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Innovative Welding Processes for New Rail Infrastructures

Periodic Reporting for period 2 - WRIST (Innovative Welding Processes for New Rail Infrastructures)

Reporting period: 2016-11-01 to 2019-01-31

The WRIST project has started from the needs of the railway transport: due to higher speeds, bigger axle loads and higher capacity demands on the infrastructure from both passenger and freigth transport, better life-cycle performances for the rail infrastructure, i.e. higher wear and rolling contact fatigue resistance will be needed. Advanced materials for rail construction with a better life-cycle performance are required (and have already been developed, f.e. the bainitic grades). However, it is felt that for these advanced rail materials the longevity of the welds would be increased by applying a welding process which creates very narrow heat affected zones, with optimum microstructure and properties.

Delivering this improved joint performance and reliability for the rails and its welds results in an extended in-service life, which in turn ensures a significant cost reduction for the maintenance of track, freeing up more capacity for rail traffic, including less unforeseen maintenance, and thus less delays for passengers and freight.

The project has delivered clear recommendations for the requirements on the geometrical shape of the weld, for use with the new, as well as direct exploitation on currently used joining techniques.

Two innovative joining technologies (automatic forged aluminothermic welding and orbital friction welding) have been developed and have shown promising results, with a smaller weld zone. This has also been shown on welds of bainitic rail grades (that possess greater resitance to the key degradation mechanism of rolling contact fatigue). However, further development of the two techniques will be necessary, before this can be directly exploited in track. Some of the auxiliary technologies developed with the AT process can be exploited directly, and can already ensure reduced maintenance costs and/or reduced maintenance time. Also, the equipment capable of orbital welding with intermediate component will open up potential applications in a wide variety of sectors.

The advances obtained in modelling will assist both the currently employed welding techniques, as well as the further development of the new technologies, resulting in a much reduced experimental optimisation phase.

With the orbital friction welding process it has been shown that it is possible to weld rail without using fluxes or shielding gasses, producing no harmful smoke, fumes or slag, therefore potentially reducing the overall environmental impact of track construction and maintenance. In future this will allow to be a key contributor to lowering the carbon footprint of railway transportation.
In the WRIST project two flexible and cost-effective joining processes for rails have been developed, with the aim to address the key degradation mechanisms experienced by welds in the current rail infrastructure.

The requirements for the joint properties and geometries have been established by a study comparing different standards for aluminothermic and flashbutt welding, coupled with analysis of measurements of a large number of weld profiles, work has been carried out to form recommendations with regards to requirements on the geometrical shape of the weld.

The first welding process that has been developed is the Advanced AluminoThermic Welding process, an adaptation of the currently used AluminoThermic Welding process, but using controlled compressive forces for improvements, This has been coupled with an enhanced cooling system, which can ensure that the total time for the track to be non-available for traffic can be reduced, as well as a weld finishing technology and a system for weld quality control and data analysis. All these anciliary technologies can also be used with the normal AluminoThermic welding process, resulting in some directly exploitable results.

The second developed joining process is the Orbital Friction Welding Process, with an intermediate component. This is a new variant of the friction welding process, which has been fully developed within the WRIST project, as well as design for a prototype, full scale machine, and construction and commissioning of this machine. As a solid-state welding process (no melting of the parent material), this is very different to the existing rail joining techniques, but offers a more energy efficient process, as well as being a very rapid welding technique. In this machine the rail stays stationary, the intermediate part performs the orbital motion that generates friction heat at the end of the rail profiles, which is then followed by a forging step. This technology has some unique selling points (also exploitable outside the rail industry, f.e. for large components, non-uniform materials).

To assist the development of both welding processes, finite element models have been established, and good progress has been shown in the validation process. For the orbital friction welding process, as well as the advanced AluminoThermic welding process, validated numerical FE-models are available, that can predict the microstructure in the weld zone, as well as the residual deformations and stress fields, thus assisting the weld quality optimisation.

Weld quality for both welding techniques have been assessed by destructive and non-destructive methods, leading to further recommendations for improvement of the welding processes. R260 welds established with the Advanced AluminoThermic welding process were tested in a double track freight railway in the Netherlands , providing data from track measurements, as a very realistic input for the analysis of the real-life performance of these types of welds. For the 350HT Advanced AluminoThermic welds laboratory testing was carried out to determine their in-service performance. Orbital Friction Welds in B360 bainitic grade underwent a more limited testing programme, focussed on the metallographical and hardness results.

The different technologies developed in this project have been assessed on their current exploitation level, the advanced cooling system is at the stage ready for commercial sale, with interested customers. The weld finishing technology is at prototype stage, ready to be tested by potential end users, the other technologies developed within this project have reached a ‘proof of concept’ stage, where further development will be needed to optimise the processes.
The project was disseminated via different channels, in order to reach a targeted audience, specifically with regards to Infrastructure Managers and contractors, the main possible users for these technologies.
input from the user interest group has shown that not only lower life cycle costs for track maintenance and renewal are seen as important, but also the process control on the welding process. With the two processes developed in this project very high process control systems have been put in place.

The orbital friction welding process has shown its benefits, like friction welding, therefore proving that rail joining without fluxes, shielding gasses, harmful smoke, fumes or slag is possible.