Research On X-ray Artifact Correction For Metal Additive Manufacturing

Additive manufacturing(AM)is an emerging novel manufacturing method,which is popular in many fields due to its simple and flexible process.However,various defects are existed in the component manufactured by AM.These defects may affect the quality of the AM component.Therefore,detecting these defects,especially internal defects,is essential.CT technology is an important non-destructive testing method.It can obtain critical information such as the size,shape and spatial position of internal defects of metal AM component.In summary,CT is a promising detection method in the field of AM.In CT imaging,abnormal images that are irrelevant to the actual structure are called artifacts.Many reasons can cause artifacts,such as positional posture errors,scattering rays,and so on.How to suppress artifacts is an essential topic in CT technology.Beam hardening artifacts and Compton scattering artifacts are two major factors degrade AM component imaging in micro CT.Therefore,the research on correction method in the detection of metal AM samples is necessary.In this paper,we focus on the scattering and beam hardening artifact correction in micro-CT imaging of metal AM component.1.A normalized beam hardening correction method is proposed.In a certain voltage range,the projection value vs distance curve of the same material under different voltages is normalized.Approximate projection value curve at any voltage is solved according to the corresponding algorithm,and the obtained approximate curve is used for linearization.Simulation experiments are carried out to verify the method at different voltages.Meanwhile,the projection images of different samples are corrected,and the correction ability of the method for beam hardening artifacts is evaluated.2.An Archimedes spiral phantom for beam-hardening correction is designed.As radius and angle of Archimedes spiral satisfy the linear relationship.Combined with the rotational scanning characteristics of the CT scanning system,the Archimedes spiral phantom is designed.The advantage of this phantom is that it can acquire projection data with small interval continuity during the rotation scan and expand the measurement range with an additional structure.Due to the limitation of manufacturing capacity,an approximation scheme was used to verify the feasibility.3.A scattering artifact correction method based on Monte Carlo simulation is proposed.The GEANT4 platform simulation was used to obtain the scattering information with the imported 3D model of AM.With less particles in simulation,both the scan projection and scatter projection are obtained.Then a weight value is set by comparing the simulated scan projection and the scan projection in real system.Finally,the weighted scatter projection is subtracted from the real scan projection.This method is proved to be effective in a correction experiment.