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Additive manufacturing (AM) processes allow complex geometries to be produced with enhanced functionality, but technological challenges still have to be dealt with, in terms of surface finish and achieved tolerances. Among the consolidated powder-bed fusion processes, electron beam melting (EBM), which allows almost stress-free parts to be manufactured with a high productivity and minimum use of support structures, suffers from a poor surface quality. Thus, finishing processes have to be performed. The same geometrical complexity, which is considered one of the benefits of AM, becomes an issue when finishing is applied, in particular when internal features are present. Unconventional isotropic superfinishing processes could be a solution to this problem since they can generate a low surface roughness on complex geometries. However, the performance characteristics, with regard to the environmental sustainability and economic aspects, need to be evaluated since they are key factors that must be considered for decision-support tools when selecting a finishing process. The technological feasibility of the isotropic superfinishing (ISF) process, applied to Ti-6Al-4V parts produced by electron beam melting, is investigated in this paper by considering the dimensional and geometrical deviations induced by the finishing treatment, and from observations of the surface morphology. A significant reduction in surface roughness, Sa, to around 4 μm, has been observed on the most irregular surfaces, although the original shape is maintained. Environmental sustainability has been analyzed for all the manufacturing steps, from powder production to part fabrication, to the finishing process, and both the cumulative energy demand and material waste have been accounted for. The economic impact of the whole manufacturing chain has been evaluated, and the advantages of the ISF process are pointed out.

Additive Manufacturing (AM) techniques enable the layer-wise fabrication of complex shapes without the need for specific production tools, reducing the economic lot size to the single unit and allowing the mass customization. Besides the technological drivers pushing AM towards several industrial applications, the energy efficiency and the time/cost performance in comparison to more conventional manufacturing processes are still to be investigated. This research focuses on the Fused Deposition Modelling (FDM) process for the production of components made either of ABS or PC-ABS. The impact of the main variables (such as the layer thickness and the infill strategy) on the process time and the energy consumption was analysed while considering the FDM unit-process. Empirical predictive models correlating the energy efficiency with the main process variables are proposed in this paper. The results confirm that the Specific Energy Consumption approach already applied to other manufacturing unit-processes can be successfully extended to FDM. Moreover, the increase in the average Deposition Rate, which is related to the deposition path, appears to be a strategy for the reduction of the specific printing energy. Such experimental evidence might suggest further energy-conscious improvements in the design of AM processes and equipment.

Over the last years, additive manufacturing (AM) has been gathering momentum both in the academic and in the industrial world. Besides the obvious benefits in terms of flexibility and process capabilities, the environmental performance of such processes has still to be properly analyzed. Actually, the advantages of additive manufacturing over conventional processes are not obvious. Indeed, different manufacturing approaches result in different amounts of involved material and in different processing energy demands. Environmental comparative analyses are hence crucial to properly characterize AM processes. In this paper, an energetic comparison between the emerging wire arc additive manufacturing (WAAM) process and a traditional machining-from-bulk solution to produce a steel blade is presented. A methodology accounting for all the material and energy flows of the whole component life cycle is proposed. Experimental measurements and environmental databases are used to quantify the primary energy demand at each stage of the life cycle. The results reveal that, for the analyzed case study, an integrated additive (WAAM)-subtractive manufacturing route enables significant material and primary energy savings with respect to traditionally applied approaches.

A maturity model for micro, small and medium enterprises (MSMEs) is introduced to assess the level of implementation of sustainability strategies and practices in this type of business. According to the literature, only a few sustainability-maturity assessment models intended for MSMEs have integrated the following three factors: environmental knowledge management, environmental strategies and good practices, and environmental management systems. The sustainability maturity model proposed here for MSMEs is capable of supporting the efforts of companies in their attempts to achieve both environmental sustainability and an improvement in their production systems. The model encompasses a four-level qualitative scale and uses supervised classification algorithms to categorize companies through data analysis techniques. After applying the model to a group of MSMEs from different productive sectors in Colombia, the results have shown that 6% of the companies were at an insufficient level, 31% were at an initial level, 45% at a developed sustainability maturity level, and 18% at a consolidated level. This result implies that the decision makers in the latter group have paid greater attention to the strengthening of sustainability progress capabilities and, hence, to the definition of a maturation route.

The emerging of the fourth industrial revolution, also known as Industry 4.0 (I4.0), from the advancement in several technologies is viewed not only to promote economic growth, but also to enable a greener future. The 2030 Agenda of the United Nations for sustainable development sets out clear goals for the industry to foster the economy, while preserving social well-being and ecological validity. However, the influence of I4.0 technologies on the achievement of the Sustainable Development Goals (SDG) has not been conclusively or systematically investigated. By understanding the link between the I4.0 technologies and the SDGs, researchers can better support policymakers to consider the technological advancement in updating and harmonizing policies and strategies in different sectors (i.e., education, industry, and governmental) with the SDGs. To address this gap, academic experts in this paper have investigated the influence of I4.0 technologies on the sustainability targets identified by the UN. Key I4.0 element technologies have been classified to enable a quantitative mapping with the 17 SDGs. The results indicate that the majority of the I4.0 technologies can contribute positively to achieving the UN agenda. It was also found that the effects of the technologies on individual goals varies between direct and strong, and indirect and weak influences. The main insights and lessons learned from the mapping are provided to support future policy.

