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Over the last decade, the enormous potential of metal additive manufacturing (AM) processes has led these technologies to establish their position in many industries. Much effort is being made toward their widespread application; however, much remains to be done to achieve full industrialization of these processes. Therefore, many companies, research centers and universities are investing in comprehensive research and development activities in order to further promote the industrialization of metal AM. This review traces the progress of metal AM technologies through an investigation of patents. In the present study, beam-based metal AM patents were searched through the Orbit Intelligence database. First, the number of patents per year was studied, indicating that, as expected, there is strong growth in AM patenting activities. The patents were afterward examined in order to highlight the key players in the field, and it was found that the main players investing in this market are: multidisciplinary companies, AM machine producers, end users working, especially in the aerospace sector, universities and research centers. The patents were then analyzed to understand the technology domains covered by each key player and their trend of investments. Finally, the patents in the field of Materials and Metallurgy were studied individually to identify the main topics faced by the most used alloy classes: Al-, Ni- and Ti-based alloys and steels. The extensive study of these patents clearly indicated that the main gaps to fill in metal AM are strongly material dependent and that it is possible to find correlations between the alloy classes, their main industrial applications and their specific AM processability issues. The current study provides insights into global trends that can help industrial markets to identify the right investment direction and research to identify topics for future investigation.

Laser Powder-based Directed Energy Deposition (LP-DED) process is a cutting-edge Additive Manufacturing (AM) technology for metal part repair and production. The disruptive potentialities of LP-DED are nowadays limited by the difficulty in the identification of the optimized set of process parameters, typically obtained from long and expensive experimental trials. In this work, a thermal simulation tool able to predict material deposition behaviour is developed using a finite element code. An original method is defined to model the material addition and energy flow. The forecasting capabilities of the model in terms of penetration depth and track dimensions are evaluated by comparing the numerical outcomes with experimental data.

Additive manufacturing (AM) technology has great potential in manufacturing complex internal channels for several applications such as satellite communication systems, electronics and gas turbine airfoils. These applications can have complex shape and make traditional finishing processes a challenge for additive parts. Therefore, it is desirable that the internal surfaces be as close as possible to the tolerance of the field of application. In this study, a complex component was designed and manufactured in AlSi10Mg alloy through laser powder bed fusion (L-PBF) process. Using the data from the 3D scans, internal surface roughness and deviations from the CAD model were calculated.

Ti-48Al-2Cr-2Nb (Ti-48-2-2) is an intermetallic alloy belonging to a family of gamma-TiAl intermetallic alloys that are attracting significant attention. Electron Beam Melting (EBM) process is today the only manufacturing process that allows effective production of parts made by these kinds of alloys. Proper process control avoids high temperatures in the surrounding areas that may generate significant residual stresses that could cause micro-cracks. In this paper, an investigation on the residual stress state on Ti-48-2-2 parts is carried out using the hole drilling method. In particular, the influence of EBM process parameters is evaluated in order to understand the effects of the residual stresses on part integrity.

Screw-extrusion-based 3D printing or fused granular fabrication (FGF) is a less widespread variant of filament-based 3D printing for polymers. An FGF printer can be fed directly from polymer granules for improved sustainability. Shorter manufacturing routes and the potential of using recycled pellets from waste plastics are key features of FGF in the circular economy framework. A modified version of a standard Prusa i3 plus printer, which was equipped with a Mahor screw extruder, is used to test the mechanical performance of polylactic acid (PLA) processed with different layer infill and printing speed. Rheological and thermal analyses are carried out to characterise the material. The energy consumption of the FGF printer was measured during the fabrication of Dumbbell specimens. Tensile test results are consistent with other investigations presented in the literature. A higher printing speed promotes FGF eco-efficiency without a detrimental effect on the material strength, whereas lower printing speed should be preferred for increased material stiffness.

Cellularized scaffold is emerging as the preferred solution for tissue regeneration and restoration of damaged functionalities. However, the high cost of preclinical studies creates a gap between investigation and the device market for the biomedical industry. In this work, bone-tailored scaffolds based on the Ti6Al4V alloy manufactured by electron beam melting (EBM) technology with reused powder were investigated, aiming to overcome issues connected to the high cost of preclinical studies. Two different elementary unit cell scaffold geometries, namely diamond (DO) and rhombic dodecahedron (RD), were adopted, while surface functionalization was performed by coating scaffolds with single layers of polycaprolactone (PCL) or with mixture of polycaprolactone and 20 wt.% hydroxyapatite (PCL/HA). The mechanical and biological performances of the produced scaffolds were investigated, and the results were compared to software simulation and experimental evidence available in literature. Good mechanical properties and a favorable environment for cell growth were obtained for all combinations of scaffold geometry and surface functionalization. In conclusion, powder recycling provides a viable practice for the biomedical industry to strongly reduce preclinical costs without altering biomechanical performance.

