Improving build quality in Directed Energy Deposition by cross-hatching

It is common practice to rotate the deposition hatch pattern by a fixed angle between deposited layers during Directed Energy Deposition (DED) additive manufacturing based on qualitative evidence presented by M. T. Ensz et al. (1998) and by K. Guan et al. (2013) that indicates hatch pattern rotation promotes microstructure and property homogeneity and mitigates lack of fusion (LoF) defect development. To quantitatively verify the role of hatch rotation angle in as-deposited materials, hatch rotation angles of 0°, 90° and 105° were applied during DED fabrication of several 316L grade austenitic stainless-steel structures. Lack of fusion defects were not detected for any hatch rotation angle; however, cross-hatching (90° or 105° hatch rotation angle) produced builds of higher strength and greater density. Parallel-hatching (0° hatch rotation angle) resulted in stronger crystallographic texture, longer grains, and lower strength than cross-hatching. No significant differences in terms of microstructure or properties were observed between the 90° and 105° hatch rotation angle builds. These results are supported by computational analysis and show that cross-hatching improves the quality of DED builds.