Additive Manufacturing (AM) has been identified as a disruptive technology, that enables the transition to Industry 4.0 and allows companies to re-think and re-design both their products and manufacturing approaches. In such a context, the opportunity of using AM to extend the life of a product through repair could also allow the founding principles of the circular economy to be implemented. This paper deals with the development of a repair procedure for mold inserts, made of H13 steel, that are used to cast aluminum cylinder heads for internal combustion engines. The repair operations were experimentally performed in a hybrid additive-subtractive manufacturing center used for Wire Arc Additive Manufacturing. Once the technological and quality results that are required by the strict industrial standards had been verified, the life-cycle energy and carbon footprint of the repair approach were quantified and compared with those of the conventional substitution-based approach. Overall, at the end of the first life of the insert, the results highlighted that the WAAM- and repair-based approach could allow potential savings for both performance metrics, compared with the insert being machined from a massive workpiece as a substitute, despite requiring several manufacturing steps and incoming feedstock material characterized by a high embodied energy. Moreover, the environmental benefits of the proposed approach are amplified when multiple repair loops are considered, even for a lower lifespan for the repaired mold insert.

Additive Manufacturing (AM) technologies revolutionized the common understanding of manufacturing with their layer-by-layer building principle. However, the literature has documented their high energy requirements, which is not in-line with the current policies of energy and emission reduction. This ambivalence of AM opens the question for the research community about the wise choice of the manufacturing process to be adopted. This paper proposes a comparative LCA method to select the best manufacturing technology between Conventional Manufacturing (CM) and EBM plus Finish Machining (EBM+FM). The Life Cycle Assessment (LCA) is conducted under cradle-to-gate boundaries. Three metrics, namely the Cumulative Energy Demand (CED), cost and CO2 emissions are considered. Characterization of unit processes is done by using the recent findings in the literature which are included in the model for both process technologies. The Specific Energy Consumption (SEC) is connected to the Material Removal Rate (MRR) and to the average Deposition Rate (DRa), respectively for machining and EBM. The main finding of this research is the description of breakeven surfaces, which separate the regions of validity between machining and EBM, as function of the Solid-to-Cavity Ratio (SCR) and the DRa. Moreover, the presented methodology gives the possibility to compare the goodness of the different sets of design rules that can be chosen for EBM, thanks to the proper evaluation of the SEC parameter. Finally, a sensitivity analysis is conducted to assess the effect of the remaining key variables.

Additive Manufacturing (AM), allowing the layer-by-layer fabrication of products characterized by a shape complexity unobtainable with conventional manufacturing routes, has been widely recognized as a disruptive technology enabling the transition to the Industry 4.0. In this context, the design of a Portable Assisted Mobile Device (PAMD) prototype was considered as a case study. The best practices of the re-design for AM were applied to three of the main structural components, and the most sustainable manufacturing approach between AM processes and the conventional ones was identified with respect to cumulative energy demand, carbon dioxide emissions and costs. The paper aims to promote the debate concerning the correlation between design choices, process selection and sustainable product development.

Wire Arc Additive Manufacturing (WAAM) is a fusion- and wire-based additive manufacturing technology which has gained industrial interest for the production of medium-to-large components with high material deposition rates. However, in-depth studies on performance indicators that incorporate economic and environmental sustainability still have to be carried out. The first aim of the paper has been to quantify the performance metrics of WAAM-based manufacturing approaches, while varying the size and the deposited material of the component. The second aim has been to propose a multi-criteria decision-analysis mapping to compare the combined impacts of products manufactured by means of the WAAM-based approach and machining.

The use of Additive Manufacturing (AM) in the production of tooling for injection molding has led to the introduction of conformal cooling as an effective way to lower the cycle time of the process. As the cooling cycle is responsible for a large portion of the energy consumed during the injection molding process, conformal cooling allows increasing the energy efficiency. However, AM could create a large upfront cost of energy for the manufacturing phase. This paper investigates a case study where a cradle-to-grave life-cycle assessment is used to evaluate the cumulative energy demand of conventional or conformal cooling molds.

Sustainability is an essential consideration in manufacturing, and within this chapter a detailed appraisal is given to sustainability for 3D printing. An in-depth review of existing research is provided, and a cradle-to-grave assessment technique is shown to assess the environmental impact of 3D printed part.

The applicability domain of Additive Manufacturing (AM) processes, apart from technological and quality results, relies on environmental and cost performance. These aspects still need to be better understood. To this aim, comparative analyses with conventional manufacturing routes are needed. In this paper, empirical cost and energy requirement models are suggested to assess subtractive- (machining) and additive- (Electron Beam Melting) based manufacturing approaches for the production of Ti-6Al-4V components. A life-cycle perspective is adopted, and all the steps from the input material production to the post-AM processing operations and the use phase are included. The analyses have been carried out considering the shape of the component, the light-weighting capabilities and the utilization time as the main factors of influence. The proposed modelling effort has allowed different decision-support charts, which are suitable for identifying the most energy-efficient or economically-advantageous manufacturing approach, to be obtained. The results have revealed that, for the considered case study, EBM could be a more energy-efficient approach than conventional machining, even without re-designing the component, due to the higher efficiency in raw material usage. As far as cost is concerned, the additive-based approach only becomes the preferable solution when the cost savings during the use phase are accounted for.