During the last decades, in industrial applications the integration of electronic components shifted its focus on reliability. In fact, the high thermal power generated by electronic systems can cause system failure and even irreversible damage, due to their ongoing miniaturization and complexity. This work aims to explore solutions for the optimal design of passive heat sinks to be fabricated by additive manufacturing. The methodology involves the use of CAE and thermal topological optimization tools, to analyse the thermal loads and the heat sink performance, and consequently to optimize the heat sink design. A simple case study allows to compare three different geometrical heat sink configurations, corresponding to the optimal solutions for three different sets of constraints, namely only volume constraints, laser-powder bed process design and internal heat generation. The predominant role of heat conduction is demonstrated and significant weight reduction and high efficiency are combined in topology optimized passive heat sinks to be fabricated by AM.

This work presents an investigation on the effect of rapid annealing on the microstructure evolution and mechanical performance of stainless steel 316L (SS316L) fabricated by Laser Powder Bed Fusion. In this process, it is well documented that the intensive thermal gradient in the heat flux direction leaves remarkable residual stress and promotes strong texture along the building direction (BD). In the current research, to swiftly reduce residual stresses, a short-term heat treatment at 1300 °C for different holding times of 10–120 s was designed and studied. Microstructural observation through the optical microscopy and scanning electron microscopy, as well as the X-ray diffraction analysis, revealed that rapid annealing longer than 30 s resulted in the gradual annihilation of the cell walls which are indeed the sub-grain boundaries (SGBs). In addition, electron backscatter diffraction outputs demonstrated that rapid annealing significantly reduced the low angle grain boundaries and attenuated the texture developed along the BD. Moreover, the analysis of grains size and shape illustrated that annealing up to 30 s recovered the structure. In contrast, longer annealing resulted in increasing the aspect ratio of grains along the direction with maximum residual strain (i.e. BD) due to activation of the strain induced grain boundary migration (SIGBM) mechanism. After the rapid annealing, the mechanical performance of the samples also indicated that annealing up to 30 s would not reduce the compressive and tensile strength more than 6%. In comparison, longer annealing resulted in 24% reduction in mechanical properties along with coarsening of dimples in the fracture surface of the samples.

Additive manufacturing (AM) processes allow producing the complex components in a layerwise fashion. The complexity includes the design of lighter and stronger components by using lattice structures that can be quickly realized through AM technologies. However, the mechanical behaviour of lattice structures is not completely known, especially in the post-treated state. Thus, this work aims to explore the effect of post-treatment on the compressive strength of specimens with lattice structures. The samples are produced using Ti-6Al-4V powder processed by Electron Beam Melting (EBM). The outcomes of this work confirm the correlation between the heat treatment and final mechanical properties.

Despite the extensive capabilities of Laser-Powder Directed Energy Deposition (LP-DED), compared to other metal additive manufacturing processes, the use of LP-DED in industry is still limited as a result of the limited knowledge on the relationships between the process parameters and mechanical behaviour. In this work, the quality of AISI 316L samples, produced by means of LP-DED and evaluated in terms of surface roughness, residual stresses and microstructure, is linked to the scanning strategy. The outcomes confirm that the deposition strategy plays a key role in the definition of the final properties of specimens.

Additive manufacturing (AM) technology has great potential in manufacturing complex internal channels for several applications such as satellite-communication microwave systems. These systems can have complex shapes and make traditional finishing processes a challenge for additive parts. Therefore, it is desirable that the internal surfaces are as close as possible to the tolerance of the field of application. In this study, a complex component, a unique waveguide device with bending, twisting and filtering functionalities, has been designed and manufactured in AlSi10Mg alloy through laser powder bed fusion (L-PBF) process. Three different prototypes with three different curvature (R of 50 mm, 40 mm and 30 mm), operating in Ku/K band, have been manufactured and tested showing a very good agreement with the desired performances. Using 3D scan data, the internal deviations from the CAD model have been evaluated showing an average deviation of the internal areas of about 0.08 mm, 0.046 mm and 0.023 mm from the CAD model for the R of 50 mm, 40 mm and 30 mm respectively The surface roughness measured in the internal channel is about Ra (arithmetic average roughness) of 8 μm ± 1.3 μm and Rz (average maximum height of the roughness profile) of 62.3 μm ± 0.34 μm.

Electron beam melting (EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications. Especially, lattice structures made by Ti–6Al–4V have represented a hot topic for the industrial sectors because of having a great potential to combine lower weights and higher performances that can also be tailored by subsequent heat treatments. However, the little knowledge about the mechanical behaviour of the lattice structures is limiting their applications. The present work aims to provide a comprehensive review of the studies on the mechanical behaviour of the lattice structures made of Ti–6Al–4V. The main steps to produce an EBM part were considered as guidelines to review the literature on the lattice performance: (1) design, (2) process and (3) post-heat treatment. Thereafter, the correlation between the geometrical features of the lattice structure and their mechanical behaviour is discussed. In addition, the correlation among the mechanical performance of the lattice structures and the process precision, surface roughness and working temperature are also reviewed. An investigation on the studies about the properties of heat-treated lattice structure is also conducted.

