Abstract
Abstract. Additive manufacturing technologies are further developing from prototype to serial production. This trend requires rising challenges to the process-accompanying quality assurance. Optical in situ quality control approaches show great potential to generate accurate measurement data, which are essential for feedback control. If a reliable referencing concept for the layer-by-layer measured data is guaranteed, contour information can be used during the manufacturing to correct occurring geometrical deviations. Within this scientific study, two methods of optical, referenced in situ control of lateral displacements of additive manufactured contours are presented. In the first approach the 2-D contour of the melting pool is analysed in relation to a position-stable reference system implemented in the powder bed. The second approach uses the translucent contour of deeper layers covered with powder as a reference. Within the image evaluation several pre-processing steps like calibration, undistortion, rectification, illumination correction and low-pass filtering are essential for reliable and correct geometric measurements. The following adapted contour detection and position determination of the referenced melting pool contours are based on an extended edge detection algorithm according to Canny (1986). With the evaluation of further manufacturing layers of already lowered powder bed levels, it is possible to specify the influence of powder application on geometrical displacements separately. This is done by a comparison of the position of the detected powder-covered melting pool contours with the previously applied melted region. Consequently a better understanding of lateral contour displacements within the additive manufacturing process is the goal, which is important for a process-accompanying correction of geometrical deviations.
Highlights
Additive manufacturing (AM) processes are being progressively established as new production technologies in industry (Gebhard et al, 2019)
The new referencing approach ensures improved measurement accuracy compared to conventional referencing approaches, which are mainly based on referencing the frame of the building chamber or additional manufactured AM reference markers in the powder bed (Cooke and Moylan, 2011; Zur Jacobsmühlen et al, 2014)
Based on the acquired and processed images, the results of the methods are presented in the following, which are used to verify lateral melting pool displacements in AM
Summary
Additive manufacturing (AM) processes are being progressively established as new production technologies in industry (Gebhard et al, 2019). They are characterised by an incremental addition of material and differ in their binding mechanisms, manufacturing materials and corresponding processing methods (DIN EN ISO/ASTM-52900, 2015). It is referred to as laser beam melting of polymers (LBM-P) and is examined as a representative of other laser-based process categories of powder bed fusion (PBF) (DIN EN ISO17296-2, 2015). Within the regarded manufacturing process a laser beam with a wavelength of 10.6 μm locally melts the standard polymer polyamide 12 (PA 12) powder layer by layer, until the sliced AM components are built up in the powder bed (Deckard, 1989). A quality monitoring of the entire manufacturing process from pre-, in-, to post-process is recommended (VDI3405, 2014)
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