This work presents a literature study over how additive manufacturing can be used to improve the performance of windings for traction machines when it comes to materials, loss minimization and thermal management, especially for concentrated windings. It continues to present the additive manufacturing methods most suitable for additively manufacturing windings. The lessons from manufacturing coils with metal binder jetting are presented, concluding that some support structures are needed which can be chemically removed later in the process which means that the full detail capability of metal binder jetting can not be utilized fully. Finally different approaches to thermal management with additively manufactured coils are modelled. The results show that compared to direct air cooled windings, additively manufactured copper coils with direct cooling can increase the maximum current by 50 %. If aluminium (AlSiMg) windings are made with both additive manufacturing and improved end-turn cooling they can match the performance of non-AM direct air cooled copper windings. 

Interest in hard-turning is steadily increasing due to its obvious benefits in terms of desirable surface integrity and improved operational efficiency. Surface microstructural variations can occur during machining due to cutting speed, tool geometry, and process conditions. Th ese variations create nanostructured white layers (WL), categorized as mechanically induced white layers (M-WL) or thermally induced white layers (T-WL). This study explored the role of retained austenite (RA) content (<2%, 12%, and 25%) on WL generation in AISI 52100 bearing steel, offering insights for optimizing hard-turning. The findings showed that, regardless of RA content, samples exhibited M-WL with no dark layer beneath the white layer when utilizing a cutting speed (VC) of 60m/min using a fresh insert. Increasing tool flank wear to 0.2mm led to the formation of T-WL and surface tensile residual stresses in specimens with higher RA content (12% and 25%). This effect was also observed at 260m/min with a fresh cutting insert. Machining at 260m/min with a worn tool (VB) of 0.2mm resulted in T-WL and surface tensile residual stresses, independent of RA content. Additionally, a 0.2mm tool wear caused a significant shift in the maximum subsurface compressive residual stre sses to greater depths, irrespective of RA content. 

Additive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

An innovative component used for the cargo handling systems of Boeing 737 aircraft is developed to improve loaders’ working conditions and protect cargo spaces, passenger luggage, and goods from damage. Since the design of the component makes it difficult to manufacture using conventional techniques, metal Binder Jetting, an Additive Manufacturing technique both faster and more cost-effective compared to the conventional laser/electron beam techniques, is used. However, there is a risk of thermally induced distortion in connection with the post-processing, specifically the sintering step. To address this, a 3D computational fluid dynamics simulation model is developed and simulations are made to identify where and when unwanted distortions may occur during the sintering process. In the simulation, the sintering process follows about 15 hours full sintering cycle with all the heating, holding and cooling stages. The simulations are compared with experiments to validate the numerical results. 

Process parameters in laser-based powder bed fusion (LBPF) play a vital role in the part quality. In the current study, the influence of different novel scan strategies on residual stress, porosities, microstructure, and crystallographic texture has been investigated for complex L-shape parts made from nickel-based superalloy Inconel 718 (IN718). Four different novel scanning strategies representing total fill, re-melting, and two different sectional scanning strategies, were investigated using neutron diffraction, neutron imaging, and scanning electron microscopy techniques. These results were compared with the corresponding results for an L-shape sample printed with the conventional strategy used for achieving high density and more uniform crystallographic texture. Among these investigated novel strategies, the re-melting strategy yielded approximately a 25% reduction in surface residual stress in comparison to the reference sample. The other two sectional scanning strategies revealed porosities at the interfaces of the sections and due to these lower levels of residual stress were also observed. Also, variation in crystallographic texture was observed with different scan strategies. © 2022 The Author(s)

In the present study, a modified H13 hot-work tool steel (M-H13) was fabricated by laser beam powder bed fusion (LB-PBF). The effect of two types of post processing, direct tempering from as-built condition (DT) and conventional quenching followed by tempering (QT), on the microstructure and mechanical properties was evaluated. The typical microstructure in QT condition was tempered martensite with carbides along lath boundaries. In DT condition, melt pool boundaries and cellular structure from as-built condition were still observed. While comparable tensile properties and hardness were obtained, DT samples exhibited significantly lower impact toughness compared to QT samples. This was attributed to the difference in work hardening ability and strain rate sensitivity originating from different microstructures obtained under these two heat treatment conditions. The study was also focused on the softening behavior and the correlation with the microstructure of the two post treatments at the elevated temperatures. It was found that the DT samples showed lower thermal softening compared to QT samples. The evolution of carbides was discussed based on the microanalysis results and the JMatPro simulation. © 2021 The Authors