Metal components produced by Additive Manufacturing (AM) technologies usually exhibit a rough surface, that in certain applications can result detrimental for the part’s functionality. Thus, it is of great interest to study the finishing processes that can be applied to the surfaces, both external and internal, of AM components. The aim of this work is the evaluation of the capabilities of a vibro-finishing process in the treatment of samples produced by Laser-Powder Bed Fusion (L-PBF) from AlSi10Mg powders. In this research, the abrasive media is identified, and the surface quality improvement is analysed in terms of surface roughness and modifications induced by the finishing treatment (i.e., edge rounding, material loss) against finishing duration. The cost of the treatment is also evaluated.

The freedom of design of AM products suffers from some limitations in case of powder bed metal processes, because AM part's integrity is affected by the residual stress state that is a consequence of the thermal history during part fabrication. Aim of this work is to evaluate the effect of part orientation on stress distribution. Thus, flat samples of AlSi10Mg alloy built along different orientations are produced by means of laser powder bed fusion (L-PBF) process, also known as Selective Laser Melting (SLM). Then, the semi-destructive hole-drilling method is used to evaluate residual stresses beneath the surfaces of samples. The outcomes of the study can be exploited to define design rules in order to both minimize support structures and optimize the orientation of the part in the building volume.

This paper provides an overview on the main additive manufacturing/3D printing technologies suitable for many satellite applications and, in particular, radio-frequency components. In fact, nowadays they have become capable of producing complex net-shaped or nearly net-shaped parts in materials that can be directly used as functional parts, including polymers, metals, ceramics, and composites. These technologies represent the solution for low-volume, high-value, and highly complex parts and products.

The combination of additive manufacturing principles and electron beam (EB) technology allows complex metal parts, featuring excellent quality material, to be produced, whenever traditional methods are expensive or difficult to apply. Today, the optimization of process parameters, for a given metal powder, is generally attained through an empirical trial and error approach. Process simulation can be used as a tool for decision-making and process optimization, since a virtual analysis can help to facilitate the possibility of exploring “what if” scenarios. In this work, a new type of modelling has been introduced for energy source and powder material properties and it has been included in a thermal numerical model in order to improve the effectiveness and reliability of Electon Beam Melting (EBM) FE simulation. Several specific subroutines have been developed to automatically calculate the powder properties as temperature functions, and to consider the position of the beam during scanning as well as the material state changes from powder to liquid in the melting phase and from liquid to solid during cooling. A comparison of the numerical results and experimental data taken from literature has shown a good forecasting capability. The average deviations of the simulation from an experimental scan line width have been found to be below about 15%.

Additive manufacturing technologies are currently envisaged to boost the development of a next generation of microwave devices intended for satellite telecommunications. Due to their excellent electromagnetic and mechanical properties, metal waveguide components are key building blocks of several radio frequency (RF) systems used in these applications. This article reports the perspectives deriving from the use of laser powder bed fusion (L-PBF) technology to the production of high-performance microwave waveguide devices. A robust design of filters has been implemented in several prototypes manufactured in AlSi10Mg alloy. The corresponding measured performance confirm the applicability of the L-PBF process to the intended applications

The adoption of metal powder-based laser process (L-PBF) for industrial applications continues to widen, due to an increasing knowledge on additive processes and the availability of new systems for industrial production. The use of L-PBF processes requires a deeper investigation and comparison on mechanical properties of conventional and additive parts. For instance, metal parts produced by L-PBF could require additional machining operations, which alter the stress state of additive components. In this work, the effect of machining operations on the residual stress state of an AlSi10Mg component produced by L-PBF is investigated by means of the semi destructive hole-drilling method.

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technique based on a laser power source that sinters powdered materials using a 3D CAD model. The mechanical components produced by this procedure typically show higher residual porosity and poorer mechanical properties than those obtained by traditional manufacturing techniques. In this study, samples were produced by DMLS starting from a Co-Cr-Mo powder (in the γ phase) with a composition suitable for biomedical applications. Samples were submitted to hardness measurements and structural characterization. The samples showed a hardness value remarkably higher that those commonly obtained for the same cast or wrought alloys. In fact, the HRC value measured for the samples is 47 HRC, while the usual range for CAST Co-Cr-Mo is from 25 to 35 HRC. The samples microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX) in order to clarify the origin of this unexpected result. The laser treatment induced a melting of the metallic Co-Cr-Mo powder, generating a phase transformation from the γ (fcc) to the ɛ (hcp) phase. The rapid cooling of the melted powder produced the formation of ɛ (hcp) nano-lamellae inside the γ (fcc) phase. The nano-lamellae formed an intricate network responsible for the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields, where a high degree of personalization is required.

