Printing patterns in additive manufacturing have been extensively studied regarding their effects on the microstructure and mechanical properties of the materials. However, weaving, a welding technique that produces good quality welds in large areas and ensures good weld penetration has not been applied in additive manufacturing. This study focuses on comparing four weaving patterns to two traditional line printing patterns in Wire arc additive manufacturing of austenitic stainless steel 316L. This thesis covers the groundwork of weaving pattern characterization, starting from optimization of printing parameters and printing path, followed by pattern characterization through measurements of voltage, current, thermal history, and thermal profile, and investigation of surface quality of the samples. Microstructure characterization was then conducted by optical microscopy, electron backscatter diffraction, and X-ray diffraction; and mechanical properties were obtained through microhardness and tensile testing. The weaving patterns showed an improved deposition rate and avoided lack-of-fusion defects compared to the line printing patterns. Two out of four weaving patterns achieved superior surface quality over the line printing patterns and are free of macro-defects such as side wall collapse and spattering. The weaving patterns have excessive heat accumulation and lower cooling rates compared to line printing patterns, which led to coarser microstructures and inferior microhardness and tensile properties. The thermal gradient is also more uniformed and aligned to the build direction, increasing the degree of grain alignment and texture of the weaving patterns across the samples.

Welding is an extensively used technology by different industries such as aerospace, automotive and marine industry. Welding involves the temporal melting of materials in order to join them together. The quality of the weld is known to depend on the fluid flow and heat transfer in the material. A way to influence the heat transfer and fluid flow, and thus the quality of the weld, is by using different power-density distributions. However, the current literature falls short when combining the different power-density distributions with weld pool behaviour. The aim of this thesis is to study the effects of laser power-density distribution on heat and fluid flow in molten metal melting pools. This will be done by running weld pool simulations using a 2D axisymmetric, flat surface model. These simulations use a top-hat, Gaussian or doughnut laser power-density distribution. Besides, the cases have been simulated for a 20 ppm and a 150 ppm sulfur concentration. That the sulfur concentration has an influence on the weld pool shape was already shown in previous studies. However, it was not known how much the influence of sulfur concentrations varied for different laser power-density distributions. The laser power-density distributions are found to have a significant influence on the weld pool shape. The doughnut power-density distribution created a three times deeper weld pool than the Gaussian and top-hat power-density distribution. The maximum temperature of the weld pool was also influenced by the power-density distribution. In the case with a sulfur concentration of 20 ppm a discrepancy of 1000 K has been found between the Gaussian and doughnut distribution. The influence of sulfur concentrations varied for different laser power-density distributions. This influence of the sulfur concentrations has been measured through the difference in aspect ratio for different sulfur concentration cases. For both the top-hat and Gaussian power-density distribution, the aspect ratio differed 0.02 when using a 20 ppm versus a 150 ppm sulfur concentrations. The doughnut power-density distribution reached a higher difference in aspect ratio of 0.1 when using a 20 ppm versus a 150 ppm sulfur concentrations. The use of different power-density distributions in weld pool simulations results in different weld pool behaviour. Besides, the combination of different sulfur concentrations with power-density distributions largely influenced shape, temperature and fluid flow of the weld pool, which results in a great variation of weld pool shapes and sizes. Because there are different requirements for different welding cases, these results are useful in order to construct a quality weld.

Metallic droplet deposition is of interest in the industry because of the potential use in additive manufacturing. This work discusses the complex phenomena involved in droplet impingement, especially the effect of temperature dependant surface tension. The volume of fluid (VOF) method is used to solve the axis-symmetric Navier-Stokes equations, which are used to describe the droplet's behaviour. Different temperature dependencies for the surface tension are modelled, to see the effect on the interface and substrate melting. Furthermore, the effect of droplet size, initial temperature on droplet shape and substrate melting is studied. To judge the accuracy of the VOF model, a series of benchmarks are tried. The VOF model used in this work is as accurate or more accurate than previous works. The results show that droplets with a higher percentage of oxygen flatten, this is due to thermo-capillary forces. A higher temperature results in more spreading of the droplet, this is because higher temperatures result in higher surface tensions. These surface tensions keep the droplet together when it first makes contact with the substrate. This causes less air is trapped underneath the droplet, which causes the droplet to spread out more. The air also causes the droplet to cool down less fast, this results in a phenomenon where the hotter droplet is solidified faster than the colder one.