Areal Surface Texture Parameters Research Articles

Sensitivities of surface texture parameters to measurement errors – A review

The surface texture is functionally important. It can be characterised using a set of parameters. The errors in determining the parameters should be small. In this paper, areal surface texture parameters are presented. The errors in the determination of areal parameters are studied, with focusing on the field parameters. Inaccuracies typical for stylus and optical methods are considered. Errors caused by the digitisation process, errors created during data processing, and parameter variations on typical surfaces are studied. The relations between measurement errors and surface texture parameters are analysed and discussed. On the basis of this review, parameters of considerable changes due to measurement errors and stable parameters are selected. Spatial parameters are robust, while the skewness and kurtosis are susceptible to measurement errors. Feature parameters with high sensitivity to measurement errors should not be used during routine measurements.

Influence of Contour Scan Variation on Surface, Bulk and Mechanical Properties of LPBF-Processed AlSi7Mg0.6.

Metal additive manufacturing technologies have great potential for future use in load-bearing aerospace applications, requiring a deeper understanding of mechanical performance and influencing factors. The objective of this study was to investigate the influence of contour scan variation on surface quality, tensile and fatigue strength for laser powder bed fusion samples made of AlSi7Mg0.6 material and to create high-quality as-built surfaces. The samples were produced with identical bulk and different contour scan parameters to accommodate the investigation of the impact of as-built surface texture on mechanical properties. The bulk quality was evaluated by density measurements according to Archimedes' principle and tensile testing. The surfaces were investigated using the optical fringe projection method, and surface quality was assessed by the areal surface texture parameters Sa (arithmetic mean height) and Sk (core height, derived from material ratio curve). Fatigue life was tested at different load levels, and the endurance limit was estimated based on a logarithmic-linear relation between number of cycles and stress. All samples were found to have a relative density of more than 99%. Surface conditions distinctive in Sa and Sk were successfully created. The resulting mean values of the ultimate tensile strength σult are between 375 and 405 MPa for 7 different surface conditions. It was confirmed that the influence of contour scan variation on bulk quality is insignificant for the assessed samples. Regarding fatigue, one as-built condition was found to perform as well as surface post-processed parts and better than the as-cast material (compared to literature values). The fatigue strength at the endurance limit for 106 cycles is between 45 and 84 MPa for the three considered surface conditions.

Effectiveness of buccal dental‐microwear texture in African Cercopithecoidea dietary discrimination

AbstractObjectivesThis study compares ISO (ISO/FDIS 25178) roughness parameters, calculated from three‐dimensional (3D) molar buccal microtexture surfaces, among African Cercopithecoidea primates with different diets.Materials and MethodsWe examined 98 lower second molars from seven African Cercopithecoidea species with diverse dietary regimes and habitat exploitation. Buccal dental surfaces were analyzed using a Sensofar Plu Neox laser scanning confocal microscope. Thirty‐eight, areal surface texture parameters were extracted (Mountain 7® software). Uni‐ and multivariate statistics were used to obtain diet‐related patterns of buccal‐microwear textures and feeding ecology to differentiate between species.ResultsBuccal‐dental 3D texture parameters discriminate between Cercopithecoidea diets. Analysis of variance (ANOVA) revealed significant variation in microwear texture between forest‐adapted Mandrillus sphinx, which showed coarse flat features, and grassland forager Theropithecus gelada, whose buccal surfaces were characterized by a high density of thin features. Buccal‐microwear textures of folivorous species (Colobus polykomos) were related to a lower density of thicker surface indentations in comparison to Papio anubis and Cercocebus atys which are adapted to the consumption of tough and hard foods. The limited interspecific variation in the buccal‐microwear textures of savanna dwellers (Chlorocebus pygerythrus and Chlorocebus aethiops) probably reflects similarities in their foraging diets.DiscussionSignificant variations between‐species demonstrate that 3D microwear ISO roughness parameters applied to buccal enamel surfaces can distinguish between the diets of Cercopithecoidea.

Parametric description of one-process surface texture

There is the problem with a proper selection of areal parameters that describe a surface texture. Analysis of the linear correlation between parameters can be helpful in the selection of parameters. One hundred surface topographies after five machining treatments (grinding, polishing, vapour blasting, milling, and one-process honing) were measured by a white light interferometer and analysed. The number of surfaces within each group was twenty. In addition, 20 surfaces after various treatments were selected. On the basis of correlation and regression analysis, sets of parameters describing individual surface groups were determined. It was found that one-process surfaces can be characterised by the following set of parameters: Sq, Sal, Str, Sdq, Sq/Sa, and Sp/Sz, the wider description contains also: Ssk, Sku, and Spd. It is possible to identify the machining process on the basis of selected areal surface texture parameters. The following pairs of parameters were chosen: Sq/Sa and Sp/Sz, Sdq and Sal, as well as Str and Spd. It was found that the Sq/Sa and Sp/Sz ratios better characterize the ordinate distribution of surface texture than Ssk and Sku.

