Objective In the process of laser solid-state phase transformation, the temperature has a significant impact on the performance of the workpiece, and the accuracy and responsiveness of temperature control are the key factors to ensure the quality of workpiece hardening. During this process, multiple variables, such as laser output power, scanning speed, and spot size, affect the temperature within the laser-affected zone of the workpiece. In addition, material attributes like composition, geometry and surface roughness also affect the temperature of laser solid-state phase transformation, and the surface temperature of the material is also affected by environmental condition and unpredictable elements like heat dissipation. Critical to the process is maintaining the temperature of the material above its austenitizing temperature and below the melting point. Insufficient temperature will inhibit the phase transformation, while excessive heat induces surface melting. And a stable temperature will contribute to the formation of a uniform phase transformation hardened layer. Thus, in order to improve the quality of solid-state laser phase transformation, developing a real-time temperature controller is necessary.

Methods A fuzzy adaptive parallel PID control method based on thermal imaging temperature measurement technology was proposed. It integrates surface sensor technology to capture temperature information across the camera's visual spectrum, and an additional fuzzy control module is introduced on top of the fuzzy PID control. This design empowers the system to evaluate temperature discrepancies across diverse points within the laser's action zone. These differential values are subsequently funneled into a fuzzy logic system, which operates concurrently with the fuzzy PID controller to jointly adjust the laser output power. This dual-control mechanism ensures rapid and meticulous temperature regulation, thereby improving control and an enhancing quality of intensification.

Results and Discussions The simulation and experimental validations of the system were conducted utilizing MATLAB/Simulink software and a laser solid-state phase transformation temperature control platform, respectively. The simulation results indicated that the performance of the FAP-PID controller was significantly improved: the rise time was shortened by 14.63%, the settling time was diminished by 28.13%, and the average steady state error was reduced by 74.92% compared with traditional PID ones. In contrast to the fuzzy PID control algorithm, the FAP-PID control algorithm further reduced the rise time by 10.26%, settling time by 16.36%, and trims down the average steady-state error by 64.29%. The experimental results also showed that the FAP-PID control algorithm reduced the rise time by 24.24%, the settling time by 34.0% and the average steady state error by 56.68% compared to the PID control algorithm. Versus fuzzy PID control algorithm, it showed a reduction of 15.38% in the settling time and 56.06% in the average steady state error. In summary, these metrics substantiated that the FAP-PID control algorithm had a faster response speed and a smaller average steady state error, showing superior control performance.

Conclusions Aiming at refining the laser solid-state phase change temperature control problem, a fuzzy adaptive parallel PID control algorithm based on thermal imaging was proposed. Through data analysis and application of the step response method, the transfer function model of the laser solid-state phase transformation system was determined. The model accurately described the dynamic characteristics of the system providing a reliable basis for controller design. Subsequently both a traditional PID controller and a fuzzy PID controller were designed, monitoring the laser solid-state phase transformation process through the thermal imaging technique, and then an FAP-PID controller was designed by incorporating fuzzy control. The simulation and experimental results affirmed the superiority of FAP-PID controller, including shortened rise time, reduced settling time, and decreased average steady-state errors. The FAP-PID control algorithm exhibited favorable performance in terms of response speed and stability, thereby substantiating its potential for extensive applications of temperature control in process of laser solid-state phase transformation.