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.

At present, economic and technological design criteria for products and processes should be matched with the minimization of environmental impact objectives. Manufacturing, material production, and product design are strictly connected stages. The choice of a production system over another could result in significant material and energy/resource savings, particularly if the component has been properly designed for manufacturing. In this scenario, Additive Manufacturing, which has been identified as a potential disruptive technology, gained an increasing interest for the creation of complex metal parts. The paper focuses on the tools, based on the holistic modelling of additive and subtractive approaches, which could be used to identify the production route allowing the lowest energy demand or CO2 emissions. The models account for the main process variables as well as the impacts due to the re-design for AM for the creation of components made of Ti-6Al-4 V.

Additive Manufacturing (AM) processes can be counted among the disruptive technologies that are capable of transforming conventional manufacturing routes. The ability to create complex geometries, the reduction in material scraps during manufacturing, and the light-weighting due to the think-additive redesign of the components represent the main points of strength of AM. However, for some applications (such as the production of metal components for the automotive and aerospace industries), the surface finishing and dimensional/geometrical part tolerancing that can be achieved via AM processes might not be adequate to satisfy the imposed product specifications, and finish machining operations are often required. A machining approach and an integrated production route, based on an additive manufacturing process plus finish machining, have been compared in this paper. The primary energy demand and the CO2 emissions have been modelled for all the life cycle stages within a sustainable development context. The main result of the research work is a criterion for the selection of the most environmentally friendly manufacturing approach, while varying the productive scenario (i.e., the masses of the process scraps, the machined chips, and the support structures). The application of such a tool to the production of metal components made of either Ti-6Al-4V or stainless steel is discussed.

Summary The additive manufacturing of metal parts represents a promising process that could be used alongside traditional manufacturing methods. The research scenario in this field is still largely unexplored, as far as the technological solutions adopted to integrate different processes are concerned and in terms of environmental and economic impact assessment. In this article, an electron beam melting (EBM) process and a machining process have been analyzed and compared using a cradle-to-grave life cycle–based approach. The production of components made of the Ti-6Al-4V alloy has been assumed as a case study. The proposed methodology is able to account for all of the main factors of influence on energy demand and carbon dioxide emissions when the component shape is varied. The results prove that, besides the direct energy intensity of the manufacturing processes, the impacts related to material usage are usually dominant. Therefore, when complex geometries have to be manufactured, the additive manufacturing approach could be the best strategy, if it enables a larger amount of material savings than conventional machining. Vice versa, when a small amount of material has to be machined off, the high energy intensity of an EBM process has a negative effect on the performance of the process.

The number of scientific papers in the field of Sustainable Manufacturing (SM) shows a strong growth of interest in this topic in the last 20 years. Despite this huge number of publications, a clear statement of the profound meaning of Sustainable Manufacturing, or at least a strong theoretical support, is still missing. The 6R framework seems to be a first attempt to rationalize this issue, as it is an axiomatic identification of its true nature. Recognizing the pursuing of one or more of the Reduce-Recycle-Reuse-Recover-Redesign-Remanufacture principles allows users to identify if any manufacturing action is in the right direction of sustainability. In the paper, the authors speculate on the use of this framework and its possible extension by referring to all the existing scientific contributions on Sustainable Manufacturing in the SCOPUS® databases as a source of data. Starting from the measurement of the distribution of the scientific papers allocated onto the 6Rs dimensions, by using both author keywords and automatically extracted multiword from texts, the distribution of the scientific papers among the 6R was derived. A new framework is proposed based on analytical text tools to compare the affinity of the applied research activities of the Italian Technologist network SOSTENERE to sustainable manufacturing and provide also a benchmarking view to describe the Italian way to SM with respect to the rest of existing applications.

Additive manufacturing (AM), which includes different technologies, allows free-form parts to be produced flexibly by selectively depositing material layer after layer. Among the various AM processes, metal wire deposition (MWD), which uses a metal wire melted by a high-energy source as feedstock, has been found to be suitable for the manufacturing of low-complexity, medium-to-large components at relatively high deposition rates. Some industrial applications have been identified, despite the quality of the as-deposited surfaces, which usually require further finishing operations. Several researches have been focused on process optimization. However, there is still a lack of consolidated knowledge concerning the environmental impact and the energy efficiency of MWD, aspects that are critically surveyed in this paper. First, the unit process level is considered, and an analysis of the needed specific energy input, while the wire flow rate and the deposited materials are varied, is carried out. Second, a framework is proposed to assess the energy requirements under a cradle-to-gate perspective.

