Arc Formation in Narrow Gap Hot Wire Laser Welding

Many heavy industrial applications, e.g. shipbuilding and offshore, rely on thick-section, high-quality welds. Unfortunately, traditional arc-based techniques are often found wanting due to a limited penetration depth and excessive heat-affected zone. The former is typically solved by having a wide groove filled by multiple weld passes, which is both costly and time consuming. Other processes such as autonomous laser or electron beams can join thick materials, but have disadvantages such as increased hardness and solidification cracks inside the welds. A promising in-between technique to join thick sheets is narrow gap multi layer laser welding (NGMLW), using less filler material while also offering more control of weld properties. This technique is often used with laser scanning optics and cold wire, or a defocused laser and electrically heated wire. This paper investigates the limitations of the latter during NGMLW, mainly using high-speed imaging to directly observe and explain process behavior. Increased deposition rates are wanted, but heating also consequently needs to be increased for proper bead fusion. Arc occurrences are found to be the cause of instabilities. They are observed occasionally even at low voltages, but more frequently at higher outputs, and then are also more disruptive to the process.