Influence of surface roughness on X-ray computed tomography dimensional measurements of additive manufactured parts

Abstract

In many industrial applications, components characterized by high surface roughness are measured by X-ray computed tomography (CT). This is the case, for example, of additive manufactured parts. Surface roughness has a strong influence on CT dimensional measurements, causing relevant measurement deviations with respect to tactile reference measurements by coordinate measuring machines (CMMs), especially for parts characterized by high surface roughness. It comes that roughness effects on CT dimensional measurements must be quantified.In this work, the influence of surface roughness on CT dimensional measurements, and the relation between tactile CMM and CT measurements are studied. Effects of larger as well as smaller surface roughness are taken into account, by means of three different additive manufactured samples characterized by different roughness. Experimental results prove the presence of a systematic error between tactile and CT measurements; the relation between this error and the Rz roughness parameter of the surface is analyzed

Utilization of Metal Additive Manufacturing (AM) in Precision Oriented Mechanical Part Production

“…This leads to a systematic error, however, CT scan seems to be the only way to evaluate both dimensional accuracy and internal defects level. According to [27], internal diameters are larger than CMM reference while external dimensions are smaller. In case of processes such as inkjet or LIFT, the need of close process monitoring is major concern.…”

Lessons learned in the design of reference fiducials for layer-wise analysis of test coupons made by laser powder bed fusion

“…Performing repeated scans can provide insight into the variability of measurement results due to, e.g., stochastic error sources such as drifts and noise in the X-ray CT acquisition, and is considered best practice. Based on previous observations [52][53][54], however, it is expected that variations in the surface sampling strategy of the relatively poor coupon surfaces from a single acquisition will dominate the expected variations from repeated acquisitions, see section 1.6. Hence, only one acquisition was performed for each test coupon.…”

“…The effect of thermal properties on the geometrical fidelity of the incorporated fiducials will be considered J o u r n a l P r e -p r o o f in future work. Based on previous studies [52,53], the uncertainty due to the poor surface quality and variations in fiducial shape due to AM-inherent geometrical distortions are expected to dominate over uncertainties in the acquisition, reconstruction, and surface determination. Table 3.…”

Qualification of CT data for areal surface texture analysis

“…Only a few studies have addressed the issue of measuring the surface roughness on classical size parts using computed tomography. Aloisi and Carmignato [1] studied and characterized the influence of surface roughness on X-ray CT dimensional measurements. They have pointed out that surface roughness causes a systematic error between classical touch probe measurements and CT measurements, but their study does not propose a direct qualification of CT measurements for 3D surface topography evaluation.…”