Named for the plates that it welds on to fixing elements, bigHead specialises in providing fasteners that are either surface-bonded or embedded in polymeric materials and composites. Polymeric composites are becoming increasingly popular due to their combination of rigidity and light weight, which makes them prized in electric vehicles, where component mass affects overall weight which can then limit range. Because vehicles utilise numerous subassemblies, the components must be able to join to others, and that means fasteners.
Embedding fasteners in composite materials, called ‘co-processing’, is more efficient than surface bonding, since it avoids the need for post-processing operations, as well as the complexity of adhesive specification and its related process engineering.
“For a customer it’s about efficiency and simplicity,” says Lawrence Cook, development engineer.
That’s the vision of the new project he leads, which can be traced back to CIMComp research at the university. This was originally conducted in cooperation with luxury carmaker Bentley, alongside which Cook worked during his time at Cranfield as a research fellow (he also did a PhD there). He recalls: “It was that work that taught us the massive challenges with embedding fasteners, such as resin ingress. At bigHead, we are applying this knowledge and expertise so we can determine where current products are going to run into problems, why this might be, and what the resolution is. What we’ve realised is that when you work holistically on the combination of mould-tooling, process integration and the fastener product concept, this is powerful in yielding solutions”.
Frequently, customers looking to create threaded fastening connection points within a composites component might only consider post-process installation techniques as a viable solution. An example might be designing in a boss feature or creating a pre-hole into which they would install a suitable fastener in a secondary operation. However, some features can prove difficult to form in the moulding process, and hole preparation is not always feasible.
The usual disadvantage of adding fasteners into the moulding process is resin ingress into the threaded portion of the fastener. As a result, part manufacturers working with bigHead fasteners in composite materials may resort to using protective caps, and then removing them after moulding. One customer that does PUR [reinforced polyurethane] mouldings for Mercedes Benz makes a part incorporating 17 bigHeads. Just screwing on the protective caps that go into the moulding takes 20-30 minutes, raising labour costs and decreasing part throughput. Developing a solution to this challenge inspired bigHead to consider applying the solution to other materials and processes. This was initially trialled and demonstrated in an SMC (sheet-moulding-compound) composite moulding with industrial partners as part of a UK-based industrial research project.
During summer 2022, students working with the company in the Cranfield Enhanced Composites and Structures Centre have successfully demonstrated production of an SMC composite compression-moulded part with two bigHead fasteners embedded which remained uncontaminated through the pressing (pictured).
That success built on a previous study project at Cranfield, one that successfully refined and demonstrated the concept of a specially-designed cassette within the tooling. Due to the small size of the tooling, it was difficult to extract learning from this work about material flow around the head of the fastener. However, it did allow bigHead and Cranfield to refine, develop and validate the sealing concept together. Reflects Cook: “Because we understand what’s happening in that tool, we know where the resin’s going to try to go. We’ve worked with the material and parameters our customers are going to be working with.”
He admits: “You wouldn’t believe how many times we have got it wrong, and how much time Krutarth [Jani, a Cranfield University research fellow] and I spent refining the design details of both the cassette and the fastener as a matching system. That’s what a customer would have to go through if we hadn’t done it, so that’s our value-add. If someone asks, ‘How do I create the sealing solution for a bigHead product in my tool?’ We can now tell them exactly how, whereas two years ago we couldn’t.”
THE BIGGER PICTURE
It’s a positive step for the manufacturer, but just one of many, Cook explains, owing to the complexity of the composite supply chain. Named for its multiple elements, composites usually consist of a polymeric material, such as epoxy or polypropylene, and a reinforcement such as glass or carbon fibre that imparts rigidity. The fibres themselves can be continuous (as seen in laminates comprising woven or non-woven reinforcements) or they can be discontinuous (as seen in SMC and injection moulding polymers). This often requires different solutions for different materials and processing concepts – something bigHead is acutely aware of. Cook continues: “With laminate materials comprising fabrics or tapes, the biggest question is how you integrate a fastener into the material or preform, in an efficient and repeatable manner. Sometimes there are insurmountable challenges to any proposed solution: it’s too slow, it causes fibre breakage, or the reinforcement is just too tightly packed.” It is well known that such issues are par for the course with composites.
