A dimensionless analysis to select directed energy deposition process parameters for proper clad formation

The growing interest in the directed energy deposition process to fabricate and repair thin wall structures has warranted a deeper understanding in the properties of the method's basic building block: clad formation. In this study, clads obtained by depositing stainless steel 316L (SS316L) powder with three different process parameters, namely laser power, laser traverse speed, and powder mass flow rate, were investigated. Repeatability was ensured through a wide sample range per parameter. From the data measurement, the clads have an average hardness close to the typical 200 Hv of SS316L materials, indicating that Hall-Petch effect is dominant. The study also shows that: (i) Laser power is the most significant factor to clad depth, but has little influence on clad thickness. (ii) Laser traverse speed is the dominant parameter to clad height. (iii) Powder mass flow rate tends to compensate depth reduction with thickness gain, resulting in no noticeable effect on clad height. Increasing laser power was observed to be the most effective way to prevent clads from forming with zero dilution, an indicator to how well the printed clad is bonded to the substrate. A dimensionless analysis was derived from the set of SS316L clads. Through validation with different stainless steel datasets and extrapolation to a larger parametric range, the analysis was demonstrated to be able to facilitate the selection of process parameters to meet given requirements on the clad dimensions. As its application is intuitive, the analysis has the potential to be adopted as a standard preprinting tool that will increase success rate, thus improving the manufacturing turnaround time.

Automated summary

The study focuses on understanding the properties of clad formation in the directed energy deposition process for fabricating and repairing thin wall structures using stainless steel 316L powder. The parameters of laser power, laser traverse speed, and powder mass flow rate were investigated, and the clads obtained showed an average hardness close to SS316L materials. It was found that laser power is the most significant factor for clad depth, while laser traverse speed is dominant for clad height. The study also introduced a dimensionless analysis that can facilitate parameter selection for desired clad dimensions, potentially improving manufacturing turnaround time.