Study On Temperature Control Of Laser 3D Deposition Process Based On PMAC

With the development of manufacturing industry, the proportion of strong laser process in manufacturing field is becoming heavier. Using closed-loop control for main processing parameters and improving the level of intelligent control are the important links for improving the quality and stability of laser process and promoting the industrialization of this technology.The purpose of this study was to implement the temperature closed-loop control in high-power laser 3D deposition process by improving the control mode of laser power and powder feeding.In this paper, the present situation of closed-loop control technology on laser processing was summarized, especially the temperature control technology. Two feasible schemes were proposed based on the analysis of the power control method of laser 3D deposition system. By comparing different schemes, the scheme with two computes, a master and a slave one, based on infrared temperature measurement technique was adopted. As master computer, IPC achieved control algorithm and sent control instructions, SCM as slave computer received instructions form IPC and controlled power, infrared thermoscope accomplished temperature sampling as control variable detecting device, each unit communicated with RS232. The adopted scheme took full advantage of the IPC powerful processing and computational capabilities and realized the advantage of programming easily, which implemented the integrating temperature control by IPC.Laser direct metal rapid prototyping process is a complex physical metallurgy process with the result of multi-parameter effects. The paper accomplished the temperature sampling of molten pool by a 2-color infrared thermoscope and overcame the difficulties of powder sputtering, plasma cloud and smoke transpiration above the measure point during laser molten pool online dynamic testing, that temperature measurement devices generally difficult to accurately measure. Experiments showed that the measurement scheme was accurate and reliable. The original system adjusts the weak current by a mechanical potentiometer, and the weak current signal after being amplified is used to control excitation current of resonant cavity, and finally implements the power control. On the basis of this control mode, another digital potentiometer circuit for weak current adjusting was designed and a switch circuit was designed to shift form one mode to the other. Handshake protocol was designed in serial communication process between master computer and slaver computer, and enhanced the anti-jamming capability and stability of the system. The results of experiments indicated that the temperature control algorithm by comparing the average temperature values with desired input temperature values was simple and effective.The corresponding relationships among the resistance value of digital potentiometer, laser power and discharge current was measured in the experiments. The results of experiments indicated that the laser process had a stable temperature, the shape quality and the geometrical accuracy by using temperature control was better than that of no use of temperature control, the melt paths were more flat, and microstructure was more uniform.