Editor’s Choice Articles

Freeform carbon fibres were 3D-printed from CH₃OH:H₂O mixtures using hyperbaric-pressure laser chemical vapour deposition (HP-LCVD). The experiment overlapped a region of known diamond growth, with the objective of depositing diamond-like carbon without the use of plasmas or hot filaments. A high-pressure regime was investigated for the first time through the precursor’s critical point. Seventy-two C-fibres were grown from 13 different CH₃OH:H₂O mixtures at total pressures between 7.8 and 180 bar. Maximum steady-state axial growth rates of 14 µm/s were observed. Growth near the critical point was suppressed, ostensibly due to thermal diffusion and selective etching. In addition to nanostructured graphite, various carbon allotropes were synthesised at/within the outer surface of the fibres, including diamond-like carbon, graphite polyhedral crystal, and tubular graphite cones. Several allotropes were oversized compared to structures previously reported. Raman spectral pressure–temperature (P-T) maps and a pictorial P-T phase diagram were compiled over a broad range of process conditions. Trends in the Raman I_D/I_G and I_2D/I_G intensity ratios were observed and regions of optimal growth for specific allotropes were identified. It is intended that this work provide a basis for others in optimising the growth of specific carbon allotropes from methanol using HP-LCVD and similar CVD processes. Full article

The wettability and high-temperature mechanical properties of porous BN/Si₃N₄ ceramics brazed with SiTi22 (wt. %) filler were studied. It is manifested that SiTi22 filler presents remarkable wetting and spreading capabilities on the porous BN/Si₃N₄ ceramic surface. An interfacial reaction layer is generated at the interface, and the thickness of the reaction layer initially grows and subsequently remains constant with the escalation of temperature. Carbon coating modification is beneficial to the wettability and high-temperature mechanical properties of porous BN/Si₃N₄ ceramics. The wetting driving force is mainly controlled by the interfacial reaction at the three-phase line of the wetting front. The mechanical properties of the carbon-coated joints are significantly enhanced in comparison with uncoated joints. The joint strength attains a maximum value of roughly 73 MPa in the shear test implemented at 800 °C. The strength of the joint is significantly enhanced mainly due to the TiN_0.7C_0.3 particles that consume energy by changing the crack propagation direction, and the SiC nanowires strengthen the connection by bridging. Full article

The effects of minor additions of the transition elements Zr, Ti, and V on the microstructure, mechanical properties, and out-of-phase thermomechanical fatigue behavior of 224 Al-Cu alloys were investigated. The results revealed that the introduction of the transition elements led to a refined grain size and a finer and much denser distribution of θ″/θ′ precipitates compared to that of the base alloy, which enhanced the tensile strength but reduced the elongation at both room temperature and 300 °C. Constitutive analyses based on theoretical strength calculations indicated that precipitation strengthening was the primary mechanism contributing to the strength of both tested alloys at room temperature and 300 °C. The out-of-phase thermomechanical fatigue test results showed that the addition of transition elements caused a slight decrease in the fatigue lifetime, which was mainly attributed to the reduced ductility and higher peak tensile stress at low temperatures. During the fatigue process, the transition element-added alloy exhibited a lower coarsening ratio, indicating higher thermal stability, which mitigated the negative impact of the reduced ductility on the fatigue performance to some extent. Considering their various properties, the addition of Zr, Ti, and V is recommended to improve the overall performance of Al-Cu 224 cast alloys. Full article

Several challenges arise during edge trimming of carbon fibre-reinforced polymer (CFRP) composites, such as the formation of machining-induced burrs and delamination. In a recent development, appropriate-quality geometric features in CFRPs can be machined using special cutting tools and optimised machining parameters. However, these suitable technologies quickly become inappropriate due to the accelerated tool wear. Therefore, the main aim of our research was to find a novel solution for maintaining the machined edge quality even if the tool condition changed significantly. We developed a novel mechanical edge-trimming technology inspired by wobble milling, i.e., the composite plate compression is governed by the proper tool tilting. The effectiveness of the novel technology was tested through mechanical machining experiments and compared with that of conventional edge-trimming technology. Furthermore, the influences of the tool tilting angle and the permanent chamfer size on the burr characteristics were also investigated. A one-fluted solid carbide end mill with a helix angle of 0° was applied for the experiments. The machined edges were examined trough stereomicroscopy and scanning electron microscopy. The images were evaluated through digital image processing. Our results show that multi-axis edge-trimming technology produces less extensive machining-induced burrs than conventional edge trimming by an average of 50%. Furthermore, we found that the tool tilting angle has a significant impact on burr size, while permanent chamfer does not influence it. These findings suggest that multi-axis edge trimming offers a strong alternative to conventional methods, especially when using end-of-life cutting tools, and highlight the importance of selecting the optimal tool tilting angle to minimize machining-induced burrs. Full article

This paper systematically explores the applications of image processing techniques in machined surface analysis, a critical area in industries like manufacturing, aerospace, automotive, and healthcare. It examines the integration of image processing in traditional Computer Numerical Control (CNC) machining and micromachining, focusing on its role in tool wear analysis, workpiece detection, automatic CNC programming, and defect inspection. With AI and machine learning advancements, these technologies enhance defect detection, surface texture analysis, predictive maintenance, and quality optimization. The paper also discusses future advancements in high resolutions, 3D imaging, augmented reality, and Industry 4.0, highlighting their impact on productivity, precision, and challenges such as data privacy. In conclusion, image processing remains vital to improving manufacturing efficiency and quality control. Full article

The finite element modeling method has been widely applied in the modeling of the cutting process to characterize the instantaneous and microscale deformation mechanism that was difficult to obtain using physical experiments. The lubrication and cooling conditions, such as minimum quantity lubrication and cryogenic liquid nitrogen, affect the thermo-mechanical behaviors and machined surface integrity in the cutting process. In this work, a grain-size-dependent constitutive model was used to model orthogonal cutting for Ti-6Al-4V alloy with MQL and LN₂ conditions. The cutting forces and chip morphologies that were measured in the cutting experiments of Ti-6Al-4V alloy were used to validate the simulated forces. The relative errors between the measured and simulated principal forces were less than 8%, while the relative errors of thrust forces were less than 19%. The predicted chip morphologies and surface grain refinement agreed well with the experimental results under the conditions with different uncut chip thicknesses and edge radii. Additionally, the relationship between the plastic displacement and grain refinement, as well as the microhardness and residual stresses under MQL and cryogenic conditions, were discussed. This work provides an effective modeling method for the orthogonal cutting of Ti-6Al-4V alloy to understand the mechanism of the plastic deformation and machined surface integrity under the MQL and LN₂ conditions. Full article

