Showing papers on "Surface roughness published in 2015"

A review of melt extrusion additive manufacturing processes: II. Materials, dimensional accuracy, and surface roughness

Abstract: Purpose – The purpose of this paper is to critically review the literature related to dimensional accuracy and surface roughness for fused deposition modeling and similar extrusion-based additive manufacturing or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature was carried out by focusing on the relationship between process and product design parameters and the dimensional and surface properties of finished parts. Methods for evaluating these performance parameters are also reviewed. Findings – Fused deposition modeling® and related processes are the most widely used polymer rapid prototyping processes. For many applications, resolution, dimensional accuracy and surface roughness are among the most important properties in final parts. The influence of feedstock properties and system design on dimensional accuracy and resolution is reviewed. Thermal warping and shrinkage are often major sources of dimensional error in finished parts. This phenomenon is explor...

Investigation into the effect of process parameters on microstructural and physical properties of 316L stainless steel parts by selective laser melting

Abstract: Additive manufacturing by selective laser melting (SLM) was used to investigate the effect of laser energy density on 316L stainless steel properties. Point distance and exposure time were varied and their impact on porosity, surface finish, microstructure, density and hardness, was evaluated. The surface roughness was primarily affected by point distance with increased point distance resulting in increased surface roughness, R a, from 10 to 16 μm. Material hardness reached a maximum of 225 HV at 125 J/mm3 and was related to the material porosity; with increased porosity leading to decreased material hardness. Different types of particle coalescence leading to convex surface features were observed (sometimes referred to as balling); from small ball features at low laser energy density to a mixture of both small and large ball features at high laser energy density. Laser energy density was shown to affect total porosity. The minimum amount of porosity, 0.38 %, was observed at an energy density of 104.52 J/mm3.

Surface Modifications and Their Effects on Titanium Dental Implants

Abstract: This review covers several basic methodologies of surface treatment and their effects on titanium (Ti) implants. The importance of each treatment and its effects will be discussed in detail in order to compare their effectiveness in promoting osseointegration. Published literature for the last 18 years was selected with the use of keywords like titanium dental implant, surface roughness, coating, and osseointegration. Significant surface roughness played an important role in providing effective surface for bone implant contact, cell proliferation, and removal torque, despite having good mechanical properties. Overall, published studies indicated that an acid etched surface-modified and a coating application on commercial pure titanium implant was most preferable in producing the good surface roughness. Thus, a combination of a good surface roughness and mechanical properties of titanium could lead to successful dental implants.

Experimental investigation and statistical optimisation of the selective laser melting process of a maraging steel

Abstract: Selective Laser Melting (SLM) is an Additive Manufacturing process (AM) that built parts from powder using a layer-by-layer deposition technique. The control of the parameters that influence the melting and the amount of energy density involved in the process is paramount in order to get valuable parts. The objective of this paper is to perform an experimental investigation and a successive statistical optimization of the parameters of the selective laser melting process of the 18Ni300 maraging steel. The experimental investigation involved the study of the microstructure, the mechanical and surface properties of the laser maraging powder. The outcomes of experimental study demonstrated that the hardness, the mechanical strength and the surface roughness correlated positively to the part density. Parts with relative density higher than 99% had a very low porosity that presented closed and regular shaped pores. The statistical optimization determined that the best part properties were produced with the laser power bigger than 90 W and the velocity smaller than 220 mm/s.

A review of surface roughness generation in ultra-precision machining

Abstract: Ultra-precision machining (UPM) is capable of manufacturing a high quality surface at a nanometric surface roughness. For such high quality surface in a UPM process, due to the machining complexity any variable would be possible to deteriorate surface quality, consequently receiving much attention and interest. The general factors are summarized as machine tool, cutting conditions, tool geometry, environmental conditions, material property, chip formation, tool wear, vibration etc. This paper aims to review the current state of the art in studying the surface roughness formation and the factors influencing surface roughness in UPM. Firstly, the surface roughness characteristics in UPM is introduced. Then in UPM, a wide variety of factors for surface roughness are then reviewed in detail and the mechanism of surface roughness formation is concluded thoroughly. Finally, the challenges and opportunities faced by industry and academia are discussed and several principle conclusions are drawn.

