## 4 Discussion  
As previously stated, one of the major challenges that the LMD process must overcome to gain traction for industrialization in fields such as aerospace, oil and gas, and construction is the generally higher cost per part compared to other conventional manufacturing technologies [1]. Indeed, the initial investment of buying an LMD system is difficult to amortize because of the limited series manufacturing that these machines are typically destined for. There are numerous approaches to making an LMD system more inexpensive, which can all be summed up as improving overall process sustainability. A requirement for sustainability is that the process should be accurate and reproducible in the realization of the designed components, avoiding the need for extensive preliminary testing and limiting the quantity of produced scrap components. As a result, LMD machine manufacturers typically provide solutions based on CNC gantry or cartesian kinematics, which are generally more precise and robust than articulated robot-based systems, but much more expensive and less flexible [21]. The investigation in this research aims to shed light on this aspect of LMD by assessing the performances in terms of geometrical accuracy of two machines with identical optical and material feeding configurations but different kinematic mechanisms and sizes and comparing them. For this scope, an oil and gas case study was chosen, and the designed component was built on both machines under identical conditions (process parameters, materials, fixture configuration, and pauses for measurements). In order to avoid over-constraints that could threaten the outcome of the builds or represent a dissimilarity between the two builds, the component was given the most freedom of deformation possible. Figure 16: Dimensional mismatch between the 3D scan of the component realized with the CNC gantry-based system and the 3D scan of the component realized with the articulated robot-based one. The analogy between the geometry and internal appearance of tracks deposited on the two machines and with the same process parameters is assessed using the cross sections shown in Figure 10. When the same set of process parameters is used, the width, height, and cross-section area of the two measured tracks match. Based on this verification, it is reasonable to assume that the analysis of geometrical inaccuracies performed via 3D scan can highlight differences in the builds due to the different kinematic configurations of the two machines. The substrate deformations during the builds were measured at predetermined time stamps. This analysis provides a history of the residual stress action on the substrate and improves the interpretation of the results of the 3D scans of the two components, which were only performed at the end of the depositions. Figure 12 clearly shows that residual stresses cause component distortion only up to a certain number of layers. The substrate does indeed deform only for the first few layers of the depositions, bending towards the center of the deposition, as expected [32]. The substrates are no longer deformed after approximately 34 layers. The substrate deformation, which is an index of the residual stresses induced by the process, is related to the process parameters chosen. Because the process parameters on both machines are the same, the deformation of the two substrates is expected to be similar. Figure 12 shows that the graphs of the substrate deformations during the two builds are highly overlapping, confirming the hypothesis. The 3D scans of the two deposited components were performed after the second deposition while the component was still attached to the substrate. This decision was made to make the measurements and their interpretation more understandable. Indeed, removing the substrate would result in a redistribution of residual stresses and a considerable change in the shape of the component.