PSI - Issue 53

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Third European Conference on the Structural Integrity of Additively Manufactures Materials (ESIAM23)

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Third European Conference on the Structural Integrity of Additively Manufactures Materials (ESIAM23) Editorial Filippo Berto a * , Francesco Iacoviello b , Abilio De Jesus c , Jan Torgersen d , Sabrina Vantadori e

a Sapienza University, Roma, Italy b University of Cassino and Southern Lazio, Cassino, Italy c University of Porto, Porto, Portugal d Technical University of Munich, Munich, Germany e University of Parma, Parma, Italy

Keywords: Additive Manufacturing, Structural Integrity, Fatigue, Fracture

Additive Manufacturing (AM) offers the possibility to fabricate products and components with unprecedent design complexity and has the potential to become a diffuse manufacturing process in many strategic sectors from aerospace to biomedical. The future success of AM is strongly linked to our capacity to properly assess the structural integrity of Additively Manufactured parts. From one side the geometrical complexity places a fundamental role in this regard on the other side how to treat from a design perspective the defects due to the process itself is a key and open challenge. Aim of ESIS Technical Committee 15 (TC15) is to create a community working in the strategic topic of structural integrity of additively manufactured components, exchanging experience, transferring data and information. Linked to the activities of TC15 in 2019 the first European Conference on the Structural Integrity of Additively Manufactured Materials (ESIAM) was organized with more than 150 participants from more than 30 countries. In 2021 the conference was held online due to the pandemic. In September 2023 a new successful in presence event has been organized in Porto (Portugal) allowing ESIAM to reach its third edition with more than 130 participants from 25 countries.

* Corresponding author: E-mail address: filippo.berto@uniroma1.it

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This volume contains the works presented at ESIAM23 and is aimed to give an update state of the art on the topic of fracture and fatigue design of additively manufactured components. Different aspects of the design are touched giving to the possibility to have a quite complete overview on the recent developments in the field. The guest editors of this volume would like to thank all the authors, participants and reviewers. Without the hard work and commitment of this community ESIAM would have not been possible. See you soon in the next ESIAM conference.

