Molten pool temperature monitoring in laser metal deposition: Comparison between single wavelength and ratio pyrometry techniques

Realising complex components in laser metal deposition (LMD) without process control can lead to heat accumulation due to varying heat dissipation capacities of the geometric features. Monitoring the temperature of the molten pool is crucial, and infrared pyrometry is a commonly employed technique. This study explores temperature monitoring using a coaxial pyrometer operating in two modes: single wavelength and ratio modes. The single wavelength pyrometer measures the target temperature through optical emission but requires knowledge of target emissivity. In contrast, the ratio pyrometer is more adaptable in LMD as it does not depend on emissivity information, but it can be affected by background interferences. Single wavelength and ratio pyrometry monitoring of the molten pool was tested in two deposition conditions, using either a small or a large laser spot, highlighting the importance of collecting the single wavelength temperature.