Topology Optimization Aerospace Bracket Design
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Problem Statement
Selective Laser Melting (SLM):
The B-0128-g Aviation Bracket is machined from a block of wrought Ti6Al4V. I this bracket for several reasons:
The lead time for this bracket is supposed to be about a week, but due to frequent supplier delays, AAC is forced to order batches of brackets several months in advance, according to its expected production schedule.
The “buy to fly” ratio of the bracket is approximately 5:1, meaning approximately 80% of the stock material is removed during machining. Although the scrap can be sold, this is still a considerable waste, and the scrap value is very low.
The bracket is stiffer and stronger than it needs to be for its application, and therefore is unnecessarily heavy. The team speculates that its weight could be reduced via design for AM, creating value to the end-user.
Additive Manufacturing Decision
Considered AM Processes
Selective Laser Melting (SLM):
SLM is an additive manufacturing process that utilizes a high-powered laser to selectively melt metal powder layer by layer. A computer-controlled laser scans across the powder bed, fusing the material into the desired shape. This process offers a high degree of precision and control, allowing for the creation of intricate and complex geometries. SLM is particularly well-suited for small-scale production of high-value components with demanding performance requirements.
Electron Beam Melting (EBM):
EBM is an additive manufacturing process that employs a high-energy electron beam to melt metal powder. The electron beam is focused onto the powder bed, melting and fusing the material layer by layer. EBM can produce dense and high-quality metal parts, especially for large-scale components. However, the high vacuum environment required for EBM can limit its application to certain materials and part geometries.
Directed Energy Deposition (DED):
DED is an additive manufacturing process that involves a focused energy source, typically a laser or electron beam, to melt metal powder or wire. The molten material is then deposited layer by layer onto a substrate, building up the desired part. DED is a versatile process that can be used for repair, additive manufacturing of large components, and cladding. It offers the flexibility to deposit a variety of materials, including metals, ceramics, and composites.
Binder Jetting:
Binder jetting is an additive manufacturing process that uses a print head to selectively deposit a liquid binder onto a powder bed. The binder solidifies, bonding the powder particles together. After the part is built, it undergoes a sintering process to fuse the powder particles, creating a solid metal part. Binder jetting is a relatively fast and cost-effective process, suitable for large-scale production of simple to moderately complex parts.
Selected Process
For manufacturing the optimized bracket, Selective Laser Melting (SLM) is most suitable process. SLM offers several advantages that align well with the requirements of a complex bracket:
High Resolution and Detail: SLM excels in producing intricate geometries with high precision. This is crucial for capturing the fine details and complex features often found in brackets. The laser-based process allows for tight tolerances and smooth surface finishes.
Design Flexibility: SLM enables the creation of complex, organic shapes that would be challenging to manufacture using traditional methods. This flexibility can lead to optimized designs that reduce weight and improve performance.
Material Diversity: SLM is compatible with a wide range of metal alloys, providing the opportunity to select the material that best suits the specific application requirements of the bracket.
Consolidated Manufacturing: SLM allows for the production of multiple components in a single build, reducing lead times and minimizing waste. This can be particularly advantageous for brackets that are part of a larger assembly.
While SLM offers significant benefits, it's important to consider its limitations:
Part Size Constraints: SLM is typically limited to smaller parts due to the build volume of the machines. However, advancements in technology are continually expanding the size capabilities of SLM systems.
Feature Size Constrains: Very small features, especially those with high aspect ratios (height to width), can be challenging to produce due to limitations in laser power density and powder flow.
Post-Processing Requirements: SLM parts often require post-processing, such as heat treatment and machining, to achieve optimal mechanical properties and surface finish. This can add to the overall manufacturing time and cost.
Material Utilization: SLM can have lower material utilization compared to other processes, as support structures are often necessary to ensure part integrity during the build process.
Fusion 360 - Generative Design Setup
Preserve and Obstacle Geometries
Load Case
SLM Design Metrics:
Maximum Feature Overhang Angle: 45° w/r/t vertical
Minimum Strut Thickness: 0.75mm
Topology Optimization and Analysis
Factor of Safety
Deformation
Mass Analysis
Original Mass: 0.526kg
New Mass: 0.142kg
Reduced mass by 73%
Factor of Safety
While my current bracket design has a FOS of 2.68, I would add material to the cross bar between the top two holes. This is to strengthen the bracket against any torsional forces, outside the load case, to the pin (i.e. a moment about the z axis).
The areas of greatest stress on my bracket can be seen in yellow, which is mainly located on the supporting arms.
Post Processing
To improve fatigue resistance of the bracket some potential post processing processes could be:
1. Solution Treatment and Aging (STA):
This process involves heating the alloy to a high temperature (beta phase region) followed by rapid quenching and then aging at a lower temperature. This can significantly improve the strength and fatigue resistance of Ti-6Al-4V by creating a fine dispersion of alpha phase particles within a beta matrix.
2. Stress Relief Annealing:
This process involves heating the alloy to a lower temperature (alpha-beta phase region) and then slowly cooling. This can reduce residual stresses caused by manufacturing processes, such as machining or welding, which can improve fatigue resistance.
Scenario 2: Higher Cost Sensitivity
Stainless Steel 316L Additive Manufacturing
For Scenario 2, I selected Stainless Steel 316L for the material. I chose this because the cost sensitivity is high so using a cheaper material and therefore a cheaper AM process (cost of nitrogen gas needed for each print instead of argon (Titanium). Additionally, there is no problem producing the same low quantity of 1000 parts/year especially since AM is more cost effective at lower production levels than traditional manufacturing processes. With this manufacturing process, I was able to create the bracket with the highest weight to strength ratio for the material. I selected this specific solution as it was the lightest of the designs while still meeting the other design requirements. A large portion of the material was removed from the base of the bracket. This is because there are no forces acting on the bracket in the X direction. For similar reasons, the crossbar between the top two connectors was significantly reduced. Lastly, the vertical supports are larger than the ones in bracket in case study 1 due to the material having a lower tensile strength.
Factor of Safety
Deformation
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