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© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons. Keywords: High-feed milling; Additive manufacturing; Fluid supply; Internal coolant channel Abstract The automotive industry encounters daily challenges as it navigates through new design trends and technological developments, which drive companies to rapidly develop new models. This scenario paves the way for new manufacturing approaches such as additive manufacturing (AM) which is transforming the manufacturing industry by enabling the production of complex geometries while minimizing material usage. Regarding the cutting tools sector, AM enables the resource-e ffi cient generation of shapes and features that are not possible with conventional subtractive processes. This work explores the feasibility of AM, specifically Laser Powder Bed Fusion (LPBF), in the creation of a complex milling tool geometry with enhanced machining e ffi ciency and increased durability in cutting applications. The final developed tool incorporates internal conformal channels, high teeth number (relatively to tool size) within a hollow interchangeable body. The combination of (post-AM) brazed PCD (PolyCrystalline Diamond) inserts, which is the hardest cutting tool material available, with enhanced tribological conditions at the cutting zone (improved cooling and lubrication of the cutting edge) and increased number of teeth is expected to promote ideal cutting conditions, therefore extending tool lifespan, which is particularly relevant in the automotive industry, where lightweight design dictates the usage of metals such as aluminium. The remarkable durability of PCD in aluminium machining makes them an ideal choice as the active cutting zone for AM produced milling tool bodies. The typical relative small series of tooling (as compared to parts produced) supports the usage of AM, which in turn boosts e ffi ciency and cost e ff ectiveness of these cutting tools. The demand for aluminium parts is rapidly increasing as the automotive industry accelerates towards light weighting and electrification, creating a favorable opportunity for the implementation of the developed tool within the automotive industry. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons. Keywords: High-feed milling; Additive manufacturing; Fluid supply; Internal coolant channel Third European Conference on the Structural Integrity of Additively Manufactures Materials (ESIAM23) Additively manufactured milling tools for enhanced e ffi ciency in cutting applications Francisco Matos a, ∗ , Henrique Coelho b , Omid Emadinia a , Rui Amaral a , Tiago Silva a , Nelson Gonc¸alves a , Joa˜o Marouvo c , Daniel Figueiredo c , Ab´ılio de Jesus a,b , AnaReis a,b a INEGI, Rua Dr. Roberto Frias 400, 4200-465, PT b DEMec, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias 400, 4200-465, PT c Palbit S.A., Rua das T´ılias s / n, 2850-582, PT Abstract The automotive industry encounters daily challenges as it navigates through new design trends and technological developments, which drive companies to rapidly develop new models. This scenario paves the way for new manufacturing approaches such as additive manufacturing (AM) which is transforming the manufacturing industry by enabling the production of complex geometries while minimizing material usage. Regarding the cutting tools sector, AM enables the resource-e ffi cient generation of shapes and features that are not possible with conventional subtractive processes. This work explores the feasibility of AM, specifically Laser Powder Bed Fusion (LPBF), in the creation of a complex milling tool geometry with enhanced machining e ffi ciency and increased durability in cutting applications. The final developed tool incorporates internal conformal channels, high teeth number (relatively to tool size) within a hollow interchangeable body. The combination of (post-AM) brazed PCD (PolyCrystalline Diamond) inserts, which is the hardest cutting tool material available, with enhanced tribological conditions at the cutting zone (improved cooling and lubrication of the cutting edge) and increased number of teeth is expected to promote ideal cutting conditions, therefore extending tool lifespan, which is particularly relevant in the automotive industry, where lightweight design dictates the usage of metals such as aluminium. The remarkable durability of PCD in aluminium machining makes them an ideal choice as the active cutting zone for AM produced milling tool bodies. The typical relative small series of tooling (as compared to parts produced) supports the usage of AM, which in turn boosts e ffi ciency and cost e ff ectiveness of these cutting tools. The demand for aluminium parts is rapidly increasing as the automotive industry accelerates towards light weighting and electrification, creating a favorable opportunity for the implementation of the developed tool within the automotive industry. Third European Conference on the Structural Integrity of Additively Manufactures Materials (ESIAM23) Additively manufactured milling tools for enhanced e ffi ciency in cutting applications Francisco Matos a, ∗ , Henrique Coelho b , Omid Emadinia a , Rui Amaral a , Tiago Silva a , Nelson Gonc¸alves a , Joa˜o Marouvo c , Daniel Figueiredo c , Ab´ılio de Jesus a,b , AnaReis a,b a INEGI, Rua Dr. Roberto Frias 400, 4200-465, PT b DEMec, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias 400, 4200-465, PT c Palbit S.A., Rua das T´ılias s / n, 2850-582, PT

∗ Corresponding author. E-mail address: fmatos@inegi.up.pt ∗ Corresponding author. E-mail address: fmatos@inegi.up.pt

2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons 10.1016/j.prostr.2024.01.033 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons. 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons.

