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Availability, Reliability Make the Case for 3DP

July 1, 2019
Sourcing hard-to-replace parts creates a new case for casting alternatives

Although foundries and diecasters continue to rely on the reliability of their designs and the quality of their products, the challenge presented by 3D-printed metal parts also involves service — the availability of a particular component on a schedule that suits the customer. So, while the global railroad market continues to demand tons of cast parts every year, the availability of locomotives, railcars, and trainsets is critically important in regard to rail traffic reliability. And that’s an opening for an alternative.

Deutsche Bahn AG has more than 7,000 workers employed to maintain several thousand vehicles, proving that acquiring and stocking spare parts involves major challenges. 3D printing is emerging as a significant advantage in sourcing of hard-to-locate spare parts. Recently, Deutsche Bahn resorted to the Gefertec 3DMP® process as part of a pilot project to improve its sourcing.

“Availability is a big issue for our company,” said Dr. Tina Schlingmann, a materials engineer who started investigating potential applications for additive manufacturing at Deutsche Bahn last year. She indicated metal AM is not only valuable in prototyping and tooling but is especially valuable in the spare parts business.

Deutsche Bahn purchases trains and locomotives and then handles vehicle maintenance in-house. One problem in servicing thousands of vehicles is that older locomotives present the maintenance crews with the challenge of obtaining parts that are no longer supplied by manufacturers.

Wheelset bearing cover — In recent years, Deutsche Bahn has researched the possibilities for additive manufacturing in more than 100 applications. According to Schlingmann, “availability-relevant parts” have been especially important to their investigations.

A recent case involved a wheelset bearing cover for a Class 294 locomotive, a model that entered service in 1966. 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 can cause a locomotive to derail.

For a foundry to deliver the replacement component would take up to nine months, and during that time the locomotive remains out of service, which leads to excessively high costs.

As part of a feasibility study, Deutsche Bahn worked to develop an alternative solution with Rolf Lenk GmbH, a mid-sized business specializing in additive manufacturing. Last year, Rolf Lenk purchased a Gefertec arc605 machine that operates with 3DMP technology, an additive manufacturing method for producing large components at high speed.

Gefertec arc machines use metal-alloy wire as a raw material in a process comparable to welding, with layers of material accumulating into the near-net shaped form of the finished part. The developer maintains this manufacturing process offers several advantages over powder-based 3D printing methods: 1) It eliminates the need for powder handling; and 2) most standard materials are readily available in wire form at significantly lower cost than metal powder.

The greatest advantage it claims is the high build-up rate — 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-based alloys, 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 sources CAD data detailing the part to generate the CNC data required to position the welding head. Then, the production of a near-net shaped workpiece is automatically completed by the Gefertec machine. Finishing can be done using conventional CNC milling. 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%.

The CAD data for parts used on older rail vehicles generally is not available in digital format, meaning a complete reverse engineering process is needed for some of Deutsche Bahn’s projects. 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. Then, the arc machine proceeds to form a workpiece as outlined above.

“Production on the Gefertec machine takes only about eight hours – including set-up,” explained Matthias Otte, project supervisor at Rolf Lenk. Afterward, the near-net shaped component requires machining. From the initial design to reverse engineering and production, the project was completed within two months. “This amount of time is only necessary for the first-time production of a workpiece,” Otte pointed out. “Depending on machine availability, we will be able to produce this component in two to three weeks.”

A finished wheelset bearing cover was thoroughly tested by Deutsche Bahn and in the German Federal Railway Authority materials lab. “In addition to the usual material science analyses, testing was conducted using computerized tomography,” Dr. Schlingmann explained. The consistently positive results validated the quality of the wheelset bearing cover produced by the 3DMP process. After the certification process for approving the component for use by Deutsche Bahn is complete, the part can be installed.

Digital parts warehouse — The feasibility study on using additive manufacturing for the wheelset bearing cover is just the beginning. Deutsche Bahn still has work to do in order to implement a standard process for sourcing replacement parts. As an alternative to operating complex and costly parts warehouses, the stockrooms could become digitalized, so that all required components are accessible in the form of digital files. Then, the parts could be produced as needed on the appropriate additive manufacturing machines. Along with improving availability, this concept would significantly lower costs, not only for manufacturing but also for transport and storage.

Another factor is that critical components must be scrapped at the end of their service life. Schlingmann emphasized the environmental impact of this approach, too. “Each component comes with a CO2 footprint that could be significantly reduced by additive manufacturing.”