Generation and categorisation of surface texture data using a modified progressively growing adversarial network

As machine learning becomes more popular in the precision engineering sector, the need for large datasets of measurement data increases. Due to the often manual, user dependent and labour-intensive measurement processes, collecting a large amount of data is often infeasible. It would, therefore, be desirable to collect a small amount of data on which to train a model to generate synthetic data that is representative of the real measurement data. To this end, we present an approach to numerical surface texture generation based on a progressively growing generative adversarial network. We show that by encoding height data into grayscale values within an image, the network can create realistic synthetic surface data both qualitatively and quantitatively. The proposed approach is general to any encoded surface; we demonstrate the model trained on two example datasets consisting of surfaces from different manufacturing processes and measured with different techniques. We finally present an extension to the generator model which automatically categorises the produced surfaces, allowing a surface of a desired category to be generated. Finally, we calculate the distributions of areal surface texture parameters for each type of surface and show that there is good agreement between the synthetic and real data.

Surface quality of printed porous materials for permeability rig calibration

ABSTRACT The enhancement of surface roughness of a textile-like porous medium fabricated by 3D printing techniques is crucial for the repeatability of permeability experiments from test to test. This paper aims at comparison of the surface quality of textile-like porous media fabricated by Stereolithography (SLA), Fused Deposition Modeling (FDM), and Multi Jet Fusion (MJF) 3D printing techniques. Hence, a 3D optical profilometer was used to evaluate the 3D areal surface texture parameters of samples according to ISO 25178. The results revealed that SLA technique produces the smoothest surface with the lowest deviation in the measured values of the surface characteristics. Also, the surface parameters such as the average roughness (Sa) and root mean square (RSM) roughness (Sq) of the top surface of MJF samples are lower than those measured for FDM sample. Furthermore, filling pattern of the FDM technique as a trajectory filament-based AM process results in rougher horizontal surfaces compared to those produced by a non-trajectory powder-based process such as MJF.

Surface Texture Characterization of Metal Selective Laser Melted Part With Varying Surface Inclinations

Abstract Additive manufacturing offers the advantage of infinite freedom to design and fabricate complex parts at reduced lead-time. However, the surface quality of additively manufactured parts remains well behind the conventionally processed counterparts. This paper aims to systematically investigate the impact of varying surface inclination angles with respect to the build direction on the resultant surface textures. A bespoke metal truncheon artifact with inclination angles varying from 0 deg to 180 deg was built by selective laser melting. Focus variation microscopy was used to measure the topography of inclined surfaces with a tilt angle of up to 132 deg. The measurement data were then analyzed to characterize the staircase effect and the particles adherent to the artifact surface. Areal surface texture parameters, including height parameters, spatial parameters, functional parameters, and feature parameters, were explored to quantify the general surface topography, the staircase effect, and the particle features. The areal surface texture characterization and particle analysis reveal the resulted surface topographies are strongly correlated with the surface inclination angles.

Effects of Heat Treatment of Selective Laser Melting Printed Ti-6Al-4V Specimens on Surface Texture Parameters and Cell Attachment

Selective laser melting (SLM) is extensively used for fabricating metallic biomedical products. After 3D printing, it is almost always advisable to apply a heat treatment to release the internal tensions or optimize the mechanical properties of the printed parts. The aim of this paper is to investigate the effects of heat treatment of SLM printed Ti-6Al-4V (Ti64) circular specimens on the areal surface texture parameters and cell attachment. Areal surface texture parameters, including the arithmetic mean height (Sa), root-mean-square height (Sq), skewness (Ssk), and kurtosis (Sku) were characterized. In addition, wavelet-based multi-resolution analysis was applied to investigate the characteristic length scales of untreated and heat-treated Ti64 specimens. In this study, the vertical distance between the highest and lowest position of cell attachment for each sampling area was defined as ΔH. Results showed that an increase in the periodic characteristic length scale was primarily due to the formation of large-scale aggregations of Ti64 metal powder particles on the heat-treated surface. In addition, MG-63 cells preferred lying in concave hollows; in heat-treated specimens, values of ΔH statistically significantly decreased from 31.6 ± 4.2 to 8.8 ± 2.8 μm, while Sku decreased from 3.3 ± 1.4 to 2.6 ± 0.6, indicating a strong influence of Sku on cell attachment.