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1. Introduction

Metal cutting is characterized by high temperatures in the tool-chip interface zone which in turn promote wear and rapid deterioration of cutting tools. Cutting fluids are employed in machining operations to reduce friction, provide cooling, and remove chips from the cutting area. By implementing cutting fluids, tool wear is reduced and the ma chined surface quality is improved. Additionally, lubricants contribute to minimizing cutting forces, leading to energy savings (Dixit et al. (2011)). The considerable potential of additively manufactured cutting tools in terms of enhancing cutting fluid supply and the inherent tribological conditions at the cutting zone is highlighted by the utilization of cutting fluid supplied through targeted channels proved to be significantly more e ffi cient than conventional cooling (Lakner et al. (2019); Rahman et al. (2000); Zachert et al. (2021)). Coolant jets directed towards the cutting zone on the insert tend to act like a hydraulic wedge to lift the chip, shortening the contact length between the insert and the material, reducing cutting forces, temperature and improving chip control. Unfortunately, the design freedom of cooling channels is limited by conventional manufacturing methods, resulting in di ffi cult (often impossible) and time-consuming drilling of bore holes for the cutting fluid throughout the tool. Additive Manufacturing (AM) techniques, such as Laser Powder Bed Fusion (LPBF), are emerging as solution to unlock higher design freedom of internal complex shapes, significantly improving flow conditions while delivering fluid directed to the cutting edge. The ability to fabricate complex parts in one machine and job, made industries to establish AM as a certified end-user product manufacturing technique (Pereira et al. (2019)). In the highly competitive and rapidly evolving automotive industry, the need for e ffi ciency and durability enhance ment of the manufacturing processes is paramount. With the automotive sector increasing its use of parts manufactured from aluminium, the supply chain is challenge to deliver more productive milling operations. Despite 3D printing not being necessarily faster than conventional machining, it reduces the number of machines and processes required given that conventionally machined tool bodies require multiple subtractive operations (i.e. turning, milling, grinding), while post-processing of 3D printed tool bodies is typically limited to brazing the cutting tips into the tool body, followed by calibration of the cutting edges (which are common steps to both additive and subtrative manufacture of tool bodies). High speed machining (HSM) has been one of the most promising technologies in recent decades due to the combi nation of increased productivity and part quality (Gatto et al. (2011)). HSM traditionally makes use of high spindle speeds, specially when machining softer alloys such as aluminium, resulting in high material removal rates (MRR) thus increasing the productivity. Increasing feed rate and cutting speeds leads to a temperature increase at the tool-chip interface which make way to accelerated deterioration of the tool cutting edges (Santos et al. (2016)). The utilization of coolant in machining operations can lead to significant benefits in terms of dimensional accuracy and improved control of heat exchange. The direction of coolant flow must be carefully controlled to ensure it directly engages the cutting zone (Kui et al., 2022), made possible through additive manufacturing. This is especially important in high productivity scenarios allowing for in which spindle speeds and number of teeth are maximized (Singh et al. (2021)), enabling viable (high) table feed speeds while attaining good surface quality. This work explores the feasibility of LPBF in the creation of a complex milling tool geometry with increased number of teeth and conformal cooling chan nels within a compact tool body. To validate geometry and e ff ectiveness of the coolant channels in directing the fluid to the cutting zone, preliminary computational fluid dynamics (CFD) simulations were also performed.

2. Experimental procedure

2.1. Milling tool design

The integration of AM o ff ers a fresh and entirely novel approach to the design of machine tools. In the first step, a milling tool featuring a internal cooling channels, high teeth number relatively to tool size and a hollow interchangeable body was designed, shown in Figure 1. The external dimensions of this cutter are approximately 14 mm in height and 40 mm in diameter. The designed tool teeth number (12) largely exceeds the conventionally manufactured milling tools with similar dimensions since these generally have between 4 to 6 teeth. Each tooth incorporates a slot where a PCD (Polycrystalline Diamond) cutting insert will be brazed in AM post-processing. PCD

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was the cutting material of choice given its remarkable durability in aluminium machining, ensuring that this tool would have an extended lifespan. The tool features four through-holes that allow the connection between the cutter body and the milling tool holder by means of four DIN 912 M3 x 16 screws. An entrance channel featuring a circular cross-section with a diameter of d channel = 1.7 mm was defined for each cutting tooth. This entrance channel then divides itself into two channels that direct the fluid from the tool to each insert cutting zone. Sharp corners, abrupt changes of direction or channel diameter were avoided during the design phase.

Fig. 1: Three-dimensional CAD model of the additively manufactured milling tool showing constructive details.

