Material extrusion (MEX) is widely used in additive manufacturing due to its simplicity and compatibility with various thermoplastics. While adhesive coating is commonly applied to enhance the watertightness of MEX-fabricated (MEXed) structures, its impact on mechanical properties remains unclear. This study investigated the effect of cyanoacrylate adhesive dip coating on the mechanical behavior of MEXed polylactic acid (PLA) specimens. Tensile specimens were fabricated in both longitudinal and transverse orientations and coated with two commercial cyanoacrylate adhesives, Loctite 401 and Alaska 4001. The coating process was repeated 2, 4, and 6 times, followed by cross-sectional observations and tensile testing. The results indicated that the cross-sectional area increased with an increasing number of coating repetitions, regardless of adhesive type or infill pattern. Tensile strength generally decreased after coating, with reductions of 10.6–14.7% after six coating cycles. In contrast, the elongation at break increased after coating treatment. For Loctite 401, the maximum increases were approximately 35.1% and 124.1% for the longitudinal and transverse specimens, respectively, while Alaska 4001 resulted in maximum increases of approximately 29.7% and 48.3%, respectively. These findings suggest that adhesive dip coating significantly alters the mechanical behavior of MEXed PLA structures and requires optimization to balance strength and ductility.

A hybrid cladding technology was developed by combining direct energy deposition (DED) and ultrasonic nanocrystal surface modification (UNSM). This is an effective process to control the mechanical properties inside the metal-clad layer, but the scope to improve the internal properties is low. Therefore, in this study, the UNSM process was applied while heating at 300 and 600℃ to increase the effectiveness of this hybrid additive process. To validate the characteristics of this method, a study on the cross-sectional properties upon application of heating was conducted. Hybrid cladding at 300 degrees produced improvements- over a 40% larger area than the results at room temperature. At 600 degrees, the hybrid cladding improved mechanical properties over a larger area by nearly 2 times. In this study, the characteristics of the roomtemperature and the high-temperature hybrid cladding process were analyzed. The proposed method shows a high improvement effect and is a promising method to improve the internal mechanical properties of the cladded layer.