Directed energy deposition-arc of aluminum-alloy curved-generatrix-shell pyramid lattice structure

Abstract

The curved-generatrix-shell pyramid lattice structure (CPLS) is an important thermal insulation and load-bearing component of hypersonic vehicles (Mach>5). Directed energy deposition-arc (DED-Arc) is an effective method for fabricating CPLSs. In this study, the characteristics of a CPLS and the unit cells of the CPLS were analyzed in detail. The CPLS consisted of row-lattice unit cells along the axis of the curved-generatrix shell and column-lattice unit cells along the circumference. The strut inclination angles and strut lengths of different rows of each unit cell were different, in contrast to the previously reported planar unit cells. Based on the characteristics of the CPLS and unit cell, the curved-generatrix shell surface slicing method was used to obtain high-accuracy curved-generatrix-surface unit-cell deposition path points, and the initial position correction, variable process parameter values, and secondary deposition were used to control the droplet deposition amount to achieve the same layer height compensation. This ensured high-precision forming of the lattice struts. In this study, the fabrication of a CPLS was the ultimate goal. Thus, an eight-axis collaborative DED-Arc system composed of a six-axis robot and a two-axis positioner was adopted. The flip and rotation angles of the positioner were regulated so that the deposition plane of the formed struts was always horizontal, avoiding the flow of liquid metal in the molten pool. Finally, a large-size aluminum-alloy CPLS consisting of 23 rows of unit cells and 33 columns of unit cells was successfully fabricated using DED-Arc on the aluminum-alloy curved-generatrix shell. The maximum error of the lattice strut forming angle was within ±0.4°, and the maximum error of the forming strut length was within ±0.26 mm.