Editor’s Choice Articles

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

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

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

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

In recent years, Additive Manufacturing (AM) has emerged as a transformative technology, with the process of Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M) gaining substantial attention for its precision and versatility in fabricating metal components. A major challenge in PBF-LB/M is the failure of the component or the support structure during the production process. In order to locate a possible residual stress-induced failure prior to the fabrication of the component, a suitable failure criterion has to be identified and implemented in process simulation software. In the work leading to this paper, failure criteria based on the Rice-Tracey (RT) and Johnson-Cook (JC) fracture models were identified as potential models to reach this goal. The models were calibrated for the nickel-based superalloy Inconel 718. For the calibration process, a conventional experimental, a combined experimental and simulative, and an AM-adapted approach were applied and compared. The latter was devised to account for the particular phenomena that occur during PBF-LB/M. It was found that the JC model was able to capture the calibration data points more precisely than the RT model due to its higher number of calibration parameters. Only the JC model calibrated by the experimental and AM-adapted approach showed an increased equivalent plastic failure strain at high triaxialities, predicting a higher cracking resistance. The presented results can be integrated into a simulation tool with which the potential fracture location as well as the cracking susceptibility during the manufacturing process of PBF-LB/M parts can be predicted. Full article

This study examined the impact of vibration-assisted drilling (VAD) on hole quality and residual stress in Ti-6Al-4V ELI (Extra Low Interstitials) material. Ti-6Al-4V ELI possesses excellent mechanical properties but presents challenges in machining, including chip evacuation, burr formation, and elevated cutting temperatures. VAD, particularly low-frequency vibration-assisted drilling (LF-VAD), has been explored as a potential solution to address these issues. The research compares LF-VAD with conventional drilling (CD) under various cutting and cooling conditions. LF-VAD exhibits higher maximum thrust forces under specific conditions, which result in accelerated tool wear. However, it also demonstrates lower RMS (root mean square) forces compared to CD, offering better control over chip formation, reduced burr formation, and improved surface roughness within the hole. Furthermore, LF-VAD generates greater compressive residual stresses on the hole’s inner surface compared to CD, suggesting enhanced fatigue performance. These findings indicate that LF-VAD holds promise for improving the hole’s surface characteristics, fatigue life, and overall component durability in Ti-6Al-4V machining applications. Full article

To save computational time and physical memory in welding thermo-mechanical analysis, an accurate adaptive mesh refinement (AMR) method was proposed based on the feature of moving heat source during the welding. The locally refined mesh was generated automatically according to the position of the heat source to solve the displacement field. A background mesh, without forming a global matrix, was designed to maintain the accuracy of stress and strain after mesh coarsening. The solutions are always carried out on the refined computational mesh using a selective integration scheme. To evaluate the performance of the developed method, a fillet welding joint was first analyzed via validation of the accuracy of conventional FEM by experiment. Secondly, a larger fillet joint and its variations with a greater number of degrees of freedom were analyzed via conventional FEM and current AMR. The simulation results confirmed that the proposed method is accurate and efficient. An improvement in computational efficiency by 7 times was obtained, and memory saving is about 63% for large-scale models. Full article

This study uses machine learning methods to model different stages of the calcination process in cement, with the goal of improving knowledge of the generation of CO₂ during cement manufacturing. Calcination is necessary to determine the clinker quality, energy needs, and CO₂ emissions in a cement-producing facility. Due to the intricacy of the calcination process, it has historically been challenging to precisely anticipate the CO₂ produced. The purpose of this study is to determine a direct association between CO₂ generation from the manufacture of raw materials and the process factors. In this paper, six machine learning techniques are investigated to explore two output variables: (1) the apparent degree of oxidation, and (2) the apparent degree of calcination. CO₂ molecular composition (dry basis) sensitivity analysis uses over 6000 historical manufacturing health data points as input variables, and the results are used to train the algorithms. The Root Mean Squared Error (RMSE) of various regression models is examined, and the models are then run to ascertain which independent variables in cement manufacturing had the largest impact on the dependent variables. To establish which independent variable has the biggest impact on CO₂ emissions, the significance of the other factors is also assessed. Full article

Analyzing the cutting process characteristics opens up significant opportunities to improve various material machining processes. Numerical modeling is a well-established, powerful technique for determining various characteristics of cutting processes. The developed spatial finite element model of short hole drilling is used to determine the kinetic characteristics of the machining process, in particular, the components of cutting force and cutting power. To determine the component model parameters for the numerical model of drilling, the constitutive equation parameters, and the parameters of the contact interaction between the drill and the machined material on the example of AISI 1045 steel machining, the orthogonal cutting process was used. These parameters are determined using the inverse method. The DOE (Design of Experiment) sensitivity analysis was applied as a procedure for determining the component models parameters, which is realized by multiple simulations using the developed spatial FEM model of orthogonal cutting and the subsequent determination of generalized values of the required parameters by finding the intersection of the individual value sets of these parameters. The target values for the DOE analysis were experimentally determined kinetic characteristics of the orthogonal cutting process. The constitutive equation and contact interaction parameters were used to simulate the short hole drilling process. The comparison of experimentally determined and simulated values of the kinetic characteristics of the drilling process for a significant range of cutting speed and drill feed changes has established their satisfactory coincidence. The simulated value deviation from the corresponding measured characteristics in the whole range of cutting speed and drill feed variation did not exceed 23%. Full article

