# Dimensional Errors Due to Overhanging Features in Laser Powder Bed Fusion Parts Made of Ti-6 Al-4V
## 4 Conclusions  
This paper has presented the first results of a statistical analysis of the dimensional error in L-PBF parts. The process parameters under investigation were the laser power, scan speed, scan spacing, scan strategy, and the layer thickness. An image processing technique was developed to measure the thickness of printed samples. A statistical study was conducted and a quadratic regression equation was developed. The interaction effects of the process parameters were plotted and clear trends can be seen in their effects on the dimensional error, which have been summarized. The ANOVA analysis showed that the laser power was the most significant process parameter in terms of the dimensional error, which is in accordance with previous research and results. In terms of the significance, the laser power was the most significant, followed by the layer thickness, scan speed, and the interaction effect of the laser power and scan speed. In the context of an optimization problem, it is also important to realize the process parameters that are insignificant for the purposes of parameter optimization within the down-facing area of an L-PBF printed part, namely the scanning pattern. In particular, the effects of the three different scanning strategies were similar and almost identical at certain points. The ANOVA analysis explained this, as the expected significance of the scanning pattern was inherently low. Therefore, any variation in the scanning pattern is only going to have a minimal effect on the overall dimensional error % of the test piece. This study establishes a starting point which can encourage further work in the area of the process modeling of the L-PBF process and characterization of dorsal formation in unsupported down-facing surfaces. The main inferences can be summarized as follows:  
* At this stage, the experimental trial conducted under the parameters of laser power of 90 w, scan speed of 1235, and scan spacing of 60 \(\upmu\)m; laser power of 90 w, scan speed of 1235, and scan spacing of 90 \(\upmu\)m; and laser power of 150 w, scan speed of 1599, and scan spacing of 75 \(\upmu\)m, gave the lowest dimensional error percentages;
* The regression equation establishes a first step and when tested with new prints, gives promising results, and validation through further data collection is required in order to improve the prediction;
* The effect of different scanning patterns within down-facing areas is negligible and any one can be chosen based on the designers' preference;
* This model must also consider other quality aspects of down-facing surfaces, such as the surface topography and curvature in the surface, and is the focus of parallel current work. In this work, the bulk area was first printed and the down-facing area (with down-facing parameters) was then printed. There is room for incorporation of the gradual changing of process parameters between bulk and down-facing areas such that they are scanned simultaneously. The current work can act as a starting point for such research;
* The data-driven process analysis methodology has shown potential to provide acceptable predictions of the dimensional performance of the L-PBF process and further work will be done to characterize dorsal formation in an effective and productive manner. The authors conclude on a positive note given the promising result obtained by modeling the L-PBF process, as this is often plagued by a low process repeatability, especially within the down-facing area, where the complex dorsal formation phenomenon further decreases the process's stability. Although understanding the effect of individual process parameters will help to improve the overall process knowledge, using the individual process parameters as such for drawing inferences can be difficult. Therefore, it is the opinion of the authors that all proceeding work must consider the inclusion of combined process parameters for characterizing the process. This includes the use of parameters such as the line energy density and popular volumetric energy density.