Electron Beam Melting (EBM) has the potentiality of being an effective system in terms of time and energy consumption. Among the different additive manufacturing processes that are available, the EBM process has shown the lowest Specific Energy Consumption (SEC) and the highest average Deposition Rate (DRa). However, there appears to be a lack of literature on the correlation between SEC and DRa. Moreover, all the literature studies have only an analysis of energy efficiency during the melting of the bulk material phase and have adopted a fixed job design. Therefore, the aim of this study has been to fill this gap. The EBM process is decomposed into small substeps and a bottom-up approach is adopted to provide models that can be used to evaluate the energy of each process subphase and to perform an energy characterisation at the unit process level. A black-box approach is applied to provide a new model for the energy efficiency of the EBM process. Different jobs have been designed to analyse the effect of a part and of manufacturing designs. Bulk material, support and lattice structures have been included. The design has therefore been aimed at investigating the effect of the building height, melted area and process themes on energy efficiency. The jobs have been produced using Arcam A2X and Standard Arcam Ti6Al4V powders. According to this research, the architecture of the machine and its control of the process have the main impact on the relationship between SEC and DRa. The design features of the part and of the job influence the position of the job on this curve and thus the relative energy and time efficiency. Additionally, the empirical approach applied to the machine subunits has highlighted that only a small part of the total energy demand is needed to power the electron beam during the melting phase, while the remaining part guarantees the good machine working conditions.

Additive Manufacturing (AM) and 3D printing are drivers for material savings in manufacturing. Owing to the continuous diffusion of 3D printing driven by low-cost entry-level material extrusion printers, sustainability of a so popular AM technology is of paramount importance. Therefore, recycling 3D printed wastes and 3D parts again at the end of their life is an important issue to be addressed. Research efforts are directed towards the improvement of the biodegradability of 3D printing filaments and the replacement of oil based feedstock with bio-based compostable plastics. The aim of this work is to describe the state of the art about development and use of recycled or biodegradable filaments in 3D printing. Beyond a critical review of the literature, open issues and research opportunities are presented.

Stochastic and non-stochastic porous structures, are used in a variety of applications such as biomedical implants, heat exchangers mass and gas separation, water purification, energy conversion and storage due to their interesting combinations of physical and mechanical properties, such as high stiffness in conjunction with very low specific weight or high gas permeability combined with high thermal conductivity. Among the technologies for the production of these porous structures, the additive manufacturing (AM) processes, such as the powder bed based selective laser melting (SLM), are of particular interest. In order to obtain this kind of structures with SLM, it is important to know the relationship between process parameters and material employed. A series of experiments were carried out to analyze the influence of the main SLM process parameters on the width and continuity of manufacture of non-stochastic porous structures and to manufacture stochastic porous structures through the scanning strategy.

In this work, an improved but still rather simple computational analysis is presented for a more detailed prediction of Electron Beam Melting (EBM) process outcomes. A fully coupled thermomechanical analysis is developed in which nonlinearities due to the variation of material properties when the material melts are included. A new analytical approach is developed to emulate the volume variation of the powder bed during heating and melting. Particularly, the expansion of the powder particles and the porosity reduction within the powder bed are considered simultaneously. The thermal expansion and the shrinkage of solid material during heating and cooling and the stress formation within the solid material are also modelled. The model can predict the geometrical transformation of the powder into solid material in an efficient way. A comparison between experimental and simulated cross-sectional areas of melted single lines is presented. Both continues line melting and fractional line melting, multi beam melting, are considered. The model shows a good ability to provide consistent and accurate forecasts. The maximum deviations between experimental and numerical results are approximately 15% for the height and 5% for the width of the melted lines, respectively. A comparison with a pure thermal model is also included, and benefits and differences between the two models are discussed.

Electro-discharge (ED) processes depend on the contemporaneous effect of many factors, which complicates process control/predictability and induced many authors in the last 60 years to work on explicative models. Studies split into two main approaches: theoretical and empirical. Theoretical works are based on the thermo-electrical theory and try to describe process phenomena by a physical model, with unavoidable assumptions and simplifications that cause a move away from veracity. On the contrary, experimentalists establish empirical models based on statistical analysis of results and optimization methods, but the findings are limited to domain-specific applications. In addition, numerous papers focus on single-spark analysis, failing in considering the interaction between successive discharges, or of transient phenomena as the presence of bubbles and debris in the gap. At present the scientific debate involves the ignition model, with two different points of view regarding the discharge-driving phenomenon: the debris bridge effect (pollutants in the dielectric drive the performances), and the dielectric strength effect (properties of the dielectric drive the performances). The paper addresses this dispute by investigating the debris formed during small-hole ED drilling of a 72 wt% Al 2 O 3 –28 wt% TiC composite. Particles are found to hollow out and pack within the gap, joining by necks. The first experimental evidence is given of the presence of chains and clusters of debris, towards a new model for electro-discharge processes that goes beyond the thermoelectric theory.

A specific technical expertise is required to machine metal–matrix composites (MMCs). It is well known, from the literature data, that MMCs cutting involves high costs and high machining times due to excessive tool wear and possible subsurface damage. In recent years, the emphasis of research has focused on understanding the mechanics and mechanisms that are responsible for the behaviour of MMCs during the material removal process. These kinds of studies would be the most effective way of understanding the machining characteristics and deformation behaviour of the material. This work is a contribution to understanding the effects of two antagonistic phenomena that determine MMCs behaviour during the cutting process, such as the thermal softening of the matrix and the matrix hardening due to strain. To this end, a simplified model that describes the behaviour of the reinforcements beneath the machined surface is proposed and experimentally validated.