Cracks usually generate during the formation of beads composed of a WC-12mass%Co cemented carbide by the laser metal deposition (LMD). Measuring temperatures of the formed bead and substrate during the LMD process is important for realizing crack-free beads. In this study, temperatures of the substrate around the formed bead during the LMD process were measured using a thermoviewer. Temperatures of the formed beads during the LMD process were predicted by simulation based on the thermal conduction analysis using the experimentally measured temperatures of the substrate. The experimental results obtained during forming the WC-12mass%Co cemented carbide beads on JIS SKH51 (ISO HS-6-5-2) substrates showed that the maximal temperatures of the substrates at 0.2 mm away from the center of the formed beads ranged from 229 °C to 341 °C at laser powers ranging from 80 W to 160 W. The predicted maximal temperatures of the formed beads were in the range of 2433 °C to 4491 °C in the simulation using a laser absorption coefficient of 0.35 for the substrate. Validity of these simulation results was discussed based on the melting point of the substrate and microstructures of the formed WC-12mass%Co cemented carbide beads. Full article

The development of the additive manufacturing (AM) technology proffers challenging requirements for forming accuracy and efficiency. In this paper, a hybrid additive manufacturing technology combining fusion-based selective laser melting (SLM) and solid-state cold spraying (CS) was proposed in order to enable the fast production of near-net-shape metal parts. The idea is to fabricate a bulk deposit with a rough contour first via the “fast” CS process and then add fine structures and complex features through “slow” SLM. The experimental results show that it is feasible to deposit an SLM part onto a CS part with good interfacial bonding. However, the CS parts must be subject to heat treatment to improve their cohesion strength before being sending for SLM processing. Otherwise, the high tensile residual stress generated during the SLM process will cause fractures and cracks in the CS part. After heat treatment, pure copper deposited by CS undergoes grain growth and recrystallization, resulting in improved cohesive strength and the release of the residual stress in the CS parts. The tensile test on the SLM/CS interfacial region indicates that the bonding strength increased by 38% from 45 ± 7 MPa to 62 ± 1 MPa after the CS part is subject to heat treatment, and the SLM/CS interfacial bonding strength is higher than the CS parts. This study demonstrates that the proposed hybrid AM process is feasible and promising for manufacturing free-standing SLM-CS components. Full article

Fused filament fabrication (FFF), colloquially known as 3D-printing, has gradually expanded from the laboratory to the industrial and household realms due to its suitability for producing highly customized products with complex geometries. However, it is difficult to evaluate the mechanical performance of samples produced by this method of additive manufacturing (AM) due to the high number of combinations of printing parameters, which have been shown to significantly impact the final structural integrity of the part. This implies that using experimental data attained through destructive testing is not always viable. In this study, predictive models based on the rapid prediction of the required extrusion force and mechanical properties of printed parts are proposed, selecting a subset of the most representative printing parameters during the printing process as the domain of interest. Data obtained from the in-line sensor-equipped 3D printers were used to train several different predictive models. By comparing the coefficient of determination (R²) of the response surface method (RSM) and five different machine learning models, it is found that the support vector regressor (SVR) has the best performance in this data volume case. Ultimately, the ML resources developed in this work can potentially support the application of AM technology in the assessment of part structural integrity through simulation and can also be integrated into a control loop that can pause or even correct a failing print if the expected filament force-speed pairing is trailing outside a tolerance zone stemming from ML predictions. Full article

Within the rapidly growing market for fiber-reinforced plastics (FRPs), conventional production processes involving molds are not cost-efficient for prototype and small series production. Therefore, new flexible forming techniques are increasingly being researched, many of which have been inspired by incremental sheet metal forming (ISF). Due to the different deformation mechanisms of woven reinforcement fibers and metal sheets, ISF is not directly applicable to FRP. Instead, shear and bending of the fibers need to be realized. Therefore, a new dieless forming process for the production of FRP supported by metal wire mesh as an auxiliary material is proposed. Two standard tools, such as hemispherical punches, are used to locally bend a reversible layup of metal wire mesh and woven reinforcement fiber fabric enclosed in a vacuum bag. Therefore, the mesh aids in introducing shear into the material due to its ability to transmit compressive in-plane forces, and it ensures that the otherwise flexible fabric maintains the intended deformation until the part is cured or solidified. Basic experiments are conducted using thermoset prepreg, woven commingled yarn fabric, and thermoplastic organo sheets, proving the feasibility of the approach. Full article

Single-point incremental forming (SPIF) has emerged as a time-efficient approach that offers increased material formability compared to conventional sheet-metal forming techniques. However, the physical interaction between the forming tool and the sheet poses challenges, such as tool wear and formability limits. This study introduces a novel sheet-forming technique called contactless single-point incremental forming (CSPIF), which uses hot compressed air as a deformation tool, eliminating the requirement for physical interaction between the sheet and a rigid forming tool. In this study, a polycarbonate sheet was chosen as the case-study material and subjected to the developed CSPIF. The experiments were carried out at an air temperature of 160 °C, air pressure of 1 bar, a nozzle speed of 750 mm/min, and a step-down thickness of 0.75 mm. A Schlieren setup and a thermal camera were used to visualize the motion of the compressed hot air as it traveled from the nozzle to the sheet. The results showed that the CSPIF technique allowed for the precise shaping of the polycarbonate sheet with minimal springback. However, minor deviations from the designed profile were observed, primarily at the starting point of the nozzle, which can be attributed to the bending effects of the sample. In addition, the occurrence of sheet thinning and material buildup on the deformed workpiece was also observed. The average surface roughness (Ra) of the deformed workpiece was measured to be 0.2871 microns. Full article

