## 5 Conclusions, Recommendations and Future Works  
This study aimed to examine the progress made in the development of additive manufacturing technology to support lean and green manufacturing. This was achieved with the use of the PRISMA approach. The systematic literature review was conducted on 158 articles that met the selection criteria. The outcome of the study indicated that additive manufacturing is more robust when compared to the conventional manufacturing technique and can be used to achieve waste reduction, reduction in emission generation, and carbon footprints with significant energy and material conservation. The findings also indicated that the additive manufacturing process also boasts time- and cost-effectiveness during manufacturing compared to the conventional manufacturing technique. However, some of its limitations include the following: selection of the appropriate build speed, product development at high resolution, biodegradability of some AM materials, biocompatibility and mechanical properties of fabricated parts, the need for postprocessing for some parts, and the composition of multi-material parts, amongst others. Although the process is energy intensive, the careful selection of the suitable additive manufacturing process to be employed based on the requirements coupled with a proper product design may result in considerable energy savings at the preprocessing, processing or postprocessing stages. Furthermore, effective process design and optimization as well as proper selection of the right material that suits an intended application are necessary to optimally harness the benefits of AM. Products manufactured with AM technology are usually lighter in weight with less material and energy consumption as well as less waste generation. This aligns the principles of green manufacturing, which focus on reducing the negative environmental impacts caused by manufacturing processes. The technology allows for a simpler, shorter and effective value chain, ensuring quick product manufacturing and part replacement compared to the conventional manufacturing techniques. It allows the use of recycled materials and gives room for product localization, thereby eliminating the economic and environmental effects of logistics and complex value chains. Sustainability can be achieved via the implementation of AM by implementing just-in-time production to reduce inventory waste. The automation of the software used for direct product manufacturing increases the precision and accuracy of parts produced, thereby reducing waste and improving product quality in line with the principle of lean manufacturing. All these benefits of AM ensure that the manufacturing process is cost-effective and environmentally sustainable. Sustainable product development ensures that the manufacturing operation is conducted in a time- and cost-effective manner with less environmental impact. Therefore, the outcome of this study indicates that there is a link among AM, green and lean manufacturing in order to achieve sustainable manufacturing goals. This study provides empirical, conceptual and theoretical findings that can assist manufacturing organizations in their quest to minimize waste generation and achieve material energy efficiency throughout product lifecycles. The study also adds to the understanding of additive manufacturing and contributes to the exiting literature on the impact of additive manufacturing on lean, green and sustainable manufacturing. The synthesis of the literature presented in this study can help manufacturing industries achieve sustainability in terms of resources, cost and environmental conservation. It is recommended that manufacturers adjust their business models to incorporate additive manufacturing, especially for developing complex and spare parts.