3D printing has been in professional use in industry for many years and enables a wide variety of products. Since the first commercially available 3D printer in 1988, which was based on the laser sintering process, a lot has changed to today’s methods and processes. The generic term for all this is the so-called “additive processes”, in which components are built up layer by layer.

Deutsche Bahn and all its suppliers also produce spare parts from metal and plastic using 3D printing. This can drastically shorten delivery times in particular. “In this way, we can ensure a better supply of spare parts and make the vehicles available to our passengers again more quickly. In particular, we are talking about parts that are associated with long delivery times or would no longer be available at all,” says Stefanie Brickwede (Project Manager 3D Printing DB).

Modern manufacturing processes include:

 

Printing process

3D printing (3DP). The material, which is in powder form, is given shape with an additional liquid binder and by means of a print head in what is known as the powder-binding process, similar to selective laser sintering. Excess powder is then extracted and can also be used to produce other components.

The desired 3D model is thus created through several hundred or even thousand layers. Both the powder and the binder can be dyed beforehand, giving the model the desired color.

Technique: Application of liquid binder on a powder bed
Material: Plastic, ceramic, metal, plaster, cellulose

 

Layer Laminated Manufacturing (LLM). Paper, metal or plastic foils are laminated together in layers and cut into shape using cutting tools (knife, hot wire, laser).

In the case of plastic films, these are bonded or polymerized; in the case of metal films, they are laser, diffusion or ultrasonic welded.

This process is particularly well suited for the cost-effective generation of solid components and large models, as they work quickly in relation to the component volume and are not very complex in terms of machine technology.

Technique: Bonding of foils in different layers
Material: Plastic films, paper, metal foils
 

Selective laser sintering (SLS) and laser melting (SLM). In selective laser melting, a powder-like material is applied in a thin layer to a base plate and completely remelted by a laser beam.

In the case of selective laser sintering, on the other hand, the material is not completely melted, but only melted on, whereby sinter necks connect the individual layers with each other.

Technique: Local melting of powdery materials by a laser
Material: Plastic, metal, sand, ceramics

 

Fused Deposition Modeling (FDM). The material, which is in solid form, is melted in a heated nozzle and then applied layer by layer to a building platform. This is a so-called extrusion process in which the material is melted from the solid phase and processed.

The material is usually acrylonitrile butadiene styrene (ABS), a plastic that is particularly suitable for heavy-duty applications.

Technique: Layer-by-layer application of molten material.
Material: ABS, wax, PLA, PC, PPSF
 

Stereolithography is the oldest additive process in which the workpiece is placed in a liquid bath of photopolymer into which it is gradually lowered. A laser passes over the starting material, liquid photopolymer, at each step to create the desired shape by curing.

After the part is fabricated, it is removed from the liquid bath and allowed to drip. The platform and all support structures are then removed from the component and the finished part is post-processed.

This makes it possible to produce filigree structures and smooth surfaces and is thus considered an extremely precise process.

Technique: Layer-by-layer curing of liquid polymers by means of a UV laser
Material: Acrylic and epoxy resins

 

3D printing in the DB Group

Corresponding design templates for a 3D printer are created from existing drawings or scanned objects. These templates usually consist of many individual vector graphics, which allow the desired component to be built up layer by layer. Then, for a metallic material, as described above, in the laser beam melting process, the material, which is in powder form, is applied in a thin layer to a base plate and completely remelted with a laser beam. This process is considered to be the best possible, especially for metals. In the selective laser beam sintering process, on the other hand, the metal is not completely melted, but merely melted on. By means of this procedure, the layers are not completely melted together, but only the so-called sintered necks. Of course, the SLM process offers better stability, but depending on the force exerted on the component, a decision is made between an SLM or SLS process, since each process has special properties necessary for the application.