2.2. Printing setup, material and parameters

The printing process starts with a pre-processing step where the scale, layout, position, and orientation of the part is set by the operator, and then finally transferred to the AM machine. The developed tools were printed using a GE Concept Laser M2 powder bed fusion system with a 245 x 245 x 350 mm build chamber. Process parameters and laser beam scanning strategies were implemented within the Materialise Magics software. Laser power up to 300 W, spot size of 130 µ m and a hatch space of 130 µ m were used. Layer thickness was set to 50 µ m , resulting in the deposit and melting of 362 layers of powder to achieve the milling tool. All printings were carried out in a nitrogen environment. Stainless steel AISI 316L was selected as the material for manufacturing the tooling prototypes given its good compromise between corrosion resistance, durability and printability. The production of two tool prototypes via laser powder-bed fusion took 2.5 hours.

3. Material and functionality assessment of AM milling tool

3.1. Material assessment

The chemical composition of the printed AISI 316L was evaluated by optical emission spectrometry using a spark emission spectroscopy, the SPECTROMAXX metal analyser equipment. Measured chemical composition is reported inTable 1.

Table 1: Chemical composition (wt.%) of 316L powder, measured and according to ASTM-F3184-16.

Element

C Mn P

Mo Fe

Min

16.00 10.0 2.0

Measured 0.020 1.40

< 0.001

< 0.001 0.68 16.78 12.42 2.35 Bal.

Max

0.030 2.00 0.045 0.030 1.00 18.00 14.0 3.0

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Material samples in the format of tensile specimens were produced in the same batch of the tooling prototype, allowing for further mechanical properties assessment. Tensile tests were performed on a 300 kN Instron 5900R testing machine. The experimental conditions are shown in Table 2. DIC (Digital Image Correlation) was employed in the tensile testing, o ff ering precise strain measurement and deformation analysis. An identical setup configuration to Cruz et al. (2020), ensured consistency in experimental conditions and data comparability.

Table 2: Experimental conditions for 316L AM samples.

Number of samples Gauge length ( L 0 ) Crosshead speed

20mm

2.5mm / min

Frequency of data acquisition 10 Hz

In Figure 2 engineering stress–strain curves for the 316L specimens are shown. The tensile testing revealed repeata bility and properties well-aligned with successfully processed additively manufactured materials and testing setups in literature Lec¸a et al. (2020). Table 3 summarizes the results of the tensile tests.

Table 3: Test resuls for 316L AM samples.

Sample Yield stress (MPa) Ultimate tensile strength (MPa) Elongation (%) 1 466.14 629.48 45.65 2 471.58 626.80 44.97

Fig. 2: Engineering stress-strain curves of AM 316L.

The transversal microstructure of AISI 316L manufactured using LPBF after polishing and etching with saturated Picral is presented in Figure 3. This microstructure has a fish-scale morphology, common in selective laser melted parts, without major defects such as porosities or inclusions Hou et al. (2020). Overlapping melt pools ensure that powder particles are totally fused together resulting in adequate layer bonding. Additionally, it is possible to see solidified melt pools encompassing elongated grains constituted by columnar and cellular dendrites a ff ected by the

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solidification direction. These results emphasise the e ff ectiveness of the LPBF process in producing components with mechanical characteristics similar (or even improved) to those manufactured through traditional methods.

Fig. 3: Optical micrograph showing the microstructure of 316L fabricated by LPBF.

3.2. Functionality assessment

The incorporation of brazed insert tips in the tool did not require additional machining step given the overall slot surface quality. The milling tool top surface (that contacts with the tool holder) was submitted to post-processing (machining and grinding) to remove support structures and to ensure its parallel alignment with the tool holder, thereby preventing any potential fluid leakage at the interface. In Figure 4 b) the additively manufactured milling tool body is presented, alongside with a picture of coolant channels, observed through a digital light microscope. In addition to visual inspection, destructive analyses of one part allowed to evaluate the internal channels, which revealed to be open and with the expected geometry. A sur face hardness of 210HV5 ± 11 was measured with a DuraScanG5 ZwickRoell hardness testing machine. External surface roughness, R a = 7.11 µ m and R z = 34.81 µ m , was measured with a portable Mitutoyo Surftest SJ-210R. The coolant channel internal roughness does not show abnormal roughness values and is comparable to the brazed tip slot roughness.