This work explores the feasibility of using the Abrasive Fluidized Bed (AFB) method to finish flat AlSi10Mg substrates manufactured by Direct Metal Laser Sintering (DMLS). Finishing was performed by rotating the substrates inside a fluidized bed of abrasives at high speeds. The interaction between the fluidized abrasives and AlSi10Mg substrates has been investigated to analyze the influence of the operational parameters, namely, abrasive type and rotational speed, on the finishing performance. The morphological features of the substrates and geometrical tolerances have been inspected by field emission gun-scanning electron microscopy (FEG-SEM) and contact gauge profilometry. After short finishing cycles, the substrates featured a smoother surface morphology, while the edges were only influenced slightly by the abrasive impacts. Abrasive Fluidized Bed (AFB) can therefore be considered a potential easy-to-automate, low cost, low time consuming and sustainable finishing technology for metal parts obtained through additive manufacturing. © 2016 Elsevier B.V.

Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near net-shaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L18 orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation. The upper surfaces of the samples were analyzed before and after shot peening. The morphology was analyzed by means of field emission scanning electron microscope. Scan speed was found to have the greatest influence on the surface roughness. Further, shot peening can effectively reduce the surface roughness.

PurposeAdditive manufacturing is today a viable industrial solution alongside traditional processes. Techniques like selective laser sintering (SLS) address the issues of digital production and mass customization in a variety of materials. Composite parts can be obtained with specific functional and mechanical properties. Building orientation during additive manufacturing often causes anisotropy of parts' properties that is still unspecified in technical information. The purpose of this paper is to investigate the mechanical performances and failure mechanisms of an aluminium‐filled polyamide and of a new alumina‐polyamide composite produced by SLS, in comparison with unfilled PA.Design/methodology/approachA specific focus is set on the evaluation of primary and secondary anisotropy in the case of metal or ceramic filler, as well as on the specific contribution of powder distribution modes and joining phenomena. Macroscopic mechanical tests and the observation of joining and failure micro‐mechanisms are integrated.FindingsThe results prove the absence of relevant anisotropy amongst specimens that are produced with the axis parallel to the plane of powder deposition. Samples whose axis is parallel to the growth direction Z, instead, reveal a significantly different response with respect to other orientations.Originality/valueAn original explanatory model is assumed and validated, based on an anisotropic distribution of the reinforcing particles during parts' production, which determines the efficacy of the strengthening mechanisms during crack propagation.

Many automotive applications require deep drilling on pressure die-cast parts in Aluminium alloys. The aim of the research was to understand if common cutting practices, usually determined on raw materials, can be successful on semimanufactured parts as well, having an inhomogeneous microstructure. A specific investigation was carried out on deep drilling of an EN AB-46000 cylinder block, varying technological parameters (cutting speed, feed, tool, lubrication). Dimensional tolerance and surface roughness were measured and statistically analyzed. The quantitative analysis of the process macroscopic performances was combined with an investigation of microstructural aspects of the material, their effects on chip formation and tool-chip interaction.

Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co–Cr–Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin e (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The e-lamellae grown on the {111} γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

Purpose – The aim of this research is to reach a deep understanding on the effect of the process parameters of Direct Metal Laser Sintering process (DMLS) on macroscopic properties (hardness and density) of AlSi10Mg parts and resulting microstructure. Design/methodology/approach – A full factorial design of experiment (DOE) was applied to determine the most significant process parameter influencing macroscopic properties of AlSi10Mg parts manufactured by DMLS process. The analysis aims to define the optimum process parameters and deduce the process window that provides better macroscopic properties of AlSi10Mg parts. Optical microscopy observations are carried out to link the microstructure to macroscopic properties. Findings – Macroscopic properties of DMLS parts are influenced by the change in process parameters. There is a close correlation between the geometry of scan tracks and macroscopic properties of AlSi10Mg parts manufactured by DMLS process. Originality/value – The knowledge of utilizing optimized process parameters is important to fabricate DMLS parts with better mechanical properties. The present research based on applying experimental design is the first analysis for AlSi10Mg parts produced in DMLS process.

Purpose – The purpose of this paper is to present a custom-built tribometer that mimics the wear of additive manufactured fixtures used in inspection of sheet metal components. Design/methodology/approach – Referring to the inspection of sheet metal parts, the fixture undergoes sliding wear during loading and unloading phases of the quality control operation. A new wear test is proposed to mimic the actual wearing conditions of the fixtures because the standards are deemed insufficient. In the tribometer, a cylindrical Alumide cantilever beam is made to slide back and forth inside a slightly bigger hole cut into a nickel-plated steel sheet. The sheet is spring loaded such that it applies a force on the specimen. The wear on the beam is measured after every 500 cycles of the beam motion. Findings – Results of some first test trials are reported to evaluate the durability of Alumide fixtures fabricated by selective laser sintering. The results are also compared to those obtained for a machined fixture made of an Al-Cu alloy. Practical implications – The proposed wear test estimates the life time of additive manufactured fixtures in terms of numbers of inspected components. The test can be extended to different materials to compare their durability. Originality/value – Today, the fabrication of custom fixtures by means of additive manufacturing technologies is a reality in many manufacturing industries. The advantage of using those production technologies for custom fixtures is well assessed in literature in terms of manufacturing times and costs, whereas little attention was given to the life time and wear behaviour of fabricated fixtures. For its practical implication, the fixture durability is indeed very important for manufactures.