Additive Manufacturing has proved to be suitable for supporting or even replacing traditional manufacturing approaches in some industrial contexts. Among the various processes that can be used to produce metal parts, Wire Arc Additive Manufacturing (WAAM) is known to be an economically convenient, welding-based direct energy deposition technique for large parts with reduced complexity. The present paper proposes a structured modelling framework to assess whether WAAM could successfully substitute machining processes. The costs, manufacturing times, energy demand and carbon footprint are considered. A case study is presented to clarify and demonstrate the applicability of the proposed methodology.

The mitigation and prevention of environmental impacts is still a challenge for most companies, especially for small- and medium-sized enterprises (SMEs). The literature shows that researchers are paying attention to the concept of eco-efficiency, and that companies are making significant efforts to develop sustainable methodologies, as a result of consumer pressure or for government enforcement reasons. However, there is still a lack of concrete initiatives implemented at SME level. The aim of this paper is to present a conceptual framework that may be used to examine to what extent SMEs understand the eco-efficiency concept and implement sustainability strategies. This has been achieved through the identification of the following four specific factors: availability of an environmental management system, environmental knowledge, organizational culture, and environmental monitoring and control. The limitations and research gaps in the specific context have been analyzed, and a conceptual framework that allows the eco-efficiency implementation to be assessed has been proposed. An exploratory study has been carried out on 17 wood industry SMEs from Bogota, Colombia. The results show that most SMEs are unaware of the existing sustainability strategies and environmental practices. Nevertheless, all the SMEs agreed that the environment requires more attention and they are therefore interested in sustainability strategies to help decrease their negative impact and increase their cost-effectiveness and competitiveness.

Additive Manufacturing processes are establishing themselves in different fields, especially due to the possibility to realize free-form and highly personalized products. Life Cycle Cost and Life Cycle Assessment analyses have been conducted to evaluate the economic and environmental sustainability of AM techniques. However, a consolidated knowledge of the risks for exposures to AM materials (as metallic powders) and of the hazards for fire and dust explosions is still missing. The paper performs an investigation on these aspects focusing on the existing literature and on the standards proposed by different international regulatory organizations. A critical review of the achieved awareness in the domestic and industrial environments is carried out, and the importance of models for the construction of risk indicators is highlighted.

Fiber reinforced polymers (FRPs) show advantageous physical-mechanical, thermal, and dielectric characteristics, making them promising candidates for weight reduction in structural applications. However, machinability is often difficult because of the specificity of their structure. This paper highlights the latest advances in CFRP drilling. Key papers are analyzed with respect to workpiece materials, geometrical tool features, and input variables (such as variation in process parameters). The influence of tool geometry and process parameters on workpiece delamination and hole quality/integrity represents the primary focus of this review. In addition, some new data are presented and discussed.

In order to characterise the environmental performance of additive manufacturing (AM) processes, comparative analyses are required. Different manufacturing approaches (such as additive and subtractive ones), besides adopting different equipment, use different kinds and amounts of material. Therefore, the material-related flow has to be followed throughout the entire product life. Differences in environmental impact arise at each step of the life cycle: material production, manufacturing, use, disposal, and transportation. A life cycle-based methodology able to take due account of all the factors of influence on the total energy demand for the production of metal components is given in this paper. Decision support tools for identifying the most sustainable manufacturing route (subtractive versus AM-based approaches) are presented for different scenarios. The aim of the present paper is to contribute to the debate concerning the environmental impact characterisation of AM processes.

The material processing industry has to deal with material and energy reduction targets, and such a need becomes more and more urgent when future energy and resource consumption predictions are considered. The optimization of machining operations has conventionally been performed by identifying the range of process parameters that lead to the maximum efficiency, which are generally defined on the basis of maximum productivity and minimum cost criteria. Cost-based models are part of the industrial cultural background, while the emerging environmental impact analysis has not yet become fully established. The paper describes an approach that is aimed at the integration of system-level models for the environmental and economic assessment of machining. Process time, cost, energy demand and carbon dioxide emissions are assumed as optimization targets. The dry and wet turning of Ti-48Al-2Cr-2Nb and Ti-6Al-4V alloys, while varying the process parameters, is considered as a case study. The results highlight that the range of process parameters that allow the maximum process efficiency to be achieved is influenced by material machinability, and that a holistic approach to process optimization appears to be a key task which is worth further research efforts.

Additive Manufacturing represents, by now, a viable alternative for metal-based components production. Therefore the designer, often, has to select among three options at process design stage: subtractive, mass conserving, and additive approaches. The selection of a given process, besides affecting the manufacturing step impact, influences significantly the impact related to the material production step. If the process enables a part weight reduction (as the Additive Manufacturing approaches do) even the use phase is affected by the manufacturing approach selection. The present research provides a comprehensive environmental manufacturing approaches comparison for components made of aluminum alloys. Additive manufacturing (Selective Laser Sintering), machining, and forming processes are analyzed and compared by means of Life Cycle Assessment techniques. The effect of weight reduction enabled by additive approach is considered. The paper aims at highlighting the strong link between manufacturing approach selection and material use. In this respect, a thorough environmental analysis of the pre-manufacturing step is developed. Moreover, the influence of eco-attributes aluminium variability on the comparative analysis results is studied. The paper, therefore, contributes to the development of a methodology for manufacturing approaches comparison, providing guidelines for green manufacturing approach selection. Results reveal that, for the analyzed case studies, the Additive Manufacturing is a sustainable solution for aluminium components only under a specific scenario: high complexity shapes, significant weight reduction, and application in transportation systems.