Throughout recent years, the implementation of nanoparticles into the microstructure of additively manufactured (AM) parts has gained great attention in the material science community. The dispersion strengthening (DS) effect achieved leads to a substantial improvement in the mechanical properties of the alloy used. In this work, an ex situ approach of powder conditioning prior to the AM process as per a newly developed fluidized bed reactor (FBR) was applied to a titanium-enriched variant of the NiCu-based Alloy 400. Powders were investigated before and after FBR exposure, and it was found that the conditioning led to a significant increase in the TiN formation along grain boundaries. Manufactured to parts via laser-based powder bed fusion of metals (PBF-LB/M), the ex situ FBR approach not only revealed a superior microstructure compared to unconditioned parts but also with respect to a recently introduced in situ approach based on a gas atomization reaction synthesis (GARS). A substantially higher number of nanoparticles formed along cell walls and enabled an effective suppression of dislocation movement, resulting in excellent tensile, creep, and fatigue properties, even at elevated temperatures up to 750 °C. Such outstanding properties have never been documented for AM-processed Alloy 400, which is why the demonstrated FBR ex situ conditioning marks a promising modification route for future alloy systems. Full article

Thermal simulation is essential in wire-arc-directed energy deposition (W-DED) to accurately estimate temperature distributions, impacting residual stress and distortion in components. Proper calibration of simulation models minimizes inaccuracies caused by varying material properties, machine settings, and environmental conditions. The lack of standardized calibration methods further complicates thermal predictions. This paper introduces a novel calibration method integrating both machine learning, as the high-fidelity (HF) model, and response surface modeling, as the low-fidelity (LF) model, within a multi-fidelity (MF) framework. The approach utilizes Bayesian optimization to effectively explore the search space for optimal solutions. A two-tiered model employs the LF model to identify feasible regions, followed by the HF model to refine calibration parameters, such as thermal efficiency (η), convection coefficient (h), and emissivity (ε), which are difficult to determine experimentally. A three-factor Box–Behnken design (BBD) is applied to explore the design space, requiring only thirteen parameter configurations, conserving resources and enabling robust model training. The efficacy of this MF model is demonstrated in multi-layer W-DED calibration, showing strong alignment between experimental and simulated temperatures, with a mean absolute error (MAE) of 7.47 °C. This method offers a replicable framework for broader additive manufacturing processes. Full article

In metal additive manufacturing, reusing collected powder from previous builds is a standard practice driven by the substantial cost of metal powder. This approach not only reduces material expenses but also contributes to sustainability by minimizing waste. Despite its benefits, powder reuse introduces challenges related to maintaining the structural integrity of the components, making it a critical area of ongoing research and innovation. The reuse process can significantly alter powder characteristics, including flowability, size distribution, and chemical composition, subsequently affecting the microstructures and mechanical properties of the final components. Achieving repeatable and consistent printing outcomes requires powder particles to maintain specific and consistent physical and chemical properties. Variations in powder characteristics can lead to inconsistencies in the microstructural features of printed components and the formation of process-induced defects, compromising the quality and reliability of the final products. Thus, optimizing the powder recovery and reuse methodology is essential to ensure that cost reduction and sustainability benefits do not compromise product quality and reliability. This study investigated the impact of powder reuse and particle size distribution on the microstructural and mechanical properties of Ti-6Al-4V specimens fabricated using a laser beam directed energy deposition technique. Detailed evaluations were conducted on reused powders with two different size distributions, which were compared with their virgin counterparts. Microstructural features and process-induced defects were examined using scanning electron microscopy and X-ray computed tomography. The findings reveal significant alterations in the elemental composition of reused powder, with distinct trends observed for small and large particles. Additionally, powder reuse substantially influenced the formation of process-induced defects and, consequently, the fatigue performance of the components. Full article

Laser wire-feed metal additive manufacturing (LWAM) is an innovative technology that shows many advantages compared with traditional manufacturing approaches. Despite these advantages, its industrial adoption is limited by complex parameter management and inconsistent process quality. To address these issues and improve geometric accuracy, this study explores how process parameters influence bead geometry. We conducted a parameter study varying laser power, wire feed rate, traverse speed, and welding angle. Using a full factorial design with a central composite design methodology, we assessed bead height and width. This allowed us to develop a model to estimate ideal process parameters. The findings offer a detailed analysis of parameter interactions and their effects on bead geometry, aiming to enhance geometric accuracy and process stability in LWAM. Moreover, we have evaluated the proposed process parameters from our developed model, which showed a significant enhancement to the overall quality. This was validated via printing a single layer and multi-layer structures. The quality of the final predicted sample using the proposed method was improved by 40% compared to the best sample produced for the Design of Experiment trials. Full article

The friction/adhesion between the tool and chip is generally large in metal cutting, and it causes many problems such as high cutting energy/rough surface finish. To suppress this, cutting fluid and tool coating are used in practice, but they are high in energy/cost and environmentally unfriendly. Therefore, this paper investigates the extraordinarily high-speed cutting (EHS cutting) mechanics of mainly soft and highly heat-conductive materials and proposes their application to solve the friction/adhesion problem in an environmentally friendly manner. In order to clarify the EHS cutting mechanics, a simple analytical model is constructed and experiments are conducted with measurement of the cutting temperature and forces. As a result, the following points are clarified/found: (1) heat softening at the secondary plastic deformation zone rather than the primary plastic deformation zone, (2) friction coefficient drop to 0.170 in EHS cutting, and (3) gradually increasing trend of cutting temperature in EHS cutting. Finally, EHS cutting is applied to dry cutting of aluminum alloys with a non-coated carbide tool and compared to conventional wet cutting with a DLC-coated carbide tool, and it is shown that a coating/coolant can be omitted in this region to achieve environmentally friendly cutting. Full article

Today, around the world, there is huge demand for natural materials that are biodegradable and possess suitable properties. Natural fibers reveal distinct aspects like the combination of good mechanical and thermal properties that allow these types of materials to be used for different applications. However, fibers alone cannot meet the required expectations; design modifications and a wide variety of combinations must be synthesized and evaluated. It is of great importance to research and develop materials that are bio-degradable and widely available. The combination of PLA+, a bio-based polymer, with natural fillers like sawdust and soybean oil offers a novel way to create sustainable composites. It reduces the reliance on petrochemical-based plastics while enhancing the material’s properties using renewable resources. This study explores the creation of continuous hexagonal-shaped 3D-printed PLA+ samples and the application of post-print fillers, specifically sawdust and soybean oil. PLA+ is recognized for its eco-friendliness and low carbon footprint, and incorporating a hexagonal pattern into the 3D-printed PLA+ enhances its structural strength while maintaining its density. The addition of fillers is crucial for reducing shrinkage and improving binding capabilities, addressing some of PLA+’s inherent challenges and enhancing its load-bearing capacity and performance at elevated temperatures. Additionally, this study examines the impact of varying filler percentages and pattern orientations on the mechanical properties of the samples, which were printed with an infill design. Full article