Ultrasmooth, extremely deformable and shape recoverable Ag nanowire embedded transparent electrode

Abstract: Transparent electrodes have been widely used in electronic devices such as solar cells, displays, and touch screens Highly flexible transparent electrodes are especially desired for the development of next generation flexible electronic devices Although indium tin oxide (ITO) is the most commonly used material for the fabrication of transparent electrodes, its brittleness and growing cost limit its utility for flexible electronic devices Therefore, the need for new transparent conductive materials with superior mechanical properties is clear and urgent Ag nanowire (AgNW) has been attracting increasing attention because of its effective combination of electrical and optical properties However, it still suffers from several drawbacks, including large surface roughness, instability against oxidation and moisture, and poor adhesion to substrates These issues need to be addressed before wide spread use of metallic NW as transparent electrodes can be realized In this study, we demonstrated the fabrication of a flexible transparent electrode with superior mechanical, electrical and optical properties by embedding a AgNW film into a transparent polymer matrix This technique can produce electrodes with an ultrasmooth and extremely deformable transparent electrode that have sheet resistance and transmittance comparable to those of an ITO electrode

Translucency of esthetic dental restorative CAD/CAM materials and composite resins with respect to thickness and surface roughness

Abstract: Statement of problem Little information is available about the translucency of monolithic CAD/CAM materials. Purpose The purpose of this study was to evaluate the translucency of restorative CAD/CAM materials and direct composite resins with respect to thickness and surface roughness. Materials and methods In total, 240 disk-shaped specimens (12×14×1 mm and 12×14×2 mm) of 3 different CAD/CAM glass ceramics (CELTRA Duo, IPS e.max CAD, IPS Empress CAD), a fine-structure feldspathic ceramic (VITA Mark II), a hybrid ceramic (VITA Enamic), a resin nanoceramic composite resin (LAVA Ultimate), an experimental (CAD/CAM nanohybrid composite resin), 2 interim materials (Telio CAD; VITA CAD-Temp), and 3 direct composite resins (Tetric EvoCeram; Filtek Supreme XTE; Tetric EvoCeram Bulk Fill) were fabricated (n=10). After 3 different surface pretreatments (polished, rough SiC P1200, or SiC P500), absolute translucency and surface roughness were measured using spectrophotometry and tactile profilometry. The influence of material type, thickness, and roughness on absolute translucency was analyzed using a multivariate analysis, 1-way ANOVA, and the Tukey HSD post hoc test ( P P Results The effect of all tested parameters was significant among the materials ( P ηP² =.988), closely followed by material (.982), and the pretreatment method (.835). The surface roughness was strongly influenced by the pretreatment method (.975) and type of material (.941). Conclusion Thickness and surface roughness are major factors affecting the absolute translucency of adhesively luted restorations.

Laser polishing of selective laser melted components

Abstract: The shape complexities of aerospace components are continuously increasing, which encourages industries to refine their manufacturing processes. Among such processes, the selective laser melting (SLM) process is becoming an economical and energy efficient alternative to conventional manufacturing processes. However, dependant on the component shape, the high surface roughness observed with SLM parts can affect the surface integrity and geometric tolerances of the manufactured components. To account for this, laser polishing of SLM components is emerging as a viable process to achieve high-quality surfaces. This report details an investigation carried out to understand the basic fundamentals of continuous wave laser polishing of SLM samples. A numerical model, based on a computational fluid dynamic formulation, was used to assist the understanding of melt pool dynamics, which significantly controls the final surface roughness. The investigation identified the input thermal energy as the key parameter that significantly affect the melt pool convection, and essentially controls the surface quality. Minimum meltpool velocity is essential to achieve wider laser polished track width with good surface finish. Experimental results showed a reduction of surface roughness from 10.2 μm to 2.4 μm after laser polishing with optimised parameters. Strategies to control the surface topology during laser polishing of SLM components are discussed.