Electromagnetic forming is applied to form metal sheet parts from both non-ferrous and ferrous materials. In this paper, the electromagnetic forming behavior of aluminum alloy, copper and steel sheets was investigated through experiments. The disk-shaped specimens were electromagnetically free bulged with increasing deformation energies and parts with different deformation depths were obtained. The deformation was done with and without clamping the movement of the specimens’ edges. The specimens were printed with a mesh of diametrical lines and concentric circles with a predetermined pitch. The mesh served to determine the displacements in the mesh nodes after the deformation of the specimens, with which the axial, radial and circumferential strains were then calculated. The experimental data obtained was subjected to statistical correlation and regression analyses, and the mathematical models for the three main strains in each material were established. The strains of AlMn0.5Mg0.5 and Cu-OF parts are maximum in the center and have a similar variation, while the FeP04 parts have the maximum strains in an intermediate zone between the center and the edge. Full article

Straining of sheet metal leads to surface roughness changes. In this study, foils of AISI 201 and AISI 304 stainless steel were strained in uniaxial tension to impose roughening of their surfaces. Thereafter, the corrosion resistance, electrical resistivity, magnetic field density, and lubricated friction of the resulting surfaces were evaluated. The effect of strain-rate on the surface roughening, and thereby on the friction against tools, corrosion resistance, and occurrence of deformation-induced martensite was investigated. The AISI 304 material showed higher roughening than AISI 201 at low strain-rate. Lubricated friction is clearly affected by the changes to the surface of the strained foils that occur. When simulating a micro-forming process, the effect of strain-induced changes should be included where possible to maintain a high fidelity of the simulation. Strain-rate, in the range tested in this work, had only a minor effect on corrosion properties; however, the martensite fraction was reduced for material elongated at higher strain-rates. Full article

Additive Manufacturing (AM) is gaining importance as an alternative and complementary technology to conventional manufacturing processes. Among AM technologies, the Atomic Diffusion Additive Manufacturing (ADAM) technology is a novel extrusion-based process involving metallic filaments. In this work, the widely used 17-4 PH stainless steel filament was selected to study the effect of different deposition strategies of ADAM technology on mechanical properties. The printed parts had mechanical properties comparable to those obtained by other more developed AM technologies. In the case of tensile and fatigue tests, obtained values were in general greatly affected by deposition strategy, achieving better results in horizontal built orientation specimens. Interestingly, the effect was also considered of machining post-process (turning), which in the case of the tensile test had no remarkable effect, while in fatigue tests it led to an improvement in fatigue life of two to four times in the tested range of stresses. Full article

Thermal conductivity (TC) is greatly influenced by the working temperature, microstructures, thermal processing (heat treatment) history and the composition of alloys. Due to computational costs and lengthy experimental procedures, obtaining the thermal conductivity for novel alloys, particularly parts made with additive manufacturing, is difficult and it is almost impossible to optimize the compositional space for an absolute targeted value of thermal conductivity. To address these difficulties, a machine learning method is explored to predict the TC of additive manufactured alloys. To accomplish this, an extensive thermal conductivity dataset for additively manufactured alloys was generated for several AM alloy families (nickel, copper, iron, cobalt-based) over various temperatures (300–1273 K). This unique dataset was used in training and validating machine learning models. Among the five different regression machine learning models trained with the dataset, extreme gradient boosting performs the best as compared with other models with an R² score of 0.99. Furthermore, the accuracy of this model was tested using Inconel 718 and GRCop-42 fabricated with laser powder bed fusion-based additive manufacture, which have never been observed by the extreme gradient boosting model, and a good match between the experimental results and machine learning prediction was observed. The average mean error in predicting the thermal conductivity of Inconel 718 and GRCop-42 at different temperatures was 3.9% and 2.08%, respectively. This paper demonstrates that the thermal conductivity of novel AM alloys could be predicted quickly based on the dataset and the ML model. Full article

This paper presents a systematic approach to developing big data analytics for manufacturing process-relevant decision-making activities from the perspective of smart manufacturing. The proposed analytics consist of five integrated system components: (1) Data Preparation System, (2) Data Exploration System, (3) Data Visualization System, (4) Data Analysis System, and (5) Knowledge Extraction System. The functional requirements of the integrated system components are elucidated. In addition, JAVA™- and spreadsheet-based systems are developed to realize the proposed system components. Finally, the efficacy of the analytics is demonstrated using a case study where the goal is to determine the optimal material removal conditions of a dry Electrical Discharge Machining operation. The analytics identified the variables (among voltage, current, pulse-off time, gas pressure, and rotational speed) that effectively maximize the material removal rate. It also identified the variables that do not contribute to the optimization process. The analytics also quantified the underlying uncertainty. In summary, the proposed approach results in transparent, big-data-inequality-free, and less resource-dependent data analytics, which is desirable for small and medium enterprises—the actual sites where machining is carried out. Full article

