Key Engineering Materials Vol. 1051

Abstract: Polymer processing in modern industry is often not efficient from the point of view of energy and material consumption. This production system must be revised to pursue a circularity of products and materials. Recent developments in additive manufacturing technologies for polymers and polymer-based composites are enabling changes of production paradigm from “Design for Manufacturing” to “Manufacturing for Design”, providing new intriguing lightweight solutions. This paper summarizes the lesson learned from the RELIVE project “REcycling of pLastic wastes integrating extrusion and additIVE manufacturing techniques”, in terms of methodology and results.

Abstract: Fibre metal laminates (FMLs), combining metal alloy sheets with fibre-reinforced polymers (FRPs), offer high specific strength and good fatigue resistance for lightweight structural applications. However, conventional manufacturing routes for thermoplastic FMLs rely on separately forming and bonding or hot pressing, which involve multi-stage forming routes, long heating cycles, high energy consumption and limited industrial scalability. To address these limitations, a novel non-isothermal one-shot forming route integrating hot form quench (HFQ) with FRP stamp forming is proposed in this study. In this process, separately heated metal and FRP blanks are stamped together in cold tools, enabling simultaneous forming and adhesive-free bonding within a single operation. U-bending forming trials were conducted using AA6082 aluminium alloy sheets and carbon fibre-reinforced polyamide 6 (CF/PA6) laminates. The influence of FRP temperature state and aluminium surface condition on forming quality and interfacial bonding performance was systematically examined. Solid-state FRP forming limited excessive polymer flow, resulting in stable bonding but a higher intra-ply void content, whereas molten-state forming promoted polymer redistribution and reduced void content at the expense of bonding performance, leading to local debonding in highly deformed regions. In addition, chromic acid etching of the aluminium surface improved bonding and mitigated debonding after forming and post-form T6 artificial ageing. These results highlight the importance of balancing polymer flow behaviour and aluminium surface condition in non-isothermal one-shot forming, providing a practical and energy-efficient route for manufacturing thermoplastic FML components.

Abstract: Electroplasticity in sheet metal forming is a relatively recent method that involves applying an electric current to metal sheets during or before the forming process. Existing research on Electro-Assisted (EA) forming primarily focused on material characterization; few studies have investigated the effect of electropulsing on loads, power, and energy consumption during sheet metal forming, and no studies have explored the reshaping of previously formed titanium sheets after the Electro-pulsed treatment (EPT). This research aims to bridge some of these gaps of knowledge by applying two different electropulsing treatments, varying in current density, to square Ti6Al4V specimens prior to shaping and reshaping. performed using dies and counter dies having different geometries. Load, power, and energy consumption data were measured to assess the benefits of EPT compared to an untreated specimen serving as a reference. The findings suggest that EPT can significantly reduce the energy consumption and forces required for both shaping and reshaping of titanium components, extending their useful life and reducing the need for remelting. The study highlights the potential of EPT as a sustainable solution for reducing the environmental impact of titanium sheet disposal and recycling, improving material efficiency, and optimizing industrial forming processes.

Abstract: Aluminum extrusion plays a critical role in lightweight structural applications and circular economy strategies. However, extrusion process design is constrained by competing objectives: increasing productivity through higher ram speeds or increased die-hole count improves throughput and material utilization yet simultaneously elevates force demand and defect susceptibility. In this work, a numerical statistical framework is proposed to identify circularity-tolerant process windows, defined as multi-objective design regions that balance productivity, product quality, and sustainability performance. A three-factor Taguchi design was employed to systematically vary ram speed, billet temperature, and die-hole count in the extrusion of AA6063. Twenty-seven full 3D thermo-mechanical extrusion simulations were conducted using the DEFORM finite element platform employing an Arrhenius-type constitutive model from literature. Key extrusion responses maximum ram force, local damage indicator, and total displacement were analyzed using Principal Component Analysis (PCA) to reveal correlations and trade-offs between productivity-oriented parameters and quality-related responses. The results demonstrate a clear divergence between productivity drivers (ram speed, die-hole count) and process capability indicators, providing quantitative evidence of the inherent productivity quality trade-off. The proposed framework enables the identification of robust extrusion operating regions suitable for circular manufacturing scenarios in aluminum extrusion. The proposed framework is particularly relevant for extrusion scenarios where process robustness must be ensured under increasing material and operational variability, such as those anticipated with higher recycled content.

Abstract: The reshaping approach is widely considered a virtuous strategy in line with the pillars of the Circular Economy. According to this approach, End-of-Life (EoL) components are subjected to a second forming process to achieve a new functional geometry. However, EoL parts often exhibit a non-uniform thickness distribution and work-hardened zones resulting from the primary manufacturing step, which makes the design of the reshaping step not trivial. Beyond the standard objectives like avoiding fracture and minimizing springback during the reshaping operations, one of the most concerning aspects is the complete removal of the geometrical features coming from the initial forming process. Flexibility and versatility of the forming process are unavoidable requirements to make the reshaping successful. Therefore, three different reshaping routes are numerically investigated in the present work: (i) reshaping by hydroforming (RH) at room temperature; (ii) reshaping by gas forming (RGF) at hot temperature; (iii) a hybrid approach, based on the combination of an intermediate deformation step via Single Point Incremental Forming followed by sheet hydroforming (RHA). The three routes share the same EoL, characterized by the presence of a deep-drawn square feature. Comparing the three routes, in terms of final shape and thinning distribution, with a reference case study (represented by the sole hydroforming process carried out on an undeformed flat blank) allowed to conclude that the feature removal and a non-severe thinning could not be achieved simultaneously: in fact, while RGF and RHA ensure a more evident suppression of the pre-existing feature, they simultaneously induce a more pronounced and localized thinning compared to the RH route.

