Acoustic Diagnostic of Laser Powder Bed Fusion Processes

Online monitoring of Laser Powder Bed Fusion is critical to advance the technology and its applications. Many studies have shown that the acoustic signal from the laser powder bed fusion process contains a large amount of information about the process condition. In this research, we used an acoustic system for the in-situ characterization of a wide variety of different single-track geometries. The internal acoustic system includes a microphone and accelerometer. The melting mode, cross-sectional shape and dimensions of Ti6Al4V single tracks at different process parameters are presented. We have established a correlation between track geometry, internal defects and acoustic signals. The parameters are varied and tested against the acoustic frequency measurements to determine the sensitivity. We determined the patterns of signal behaviour in the event of anomalies (spatter, balling, pores, undercut). The characteristic features of the process are traced to a commercial machine. Well described dataset with correlated monitoring data and signal tracks properties obtained and can be used for building classification model and quality prediction. All this is aimed at creating a database of experimental data that will be a key for LPBF digitalization and control, allowing real-time control of the process to optimize part quality and, more importantly, help with decision-making algorithms.

Optical diagnostics of selective laser melting and monitoring of single-track formation

The article presents the optical diagnostics results of the selective laser melting process of single-track production. The track defects detection (such as balling effect, powder free zone formation, sparking) was shown, as well as the visualization of the independent particles consolidation in a solid track. The metal evaporation and the formation of the melt pool specific gas dynamic conditions were considered as important physical phenomena. The velocities of the particle emission from the melt pool, the rate of their involvement, and the velocity of the gas flow were estimated. The results make it possible to evaluate the kinetics of mass transfer under selective laser melting process. The surface thermal field of the laser-irradiated zone strongly influences the material qualitative characteristics after selective laser melting. The results becomes the basis for the development of optical monitoring and diagnostic systems for laser additive manufacturing processes based on the melt pool temperature online controlling

Process quality assessment with imaging and acoustic monitoring during Laser Powder Bed Fusion

Acoustic monitoring of laser powder bed fusion (LPBF) has shown a high sensitivity to stochastic defects, e.g., cracks, pores and lack of fusion (LOF), and melting instability. The advantage of this method is the possibility to filter raw data and extract acoustic signal features for the data analysis, thus minimizing data and computing time. In this research during the build of components from hot work tool steel powder, acoustic signals and powder bed images were acquired for post-process data analysis and search for correlations with LOF. Different densities caused by LOF were obtained by changing the shielding gas velocity. In the analysis, selected combinations of features with the relationship between the build phases and the final properties such as density and surface roughness, were investigated. For the current dataset prediction of the optimal state showed an accuracy of 98%. This investigation suggests the applicability of the smart data-centric machine learning method to predict the relationship of process parameters, monitoring signals, and material properties. © 2022 The Authors. Published by Elsevier B.V

Laser beam profiling: experimental study of its influence on single-track formation by selective laser melting

In the article the experimental study of influences of laser beam profiling on the microstructure of the material obtained by selective laser melting is presented. Microstructure was researched by the example of single-track formation. For these needs the optical and video-monitoring stand was constructed. The defects of single-track formation were obtained by microscopy and video monitoring. The technological gaps for each laser beam profile give the possibility to use higher power for laser systems in the future with the purpose to improve productivity of SLM processing

Experimental Approbation of Selective Laser Melting of Powders by the Use of Non-Gaussian Power Density Distributions

AbstractExperimental results on laser beam modulation at selective laser melting (SLM) are presented. The modulation is a possible way to improve the efficiency of the SLM process. The optical diagnostics shows the energy loss up to 30%. This could be a consequence of high thermal gradients in the melt pool resulted by the Gaussian power density distribution. The Gaussian distribution can be changed to the flat-top one or to the inverse-Gaussian (donut) one. An experimental stand with a 200W laser source was developed. Twenty single tracks for each of the three modes were obtained for a Co-Cr alloy. The samples were studied by scanning electronic microscopy (SEM) on irregularity. Optical diagnostics by high velocity camera (HVC) shows that the use of the non-Gaussian laser beam distributions can significantly reduce the width of the free-of-powder consolidation zone, which is considered as the main reason for irregularity of single tracks. A better metallurgical bonding of the single tracks with the substrate was obtained by the use of the flat-top laser beam. Both of these facts show a significant influence of the laser beam energy distribution on the energy loss at SLM, especially for high power laser sources. The observed escape of granules shows a possible influence of the dynamic factor. The use of the non-Gaussian distributions can enhance 3D parts, for example, improve the geometrical tolerance and decrease the residual porosity

An investigation into the properties of 3D printed Ti6Al4V FCC lattice structures with different strut thicknesses

Metal additive manufacturing of titanium and its alloys can produce complicated geometries cost-effectively while maintaining biocompatibility. It is known that the material property differences between bone and Ti6Al4V cause stress shielding, leading to bone failure around the implant. Using lattice structures is effective at reducing elastic modulus while improving osteointegration. However, it is important first to characterise the as-printed material to investigate the effects of lattice structures on the bulk material properties. Understanding the microstructure, porosity, and related mechanical properties can discern the bulk material properties of the unit cell. The microstructure of printed samples was found to be martensitic. The printed samples contained porosity with strut thickness deviations ranging from the design from 44.29 % (t = 0.50 mm) to 28.43 % (t = 1 mm). It was found that the high amount of porosity resulted in considerable variation in compression material properties

Modeling of 3D technological fields and research of principal perspectives and limits in productivity improvement of selective laser melting

Nowadays the technological perspectives of selective laser melting are limited by available equipment on the market. Most of the manufactures produce SLM-machine with the maximum power of laser system 200 W, this makes processing very slow and it significantly reduces the field of potential applications for the technology. Meanwhile the limits of laser power are linked to a problem of its effective use. In the current work, the future perspectives of technology are investigated by modeling of 3D technological fields