Abstract
Industrial adoption of additive manufacturing (AM) processes demands improvement in the geometrical accuracy of manufactured parts. One key achievement would be to ensure that manufactured layer contours match the correspondent theoretical profiles, which would require integration of on-machine measurement devices capable of digitizing individual layers. Flatbed scanners should be considered as serious candidates, since they can achieve high scanning speeds at low prices. Nevertheless, image deformation phenomena reduce their suitability as two-dimensional verification devices. In this work, the possibilities of using flatbed scanners for AM contour verification are investigated. Image distortion errors are characterized and discussed and special attention is paid to the plication effect caused by contact imaging sensor (CIS) scanners. To compensate this phenomena, a new local distortion adjustment (LDA) method is proposed and its distortion correction capabilities are evaluated upon actual layer contours manufactured on a fused filament fabrication (FFF) machine. This proposed method is also compared to conventional global distortion adjustment (GDA). Results reveal quasi-systematic deformations of the images which could be minimized by means of distortion correction. Nevertheless, the irregular nature of such a distortion and the superposition of different errors penalize the use of GDA, to the point that it should not be used with CIS scanners. Conclusions indicate that LDA-based correction would enable the use of flatbed scanners in AM for on-machine verification tasks.
Highlights
Additive manufacturing (AM) encompasses a wide range of processes whose common characteristic is that three-dimensional parts are built from two-dimensional layers deposited on top of each another
Results show that theaverage arithmetic mean the standard deviations calculated for distances along the Results show that the arithmetic mean of the standard deviations calculated for distances along the sensor axis was 1.7 μm, whereas the correspondent standard deviation is 0.9 μm
The presence of a lateral seam along the vertical walls of fused filament fabrication (FFF) parts is a well-known phenomenon, Results revealed that contours processed with local distortion adjustment (LDA) are clearly more similar to those digitized related to the combined dynamics of material flowing from the nozzle and XY movement jerk by the coordinate measuring machine (CMM) than contours processed with global distortion adjustment (GDA) or theoretical scale adjustment (TSA)
Summary
Additive manufacturing (AM) encompasses a wide range of processes whose common characteristic is that three-dimensional parts are built from two-dimensional layers deposited on top of each another. It is known that flatbed scanners introduce deformation errors in the digital images that could reduce their suitability as two-dimensional verification devices This disadvantage has been analyzed by several researchers. De Vicente [27] proposed a model that allows a flatbed scanner to be used as a bi-dimensional coordinate measurement machine They divided their procedure in two stages: in the initial one they performed an adjustment based on self-calibration [28] of the measuring system where the geometrical errors of the equipment are eliminated; in the final stage a calibration procedure is performed, so that a calibration parameter Ck is calculated. Scanning operations of AM profiles reflected in this work had been performed off-line
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