A layerwise monitoring methodology based on blue laser line profilometer for Material Extrusion processes

Abstract

Material Extrusion (MEX) is an Additive Manufacturing technology widely used for the fabrication of polymeric, metallic and composite parts with clear advantages. In the last decades, the growing interest of such industries like aerospace, medical, automotive and R&D has driven technological improvements of MEX to make the technology more reliable and repeatable. Although, defects and geometric dimensional inaccuracies are still known to affect the process, limiting the applicability of MEX for the realization of functional parts. Recently, in-process monitoring methods have been implemented for a rapid detection of defects and process anomalies, activating, eventually, the control of the process. In this work, an innovative layerwise monitoring methodology based on a high-resolution blue laser line profilometer applied to a MEX process, was proposed. By analyzing the point clouds of each layer, with proper quality indexes, it was possible to compute the layer height deviation and to evaluate the surface quality in terms of occurrence of defects. In particular, the quality indexes presented in this work were representative of the layer height accuracy, the occurrence and distribution of defects on the layer surface and the stability of the process (respectively the so-called indexes were ADLH, RAD and the slope s). Different process conditions were generated by varying the raster angle and the sample location on the building platform.

On-Machine LTS Integration for Layer-Wise Surface Quality Characterization in MEX/P

“…Although particularly popular in metal AM [21][22][23], layer-wise monitoring has also been applied in MEX/P, primarily through three different sensing technologies: thermal sensing [24], 2D vision [25,26], and 3D vision [16,23,[27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Monitoring the 3D layer topography offers distinct advantages over thermal and two-dimensional sensing, as it allows for direct measurement of layer features, like layer height [27,28], or in-plane defects [16,23,30,31].…”

“…The analysis of previous research efforts in LTS-based layer-wise monitoring of MEX/P part quality leads to the definition of several key aspects, like the integration strategy, the vertical repeatability, or the objective quality characteristic. The summary in Table 1 shows how most authors decided to integrate commercial LTS models [16,[28][29][30]35,37,38], although there are also examples of built-in-house sensor arrangements [27,36]. The layer-wise inspection could take place using pure on-machine solutions, where the LTS has been fully integrated into the manufacturing equipment [16,27,30,31,36] or has been attached to actuated [28,37,38] or fixed [29,35] off-machine arrangements.…”

“…The summary in Table 1 shows how most authors decided to integrate commercial LTS models [16,[28][29][30]35,37,38], although there are also examples of built-in-house sensor arrangements [27,36]. The layer-wise inspection could take place using pure on-machine solutions, where the LTS has been fully integrated into the manufacturing equipment [16,27,30,31,36] or has been attached to actuated [28,37,38] or fixed [29,35] off-machine arrangements. The scanning strategy and the relative movement between part and LTS are conditioned by the type of integration used.…”

“…The metrological characteristics of each LTS largely condition the type of quality characterization. Thus, solutions with low vertical resolution are applied to part height monitoring [27] or coarse defects [30,35]. LTS with intermediate performance are more versatile and have been used to evaluate the underfill and overfill issues [28,35,38], layer height deviations [34,35,37], warpage [37] or even the accuracy of the deposition trajectory [16].…”

“…Thus, solutions with low vertical resolution are applied to part height monitoring [27] or coarse defects [30,35]. LTS with intermediate performance are more versatile and have been used to evaluate the underfill and overfill issues [28,35,38], layer height deviations [34,35,37], warpage [37] or even the accuracy of the deposition trajectory [16]. On the other hand, the characterization of surface texture requires a high-resolution LTS and has been mostly beyond the scope of research efforts in this field, although its usefulness has been explored in off-machine arrangements [29].…”