Fig. 4: (a) Cooling channel interior; (b) Additively manufactured milling tool body; (c) Tool body mounted on holder.

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4. Fluid supply CFD simulation

4.1. Numerical procedure

Conventional milling cutters coolant channels are usually conventionally manufactured which can result in sharp edges, which adversely a ff ect the flow characteristics of the cutting fluid. During the design phase, abrupt changes in channels direction were avoided, given that elbow geometries are susceptible to negatively impact lubrication flow control and its uniform distribution. Moreover, flow velocity increases with the decrease of the curvature radius of the pipe elbow, resulting in a more homogeneous lubricant flow Lakner et al. (2019); Lin et al. (2021). Several researchers were able to generate approximated solutions of coolant flow in the internals of cutting tools with the aid of computational fluid dynamics methods Lakner et al. (2019); Fallenstein and Aurich (2014); Biermann and Oezkaya (2017). CFD simulation was used to investigate the lubricant flow in the cooling channels and fluid interaction with the cutting insert zone, in order to validate if the lubricate was being e ffi ciently directed to the cutting zone. The CFD simulation software ANSYS FLUENT was used. Cutting fluid properties were simplified with the properties of water. The simulation of turbulent flow involves the application of turbulence models that rely on the Reynolds-Averaged Navier-Stokes equations (RANS). Hence, the RANS modelling significantly reduces the computational workload and resource demands, making it a widely adopted method for practical engineering purposes. The chosen turbulence modelwas κ − ω SST (shear stress transport), a widely used turbulence model which combines the favorable near-wall characteristics of the κ − ω model with the robust properties of the κ − ϵ model at free flow regions, such as inlets and areas far from walls Menter et al. (2003). The coupled method, that solves the momentum and pressure-based continuity equations together, was used as the solution algorithm. Average surface roughness was considered in the simulation of the coolant channel geometries.

Table 4: CFD simulation fluid properties

Property

Air

Water

Density, kg / m 3

1.225 998.2

Specific heat, J / kgK

4216

Thermal conductivity, W / mK

0.024 0.677 1.79e-5 0.001

Viscosity, kg / ( ms )

4.2. Coolant jet numerical characterization and experimental validation

To validate and find critical zones in the channel geometry, the cutting fluid velocity distribution within the coolant channels was simulated. The simulation revealed a higher tendency for the cutting fluid to flow through the lower channel. In an ideal design, the fluid would be evenly distributed between the two channels. However, it is evident that due to the design, the fluid encounters less resistance when exiting through the lower channel, following a more straightforward path and avoiding the directional changes observed in the top channel. This phenomenon is possibly created by fluid recirculation in the top channel. Despite this, the creation of separate lubricant entries for the top and lower cooling channel was not feasible due to the relatively small tool size and lack of space for independent channels. It can clearly be seen, that the designed channel geometries and the outlet location of the coolant channels leads to a focused coolant flow, directed to the active cutting zone. Simulation results correlated well with the experimental testing of the tool, confirming that the fluid was suc cessfully directed at the cutting zones, ensuring a good lubrication of the tool-chip interface. In addition, the fluid exiting by the lower channel exhibits a more concentrated flow, whereas the upper channel demonstrates higher fluid dispersion.

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Fig. 5: Cutting fluid velocity distribution: a) front view; b) half plane view; c) cutting fluid supply in operation.