While Inconel 718 is a widely used engineering material in industrial fields such as the aerospace and automotive fields, the machined surface integrity has a significant effect on the performance of its components and parts. In this work, the laser-assisted micro-milling process of Inconel 718 is investigated using a combination of experiments and finite element simulations. Firstly, an experimental platform of laser-assisted milling is built, and a three-dimensional thermal–mechanical coupled finite element model of laser-assisted milling of Inconel 718 is then established. Secondly, laser-assisted milling experiments and finite element simulations are conducted to investigate the impact of laser assistance on cutting force, chip morphology, tool wear and surface topography of Inconel 718 under a milling process. The results indicate that laser-assisted milling results in a moderate reduction in cutting forces while enhancing surface integrity and chip continuity, as compared with ordinary milling. Thirdly, orthogonal experiments of laser-assisted milling of Inconel 718 are conducted to discover the optimal processing parameters, including spindle speed, feed per tooth, milling depth and laser parameters. Finally, single-factor experiments are conducted to investigate the effect of laser power on cutting force, chip morphology, tool wear, groove burr and surface roughness in the laser-assisted milling of Inconel 718. And, a minimal surface roughness Sa of 137 nm for Inconel 718 accompanied by minimal tool wear is experimentally obtained via laser-assisted milling. These findings highlight the effectiveness of applying laser assistance in enhancing the machinability of difficult-to-machine materials for achieving desirable machined surface integrity. Full article

Shearing high-strength steels often leads to a subpar cut quality and excessive stress on the tool components. To enhance the quality of the cut surface, intricate techniques like fine blanking are commonly employed. However, for applications with lower quality requirements, precision shear cutting offers an alternative solution. This research paper introduces a novel approach to directly superimpose radial stress on a workpiece during the precision shear cutting process and showcases for the first time how the application of direct stress superimposition can impact the cut surface by concurrently modifying the shear cutting edge and punch surface. A statistical experimental design is employed to investigate the interrelationships between the parameters and their effects. The results indicate that the overall cut quality, including cylindricity, clean-cut angle, rollover height, and tool stress, defined by punch force and retraction force, is influenced by the superimposed stress. Regarding the clean-cut zone, the statistical significance of direct radially superimposed stress was not observed, except when interacting with sheet thickness and clearance. Additionally, the sheet thickness and cutting gap emerged as significant parameters affecting the overall quality of the cut surface. Full article

Laser-based powder bed fusion is an additive manufacturing process in which a high-power laser melts a thin layer of metal powder layer by layer to yield a three-dimensional object. An inert gas must remove process byproducts formed during laser processing to ensure a stable and consistent process. The process byproducts include a plasma plume and spatter particles. An NC sensor gantry is installed inside a bespoke open-architecture laser-based powder bed fusion system to experimentally characterize the gas velocity throughout the processing area. The flow maps are compared to manufactured samples, where the relative density and melt pools are analyzed, seeking a potential correlation between local gas flow conditions and the components. The results show a correlation between low gas flow velocities and increased porosity, leading to lower part quality. Local flow conditions across the build plate also directly impact components, highlighting the importance of optimizing the gas flow subsystem. The experimental flow analysis method enables optimization of the gas flow inlet geometry, and the data may be used to calibrate the computational modeling of the process. Full article

Multi-material additive manufacturing (AM) attempts to utilize the full benefits of complex part production with a comprehensive and complementary material spectrum. In this context, this research article presents new processing strategies in the field of polymer- and metal-based multi-material AM. The investigation highlights the current progress in powder-based multi-material AM based on three successfully utilized technological approaches: additive and formative manufacturing of hybrid metal parts with locally adapted and tailored properties, material-efficient AM of multi-material polymer parts through electrophotography, and the implementation of UV-curable thermosets within the laser-based powder bed fusion of plastics. Owing to the complex requirements for the mechanical testing of multi-material parts with an emphasis on the transition area, this research targets an experimental shear testing set-up as a universal method for both metal- and polymer-based processes. The method was selected based on the common need of all technologies for the sufficient characterization of the bonding behavior between the individual materials. Full article

Driven by high energy prices, AHSS are still gaining importance in the automotive industry regarding electric vehicles and their battery range. Simulation-based design of forming processes can contribute to exploiting their potential for lightweight design. Fracture models are frequently used to predict the material’s failure and are often parametrised using different tensile tests with optical measurements. Hereby, the fracture is determined by a surface crack. However, for many steels, the fracture initiation already occurs inside the specimen prior to a crack on the surface. This leads to inaccuracies and more imprecise fracture models. Using a method that detects the fracture initiation within the specimen, such as acoustic emission analysis, has a high potential to improve the modelling accuracy. In the presented paper, tests for fracture characterisation with two AHSS were performed for a wide range of stress states and measured with a conventional optical as well as a new acoustical measurement system. The tests were analysed regarding the fracture initiation using both measurement systems. Numerical models of the tests were created, and the EMC fracture model was parametrised based on the two evaluation areas: a surface crack as usual and a fracture from the inside as a novelty. The two fracture models were used in a deep drawing simulation for analysis, comparison and validation with deep drawing experiments. It was shown that the evaluation area for the fracture initiation had a significant impact on the fracture model. Hence, the failure prediction of the EMC fracture model from the acoustic evaluation method showed a higher agreement in the numerical simulations with the experiments than the model from the optical evaluation. Full article