The specific energy consumption of Additive Manufacturing (AM) unit processes for the production of metal parts could be much higher than that of more traditional manufacturing routes, such as machining. However, AM, due to its intrinsic process peculiarities, including the flexible realization of (almost) any kind of complex shape, has a great potential for improving the material use efficiency, with positive environmental impact benefits from the material production to the product use and disposal at the end of first life. Aim of this paper is to assess the role of the design choices on the environmental AM process sustainability. An integrated design methodology (accounting for the product re-design via topological optimization, the design of support structures, and the design of allowances and features for post-AM finishing operations) for components produced by means of laser powder bed fusion processes is considered. One resource (the cumulated energy demand) and one emission (carbon dioxide) are assumed as metrics for the impact assessment across the product life cycle. The results demonstrate the importance of a proper design for AM to improve the overall energy and emission saving potential.

Awareness about the environmental performance of manufacturing approaches has arisen. Comparative analyses of different manufacturing approaches as well as decision support methods should be developed in the field of metal shaping processes. The present paper aims at tuning a decision support tool for identifying when mass conserving approaches (forming based) are actually preferable over machining processes for manufacturing aluminum based components. A full LCA is developed for comparing the environmental performance of forming and machining approaches as the batch size and geometry complexity hang. The impact of the used metric on the comparative results is analyzed. Results reveal that primary energy can be used as reliable metric for identifying environmentally friendly manufacturing processes.

Additive Manufacturing is under the spotlight as potential disruptive technology, particularly for the production of complex-shaped structural metallic components. However, the actual AM process capabilities present some limitations in achieving the strict part quality requirements imposed by the aerospace and automotive sectors. Therefore, the integration of AM and conventional manufacturing represents an emerging scenario to be investigated. In this paper, a pure machining process and a hybrid production route (based on EBM and finish machining) are compared. The influence of material usage-related factors on costs and energy demand is discussed. The results prove that, despite precise process judgments are case-specific, the proposed methodologies are suitable to provide guidelines for identifying the optimal manufacturing route under multiple design objectives.

Titanium-based alloys are commonly applied in high-performing structural components. Their machinability could be penalized by severe tool wear and poor surface quality. As a result, cutting fluids are widely used to improve the production rate without negatively affecting the machined surface integrity and the tool life. The experimental research activities presented in this paper are focusing on the effects of dry and near-dry cutting conditions on machining process performance when turning Ti-6A1-4V. Minimum Quantity Cooling/Lubrication systems have been exploited to supply low cutting fluid volumes to the cutting area in the form of a precision metered droplets mist. The conventional flood cooling (i.e., wet cutting) has been assumed as benchmark. Results are discussed with respect to tool wear/life, cutting forces, process power demand, surface quality, lubricoolant consumption, and human health hazards. All the main factors of influence are highlighted, and guidelines for identifying the trade-off between the minimization of environmental impact and the enhancement of process productivity are proposed.

The physical and mechanical properties of advanced composite materials promote their application in structural components for the aerospace and automotive sectors. However, limitations in their machinability are due to anisotropy/inhomogeneity, poor plastic deformation, and abrasive behavior. For CFRP drilling, the process efficiency is heavily influenced by cutting conditions and tool geometry. This paper reports the outcomes of experimental diamond drilling tests. A 4-mm thick carbon-epoxy composite laminate was machined. The plate was made of ten layers, in which the carbon fibers were intertwined at 90°. 6-mm diameter core drills were used. Core drills were characterized by an electroplated bond type and an AC32-H diamond grain type. Four different tool grit size ranges were tested: (1) 63/53 μm, (2) 125/106 μm, (3) 212/180 μm, and (4) 212/180 plus 63/53 μm. The results are reported in terms of workpiece delamination, thrust force, torque, and chip morphology. Overall, the results allow identifying the cutting conditions for the minimum drilling-induced delamination while retaining a satisfactory process productivity.

This study reports the effects of the addition of different woody bulking agents and pelletizing pressure on the final bulk density, durability and compression resistance of pellets manufactured from composted pig solid fraction. Two pressure levels (3.5 and 5.0 MPa) and three different types of compost (SFC - pig solid fraction, BC - pig solid fraction mixed with woody biochar, and WC - pig solid fraction mixed with wood chips) were investigated. The study shows that the different pressures adopted - in the range of 3.5 to 5.0 MPa - and the addition of woody bulking agents did not significantly affect the physical and mechanical properties of the pellets. However, according to the results of the study, the particle dimension of the woody bulking agents plays a key role in the mechanical properties of the pellets; the smaller the particles, the higher the pellet mechanical properties. The pelletizing process increased the bulk density of the investigated composts, and pellet durability was always high (> 80%). Nevertheless, when comparing the two bulking agents, the best results in terms of final quality were observed for pellets made from pig solid fraction mixed with woody biochar.