This research investigates the correlation between polymer melt viscosity, tensile properties, and injection molding energy consumption for three grades of polypropylene: a virgin grade, a recycled grade, and a modified recycled grade. Cold runner and hot runner molds are considered. The experiments focus on characterizing the thermal and mechanical energy drawn by the injection molding machine during the cycle. The data collected from the experiments are used to calculate the embodied energy as a function of the polymer viscosity and processing conditions. The analysis of the relationship between polymer rheology and processing provided guidelines for the molded parts’ embodied energy and mechanical characteristics. These guidelines and estimation techniques will support sustainable design for manufacturing practices. Full article

By combining the ring rolling and roll bonding processes, the product spectrum can be additionally expanded. Since a successful composite ring rolling process requires a higher growth tendency for the inner ring, previous publications commonly included a softer inner ring to reduce the flow resistance of the inner ring or specific geometries for rings and tools. In this work, the material combination of a 100Cr6 (DIN 1.3505, AISI 52100) outer ring and a 42CrMo4 (DIN 1.7225, AISI 4140) inner ring is used to show that the composite ring rolling process is also possible for material combinations with a balanced flow stress ratio and equal wall thicknesses. In earlier publications, the influence of temperature was neglected. As the influence on the yield stress and thus on the success of the process has a significant influence, this should be considered in order to be able to make a reliable statement. For this purpose, the bond formation of the two materials was investigated by bonding experiments, and an existing bond formation model was extended with respect to the temperature dependency. On the basis of this model, the process control parameters were investigated using FE simulations, and a ring rolling experiment was carried out. Full article

Additive friction stir deposition (AFSD) is a solid-state metal additive manufacturing technique, which utilizes frictional heating and plastic deformation to create large deposits and parts. Much like its cousin processes, friction stir welding and friction stir processing, AFSD has seen the most compatibility and use with lower-temperature metals, such as aluminum; however, there is growing interest in higher-temperature materials, such as titanium and steel alloys. In this work, we explore the deposition of an ultrahigh-temperature refractory material, specifically, a tantalum–tungsten (TaW) alloy. The solid-state nature of AFSD means refractory process temperatures are significantly lower than those for melt-based additive manufacturing techniques; however, they still pose difficult challenges, especially in regards to AFSD tooling. In this study, we perform initial deposition trials of TaW using twin-rod-style AFSD with a high-temperature tungsten–rhenium-based tool. Many challenges arise because of the high temperatures of the process and high mechanical demand on AFSD machine hardware to process the strong refractory alloy. Despite these challenges, successful deposits of the material were produced and characterized. Mechanical testing of the deposited material shows improved yield strength over that of the annealed reference material, and this strengthening is mostly attributed to the refined recrystallized microstructure typical of AFSD. These findings highlight the opportunities and challenges associated with ultrahigh-temperature AFSD, as well as provide some of the first published insights into twin-rod-style AFSD process behaviors. Full article

In milling processes in which material removal is performed periodically from solid material, dynamic effects are generally considered to be responsible for instabilities and subsequent productivity limits. Usually, in such applications, the process-inherent complex dynamic load spectrum on machines, tools and workpieces is considered together with vibration-based relative displacements that can be attributed to the regenerative effect. There are numerous techniques in the literature addressing the suppression of these dynamic effects, but they require a large amount of analysis and implementation effort as well as specific expert knowledge. The approach presented here, however, provides a universally applicable method for suppressing chatter vibrations and deflections. By applying structure elements to the flanks of the minor cutting edges of HSS end mills, it was possible to increase the chatter-free limiting depth of cut a_p,crit in the milling processes of the aluminum alloy EN AW-7075. Structured tools were used in ramp milling tests to investigate various effects, such as the influence of certain geometric design features on the stabilization potential compared to a reference tool. Furthermore, the effects of varied process parameter configurations and wear-related effects on the performance of the tool concept were focused on as well. The three key design features of the cutting edge and the structured profiles were identified from the results of the investigation, which, when combined in the most efficient design, in each case led to the development of an optimized structure and process configuration with cumulative potential for increasing the stability limit up to 200%. Full article

This paper presents a comprehensive analysis of the utilization of 3D printing technology for the fabrication of ceramic shells in the context of investment casting. This study encompasses an exploration of various 3D printing techniques such as binder jetting technology and lithography-based ceramic manufacturing applied to ceramic materials tailored for investment casting applications for different materials. Comparative analyses between conventionally manufactured shells and those produced through 3D printing techniques are presented, shedding light on the potential advantages and challenges associated with the adoption of additive manufacturing in investment casting processes. The findings of this study reveal that both methods offer viable solutions for creating ceramic materials suitable as shells for investment casting. Both lithography-based ceramic manufacturing and binder jetting technology exhibit unique advantages and challenges. Lithography-based ceramic manufacturing demonstrates a superior surface finish and resolution, making it particularly suitable for intricate designs and fine details. On the other hand, binder jetting technology presents advantages in terms of speed and scalability, allowing for the rapid production of larger components. Full article

The additive manufacturing technology powder bed fusion of metal with a laser beam (PBF-LB/M) is industrially established for tool-free production of complex and individualized components and products. While the in-processing is based on a layer-by-layer build-up of material, both upstream and downstream process steps (pre-processing and post-processing) are necessary for demand-oriented production. However, there are increasing concerns in the industry about the efficient and economical implementation and validation of the PBF-LB/M. Individual products for mass personalization pose a particular challenge, as they are subject to sophisticated risk management, especially in highly regulated sectors such as medical technology. Additive manufacturing using PBF-LB/M is a suitable technology but a complex one to master in this environment. A structured system for holistic decision-making concerning technical and economic feasibility, as well as quality and risk-oriented process management, is currently not available. In the context of this research, a framework is proposed that demonstrates the essential steps for the systematic implementation and validation of PBF-LB/M in two structured phases. The intention is to make process-related key performance indicators such as part accuracy, surface finish, mechanical properties, and production efficiency controllable and ensure reliable product manufacturing. The framework is then visualized and evaluated using a practice-oriented case study environment. Full article

This paper reports on an experimental investigation that used a full factorial design to study the main effects and the interaction effect of layer thickness and compaction thickness on the green part density in the binder jetting additive manufacturing of silicon carbide. A two-variable, two-level full factorial design was employed. The results show that the green part density was higher at the low level of layer thickness and at the high level of compaction thickness. These results can be useful in selecting the values of printing variables, enabling the fabrication of green parts with a desirable density that is crucial for advanced ceramic applications. Full article

