For more than 7,000 Deutsche Bahn employees responsible for maintaining a fleet of several thousand vehicles, the storage and procurement of spare parts involves major challenges. 3D printing of components improves availability of hard-to-procure spare parts. The GEFERTEC 3DMP process was implemented for the first time as part of a pilot project.
“Availability is a big issue for our company,” says Dr. Tina Schlingmann, who started investigating potential applications for additive manufacturing at Deutsche Bahn last year. According to the materials science specialist, this technology is not only valuable in prototyping and tooling, it is especially valuable in the spare parts business. Deutsche Bahn purchases trains and locomotives and then handles vehicle maintenance in-house. One of the problems in servicing thousands of vehicles is that, for older locomotives, maintenance crews are often faced with the challenge of obtaining parts no longer supplied by manufacturers.
Nine months delivery time for wheelset bearing cover
Over the past few years, Deutsche Bahn has researched the possibilities of additive manufacturing in more than 100 use cases. According to Schlingmann: “Availability-relevant parts are especially important.” A recent case involved a wheelset bearing cover for a Class 294 locomotive, a model that was put into service in the 1960s and 1970s. The original casting has a diameter of 374 mm, a height of 78 mm, and weighs 11.5 kg. If the cover is missing, lubricant can leak out, resulting in damage to the bearing. In a worst-case scenario, this problem can cause the locomotive to derail. Delivery of the component takes up to nine months. During this time the locomotive is out of service, which leads to excessively high costs.
As part of a feasibility study, Deutsche Bahn worked on developing an alternative solution with Rolf Lenk GmbH, a medium-sized company that specializes in additive manufacturing. Last year, Rolf Lenk purchased a GEFERTEC arc605 machine that operates with 3DMP technology (see info box) and uses additive manufacturing to produce large components at high speed.
The 3DMP process cost-effectively produces near-net shaped metal blanks comparable to those produced using standard machining methods. The 3DMP process uses wire as a raw material that is welded layer for layer into the final workpiece.
This manufacturing process offers a number of advantages over 3D printing methods that use powder as a raw material. It eliminates the need for complicated powder handling. Plus, most standard materials are readily available in wire form at lower costs. But the biggest advantage is the high build-up rate of up to 600 cm3 per hour, depending on the material used. This makes the arc machine suitable for fast and economical production of larger workpieces made of steel, nickel-base, titanium or aluminum.
The arc machine is available in a 3-axis version for workpieces up to approximately 3 m3, a 5-axis version for workpieces up to 0.8 m3, and a compact 5-axis version for workpieces up to 0.06 m3. Specially developed CAM software uses the CAD data from the workpiece to generate the CNC data required for the exact positioning of the welding head.
Finishing can be done using conventional CNC milling technology. Material utilization in the 3DMP process is optimized to lower costs compared to other manufacturing processes – especially for high-priced materials like titanium. Depending on the application, manufacturing costs can be reduced by up to 60%.
3D data in digital format is not generally available for parts used on older rail vehicles. This makes reverse engineering necessary. After this step is finished, the 3D data must be processed for the GEFERTEC arc machine. The 3DMP CAM software used for this purpose generates special CNC data from the digital model of the part. The arc machine then creates a workpiece by successively adding welded layers. “Production on the GEFERTEC machine takes only about eight hours – including set-up,” explains Matthias Otte, project supervisor at Rolf Lenk. Afterwards, the near-net shaped component requires machining. From the initial design to reverse engineering and production, the project was completed within two months. Otte points out: “This amount of time is only necessary for the first-time production of a workpiece. Depending on machine availability, we will be able to produce this component in two to three weeks.”
The finished component was thoroughly tested by Deutsche Bahn as well as in the German Federal Railway Authority materials lab. “In addition to the usual material science analyses, testing was conducted using computerized tomography,” Dr. Schlingmann explains. The consistently positive results validated the high quality of the wheelset bearing cover produced using the 3DMP process. After the certification process for approving the component for use by Deutsche Bahn is complete, the part can be installed.
Vision of the future – the digital parts warehouse
As an alternative to operating complex and costly parts warehouses, the stockrooms could become digitalized. This would provide all required components in the form of digital files. The parts could then be produced as needed on the appropriate machines in an additive manufacturing process. Along with improving availability, this concept would significantly lower costs. In addition to manufacturing costs, it is important to take into account the costs of transport and storage.
Another factor is that critical components must be scrapped at the end of their service life. Dr. Schlingmann emphasizes the environmental impact of this approach: “Each component comes with a CO2 footprint that could be significantly reduced by additive manufacturing.” Therefore, the use of this technology for producing spare parts is perfectly in line with the Deutsche Bahn “That’s Green” environmental campaign.