Corrosion attack of steel in concrete has been studied by means of an experimental analysis on reinforced concrete ties under both static/cyclic loading and accelerated corrosion. Crack opening zones across crack locations due to load have been analysed; corrosion concentration around crack site has been observed. A quantitative evaluation of local damage is presented by means of a mechanical procedure using 3D scanning and data post-processing. The results show the influence of the presence of corrosion, stress amplitude and the type of loading on local damage. A comparison with other results found in literature is shown.

Ceramic matrix composites (CMCs) can be attractive for structural applications, but their machining by conventional methods is expensive and often critical. Complex geometries on advanced ceramics require contactless processes, such as electrodischarge machining or drilling (EDD). These proved to be viable for CMCs with electrical resistivity below a critical value in the range of 1–3 Ω m. The condition is complied with by many CMCs: an example is alumina with titanium carbide. Material removal of ceramics by electrical discharges is a complex process involving different mechanisms, depending on the process setup. The paper describes an experimental study on EDD of 0.4-mm diameter holes with an aspect ratio of 20 in Al2O3–TiC, using copper electrodes. Peak current (I p), pulse-on time (t on), and pulse-off time (t off) are varied as independent variables. Four performance indicators are measured: material removal rate, electrode wear rate, overcut, and surface roughness (R a, S a). Empirical models are proposed to describe the effect of process parameters on the output indicators. The analysis is supported by the observation of the surface and subsurface morphology, with the aim of investigating the material removal mechanisms and attaining a full comprehension of macroscopic results. It is found that removal mostly occurs by melting and evaporation and that surface morphology is determined by two phenomena ruled by pulse power. A process description is proposed, built around power as the ruling factor.

In order to face the demands of today’s competition, i.e. short time-to-market for customized products in small batches, in the field of moulds construction a growing interest is seen for materials that combine high mechanical properties with the possibility of a quicker and easier machining (Klocke, 1998). Aluminium alloys offer many machining advantages such as excellent machinability and finish degree with high cutting speed, low cutting forces, outstanding tool life (Kishawy et al., 2005; Schultz & Moriwaki, 1992). Elevated thermal exchange and weight reduction, which means easier handling, compared to steels are additional characteristics that lead to increasing applications in the automotive and aerospace industry and in the field of mould production (Amorim & Weingaertner, 2002; Ozcelik et al., 2010). The use of Aluminium moulds, whose thermal conductivity is up to 5 times higher than of traditional steel moulds, ensures an impressive reduction of cooling time at closed mould, which is the longest step in polymers injection moulding cycle. Moreover, high thermal exchange promotes a better workpiece accuracy, lower risk of warpage and sink marks, lower molded-in stresses (Erstling, 1998). Good corrosion resistance of Aluminium is an additional advantage in processing molten polymers. Relatively recent Aluminium alloys derived by aeronautical uses offer high tensile strength and hardness: the gap with steels is thus reduced or even reversed in terms of specific properties (Amorim & Weingaertner, 2002; Starke & Staley, 1996). Wrought heat-treatable alloys develop high specific strength thanks to age-hardening and have been widely used for airframes. Above all Al-Cu alloys (2xxx series) and Al-Zn alloys (7xxx series) are recognized for best damage tolerance and strength, respectively (Starke & Staley, 1996). The addition of transition elements, i.e. Cr, Mn or Zr, leads to dispersions capable of controlling the grain structure. Two examples of such alloys are Al 2219 and Al 7050, which are good candidates for injection moulds applications. If the first examples of Aluminium moulds for plastic injection were limited to preproduction, the properties of these new alloys match the requirements of medium production volumes (up to 10000 parts/ year), which today are also the main market demand (Miller & Guha, 1998; Erstling, 1998; Klocke, 1998; Amorim & Weingaertner, 2002; Pecas et al., 2009).

Titanium and Cr-Co-Mo alloys are the most attractive metallic biomaterials for orthopedic and dental implants: selective laser sintering technique may use these materials but it still remains limited in terms of foreseeable performances as function of process parameters. The method essentially relies on empirical, experimental knowledge and still lacks a strong theoretical basis. This paper investigates the orientation influence on mechanical performances of Ti6Al4V grade 5 and Cr-Co-Mo specimen built by selective laser sintering. The tensile strength and the rupture surface observation allow to explain the tensile strength values obtained as a function of the fine microstructure that is confirmed by metallographic observation.

