November 5, 2018 / Press Release

Lightweight construction in aeroplane interiors

Bucher and Ensinger develop composite-based series-produced components

Lightweight and high-strength materials have become indispensable for high-end applications in the aviation industry. In passenger aircraft every kilogram counts, which is why metals are increasingly being replaced with plastics-based solutions, also in interior design. Thermoplastic composites, in particular, offer companies kitting out aeroplanes significant weight reduction without requiring them to make compromises in terms of mechanical properties. A project by companies Bucher Leichtbau and Ensinger shows that making the switch to fibre-reinforced composites can provide additional technical advantages.

Bucher Leichtbau AG, headquartered in Fällanden (Switzerland), is a specialist for aircraft interiors and automotive equipment. Among other things, the aviation division of the corporate group develops and produces galleys and cabinets for passenger aircraft. A full module of this type can accommodate a load corresponding to eight times its own weight and has to be able to withstand accelerations that are at least nine times that of gravitational acceleration. Here, a distinction is drawn between flight loads (normal flight conditions such as take-off, landing, turbulence) and emergency landing loads (controlled emergency landing or aborted take-off). The required minimum operating life of the modules produced, is for example 25 years for Airbus and Boeing.

Initial situation: Material and installation costs

For safety reasons, all metal mountings for electrical plug-in connections in commercial aviation must be earthed. With electrically conductive, supporting structures in the Bucher aluminium galleys, an existing fastening screw equipped with the necessary corrosion protection measures is often sufficient.

If, however, the metal connector mountings are positioned on non-conductive structures in the galleys, an additional cable is required for the electrical earthing. This earthing cable must be secured at regular intervals which drives a requirement for additional fastening threads, spacer bolts, cable clamps and screws.

In addition to the material input for the cable routing, high costs arise for planning and installation: The design work includes making an entry in the schematic circuit diagram; what is more, a resistance measurement must be defined in the test plan for every earthing cable. This must also be incorporated into the relevant maintenance guidelines and operating instructions, as well as into the authorisation documents. During production, the contact resistance must be recorded and a corrosion protection coating be applied with every earth connection.

Metal substitute removes the need for earthing

The work and costs involved in an earth connection can be completely eliminated if the connector mountings previously made from metal are replaced by a non-conductive variant. Because of the operating temperature and fire safety requirements, however, it is not possible to use a low-cost, standard plastic.

For Bucher, the sought-after technical alternative needed to be capable of replacing a large number of existing sheet aluminium parts one-to-one so as to minimise the work and costs involved in switching when they were introduced. For this demand to be met, a rigid, high-strength material is required.

Owing to the relatively small quantities of the different connector mountings, a solution with high tool costs was not an option. Initial trials with locally remodelled parts made from fibre-reinforced, thermoplastic sheet material did not show satisfactory results in the remodelled zones.

Thermoplastic composite components

The breakthrough was achieved during their first cooperative venture with Ensinger GmbH. On the basis of Bucher's requirement specifications, the Otelfingen (Switzerland)-based Composites division developed a solution on the basis of thermoplastic fibre-reinforced composite. A pre-preg approved for the aviation industry with glass fibre and a PEI matrix (polyetherimide) was chosen for the material. After a brief optimisation phase, it was possible to manufacture the first series-produced parts. Because of the specialist processing techniques, two of the Ensinger’s sites are involved in the production of the connector mountings:

At the Otelfingen site, Ensinger's composite experts produce semi-finished parts in an angular shape from the PEI pre-pregs. Unlike comparable components, these blanks are not cut to size from a thick laminate and thermoformed but, using individual pre-preg layers, pressed in a tool into the defined form. Among other things, this process offers the advantage of reducing the springback effect.

The CNC processing of the fibre composite parts takes place at Ensinger’s subsidiary Trig Engineering Ltd in Bridgwater, Somerset (UK). Trig Engineering, which specialises in the production of precision parts from thermoplastic high-performance plastics and composite materials, operates in accordance to the aerospace AS9100 revision D standard and is a member of Ensinger’s international machining group. From the angular blanks produced in Otelfingen, Trig Engineering Ltd precision machine the connector mountings to final product specification.

