In situ quality control of the selective laser melting process using a high-speed, real-time melt pool monitoring system

This paper discusses the principle and the relevance of an in situ monitoring system for selective laser melting (SLM). This system enables the operator to monitor the quality of the SLM job on-line and estimate the quality of the part accordingly. The monitoring system consists of two major developments in hardware and software. The first development, essential for a suitable monitoring system, is the design of a complete optical sensor set-up. This set-up is equipped with two commercially available optical sensors connected to a field-programmable gate array (FPGA) which communicates directly with the machine control unit. While the sensors ensure a high-quality measurement of the melt pool, the FPGA’s main task is to transfer the images from the sensors into relevant values at high sample rates (above 10 kHz). The second development is the data analysis system to translate and visualize measured sensor values in the format of interpretable process quality images. The visualization is mainly done by a “mapping algorithm,” which transfers the measurements from a time-domain into a position-domain representation. Further off-line experiments illustrate an excellent compatibility between the in situ monitoring and the actual quality of the products. The resulting images coming out of this model illustrate melt pool variations which can be linked to pores that are present in the parts.