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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 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 10kHz). 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 offline 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.

S e le c tiv e L a s e r M e ltin g of C ra c k -F re e H ig h D e n s ity M 2 H igh S p e ed S te e l P arts by B a s e p la te P re h e a tin g Cracks and delamination, resulting from residual stresses, are a barrier in the world of additive manufacturing and selective laser melting (SIM) that prohibits the use of many metals in this field. By preheating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests were performed with M2 high speed steel (HSS). The influence of preheating on density and mechanical and physical properties is investigated. The paper shows many promising results for the production of SLM parts in materials that are very sensitive to crack formation and delamination. When using a preheating of 200 °C, crack-free M2 HSS parts were produced with a relative density of 99.8%.