On-machine and in-process surface metrology for precision manufacturing

The fractal characteristics of a series of fractured AISI 4340 steel specimens were studied experimentally by means of vertical sections through the fracture surface. Extensive fractal data have been generated for both the fracture surfaces and their profiles. Fractal plots for the irregular profile curves differ significantly from those of the infinitely subdivisible curves with “self-similarity” as postulated by Mandelbrot. Instead of a linear fractal curve and constant fractal dimension D , we find a reversed sigmoidal curve (RSC) and variable D . Because of the inadequacies of the linear Richardson fractal equation, we have developed an alternative procedure whereby constant slopes β and γ are obtained from the RSCs for both profiles and surfaces respectively. Since a fractal equation for surfaces apparently does not exist, we propose one that parallels the Richardson equation for profiles. Slopes from the RSCs are related to the new constant fractal dimensions D β and D γ in the modified fractal equations for profiles and fracture surfaces. Some insight into the physical nature of the fractal dimension is afforded by its close similarity to fracture roughness parameters that have simple physical meanings. It is believed that the results of the extensive study may have general validity for the irregular complex curves and surfaces of nature.

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Fractals in fractography

Geometrical metrology for metal additive manufacturing

Manufacturing of multiscale structured surfaces

Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface roughness, which is, in some cases, one of the major limitations of the EBM process. The aim of this work is to investigate the effects of the orientation and the slope of the EBM surfaces on the surface roughness. Additionally, the machine repeatability is studied by measuring the roughness of surfaces built at different positions on the start plate. To these aims, a specific artefact was designed. Replicas of the artefact were produced using an Arcam A2X machine and Ti6Al4V powder. Descriptive and inferential statistical methods were applied to investigate whether the surface morphology was affected by process factors. The results show significant differences between the upward and downward surfaces. The upward surfaces appear less rough than the downward ones, for which a lower standard deviation was obtained in the results. The roughness of the upward surfaces is linearly influenced by the sloping angle, while the heat distribution on the cross-section was found to be a key factor in explaining the roughness of the downward surfaces.

Surface Roughness Characterisation and Analysis of the Electron Beam Melting (EBM) Process

This work studies multiscale analyses and characterizations of surface topographies from the engineering and scientific literature with an emphasis on production engineering research and design It highlights methods that provide strong correlations between topographies and performance or topographies and processes, and methods that can confidently discriminate topographies that were processed or that perform differently These methods have commonalities in geometric characterizations at certain scales, which are observable with statistics and measurements It also develops a semantic and theoretical framework and proposes a new system for organizing and designating multiscale analyses Finally, future possibilities for multiscale analyses are discussed

Xiang Jane Jiang

Papers

Multiscale analyses and characterizations of surface topographies