Optimizing interlayer cooling for SUS316L thin wall fabricated by directed energy deposition

Abstract

The direct energy deposition (DED) process requires proper interlayer cooling (IC) to avoid geometric failure caused by overheating of the midsection. This study suggests an optimum IC step based on a constitutive equation, instead of trial and error, to ensure the geometric stability of DED-processed 316 L stainless steel within a short period. The temperatures after cooling (TC) were acquired per layer of building and precisely measured using a constitutive model. Subsequently, a cooling period to maintain a target TC was calculated for the 30-layered DED specimen using the model. The optimum IC step varied with the number of deposited layers: (i) non-IC up to the fourth layer, (ii) IC step of 1.05 s for the fifth layer, and (iii) IC step of 2.21 s for the subsequent layers. The developed approach resulted in a remarkable improvement in geometric stability (geometric error of 5.9%) compared with the DED specimen fabricated without an IC step (error of 33.5%). Furthermore, the processing time was reduced by 30% compared with a conventional IC step with a fixed interval of 5 s. The developed approach also led to homogeneous grain refinement and a resulting increase in microhardness.

Keywords

• Directed energy deposition
• Interlayer cooling
• Constitutive equation
• Stainless steel
• Geometric stability
• Microstructure