Dynamic machine tool simulation models can be used for various applications such as process simulations, design optimization, and condition monitoring. However, all these applications require that the model replicates the real system’s behavior as accurately as possible. Next to carefully building the model, the parameterization of the model, that is, determining the parameter values the model is based upon, is the most crucial step. This paper describes the application of both sensitivity-based and black-box parameter identification to a machine tool. It further provides a comparison between these two methods and the method of sequential assembly. It is shown that both methods can increase the mode shape conformity by more than 25% and significantly reduce damping deviations. However, sensitivity-based parameter identification is the most economical method, offering the chance to update a dynamic machine tool model within minutes. Full article

Fatigue properties of parts are of particular concern for safety-critical structures. It is well-known that discontinuities in shape or non-uniformities in materials are frequently a potential nucleus of fatigue failure. This is especially crucial for the Ti6Al4V alloy, which presents high susceptibility to the notch effect. This study investigates how post-processing treatments affect the mechanical performance of Ti6Al4V samples manufactured by laser powder bed fusion technology. All the fatigue samples were subjected to a HIP cycle and post-processed by machining and using combinations of alternative mechanical and electrochemical surface treatments. The relationship between surface properties such as roughness, topography and residual stresses with fatigue performance was assessed. Compressive residual stresses were introduced in all surface-treated samples, and after tribofinishing, roughness was reduced to 0.31 ± 0.10 µm, which was found to be the most critical factor. Fractures occurred on the surface as HIP removed critical internal defects. The irregularities found in the form of cavities or pits were stress concentrators that initiated cracks. It was concluded that machined surfaces presented a fatigue behavior comparable to wrought material, offering a fatigue limit superior to 450 MPa. Additionally, alternative surface treatments showed a fatigue behavior equivalent to the casting material. Full article

The innovative Green Ceramic Hybrid Machining (GCHM) process sequentially combines milling with a cutting tool (GCM, Green Ceramic Machining) and laser beam machining (GCLBM) of a ceramic material (black Y-TZP in this study) at the green stage mainly to increase productivity, avoid taper angle limitations of laser beam machining, and obtain micro-features. The study focuses on the reliability and the repeatability of the properties of sintered parts obtained by three manufacturing processes (GCM, GCLBM, GCHM) to assess the performance of hybridisation. It turns out that GCHM is a compromise of both milling and laser beam processes; it increases the repeatability of the surface quality and it slightly reduces (less than 7%) the flexural strength by comparison to milling for a similar reliability. The study also highlights that the surface quality of GCLBM processed parts relies on of the surface generated by the previous operation. Milling that surface at the previous step is therefore recommended, corresponding to the sequence adopted by GCHM. Full article

Nickel-based Ni-Cr-Si-B self-fluxing alloys are excellent candidates to replace cobalt-based alloys in aeronautical components. In this work, metal additive manufacturing by directed energy deposition using a laser beam (DED-LB, also known as LMD) and gas-atomized powders as a material feedstock is presented as a potential manufacturing route for the complex processing of these alloys. This research deals with the advanced material characterization of these alloys obtained by LMD and the study and understanding of their solidification paths and strengthening mechanisms. The as-built microstructure, the Vickers hardness at room temperature and at high temperatures, the nanoindentation hardness and elastic modulus of the main phases and precipitates, and the strengthening mechanisms were studied in bulk cylinders manufactured under different chemical composition grades and DED-LB/p process parameter sets (slow, normal, and fast deposition speeds), with the aim of determining the influence of the chemical composition in commercial Ni-Cr-Si-Fe-B alloys. The hardening of Ni-Cr-Si-Fe-B alloys obtained by LMD is a combination of the solid solution hardening of gamma nickel dendrites and eutectics and the contribution of the precipitation hardening of small chromium-rich carbides and hard borides evenly distributed in the as-built microstructure. Full article

This paper introduces a new formability test based on double-action radial extrusion to characterize material formability in the three-dimensional to plane-stress material flow transitions that are found in bulk metal-formed parts. The presentation draws from a multidirectional tool, which was designed to convert the vertical press stroke into horizontal movement of the compression punches towards each other, aspects of experimental strain determination, fractography, and finite element analysis. Results show that three-dimensional to plane-stress material flow transitions at the radially extruded flanges lead to different modes of fracture (by tension and by shear) that may or may not be preceded by necking, such as in sheet metal forming. The new formability test also reveals adequate characteristics to characterize the failure limits of very ductile wrought and additively manufactured metallic materials, which cannot be easily determined by conventional upset compression tests, and to facilitate the identification of the instant of cracking and of the corresponding fracture strains by combination of the force vs. time evolutions with the in-plane strains obtained from digital image correlation. Full article

