Wire arc additive manufacturing (WAAM) is attributed to higher material deposition rates and medium to large build volumes. Integration of multi-axis (more than three) material deposition kinematics in WAAM can bring a paradigm shift in the metal additive manufacturing industry. The material build-up mechanism employing directed energy deposition results in localized melting and solidification of feeding wire making the fabricated structure inherently prone to deposition defects such as dimensional distortion, residual stresses, solidification cracking, and porosity. Optimization of welding process parameters can improve cracking and porosity behavior. However, the problem of distortion is inevitable, and current mitigation strategies rely on post-processing or symmetric material deposition; while the former decreases the effectiveness of WAAM and increases costs, the latter could only be implemented for specific parts. Tackling this problem with the help of computational design tools is a recent approach, and Fabrication Sequence Optimization dictating material deposition is numerically predicted to limit the extent of the distortion effectively compared to conventional planar horizontal deposition; however, this still lacks experimental validation. This research presents a series of fabrication experiments using Al5356 Aluminum-magnesium alloy wire in a 6-axis robotic WAAM setup in two parts: (1) Process parameters identification for optimal bead characteristics for Al5356 wire, (2) Fabrication of single-bead multi-layered thin-walled shell structures using planar and optimized material deposition. A digital image correlation-based non-contact in-situ distortion measurement setup is constructed to analyze strain development during fabrication process and 3D scanning of fabricated structures is performed to estimate dimensional deviation. The experimental findings revealed an improvement in geometrical formation and a qualitative indication of distortion minimization with an optimized fabrication sequence.

Wire Arc Additive Manufacturing (WAAM) is a manufacturing technique with the ability to produce large metal parts with relatively complex geometrical shapes. One obstacle limiting full exploitation of WAAM in the industry is uncertainty on the mechanical properties of manufactured parts. Mechanical properties are strongly influenced by the microstructure of the material which is a product of the thermal history of the material. Thermal history of parts manufactured with WAAM is complex which leads to uncertainty on mechanical properties and microstructure. Therefore a methodology to predict thermal history, microstructure and hardness of metal-based additive manufactured parts is presented, validated and applied in this study. The methodology is applied to high strength low alloy s690 steel parts produced with WAAM. First a part level thermal process model is utilised to predict the thermal history. Subsequently, a model is developed to predict the microstructure by modelling microstructure phase transformations. Based on thermal history and microstructure phase fractions, Vickers hardness is predicted. Predictions are validated with experimental measurements and observations obtained from a collaborating master thesis. Part temperatures of the thermal model agreed well with measurements. Although the predicted microstructure phase fractions show a lower ferrite content than experimentally observed, the trend of the microstructure phase fractions along the part height is the same in the prediction and the experiment. The predicted hardness is 49 HV higher than the measured hardness. However, hardness predictions and measurements show the same trend along the part height. The methodology to predict the thermal history, microstructure and hardness was applied on a study in which the height of a wall was varied and on a study on a geometry in which two walls cross each other at the center. For both studies the martensite content decreases over the part height, whilst the bainite content increases over the part height. This is caused by the decrease of cooling rate over the part height. Hardness also decreases over the part height. For both the change in microstructure phases and the hardness over the part height, the largest change was observed at the bottom of the part. For the study with the crossing geometry, no significant difference was found for the microstructure and hardness between the center and side of the crossing.

As a type of powder-bed-based Additive Manufacturing (AM), Selective Laser Melting (SLM) is widely used for building metallic lattice structures. However, during SLM process, geometrical imperfections and defects, such as strut over-sizing or under-sizing, typically exist in components due to overheating, which strongly influence their mechanical response. Therefore, it is common that the as-built lattice has discrepancies from the designed lattice structure in mechanical properties. The main aim of this study is to simulate the transient temperature field of lattices during SLM process to predict the possible manufacturing issues for the improvement of product quality. Based on a technique, the moving grid method, growing struts of a lattice whilst it being built by SLM can be regarded as moving domain problems, and thermal process of a building lattice can be simulated numerically. The primary contribution of this study is to evaluate the effect of process parameters, including laser power, energy density and material deposition rate, on thermal evolution of a lattice during SLM. Another contribution is related to the comparison of transient temperature field between different lattice architectures. Analyzing the influences of various factors is important to recognize the thermal evolution of a building lattice. The results reported in this study offer a reference for quality improvement of produced parts, to realize that both geometry and mechanical properties of the as-built lattices as close as possible to their as-designed counterparts.