Fatigue strength assessment of additively manufactured metallic structures considering bulk and surface layer characteristics

This paper extends a previously published fatigue strength estimation methodology for additively manufactured metallic bulk material by additionally accounting for effects of as-built surface layers. Interaction of intrinsic defects and surface texture convergently initiates fatigue failure. Holistic consideration of influencing factors significantly contributes to scientific fatigue assessment of structures fabricated by Laser-Powder Bed Fusion (L-PBF). Surface texture is highly dependent on the building parameters and performed post treatments. Three dimensional, optical topography scans form the basis of determining representative areal surface texture parameters. Areal notch valley depth Sv, alongside notch radii ρ evaluation, enables usage of a modified Peterson’s approach. Effects of notch-like roughness features are quantified by a reduction factor ks, as analogously published for bulk material imperfections kb. Superimposition of ex- and intrinsic material characteristics is empirically assessed by an interaction exponent derived from experimental fatigue data. Macroscopic, tensile residual stresses acting as mean stresses are considered by Smith-Watson-Topper’s approach. Unifying presented influencing factors derives a comprehensive model, conceived to estimate fatigue strength of additively manufactured metallic structures. Regardless of post processing condition, sound applicability of developed design approach is substantiated by averaging −7.1%, comparing estimated fatigue strength to experimental results.

Areal Surface Texture Parameters for Copper/Glass Plating Adhesion Characteristics

Abstract Glass as an alternative printed circuit board material and interposer has been investigated for use in the micro-electronics industry. Electroless copper plating is used to provide the conductive layer, but there is limited understanding of how the surface topography of the glass substrate affects the copper/glass bonding strength exhibited in the current literature. A laser ablation technique was used to prepare glass surfaces with micro-scale structured features in this study, and these features were characterized quantitatively using areal surface texture parameters. The copper/glass bonding adhesion strength was quantified using a scratch testing technique, and the relationships between the critical loads measured and the areal surface parameters, as well as discussion of the underlying mechanisms, are presented in this report. Statistical analysis was employed to identify the most relevant areal parameters that may be used for prediction of the copper/glass bonding strength and for design of adhesion promoting surface textures. The experimental results suggest that the most significant areal surface texture parameters to consider are Sq, Sdq, Sdr, Sxp, Vv, Vmc, and Vvc, and the recommended value range for each parameter for optimal plating adhesion performance is given.

Surface extraction from micro-computed tomography data for additive manufacturing

Surface topography and surface finish are two significant factors for evaluating the quality and dimensional accuracy of additive manufacturing (AM) parts. In general, compared with traditional subtraction and forming manufacturing techniques, the nature of the rough surface and the geometric complexity make the surface of AM parts "another surface," and traditional methods such as coordinate machine measurement may not be applicable. Most research on surface extraction focuses on regular surfaces, such as flat, cylindrical, or spherical surfaces, but less has been done with irregular surfaces. This paper presented an approach for extracting irregular surfaces based on micro-computed tomography (μ-CT) data of AM parts. The extracted data sets were then compared with data sets obtained by a structured light system (SLS). Areal surface texture parameters, cloud comparison methods, and statistical methods were applied to evaluate the difference between the surface data obtained by the two systems. The results showed that the two surface data correlated well and confirmed the capability of the proposed method for surface extraction from irregular surfaces. This work will contribute to the further multi-sensor data fusion for metrology and provide valuable information for near-surface defects prediction with real-time in-situ metrology method in additive manufacturing.

Performance verification of areal surface texture measuring instruments with the Sk-parameters

The calibration, adjustment, performance specification, and verification of areal surface texture measuring instruments are a topical subject in standardization. While a calibration framework has been prepared and is currently being tested for its practical application, additional studies are required for the verification based on areal surface texture parameters. Currently, mostly amplitude-based parameters like Sa or Sq are applied. However, it is useful to adapt verification towards more meaningful surface texture parameters. We describe different use-cases based on the Sk-parameters of ISO 25178-2 that are associated with functional characteristics of the workpiece. Material measures for the mapping of the Sk-parameters are designed based on component surfaces with a model-based design approach. These material measures enable practical performance verifications with functional characteristics. The designed material measures are manufactured by micro-milling with tool radii of (10–100) µm. The versatility and the nanometer precision of the design approach are presented for different machining parameters.

