Composites are turning into a highly pivotal element in the Aerospace and Defense (A&D) sector. In fact, Tech-Clarity’s Composite State of the Market study found that A&D companies overwhelmingly turn to composites to help with light weighting so that they can improve performance and realise better fuel economy. The study also found that while composites offer significant benefits, the expense of the material means companies should look at ways to get better insight. Inspecting how composites can be utilised in the A&D industry, Tech - Clarity examined 181 A&D manufacturers. The study examines two parts – springback and manufacturing planning – that can be a cause for roadblocks when working with composites.
Springback can cause significant issues for A&D companies. Springback is a manufacturing defect that can occur while the composite part is curing. Due to shrinkage, the material can deviate from the original molded shape. When this happens, the part is out of tolerance. Depending on how severe the distortion is, manufacturers have to spend extra time correcting the part to get it within tolerance so that they can assemble it. The good news is that companies, who have adopted best practices for composites, are much less likely to experience springback. Some of those best practices include using design guidelines and communicating ply level design information by providing direct access to the composite data in the engineering model.
Manufacturing planning is another important part of producing quality composite parts. It is especially crucial to produce parts exactly as designed. By following manufacturing planning best practices, one is more likely to produce composite parts as designed. Best practices involve leveraging an accurate engineering model.
Manufacturers find that springback is usually severe enough that the distortion is outside of tolerance. When this happens, it takes extra time to properly adjust parts so that they fit together. In other cases, the distortion is so bad that one cannot correct it, hence parts have to be scrapped. Given the expense of carbon fibre, this can significantly drive up cost. Companies, who take the right steps to minimise springback, will be much better positioned to have a competitive advantage. A whopping 70% of respondents indicate that they have problems with springback in curved panels. However, almost a third of respondents find that they even have problems with flat panels. Springback also comes from a variety of sources, but most commonly from resin shrinkage and fibre deviation.
Corrective actions for springback
When springback occurs, the most common methods involve using a liquid shim or force fitting the part into the assembly. Both involve extra steps during the assembly process that take extra time. Figure 1 shows the most common practices for avoiding springback. The results show that A&D manufacturers are more likely to take the easiest and fastest approach of updating the tool rather than making design adjustments or ongoing process monitoring.
Identifying top performers
Considering that springback is a source of excess time and cost, companies looking to save money should examine it more closely. Given how common it is, there is still work to do to reduce its occurrence. To identify some of these best practices, Tech-Clarity researchers isolated Composite top performers. These companies were categorised according to how well they meet their targets for composite parts. The metrics used include the ability to meet:
Design due dates
Product development budget
Production cycle times
The top 20 per cent, who do the best job of meeting these targets, were considered Composite top performers and everyone else was labeled average. Based on the results, Composite top performers do a better job of managing their processes.
Compared to average performers, Composite top performers are 32% less likely to experience springback. They are 41% more likely to use design guidelines compared to their peers. Interestingly, beyond performance categories, companies who tend to specialise and stick with only one type of fibre, tooling, mould, and moulding material, are less likely to experience problems with springback.
On the other hand, those who take a variety of approaches and use different fibres, weave architectures, tooling, etc. can offer more options to support different applications. However, it becomes harder to develop the internal expertise and guidelines to avoid springback. Many manufacturers, who do not experience problems with springback, offer advice to avoid it. The advice falls in four buckets:
Experimentation: Making adjustments to the parts
Manufacturing adjustments: Adjusting production parameters & closely monitoring the cooling & curing process
Experience: Relying on expertise to make the right design decisions
Design and analysis: Using analysis and calculations to guide design decisions
These suggestions have their benefits as well as some drawbacks. The first two options occur during production. Manufacturing adjustments offer similar benefits. The second two options happen during design. For these options, experience is extremely helpful.
Many commented that they take care of springback during development and that calculations are key. One manufacturer said, “We take care of springback problems during design. We also use analysis to avoid any problems.” This approach may add a little time during design, but it takes less time to run simulations than it does to run those same experiments on the production floor. In addition, you avoid the costly waste.
Planning for manufacturing
Once engineering work is complete, parts are ready for production. With composites, the link between the design model and produced part is especially critical. Even a slight adjustment in fibre orientation can have a significant impact on strength. As such, produced parts must match the as-designed model as closely as possible or they may not meet the engineering criteria they were designed for. Manufacturing planning is a critical step to ensure parts are produced correctly. Most companies producing composite parts have a manufacturing planning system they use for composite parts.
Most companies use a variety of methods to communicate ply level design data to manufacturing. Overall, 2D drawings are the most common method. However, compared to average companies, Composite top performers are 84% more likely to provide direct access to the composite data in the engineering model. Using the engineering model directly saves time and leaves little room for misinterpretation or errors. However, the right technology must be in place to make it work. Furthering the use of engineering tools, the majority of A&D manufacturers use the design tool to create visual aids for composite parts, although many also use office applications.
By taking the information directly from the design tool, you can reuse more information rather than recreate it. This saves time and reduces the risk for errors.
Don’t overlook the time impact of changes
Developing the manufacturing plan is a critical piece of producing quality parts. A significant amount of time goes into creating them, but an almost equal amount of time goes into making changes. Overall, it takes over a day to get the plan ready. To implement changes, for most companies, the process is currently very manual.
Given how manual the process is for 83% of respondents, there is an opportunity to reduce some of the time spent on manufacturing plans, especially changes. With better automation, rather than wasting time making manual updates, you can spend it on producing parts instead.
Considering programming trends
There is a fairly even distribution among approaches for creating programs to run automated fibre placement. Using the machine vendor’s software is the most common approach, but internally developed software and third party software are used with nearly equal frequency. A&D manufacturers tend to use automated layup machines from 2.2 different vendors. Changes are not easy here either as it takes 0.7 days to make a change to an automated layup programme.
Adopting best practices
Many A&D companies have turned to composites to help them improve performance and realise better fuel economy. However, the A&D industry is also under significant pressure to lower costs. Addressing manufacturing defects, such as, springback as well as better manufacturing planning can help A&D companies take advantage of the benefits of composites while improving design and production efficiency and lowering costs.
Springback can be a considerable source of excess cost and waste. Typically, springback causes parts to be out of tolerance so manufactures have to waste time correcting parts, or worse, scrapping them. By adopting best practices, such as, using design guidelines, A&D manufacturers can avoid springback.
Adopting best practices for manufacturing planning is another area where A&D manufacturers can improve quality. It is crucial that composite parts are manufactured as designed to ensure performance. By adopting practices, such as, leveraging the engineering composite model for manufacturing planning and automating changes, A&D manufacturers will be better positioned to produce parts as designed, without quality issues.