5. Conclusions and future work

Additive manufacturing reduces the design constraints on coolant channel course, allowing to avoid sharp-edged transitions and enabling to direct the cutting fluid to the cutting edge. The presented work explored the feasibility of additively manufacturing a milling tool incorporating conformal refrigeration channels, high teeth number within a hollow interchangeable body. The following conclusions were draw: • The production of a milling tool featuring internal refrigeration channels with small diameters revealed to be feasible through LPBF. This research additionally validates and suggests the usage of a methodology for the production of specially design cutting tools (i.e. intricate geometries), highly relevant for small series production of milling tool bodies. • Additive manufacturing has allowed for the creation of an intricate and detailed part, featuring a significant number of small teeth, which would have been exceptionally challenging to produce using conventional man ufacturing methods. By consolidating the production of the tool into a single step, AM minimizes the need for intricate machining, thereby optimizing both time and resource utilization. It additionally validates the usage of a methodology for the production of specially design cutting tools (i.e. intricate geometries), highly relevant for small series. • The good alignment between the numerical and the fluid dispersion observations underscores the e ff ectiveness of computational fluid dynamics as a valuable tool for the design and optimization of coolant channels. The present work has highlighted the necessity for further research particularly in terms of experimental testing such as performance benchmark of the developed tool through milling tests with force acquisition and wear tendencies benchmark. Coupled with experimental testing, a detailed analysis of the vibration behavior of the cutting tool is also a future research topic. In further investigations the use of computer tomography could be used to better study the dimensional accuracy of AM internal channels. The surface roughness of the cooling channels did not appear to be considerably high, but given that lowering channel roughness would improve the cutting fluid supply, post processing of the coolant channels with abrasive flow machining can be considered a future research area.

Acknowledgements

The authors gratefully acknowledge the funding from Project Hi-rEV—Recuperac¸a˜o do Setor de Componentes Au tomo´veis (C644864375-00000002), cofinanced by Plano de Recuperac¸a˜o e Resilieˆncia (PRR), Repu´blica Portuguesa, through NextGeneration EU.

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1. Introduction 1. Introduction

Nowadays, the impact of the railway sector on the economy, social, and environmental sectors has been debated among governmental institutions. Regardless of the type of rail transportation, both freight and passenger trains point to be beneficial for the world’s future if the sector can compete with the other transportation industry. For the pop ulation, railway transportation is a good choice either for short, medium, or relatively long distance trips if they can provide comfort and good trip experiences. Additionally, since trains permit avoiding tra ffi c jams, the population has preferred the railway vehicle to travel to work. Still, the railway can be competitive with the aeronautical industry, since the waiting time to board can be quite inferior. Despite all the advantages that the railway industry can pro- Nowadays, the impact of the railway sector on the economy, social, and environmental sectors has been debated among governmental institutions. Regardless of the type of rail transportation, both freight and passenger trains point to be beneficial for the world’s future if the sector can compete with the other transportation industry. For the pop ulation, railway transportation is a good choice either for short, medium, or relatively long distance trips if they can provide comfort and good trip experiences. Additionally, since trains permit avoiding tra ffi c jams, the population has preferred the railway vehicle to travel to work. Still, the railway can be competitive with the aeronautical industry, since the waiting time to board can be quite inferior. Despite all the advantages that the railway industry can pro-

∗ Corresponding author. E-mail address: vtgomes@fe.up.pt ∗ Corresponding author. E-mail address: vtgomes@fe.up.pt

2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons 10.1016/j.prostr.2024.01.035 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons. 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the ESIAM23 chairpersons.

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vide, for being a competitive choice in the transportation industry, rail vehicles are required to be accessible to the population, fast enough without putting the passenger’s safety in danger. In the railway players and manufacturers, some concerns are related to the maintenance downtimes and own weight of the vehicle. In case of a lack of stock of vital components for operating, the vehicles can be disabled until the com ponent is repaired or replaced, which may cause some constraints since they need to be produced or requested by the manufacturer. Therefore, additive manufacturing, AM, has a large range of applicability since it permits manufacturing new spare parts at high speed and low cost, making AM an alternative more viable than conventional manufacturing processes. Moreover, AM can be applied for just-in-time production processes which might reduce significantly the need for large warehouses to keep thousands of individual spare parts for the case of failures of certain components still having a low failure probability (Makerverse (2022); Massivit (2022)). Taking into account these advantages, some players have invested in new technologies based on additive processes to improve the quality of their services. This short paper intends to introduce briefly the position of some railway players in relation to the application of AM for railway industry besides some application scientific studies of AM in railway rolling stock components.

