The increasing interest in Additive Manufacturing (AM) is due to its huge advantage in producing parts without any geometrical limitations. It is due to this reason, AM is extensively utilized in automotive, aerospace, medical and dental applications. Despite their popularity, AM is often associated with inferior surface quality which is one of the many reasons why it has failed to fully replace traditional methods. Hence, AM is always followed by a subsequent post-processing step to produce the end-product. To establish control over the surface quality it is first necessary to fully understand the surface behaviour concerning the factors affecting it. In this paper, the focus is mainly on having a better understanding of the surfaces by using scale-sensitive fractal analysis. In addition, the paper documents the influence of build inclination and post-processing in particular shot blasting on surface topography and utilizes a multi-scale approach to identify the most important scale and parameters for characterization. Results of this study reveal that shot blasting has a minimalistic effect on surface features at a large scale as it cannot remove the waviness completely. At smaller scales, blasting imparts additional features on the surface due to the impact of abrasive particles at high pressure. At the intermediate scales, the influence of shot blasting is highest as it successfully eliminates the surface features comprising of partially melted powder particles and stair-step effect. © 2020 IOP Publishing Ltd.

The highly complex nature of as printed metal AM surfaces pose other challenges for making measurements compared to surfaces made with many conventional processing methods. The high complexity is caused by high aspect ratios, a mix of high and low reflexivity, steep angles etc. It is not clear which method is the most suitable for measuring these surfaces. The objective of this study was to compare four different measurement modes available in one instrument to evaluate the advantages and drawbacks of the respective techniques regarding measurements of metal AM surfaces. The evaluated measurement modes are Confocal Microscopy, Coherence Scanning Interferometry, Focus Variation and Confocal Fusion. The effect of advantages and drawbacks of studied techniques was tested on typical surfaces produced by L-PBF process. Surfaces printed at 0° and 90° inclinations were compared regarding the measurement results achieved from the different methods. The Power Spectral Density analysis and visual comparison were used for the examination of studied measurements methods. Besides the comparison of areal measurements acquired by different modes available in the instrument also extracted profile measurements were compared with profile images acquired using an Optical Microscope. This study reveals that confocal fusion is a promising technique for AM surface characterisation, due to the highest amount of valid data points in the typical measurement. The new approach developed in the study showed that PSD analysis can be used for evaluation of fill in algorithms incorporated in different software. Results of the profile comparisons help to illustrate features that can be depicted by surface measurements, applying different measurement principles, as well as enables comparison of raw profile data between different types of measurements. Further investigation of measurements on AM surfaces in the frequency domain will bring more understanding about the limitations of measurement techniques. © 2020 IOP Publishing Ltd.

In this study, several surface topographies typical for dental implants were evaluated by different measurement techniques. The samples were prepared by machine turning, wet chemical etching and electrochemical polishing of titanium discs. The measurement techniques included an atomic force microscope (AFM), coherence scanning interferometer (CSI) and a 3D stereo scanning electron microscope (SEM). The aim was to demonstrate and discuss similarities and differences in the results provided by these techniques when analyzing submicron surface topographies. The estimated surface roughness parameters were not directly comparable since the techniques had different surface spatial wavelength band limits. However, the comparison was made possible by applying a 2D power spectral density (PSD) function. Furthermore, to simplify the comparison, all measurements were characterized using the ISO 25178 standard parameters. Additionally, a Fourier transform was applied to calculate the instrument transfer function in order to investigate the behavior of CSI at different wavelength ranges. The study showed that 3D stereo SEM results agreed well with AFM measurements for the studied surfaces. Analyzed surface parameter values were in general higher when measured by CSI in comparison to both AFM and 3D stereo SEM results. In addition, the PSD analysis showed a higher power spectrum density in the lower frequency range 10−2–10−1 µm−1 for the CSI compared with the other techniques. © 2018 IOP Publishing Ltd

In this paper, an attempt is made to explain the surface texture of Selective Laser Melting (SLM) parts more satisfyingly than the existing methods. Investigations were carried out on the 316L stainless steel SLM samples. To account for most of the surface conditions, a truncheon artefact was employed for the analysis. A Stylus Profilometer was employed as a metrology tool for obtaining the 3D surface measurements. A methodology is proposed to extract and characterize the topographic features of Additive Manufactured (AM) surfaces. Here, the overall roughness of the surface is segregated into the roughness of the powder particles and the waviness due to thermal and the “staircase” effects. Analyzing these features individually results in an increased understanding of the AM process and an opportunity to optimize machine settings.