The fasteners themselves are no simpler. In comparison with screws, nuts or other standard fastening products, where suppliers can offer reams of information about tightening torque, preload rules, and installation, bigHead fasteners cannot be categorised in the same way. Many of bigHead’s products are designed to be as thin as possible: this requires special consideration when it comes to assembly design, in terms of loadability and tightening torque.
Co-processing poses another challenge. “Not only do you have to determine the correct product, but you also have to develop the method of getting it in there, and that’s not described by rules,” Cook observes.
Enter Cranfield, and in particular its composites centre, whose principal composites manufacturing research fellow is Andrew Mills, under whom until recently was former student Oli le Marquand-Brown. He has joined bigHead after finishing his master’s degree last year, augmenting the capabilities that Cook can offer. Le Marquand-Brown says: “By working with Cranfield, we learn what to point out to the customer. Because we’ve gone through a process already, we are likely to have discovered the pain points. This means we can discuss these right at the start of the project, avoiding a situation in which we have produced the right product for the customer, but when they try to process it they run into unforeseen difficulties.
“We’re looking at the common challenges in using our products, understanding why they are challenging and developing resolutions. Cranfield is the perfect place for this, with people that understand the materials and the customer experience, together with young students and researchers without preconceived ideas. They are free-thinking and may use the experience they might have gained in automotive engineering or aerospace engineering to say, ‘I can see a way to do this.’”
He continues: “If you want to build understanding on a composite engineering topic, there is no better place to look. For instance, should you need to discover how SMC material flows around in a tool, there are probably over 30 papers available here to be digested, and the knowledge applied to further research.
The company’s connection with Cranfield University began in earnest with a formal Knowledge Transfer Partnership, or KTP, programme, about five years ago, now completed. That project showed the value of working with the university, which was originally founded as the College of Aeronautics in 1946, and now focuses exclusively on postgraduate education, with a strong focus on engineering.
TARGETING STANDARD PRODUCTS
The strategic cooperation fits into bigHead’s broader marketing plan, to organise its product range and bring some simplicity to composites customers that have enough on their plate keeping up with ever evolving materials, processes and supply chains.
The company, which has some 4,500 bigHead product designs on its books, has organised a ‘core range’ of 152 products, producing guidance and case study material that is published and available for download in its online ‘TechHub’. bigHead is looking to expand on this approach later this year.
The overriding goal for bigHead is to enable customers to make better informed decisions, earlier in the design process. As Cook puts it, “We always want to be able to say to the customer, yes there are some details to go through, but in principle this is what you can expect. Here it is; here’s how you do it; and we can provide you some guideline data for it. This seems to be working well for us, and our Bossard colleagues tell us that is a huge value-add.” (The Swiss fastener and logistics conglomerate bought bigHead in 2014.)
Now, bigHead hopes to extend its knowledge base by placing Cook and le Marquand-Brown on the doorstep of Cranfield University’s facilities and expertise – the two recently moved into an office within Cranfield University Technology Park.
“The process of application engineering starts with engaging with the customer’s production problem,” explains le Marquand-Brown. “We’ll talk about the fastening requirements and identify the right product and then we’ll talk about how to get it into the customer’s tooling. We’ll agree if they, or we, will make the cassettes. We’ll always be aiming to work at 80% demonstration, and 20% refining final details.”
The SMC tooling project is a case in point of how Cranfield supports this 80:20 approach. If Cook and le Marquand Brown have an idea about how to seal bigheads to prevent resin ingress, they can test this within Cranfield’s laboratories. If it works, they can they go away and further develop the idea for customer use. Cook explains: “Rather than develop a bespoke product from a blank sheet every time, we will be able to tell the customer that there is a standardised offering and that we can provision for it within your tooling and production.”
Cook concludes: “The level of customer service that we are providing is invaluable, being based on multiple sources of expertise. Solutions, as in how to process the fastening, usually require some input from the tooling guys, some from the design guys and some from the assembly guys. Our unique ability is that we are happy to engage at the design level and then talk to a different group of stakeholders doing the moulding, so we know what they are designing. We’ll help get the fastener into the tooling, and when it gets down to final assembly, we’ll also help the guys understand how to fasten on to this bigHead, so we support across all three activities.”
