The Application Using Optical Fiber To Monitoring The Temperature And Strain In Welding Process

In order to realize the real-time monitoring of temperature and strain during thelaser and ultrasonic welding based on the Fiber Bragg grating (FBG), the processparameters of metallization for FBG, ultrasonic and laser welding, and the real-timemonitoring for welding process based on FBG were investigated.The metallization for FBG was realized by electroless cobalt plating andelectroplating nickel. The process parameters optimization of electroless cobaltplating was achieved by adjusting the content of NaOH in the electroless platingsolution. Results show:(i) Under the optimal conditions, the compact and soundbonding between coating surface and FBG can be obtained.(iii) The temperaturesensitivity of FBG is12.21pm/℃when the coating thickness is5.0μm. In order tobetter metallize for FBG, the electroplating nickel was applied after the electrolesscobalt plating. The temperature sensitivity coefficient of FBG with the coat thicknessof280μm was19.58pm/℃after the electroplating nickel, and the performancetesting experiment of the metallized FBG during the effective temperature range wascarried out. The results showed that the metallized FBG worked well under the hightemperature environment of670℃, and the wavelength and temperature exhibited agood linear correlation.The process parameters of ultrasonic welding for1060aluminum/N4nickeldissimilar metals was studied by the varation of single factor method, and the modelfor weld width and penetration of laser welding for316L stainless steel wasestablished by the secondary general spiral regression equation model. The studyshowed that there was no reaction layer but some4μm diffusion layer in ultrasonicwelding interface. Meantime, the welding joint fracture of the tensile test presented aductile fracture. For the laser welding of316L stainless steel, the regression equationof weld width and penetration extremely significant and the confidence were above99%. The model was applied to predict the weld width and penetration underdifferent welding parameters, and the maximal error was12.2%.For the real-time monitoring of temperature and strain for HAZ of laser welding process for Q235steel and weld zone of ultrasonic welding for1060aluminum bymetallized FBG, the temperature and strain sensitivity coefficients of the metallizedFBGs were calibrated by using the temperature controller and strain gauge,respectively. The calibrated FBGs were applied for the real-time monitoring of thewelding process. The results of real-time monitoring showed that:(i) for the laserwelding process, the maximal temperature and strain with the distance to the weldseaming of5mm and10mm were100.01℃,326.3με and62.32℃,139.8με,respectively, which the maximal difference between the measured values ofthermocouple and strain gauge was only4.1%and14.8%, respectively;(ii) for theultrasonic welding process, two measured temperature and strain values at the weldseaming were52.31℃,267.64με and49.00℃,325.44με, which the maximaldifference between the measured value of thermocouple was15.5%. After comparingthe real-time monitoring values of metallized FBG with the measured values ofthermocouple and strain gauge, the results showed a quite accuracy and exhibited ahigh repeatability, which indicated that the metallized FBG could be applied toreal-time monitor for the laser and ultrasonic welding.