Design for manufacture is a well-known phrase but is not always applied to composites. That is not necessarily because it is overlooked, but more because composites require a certain amount of practical knowledge and experience to get right.
For newcomers, composites can seem temperamental and well-established OEMs such as Boeing and McLaren have had more than a fair share of pitfalls and struggles getting the materials to really work.
Simply swapping one material for another to achieve a result is far from ideal. Yet engineers can fall into the trap of trying to make a like-for-like part and expect the lighter material to automatically give a part significant performance gain.
In an interview with Engineering Materials magazine, Dan Fleetcroft, technical director at Performance Engineered Solutions (PES) said, “I call it the black metal syndrome.
“If you have had no experience or exposure to composite materials, then there is a great potential for not getting the most out of it and you can actually cause yourself a lot of trouble trying to make a black metal part.”
First experiences with composites, particularly if they are unguided, can be disastrous. There are a number of common pitfalls that tend to catch engineers out. If you have limited experience with the materials, it is a good idea to talk to someone and get advice in either a formal or informal capacity.
“They don’t have to be involved in the final design but can go through the things to consider when designing a composite part,” says Fleetcroft.
“Things like tooling and moulding, fibres, resins; there is a vast amount to think about. You don’t want to invest a lot of time designing a part which is so difficult to manufacture it makes it uneconomical or impractical to produce.”
Composite parts often need specific tooling made for them and, though an actual part might be well thought out, the tooling specified may be ineffective or off the mark.
Additionally, experience counts for a lot when producing composite parts and knowing how to lay up the different sheets of fibre to optimise strength and stiffness for a specific application involves a real understanding of composites to unlock the full performance benefits of the material.
While some engineers think there is some black magic involved, it is the same as any material, it is knowledge and experience that will deliver the best results.
“You can tailor properties within a composite component that you can’t achieve in any other material,” says Fleetcroft. “But there is also a high degree of understanding required to make those parts optimised for cost, manufacture and performance.
“Joining steel parts together is obvious, but you might have a large, one-piece, composite part and, if the fibres are laminated in the wrong orientation, it could cause a catastrophic failure. Imagine if that is an aircraft wing.
“So, it also depends on the criticality of what you are doing. Most parts will actually perform OK with a generic layup, probably showing some improvement, but are they really optimised and exploiting what a composite can really do?”
Much of the time, composite parts are outsourced to specialist manufacturing shops to be made. This can be helpful in ‘sanity checking’ a part, as it is in their interest to make sure they can deliver what the customer expects. For this reason, it is not unusual for a specialist composite manufacturer to recommend changes to lay up, orientation of fibres or even combine components together to make a single part.
In some cases, manufacturing facilities ask for the designs and do the tooling themselves. They may even go so far as to specify a laminate or recommend ways of optimising the design further from a cost or structural basis.
It is important not to assume that if you have tried unsuccessfully to apply composites in the past that they do not work. Generally, the failure is through lack of knowledge and poor application. Advancements in composite materials and manufacturing techniques are continually developing and could very easily meet a performance criterion that may not have even been a consideration a few years ago.
See full Engineering Materials article.