Nowadays manufacturing technologies have to be evaluated not only for the technical features they can provide to products, but also considering the environmental perspective as well. As long as the technological feasibility of a given process is guaranteed, processes minimizing resources and energy consumption have to be selected for manufacturing. With respect to this topic, the research studies in the domain of metal processing technologies predominantly focus on conventional material removal processes as milling and turning. Despite some exceptions, many other non-machining technologies, such as metal forming processes, are still not well documented in terms of their energy and resource efficiency, and related environmental impact. In this paper, an environmental challenge between two traditional technologies is developed: the environmental performances of a partial hot extrusion process and of a turning processes are quantified and compared. A Life Cycle Assessment (LCA) approach is implemented to properly analyze the considered processes. The material production step and the manufacturing phase to obtain a simple axy-symmetric aluminum component is considered for the Life Cycle Inventory (LCI) data collection step. Besides, the material and consumables usage and the consumed electrical power are measured in order to quantify the energy consumption of the manufacturing phase. Further, the environmental impacts related to the manufacturing of the extrusion dies and of the turning process are included in the analysis. The paper presents an early step of a wider research project aiming at identifying the greenest technologies as functions of given product features.

Several generations of gamma titanium aluminides have been developed over time, and they are nowadays commercially available. The differences in chemical composition, as well as the thermal treatments, greatly influence the properties of the alloys. This implies considerable effects on the production process performances. Benchmark trials were performed on three γ-TiAl alloys: Ti–48Al–2Cr–2Nb, Ti–43.5Al–4Nb–1Mo–0.1B, and Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB 2 XD, focusing on machinability and material characterization. The extremely dissimilar results obtained when turning and milling can be traced back to the different microstructures, as well as to the alloying elements, factors both affecting the mechanical and thermal material properties.

Gamma titanium aluminides are heat-resistant intermetallic structural alloys with many attractive properties such as low weight, high stiffness, high refractoriness and high temperature strength. These alloys are excellent candidates to be used as alternative to Nickel-based superalloys for thermally and mechanically stressed components in aerospace and automotive engines. The material properties, however, lead to γ-TiAl difficult machinability, resulting in poor surface quality. In this paper, the geometrical accuracy of holes drilled on a Ti-48Al-2Cr-2Nb γ-TiAl component, produced via Electron Beam Melting (EBM), is analyzed. Particularly, the Design of Experiments (DoE) technique was selected because of its usefulness in determining simultaneously the individual and interactive effects of many variables, that could affect the output results. Experiments were conducted with uncoated carbide drills, varying the cutting parameters. Machined holes were measured by means of a coordinate measuring machine. Hole quality was assessed focusing on the dimensional and geometrical errors, in terms of both cylindricity and roundness, and taking into account the tool wear and the hole depth.

The attention to the environmental impact analysis of manufacturing processes has been increasing. Energy consumption is one of the main players for material removal processes. Models for estimating the specific energy consumption or for computing the total direct energy requirements have been developed over time. This paper proposes a comprehensive model for the system-level energetic analysis of machining processes, which includes all the activities related to workpiece material production, material removal, tool and cutting fluid production and usage. The application of the model to the turning of a Ti-6Al-4V alloy (under wet, MQL, and dry cutting conditions) is presented and discussed. The results allow identifying the optimum process parameters for energy consumption minimization.

The industrial world is facing the challenge of reducing emissions by means of energy- and resource-efficient manufacturing strategies. In some cases, the exerted emissions and the energy demands related to conventional manufacturing processes are not as intensive as those required to extract and produce the raw materials of which the workpieces are made. Therefore, the consciousness of the impact of material usage and the eco-informed choice of the end-of-life scenarios are both needed in view of sustainable development. Aim of this paper is to offer a contribution to a better understanding of the environmental impact of forming and machining processes, for the production of Al-based components, when varying the aluminum recycling strategy.

Metallic material processing plays a significant role in terms of global environmental impact. As a result, energy- and resource-efficient strategies in the metal shaping technology domain need to be identified urgently. Recently, the scientific world has been paying more and more attention to the environmental impact analysis of manufacturing processes. Despite this increased attention, the state of the art in the domain of environmental impact analysis of metal shaping processes is still characterized by gaps in knowledge and in methodologies. In particular, metal forming processes are still not well documented, in terms of their environmental impact, and there is a lack of systematic and comparative approaches. This paper offers a contribution to a better understanding of the environmental impact of forming and machining processes. A thorough methodology has been developed to take into due account all the environmental factors of influence on both of the considered technologies. A comparative analysis has been performed, varying the production batch size and part geometry. The importance of an environmental performance analysis that can include both batch size and geometry variations is discussed and highlighted throughout the paper. Finally, the application of the proposed methodology has resulted in the setting up of an eco-design tool, here defined as a Process Sustainability Diagram (PSD), which allows the greenest technology to be selected for the analyzed case study, while varying the considered factors of influence.