The residual stress state of the machined sub-surface influences the service quality indicators of a component, such as fatigue life, tribological properties, and distortion. During machining, the radius of the cutting edge changes due to tool wear. The cutting-edge rounding significantly affects the residual stress state in the part and the occurring process forces. This paper presents a tool wear prediction model based on in-process measured cutting forces. The effects of the cutting-edge geometry on the force behavior and the machining-induced residual stresses were examined experimentally. The resulting database was used to realize a Machine Learning algorithm to calculate the hidden value of tool wear. The predictions were validated by milling experiments using rounded cutting edges for different process parameters. The microgeometry of the cutting edge could be determined with a Root Mean Square Error of 8.94 μm. Full article

Wire arc additive manufacturing (WAAM) is an emerging and promising technology for producing medium-to-large-scale metallic components/structures for different industries, i.e., aerospace, automotive, shipbuilding, etc. It is now a feasible alternative to traditional manufacturing processes due to its shorter lead time, low material waste, and cost-effectiveness. WAAM has been widely used to produce components using different materials, including copper-based alloy wires, in the past decades. This review paper highlights the critical aspects of WAAM process in terms of technology, various challenges faced during WAAM process, different in-process and post-process operations, process monitoring methods, various gases, and different types of materials used in WAAM process. Furthermore, it briefly overviews recent developments in depositing different copper-based alloys via WAAM process. Full article

X-ray-computed tomography (CT) is today’s gold standard for the non-destructive evaluation of internal component defects such as cracks and porosity. Using automated standardized evaluation algorithms, an analysis can be performed without knowledge of the shape, location, or size of the defects. Both the measurement and the evaluation are based on the fact that the component has no internal structures or cavities. However, additive manufacturing (AM) and hybrid subtractive procedures offer the possibility of integrating internal structures directly during the building process. The examination of powder bed fusion (PBF) samples made of Ti64 and PA12 showed that the standardized evaluation methods were not able to identify internal structures correctly. Different evaluation methods for the CT-measured values were analyzed and recommendations on a procedure for measuring internal structures are given. Full article

In this work, an innovative manufacturing approach that includes a fully linked and integrated manufacturing system consisting of a laser-based directed energy deposition (DED-LB/M) module and a forming press is presented. The alternating additive manufacturing (AM) process is based on a combination of a DED-LB/M process using a laser power of 600 W and a feed rate of 400 mm/min and a subsequent forming process, in which the structure is upset with a hydraulic press using a constant forming force of 500 kN in order to smooth the surface and influence the accuracy of the components. For the generation of a fundamental process understanding, a cuboid, basic shape was chosen as geometry for the investigations. The aim is to improve part properties by applying the process steps to generate part properties, which are superior to solely additive manufactured material. It is shown that the geometry of additive manufactured structures can be adapted, and the top surface can be smoothed due to the forming operation. The mean roughness value Rz decreases up to 50% after the forming operation. The hardness can be increased by work hardening. Of special interest is that the higher hardness can be kept up even though a further DED-LB/M process step and forming operation are applied to the additively manufactured and formed structure again. Finally, an analysis of the new manufacturing approach regarding its potential is given. Full article

Ultrafast lasers are proven and continually evolving manufacturing tools. Concurrently, additive manufacturing (AM) has emerged as a key area of interest for 3D fabrication of objects with arbitrary geometries. Use of ultrafast lasers for AM presents possibilities for next generation manufacturing techniques for hard-to-process materials, transparent materials, and micro- and nano-manufacturing. Of particular interest are selective laser melting/sintering (SLM/SLS), multiphoton lithography (MPL), laser-induced forward transfer (LIFT), pulsed laser deposition (PLD), and welding. The development, applications, and recent advancements of these technologies are described in this review as an overview and delineation of the burgeoning ultrafast laser AM field. As they mature, their adoption by industry and incorporation into commercial systems will be facilitated by process advancements such as: process monitoring and control, increased throughput, and their integration into hybrid manufacturing systems. Recent progress regarding these aspects is also reviewed. Full article

VDM Alloy 780 is a novel Ni-based superalloy that allows for approximately 50 °C higher operating temperatures, compared to Inconel 718, without a significant decrease in mechanical properties. The age hardenable NiCoCr Alloy combines increased temperature strength with oxidation resistance, as well as improved microstructural stability due to γ′-precipitation. These advantages make it suitable for wear- and corrosion-resistant coatings that can be used in high temperature applications. However, VDM Alloy 780 has not yet been sufficiently investigated for laser metal deposition applications. A design of experiments with single tracks on 316L specimens was carried out to evaluate the influence of the process parameters on clad quality. Subsequently, the quality of the clads was evaluated by means of destructive and non-destructive testing methods, in order to verify the suitability of VDM Alloy 780 for laser metal deposition applications. The single-track experiments provide a basis for coating or additive manufacturing applications. For conveying the results, scatter plots with regression lines are presented, which illustrate the influence of specific energy density on the resulting porosity, dilution, powder efficiency, aspect ratio, width and height. Finally, the clad quality, in terms of porosity, is visualized by two process maps with different mass per unit lengths. Full article

