Evaluation of Process Parameters Modifications on Directed Energy Deposition Manufactured Parts Obtained in a Hybrid Additive Manufacturing Machine

Abstract

In order to combine advantages of both additive and subtractive manufacturing, hybrid machine tools have been developed. In the hybrid process, directed energy deposition (DED) is the most used additive manufacturing technology due to its adaptability to CNC milling centers. However, in order to assure the integrity of a printed part, several process parameters must be set appropriately. Not only there are several parameters, but also some of these parameters influence different variables — e.g.: scan speed influences both the energy input per unit area and the powder volume that is deposited. In addition, another fact that complicates the achievement of a good quality in a workpiece is that some relevant parameters for additive manufacturing cannot be controlled due to CNC milling center constraints (e.g.: atmosphere). In this work, laser power (280 to 340 W) and scan speed (5 to 7 mm/s) were systematically varied to print 316L test samples with the aim of building a quality matrix. In the future, this matrix will be used to create strategies to optimize the quality of printed parts. Optical stereoscopy shows that the higher the laser power, the higher the sample, indicating that more powder is melted and deposited with an increasing laser power. By fixing the laser power and increasing the scan speed, printed samples were lower, indicating that less powder was deposited. Other parameters were preliminarily tested — e.g.: sample size and shield gas flow. Decreasing the sample size from 9 to 6 mm was sufficient to double the sample height, showing that the heat transfer rate was dramatically changed. Findings of this study shows that all process parameters act together and are determining factors for a good quality printed part. Moreover, it was noted that sample integrity is very sensitive to minimal changes in some process parameters.