Keeping the Wheels Rolling

Image showing a Deutsche Bahn train

(Photo: Strandperle GmbH)

In a large-scale company project, Deutsche Bahn (German rail) is investigating 3D printing (additive manufacturing) as a costeffective, high-quality means of reproducing critical components. Owing to their exceptionally high durability and their broad spectrum of applications, silicone rubbers rank highly among the materials currently under consideration.

Germany’s Deutsche Bahn AG rail operator (DB AG) runs roughly 40,000 trains a day on a rail network spanning 33,400 kilometers. Keeping that fleet moving requires a sophisticated logistics chain and a constant supply of crucial components.

The railway network itself consists of the track route, permanent way, track bed, overhead power lines and power supply. And the varied nature of the vehicle pool is no less complex, explains Florens Lichte, who leads the 3D-printing project at Deutsche Bahn: “We’re dealing with over 100 years of railroad history – beginning with roughly ten different manufacturers and ending with over 100 different trains and models.” The ICE high-speed train alone has been operating since 1989 and is now in its fourth generation. “One of the greatest challenges we face, especially when it comes to spare parts, is the supply of materials,” Lichte points out.

Ensuring a consistent Supply Chain

In order to continue meeting this challenge going forward, DB AG launched a company-wide 3D-printing project in 2015. All the company’s divisions are involved in the search for new ways of leveraging this innovative production method to keep the trains and their logistics systems running. This includes 3D printing with silicone rubber compounds, as offered by the WACKER brand ACEO®.

The driving force behind the project is the maintenance division headed by Lichte, who carried out his first 3D project when he joined the company in 2014. Back then, he printed simple coat hooks, but the experience introduced him to the technology. Under his tutelage, those first coat hooks grew into 50 more applications in 2016 alone, for a total of 1,000 3D-printed parts. That figure doubled in 2017, and a specific goal of 15,000 items has been set for 2018.

The reason why railroad companies, of all businesses, would be eyeing 3D printing becomes clear when we take a closer look at the many ways the technology could be applied. The German rail network, for example, still has 800 entirely mechanical signal towers, and the complex process of modernizing them would simply not be worth the effort.

Both the infrastructure and the locomotive fleet require a constant supply of spare parts that, for a variety of reasons, can no longer be procured – either because production has been discontinued or because the supplier has gone bankrupt. As Lichte explains, the supply chain contains a particularly large gap: “We’re always running into problems with spare parts – especially when obsolete technology is involved. The depreciation period for a train is 25 years, but its service life can often be as long as 40 to 50 years. And generally speaking, manufacturers only guarantee availability of spare parts for 15 years.”

Screening new Technologies and Materials

Over the course of the project, Lichte’s team has to deal with a wide range of materials and production technologies, regularly screening the entire 3D-printing market to find new technologies and to determine how mature they are. Identifying parts and meeting supplier qualification requirements quickly push these mostly young companies to their limits. Parts have to comply with normative standards so that they can be used under live operating conditions. At present, Deutsche Bahn uses two material groups: metals and organic plastics.

Plastics represent the most widely used material for industrial-scale components ranging up to 60 centimeters in size. Up to now, DB AG has relied primarily on polyamides or polyether imides, often incorporating flame-resistant additives. The printed spare parts are mostly installed in non-safety-critical applications in the engine room or passenger areas; these include headrest casings, housing covers or clips for window blinds.

Silicone elastomers are an exceptionally good choice of material for applications in which plastics are subjected to significantly higher stresses. They are stable, yet elastically deformable plastics that yield to tensile and compressive forces and then return to their original shape – just like other plastics based on organic materials. Since silicone elastomers offer significant advantages over their organic counterparts in terms of stability and resistance to various influencing factors, DB AG is currently paying very close attention to 3D printing with this material. In addition to their remarkable resistance to thermal and thermo-oxidative stress, for instance, silicone elastomers are less sensitive to UV or electromagnetic radiation and withstand hot water and steam. These properties make them especially interesting for safety-critical applications.

“It’s particularly hard to find spare parts like diaphragms for brake components,” says Lichte. “We identified this as an opportunity for our project, and during the market-screening process, we came across ACEO®. They are one of the few partners offering elastomeric components we could take seriously.”

Joining Forces: DB’s Partnership with ACEO®

Initial contact in the fall of 2017 led to a joint workshop at the DB Fahrzeuginstandhaltung GmbH facility (full-service rail-vehicle maintenance provider) in Fulda, Germany, where DB AG and ACEO® developers and engineers met to begin discussions and identify potential applications and challenges. “The chance to share our expertise with Deutsche Bahn – just two years after we launched – is another milestone for us,” explains ACEO® project manager Dr. Bernd Pachaly.

As a result of this partnership, there are plans to make a brake diaphragm as an initial test part. The idea is to develop a diaphragm that can be installed as a component in the control valve of a train brake. Designed as an 11-cm-diameter, plate-shaped disk with a sealing lip, this diaphragm is relatively thin at just four millimeters, yet, as Florens Lichte stresses, it must of course meet the most demanding material requirements. “ACEO® silicones are definitely in a class by themselves,” he says. “Many competing products very quickly become brittle, making them unsuitable as train components. ACEO® offers us great potential not only in this one application.” Long-term testing is already in the planning stages, and both WACKER and DB are confident that they will find further areas to work on.

Advocating the Opportunities of 3D Printing

What ultimately matters is using innovative technologies like 3D printing to make sure the fleet keeps moving. Which is why DB AG intends to cooperate with suitable partners to create trailblazing solutions that can be integrated into dayto-day operations in the medium to long term. The project phase of the company’s 3D-printing initiative is expected to last until 2019, after which the results will be transferred to production. Until that time, however, their plan is to put new 3D-printing technologies to the test. “3D printing is perfect for producing a few individual parts or small batches that you need on short notice,” explains Lichte, who studied mechanical engineering and business administration. “In other words, the higher price tag for 3D-printed parts is not an issue if it means we can keep the materials flowing.”

Before that can happen, however, the variety of 3D-printing applications first has to be anchored in the minds of developers within the company. Lichte has so far conducted over 40 workshops at various sites, where the project team talks with participants directly to make them aware of the possibilities the technology offers, while collecting and following up on ideas from actual operations. What can 3D printing do? What are its limitations? What direction is the technology headed? To what extent has it already been applied on an industrial scale? What ideas have already been implemented in the company? Lichte and his DB team revisit these questions each and every day. “It’s easiest to just bring a sample part with me. If you want to make something tangible, nothing is more convincing than putting a printed part in someone’s hand.”