Wire + Arc Additive Manufacturing (WAAM) is a potential high deposition rate process that can be efficaciously used to manufacture and repair functional components. To manufacture functional components out of WAAM, the first requirement is to reach near net geometrical and shape of the build, considering the costs to redress the built part. The functionality of the builds (mechanical properties and occasionally wear/corrosion resistance) complements the requirements. As-built parts produced by WAAM have inherent lateral surface waviness (undulated surface) and may deviate from the target dimension, post processing is often required to eliminate lateral surface waviness and oversizing, i.e., to remove the extra material in such a way that all the surfaces turn evenly flat and match the design dimensions. Post-working costs must be mitigated to make WAAM manufacturing competitive with other subtractive or forming methods. The amount of this extra material which leads to lateral surface waviness varies with parametric set and can be reduced by selecting parametric set which produce minimum residual material. Therefore, somehow different from welding operations, WAAM parametrization is critical for the shape and dimensional tolerances. Parametrization of WAAM is a difficult task, because multiple parameters are involved and parameters are inter-dependent on each other, making overall process complex. In addition, a set parameterization that attends geometric aspects may not fulfill the functionality requirements. An approach to study WAAM would be through operational maps which can be used to select parametric set for a given target dimension and functional properties. Upon parametrization, operational map will indicate the workable parametric set for a range of LW and which is called as working envelope.

The objective of this work was the development of a methodology to parametrize WAAM, aiming dimension repeatability, tolerances and mechanical performance of the build, such that desirable quality and cost can be achieved. Desired quality here means presence of no imperfections and discontinuities that impairs functionality. The consumables were chosen to match benchmarked mechanical properties of high strength low alloy steels, using as novity in WAAM a metal-cored wire as feedstock.

The work development had 4 stages. As a starting point, the stage named "Mock Design" had the objective of finding, without experimentation, a rough operational map to visualize the expected operational map and further reduce the number of experiments. The layer dimension was estimated from deposition rates of the consumable datasheet and assuming semi-circular cross-section of the deposited layers.

At the second stage, "Pre-requisite for realistic operational map", the objective was to determine the actual melting rate and the workable limits of I and TS with the chosen consumable and equipment. This approach resulted in a 2nd approximation operational map with a working envelope, yet roughly estimating the layer cross-sections.

Within the "Realistic operational map" stage, a design of experiment was applied to cover the working envelope already defined in the previous stage and long and tall walls were additively manufactured. Actual values of LW (external and effective) measured, geometrical parameters (waviness and buy-to-apply indexes) were calculated and a realistic operating envelope was reached. Justifications for the behaviour of the metal deposition at different areas of the operating envelope were devised.

The operational envelope was further validated (4th stage) by selecting a target LW and finding corresponding three parametric set (covering the whole range of operational map) to produce walls on which geometry, mechanical characterisation and production time study was acceptable. Tensile tests were carried out in longitudinal and transverse direction. Hardness profile on the cross section from the bottom to top were raised.

Finally, a brief simulation of deposition time was developed to demonstrate the weight of the TS on the final deposition time and wall quality, as a function of a target wall width. The geometrical characterisation showed high precision in achieving target dimension. For a target LW, it was also found that there were no imperfections or discontinuities present in the walls built according to X-ray radiography and bend test. However, some drop of mechanical properties and anisotropy were observed when the TS was higher, although matching in general the benchmark.

As a conclusion, this approach (operational map) helped in determining the combination of I and TS which leads to either higher robustness, fast production, better mechanical properties or less material to be removed in post processing for a target LW, facilitating the decision making.