The recent success of the process monitoring method Electron Optical Imaging, applied in the additive manufacturing process Electron Beam Powder Bed Fusion, necessitates a clear understanding of the underlying image formation process. Newly developed multi-detector systems enable the reconstruction of the build surface topography in-situ but add complexity to the method. This work presents a physically based raytracing model, which rationalises the effect of detector positioning on image contrast development and masking. The model correctly describes the effect of multiple scattering events on vacuum chamber walls or heat shields and represents, therefore, a predictive tool for designing future detector systems. Most importantly, this work provides a validated method to compute build surface height gradients directly from experimentally recorded electron-optical images of a multi-detector system without any calibration steps. The computed surface height gradients can be used subsequently as input of normal integration algorithms aiming at the in-situ reconstruction of the build surface topography. Full article

Additive Manufacturing (AM) has been a growing industry, specifically when trying to mass produce products more cheaply and efficiently. However, there are too many current setbacks for AM to replace traditional production methods. One of the major problems with 3D printing is the high error rate compared to other forms of production. These high error rates lead to wasted material and valuable time. Furthermore, even when parts do not result in total failure, the outcome can often be less than desirable, with minor misprints or porosity causing weaknesses in the product. To help mitigate error and better understand the quality of a given print, the field of AM monitoring in research has been ever-growing. This paper looks through the literature on two AM processes: fused deposition modeling (FDM) and laser bed powder fusion (LBPF) printers, to see the current process monitoring architecture. The review focuses on the optical monitoring of 3D printing and separates the studies by type of camera. This review then summarizes specific trends in literature, points out the current limitations of the field of research, and finally suggests architecture and research focuses that will help forward the process monitoring field. Full article

This paper describes a hybrid manufacturing approach for silicon carbide (SiC) freeform surfaces using binder jet additive manufacturing (BJAM) to print the preform and machining to obtain the design geometry. Although additive manufacturing (AM) techniques such as BJAM allow for the fabrication of complex geometries, additional machining or grinding is often required to achieve the desired surface finish and shape. Hybrid manufacturing has been shown to provide an effective solution. However, hybrid manufacturing also has its own challenges, depending on the combination of processes. For example, when the subtractive and additive manufacturing steps are performed sequentially on separate systems, it is necessary to define a common coordinate system for part transfer. This can be difficult because AM preforms do not inherently contain features that can serve as datums. Additionally, it is important to confirm that the intended final geometry is contained within the AM preform. The approach described here addresses these challenges by using structured light scanning to create a stock model for machining. Results show that a freeform surface was machined with approximately 70 µm of maximum deviation from that which was planned. Full article

Computer-aided manufacturing (CAM) techniques for hybrid manufacturing have led to new application areas in the manufacturing industry. In the tooling industry, cooling channels are used to enable specific heating and cooling cycles to improve the performance of the process. These internal cooling channels have been designed with limited manufacturing processes in mind, so, until recently, they were often straight in shape for cross-drilling operations and manufactured from a cast billet. To show a novel application of this common technology, a tool with integrated conformal cooling channels was manufactured using hybrid manufacturing (blown-powder DED and CNC machining) techniques. The computer-aided manufacturing strategy used, and the lessons learned are presented and discussed to enable future work in this industrial application space. Full article

The paper presents the microstructural characterization of the chip roots in high-speed steels and ceramic Ti₃SiC₂. The process of chip formation and the obtaining of adequate samples were carried out using the quick-stop method. The tests were carried out during the milling process; the “quick stop” method was carried out in order to obtain samples of the chip roots. This method was developed in-house by the authors. The chip roots were microscopically studied by means of a light microscope (LM) and a scanning electron microscope (SEM). Before the actual analysis, preparation was performed based on the standard metallographic technique. The analysis of the high-speed steels samples showed that, for the used cutting conditions, a discontinuous chip with a built-up edge (BUE) was formed. During the processing of the Ti₃SiC₂ ceramic, a significant difference was manifested in the chip formation process and a powder-like chip was produced. After utilizing a careful cutting process, a chip pattern was observed, from which it is evident that chip breakage during ceramic processing occurs without prior plastic deformation. In addition, the cutting force F_c was also measured during the milling process of the high-speed steels and the ceramic, and it was correlated with the cutting speed, feed per tooth and depth of cut. Full article

Additively manufactured thin-walled structures through selective laser melting (SLM) are of great interest in achieving carbon-neutral industrial manufacturing. However, residual stresses and warpages as well as recoater crashes often occur in SLM, leading to the build failure of parts, especially for large-scale and lightweight geometries. The challenge in this work consists of investigating how the recoater affects the warpage and (sometimes) causes the failure of different thin-walled Ti6Al4V parts (wall thickness of 1.0 mm). All these parts are printed on the same platform using a commercial SLM machine. After the loose powder removal and before the cutting operation, a 3D-scanner is used to obtain the actual warpage of each component. Next, an in-house coupled thermo-mechanical finite element model suitable for the numerical simulation of the SLM process is enhanced to consider the recoater effects. This numerical framework is calibrated to predict the thin-walled warpage as measured by the 3D-scanner. The combination of numerical predictions with experimental observations facilitates a comprehensive understanding of the mechanical behavior of different thin-walled components as well as the failure mechanism due to the recoater. The findings show that the use of a higher laser energy input causes larger residual stresses and warpage responsible for the recoater crashes. Finally, potential solutions to mitigate the warpage and the recoater crashes in the SLM of lightweight structures are assessed using the validated model. Full article

