African Fusion July-August 2024

Portevin Lecture at IIW 2023 in Singapore

This paper, delivered by Tomoyuki Ueyama of OTC in Japan as the Portevin Lecture at IIW 2023 in Singapore, reviews technology targeting carbon neutrality, including: a low heat input and low spatter GMAW process; a laser-arc hybrid process; high-current buried-arc GMAW; and cold spot joining. An overview of the state-of-the-art development of welding and joining technology

S oon after World War II, Japan’s welding technology was said to be more than 30 years behind that of Europe and the United States. However, as a result of the efforts of welding researchers and engineers in Japan, the country became a world leader in welding technology in the 1970s and 1980s, following rapid economic growth. In addition, progress was made in developing power electronics and microprocessors in the arc welding field. As a result, welding processes and their systems were developed to improve welding productivity and quality, including heat input control and spatter reduction [1, 2] . Technological development in the welding and joining fields is being undertaken underpinned by carbon neutrality, a global social issue, along with eliminating labour shortages due to the declining birthrates and aging populations. With this perspective, this paper introduces the status of welding and joining technology development in Japan from a process perspective. Gas metal arc welding processes Spatter Reduction The leading cause of spatter generated during GMA welding is

the expulsion of molten droplets from the molten pool and wire tip. This occurs when the welding arc re-ignites arcs after a high short-circuit current is energized during short-circuit conditions. Therefore, to avoid this phenomenon, current waveform con trol [3] and wire feed/current waveform synchronisation control [4] have been developed to suppress the expulsion phenomenon by rapidly reducing the short-circuit current just before re-arcing from a short circuit occurs, thereby suppressing spatter generation – as shown in Figures 1 and 2. However, although these processes were effective in reducing spatter at welding currents in the short-circuit transfer region of 180 A or less, they were less effective in reducing spatter at weld ing currents in the globule transfer region exceeding 180 A (200 to 300 A), which is applied for welded structures of medium and thick steel plates. As shown in Figure 3, by superimposing a triangular wave in the initial stage of arc re-ignition after a short circuit, the wire fed at high speed can be efficiently melted with a high peak current, and the repelled force can be effectively reduced with a low peak

Figure 1: Controlled Bridge Transfer (CBT) Process.

Figure 3: CBT-Expanded process.

Figure 4: New current waveform suppress repelled transfer and instantaneous short-circuiting.

Figure 2: Schematic of wire feed control with arc phenomena.

12

July-August 2024

AFRICAN FUSION