Abstract: The utilisation of friction-induced solid-state recycling, methodically adapted to the CoNform process, facilitates the continuous production of semi-finished products. The material intended for recycling is conveyed continuously via a rotating wheel. The volume flow is influenced by fixed surfaces, deflections, and constrictions, thereby creating an asymmetrical flow profile. In order to effect a change in the mechanical properties of the semi-finished product, the material fed into the process can be modified. This enables the amalgamation of two alloys or the direct transition between them. The inhomogeneous flow conditions present within the tool give rise to the mixing of materials, thereby creating a graded multi-material zone. The multi-material zone was divided into different areas and traced back to the process conditions. Within the transitions, the connections between the alloys were examined, as well as the influence on the boundary layer. Material properties were determined for the individual areas and located along the length of the profile.

Abstract: Hot-dip galvanizing (HDG) is a widely adopted industrial process for enhancing the corrosion resistance and service life of steel products; however, it is also characterized by high energy and material consumption. In this study, a process-oriented Life Cycle Assessment (LCA) is applied to compare the environmental performance of two industrial steel wire coating routes: conventional hot-dip zinc (Zn) coating and zinc–aluminum (Zn–Al) coating. The analysis is based on primary data collected from an industrial galvanizing line operated by Metallurgica Abruzzese S.p.A. (Italy) and focuses exclusively on the manufacturing stage, using a gate-to-gate approach. The system boundary includes surface preparation, thermo-metallurgical coating treatment—comprising induction annealing, hot-dip galvanizing and, for the Zn–Al route, an additional molten Zn–Al bath—followed by wire cooling and final handling operations. Results show that the Zn–Al coating route leads to a significantly higher environmental impact at the manufacturing stage, with an approximately 44% higher GWP100 compared to conventional Zn coating. Contribution analysis reveals that this increase is primarily driven by the additional thermo-metallurgical coating step, which entails higher material input and thermal energy consumption, rather than by aluminum content alone. The findings highlight the dominant role of material selection and thermal process management in determining the environmental performance of industrial galvanizing lines.

Abstract: The mitigation of primary resource exploitation and their usage within linear economies ultimately leads to systematic leakages from economy and the depletion of natural resources. In contrast, a circular instead of a linear economy aims towards minimizing these leakages by reintroducing all resources to economy without negative externalities. Within the circular economy (CE), manufacturing plays a vital role for the conversion of resources towards products. For a manufacturing system, it is hence of critical importance to understand the implications and requirements of CE for production. The present study develops the Ready4CM “Ready For Circular Manufacturing” principle. Manufacturing systems are considered in the light of serving the needs of CE, where manufacturing flexibility, scalability and reconfigurability may pave the way but need to be controlled sufficiently to achieve resilience towards more drastic uncertainties of used materials. Not only focusing on process, but also on machine and tool, this paper contributes towards CE by identifying systematic aspects of circularity in manufacturing systems. We embedded our contribution in existing frameworks that calculate and balance sustainability potentials within circular economy while our approach, Ready4CM, aims to identify and summarize a comprehensive understanding of technical premises for manufacturing processes to serve and facilitate CE.

Abstract: Climate change is progressing rapidly, posing severe risks to the environment and making sustainability and circularity key challenges for future industrial development. Greenhouse gas emissions are largely driven by human activities within industrialized societies, requiring adaptation at individual, societal, and industrial levels. Metal forming technologies can contribute significantly to this transformation by improving material efficiency, process efficiency, product efficiency, and circularity. Material efficiency is particularly important, as material production accounts for the largest share of industrial emissions. Process efficiency offers a high leverage effect, due to the large production volumes in forming process chains, while product efficiency reduces energy consumption during usage and enhances the performance of energy generation systems. Circularity supports sustainability by extending material lifecycles through reuse and recycling, thereby avoiding energy-intensive primary production. This paper presents an overview of exemplary sustainability contributions in metal forming process chains. For open-die forging, it can, for example, be shown, that digital twins, virtual reality–based operator training and real-time assistance systems are measures to improve material and process efficiency. A circularity approach for open-die forging is presented, with a remanufacturing concept for large shafts based on re-forging end-of-life components, in order to heal fatigue-related damage by forming. Increased material, process and product efficiency is demonstrated by a use case study of forging hollow rotor shafts for wind turbines. Whereas, the hollow-forging allows for weight reduction in the rotor component and thus enables higher power density of the generator, thinner tower designs and reduced logistic costs. Additionally, the use of an innovative air-hardening ductile (AHD) steel can eliminate the energy-intensive heat treatment in the process chain.

Abstract: In the global transition towards renewable energy, a leading role is played by photovoltaic (PV) technologies. However, the increasing growth of installed PV panels, together with the rise of the number of modules reaching their end-of-life phase, make the sustainable management of electronic waste a crucial aspect. The reduction of energy consumption and polluting emissions and the maximization of material recovery represent the ultimate purpose of demanufacturing processes. Here, cryogenic delamination is proposed as an innovative strategy, as it exploits the thermal and mechanical properties of PV module constituents to achieve the cleanest possible separation of layers, allowing for the recovery of strategic materials (silicon, aluminium, silver, copper). This work aims to combine experimental and numerical approaches in order to obtain a comprehensive understanding of the fundamental mechanisms governing the process: the overall objective is represented by the process optimization to enable the exploration of various operating conditions without the need for costly and time-intensive experimental campaigns and, ultimately, the implementation of such technology at the industrial scale.