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Design and implementation of a multi-sensor coaxial monitoring system with correction strategies for selective laser melting of a maraging steel

[+] Author and Article Information
Ali Gökhan Demir

Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156 Milan, Italy
aligokhan.demir@polimi.it

Chiara De Giorgi

Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156 Milan, Italy
chiara.degiorgi@polimi.it

Barbara Previtali

Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, 20156 Milan, Italy
barbara.previtali@polimi.it

1Corresponding author.

ASME doi:10.1115/1.4038568 History: Received February 23, 2017; Revised November 14, 2017

Abstract

Development of monitoring devices becomes crucially important in selective laser melting due to the high process complexity and the high value of the products obtained. This work discusses the design of a coaxial monitoring system for SLM using multiple sensors. In particular, an optical model is developed for the propagation of the process emission from the workpiece to the monitoring module. The model is used to determine the field of view around the monitored zone. The lens arrangements and the optical filters are chosen according to the model results. They were implemented to construct a monitoring module consisting of two CCD cameras viewing visible and near-infrared wavelength bands, as well as a photodiode viewing the back-reflected laser emission, all integrated in a coaxial configuration. The system functionality is tested with a prototype SLM machine during the processing of 18Ni300 maraging steel, a material known to be prone to porosity. In particular, different remelting strategies were employed as possible correction strategies to reduce porosity. The signals were interpreted as being indicators of the change in absorptivity of the laser light by the powder bed, of the plasma and molten pool, as well as of the evolution of the temperature field.

Copyright (c) 2017 by ASME
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