The rising awareness of energy consumption and the environmental impact of manufacturing underline the need to implement structured approaches, such as a life cycle assessment, or metrics for process evaluation. Energy savings on their own are not sufficient to increase the process efficiency of industrial finishing operations, since the results, in terms of machined part quality, have to be accounted for. The research work presented in this paper applies sustainable development concepts to an industrial case study. A shaping grinding process (a flute grinding operation for tap manufacturing) has been assessed experimentally. The effects of variations in the process parameters have been discussed, with respect to processing time, energy consumption, and product quality/integrity. Whenever the optimization goals are in contrast, a trade-off between product requirements and process sustainability has to be introduced. In order to achieve energy savings, without altering the performance of the product, a specific efficiency sustainability indicator has been implemented and coupled to the life cycle inventory phase. The results provide a tool that can assist the decision-making stage and can be incorporated into a business strategy development framework.

Nanocomposite coatings have been widely studied over the last years because of their high potential in several applications. The increased interest for these coatings prompted the authors to study the tribological properties of two nanocomposites under dry and lubricated conditions (applying typical MQL media), in order to assess the influence of the surface and bulk properties on friction evolution. To this purpose, multilayer and nanocomposite AlSiTiN and AlSiCrN coatings were deposited onto tungsten carbide-cobalt (WC-Co) samples. Uncoated WC-Co materials were used as reference. Coatings were analyzed in terms of hardness and adhesion. The structure of the samples was assessed by X-ray diffraction (XRD), while the surface composition was studied by XPS analysis. Friction tests were carried out under both dry and lubricated conditions using an inox ball as counterpart. Both coatings showed high hardness and good adhesion to the substrate. As far as the friction properties are concerned, in dry conditions the surface properties affect the sliding contact at the early beginning, while bulk structure and tribolayer formation determine the main behavior. Only AlSiTiN coating shows a low and stable coefficient of friction (COF) under dry condition, while the use of MQL media results in a rapid stabilization of the COF for all the materials.

The high-performance machining of difficult-to-cut alloys requires the development and optimization of high-performance tools, able to withstand the thermo-mechanical tool load without compromising the surface quality of produced components. In this context, the machinability of titanium aluminides still represents a demanding challenge. In this paper, the performance of cubic boron nitride (CBN) and polycrystalline diamond (PCD) cutting inserts is compared to that of uncoated and coated carbide tools. Longitudinal external turning tests were performed on a Ti-43.5Al-4Nb-1Mo-0.1B (TNM) at.% cast and hot isostatically pressed (HIPed) γ-TiAl alloy, by using a conventional lubrication supply. In addition, PCD tools were also applied under cryogenic cooling with liquid nitrogen. Results proved that PCD cutting tools have the potential to improve the machining productivity of titanium aluminides, due to their high hardness and excellent thermal conductivity. A noteworthy further increase of tool life was possible by using PCD cutting inserts under cryogenic cooling conditions.

Gamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb-0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process conditions.

Advanced structural materials for high-temperature applications are often required in aerospace and automotive fields. Gamma titanium aluminides, intermetallic alloys that contain less than 60 wt.% of Ti, around 30–35 wt.% of aluminum, and other alloy elements, can be used as an alternative to more traditional materials for thermally and mechanically stressed components in aerospace and automotive engines, since they show an attractive combination of favorable strength-to-weight ratio, refractoriness, oxidation resistance, high elastic modulus, and strength retention at elevated temperatures, together with good creep resistance properties. Unfortunately such properties, along with high hardness and brittleness at room temperature, surface damage, and short and unpredictable tool life, undermine their machinability, so that gamma-TiAl are regarded as difficult to cut materials. A deeper knowledge of their machinability is therefore still required. In this context the paper presents the results of an experimental campaign aimed at investigating the machinability of a gamma titanium aluminide, of aeronautic interest, fabricated via electron beam melting and then thermally treated. Milling experiments have been conducted with varying cutting speed, feed, and lubrication conditions (dry, wet, and minimum quantity lubrication). The results are presented in terms of correlation between cutting parameters and lubrication condition with tool wear, surface hardness and roughness, and chip morphology. Tool life, surface roughness, and chirp morphology showed dependence on the cutting parameters. Lubrication conditions were observed to heavily affect tool wear, and minimum quantity lubrication was shown to be by far the method that allows to extend tool life.

Gamma-titanium aluminides present an attractive combination of low density, high melting temperature, good oxidation and burn resistance, high modulus and strength retention at elevated temperatures, and good creep properties. For this reason they are promising candidates as advanced structural materials for high temperature applications. However due to their high strength, high hardness and brittleness at room temperature, g-TiAl alloys are regarded as difficult-to-cut materials. Many efforts have been done during the last 20 years to introduce TiAl-based alloys into the aerospace and automotive market as engineering components. But for the application and diffusion of this new heat-resistant light-weight material for high performance components, a deeper knowledge of their machinability is still required. In this context, and given the increasing attention to the environmental aspects related to the manufacturing processes, the present research work is aimed at investigating two key aspects: the influence of cutting parameters and cooling conditions, on tool wear, surface finishing and power consumption in milling operations of a g-TiAl alloy.