Powder bed fusion processes based additively manufactured SS 316L components fall short of surface integrity requirements needed for optimal functional performance. Hence, machining is required to achieve dimensional accuracy and to enhance surface integrity characteristics. This research is focused on comparing the material removal performance of 316L produced by PBF-LB (laser) and PBF-EB (electron beam) in terms of tool wear and surface integrity. The results showed comparable surface topography and residual stress profiles. While the hardness profiles revealed work hardening at the surface where PBF-LB specimens being more susceptible to work hardening. The investigation also revealed differences in the progress of the tool wear when machining specimens produced with either PBF-LB or PBF-EB. .

Additive manufacturing (AM) of large-scale polymer and composite parts using robotic arms integrated with extruders has received significant attention in recent years. Despite the contributions of great technical progress and material development towards optimizing this manufacturing method, different failure modes observed in the final printed products have hindered its application in producing large engineering structures used in aerospace and automotive industries. We report failure modes in a variety of printed polymer and composite parts, including fuel tanks and car bumpers. Delamination and warpage observed in these parts originate mostly from thermal gradients and residual stresses accumulated during material deposition and cooling. Because printing large structures requires expensive resources, process simulation to recognize the possible failure modes can significantly lower the manufacturing cost. In this regard, accurate prediction of temperature distribution using thermal simulations is the first step. Finite element analysis (FEA) was used for process simulation of large-scale robotic AM. The important steps of the simulation are presented, and the challenges related to the modeling are recognized and discussed in detail. The numerical results showed reasonable agreement with the temperature data measured by an infrared camera. While in small-scale extrusion AM, the cooling time to the glassy state is less than 1 s, in large-scale AM, the cooling time is around two orders of magnitudes longer. © 2022 by the authors

This paper investigates the characteristics and the formation of white layers and dark layers induced by hard turning of through-hardened AISI 52,100 steel. The investigation showed that different types of white layers exist e.g., formed predominantly through excessive thermal or mechanical energy loading. The thermally induced white layer is formed when the cutting temperature is above the critical austenitisation temperature for the material. The nano-sized microstructure is initiated through dynamic recovery, which transitions to dynamic recrystallisation when the temperature rises above the onset temperature for dynamic recrystallisation. The corresponding white layer is characterised by a higher retained austenite content compared to the unaffected material, and the presence of a dark layer beneath the white layer. The white layer and the adjacent dark layer are found to be ∼12% harder and 14% softer, respectively, compared to the unaffected material. On the other hand, the mechanically induced white layer is formed through severe plastic deformation, where the formation is controlled by dynamic recovery and results in an elongated and broken-down substructure. Neither austenite nor an adjacent dark layer could be found for such white layers. The mechanically induced white layer is ∼26% harder than the unaffected material. For both types of white layer, (Fe, Cr)3C carbides are found in the microstructure. The investigation shows that the heating rate, cooling rate, pressure, and duration of contact between the cutting tool and workpiece surface should also be considered to understand the underlying formation mechanisms. The characteristics of the examined white layers and the cutting conditions are summarised in a descriptive phenomenological model in order to create a systematic approach for the definition of the different types of white layers. 

With the improvement in technology, additive manufacturing using metal powder has been a go-to method to produce complex-shaped components. With complex shapes being printed, the residual stresses (RS) developed during the printing process are much more difficult to control and manage, which is one of the issues seen in the field of AM. A simplified finite element-based, layer-by-layer activation approach for the prediction of residual stress is presented and applied to L-shaped samples built in two different orientations. The model was validated with residual stress distributions measured using neutron diffraction. It has been demonstrated that this simplified model can predict the trend of the residual stress distribution well inside the parts and give insight into residual stress evolution during printing with time for any area of interest. Although the stress levels predicted are higher than the measured ones, the impact of build direction on the development of RS during the building process and the final RS distributions after removing the base plate could be exploited using the model. This is important for finalizing the print orientation for a complex geometry, as the stress distribution will be different for different print orientations. This simplified tool which does not need high computational power and time can also be useful in component design to reduce the residual stresses. © 2021 by the authors.