M. J. Yadegari

Additive manufacturing (AM) is a cutting-edge technique for producing mechanical and structural components that is a key player in the fourth industrial revolution, the digital industrial transformation. AM technology has gained widespread popularity in recent years due to its unique advantages, such as the ability to manufacture parts with complex geometry and optimal topology, as well as multipart assemblies. These characteristics have completely transformed traditional manufacturing methods [1], [2].

The construction industry can make use of various metal 3D printing methods, such as Powder Bed Fusion (PBF), which includes SLM and EBM, and Directed Energy Deposition (DED), which includes LMD, LMWD, and WAAM processes. These techniques are commonly used for manufacturing metal components [3].

Metal additive manufacturing has been used in construction for smaller parts like façade nodes and joints, but there are also plans to develop a full-sized structures such as pedestrian bridge (several of these projects are depicted in below figures).

Fig. 1. Nematox façade node.

Fig. 2. Arup lighting node.

Fig. 3. The MX3D bridge.

In order to decrease global CO2 emissions and enhance energy efficiency, the construction industry can adopt metal 3D printing as an additional technology to traditional manufacturing. This will enable the creation of parts with customized properties that fulfill performance standards while minimizing material usage and waste, thereby improving resource-efficiency and workplace safety. In addition to optimizing geometry, there is potential to take advantage of mixed material properties (using stronger materials in areas with higher stress and more ductile materials where needed), anisotropy (orienting the print layers to increase stiffness), and thermal prestressing (using a scanning strategy that creates opposite residual stresses to those caused by load application) [4].

The construction industry can benefit greatly from the use of additive manufacturing, but it also presents new challenges and requirements. These include the need for engineers to have advanced digital skills, increased use of sophisticated computational analysis, and a shift in approach towards designing and verifying structures with a greater focus on inspection and load testing [5].

The use of advanced additive manufacturing technologies, such as multi-material and metamaterials techniques, can result in highly customized and high-performance engineered designs [6,7]. Multi-material additive manufacturing (MMAM) allows for the incorporation of multiple materials or varying compositions within a single component (As shown in Fig. 4), leading to increased functionality and complexity. This approach offers numerous opportunities for the creation of complex, personalized, and valuable products with enhanced properties. By integrating materials at different scales, such as electrical, thermal, mechanical, optical, and multifunctional properties, the properties of components can be tailored to specific needs [8].

Fig. 4. General classification of Multi-materials and their respective improvements in properties [8].

The integration of AM with multiple materials can bring about significant changes in manufacturing and construction. MMAM enables the creation of objects with different material properties without the need for additional assembly or complex architecture design. This modification can address inefficiencies in production by reducing the number of required processes and offering solutions to challenges associated with material connection. The goal of MMAM is to address common issues in the construction industry, such as excessive material consumption, limited adaptability to environmental conditions and structural demands, and complexity in assembly and construction procedures [8].

The current limitations of AM methods in printing metals are due to machine-specific restrictions, which restrict the fabrication of single-metal compositions at a given time. However, a new powder-feeding design with multiple material feeding sources can resolve this issue, or premixed powders can be used to print multifunctional components (Fig. 5). The directed-energy deposition (DED) process is a popular MMAM method that has garnered attention due to its ability to manufacture large-scale components quickly and without the need for powder recycling. Additionally, multiple or mixed powder-feeding systems are feasible (Fig. 6) [8,9].

Fig. 5. Illustration of LPBF processing premixed dissimilar powders [8].

Fig. 6. Process description of depositing multiple materials using DED process [9].

Metal additive manufacturing presents significant opportunities for innovation in the construction industry. However, it also poses certain challenges, including inherent variability in material and geometry, as well as limitations in the current state of the technology that may be overcome as manufacturing capabilities improve.

Buchanan and Gardner [5], propose several ideas for leveraging the unique features of additive manufacturing, particularly with regard to geometric flexibility and material property optimization. They suggest designing hollow structures to prevent global and local buckling of columns, as well as perforated shear keys to enhance composite action with infill materials (such as CFT columns) (Fig. 7). Additionally, they propose designing two-span beams with additional stiffening in key locations and adjusting flange thickness (Fig. 8). Finally, they suggest an initial plan for optimizing material strength and ductility through the use of functionally graded materials. This approach involves using high-strength materials in regions of high moments (such as the mid-span of beams), while using higher ductility materials in areas such as connections where ductility demands are high (Fig. 9).

Fig. 7. Examples of possible AM hollow structural members featuring (a) varying wall thickness to enhance member buckling performance, (b) internal stiffening to improve local buckling resistance and (c) perforated shear keys to enhance composite action with infill material [5].

Fig. 8. replacement metal AM beam, with varying flange thickness and additional stiffening in key locations [5].

Fig. 9. Possible functionally graded AM beam, as part of a hybrid structure [5].

References