It's a hole new world

Mike Richardson discovers how Dormer Tools' new Research Technology Centre helps its customers out of a hole by providing an understanding of the structure and machining characteristics of composites.

Composite materials are becoming increasingly important in the manufacture of aircraft airframes, due largely to their excellent strength to weight ratio and corrosion resistance. And increasingly more aerospace companies embrace composite material technology, the need for this specialised knowledge increases. It is for this reason that Dormer Tools has invested in the creation of a Research Technology Centre (RTC) at the Advanced Manufacturing Park, Sheffield in collaboration with partners such as the Advanced Manufacturing Research Centre and Sheffield University.

Here, extensive development work on cutting tool geometries, substrates and coatings is carried out to address the machining issues presented by the laminate structure of composite materials, namely: delamination between layers at hole entry/exit; splintering – composite fibres breaking off or protruding at hole entry/exit; and composite fibres fraying into the hole. The theoretical and practical work undertaken by the RTC has already resulted in tangible advances in tooling technology.

“The Research Technology Centre is designed to help us to gain more knowledge and insight about composite materials,” begins Dormer's key account manager, aerospace and composites, Ricky Payling. “Although the reasons behind using carbon fibre composites for its strength to weight ratio properties are well understood, the machining of it can be difficult. The main focus for the RTC is to develop the right tooling to machine it efficiently and the machining strategies required in terms of educating people how to use the tools.”

Payling claims that if you consider the manufacture of composite parts, around 60% of machining applications concern drilling and holemaking for rivets and special fittings.

“A huge portion of the machining involves drilling operations; the remainder is milling, trimming or edge of part profiling and reaming,” he confirms. “Drilling is a big focus for Dormer, but we're also developing new milling cutters and reamers. The joining of composite structures is a black art itself and is still very much based on riveting. The present capabilities of adhesive joining technology would seem to indicate that this is unlikely to change for the foreseeable future.”

Keep them separated

The other issue vexing manufacturers is the problem associated with aluminium and composite materials sandwiched together in close proximity. Here, an adverse chemical reaction occurs and is the main reason why composite materials need coating so that they aren't directly in contact with the aluminium.

“This is why aircraft OEMs tend to favour titanium because it's lighter and stronger and can be used in harmony with composite materials,” Payling continues. “However, the problem here is that titanium is much harder to machine and when used with composites, will often need to be machined ‘dry'. This in turn creates increased heat, which can damage the composite material.

“Everyone is looking for the optimum solution for drilling composite and titanium stack material in one hit, problem free. Drilling the composite part of the sandwich is fine; the problems begin once you reach the titanium because you cannot drill it at the same speed and feed. The swarf can be really problematic and has abrasive properties that score and damage the composite material.

One solution would be to perform two- and three-shot drilling, which involves cutting a small diameter hole first and then gradually opening it out to finished size. Unfortunately this multiplies the amount of tools that can wear out.

Payling says another business reason for Dormer establishing its RTC concerns skills development and training: “A huge task for the RTC is to research these products and then train our technical sales engineers to ensure they have the competencies to demonstrate their knowledge and win this business. Dormer is working towards offering a total package which involves hand held, semi automatic drilling techniques, as well as different assembly processes too. However, many aerospace companies are now looking at the latest trends in automation by using robotics to try and improve accuracy and production.”

The composition of carbon fibre reinforced plastics presents issues of concern for the holemaking process. And as new material technologies evolve rapidly, Dormer is investigating the classification of carbon composites.

“This would make it easier to cross reference and categorise materials – as we do already with, for example, steel; the problem is that we still cannot classify composite materials very easily,” he notes. “There are just so many variations and structures in terms of the way that fibres are laid up in different directions - plus there is the use of different resins too. If we could classify each one, then we'd know which type of drill suits each grade of composite material and apply a set of speed and feed parameters based on its behavioural characteristics under machining conditions. New and very different materials are developing, such as Metal Matrix Composites (MMCs), so material technologies are challenging, and this places demands on us to find solutions.”

Working hand in hand

Payling notes that while the UK supply chain's thirst for composite manufacturing technologies continues unabated, some suppliers are struggling to keep pace with its rapid evolution. “Our roadmap will involve the continuous development of products and processes, not only for the design of tools, but for the machining strategies too,” he concludes. “New composite products present a challenge for any manufacturing process, so the RTC must work hand in hand with the manufacturing industry, disseminate this information to its employees and customers and help provide everyone with a core competence.

“Research into the structure and machining characteristics of composites is gathering pace and as such, the RTC places Dormer and its partners on a fast track to understanding these materials and most importantly, providing customers with tooling solutions that offer increased productivity, improved quality and reduced costs.”

www.dormertools.com
 

Related Articles

Good vibrations!

Providing custom-designed cutting tool solutions for composite components, Walter AG explains how vibration drilling can help guarantee high quality for stack machining.
7 years ago Features

It’s a material whirl!

Bindatex – Europe's only independent specialist in the precision cutting of advanced materials – is working with BAE Systems to create an agile UK supply chain. Aerospace Manufacturing reports.
8 years ago Features

Six of the best

Mike Richardson meets Velocity Composites' director Gerry Johnson and managing director, Darren Ingram to hear how the company's total kit provision of engineered kits for the aerospace industry is knocking material waste for six!
8 years ago Features
Most recent Articles

Carter enjoys success at HAI HELI-EXPO event

Acknowledged as the World’s largest vertical aviation conference and trade show, HAI HELI-EXPO 2024 provided precision bearing specialists Carter Manufacturing a perfect opportunity to exhibit its extensive range of aerospace bearing installation, removal and testing tools, along with PMA bearing options.
1 day ago News

Login / Sign up