Additive manufacturing (AM) is increasingly used for fabricating parts directly from digital models, usually by depositing and bonding successive layers of various materials such as polymers, metals, ceramics, and composites. The design freedom and reduced material consumption for producing near-net-shaped components have made AM a popular choice across various industries, including the automotive and aerospace sectors. Despite its growing popularity, the accurate estimation of production time, productivity and cost remains a significant challenge due to the ambiguity surrounding the technology. Hence, reliable cost estimation models are necessary to guide decisions throughout product development activities. This paper provides a thorough analysis of the state of the art in cost models for AM with a specific focus on metal Directed Energy Deposition (DED) and Powder Bed Fusion (PBF) processes. An overview of DED and PBF processes is presented to enhance the understanding of how process parameters impact the overall cost. Consequently, suitable costing techniques and significant cost contributors in AM have been identified and examined in-depth. Existing cost modelling approaches in the field of AM are critically evaluated, leading to the suggestion of a comprehensive cost breakdown including often-overlooked aspects. This study aims to contribute to the development of accurate cost prediction models in supporting decision making in the implementation of AM. Full article

Precise electrochemical machining (PECM) is being used increasingly to produce turbine blades (high-pressure compressors) from difficult-to-machine materials such as Inconel. However, the challenges associated with PECM are particularly pronounced for filigree workpieces characterized by high aspect ratios and thin-walled geometries. The need for high-pressure flushing within the working gap to renew the electrolyte poses a dilemma because it induces unwanted deflection in these thin-walled structures. This problem is intensified by the mechanical oscillation of the tool applied to promote flushing efficiency. The superposition of mechanical tool oscillation and turbulent flushing, which exacerbate fluid–structure interaction, has been identified as the essential cause of workpiece deflection. The aim of this paper is to present an experimental setup coupled with numerical methods to better investigate the phenomenon of workpiece deflection during PECM. In the first part of this work, a novel tool system for investigating the phenomenon of workpiece deflection in PECM is presented. The tool system combines typical PECM tool–workpiece arrangements for double-sided machining and a unique electrolytic mask that provides optical access to the working gap, allowing in situ measurements. After validating the tool system by experimental tests, the workpiece deflection is investigated using high-speed imaging. In a next step, analytical studies of the flushing conditions during machining operations are carried out. These investigations are followed by a structural investigation of the workpiece to improve the understanding of the deflection behavior of the workpiece. In addition, the effect on the blade tip caused by the continuously decreasing moment of inertia of the blade due to their thinning during machining is analyzed. Full article

In the context of directed energy deposition (DED), the production of complex components necessitates precise control of all processing parameters while mitigating undesirable factors like heat accumulation. This research seeks to explore and validate with various materials the impact of a geometry-based analytical model for minimizing heat input on the characteristics and structure of the resultant DED components. Furthermore, it aims to compare this approach with other established methods employed to avoid heat accumulation during production. The geometry of the fabricated specimens was assessed using a linear laser scanner, cross-sections were analyzed through optical microscopy, and the effect on mechanical properties was determined via microhardness measurements. The specimens manufactured using the developed analytical model exhibited superior geometric precision with lower energy consumption without compromising mechanical properties. Full article

In this study, the effects of the δ phase and annealing twins on the hardness, tensile properties, and Charpy impact toughness of Inconel 718 fabricated using L-PBF were investigated. The as-printed components underwent two stages of heat treatment to modify their microstructure and phases. The δ phase was induced through solid-solution heat treatment at 980 °C for 1 h, while annealing twins were formed at 1100 °C for 3 h. Following precipitation hardening, specimens containing δ precipitates exhibited a higher ultimate tensile strength (13%), yield strength (27%), and hardness (12%) compared to those rich in annealing twins. The enhanced mechanical strength was attributed to the presence of δ precipitates and differences in the extent of recrystallization, leading to variations in the density of retained lattice defects, including subgrain boundaries and primary phases. Conversely, specimens with annealing twins demonstrated a significantly higher impact toughness (four times) and ductility (twice) than those with δ precipitates. Annealing twins were found to enhance plasticity by impeding dislocation movement, while δ precipitates reduced plasticity by acting as sites for void formation and crack propagation. Microstructural, compositional, phase, crystallographic, and fractographic analyses were conducted using OM, SEM, TEM, and XRD techniques to identify the factors influencing the observed differences. The results indicate that the heat treatment approach involving annealing twins can effectively enhance the ductility of Inconel 718 while maintaining the necessary mechanical strength. Full article

Dissimilar welds between ferritic and austenitic stainless steels are widely used in industrial applications. Taking into account the issues inherent to arc welding, such as the high heat input and the need to carry out multiple passes in the case of thick plates, a procedure with two simultaneous laser beams (working in a single pass) and consumable inserts as filler metal has been considered. Particular attention was paid to the choice of the filler metal (composition and amount), as well as welding parameters, which are crucial to obtain the right dilution necessary for a correct chemical composition in the weld zone. The first experimental investigations confirmed the achievement of a good weldability of the dissimilar pair ASTM A387 ferritic/AISI 304L austenitic steel, having ascertained that the microstructure of the weld zone is austenitic with a little amount of residual primary ferrite, which is the best condition to minimize the risk of hot cracking. Full article

Laser powder bed fusion (LPBF) is a promising metal additive manufacturing technology for producing functional components. However, there are still a lot of obstacles to overcome before this technology is considered mature and trustworthy for wider industrial applications. One of the biggest obstacles is the difficulty in ensuring the repeatability of process and the reproducibility of products. To tackle this challenge, a prerequisite is to represent and communicate the data from the part realisation process in an unambiguous and rigorous manner. In this paper, a semantically enriched LPBF part data model is developed using a category theory-based modelling approach. Firstly, a set of objects and morphisms are created to construct categories for design, process planning, part build, post-processing, and qualification. Twenty functors are then established to communicate these categories. Finally, an application of the developed model is illustrated via the realisation of an LPBF truncheon. Full article

Directed energy deposition-laser beam/powder (DED-LB/Powder) is an additive manufacturing process that is gaining popularity in the manufacturing industry due to its numerous advantages, particularly in repairing operations. However, its application is often limited to case studies due to some critical issues that need to be addressed, such as the degree of internal porosity. This paper investigates the effect of the most relevant process parameters of the DED-LB/Powder process on the level and distribution of porosity. Results indicate that, among the process parameters examined, porosity is less affected by travel speed and more influenced by powder mass flow rate and laser power. Additionally, a three-dimensional finite element transient model was introduced, which was able to predict the development and location of lack-of-fusion pores along the building direction. Full article