Surface finishing of additively manufactured Inconel 625 complex internal channels: A case study using a multi-jet hydrodynamic approach

The surface roughness of components built using the laser powder bed fusion (L-PBF) process is poor. Surface finishing the internal channels of L-PBF components is a challenge. We propose a multi-jet hydrodynamic approach to enhance the surface finish quality of the internal channels. We investigate the hydrodynamic finishing on L-PBF Inconel 625 linear, stepped, and non-linear internal channels with diameters 5 to 1 mm and length up to 100 mm (replicating the geometries in rocket injectors, fuel nozzles, and cooling channels). The multi-jet hydrodynamic finishing approach improved the surface quality by 60–90 % (final Ra, Sa ≤ 1 μm and Rz, Sz ≤ 20 μm), using an abrasive concentration of ≤1 % in 15 min. of processing time. Areal surface texture parameters Sdr and roughness ratio r ≈1, evidenced the uniformity of the surface finish with dominant abrasive microcuts, regardless of the initial non-uniform additive manufactured surface. Most of the surface finished channels had excellent dimensional integrity and internal contour circularity. We then discussed the advancements required in metal additive manufacturing and internal surface finishing—to safely deploy L-PBF components with micro internal channels in fuel injection and fluid transfer applications.

Multiphase hydrodynamic flow finishing for surface integrity enhancement of additive manufactured internal channels

Abstract The surface finishing of internal channels for components built using additive manufacturing is a challenge. The resulting surface finish uniformity of additive manufactured internal channels (such as fuel transfer lines and cooling passages) is an issue. Therefore, we propose a novel surface finishing technique using controlled hydrodynamic multiphase flow with abrasion phenomenon to overcome the challenges in the surface finishing of additive manufactured internal channels. In this study, we performed the internal surface finishing on AlSi10Mg components manufactured by direct metal laser sintering. We investigated the surface finish potential of the proposed hydrodynamic cavitation abrasive finishing (HCAF) by varying the process parameters, namely, the hydrodynamic upstream and downstream fluid pressures, fluid temperature, abrasive concentration, and processing time. The HCAF process resulted in greater than 90 % (Ra and Rz) surface finish improvements with an acceptable thickness loss from the internal channels. We precisely mapped the surface morphology transformation at the demarcated zones over the processing time and explained the material removal mechanism. In addition, we analyzed and discussed the surface integrity of the channels in terms of the microstructure, surface hardness, and residual stress. Furthermore, we performed large-area surface topography measurements. Then, we analyzed the resulting areal surface texture parameters to determine the uniformity and flatness of the surface after internal surface finishing. Finally, we discussed the significance of using the proposed HCAF process for complex additive manufactured internal channels.

Polymer powder bed fusion surface texture measurement

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.

Micro milling of areal material measures –Study on surface generation for different up and down milling strategies

Abstract Ball end micro milling is a suitable process for the manufacturing of freeform surfaces and therefore appropriate for the manufacturing of material measures according to ISO 25178-70. In previous studies of the authors, ball end micro milling of areal material measures with specified microstructures was experimentally investigated and the influence of the cutting parameters, as well as the influence of the control dataset parameters and the tilt angle were systematically analyzed. The influences of the surface generation strategy (up or down milling) and the chosen tool path on the surface quality of the manufactured structure are investigated experimentally in this study. For this purpose, a full factorial experimental design is created in which two different areal material measure geometries (ACS and AFL as described in ISO 25178-70) are examined applying two different tools in two different surface generation strategies (up or down milling). In addition, two different cases per surface generation strategy are tested: the tool is retracted in the milled groove (case 1: reverse movement with engaged tool) or the tool is lifted between two paths (case 2: reverse movement without tool contact). On the basis of these two cases it is possible to evaluate how the repeatability of the z-axis (case 1) or the smaller short-wavelength roughness due to the second cut (case 2) influences the surface quality of the milled structure. In addition, a meander-shaped tool path is tested as reference: the tool moves alternately in up and down milling direction without lifting from the workpiece. The meander-shaped tool path is the most time-efficient and was applied in previous studies. As a result, information on the influence of the milling strategy on dimensional accuracy and surface roughness is provided. The quality of the manufactured surfaces is compared both quantitatively (based on areal surface texture parameters) and qualitatively (measured topography compared to nominal geometry).

Functional tolerancing of surface texture – a review of existing methods

Surface texture parameters can provide a link between texture, its processing and function. Recent surveys and industrial experience have shown that the ISO 25178 areal surface texture parameters have not received the level of traction in industry that was predicted when introduced despite the fact that the areal parameters were predicted to have more functionally relevant characterisations than the ISO 4287 profile parameters. The objective of the paper is to enable more functionally relevant specifications of surface texture to be taken up by industry and the scientific community by increasing the knowledge of the ISO 25178 texture and novel feature parameters, and their potential use, as well as knowledge about methods for establishing functionally relevant surface texture specifications. In the paper, existing methods for functional tolerancing of surface texture are reviewed and discussed, examples of applications are given and a direction for continued research is presented.