A systematic investigation of roughness height and wavelength in turbulent pipe flow in the transitionally rough regime

Abstract: Direct numerical simulations (DNS) are conducted for turbulent flow through pipes with three-dimensional sinusoidal roughnesses explicitly represented by body-conforming grids. The same viscous-scaled roughness geometry is first simulated at a range of different Reynolds numbers to investigate the effects of low Reynolds numbers and low , where is the pipe radius and is the roughness height. Results for the present class of surfaces show that the Hama roughness function is only marginally affected by low Reynolds numbers (or low ), and observations of outer-layer similarity (or lack thereof) show no signs of sensitivity to Reynolds number. Then, building on this, a systematic approach is taken to isolate the effects of roughness height and wavelength in a turbulent wall-bounded flow in both transitionally rough and fully rough regimes. Current findings show that while the effective slope (which for the present sinusoidal surfaces is proportional to ) is an important roughness parameter, the roughness function must also depend on some measure of the viscous roughness height. A simplistic linear–log fit clearly illustrates the strong correlation between and both the roughness average height (which is related to ) and for the surfaces simulated here, consistent with published literature. Various definitions of the virtual origin for rough-wall turbulent pipe flow are investigated and, for the surfaces simulated here, the hydraulic radius of the pipe appears to be the most suitable parameter, and indeed is the only virtual origin that can ever lead to collapse in the total stress. First- and second-order statistics are also analysed and collapses in the outer layer are observed for all cases, including those where the largest roughness height is a substantial proportion of the reference radius (low ). These results provide evidence that turbulent pipe flow over the present sinusoidal surfaces adheres to Townsend’s notion of outer-layer similarity, which pertains to statistics of relative motion.

Flashover of insulators in vacuum: the last twenty years

Abstract: This paper reviews the last twenty years of work concerning surface flashover of insulators in vacuum. It complements an earlier review paper [H.C. Miller, Flashover of Insulators in Vacuum, IEEE Trans. Electr .Insul., Vol. 28, pp. 512-527, 1993]. The surface flashover voltage of insulators in vacuum depends upon many parameters, such as material, geometry, surface finish, and attachments to electrodes, but also on the applied voltage waveform, duration, single pulse or repetitive, and on the process history of the insulator, operating environment, and previous applications of voltage. Suggestions are made for choosing the material, geometry, and processing when selecting an insulator for a particular application. Some specific techniques for improving the holdoff voltage of insulators are recommended.

Superhydrophobic and anti-icing properties at overcooled temperature of a fluorinated hybrid surface prepared via a sol–gel process

Abstract: A superhydrophobic surface with anti-icing performance has been the focus of research, but few studies have reported the effective and low cost strategy that met the requirements under overcooled conditions. In this article, the fluorinated sol-gel colloid coatings were simply prepared via hydrolytic condensation of nanosilica sol, methyltriethoxysilane (MTES) and 3-[(perfluorohexylsulfonyl)amino]propyltriethoxysilane (HFTES). The multi scale morphology and chemical composition of the artificial surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The influence of the surface roughness structure and fluorinated groups on the wettability and freezing delay time of the colloid surface under overcooled conditions were explored. As the HFTES content was higher than 6 wt%, the prepared colloid surface showed excellent superhydropobicity with a contact angle (CA) of about 166° at room temperature. The CA gradually reduced with the decrease of the temperature. Only the samples with high HFTES contents (above 30 wt%) exhibited special superhydrophobic and anti-icing properties under freeze temperature. Besides the surface roughness structure, the high fluoride enrichment on the surface plays a major role in the superhydrophobic and anti-icing properties under overcooled conditions.

