Ever since the days of the Wright Brothers, and all through the history of aviation, reducing weight, increasing efficiency and improving safety have been central to the design of the modern aircraft. With economic considerations becoming more and more central to both aircraft designers and businesses, the replacement of traditional metals with plastics (both in the aircraft interiors and fuselage) is gathering pace. One long established company working in the highly skilled Northern Ireland aviation sector has come up with some new and interesting metal to plastics conversion options. Denroy Plastics (based in Bangor Northern Ireland) conducts much of its work within the Aerospace and Defence sectors, providing cutting edge technology for the building of a range of aircrafts.
Metal to Plastic conversion
As weight reduction is key to modern aerospace design, Denroy has developed products which reduce weight, costs and streamline the manufacturing process for aircrafts through converting metal components and assemblies to plastic.
Developments in the aerospace industry have resulted in a much higher usage of composite structures. Airbus state that their new A380 consists of at least 22% structural composites. Whilst 50% of the structural airframe within Boeing’s 787 Dreamliner is made of composite materials.
As one of the UK’s foremost providers of precision plastics injection mouldings, Denroy is the only global company integrating the material Victrex ‘PEEK ESD101’ within their processes. Victrex PEEK is one of the highest performing engineering thermoplastics in the world, its chemical, hydrolysis and high wear resistance makes it key to the metal to plastic conversion process.
Victrex PEEK enables Denroy to improve the integrity of Aerospace products and components whilst reducing the overall weight and cost of production. At the heart of this process is the continual introduction and improvement of engineered plastic resins which have the strength and durability to compete with metal. This process of conversion enables intricate processes like the moulding of plastic parts into complex shapes to be performed at a much lower cost than machining metal components.
In addition to cost and weight reduction, safety improvements are paramount within modern aerospace design. With any process as radical as that of metal to plastic conversion, risks do exist, thus, cutting edge research and development are key to understanding the properties of the materials used in cutting edge design.
In scenarios of potential danger, like lightning strikes, Denroy acknowledge that composite structures do not readily conduct away extreme electrical currents and electromagnetic forces (in the way metals do). Composite materials are either not conductive at all or are significantly less conductive than metals. For that reason, lightning strike protection (LSP) has been a significant concern since the first composites were used on aircrafts more than 30 years ago.
To date, conductive paths in composite structures have been established in one of the following ways: (1) bonding aluminium foil to the structure as the outside ply; (2) embedded one ply down in the composite structure.
As lightning strikes can attach to metal fasteners used in the composite structure, it is necessary to prevent arcing or sparking between them; thus, it is necessary to encapsulate fastener nuts in plastic caps to avoid such danger.
All of the services that run through these aircraft structures have traditionally been located or retrained using metallic brackets, which again can cause concerns with sparking. One solution is to use PEEK ESD101 (due to its properties as an advanced engineering polymer) for the manufacture of these brackets due to its specific surface resistivity. In terms of resistivity, PEEK ESD101 is dissipative; it offers tight control of surface resistance within the important ESD region of 106 and 109 Ohms/sq, thus providing a modern solution to potentially dangerous aviation scenarios.
Denroy apply PEEK ESD101 to the following products and components including;
- cable clamps assemblies,
- cabin air vents, and
- ammunition containers,
- shell nose cones,
- firing handgrips,
- missile components.
Denroy’s Chairman, John Rainey who has over 40 years’ experience in the aviation plastics field talked about his company’s ongoing work within metal to plastic conversions;
“Through the utilisation of materials like Victrex “PEEK ESD101”, we are the only injection moulding company worldwide using this grade of material for aerospace applications. We believe that the high wear resistance, excellent stiffness and Fuel / Chemical resistant creates a niche in the Aerospace market and effectively secures our future as a world leader in plastic conversion”.
Metal to plastic conversion allows Denroy to improve products via;
- Designing consolidate parts and creating additional performance features
- The ability to integrate complex shapes and geometries
- Combining materials using multi shot and insert moulding
- Developing high performance plastics with increased strength and durability
- Continually improving aesthetics
- Developing plastic materials which absorb impact and reduce noise
- The reduction of costs
- Reducing secondary operations, such as painting, machining or assembly
- Improving production consistency
- Reducing shipping and operating costs
- Reducing scrap and waste thus creating a more sustainable environmentally friendly production process
- Reducing labour and time, eliminating secondary operations and assembly
- Expertise in plastic injection moulding which creates a faster and more consistent manufacturing process than metal fabrication
A typical development project includes the following stages;
- initial concept generation
- the creation of 3D CAD models, material selection
- simulation of the moulding process
- procurement of injection mould tooling
- tool trials and full volume production
The example below shows the process in motion, with a simple redesign of a metal part with two threaded holes. Part has been replaced by an injection moulding and 2 clip nuts.
Density of aluminium = 2.7 g/cm³
Density of Fortron = 1.65 g/cm³
Weight saving of approx. 40%
See below for further examples of Metal to plastic conversion;
Original Metal multi-part assembly
New Design with snap fit coolant bottle
- Weight reduction of 70%
- Costing saving of 65%
- Less componentry
Denroy will soon begin work on the development of a 1,250 square meter aerospace centre of excellence including an 800 square meter production facility. John Rainey is determined that Denroy not only flourish but lead in the Aerospace centre through the development of world class R & D facilities; “We aim to commence building on our Aerospace centre of excellence by 2015. The centre will contain an ‘advanced materials R&D facility’ which will enable us to lead the way on plastic processes within the Aerospace sector.”
John Rainey concluded by stating that;
“Plastic products today are no longer regarded as second rate but are seen as items made of modern ‘space age’ material which are superior to the metal products that they replace.”