Assembly of an Additive Manufactured GRCop-84 Copper Alloy Lower Hybrid Current Drive Launcher Antenna With Pulsed 1070-nm Fiber Laser Welding

Laser powder bed fusion (L-PBF) enabled additive manufacture (AM) of lower hybrid current drive launcher components from Glenn Research Copper 84 (GRCop-84), a Cr2Nb precipitation hardened alloy with high tensile strength and conductivity. Build volume limitations require AM of modular segments that are joined together with laser welding. A fixturing system was developed to align and compress 0.5-mm thick butt weld joints, shield internal surfaces with argon gas, and prevent distortion during assembly. An external fixture and clamping plate align launcher sections while providing beam access for a pulsed 1070-nm fiber laser, while an internal microjack expands within the waveguide segments eliminating height offset between joining sections and distributing argon shield gas. Conduction mode welding prevents keyhole formation and beam penetration into the waveguide interior, eliminating spatter and producing a smooth bottom weld bead. Surface roughness of $R_{a} $ = $2.34 ~\mu \text{m}$ on the top surfaces and $R_{a} $ = $3.17 ~\mu \text{m}$ on the bottom surfaces are achieved. The mean ultimate tensile strength (UTS) of welds was 476 MPa, similar to the 520-MPa UTS following a 900 °C 5-h heat treatment.