New brake-pad materials are inhomogeneous compounds with a variety of metallic and ceramic phases, whose interaction with the tool during the grinding operation is not fully understood. Yet, ground surface quality strongly influences the bedding-in phase. This research surveys how grinding operation affects the pad surface. The purpose is pursued by adopting an investigation protocol merging macroscopic outcomes with the study of chip-removal mechanisms and of the ground surface morphology in the microscale. A specific set of grinding tests is carried out on the friction material under different kinematic conditions. Macroscopic indicators of the process performances are measured and modeled. At a closer look, the ground surface shows a complex morphology that cannot be completely described by roughness values, but depends on how the various phases are distributed in the material and how they are affected by the tool during abrasion. A multiscale inspection procedure is proposed to assess the performances of a machining operation on complex materials, where the descriptive power of standard technological tests becomes inadequate.

PurposeThis paper aims to develop a deep characterization of PA‐Al2O3 composite for selective laser sintering (SLS). Tension test is used to determine main mechanical characteristics of the material, both at room temperature and at 100°C. An accurate knowledge of the parts' performances as a function of the building orientation, is fundamental to understand the manufacturing anisotropy. Particular attention is dedicated to the joining and failure micromechanisms ruling the macroscopic characteristics, on the basis of the knowledge developed by the authors on SLS of both metal and polymeric powders.Design/methodology/approachSpecimens have been built with different orientations in regard to powder deposition plane and laser path. Tension test is used to determine main mechanical characteristics of the material, both at room temperature and at 100°C. A particular attention is dedicated to the joining and failure micromechanisms ruling the macroscopic characteristics of the composite material by means of optical and scanning electron microscope (SEM) observations.FindingsThe sintered material shows an evident anisotropy in the growth direction (z‐axis), as well as it seems to be not sensitive to the sintering direction at room temperature (x, y, xy). At 100°C the effect of sintering direction becomes more evident and a different behaviour results considering x‐ and y‐direction, respectively. Accurate SEM characterization has been carried out to understand the effect of the manufacturing anisotropy on the mechanical performances, both in terms of additive construction and laser sintering strategy. The observation of the rupture surfaces showed that cracks originate from the external surface and propagate initially by the ductile failure of the polymeric matrix, up to the sudden fracture of the whole section.Originality/valuePrevious studies concerning polyamide charged parts confirm the importance of fabrication parameters and geometry on the final performances, due to anisotropic heat supply and transfer phenomena. The originality of the paper is in the investigation on both at room temperature and at 100°C. Moreover, a model is proposed where it is hypothesized that the layer‐by‐layer construction is only marginally responsible of the anisotropic behaviour of the material.

Microwave sintering of SLS green parts made of 420 L stainless steel has been performed applying microwaves at the frequency of 2.45 GHz. The use of single mode and multi-mode microwave furnaces allowed to find the most suitable sintering conditions in absence of auxiliary microwave absorbers. In case the electric field intensity reaches a threshold value, able to trigger breakdown phenomena, sintering is rapidly achieved, but at the cost of homogeneity and process controllability. A lower electric field intensity allows, instead, to achieve complete sintering of the green parts in 10 to 20 minutes time, which results considerably shorter than current state of the art conventional sintering of SLS green parts. Comparison between microwave and conventionally sintered parts showed that the final product present a similar microstructure, with the presence of Cr-rich regions whose extension is a function of the microwave processing time

The grinding of friction material brake pad, necessary to ensure a flat surface, generates the surface roughness which highly influences the friction coefficient. This paper deals with an experimental activity focused on the evaluation of the surface roughness after a grinding operation of an innovative sintered friction material. A regression analysis has been used to model the relationship among surface roughness and kinematic parameters. An instrumented tangential grinding machine controlled by a CNC system has been used in this activity. During the process the normal and tangential grinding forces have been measured by a force measurement device.

Till now aluminium moulds have been employed only for pre-production; with the alloys A12219 and A17050, which have outstanding properties, we can think about medium productions of plastic components obtained by injection moulding. To evaluate the machinability of these alloys and understand the correlations among process parameters, dimensional tolerances, surface finish and electrode wear, some tests have been made by Electro Discharge Machining. The electrodes and the machined surfaces have been also observed at OM, SEM to understand the EDM mechanisms. Comparison tests have also been done on A17075, commonly employment for pre-production moulds, to have precise control data.

Microwave processing has gained worldwide acceptance as a novel method for heating and sintering a variety of materials, as it offers specific advantages in terms of speed, energy efficiency, process simplicity, finer microstructures, and lower environmental hazards. Microwave assisted post-treatment of green metal parts (AISI 420 metal powder with 2–3 wt% polymeric binder) proved to be a new method, suitable for near-net-shape and net-shape manufacturing. Green parts exposed to high intensity microwave fields, using either single mode or multimode microwave applicators operating at 2.45 GHz ISM frequency, were investigated in terms of densification behaviour, microstructure and joining micromechanism. The results, in terms of microstructure and shape retention are comparable to the conventional heating ones, reported in literature, but they have been obtained in much shorter time.

