Light aluminium manufacturing for high speed trains

A brief timeline of the use of light alloy semi-finished products in rail vehicles and the situation in Europe.

by Alberto Pomari

The history of the applications of aluminium with structural functions in the railway sector is relatively recent, just like the history of the production technology of this material. Apart from those uses which we could label as secondary, such as windows, mouldings and the like, the use of light alloys in the construction of carriages may actually be traced back only to 30-40 years ago.
Filippo Tommaso Marinetti in the Manifesto of the Futurist cuisine in 1931 stated: “…we are preparing an agility of Italian bodies adequate for the very light aluminium trains which will replace the current heavy iron, wood and steel ones”, a Verne-style, enlightened anticipation of the forthcoming future. Actually, little more than three years later, the world’s first prototype of a train made out of light alloy was produced, an example, surprising at the time, of the use of aluminium alloys in the railway industry: a train manufactured for the best part using aluminium alloys which covered the distance from Los Angeles to New York at the remarkable speed of 223 km/h, as shown by a film by Istituto Luce which may be easily found on Youtube. This prototype was presumably realized making wide use of metal sheets, assembled and riveted together. Unfortunately we do not have information in this respect, but it is undoubtedly recorded that the first light metal train was produced in a single specimen and was never mass produced. We must move on to 1963 to find the first example of an underground train made out of aluminium, the Subway in Toronto, Canada, opened in 1954, and the first case in the world to use, in 1963, trains entirely made out of light metal. Even in this case information available is scarce and it is presumed that the vehicles were always made out of aluminium-magnesium alloys, nailed and riveted. Towards the end of the 70s and the beginning of the 80s, extrusions of such alloys as 6000 Al-Mg-Si and Al-Zn-Mg began to be used for this type of use, to make structural parts of the carriages; these were preferred with respect to other families of aluminium alloys fit for plastic machining for the better combination of ease of extrusion, mechanical strength, resistance to weathering and ease of welding. In Italy one of the first high-speed trains which used extrusions in 7000 alloys to build carriages was the first of the large family of “Pendolino” trains, the FS ETR 401 model built by Fiat’s railway department in Savigliano. This model, even though it was created as a unique specimen in 1976, began to show that the use of aluminium alloys could definitely contribute to the lightening of the carriages, allowing a reduction of consumption and increasing the number of passengers who could be transported.
Successive examples are rather numerous and all main manufacturing companies have adopted aluminium alloys for some time now, for all types of rail vehicles, from high-speed trains, to Intercity trains, right up to light rail carriages. Meanwhile the development of new alloys, especially those in the 6000 family, allowed to create increasingly convincing and competitive design solutions. The 6005 alloy, suggested in many variations, is the one nowadays mostly used to produce the large extrusions for railway structures.
Today the enormous progress in aluminium machining is increasingly aiming towards cases made by assembling few elements known as large extrusions, which on their own make up the walls and roof of the case, and which do not require any type of structure apart from the simple single-block side. This technology has the advantage of cutting down costs of successive machining considerably, and of producing very light elements, to the extent that the case made up of extruded elements may be as much as a few tons lighter than a steel equivalent. Besides, it is possible to obtain a much more accurate respect of allowances (even of one order of magnitude), and a better surface finishing, eliminating the unsightly “bumps” typically formed as sheet metal settles down.

The European aluminium market in railway transportation
Even though it represents a market niche no greater than 2-3% of the total of final uses for extrusions, the railway market remains one of the most important and interesting segments for the development of extrusion technologies, for the selection of new alloys and above all for material assembly techniques. In the latter field, welding represents a technological test for all builders and extruders. Traditional MIG welding has nowadays been replaced by Friction Stir Welding or by the brand new Laser welding. But going back to the European market, the following graph shows the production of carriages in 2016, subdivided into three categories of high speed trains, Intercity trains and subway trains. In the case of High-Speed trains, the use of light metal per carriage is significantly greater, in percentage terms, with respect to the other types of trains. The graph shows the estimated production of aluminium carriages in the EU.
High-Speed trains stand out for the presence of larger extrusions (it is necessary to reduce the number of welded components to obtain greater strength for the structures) and for the great length of the carriages, up to 25 metres or more, with the exception of HS trains by Spanish manufacturer Talgo which use structural trolleys between carriages, cutting down to about 13 metres the length of the single carriage. Intercity trains, with an intermediate speed, may reach a speed of 200 km/h and normally carry a larger number of passengers with respect to the other categories. Subway carriages use on average from three to four tons of extrusions, except for builders only using aluminium for roofs or other parts of the structure. Germany is currently the European country with the largest production capacity. Siemens, Bombardier and Alstom have different production sites in this country. The Italian case is representative of the industrial occurrences of the past few year in our country. All plants have been sold to foreign companies: Ansaldo Breda to Hitachi and previously Fiat Ferroviaria to French-owned Alstom. We did not include Russia’s production, which has been increasing remarkably during these last few years; in this country investments in the railway sector could provide an exceptional drive to the European industry. In a market characterized by a reduced number of players it is not easy to find official statistical data, but we may in any case estimate an overall consumption of extrusions of about 30,000 tons per year, for about 90% used for structural purposes, while 10% is to be attributed to interiors applications, such as luggage racks, windows, tables, furniture etc. As may be seen from the graph, the market share which may be attributed to extra-EU producers is lower but still remarkable. Actually, in spite of all evident difficulties regarding logistics, producers from the Far East earned a sizeable market share, and it is easy to predict that this will grow on account of the competitiveness and consistency of the oriental supply. It is almost incredible that profiles in bars over 20 metres long and weighing about 600 or 700 kilos, or extruded panels, machined mechanically or actually welded, may reach us from so far at competitive conditions, both from a commercial and technological standpoint, but in any case this is the situation. The great competition which exists among train manufacturers is increasingly driving them towards relocation or outsourcing of components, and the absence of local content in calls for tender definitely does not help European aluminium producers.