Polymer powder bed fusion surface texture measurement

Marc-Antoine De Pastre,Nicola Senin,José A Albajez García,Yann Quinsat,Richard Leach,Adam Thompson

doi:10.1088/1361-6501/ab63b1

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.

Highlights

We considered three of the most common areal surface measurement technologies: laser scanning confocal microscopy (CM) [24,25], focus variation (FV) [26, 27] and coherence scanning interferometry (CSI) [28,29,30,31]
More powerful tests could be adopted to obtain a further refinement in the assessment of discrepancy, but in this work we focus on providing an overview of where the major discrepancies are found in relation to the generation of surface texture parameters
Measurements of polymer Laser powder bed fusion (LPBF) surfaces have been performed with using contact stylus, CSI, FV, CM and x-ray computed tomography (XCT)

Summary

Introduction

Examples of these geometries include lattices and other complex structures that often contain features inaccessible to conventional machine tools [3]. The most developed of the AM technologies fall into the powder bed fusion process family [4]. Laser powder bed fusion (LPBF) is of particular interest to the manufacturing community, because it does not require support structures when using polymer materials. Not needing support structures means that there is a significant design freedom afforded to parts made using polymer LPBF, even when compared to

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Results

Discussion

Conclusion