This study presents a novel multi-material additive manufacturing (MMAM) strategy by combining virgin polylactic acid (vPLA) with recycled polylactic acid (rPLA) in a layered configuration to improve both performance and sustainability. Specimens were produced using fused deposition modelling (FDM) with various vPLA: rPLA ratios (33:67, 50:50, and 67:33) and two distinct layering approaches: one with vPLA forming the external layers and rPLA as the core, and a second using the reversed arrangement. Mechanical testing revealed that when vPLA is used as the exterior, printed components exhibit tensile strength and elongation improvements of 10–25% over conventional single-material prints, while the tensile modulus is largely influenced by the distribution of the two materials. Thermal analysis shows that both vPLA and rPLA begin to degrade at approximately 330 °C; however, rPLA demonstrates a higher end-of-degradation temperature (461.7 °C) and increased residue at elevated temperatures, suggesting improved thermal stability due to enhanced crystallinity. Full-field strain mapping, corroborated by digital microscopy (DM) and scanning electron microscopy (SEM), revealed that vPLA-rich regions display more uniform interlayer adhesion with minimal voids or microcracks, whereas rPLA-dominated areas exhibit greater porosity and a higher propensity for brittle failure. These findings highlight the role of optimal material placement in mitigating the inherent deficiencies of recycled polymers. The integrated approach of combining microstructural assessments with full-field strain mapping provides a comprehensive view of interlayer bonding and underlying failure mechanisms. Statistical analysis using analysis of variance (ANOVA) confirmed that both layer placement and material ratio have a significant influence on performance, with high effect sizes highlighting the sensitivity of mechanical properties to these parameters. In addition to demonstrating improvements in mechanical and thermal properties, this work addresses a significant gap in the literature by evaluating the combined effect of vPLA and rPLA in a multi-material configuration. The results emphasise that strategic material distribution can effectively counteract some of the limitations typically associated with recycled polymers, while also contributing to reduced dependence on virgin materials. These outcomes support broader sustainability objectives by enhancing energy efficiency and promoting a circular economy within additive manufacturing (AM). Overall, the study establishes a robust foundation for industrial-scale implementations, paving the way for future innovations in eco-efficient FDM processes.

Over the years, the cumulative environmental impact from human activity has disrupted the stability of the natural world, warming the planet above pre-industrial levels. Whilst unprecedented in many ways, reducing industrial emissions from greenhouse gases could help stabilise rising temperatures. Thus, the exploration for more sustainable manufacturing solutions that reduce carbon emissions is imperative. However, some traditional manufacturing (TM) processes, such as sand casting, which, despite its versatility to produce products in many shapes and sizes from almost any metal or alloy, are typically energy-intensive activities. Conversely, metal additive manufacturing (MAM) enables users to manufacture more complex, lighter and near net shapes with the ability to consolidate manufacturing workflows. Consequently, MAM has been reported to be an energy-efficient alternative. Yet, evidence in the literature on the environmental impact of some MAM processes is limited, especially for material extrusion (ME) additive manufacturing (AM) methods such as the atomic diffusion additive manufacturing (ADAM) process. Thus, this paper explores the feasibility of performing a life cycle assessment (LCA) for the ADAM process compared to sand casting. Preliminary results indicate that the ADAM process demands 71.04 kWh/kg and 16.57 CO₂ equivalent (CO₂−eq) more for manufacturing 1kg of 17-4 precipitation hardened stainless steel (17-4 PH SS) compared to sand casting. Thus, the findings collected from this pilot study justify future research efforts to converge on developing a novel model for performing a comprehensive cradle to grave LCA for ADAM to compare against sand casting and other TM processes such as CNC milling and investment casting.

This chapter focuses on the most current understanding of the environmental impact of metal additive manufacturing (MAM). In recent years, the initiative to reduce global greenhouse gas (GHG) emissions has led to substantial progress in understanding the contribution of manufacturing processes concerning global warming. However, without intervention, Earth’s temperature is likely to rise by 1.5 °C between 2030 and 2052. Consequently, for a more sustainable future, the environmental impact of a product’s lifecycle should be accurately assessed and transparent. This includes all phases from mining and extraction to primary material production, feedstock production, processing, post-processing, and product disposal. While MAM has been promoted by academia and industry as a more sustainable manufacturing process, this has not been well demonstrated. There is a lack of a comprehensive comparison of energy consumption of the different MAM processes. Likewise, to establish how to implement a manufacturing process responsibly, a distinction based on systematic studies must also be made between the environmental impact of MAM compared to traditional manufacturing (TM) processes such as casting, forging, CNC machining, and powder metallurgy. The lack of defined ecological differences may also prevent the future adoption of MAM; therefore, characterising and comparing the environmental impact for sustainability is urgent. Based on the literature, this chapter first examines the energy consumption of MAM and TM to develop an appreciation for the possibilities and implications of using MAM to encourage sustainable manufacturing practices by raising awareness of the effects of energy-intensive processes. The sustainability benefits of MAM are also discussed as well as recent developments in the sphere of smart manufacturing such as the internet of things (IoT), hybrid manufacturing (HM), big data analytics (BDA), and machine learning (ML) which all have the potential to strengthen sustainable manufacturing significantly. Although this chapter demonstrates substantial progress for MAM on many fronts, studies indicate that printing consumes substantially more energy than TM processes. On the other hand, integrating various data-driven technologies to create smart and sustainable additive manufacturing (SSAM) systems may ensure that products and process parameters are optimised and that energy consumption can be adequately controlled, which is helpful for a cleaner environment. <!----> <!----> <!----> <!---->