Cooling–lubricating processes have a big impact on cutting force, tool wear, and the quality of the machined surface, especially for hard-to-machine superalloys, so the choice of the right cooling–lubricating method is of great importance. Nickel-based superalloys are among the most difficult materials to machine due to their high hot strength, work hardening, and extremely low thermal conductivity. Previous research has shown that flood cooling results in the least tool wear and cutting force among different cooling–lubricating methods. Thus, the effects of the flood oil concentration (3%; 6%; 9%; 12%; and 15%) on the above-mentioned factors were investigated during the slot milling of the GTD-111 nickel-based superalloy. The cutting force was measured during machining with a Kistler three-component dynamometer, and then after cutting the tool wear and the surface roughness on the bottom surface of the milled slots were measured with a confocal microscope and tactile roughness tester. The results show that at a 12% oil concentration, the tool load and tool wear are the lowest; even at an oil concentration of 15%, a slight increase is observed in both factors. Essentially, a higher oil concentration reduces friction between the tool and the workpiece contact surface, resulting in reduced tool wear and cutting force. Furthermore, due to less friction, the heat generation in the cutting zone is also reduced, resulting in a lower heat load on the tool, which increases tool life. It is interesting to note that the 6% oil concentration had the highest cutting force and tool wear, and strong vibration was heard during machining, which is also reflected in the force signal. The change in oil concentration did not effect the surface roughness. Full article

Strategies for obtaining deep slots in soft materials can vary significantly. Conventionally, the tool travels along the slot, removing material mainly with the side cutting edges. However, a “plunge milling” strategy is also possible, performing the cut vertically, taking advantage of the tip cutting edges that almost reach the center of the tool. Although both strategies are already commonly used, there is a clear gap in the literature in studies that compare tool wear, surface roughness, and productivity in each case. This paper describes an experimental study comparing the milling of deep slots in AA7050-T7451 aluminum alloy, coated with a novel DLCSiO500W3.5O₂ layer to minimize the aluminum adhesion to the tool, using conventional and plunge milling strategies. The main novelty of this paper is to present a broad study regarding different factors involved in machining operations and comparing two distinct strategies using a novel tool coating in the milling of aeronautical aluminum alloy. Tool wear is correlated with the vibrations of the tools in each situation, the cycle time is compared between the cases studied, and the surface roughness of the machined surfaces is analyzed. This study concludes that the cycle time of plunge milling can be about 20% less than that of conventional milling procedures, favoring economic sustainability and modifying the wear observed on the tools. Plunge milling can increase productivity, does not increase tool tip wear, and avoids damaging the side edges of the tool, which can eventually be used for final finishing operations. Therefore, it can be said that the plunge milling strategy improves economic and environmental sustainability as it uses all the cutting edges of the tools in a more balanced way, with less global wear. Full article

In this study, the welding thermal cycle, as well as the microstructural and mechanical properties of welded AA6061-T6 plates, were studied. The plates were prepared and bead-on-plate welded using gas metal arc welding (GMAW). Numerical simulations using SYSWELD^® were performed to obtain the thermal distribution in the welded plates. The numerical heat source was calibrated using the temperatures obtained from the experimental work and the geometry of the melting pool. The mechanical properties were obtained through microhardness tests and were correlated with the welding thermal cycle. Moreover, the mechanical behavior and local deformation in the heat-affected zone (HAZ) were investigated using micro-flat tensile (MFT) tests with digital image correlation (DIC). The mechanical properties of the subzones in the HAZ were then correlated with the welding thermal cycle and with the microstructure of the HAZ. It was observed that the welding thermal cycle produced microstructural variations across the HAZ, which significantly affected the mechanical behavior of the HAZ subzones. The results revealed that MFT tests with the DIC technique are an excellent tool for studying the local mechanical behavior change in AA6061-T6 welded parts due to the welding heat. Full article

Knowing the tolerance interval capabilities (TICs) of a manufacturing process is of prime interest, especially if specifications link the manufacturer to a customer. These TICs can be determined using the machine performance concept of ISO 22514. However, few works have applied this to Additive Manufacturing printers, while testing most of the printing area as recommended takes a very long time (nearly 1 month is common). This paper, by proposing a novel part design called COMPAQT (Component for Machine Performances Assessment in Quick Time), aims at giving the same level of printing area coverage, while keeping the manufacturing time below 24 h. The method was successfully tested on a material extrusion printer. It allowed the determination of potential and real machine tolerance interval capabilities. Independently of the feature size, those aligned with the X axis achieved lower TICs than those aligned with the Y axis, while the Z axis exhibited the best performance. The measurements specific to one part exhibited a systematic error centered around 0 mm ± 0.050 mm, while those involving two parts reached up to 0.314 mm of deviation. COMPAQT can be used in two applications: evaluating printer tolerance interval capabilities and tracking its long-term performance by incorporating it into batches of other parts. Full article

Conventional path-planning strategies for GMA-WAAM may encounter challenges related to geometrical features when printing complex-shaped builds. One alternative to mitigate geometry-related flaws is to use algorithms that optimise trajectory choices—for instance, using heuristics to find the most efficient trajectory. The algorithm can assess several trajectory strategies, such as contour, zigzag, raster, and even space-filling, to search for the best strategy according to the case. However, handling complex geometries by this means poses computational efficiency concerns. This research aimed to explore the potential of machine learning techniques as a solution to increase the computational efficiency of such algorithms. First, reinforcement learning (RL) concepts are introduced and compared with supervised machining learning concepts. The Multi-Armed Bandit (MAB) problem is explained and justified as a choice within the RL techniques. As a case study, a space-filling strategy was chosen to have this machining learning optimisation artifice in its algorithm for GMA-AM printing. Computational and experimental validations were conducted, demonstrating that adding MAB in the algorithm helped to achieve shorter trajectories, using fewer iterations than the original algorithm, potentially reducing printing time. These findings position the RL techniques, particularly MAB, as a promising machining learning solution to address setbacks in the space-filling strategy applied. Full article

This critical review provides a comprehensive analysis of various condition monitoring techniques pivotal in additive manufacturing (AM) processes. The reliability and quality of AM components are contingent upon the precise control of numerous parameters and the timely detection of potential defects, such as lamination, cracks, and porosity. This paper emphasizes the significance of in situ monitoring systems—optical, thermal, and acoustic—which continuously evaluate the integrity of the manufacturing process. Optical techniques employing high-speed cameras and laser scanners provide real-time, non-contact assessments of the AM process, facilitating the early detection of layer misalignment and surface anomalies. Simultaneously, thermal imaging techniques, such as infrared sensing, play a crucial role in monitoring complex thermal gradients, contributing to defect detection and process control. Acoustic monitoring methods augmented by advancements in audio analysis and machine learning offer cost-effective solutions for discerning the acoustic signatures of AM machinery amidst variable operational conditions. Finally, machine learning is considered an efficient technique for data processing and has shown great promise in feature extraction. Full article

The aim of this paper is to establish a valid procedure for better understanding all of the phenomena associated with the high-speed machining of glass fiber-reinforced plastic (GFRP) composites. Both rectangular and circular specimens were machined at high cutting speeds (up to 50 m/min) in order to understand what occurred for all values of fiber orientation angles during machining operations. An innovative testing methodology was proposed and studied to investigate the phenomenon of burr formation and thus understand how to avoid it during machining operations. To this end, the forces arising during the machining process and the roughness of the resulting surface were carefully studied and correlated with the cutting angle. Additionally, the cutting surface and chip morphology formed during cutting tests were examined using a high-speed camera. Close correlations were found between the variations in the cutting forces’ signals and the trends of the surface roughness and the morphology of the machined surface. Full article