Ultrafiltration Membranes with Structure-Optimized Graphene-Oxide Coatings for Antifouling Oil/Water Separation

Abstract: Fouling of ultrafiltration (UF) membranes in oil/water separation is a long-standing issue and a major economic barrier to their use in a broad range of applications. Currently reported membranes typically show severe fouling, resulting from the strong oil adhesion on the membrane surface and/or oil penetration inside the membranes. This greatly degrades their performance and shortens service lifetime. Here, the use of graphene oxide (GO) as a novel coating material for the fabrication of fully recoverable, UF membranes with desired hierarchical surface roughness is accomplished by a facile vacuum filtration method for antifouling oil/water separation. The combination of ultrathin, “water-locking” GO coatings with the optimized hierarchical surface roughness, provided by the inherent roughness of the porous supports and the corrugation of the GO coatings, minimizes underwater oil adhesion on the membrane surface. Cyclic membrane performance evaluation tests revealed approximately 100% membrane recovery by facile surface water flushing, establishing their excellent easy-to-recover capability. The novel GO functional coatings with optimized hierarchical structures may have broad applications in oil-polluted environments.

Effect of surface roughness on osteogenesis in vitro and osseointegration in vivo of carbon fiber-reinforced polyetheretherketone–nanohydroxyapatite composite

Abstract: As United States Food and Drug Administration-approved implantable material, carbon fiber-reinforced polyetheretherketone (CFRPEEK) possesses an adjustable elastic modulus similar to cortical bone and is a prime candidate to replace surgical metallic implants. The bioinertness and inferior osteogenic properties of CFRPEEK, however, limit its clinical application as orthopedic/dental implants. In this study, CFRPEEK–nanohydroxyapatite ternary composites (PEEK/n-HA/CF) with variable surface roughness have been successfully fabricated. The effect of surface roughness on their in vitro cellular responses of osteoblast-like MG-63 cells (attachment, proliferation, apoptosis, and differentiation) and in vivo osseointegration is evaluated. The results show that the hydrophilicity and the amount of Ca ions on the surface are significantly improved as the surface roughness of composite increases. In cell culture tests, the results reveal that the cell proliferation rate and the extent of osteogenic differentiation of cells are a function of the size of surface roughness. The composite with moderate surface roughness significantly increases cell attachment/proliferation and promotes the production of alkaline phosphatase (ALP) activity and calcium nodule formation compared with the other groups. More importantly, the PEEK/n-HA/CF implant with appropriate surface roughness exhibits remarkably enhanced bioactivity and osseointegration in vivo in the animal experiment. These findings will provide critical guidance for the design of CFRPEEK-based implants with optimal roughness to regulate cellular behaviors, and to enhance biocompability and osseointegration. Meanwhile, the PEEK/n-HA/CF ternary composite with optimal surface roughness might hold great potential as bioactive biomaterial for bone grafting and tissue engineering applications.

Roughness Effects on Flow and Heat Transfer for Additively Manufactured Channels

Abstract: Recent technological advances in the field of additive manufacturing (AM), particularly with direct metal laser sintering (DMLS), have increased the potential for building gas turbine components with AM. Using DMLS for turbine components broadens the design space and allows for increasingly small and complex geometries to be fabricated with little increase in time or cost. Challenges arise when attempting to evaluate the advantages of DMLS for specific applications, particularly because of how little is known regarding the effects of surface roughness. This paper presents pressure drop and heat transfer results of flow through small, as produced channels that have been manufactured using DMLS in an effort to better understand roughness. Ten different coupons made with DMLS all having multiple rectangular channels were evaluated in this study. Measurements were collected at various flow conditions and reduced to a friction factor and a Nusselt number. Results showed significant augmentation of these parameters compared to smooth channels, particularly with the friction factor for mini-channels with small hydraulic diameters. However, augmentation of Nusselt number did not increase proportionally with the augmentation of the friction factor.Copyright © 2015 by ASME

Prediction of surface roughness during hard turning of AISI 4340 steel (69 HRC)

