Overview

This blog explores the present state of the composites design applied with the DFM approach.

• AFP Composites design approach
• The cost/weight optimization approach
• Coupon to FEA approach
• Test-cost optimized design framework
• Design for Manufacturing strategy at SAAB Aerostructures
• DFM Software approach
• Building block approach

Abbreviations

AFP - Automated Fiber Placement

DFM - Design For Manufacturing

AFP Composites Design Approach

AFP manufacturing process kinematics, process parameters, and gathered data from the process are constantly used to optimize the design of the part, Contrary to other composites layup processes where the laminates are made either by complete sheets or by continuous processes, AFP works like true Additive manufacturing technology, enabling the placement of right material in the right shape, orientation, etc. This leads to a solution space that is very vast for a manual designer to explore. Thus generative designs that is constrained by AFP process limitation populate the solution space. Selecting the most suitable solution and producing it a few times, can provide an infinite improvement loop from the process data, [Link]

The cost/weight optimization approach

The cost/weight optimization framework works by accounting for the material consumption and process time, it is trying to find tradeoffs between the structural

performance of a component and its manufacturing cost. The methodology is aimed to be used in the preliminary design phase; thus, the output of the optimization is neither detailed manufacturing documentation nor a ply book. The introduction of a draping model in this phase is rather a way to

1. Provide the cost model with more detailed manufacturing knowledge
2. To perform a structural analysis with fiber angles closer to reality and producibility constraints
3. To show that the choice of the draping strategy can influence the cost and weight balance of a component. [Link]

Coupon to FEA Approach

After the mechanical characterization of the CFRP material, it is possible to calibrate the numerical material model, to properly design and perform experimental tests on

thin-walled tubular structures. The simplified tested model is later extended to the conical crash component. In such cases, manufacturing is always assumed to be hand layup work [Link]. A similar approach is also touted by commercial designers as well in the automotive industry [Link].

Test-cost optimized design framework

Optimization of manufacturing cost, NDT cost, and the weight formed by a simplified version of the direct operating cost. It's a very academic framework and is very rarely used in commercial operations. [Link]

Design for Manufacturing strategy by SAAB Aerostructures

The DFM method developed is focusing on efforts in the first phase of the product development process called preliminary product development. There are six stages in the implementation of the DFM method [Link]

1. Map the product - the first step is to divide the product parts into components
2. Investigate integration possibilities - the designer must answer questions on the Possibilities of Integration compared to the cost-benefit of unified structures
3. Generate concepts - the designers generate different concepts that integrate the components. A DFM knowledge database should serve to support this process.
4. Analyze concepts - the generated concepts should at this stage be evaluated and analyzed for DFM.
5. Select concept - based on the decision matrix in the selected concepts are evaluated based on manufacturability, production of technically difficult structures and designs, etc.
6. Evaluate product - the concept selected will be further developed to a maturity level similar to that at the Preliminary Design Review (PDR).

DFM Software approach

This approach mainly relies on having CATIA software in-house. A simplified process overview is shown in the video here. Essentially a serialized approach to design i.e. Shape design -> material assignment -> manufacturability; ignores the benefits of composites tailorability and treats the composites design as a sheet metal design. This limits the exploration capability of the user to draw strip-by-strip the part and draw with the limitation of the provided suit. Siemens offers a similar suit called Fibersim, following a similar design philosophy these suits try to provide a complete workflow. The key dropback is the high cost and rigidity in the design philosophy,

Building block approach  

The approach is used to ensure requirements/specifications are met while at the same time reducing risk by demonstrating material equivalency between successive layers. That is, at each scale, the part behavior can be described or predicted from the lower scale. Simply put, the materials and structures on the aircraft behave as expected from the lab-scale tests. This can be subdivided into chemical, physical, and mechanical perspectives: for example, is the degree of cure the same, is the volume fraction the same, is the compressive strength the same. As large-scale testing is particularly expensive, the idea is to minimize the number of large-scale tests by increasing the number of cheaper, coupon-level tests. [Link]

Key Takeaways

• Composites material processing with different manufacturing methods has a lot of variety, this opportunity presents itself as a new challenge of finding the best design route.
• For structural components for aircraft, the automotive industry's different approaches work better, as the cost to production volume is vastly different.
• Many design frameworks do not consider the composite manufacturing processes and their unique capabilities while designing the part.

About Addcomposites

Addcomposites is the provider of the Automated Fiber Placement (AFP) ecosystem - including the Fiber Placement System (AFP-XS), 3D Simulation and Programming Software (AddPath), and Robotic Cells (AddCell). With the leasing program for the AFP system (AFPnext), composites manufacturers can work with thermosets, thermoplastics, dry fiber placement, or in combination with 3D Printers on a monthly basis.

Sources

• Automated fiber placement: A review of history, current technologies, and future paths forward
• Cost/weight optimization of composite prepreg structures for best draping strategy
• Lightweight design and crash analysis of composite frontal impact energy-absorbing structures
• Cost optimization of composite aircraft structures including variable laminate qualities
• Design for Manufacturing of Composite Structures for Commercial Aircraft – The Development of a DFM Strategy at SAAB Aerostructures
• Composites Engineering and Manufacturing preparation

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