In the last fifteen years, several groups have investigated metal injection moulding (MIM) of NdFeB powder to produce isotropic or anisotropic rare earth magnets of greater geometric complexity than that achieved by the conventional pressing and sintering approach. However, due to the powder’s high affinity for oxygen and carbon uptake, sufficient remanence and coercivity remains difficult. This article presents a novel approach to producing NdFeB magnets from recycled material using Powder Extrusion Moulding (PEM) in a continuous process. The process route uses powder obtained from recycling rare earth magnets through Hydrogen Processing of Magnetic Scrap (HPMS). This article presents the results of tailored powder processing, the production of mouldable feedstock based on a special binder system, and moulding with PEM to produce green and sintered parts. The magnetic properties and microstructures of debinded and sintered samples are presented and discussed, focusing on the influence of filling ratio and challenging processing conditions on interstitial content as well as density and magnetic properties. Full article

Various defects are produced during the laser powder bed fusion (L-PBF) process, which can affect the quality of the fabricated part. Previous studies have revealed that the defects formed are correlated with molten pool dimensions. Powder particles are thinly spread on a substrate during the L-PBF process; hence, powder packing properties should influence the molten pool dimensions. This study evaluated the influence of particle size on powder packing properties and molten pool dimensions obtained through numerical simulations. Using particles with different average diameters ($D_{av}$) of 24, 28, 32, 36, and 40 $\mathsf{\mu }$m, a series of discrete-element method (DEM) simulations were performed. The packing fraction obtained from DEM simulations became high as $D_{av}$ became small. Several particles piled up for small $D_{av}$, whereas particles spread with almost one-particle diameter thickness for large $D_{av}$. Moreover, the packing structure was inhomogeneous and sparse for large $D_{av}$. As a result of multiphysics computational fluid dynamics (CFD) simulations incorporating particles’ positions as initial solid metal volume, the molten pool width obtained was hardly dependent on the $D_{av}$ and was roughly equivalent to the laser spot size used in the simulations. In contrast, the molten pool depth decreased as $D_{av}$ decreased. Even if the powder bed thickness is the same, small particles can form a complex packing structure by piling up, resulting in a large specific surface area. This can lead to a complex laser reflection compared to the large particles coated with almost one-particle thickness. The complex reflection absorbs the heat generated by laser irradiation inside the powder bed formed on the substrate. As a result, the depth of the molten pool formed below the substrate is reduced for small particles. Full article

Minimum quantity lubrication (MQL) technologies possess great potential for improving the sustainability of manufacturing processes, which can reduce the absolute quantity of metalworking fluid (MWF) and also enable near-dry chips that are easier to recycle. During drilling in particular, the MWF is transported to the contact zone through internal cooling channels of the drilling tool. The MWF supply and its associated flow behaviour in the transfer from the outlet of the cooling channels to the contact zone have not been sufficiently investigated yet. Great potential is seen in the proper delivery of the MQL into the contact zone. This work aims to visualize and quantify the cooling lubricant supply into the cutting zone using the MQL technique. The visualization of the MQL application is made possible by high-speed shadowgraphic imaging. Detailed image processing is used to evaluate the resulting images. The developed evaluation routine allows for the assessment of the impact of the main process parameters such as the varying pressure of the aerosol generator and the cooling channel diameter. It is found that the oil leaves the cooling channels at the tip of the drill bit in the form of ligaments. An increase in pressure and cooling channel diameter leads to an increase in the frequency of oil ligament separation. Three main flow regimes are identified with different separation frequencies. Low inlet pressures result in intermittently dispersed droplets. The most upper pressure levels lead to an almost continuous dispersion of the oil. At the same time, the air and oil mass flow rates also increase. Full article

This work emphasizes an innovative approach utilizing 3D imaging technology based on synchrotron radiation to assess the microstructure of second-phase iron particles and the porous structure within 3D-printed PLA/magnetic iron composites at different printing angles. The study examines how these observations relate to the material’s ductility when processed using fused filament fabrication. In particular, this study examines the impact of one processing parameter, specifically the printing angle, on the microstructure and mechanical behaviour of a polylactic acid (PLA)–iron (PLI) composite designed for magnetic actuation. Fused filament fabrication is employed to produce PLI tensile specimens, with varied printing angles to create different layups. X-ray microtomography is utilized to analyse the microstructure, while tensile mechanical properties are evaluated for all composites, with findings discussed in relation to printing angle conditions. Scanning Electron Microscopy is used to examine the fractography of broken specimens. Results indicate that the printing angle significantly influences the tensile properties and mechanical anisotropy of 3D-printed PLI composites, with an optimal 45°/45° layup enhancing tensile performance. These findings suggest that 3D-printed PLI composites offer a cost-efficient means of producing bio-sourced, light-adaptive materials with intricate magnetic actuation capabilities. By quantifying the modulation of mechanical properties based on printing parameters that influence microstructural arrangement, the research sheds light on a novel aspect of composite material characterization. Full article

Context—Rapidly solidified aluminium alloy (RSA 443) is increasingly used in the manufacturing of optical mold inserts because of its fine nanostructure, relatively low cost, excellent thermal properties, and high hardness. However, RSA 443 is challenging for single-point diamond machining because the high silicon content mitigates against good surface finishes. Objectives—The objectives were to investigate multiple different ways to optimize the process parameters for optimal surface roughness on diamond-turned aluminium alloy RSA 443. The response surface equation was used as input to three different artificial intelligence tools, namely genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE), which were then compared. Results—The surface roughness machinability of RSA443 in single-point diamond turning was primarily determined by cutting speed, and secondly, cutting feed rate, with cutting depth being less important. The optimal conditions for the best surface finish Ra = 14.02 nm were found to be at the maximum rotational speed of 3000 rpm, cutting feed rate of 4.84 mm/min, and depth of cut of 14.52 µm with optimizing error of 3.2%. Regarding optimization techniques, the genetic algorithm performed best, then differential evolution, and finally particle swarm optimization. Originality—The study determines optimal diamond machining parameters for RSA 443, and identifies the superiority of GA above PSO and DE as optimization methods. The principles have the potential to be applied to other materials (e.g., in the RSA family) and machining processes (e.g., turning, milling). Full article