2. Application Fields of the Additive Manufacturing in the Railway Rolling Stock

According to the literature and the current developed works, possible applications fields for AM in the railway rolling stock sector are in replacement, reparation, and development of new designs as schematized in Fig. 1 (Zhengkai et al. (2023)). 3. AM Applications

Railway Rolling Stock

Additive Manufacturing

New Designs Development of optimized geometries and materials with high strenght-weight ratio

Replacement of conventional or obsolete spare parts

Reparation of big size components (surface defects)

04 / 15 Fig. 1. Illustration of possible railway rolling stock manufacturing areas for additive manufacturing, (Zhengkai et al. (2023)).

2.1. Replacement of Spare Parts

Several players have been introducing the AM process in the production of spare parts for the replacement of conventional parts. Some of these replacements are made due to certain spare parts becoming obsolete. These changes have shown many advantages to players in the sector in terms of speed and production cost. In the case of SNCF, the major player in the French railway industry, AM has been integrated into the projects of spare parts. Its implementation allowed avoiding long downtimes and also increasing e ffi ciency in part stock management and reduce delivery times by 85 %. Also, Alstom implemented AM to produce new drain plugs of TPU 92A for tramways in the Algeriam Setif network. AM had a reduction in costs of 80 %. Additionally, AM was employed in the jigs and fixtures of electronic and electric parts, whose production took into account safety certifications for example EN 45545 standard (Zhengkai et al. (2023); Railway International (2022); KIMYA (2021); AMFG (2019)). Fig. 2 - A illustrates a pull-out box whose shell was produced by AM and additively-manufactured cable guides with safety

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certification illustrated in Fig. 2 - B and Fig. 2 - C. A few years ago, CAF manufacturing company developed the first light train integrating a series of additively-manufactured front-end components as shown in Fig. 2 - D. In the production of these components, advanced polymers were used (AMFG (2019)).

(

- -

)

Fig. 2. A - AMmed pull-out box shell (Railway International (2022)), B - AMmed cable guides (KIMYA (2021)), C - Application of AMmed cable guides (KIMYA (2021)), D - Front-end of a tram produced by additive manufacturing process, (AMFG (2019)); E - AMmed parts produced by fused deposition modelling (AMFG (2019)); F - Prototype of a seat for train manufactured by AM, (Madeleine (2022)). With respect to the interior of the train, AM has been also employed in the development of some components printed by fused deposition modelling, FDM, such as folding shelves, handles, armrests, and seats (see Fig. 2 - E) (AMFG (2019)). In the development of seats, the manufacturer states that joining AM process allowed to reduce in 90% the cost production (see Fig. 2 - F). Additionally, by optimizing the manufacturing process of these seats, the manufacturer reduced the time of manufacturing and assembling process by around five times (Madeleine (2022)). Other examples of AM applications are roll stops for railway carriages (VoxelMatters (2020)) and wheel-set bearing covers (AMFG (2019)). In the last example, the application of Wire Arc Additive Manufacturing technology allowed a reduction in production costs and production time of around 30%.

Fig. 3. A - Roll stops for railway carriages produced by AM with milling finishing (VoxelMatters (2020)), B - Near-net-shape wheel-set bearing cover (left) and a post-machined part (right) (AMFG (2019)).

A 3D-printed near-net-shape wheelset bearing cover

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2.2. Repair of Components

In operation or even during the assembling process, rolling stock components such as wheel-set, gear seat, and axle bodies might be damaged causing surface defects such as scratches, and dents, among others (Zhengkai et al. (2023)). Ignoring the appearance of these defects will reduce the mechanical resistance of the component, and might cause an early failure than expected. In order to avoid the replacement of such large components, the reparation of the damaged surface can be made by additive processes. The Directed Energy Deposition technologies, DED, has been used for rapid reparation of components damaged locally (Saboori et. al. (2019); Piscopo (2022); Lewis et. al. (2019); Hua and Zhou (2022)). For example, an axle train with a notch was repaired with laser cladding in the laboratory, as illustrated in Fig. 4 - A. The axle specimen was tested posteriorly under fatigue rotating bending conditions, not exhibiting significant di ff erences in the resistance among non-clad and clad specimens. Another application is found in (Zhu et. al. (2019)), where laser cladding was applied to repair local defects on railway wheels (see Fig. 4 - B).

