In-situ measurement and monitoring methods for metal powder bed fusion: an updated review

Abstract

The possibility of using a variety of sensor signals acquired during metal powder bed fusion processes, to support part and process qualification and for the early detection of anomalies and defects, has been continuously attracting an increasing interest. The number of research studies in this field has been characterised by significant growth in the last few years, with several advances and new solutions compared with first seminal works. Moreover, industrial powder bed fusion systems are increasingly equipped with sensors and toolkits for data collection, visualisation and, in some cases, embedded in-process analysis. Many new methods have been proposed and defect detection capabilities have been demonstrated. Nevertheless, several challenges and open issues still need to be tackled to bridge the gap between methods proposed in the literature and actual industrial implementation. This paper presents an updated review of the literature on in-situ sensing, measurement and monitoring for metal powder bed fusion processes, with a classification of methods and a comparison of enabled performances. The study summarises the types and sizes of defects that are practically detectable while the part is being produced and the research areas where additional technological advances are currently needed.

Perspective Chapter: Direct Energy Deposition of Cu-Fe System Functionally Graded Materials – Miscibility Aspects, Cracking Sources, and Methods of Assisted Manufacturing

“…Metal laser additive manufacturing (AM) includes a complex of precise rapid fabrication methods (selective laser sintering -SLS, also known as Direct Metal Laser Sintering™ -DMLS; selective laser melting -SLM, also known as laser powder bed fusion -LPBF, and LaserCUSING™; direct energy deposition -DED, also known as laser directed energy deposition -LDED; laser metal deposition -LMD, direct metal deposition -DMD, Laser Engineered Net Shaping -LENS™, direct laser deposition -DLD, laser solid forming -LSF, laser metal deposition shaping -LMDS, and 3D laser cladding), which allows the creation of complex parts without assembly operations along with the low material waste. The AM also provides a possibility of in situ control and adjustment of process parameters for the better quality of the resulted parts using methods of laser-induced breakdown spectroscopy [1], acoustic emission sensors [2], machine learning [3], which allows the prediction of resulted phase composition and mechanical behavior of the parts, co-axial spatially integrated pyrometry [4], direct metal tooling [5], etc. The AM allows the fabrication of products not only from a single material but from a combination of two and more materials, which may have significantly different properties (such as alloys of Cu and Ni [6], Ni and Fe [7], Ni and Ti [8], Ti and Fe [9,10], Cu and Fe [11,12], Al and Fe [13], Al and Ti [14]).…”

In Situ Monitoring of Powder Bed Fusion Homogeneity in Electron Beam Melting

“…Because of this, a whole body of scientific literature and industrial research has been devoted to in situ measurement and monitoring methods suitable to detect the onset of process defects and the origination of unstable process conditions, exploiting sensor data acquired during the process. Recent studies reviewed the literature devoted to in situ monitoring of PBF and summarized the most recent advances and achievements in this field [1,2].…”

“…Powder recoating errors may also be responsible for defect propagation from one part to another within the same build and from one layer to another. Because of this, almost all laser PBF (L-PBF) system developers currently provide their machines with embedded powder bed cameras and, in some cases, with basic automated powder bed anomaly detection capability, albeit commonly limited to macroscopic errors [1,2]. Images acquired after the melting phase, once the solidification of the scanned area has occurred, may be used for different aims, such as detecting undesired surface irregularities in the solidified layers, as possible sources of internal and surface defects [6][7][8][9][10], or signaling possible deviations with respect to the nominal shape in the layer, as evidence of geometrical errors [11][12][13][14][15].…”

Electron-Optical In Situ Imaging for the Assessment of Accuracy in Electron Beam Powder Bed Fusion

“…A large variety of methods operating at different time and length scales was investigated in recent years. A general overview of this dynamic field of research may be obtained from comprehensive review papers [ 17 , 18 , 19 , 20 ]. Within this context, in situ assessment of geometrical and dimensional accuracy of the molten layers is only one aspect.…”

“…In PBF-EB, due to the high processing temperature and the associated incandescence of the build surface, imaging in the visible range is hardly applied. Most investigations deal with infrared (IR) imaging [ 20 ] which also contains information on surface temperature [ 30 , 31 ]. Price et al [ 32 ] applied a near infrared (NIR) camera to measure the decreased cooling rate in an overhang region which is supposed to affect thermal stresses and thus distortion.…”