Deutsche Bahn has also literally jumped on the bandwagon and has been producing its own spare parts for vehicle maintenance using 3D printing since 2014, among other things. Where in 2016 around 1,000 spare parts were printed, two years later this figure had already risen to 7,500 parts. The goal according to Sabina Jeschke, DB board member responsible for digitization and technology, was to produce up to 10,000 spare parts produced by 3D printing in 2021. But in the meantime, there are even more than 20,000 parts that have been printed in more than 180 use cases throughout the DB Group. Viewed in terms of the entire spare parts market, this would be just under 5%. In addition to simple coat hooks, ventilation grilles and headrests, the company also produces complex transverse damper brackets and an add-on part made of aluminum, such as the so-called box gate of an ICE, which is responsible for the safe running of the car in tight curves.

These components are sourced both internally and from external service providers. Particularly for components that are no longer available on the market, additive processes represent an economical spare parts management option for DB. This also makes it possible to produce small and very small batches of spare parts that are rarely needed. This in turn avoids delivery times and expensive storage costs.

For example, the delivery time for a metal printed box backdrop for an ICE2 can be reduced from around ten months to two months. The production time, i.e. the printing time for this part, takes around seven hours. However, there are also parts that have a production time of around 50 hours. This is followed by a subsequent assessment, testing and approval, which can then add up to around 28 days.

In the meantime, more than 130 different parts can be produced at the push of a button in railroad technology.

Another advantage of 3D printing, says Sabina Jeschke: “With the breakthrough in metal printing, we can now gradually ensure a faster supply of spare parts and the vehicles can be put back on the track quickly. Likewise, valuable raw materials are also saved, as large quantities of spare parts no longer need to be stored and the print-on-demand process means that only the raw material currently required is consumed. Production waste is minimized, inventories are reduced and transport routes are eliminated.8

In addition to Siemens, one of the spare parts suppliers in 3D printing for DB, ALSTOM is also exploring the possibilities of additive printing technologies. A global program called 3D4SPARES, which operates under the leadership of ALSTOM’s supply chain team, is exploring the possibilities of 3D scanning and printing as an expanded option for its spare parts and repair business. The team, which has close contact with research and development labs, universities, associations, 3D printer manufacturers and young companies, is primarily looking after the “rapid prototyping”, molds, direct manufacturing and repair application areas here.

For ALSTOM, the ability to respond quickly to customer requests, solving problems in spare parts procurement and reducing costs for small series have also been confirmed as advantages. The next step is to integrate this process into component production.

Dealing with new technologies requires qualification. For example, Deutsche Bahn has also been teaching the production of individual parts in a wide variety of 3D printing processes in its vocational training programs since 2019 in order to prepare trainees as optimally as possible for the requirements of the future working world. “The qualification courses are constantly being further developed and brought up to the latest technological standards. They thus form the basis for the development of innovations in the DB Group and are an important component of the umbrella strategy Strong Rail.” 10

 

List of sources

[1] Dreidimensionale Drucke (3DP): https://lkt.mb.uni-magdeburg.de/html/3dp/

[2] Laminated Object Manufacturing (LOM): https://www.lboro.ac.uk/research/amrg/about/
the7categoriesofadditivemanufacturing/sheetlamination/

[3] Selektives Laserstrahlsintern (SLS) und Laserstrahlschmelzen (SLM):
https://www.rioprinto.com/3d-druck-designrichtlinien-sla.html

[4] Fused Depostion Modeling (FDM): https://www.rioprinto.com/3d-druck-designrichtlinien-sla.html

[5] Stereolithografie: https://www.rioprinto.com/3d-druck-designrichtlinien-sla.html

[6] Mantelhaken: 3D-gedruckte Ersatzteile auf der Schiene, EisenbahnIngenieur 07.2017

[7] Additiv gefertigtes Aluminium-Anbauteil des ICE-Fahrmotors: 3-D-Druck bei der Bahn,
EisenbahntechnischeRundschau 12.2015

[8] deutsche Bahn produziert erstmals Ersatzteile aus Metall, Bahn im Bild 19.07.19

[9] Betriebsrelevante Ersatzteile on Demand, RailBusiness 15.07.19

[10] Starke Schiene – 3D-Druck: https://www.starkeschiene.training/3D-Druck 29.01.21