Geometrical optimization of structural components is a topic of high interest for engineers involved with design activities mainly related to mass reduction. The study described in these pages focuses on the optimization of plates subjected to bending for which stiffness is obtained by a pattern of ribs. Although stiffening by means of ribs is a well-known and old technique, the design of ribs for maximum stiffness is often based on practice and experience. Classical optimization methods such as topological, topographical and parametric optimization fail to give an efficient design with a reasonable programming effort, especially when dealing with many and complex constraints. These constraints are both technical and technological. A most promising technique to obtain optimal rib patterns was to define a set of feasible rib trajectories and then to select the subset with the most efficient combinations. The result is not unique and a method to select the optimal patterns is required. In fact, the stiffening effect increases with increasing rib length, but at a greater cost. A trade-off must be found between structural performance and cost: The tools to guide this selection process is the main objective of the paper, with particular attention in evaluating the stiffening due to the presence of beads on the plate with a close link with the production system and possible technological constraints which can occur during manufacturing processes, such as minimum rib distance or the presence of discontinuities or the presence of holes or other elements on the plate. A special tool with enforced rib cross section is considered, and optimal rib deployment has to be found. Numerical examples attached show the methodology and obtainable results.

The reduction of CO2 emissions is an urgent objective to pursue. The scientific and the industrial world have gathered such challenge, starting to find out energy- and resource-efficient manufacturing strategies. From the literature review, in the domain of environmental impact analysis of manufacturing processes, two relevant knowledge gaps can be spotted: (1) the metal forming processes (and, in particular, the bulk forming processes) are still not well documented, and (2) there is a lack of systematic and comparative studies on energy and material flows enabling the identification of environmentally-friendly manufacturing design strategies. This research offers a contribution to a better understanding of the environmental impact of forming and machining processes. The performance of the two processes is evaluated and compared with the varying of the material usage related factors. The impacts on the final results of the aluminum recycling strategy as well as of the applied method to account for benefits of recycling are analyzed. Therefore, the paper represents an effort aimed at tuning and improving a methodology able to thoroughly analyze the environmental impact of a given process, and to better compare different manufacturing strategies from the environmental point of view.

The scientific studies in the domain of environmental sustainability of metal processing technologies predominantly focus on conventional material removal processes, as milling and turning. Despite some exceptions, many other non-machining technologies, such as metal forming processes, are still not well documented in terms of their energy and resource efficiency. Moreover, to properly evaluate the environmental impact of a given process, a standing-alone approach is no longer sufficient. In order to offer a valuable contribution in the domain of metal shaping sustainability, the present paper proposes a thorough methodology entailing to compare, from the environmental point of view, two traditional technologies: a hot extrusion process (mass conserving approach) and a turning (subtractive) one. A Life Cycle Assessment (LCA) based approach is implemented to properly analyze the considered processes. An axi-symmetric aluminum component was selected to develop the analysis on. Besides the analysis of material flows occurring all along the life cycle of the component, the material use and the consumed electrical energy necessary for the tools manufacturing are measured to properly quantify the environmental impact of the production phases. The most relevant influencing factors within each technology are identified and quantified. Moreover, an analysis of the environmental performance of the two processes at the varying of the batch size is presented. The paper aims at providing some general guidelines for the identification of the greenest technology as the main influencing factors change. © 2014 Elsevier Ltd. All rights reserved.

Wire electrical discharge machining (WEDM) is a manufacturing process suitable for high-precision cutting of complex and irregular shapes through difficult-to-machine electrically conductive components. In recent years, wire EDM has become a key non-traditional machining process, widely used in the aerospace and automotive industry. Although this technology has been broadly investigated, literature is still limited on the use of wire EDM for intermetallic alloys, and the applications on gamma titanium aluminides are rather unexplored. Such materials are attracting considerable interest due to the outstanding combination of properties, and they have proved to be eligible for thermo-mechanically stressed parts of aeroengines. Nevertheless, the poor machinability of gamma titanium aluminides has been reported in conventional (i.e. turning, milling, and drilling) and non-conventional machining, such as ECM. Further, machinability results strictly depend on the chemical composition of the specific alloy. This paper investigates the interactions between common process parameters of WEDM and final quality of the generated surface, through analysis of variance (ANOVA) and regression models based on experimental results. In particular, the paper is focused on the effects of pulse on time, pulse off time, servo-reference voltage, and wire tension on the surface finish during the WEDM of a Ti-48Al-2Cr-2Nb (at. %) γ-TiAl alloy. Results are discussed and compared with reference to the models available in literature.

Air heat exchangers are made with tubes joined to finned pack. The connection between tubes and fins can be obtained through a mechanical process where an ogive is pushed inside the tube with smaller internal diameter causing its expansion. Residual plastic deformation provides the assembly with the fins. Accurate connection over the whole contact area of the tubes and fins is essential for maximum heat exchange efficiency. The goal of this work is to study and develop a finite element model able to effectively simulate expansion forming, allowing process analysis and, eventually, process optimization. The paper is divided into a first experimental part, where the materials used for the heat exchangers are characterized, and a second numerical part where models have been developed on the basis of the experimental data. The developed models are used to identify the material properties with an inverse method, and then to study the technological process of tube expansion by using a simplified but sufficiently accurate description. The model has proved to be an effective design tool, as it can evaluate the influence of the main parameters on the process and so optimize production according to technological variations.