On-line Temperature Measurement of Laser Welding with Magnetic Nanoparticles

The magnetization of magnetic nanoparticles (MNPs) is temperature-sensitive, which makes the magnetic field around them to changing with temperature. The temperature of the MNPs can be obtained by measuring the intensity of the magnetic field. This paper proposes an on-line temperature measurement method of laser welding with magnetic nanoparticles, which shows potentials for on-line monitoring of welding quality, and thus provides a new way for the automation of welding process. Based on the Langevin theorem and Bloch Law, a relationship equation is established between the temperature and magnetization of MNPs excited by DC magnetic field. The magnetization of the MNPs is first detected by a coil, and then the temperature is calculated. A thermal insulation device is designed to prevent the heat radiation generated during the welding process from affecting the accuracy of the temperature measurement. The results of laser welding experiments show that the temperature measurement signals of MNPs correlate well with those of thermocouple, indicating the feasibility of using MNPs for on-line temperature measurement during laser welding.