The hard abrasive ceramic component which increases the mechanical characteristics of metal matrix composites (MMC) causes quick wear and premature tool failure in the machining operations. The aim of the paper is to compare the behaviour of high rake angle carbide tools with their diamond coated versions in high-speed machining of an Al 2 O 3 Al 6061 MMC. The influence of the cutting parameters, in particular cutting feed and speed, on tool wear and surface finish has been investigated. The higher abrasion resistance of the coatings results in increased tool life performances and different chip formation mechanisms.

Metal matrix composites are manufactured in a variety of grades and forms, but machining is usually necessary to obtain finished engineering components. The presence of the hard reinforcing ceramic makes these materials difficult for conventional machining. Wire electro discharge machining (WEDM) is used for the processing of heat-treated high-quality alloys or for the machining of complex shapes in advanced materials. This paper describes WEDM tests performed under one roughing and two finishing conditions on two composites, SiC/2009Al alloy with 15% whiskers and with 20% particles reinforcement. Some roughed and some finished surfaces were glass-bead peened. To understand the reinforcement and the behaviour of the matrix during the machining of both composites, the machined surfaces, their sections and profiles were examined by scanning electron microscopy, and energy dispersive semi-quantitative analyses of X-rays were also carried out. The surface roughness for the process parameters used are indicated.

Wire Electrical Discharge Machining (WEDM) is one of the most versatile and useful technological processes for cutting complex shapes made of conductive materials such as those typical of aerospace applications. With the aim to optimize process parameters, this paper studies the surface and subsurface modifications of INCONEL® alloy 718 (UNS N07718) machined by WEDM using a Zinc coated brass wire. Machining was performed under roughing and finishing conditions by setting different values of discharge energy and wire feed rate. Surface roughness of the cut surfaces was measured as well as the micro-hardness profile on polished sections. WED-machined surfaces and their cross sections were also observed by Scanning Electron Microscope (SEM) and analyzed by Energy Dispersive X-ray Spectroscopy (EDS) to evaluate possible variations of the surface chemical composition. In this investigation, results are discussed as a function of the feed rate and of the single pulse discharge energy, which is determined by duration, peak current and discharge voltage of the discharge pulse. The research demonstrates that the required surface roughness can be achieved by properly setting the feed rate and the single pulse discharge energy on the WEDM machine. Experimental results also show that under the re-melted layer thickness no significant white layer formation or thermal modification occur, indicating that the chosen set of operating parameters minimizes secondary and unwanted chemical reactions.

Cobalt-base alloys are generally used in applications that require wear, corrosion and heat resistance. In particular, Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloy is adopted in the aerospace and medical field. These applications are characterized by low volumes and high personalization, so they could take advantage by the employment of additive technologies, such as Direct Metal Laser Sintering (DMLS). This technology still has limitations for the manufacture of small cavities, such as holes with diameters below 0.6 mm and high aspect ratio, which require drilling of the additive manufactured part. Scope of this research is to investigate the effects of Electro-Dicharge Drilling (EDD) on surface and subsurface features of CoCrMo samples built by DMLS. High aspect ratio holes are produced with diameter of 0.6 mm and depth fifteen times higher. The attractiveness of ED machining for thin deep geometries stems from then absence of physical contact between tool and workpiece, which makes machining forces negligible and minimizes tool deformation. Micro features can be produced with a high accuracy irrespective of the material hardness and strength. Material Removal Rate (MRR), Electrode Wear (EW) and surface roughness are investigated versus the process parameters. Results are supported by the study of material removal mechanisms and surface morphology in the microscale, to account for the macroscopic trends

Direct Metal Laser Sintering (DMLS) is capable of producing complex shaped metallic parts with superior mechanical properties than those obtained from conventional processes. Thus the application of this technology is increasing in aerospace, automotive and also in medical fields. The high mechanical performances of metal parts are mainly due to the rapid melting and solidification of the powder. As a consequence a very fine microstructure is obtained. Moreover the parts are subjected to further post-processing operations, such as shot-peening or polishing, to improve the outer surface finish. This article is focused on the investigation of the mechanical properties of AlSi10Mg parts produced by DMLS. Thus tensile and Charpy specimens are produced and tested in the "as-built" status and after different post-processing conditions. The results show that the post-processing operations enhance the mechanical properties of DMLS parts.

Resin Transfer Moulding (RTM) is a low-cost process for the production of composite parts with thermosetting resins. However, the economic convenience is lost in the case of large components, such as aeronautical panels, because of the high tooling cost. Step milling of a resin master for the electro-deposition of a nickel shell is proposed in this study as a valid alternative for the fabrication of a resin transfer mould. This solution allows overcoming the limitations regarding part size and cutting down tooling costs, but the expected dimensional accuracy needs to be assessed. On the field of materials, innovative thermoplastic resins are now available that can be used in the formof lowviscosity oligomers for optimal mould filling and fibre impregnation. Subsequent in situ polymerization provides high toughness composites. Cyclic Butylen Terephtalate (CBT), which polymerizes into PBT (Poly-Butylen Terephtalate), is studied in this work. The research focuses on two objectives: quantifying the dimensional accuracy of the technological chain and setting up the process of in situ polymerization