Copper-based materials have long been used for their outstanding thermal and electrical conductivities in various applications, such as heat exchangers, induction heat coils, cooling channels, radiators, and electronic connectors. The development of advanced copper alloys has broadened their utilization to include structural applications in harsh service conditions found in industries like oil and gas, marine, power plants, and water treatment, where good corrosion resistance and a combination of high strength, wear, and fatigue tolerance are critical. These advanced multi-component structures often have complex designs and intricate geometries, requiring extensive metallurgical processing routes and the joining of the individual components into a final structure. Additive manufacturing (AM) has revolutionized the way complex structures are designed and manufactured. It has reduced the processing steps, assemblies, and tooling while also eliminating the need for joining processes. However, the high thermal conductivity of copper and its high reflectivity to near-infrared radiation present challenges in the production of copper alloys using fusion-based AM processes, especially with Yb-fiber laser-based techniques. To overcome these difficulties, various solutions have been proposed, such as the use of high-power, low-wavelength laser sources, preheating the build chamber, employing low thermal conductivity building platforms, and adding alloying elements or composite particles to the feedstock material. This article systematically reviews different aspects of AM processing of common industrial copper alloys and composites, including copper-chrome, copper-nickel, tin-bronze, nickel-aluminum bronze, copper-carbon composites, copper-ceramic composites, and copper-metal composites. It focuses on the state-of-the-art AM techniques employed for processing different copper-based materials and the associated technological and metallurgical challenges, optimized processing variables, the impact of post-printing heat treatments, the resulting microstructural features, physical properties, mechanical performance, and corrosion response of the AM-fabricated parts. Where applicable, a comprehensive comparison of the results with those of their conventionally fabricated counterparts is provided. Full article

Laser beam welding as a reliable tool for high-precision joining of batteries or microelectronics is more and more the choice for achieving reproducible results in production processes. In addition to a high automation capability, the precise control of the energy deposition into the material plays an important role, especially when highly reflective materials, such as copper or aluminum, must be welded together. Alongside the use of highly brilliant fiber lasers in the near-infrared range with a focal diameter of a few tens of micrometers, diode lasers in the wavelength range of 445 nm are increasingly being used. Here, beam diameters of a few hundred micrometers can be achieved. With a wavelength of 445 nm, the absorptivity in copper can be increased by more than a factor of 10 compared to a near-infrared laser beam sources in solid state at room temperature. This paper presents the in situ X-ray observation of laser welding processes on CuSn6 with a laser beam source with a wavelength of 445 nm using synchrotron radiation at DESY Petra III Beamline P07 EH4 in Hamburg, Germany. For the experiments, the laser radiation was focused via two separate optics to focal diameters of 362 µm and 609 µm. To characterize the dynamics of the vapor capillaries depending on the different focal diameters d_F, the parameters were varied with respect to laser power P_L and feed rate v. For the investigations, a synchrotron beam of 2 × 2 mm² in size with a photon energy of 89 keV was used, and the material samples were analyzed by means of phase-contrast videography to show the boundaries between solid, liquid, and gaseous material phases. The results of this paper show the welding depths achieved and how the geometry of the vapor capillary behaves by changing the focal diameter, laser power and feed rate. Full article

In incremental sheet forming (ISF), the geometrical accuracy is still a challenge that is only solved for specific applications. The underlying mechanisms of geometrical defects in ISF are very complex and still not fully understood. Nevertheless, the process understanding is constantly evolving. Recent work has shown, for example, how bending moments resulting from residual stresses affect geometric accuracy. It has become clear that resulting bending moments with an axis parallel to the main tool path direction are dominant. Based on that, the current paper investigates the hypothesis that linear and parallel tool paths lead to an unfavourable accumulation of residual bending moments along a common axis, and whether this accumulation effect can be reduced by wave-shaped tool paths. Thus, the described research investigates the influence of novel path strategies on the residual bending moments and the resulting geometrical deviations. The path strategies are based on wave-shaped path lines, whereas the curvature is within the sheet plane. The investigations focussed on a rectangular sheet that is clamped at its shortest edges and a part geometry-sensitive to springback. Experimental and numerical investigations show a significantly positive influence of some investigated path strategies on the geometric deviation, compared to a conventional path strategy. Full article

Optical measurements are increasingly widely used as preferential techniques to evaluate dimensional and surface quantities in micro-products. However, uncertainty estimation is more critical on micro-products than macro, and it needs careful attention for evaluating the obtained quality, the requested tolerance, and the correct setting of experimental process settings. In this study, optical measurements characterized micro-injected products by linear and surface acquisition and considered all the sources contributing to uncertainties. The results show that the measure uncertainty could be underestimated if only the standard deviation on simple measurements is considered; this could cause a significant restriction of the estimated range covering the measured values. Furthermore, the findings confirm that the correct evaluation of the potential uncertainties contributes to accurately assessing the process behavior and improving product quality. Full article

The metal spinning process has been observed in recent major investigations carried out using finite element analysis. One interesting idea has proposed simulating a rotating disc for the simulation of the metal spinning process to reduce computational time. The development of this concept is presented in this paper, including the formal mathematical transformation from the inertial frame to the rotating reference frame, specific FEM configurations with mesh sizes based on a minimized aspect ratio, a mesh convergence study, and the application of a feed rate scale. Furthermore, in the context of the rotating reference frame, the flange geometry after wrinkle initiation is investigated, including the number of peaks and their amplitudes. Using this new approach, it was found that the number of peaks gradually increases from two to eight peaks while their amplitude decreases. In the case of severe wrinkles, the number of peaks stays at four while the amplitude increases dramatically. The intermediate path proves capable of increasing the number of peaks while maintaining a low amplitude. These results will make it possible to design new paths, facilitating the production of defect-free spun parts. Full article

Wire and arc additive manufacturing (WAAM) is a metal deposition technique with a fast rate and the possibility of a high volume of deposition. Because of its fast deposition and high heat input, the manufactured products have poor surface quality. This paper presents a study on the machining of Inconel 718 wall-shaped additive manufacturing (AM) products, a necessary step for the improvement of surface quality. Considering the possibility that the characteristics of the milling processes of AM products might differ from those of traditionally manufactured parts, in this research, two types of Inconel 718 were studied and compared: one was manufactured using WAAM, and the other was an Inconel 718 rolled bar (Aerospace Material Specifications 5662). Using the testing procedure, a conventional two-flute cutting tool was used to assess their machinability. For this process, multiple passes were performed at three different heights of the samples. Considering the peculiarities of the AM products, such as their uneven surfaces, dendritic microstructures, and anisotropy, the results were analyzed. After the machining operation, the effects on the products were also studied by analyzing their surface quality. This study found a higher stability in the cutting process for the AMS 5662 samples relative to the WAAM parts with less variability in the cutting forces overall, resulting in better surface quality. Full article

Incremental sheet forming (ISF) is an advanced flexible manufacturing process to produce complex 3D products. Unlike the conventional stamping process, ISF does not require any high cost dedicated dies. However, numerical computation for large-size ISF processes is time-consuming, and its accuracy for spring back due to unclamping tools after ISF cannot satisfy industrial demand. In this paper, an advanced numerical model considering complicated forming tool paths, trimming, and spring back was developed to efficiently simulate the multi-stage deformation phenomena of incremental sheet forming processes. Numerical modeling accuracy and efficiency are investigated considering the influence of tool path, material properties of the blank, mesh size, and boundary conditions. Through a series of case studies and comparisons with experimental results, it is observed that the numerical model with kinematics material properties and a moderate element size (5 mm) may reproduce the deformation characteristics of ISF with good accuracy and can obtain practical efficiency for a large-size ISF part. Full article

