Process Monitoring of Additive Manufacturing by Using Optical Tomography

Abstract

Selective Laser Melting (SLM) is a 3D-printing-process which provides the possibility to construct complex geometries by layered manufacturing of components with metallic powder. At MTU Aero Engines the optical tomography (OT) was developed as an Online Process Monitoring system which documents the complete welding process during the SLM fabrication procedure. Some details of the camera-system are shown. To create probability of detection (POD) curves, different specimens are investigated with digital radiography. To detect the small lack of fusion defects the specimens were plastified in order to increase the volume of the defects. Results of plastified specimens are presented.

Predicting laser powder bed fusion defects through in-process monitoring data and machine learning

“…; EOSTATE PowderBed records image of powder bed after re-coating and after exposure; EOSTATE MeltPool sampled melt emission at 400-900 nm; EOSTATE Exposure OT integrated melt emission at 900 nm. The principles of OT technique are simple [18][19][20]: an optical sCMOS (scientific complementary metaloxide semiconductor) camera with high lateral resolution is exploited to captures thermal radiation signal of the top layer during the laser PBF melting and solidification process. A near infrared band-pass filter (narrow band with center 900 nm and half width 25 nm) is used to separates thermal radiation from the other emissions e.g., plasma emissions and back reflected laser light (1060 nm).…”

“…Different sensors, e.g., acoustic sensors [8,9], high resolution optical camera [10][11][12], high speed camera [13], infrared thermography [14][15][16], infrared (IR) camera [17], optical tomography [18][19][20][21], synchrotron X-ray [22,23], etc., can be applied for the monitoring of the L-PBF process. These sensors reveal diverse phenomena of the powder bed and melt pool: e.g., powder bed surface topography (before and after exposure), spattering, balling, pore formation, cracking, and deformation.…”

Metal Laser-Based Powder Bed Fusion Process Development Using Optical Tomography

“…Optical Tomography in AM was originally developed for quality assurance, in which validation of the print result is performed through the thermal history monitoring of consecutive builds [30]. The first build is quality-controlled, and after this, the identical thermal history of subsequent builds can be declared successful.…”

In-Situ Defect Detection in Laser Powder Bed Fusion by Using Thermography and Optical Tomography—Comparison to Computed Tomography

“…Zenzinger et al [26] were able to capture the thermal emissions of the melting process by using a CMOS camera equipped with a suitable band pass filter. Deviations in the signals derived from optical tomography (OT) were attributed to welding disturbances, which were correlated to micro computed tomography (µCT) data in [30] and data from digital radiography [31]. They achieved a pixel size of approximately 0.1 mm × 0.1 mm.…”

“…They achieved a pixel size of approximately 0.1 mm × 0.1 mm. However, a detailed high-resolution signal to defect correlation is not yet possible [31]. Due to their longtime exposure concept, their system differs from infrared camera systems with high temporal dynamics.…”