Additive manufacturing (AM) has revolutionized part manufacturing, offering unprecedented design freedom and the ability to fabricate intricate structures. Computational design methods like topology optimization (TO) effectively capitalize on AM's design freedom. However, manufacturability constraints must be considered to ensure reliable manufacturing. A significant constraint is local overheating, prevalent in metal additive manufacturing, leading to defects, part distortion, and diminished mechanical properties. While overhangs are commonly associated with overheating, they are not the only geometric features prone to overheating. This thesis addresses the overheating issue in topology optimization by a novel geometric approach. Specifically, we propose to estimate the local conductivity around each element by evaluating the material distribution in its vicinity. This is then used to generate a pseudo temperature field (i.e., hotspot map) to assess overheating risks. Formulated as a constraint in topology optimization, our approach creates optimized structural layouts free of local overheating during additive manufacturing. Additionally, the approach is implemented in space-time topology optimization, limiting overheating risks by simultaneous optimization of structural layout and fabrication sequence. Compared with existing overheating prevention methods, the geometry-based constraint demonstrates significant computational advantages. Transient thermal AM simulations were conducted on the final designs obtained using the physics-based method from the literature and the novel geometry-based overheating prevention method. The numerical results have shown that the proposed geometric approach is efficient and effective in controlling local overheating in topology optimization for metal additive manufacturing.

Improving sustainability in industrial processes is a key topic for the welfare of the environment. One of the major environmental problems caused by industrial processes is industrial waste production. In the automotive industry, the use of polymers such as PA12 for prototyping produces tons of waste per year which are generally destined to incineration. Recycling could help reduce waste, but recycling procedures can be resource-consuming, therefore it might not always be efficient or more sustainable than traditional practices. In most cases, recycling involves extra steps in the process value chain, including finances, transportation, workforce, as well as machinery. To make sure recycling has positive effects in terms of sustainability on industrial processes, a framework to assess the sustainability of recycling procedures is needed.

In this study, it is proposed an assessment framework which considers four pillars of sustainability: (1) technical, (2) environmental, (3) economic, and (4) social. While the environmental, economic, and social pillars are usually considered in sustainability assessments, the technical pillar has been neglected and should be considered in understanding the sustainability of recycling procedures. This framework can be applied to gain insights into recycling procedures’ sustainability and help as a tool to decide which procedure to adopt. Likewise, it considers the company’s needs and objectives, as fundamental factor for the evaluation. In recycling procedures, the technical pillar should include indicators related to resource efficiency but also recycled material quality, an essential factor when evaluating their effectiveness. Such a framework, consisting of a ten steps approach, aims to facilitate the adoption of recycling procedures, through qualitative and quantitative assessments, on the basis of a set of indicators, selected within the four pillars of sustainability.
From the analysis of the current system, to the definition of objectives, design of the pathways, and the evaluation of sustainability indicators, the framework aims to allow companies to systematically assess and select a sustainable pathway in terms of defined objectives and environmental regulations.

The framework was applied to the case study of mechanical recycling of PA12 waste from automotive prototyping. The aim is to reduce plastic parts waste, to be turned into filament for Additive Manufacturing technologies for use as jigs and fixtures. Following systematically the assessment framework, ten potential recycling pathways were identified and compared. Major differences among them include the ratio of waste parts to virgin material, and filament extrusion location. The sustainable recycling pathway that resulted from the evaluation features the shortest transportation distances (connected to lower carbon footprint and energy consumption, and higher flexibility). The application of the framework provided a trade-off analysis, where not only the interests on the environment are considered, but particular attention is given to companies’ needs and opportunities.