Temperature Monitoring in Selective Laser Melting of Inconel 625

Abstract

The objective of this research was to develop a system to effectively monitor temperature in the selective laser melting of Inconel 625. This study established a monitoring system that collects temperature data and describes its relationship with process parameters, develops a control simulation based on the obtained results and determines how to change input parameters in situ. Such research was driven by the unreliability of additively manufactured components, which often contain internal voids and cracks as well as display poor surface finish. With the need for improved part quality, a temperature monitoring system, a promising method of solving several quality issues, proves necessary. This monitoring system was developed using a pyrometer and a thermal imager mounted on a powder bed metal printer to record the peak temperature of the melt pool. Experiments found that both laser power and scan speed affect the peak melt pool temperature of Inconel 625: as the peak melt pool increases as power increases and as scan speed decreases. A subset of experiments run with a thermal camera further revealed that there is no discernible temperature trend across the laser track, meaning that there was no significant difference in temperature at the start, middle or end of the track. The thermal camera also revealed that temperature across the melt pool resembled a second order response to laser input. Furthermore, according to preliminary offline measurements taken of the primary dendrite arm spacing (PDAS) of Inconel 625 coupons, PDAS increases with peak temperature. In addition to implementing and testing the monitoring system, this research created and simulated a first order model of the system using a discreet proportional integral derivative controller. Lastly, two separate methods were found to interface a controller with the Omnisint 160 in order to change the laser power based on the temperature feedback