Fused Deposition Modeling (FDM) is mostly used to develop functional prototypes and in some applications for end-use parts. It is important to study the surfaces produced by FDM to understand the certainty of process. Truncheon design test artefacts are printed at different print settings and surfaces are measured using stylus profilometer. Taguchi’s design of experiments, signal-to-noise ratio and multiple regression statistics are implemented to establish a concise study of the individual and combined effect of process variables on surface texture parameters. Further, a model is developed to predict the roughness parameters and is compared with experimental values. The results suggest significant roughness parameter values decrease with increase in build inclination and increases with increase in layer thickness except the roughness peak count. © 2018 The Authors. Published by Elsevier B.V

A major drawback of the optical microscope is its limitation to resolve finer details. Many microscopes have been developed to overcome the limitations set by the diffraction of visible light. The scanning electron microscope (SEM) is one such alternative: it uses electrons for imaging, which have much smaller wavelength than photons. As a result high magnification with superior image resolution can be achieved. However, SEM generates 2D images which provide limited data for surface measurements and analysis. Often many research areas require the knowledge of 3D structures as they contribute to a comprehensive understanding of microstructure by allowing effective measurements and qualitative visualization of the samples under study. For this reason, stereo photogrammetry technique is employed to convert SEM images into 3D measurable data. This paper aims to utilize a stereoscopic reconstruction technique as a reliable method for characterization of surface topography. Reconstructed results from SEM images are compared with coherence scanning interferometer (CSI) results obtained by measuring a roughness reference standard sample. This paper presents a method to select the most robust/consistent surface texture parameters that are insensitive to the uncertainties involved in the reconstruction technique itself. Results from the two-stereoscopic reconstruction algorithms are also documented in this paper. © 2018 IOP Publishing Ltd.

Deemed as one of the established additive manufacturing technique, fused deposition modelling (FDM) is commonly used for creating functional prototypes. Additive manufacturing, in general, generates surfaces that are different compared to conventional manufacturing and consists of features that are either not well-defined or satisfactorily characterized using the existing surface standards. The generated surfaces vary with respect to different techniques, materials, geometries and process parameters Additive manufacturing boosts of manufacturing individualized parts and as claimed, product with complex design can be easily manufactured but the problem lies in manufacturing it with highest surface quality or produce a well-defined robust surface. The aim of the study is to characterize the FDM surfaces generated at different process settings using areal surface parameters. The experimental study includes surface measurements of study sample build at different orientation and layer thickness. A general statistical methodology is implemented to identify the deterministic features on the manufactured surface. The results include topography characterization using the significant features and detailed study on the influence of geometry and process settings on FDM surfaces.

In the European Joint Research Project 'Multidimensional Reflectometry for Industry', a new gloss scale was developed with the aim to represent different levels of gloss, hue, roughness, and refractive indices. In this paper, the surfaces of six selected samples were thoroughly investigated using various measuring techniques in order to verify the outcome of the novel manufacturing processes in terms of distinct levels as well as types of surface roughness. The aim of the evaluation was to capture surface structures in different wavelength intervals utilizing a confocal microscope, a coherence scanning interferometer, and an atomic force microscope. Power spectral density functions were also calculated from the measurements and used to determine suitability of techniques for different roughness scales. The measurements show that the expected surface characteristics as well as different RMS roughness values are intimately connected to the perceived glossiness.

3D analysis of surface topography is becoming a more used tool for industry and research. New ISO standards are being launched to assist in quantifying engineering surfaces. The traditional optical measuring instrumentation used for 3D surface characterization has been optical interferometers and confocal based instrumentation. However, the resolution here is limited in the lateral dimension to the wavelength of visible light to about 500 nm. The great advantage using the SEM for topography measurements is the high flexibility to zoom from low magnifications and locating interesting areas to high magnification of down to nanometer large surface features within seconds. This paper presents surface characterization of dental implant micro topography. 3D topography data was created from SEM images using commercial photogrammetric software. A coherence scanning interferometer was used for reference measurements to compare with the 3D SEM measurements on relocated areas. As a result of this study, measurements emphasizes that the correlation between the accepted CSI measurements and the new technology represented by photogrammetry based on SEM images for many areal characterization parameters are around or less than 20%. The importance of selecting sampling and parameter sensitivity to varying sampling is high-lighted. Future work includes a broader study of limitations of the photogrammetry technique on certified micro-geometries and more application surfaces at different scales. © Published under licence by IOP Publishing Ltd.