enables the creation of deep drawn features. This multi-functionality reduces the need for additional specialized equipment or process steps, thereby limiting the increase in overall process 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 method effectively prevents surface defects, ensuring a smooth, defect-free finish with reduced aerodynamic drag on aircraft exterior assemblies.
Implementation Method 1
supplying positive gas pressure between the die and the pack while the pack is being expanded in order to counteract the forming pressure to suppress surface mark off
Implementation Method 2
Superplastic forming and diffusion bonding (SPF/DB) may be used to form monolithic metal structures having complex shapes and deep drawn features
Data Source
AI summary
A method of forming a pack in a die by superplastic formation and diffusion bonding comprises applying a forming pressure within the pack to expand the pack within the die; and supplying gas between the die and the pack to apply a back pressure around an outside of the pack while the pack is being expanded to counteract the forming pressure to reduce surface mark off.