For most fastening brackets there are several versions with different dimensions. Thanks to the flexible process, it is also possible to produce high-quality, special designs with contours or drilled holes and with short lead times.

Simpler, more cost-effective, and lighter

The manufacturing costs for the new plastic mountings are significantly higher than the previous version in aluminium. However, the savings in terms of engineering and production of the cabinets means that the new solution is still considerably more straightforward and importantly more cost-effective in total. As the galleys are lighter thanks to the use of composite components, the airlines benefit in the long term. Because every kilogram of additional weight which does not have to be taken into the air saves money.

Thanks to Ensinger's preform technology, differences in wall thicknesses are also possible when producing angles. So in a similar way to with a forked branch, the corner section under high strain can be reinforced, while in the sections which are not under as high strain (e.g. on the arms), material can be conserved. The manufacturing technique is referred to as the ‘near net shape’ process. Depending on the component geometry, significant material and weight savings are possible with this technology – whilst maintaining comparable strength and rigidity.

About Ensinger

The Ensinger group is engaged in the development, manufacture and sale of compounds, semi-finished materials, profiles and technical parts made of engineering and high performance plastics through extrusion, machining and injection moulding. With a total of 2,400 employees at 33 locations, the family-owned enterprise is represented worldwide in all major industrial regions with manufacturing facilities or sales offices.

About Bucher

Flying with a minimum of weight and a maximum of stability. This was the idea that shaped Heinrich Bucher's thinking when he founded the company in 1953. Today, we continue to apply his vision with our unique lightweight construction principle. And thanks to our years of experience working with aluminium and plastics, we are able to offer a diverse range of products, in which you can sense and feel what drives our company – an innovative spirit and an unwavering commitment to meeting specific customer requirements. Our goal is to develop more efficient solutions that achieve cost advantages for the customer. We do this at our sites in Faellanden (Switzerland), Everett (USA) and in Sinn-Fleisbach (Germany).

Our range of products is divided into four different application areas:
– Catering: Galleys for single aisle and long range aircraft
– Cabin: Stowage units, front row monuments, crew work stations, partition walls and doghouses; Seat components / furnishing (video systems, tables, consoles etc.)
– Medical Systems: Cabin interior solutions for air rescue and air ambulance aircraft; Stretcher systems for passenger aircraft
– VIP Interior: Interior solutions for VIP aircraft and vehicles (folding tables, on-board lockers etc.)

Among other things, Bucher develops and produces galleys for passenger aircraft. A full module of this type must withstand stresses at least nine times those from gravitational acceleration.
Ensinger's finished components. The connector mountings come in versions with different dimensions. Thanks to the continuous, straightened fibres, the thermoplastic composite material has significantly higher strength and rigidity than short fibre-reinforced plastics.
Before CNC processing: Blank for a bracket for a plug-in connection. Fibre composite consists of a pre-preg approved for the aviation industry with glass fibre which is embedded in a PEI matrix.
The connector mounting (centre of image) is the first joint project between Bucher Leichtbau and Ensinger. The series-produced part manufactured from glass fibre reinforced PEI in a variety of dimensions replaces an aluminium bracket previously used – which had to be earthed. The thermoplastic composite material is not electrically conductive, as a result of which the material and installation costs for the earthing cable previously needed can be eliminated. In addition, it was possible to significantly reduce the weight of the cable module as a whole.
Thanks to Ensinger's preform technology, differences in wall thicknesses are also possible when producing angles. Thus the corner section that is under high strain can be reinforced, while in the sections which are not under as high strain (e.g. on the arms), material can be conserved. With the aid of this near net shape technology a significant weight reduction is possible – whilst maintaining comparable strength and rigidity.

Your Contact for Editorial Questions

Jörg Franke

Ensinger GmbH
Phone +49 7032 819 202


Sonia Booz

Bucher Leichtbau AG
Faellanden, Switzerland
Marketing Manager
Phone +41 44 806 24 24