Machining new materials in the aerospace industry: MÉCANUMÉRIC, expertise at the service of innovation
Why talk about machining new materials in the aerospace industry?
In terms of technical and technological requirements, the aerospace industry, driven by its perpetual quest for lightness, is one of the most advanced cutting-edge sectors. While the weight criterion has always been a determining factor in the constant process of innovation that underpins it, it should be noted that this increase in performance was essentially aimed at expansionist prospects. In short, how to do things bigger, further and cheaper.
Today, however, the objective is no longer so much to improve profitability as to ensure the long-term survival of the sector. As a result, the policy of MORE, driven by an abundance of resources, has given way to that of BETTER, which favours optimising their use, with a growing focus on environmental sustainability.
The use of new materials plays an essential role in this dynamic. Composites, thermoplastic polymers, light metals and super alloys offer significant advantages, such as weight reduction, increased resistance to wear and mechanical stress, design flexibility, improved comfort and safety, reduced maintenance costs and times, etc.
In the medium term, they offer significant potential for optimising manufacturing and operating costs, as well as environmental and energy costs.
The challenge of CNC machining of composites, light metals and polymers
Faced with such a reservoir of innovation, it's hardly surprising to see the emergence of strong competition among industrial subcontractors in the aerospace sector.
However, these materials not only provide solutions, they also pose challenges, particularly in terms of CNC machining, due to their structural complexity and specific properties.
The challenge therefore lies with the players in the supply chain, who will have to acquire or perfect their mastery of these technologies while maintaining their competitiveness, by reducing machining costs and increasing production rates.
This is where MÉCANUMÉRIC comes in.
Recognised as an international specialist in the design and manufacture of machine tools for the most demanding applications for 30 years, the company has become a key partner for the complex machining of composite and polymer materials in the aerospace industry.
It offers cutting-edge expertise and innovative CNC solutions tailored to the needs of its aerospace customers, including milling of complex aluminium and light metal parts, high-pressure water-jet cutting of composites, and thermoforming of thermoplastic and thermoset polymers.
Composites and their uses in aeronautics
The family of materials most representative of this race for innovation is undoubtedly that of composites. The evolution of their proportion in the materials mix of Airbus aircraft is an excellent illustration of this. In 1980, carbon fibre/epoxy composites made up no more than 10% of the structural weight of an A300, but 50 years later they now account for more than 50% of the structural weight of an A350-900 XWB.
Carbon fibre / Epoxy composites (CFRP)
Probably the most widely used category of composite, both in industry and in everyday use, carbon fibre/epoxy composites are mainly used in the manufacture of fuselages, wings, VTPs and HTPs. They are made up of layers of woven carbon fibres impregnated in an organic matrix, generally a polymer resin, which holds the fibres together and fixes them in their final shape.
Advantages:
Composite materials with an organic matrix are characterised by a highly advantageous strength-to-weight ratio. Thanks to their low density (1.8), high resistance to mechanical, thermal and chemical stresses, and design flexibility, they can be used to make complex, high-strength parts. They can be used to make complex and sometimes gigantic parts, while offering high resistance to impact and temperature.
The electromagnetic properties of these composites also enable RAM materials to be manufactured. Their laminar structure and the possibility of adding other materials to the mix (ferrites, iron oxide, etc.) give them the ability to modify or absorb electromagnetic waves, making the radar-equivalent surface area of devices virtually zero.
Carbon graphite composites (C/C)
Carbon/Carbon composites are manufactured by superimposing carbon fibre set in an organic binder, which is then subjected to pyrolytic treatment. The heat and pressure transform the organic compounds into almost pure carbon, which amalgamates into larger graphite crystals, giving the material its properties, particularly its extreme hardness.
Advantages:
In addition to the lightness characteristic of this family of materials, C/C composites are distinguished by their ability to retain their mechanical properties at temperatures that can exceed 2,000°C. They also have particularly good thermal conductivity properties. Although high in the fibre direction, even higher than that of copper under certain conditions, it is low in the transverse direction (Δ ^10-100).
For these reasons, they are mainly found in systems subject to the most intense friction forces, such as aircraft brakes, spacecraft heat shields and tiles, and certain jet engine components. Their properties enable them to limit the rise in temperature when high friction forces are converted into thermal energy, and to effectively dissipate the heat produced at the interface, in convective or radiative form.
Meeting the machining requirements of the aerospace industry
While the intrinsic characteristics of composites give them exceptional properties, it is important to note that they are also synonymous with sleepless nights for materials engineers.
Over and above the complexity of the lengthy and costly manufacturing process, what we are particularly interested in here are the difficulties posed by the machining of finished parts.
Yes, these materials present real challenges for those who undertake to work them without the appropriate methods and tools.