Biomass–fungi biocomposite materials are derived from sustainable sources and can biodegrade at the end of their service. They can be used to manufacture products that are traditionally made from petroleum-based plastics. There are potential applications for these products in the packaging, furniture, and construction industries. In the biomass–fungi biocomposite materials, the biomass particles (made from agricultural waste such as hemp hurd) act as the substrate, and a network of fungal hyphae grow through and bind the biomass particles together. Typically, molding-based methods are used to manufacture products using these biocomposite materials. Recently, the authors reported a novel extrusion-based 3D printing method using these biocomposite materials. This paper reports a follow-up investigation into the effects of mixing parameters (mixing time and mixing mode) on fungal growth in biomass–fungi mixtures prepared for 3D printing and the effects of printing parameters (printing speed and extrusion pressure) on fungal growth in printed samples. The fungal growth was quantified using the number of fungal colonies that grew from samples. The results show that, when mixing time increased from 15 to 120 s, there was a 52% increase in fungal growth. Changing from continuous to intermittent mixing mode resulted in an 11% increase in fungal growth. Compared to mixtures that were not subjected to printing, samples printed with a high printing speed and high extrusion pressure had a 14.6% reduction in fungal growth, while those with a low printing speed and low extrusion pressure resulted in a 16.5% reduction in fungal growth. Full article

Ti6Al4V alloy (Ti64) is a popular material used in the aerospace, medical, and automotive industries due to its excellent mechanical properties. Laser Powder Bed Fusion (LPBF) is a promising manufacturing technique that can produce complex and net-shaped components with comparable mechanical properties to those produced using conventional manufacturing techniques. However, during LPBF, the rapid cooling of the material can limit its ductility, making it difficult to achieve high levels of ductility while maintaining the required tensile strength for critical applications. To address this challenge, this study presents a novel approach to controlling the microstructure of Ti64 during LPBF by using a border design surrounding the main parts. It is hypothesized that the design induces in situ martensitic decomposition at different levels during the fabrication process, which can enhance the ductility of the material without compromising its tensile strength. To achieve this aim, a series of Ti64 samples were fabricated using LPBF with varying border designs, including those without borders and with gaps from 0.5 to 4 mm. The microstructure, composition, and mechanical properties of the Reference sample were compared with those of the samples fabricated with the surrounding border design. It was found that the latter had a more homogenized microstructure, a higher density, and improvements in both ductility and tensile strength. Moreover, it was discovered that the level of property improvement and martensitic transformation can be controlled by adjusting the gap space between the border and the main part, providing flexibility in the fabrication process. Overall, this study presents a promising approach for enhancing the mechanical properties of Ti64 produced via LPBF, making it more suitable for critical applications in various industries. Full article

The electro-discharge (ED) drilling of precision boreholes in difficult-to-machine materials, particularly with respect to the cost-effectiveness of the overall process, is still a challenge. Flushing is one key factor for the precise machining of boreholes, especially with high aspect ratios. Therefore, the influence of internal and external flushing geometries for six types of brass tool electrodes with a diameter of 3 mm with and without a helical groove was analyzed experimentally and numerically. Using this helical external flushing channel, drilling experiments in X170CrVMo18-3-1 (Elmax Superclean) with an aspect ratio of five revealed a material removal rate (MRR) that was increased by 112% compared with a rod electrode, increased by 28% for a single-channel tool electrode and decreased by 8% for a multi-channel tool electrode. Signal analyses complemented these findings and highlighted correlations between classified discharge event types and the experimental target parameters. Amongst others, it was verified that the arcing frequency ratio drove the electrode wear rate and the beneficial frequency ratio correlated with the MRR and the surface roughness Ra. Sophisticated 3D computational fluid dynamics (CFD) models of the liquid phase were introduced and evaluated in great detail to demonstrate the validity and further elucidate the effect of the external flushing channel on the evacuation capability of debris and gas bubbles. The presented methods and models were found to be suitable for obtaining in-depth knowledge about the flushing conditions in the ED drilling working gap. Full article

Unique friction-based self-piercing riveting (F-SPR) was employed to join high-strength, low-ductility aluminum alloy 7055 for lightweight vehicle applications. This study aimed to maximize the joint strength of the AA7055 F-SPR joint while avoiding cracking issues due to low ductility at room temperature. A fully coupled Eulerian–Lagrangian (CEL) model was employed to predict the process temperature during F-SPR, and the temperature field was then mapped onto a 2D axisymmetric equivalent model for accelerated numerical analysis. The geometry, dimensions, and material strength of the rivet, as well as the depth of the die cavity and plunging depth, were investigated to enhance joint formation. Also, a static finite-element analysis model was developed to predict and analyze the stress distribution in the rivet under different mechanical testing loading conditions. Overall, the numerical model showed good agreement with the experiment results, such as joint formation and mechanical joint strength. With the aid of virtual fabrication through numerical modeling, the joint design iterations and process development time of F-SPR were greatly reduced regarding the goal of lightweight, high-strength aluminum joining. Full article

High-strength steels (HSS) appear as a good alternative to common steels to reduce vehicle weight, thus reducing fuel consumption. Despite the excellent mechanical behavior towards its lower weight, its application in industry is still limited, as manufacturing such materials suffers from limitations, especially regarding formability. The literature shows springback to be the most common problem. Among the parameters that can be studied to minimize this problem, the temperature appears, according to the literature, to be one of the most influential parameters in minimizing springback. However, the consequence of the temperature increase on the forming limits of materials is not completely understood. This study proposes to determine the consequences of the use of the temperature rise technique in the forming limits of high-strength steels. Two different steels were studied (HSLA 350/440 and DP 350/600). To evaluate the formability, the Nakazima method was used (practical). Finite element models were made which describe the material as well as Nakazima experimental behavior. To predict the forming limit strains via the numerical method, the thickness gradient criterion was applied. The practical and computational results were compared to validate the finite element model. Four different temperature ranges were analyzed. In general, it was found that 400 °C has a negative impact on the forming limits of both steels. This negative effect was found to be due to the alloying elements, such as silicon and manganese, present in the alloy. These alloying elements take part in the increase and decrease in resistance coefficient at the elevated temperature. For HSLA 350/440 steel, the forming limit strain decreased with an increase in temperature up to 600 °C and then increased at 800 °C; whereas for DP 350/600 steel, the forming limit strain decreased till 400 °C and then increased for 600 °C and 800 °C. Another factor which might have contributed to the behavior of the DP steel is the interaction of hard martensite with soft ferrite phase. Full article