African Fusion July-August 2024

Portevin Lecture at IIW 2023 in Singapore

period in the 10s of millisecond range to stop the arc, so that a hemispherical joint shape in which the ends of the flat copper wires are always symmetrical can be obtained – as shown in Figure 11.

adjusts the pulse peak time so that the short-circuit occurs during the base period [9] . Figure 8 verifies the suppression of spatter and undercut during high-speed welding. In the first half of the bead, the set voltage is high relative to the welding speed, and although there is no spatter, undercuts occur. In the central part, the set voltage was lowered to suppress undercut, resulting in a short arc length, which caused short circuiting and spatter generation. In the latter part, spatter generation is suppressed while maintaining a short arc length by automatically adjusting the pulse peak time, and there is no undercut.

Figure 10: One cycle of rectangular copper wire melting with the PJT welding process.

Figure 8: Effect of self-adjustment pulsed GMAW on undercut and spatter generation. The Plasma Jet TIG welding process Segment conductor (SC) distributed winding stators are used in motors for driving EVs [10] . Loss reduction due to stator winding resistance is also necessary and is one of the quality targets re quired for the welding and joining the flat copper wire that makes up the stator coil. TIG and laser welding are the main joining processes for welding flat copper wire. In TIG welding, as shown in Figure 9, an inner gas of the same or different type as the shielding gas flows through an inner gas nozzle installed around the electrode, causing the arc to constrict and a pulse current output of several hundred Hz ensures arc stiffness. This welding method (Plasma Jet TIG or PJT) [11] , has been devel oped and applied as a superior process to laser welding in terms of production efficiency, weld quality, and equipment installation cost using multiple welding systems.

Figure 11: Joining results of rectangular copper wire with the PJT welding process. The Laser Arc Hybrid welding process Laser-arc hybrid welding is being researched and developed to overcome the disadvantages of arc welding and laser welding: by utilizing the advantages features of each process [12, 13] . An example of a welding robot used for laser-arc hybrid weld-

Figure 9: Plasma Jet TIG (PJT) welding.

Figure 10 shows the melting phenomenon of a flat copper wire using a constricted pulsed arc and the current waveform control sequence. The PJT arc has more stiffness and is more directional than the conventional TIG arc, and the plasma-like arc instantly melts and integrates the two flat copper wire ends to form a sym metrical molten hemisphere. This phase is followed by a downslope

Figure 12: Laser-arc hybrid robotic system.

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July-August 2024

AFRICAN FUSION