Abstract: Various regression models were applied to the hard turning of AISI 4340 (69 HRC) steel.Random forest and Quantile regression models are used for modelling and machining for the first time.Feed rate is more dominant than cutting speed in influencing the surface roughness.Multiple regression models are robust when the surface roughness is below 1µm. In this study, 39 sets of hard turning (HT) experimental trials were performed on a Mori-Seiki SL-25Y (4-axis) computer numerical controlled (CNC) lathe to study the effect of cutting parameters in influencing the machined surface roughness. In all the trials, AISI 4340 steel workpiece (hardened up to 69 HRC) was machined with a commercially available CBN insert (Warren Tooling Limited, UK) under dry conditions. The surface topography of the machined samples was examined by using a white light interferometer and a reconfirmation of measurement was done using a Form Talysurf. The machining outcome was used as an input to develop various regression models to predict the average machined surface roughness on this material. Three regression models - Multiple regression, Random forest, and Quantile regression were applied to the experimental outcomes. To the best of the authors' knowledge, this paper is the first to apply random forest or quantile regression techniques to the machining domain. The performance of these models was compared to ascertain how feed, depth of cut, and spindle speed affect surface roughness and finally to obtain a mathematical equation correlating these variables. It was concluded that the random forest regression model is a superior choice over multiple regression models for prediction of surface roughness during machining of AISI 4340 steel (69 HRC).

Bioinspired, roughness-induced, water and oil super-philic and super-phobic coatings prepared by adaptable layer-by-layer technique

Abstract: Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, anti-icing, self-cleaning, anti-smudge, and oil-water separation applications. Many previous bioinspired surfaces are of limited use due to a lack of mechanical durability. Here, a layer-by-layer technique is utilized to create coatings with four combinations of water and oil repellency and affinity. An adapted layer-by-layer approach is tailored to yield specific surface properties, resulting in a durable, functional coating. This technique provides necessary flexibility to improve substrate adhesion combined with desirable surface chemistry. Polyelectrolyte binder, SiO2 nanoparticles, and silane or fluorosurfactant layers are deposited, combining surface roughness and necessary chemistry to result in four different coatings: superhydrophilic/superoleophilic, superhydrophobic/superoleophilic, superhydrophobic/superoleophobic, and superhydrophilic/superoleophobic. The superoleophobic coatings display hexadecane contact angles >150° with tilt angles 160° with tilt angles <2°. One coating combines both oleophobic and hydrophobic properties, whilst others mix and match oil and water repellency and affinity. Coating durability was examined through the use of micro/macrowear experiments. These coatings display transparency acceptable for some applications. Fabrication via this novel combination of techniques results in durable, functional coatings displaying improved performance compared to existing work where either durability or functionality is compromised.

Parametric modeling and optimization for wire electrical discharge machining of Inconel 718 using response surface methodology

Abstract: Inconel 718 is a high-nickel-content superalloy which possesses excellent strength at elevated temperatures and resistance to oxidation and corrosion. This alloy has wide applications in the manufacturing of aircraft engine parts such as turbine disks, blades, combustors and casings, extrusion dies and containers, and hot work tools and dies, but the inherent problems in machining of superalloys with conventional techniques necessitate the use of alternative machining processes. The wire electrical discharge machining (WEDM) process has been recently explored as a good alternative of conventional machining methods, but there is lack of data and suitable models for predicting the performance of WEDM process particularly for Inconel 718. In the present work, empirical modeling of process parameters of the WEDM has been carried out for Inconel 718 using a well-known experimental design approach called response surface methodology. The parameters such as pulse-on time, pulse-off time, peak current, spark gap voltage, wire feed rate, and wire tension have been selected as input variables keeping others constant. The performance has been measured in terms of cutting rate and surface roughness. The models developed are found to be reliable representatives of the experimental results with prediction errors less than ±5 %. The optimized values of cutting rate and surface roughness achieved through multi-response optimization are 2.55 mm/min and 2.54 μm, respectively.