Process observation in fiber laser–based selective laser melting

Abstract

Abstract. The process observation in selective laser melting (SLM) focuses on observing the interaction point where the powder is processed. To provide process relevant information, signals have to be acquired that are resolved in both time and space. Especially in high-power SLM, where more than 1 kW of laser power is used, processing speeds of several meters per second are required for a high-quality processing results. Therefore, an implementation of a suitable process observation system has to acquire a large amount of spatially resolved data at low sampling speeds or it has to restrict the acquisition to a predefined area at a high sampling speed. In any case, it is vitally important to synchronously record the laser beam position and the acquired signal. This is a prerequisite that allows the recorded data become information. Today, most SLM systems employ f -theta lenses to focus the processing laser beam onto the powder bed. This report describes the drawbacks that result for process observation and suggests a variable retro-focus system which solves these issues. The beam quality of fiber lasers delivers the processing laser beam to the powder bed at relevant focus diameters, which is a key prerequisite for this solution to be viable. The optical train we present here couples the processing laser beam and the process observation coaxially, ensuring consistent alignment of interaction zone and observed area. With respect to signal processing, we have developed a solution that synchronously acquires signals from a pyrometer and the position of the laser beam by sampling the data with a field programmable gate array. The relevance of the acquired signals has been validated by the scanning of a sample filament. Experiments with grooved samples show a correlation between different powder thicknesses and the acquired signals at relevant processing parameters. This basic work takes a first step toward self-optimization of the manufacturing process in SLM. It enables the addition of cognitive functions to the manufacturing system to the extent that the system could track its own process. The results are based on analyzing and redesigning the optical train, in combination with a real-time signal acquisition system which provides a solution to certain technological barriers. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Process defects andin situmonitoring methods in metal powder bed fusion: a review

“…In addition, the scanning speed in EBM is higher than in SLM, which makes the continuous monitoring of the melt pool and the heat affected zone during the process more challenging. Clijsters et al, 2014;Craeghs et al, 2010Craeghs et al, -2011Craeghs et al, 2010Craeghs et al, -2012Clijsters et al, 2014;Berumen et al, 2010;Van Gestel, 2015Shape Craeghs et al, 2011Berumen et al, 2010;Van Gestel, 2015;Doubenskaia et al, 2015 Temperature intensity Craeghs et al, 2011;Berumen et al, 2010;Chivel, 2013;Clijsters et al, 2014;Doubenskaia et al, 2012;Pavlov et al, 2010;Thombansen et al, 2015;Berumen et al, 2010;Van Gestel, 2015;Yadroitsev et al, 2014;Chivel, 2013; Temperature profile Doubenskaia et al, 2012;Gong et al, 2013b;Price et al, 2012 Track (scan path)…”

“…Track geometry Doubenskaia et al, 2015Kanko et al, 2016 Temperature/ intensity profile Bayle and Doubenskaia, 2008;Thombansen et al, 2015 Grasso et al, 2016 3.2. In-situ sensing equipment and set-ups The mainstream sensors and in-situ data collection devices proposed in the literature can be grouped into the following major categories: i) non-contact temperature measurements (i.e., pyrometers and infrared (IR) imaging), ii) imaging in the visible range, iii) low-coherence interferometric imaging.…”

Contributions for the next generation of 3D metal printing machines

“…To contribute to process monitoring, a sensor system based on a pyrometer was developed to spatially observe the course of the melting temperature during the SLM process in order to assess the current layer, adapting the processing strategy for subsequent layers, configuring a self-optimizing strategy for SLM process [9]. Figure 3 shows the schematic design.…”

“…Figure 3 shows the schematic design. Monitoring system for SLM process using pyrometer detection [9].…”

In situ morphology-based defect detection of selective laser melting through inline coherent imaging

“…Additional contributions to the development of SLM optical monitoring technology have also been realized through improvements in imaging capabilities, such as those made by Thombansen et al (2014) who have developed a retro-focus pyrometer-based system aimed at overcoming imaging limitations associated with coaxial monitoring through -theta scanners.…”