Model-based design of areal material measures with component surfaces

The calibration and verification of areal surface topography measuring instruments is usually performed with artificial geometries that do not correspond to a practical measuring task like gratings or step height artefacts (ISO 25178-70:2014). While these processes have a sufficient process capability to meet the requirements of many industrial measurement applications, there are more and more applications that require small tolerances, which results in the necessity of a performance verification that is more closely related to the later performed measuring task. With a model-based design approach it is possible to design material measures based on component surfaces for an application-oriented performance verification. The initial point is a measured dataset, which is evaluated and virtually transformed in a way that on the one hand the target properties are met, but on the other hand also the functional properties of the surface that are relevant for the specific application are preserved. Based on the subsequent application of virtual manufacturing and measuring processes, also impacts from these processes can be considered in the design of the verification sample. In this study, we extend the basic approach that has been developed for the design of profile material measures e.g. with the manufacturing principle of ultra-precision turning (Seewig, Eifler, Schneider, Aurich Proc. CIRP 45 (2016), 259-262; Eifler, Schneider, Seewig, Kirsch, Aurich Eng. Sci. Technol. 4 (2016) 1993-2001. Seewig, Eifler, Schneider, Kirsch, Aurich Surf. Topog.: Met. Prop. 4 (2016) 024010. Eifler (2016)). to areal material measures and a corresponding manufacturing principle of micro-milling. With the model-based design approach, component surfaces are used to determine two different material measures that feature defined values of the surface texture parameters Sa, Sq, Sk, Svk, Spk as a case study. It will be shown that the areal surface texture parameters can be mapped to the designed material measures that enable a practical performance verification.

Improved non-contact 3D field and processing techniques to achieve macrotexture characterisation of pavements

Macrotexture is required on pavements to provide skid resistance for vehicle safety in wet conditions. Increasingly, correlations between macrotexture measurements captured using non-contact techniques and tyre-pavement contact friction are being investigated in order to enable more robust and widescale measurement and monitoring of skid resistance. There is a notable scarcity of research into the respective accuracy of the non-contact measurement techniques at these scales. This paper compares three techniques: a laser profile scanner, Structure from Motion photogrammetry and Terrestrial Laser Scanning (TLS). We use spectral analysis, areal surface texture parameters and 2D cross-correlation analysis to evaluate the suitability of each approach for characterising and monitoring pavement macrotexture. The results show that SfM can produce successful measures of the areal root mean square height (Sq), which represents pavement texture depth and is positively correlated with skid resistance. Significant noise in the TLS data prevented agreement with the laser profiler but we show that new filtering procedures result in significantly improved values for the peak density (Spd) and the arithmetic peak mean curvature (Spc), which together define the shape and distribution of pavement aggregates forming macrotexture. However, filtering the TLS data results in a trade-off with vertical accuracy, thus altering the reliability of Sq. Finally, we show the functional areal parameters Spd and Spc are sensitive to sample size. This means that pavement specimen size of 150 mm × 150 mm or smaller, when used in laboratory or field observations, are inadequate to capture the true value of areal surface texture parameters. The deployment of wider scale approaches such as SfM and spectrally filtered TLS are required in order to successfully capture the functional areal parameters (Spc and Spd) for road surfaces.

Effects of vibratory finishing of 304 stainless steel samples on areal roughness parameters: A correlational analysis for anisotropy parameters

Characterizing abrasive manufacturing processes and their resulting surfaces has been subject to numerous examinations. Because ground surfaces are inherently stochastic, surface anisotropy is a particular interesting feature as it describes the general effectiveness of the finishing process that should remove deterministic patterns from the surface topography. In the standardization process of areal surface topography measurement, different approaches for quantifying topography randomness have been proposed. This paper describes a comprehensive analysis of the resulting surface anisotropy of a vibratory finishing process. Experiments are carried out by measuring the same surface area spot after various lengths of time of vibratory finishing. After a rough grind, a vibratory finishing process is applied to multiple samples and after different time steps in the finishing process, the surface topography is measured. The topography datasets are evaluated in order to determine the progression of the loss of anisotropy due to the stochastic finishing process. Several techniques to characterize the anisotropy of a surface are applied and compared. A correlational analysis to other areal surface texture parameters was performed, finding that texture aspect ratio (Str) was the best descriptor for directionality because it had little correlation to other parameters. The parameter had less than 40% correlation to all other examined parameters – indicating that other effects like the change in the roughness amplitude do not falsify the correct determination of the anisotropy when the parameter is applied.