What's more, it's worth remembering that aeronautical machining requires extremely high precision with ridiculously low margins of error due to the critical nature of the components involved. As a result, machining composite materials for the aerospace industry requires specialised equipment and processes to ensure the quality of parts with a high degree of repeatability.
What are the difficulties in machining composite materials ?
Laminar structure and constitutive anisotropy :
The anisotropic nature of their structure is a real challenge for CNC machines and their tools. Composite materials can have variable properties due to the dispersion and orientation of the fibres, as well as their initial manufacturing quality. This makes machining composites more difficult, not only because the material properties vary from zone to zone, but also because the cutting forces generate shear forces and vibrations that can lead to delamination of the layers.
To overcome this phenomenon, the machining parameters need to be adapted and the vibrations need to be controlled.
A CNC machining centre designed to work with composites must be capable of fine-tuning the spindle power, rotation speed and feed rate dynamically to adapt machining to the strength of the material. This avoids problems such as excessive tool wear or damage to the part.
It must also be equipped with an advanced vibration control system to minimise the negative impact of vibrations.
Some examples of projects carried out for and by Mécanuméric customers in the aerospace sector:
Brittle nature :
While the carbon that makes up the fibre of composites is renowned for its high resistance to compression and stretching, this is not the case when it comes to torsion. It is this latter stress that is applied to the part of the material in contact with the spindle.
In order to avoid delamination and refine the surface roughness, the engagement of the milling tool must be carefully studied. Various techniques are employed for this purpose, such as up and down milling and high-speed machining.
Abrasive nature :
Carbon fibres are very tough and abrasive, which can cause rapid wear to traditional cutting tools. Special tungsten carbide or diamond tools are often required to withstand this.
What's more, the chips generated when machining composites can be problematic because, as well as being abrasive, they are also sticky and difficult to evacuate. They can damage machined surfaces, clog tools and cause unwanted vibrations. A CNC machine incorporating effective chip management is essential to maintain machining quality.
Heat sensitivity of EPOXIDES :
Some composite materials are sensitive to the heat generated during machining. Resins generally do not undergo deformation before 290°C. However, certain machining functions, such as milling, can reach local temperatures of around 900°C if nothing is done to limit the rise in temperature. The accumulation of heat can then lead to deformation, degradation or changes in material properties.
Special techniques, such as the use of coolants or high-speed dry machining, and temperature sensors are needed to preserve the structural integrity of the material.
The evolution of composite machining methods
Driven by the high potential of these materials, the machining of composites has undergone major changes over the years.
Milling composite materials
While traditional machining methods, such as drilling and milling, produced cracks and damage in composite parts, an innovative company in the CNC machining sector, such as MÉCANUMÉRIC, has developed machines and methods designed to meet the challenge of machining this family of materials, while complying with the requirements of the aerospace sector.
The MECAPRO NL 3-axis cutting and milling machine, designed for intensive industrial use, is a perfect example. With "catalogue" dimensions of up to 7,610 x 2,600 mm of usable travel (or more in customised design), it incorporates the advanced functions required for machining composites:
- high-speed machining
- lubrication,
- suction nose for swarf management,
- vacuum table to hold workpieces
- spindle power and feed speed control
- Shock and vibration sensors with alerts,
- temperature sensors with alerts.
Water-jet cutting of composite materials
At the same time, new cutting technologies such as water-jet cutting machines have enabled the development of vibration-free machining processes that produce high-quality results.
MECANUMERIC's range of CNC high-pressure water-jet cutting machines can be used to machine highly resistant technical parts in composites. Using pure water, or mixed with abrasive for the hardest of materials, the precise and powerful water jet performs high-precision cutting, even for complex shapes, while fully preserving the molecular structure of the material being cut. It's an ideal solution for applications requiring strict tolerances and a high-quality surface finish.
In addition to meeting the challenges posed by machining composite materials (anisotropy, hardness and abrasiveness), a machine like the MECAJET II has the luxury of being extremely versatile. It can cut a wide range of materials, from the softest to the most rigid, while maintaining micrometric precision.
Thanks to MÉCANUMÉRIC's technological expertise, composite materials are now more accessible to manufacturers, with faster processing times and greater repeatability.
MÉCANUMÉRIC: A CNC machining solution for every application
It should be noted that specific requirements vary according to the type of composite material, the geometry of the part and the machining conditions.
As a result, it is important to choose a CNC machining centre and machining parameters that meet the specific needs of the composites being machined.
MÉCANUMÉRIC is particularly committed to its duty to advise its customers, and provides them with access to the CARE service. Comprising more than 20 people who can be involved from the project design stage, they ensure that MÉCANUMÉRIC's expertise and know-how are passed on, so that every user gets the best out of their CNC machines.
The test unit, which supports manufacturers wishing to work with new materials or improve the quality/machining time of their parts, is particularly popular for the most complex applications.