Fig. 4. Laser cladding for reparation of: A - railway axle (TWI (2023)), B - railway wheel (Wila Laser Cladding Tech (2023)).

2.3. Development of New Design for Parts

https://www.twi-global.com/media-and- AM may be also employed in the development process of new designs of railway rolling stock parts. ALSTOM improved the design of anti-roll system support in train bogies by combining the topology optimization with selective laser melting, SLM, process reducing the weight by 70% (Alstom (2022)). Additionally, brake suspension links (see Fig. 5), secondary vertical damper seats, anti-snake damper seats, and lateral stops were also optimized in terms of weight and geometry permitting a weight reduction in 56, 72, and 27 %, respectively for the last three components (Zhengkai et al. (2023)). Due to the additive characteristics of the AM process, AM can be integrated with new computation methodolo gies in the manufacturing process, such as topological optimization and the development of components with lattice structures. Lattice structures along with topological optimization allow optimizing the weight of the components in order to maximize the the specific strength and specific sti ff ness. Structures such as aluminium honeycomb panels and sandwich panels are some examples of the lattice structures applied in high-speed train body floor and skirt plates (Guo (2022); Zhengkai et al. (2023)). In addition, additive manufacturing can be used in the production of molds. Accordingly Zhengkai et al. (2023), axle boxes produced from sand molds manufactured by AM allowed to reduce the production time in four times without a ff ecting the structural, geometrical and surface quality requirements.

2.4. A Future Perspective for AM in the Railway Rolling Stock

As presented in Fig. 1, the AM process may be applied in di ff erent applications, mainly in maintenance and new designs to increase the weight-strength ratio of the components. In accordance with presented in (Zhengkai et al.

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(2023)), AM technology may be introduced gradually over time, as the knowledge of AM in the railway rolling stock area also increases. For example, in the near-term, maintenance practices supported with AM for reparation and re placement of spare parts can be an option. In a medium-term, AM can be applied for the redesign of conventional parts supported with techniques of topological optimization and lattice structures. In longer-term, AM could be per fectly introduced in the new design of parts, and vehicles, and also renew the railway industry for example with the implementation of decentralization manufacturing.

Fig. 5. A - Suspension bracket of a dt4 brake calliper unit (TCTMagazine (2020)), B - Brake suspension link (Boissonneault (2019)).

https://www.tctmagazine.com/additive-manufacturing-3d-

https://www.voxelmatters.com/first-3d-printed-safety

3. Concluding Remarks

In this paper, some applications and ongoing practices of AM technology for the railway rolling stock sector were presented. Additionally, it was seen that AM can be gradually implemented as the evolution of knowledge of AM in the railway industry rises, since currently, there is not enough knowledge of AM in the railway rolling stock area. However, the implementation can be summarized in the three phases. In the first phase, AM can be introduced for the reparation of damaged components and replacement of obsolete spare parts. Then, for the redesign of lightweight parts and lastly, the design of lightweight trains with strong shifts in the manufacturing methods. In spite of this paper showing a promising future for AM in the railway industry, there is a notable lack of knowledge of the applicability of AM in rolling stock components. Nevertheless, this indicates that there is a wide range of possibilities to explore.

Acknowledgements

The authors thank to Research Projects:

• FERROVIA 4.0, with reference POCI-01-0247-FEDER-046111, co-financed by the European Regional Develop ment Fund (ERDF), through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020), under the PORTUGAL 2020 Partnership Agreement; • SMART WAGONS - DEVELOPMENT OF PRODUCTION CAPACITY IN PORTUGAL OF SMART WAGONS FOR FREIGHT with reference nr. C644940527-00000048, investment project nr. 27 rom the Incentive System to Mobilising Agendas for Business Innovation, funded by the Recovery and Resilience Plan and by European Funds NextGeneration EU;

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