The damage layer produced during the Niobium sheets and cavity fabrication processes is one of the main reasons why cavities have to undergo an extensive surface preparation process to recover optimal superconducting properties. Today, this includes the use of lengthy, costly, and dangerous conventional polishing techniques as buffered chemical polishing (BCP), or electro-polishing (EP). We propose to avoid or at least significantly reduce the use of acids. We developed a novel method based on metallographic polishing of Nb sheets, consisting of 2–3 steps. We demonstrate that this surface processing procedure could be transferred to large dimensions and an industrialized scale thanks to the limited number of steps and its compatibility with standard lapping polishing devices. Full article

Consistent high volumetric performance of machine tools is an essential requirement for high-quality machining. Periodic machine tool calibration ensures said performance and allows for timely corrective actions preventing scrap or rework. Reducing the duration of the calibration process decreases associated cost through non-productive downtime and allows for data acquisition in thermal real-time. The authors enhance an indirect calibration method based on measuring points within the machine volume using a laser tracker by removing the necessity for standstill. To circumvent requiring high fidelity space and time synchronization between metrology system and machine tool, only deviations perpendicular to the path are considered. To do so, the 3D laser tracker data are rotationally transformed such that one axis aligns with the motion direction and can subsequently be omitted as input data for the system of equations solving for geometric errors. Due to the absence of unique measurement-point-to-machine-point mapping, data alignment between nominal path and measurement data is proposed as an iterative alignment process of points to path. The method is tested simulatively and experimentally. It demonstrated conformity to the simulation as well as to the pre-existing calibration method based on laser trackers and shows good agreement with the direct calibration device API XD Laser. Full article

A distinctive characteristic of the powder bed fusion with electron beam (PBF-EB) process is the sintering of the powder particles. For certain metallic materials, this is crucial for the success of the subsequent step, the melting, and, generally, the whole process. Despite the sintering mechanisms that occur during the PBF-EB process being similar to well-known powder metallurgy, the neck growth rates are significantly different. Therefore, specific analyses are needed to understand the influence of the PBF-EB process conditions on neck growth and neck growth rate. Additionally, some aspects, such as the rigid body motion of the particles during the sintering process, are still challenging to analyze. This work systematically investigated the effects of different particle diameters and particle diameter ratios. Additionally, the impact of the rigid body motion of the particles in the sintering was analyzed. This work demonstrated that the sintering results significantly depended on the EB-PBF process conditions. Full article

Given its layer-based nature, additive manufacturing is known as a family of highly capable processes for fabricating complex 3D geometries designed by means of evolutionary topology optimization. However, the required support structures for the overhanging features of these complex geometries can be concerningly wasteful. This article presents an approach for studying the manufacturability of the topology-optimized complex 3D parts required for additive manufacturing and finding the optimum corresponding build direction for the fabrication process. The developed methodology uses the density gradient of the design matrix created during the evolutionary topology optimization of the 3D domains to determine the optimal build orientation for additive manufacturing with the objective of minimizing the need for support structures. Highly satisfactory results are obtained by implementing the developed methodology in analytical and experimental studies, which demonstrate potential additive manufacturing mass savings of 170% of the structure’s weight. The developed methodology can be readily used in a variety of evolutionary topology optimization algorithms to design complex 3D geometries for additive manufacturing technologies with a minimized level of waste due to reducing the need for support structures. Full article

Metal additive manufacturing has reached a level where products and components can be directly fabricated for applications requiring small batches and customized designs, from tinny body implants to long pedestrian bridges over rivers. Wire-fed directed energy deposition based additive manufacturing enables fabricating large parts in a cost-effective way. However, achieving reliable mechanical properties, desired structural integrity, and homogeneity in microstructure and grain size is challenging due to layerwise-built characteristics. Manufacturing processes, alloy composition, process variables, and post-processing of the fabricated part strongly affect the resultant microstructure and, as a consequence, component serviceability. This paper reviews the advances in wire-fed directed energy deposition, specifically wire arc metal additive processes, and the recent efforts in grain tailoring during the process for the desired size and shape. The paper also addresses modeling methods that can improve the qualification of fabricated parts by modifying the microstructure and avoid repetitive trials and material waste. Full article

Laser powder bed fusion, particularly the selective laser melting (SLM), is an additive manufacturing (AM) technology used to produce near-net-shaped engineering components for biomedical applications, especially in orthopaedics. Ti6Al4V is commonly used for producing orthopaedic implants using SLM because it has excellent mechanical qualities, a high level of biocompatibility, and corrosion resistance. However, the main problems associated with this process are the result of its surface properties: it has to be able to promote cell attachment but, at the same time, avoid bacteria colonization. Surface modification is used as a post-processing technique to provide items the unique qualities that can improve their functionality and performance in particular working conditions. The goal of this work was to produce and analyse Ti6Al4V samples fabricated by SLM with different building directions in relation to the building plate (0° and 45°) and post-processed by anodization and passivation. The results demonstrate how the production and post processes had an impact on osteoblast attachment, mineralization, and osseointegration over an extended period of time. Though the anodization treatment result was cytotoxic, the biocompatibility of as-built specimens and specimens after passivation treatment was confirmed. In addition, it was discovered that effective post-processing increases the mineralization of these types of 3D-printed surfaces. Full article