Polymer powder bed fusion surface texture measurement

Abstract

Polymer laser powder bed fusion (LPBF) surfaces can be challenging to measure. These surfaces comprise complex features including undercuts, deep recesses, step-like transitions, a large range of measurement scales and unfavourable optically materials properties. While recent research has begun to examine the nature of these surfaces, there has not yet been significant effort in understanding how different measurement instruments interact with them. In this paper, we compare the results of LPBF surface topography measurements using a series of different instrument technologies, including contact stylus, focus variation microscopy, coherence scanning interferometry, laser scanning confocal microscopy and x-ray computed tomography. Measurements are made on both side and top surfaces of a cubic polyamide-12 LPBF sample. Different instrument behaviours are highlighted through qualitative visual inspection of surface reconstructions. Further comparisons are then performed through evaluation of profile and areal surface texture parameters and statistical modelling of surface topographies. These analyses allow for the identification both of discrepancies between texture parameters and discrepancies between local topographies reconstructed from measurements. Instrument repeatability metrics are also presented for each measurement of the test surfaces. Results show that discrepancies in measurements made on the acquired datasets are often similar in magnitude to the size of the features present on the surfaces. Conclusions are drawn regarding the suitability of various surface measurement instruments for polymer LPBF surfaces.

An investigation into the mechanisms that influence laser sintered polyamide-12 top surfaces

“…Top surfaces were almost all asperity peak dominated in concurrence with results obtained by both De Pastre et al (2020) and Nar et al (2021).…”

“…It is well established that laser sintered surfaces are a function of the powder feedstock used (Petzold et al , 2019; Pham et al , 2008; Schmid et al , 2017), the processing parameters employed (Mavoori et al , 2019; Petzold et al , 2019; Sachdeva et al , 2013) and the orientation in which parts are digitally placed within the build envelope (Bacchewar et al , 2007; De Pastre et al , 2020). It is also widely agreed upon that the mechanisms that drive the formation of different laser sintered surface topographies vary depending on these considerations.…”

Optical metrology for digital manufacturing: a review

“…In metal AM, for example, surface features such as a large range of scales of interest, step-like transitions, overhangs, highly reflective and opaque surface regions cause significant difficulty for a variety of measurement instruments [103,109,110]. Polymer AM surfaces exhibit similar difficulties in measurement [111], with the added complexity of material translucency. While AM surfaces arguably exhibit the widest plethora of difficultto-measure surface features simultaneously, many modern manufacturing processes come with their own challenges.…”

A Methodology for Computed Tomography-Based Non-Destructive Geometrical Evaluations of Lattice Structures by Holistic Strut Measurement Approach

“…The measurement qualification approach allows having an insight into the accuracy of the CT measurements as compared to a reference measurement obtained from other measuring techniques. Optical profilometer based measurements have shown a good measurement uncertainty in [27,36,37,38]; hence, it is utilized for our reference measurement. Individual strut elements were measured with an Alicona optical profilometer with an objective of 10X.…”