RAIL
THE RIGHT TRACK
Angel Trains Data and Performance Engineer James Brown details the stringent compliance standards 3D printed parts must meet before installation within the rail sector.
N
o one is more trusted than a transport engineer; every minute, millions of people (at least in pre-pandemic times) turn their car’s ignition, fasten their aircraft seatbelt or board their train, putting their faith in the underlying engineering to see them safe to their destination. This trust is partly why when things do go wrong, it can be so shocking, yet it is the learning from such disasters, codified in countless standards and regulations, that makes the transport industry so safe and so trusted. The railway industry, as the oldest transportation industry, has the longest history of safety incidents to learn from. However, this means it also tends to have the most comprehensive compliance requirements, which can be a barrier to new technologies, such as additive manufacturing. Railway fire standards are the most stringent of all transport sectors; exceeding even those of aviation, driven by the rationale that even in case of a train fire the safest option is still to keep passengers onboard, moving carriages away from the fire. Hence trains are designed for very long fire survivability. These requirements are codified in the standard EN45545-2. Frustratingly for suppliers, the tests specified by EN45545-2 are bespoke, making it difficult to read across results from fire tests used in other industries. As a rule of thumb, 3D printed materials rated V-0 should meet EN45545-2 requirement set R24 – which allows parts of up to 500g. Currently, we have only managed to get two materials, ULTEM 9085 (black) and Antero 800NA, to meet all railway requirements allowing them to be used without constraint. The railways are also a high vibration environment, and this is
compounded by the very high duty cycles of our vehicles, with many of our trains running 20 hours a day for over 40 years. Hence fatigue performance of any structurally loaded part is critical. The load cases for design of rail vehicles in the UK are given in standard GM/RT2100. Meeting these are a challenge given the lack of fatigue data for most 3D printed materials. For parts fitted to the exterior of a vehicle, a further requirement is impact resistance due to the exterior of rail vehicles regularly being struck at high speed by rocks bouncing up from the track. The high duty cycle of rail vehicles also poses longevity challenges for 3D printed parts. Trains can see incredibly high passenger densities from the rush hour commute, to rowdy football fans travelling to a match. To survive this, 3D printed parts must be incredibly hard wearing and easy to clean, yet the post-processing and coating of 3D printed parts can be their Achilles heel, and this is the area we have struggled the most with in getting parts approved. For UK rail vehicles we require coatings with sufficient adhesion to meet a crosscut test with a score of 0 or 1 as specified by BS EN ISO 2409:2013.
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PEKK TESTED TO ISO 5658-2: 2006 SPREAD OF FLAME
have now taken a number of materials and parts through the process and are seeing numerous parts from train armrests to toilet components being rolled out across our train fleets. For new suppliers looking to enter the market we are always open to new materials that are cheaper or better than those we use currently, and with our partners in the trade body Mobility Goes Additive we can assist in getting new materials approved. However, we do expect those companies marketing “Industrial” solutions to have at least done some research and testing into compliance issues prior to approaching industrial customers.
While the above compliance requirements do seem onerous, they can be overcome. At Angel Trains we
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IMPACT TESTING OF COATED PEKK AT 82MPH
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