Showing papers on "Surface roughness published in 2017"

Influences of processing parameters on surface roughness of Hastelloy X produced by selective laser melting

Abstract: Selective laser melting (SLM) technology is a layer-wise powder-based additive manufacturing method capable of building 3D components from their CAD models. This approach offers enormous benefits for generating objects with geometrical complexity. However, due to the layer-wise nature of the process, surface roughness is formed between layers, thus influenced by layer thickness and other processing parameters. In this study, systematic research has been carried out to study the influence of processing parameters on surface roughness in Hastelloy X alloy. All samples were manufactured using an EOSINT M 280 machine. Laser power, scan speed, layer thickness and sloping angle of a surface were systematically varied to understand their effects on surface roughness. The arithmetic average roughness, Ra, was measured using a surface roughness tester, and optimum conditions for achieving the lowest roughness for both up-skin surfaces and down-skin surfaces have been obtained. The formation mechanism for the roughness on these two types of surfaces has been studied. Computer simulation was also used to understand thermal profiles at those two surfaces and their resultant influence on surface roughness. The simulated result has been found to be consistent with the measured result. Contour scan and skywriting scan strategies were found to be helpful for reducing the surface roughness.

Surface modification of epoxy using an atmospheric pressure dielectric barrier discharge to accelerate surface charge dissipation

Abstract: In this paper, an atmospheric-pressure dielectric barrier discharge is used to modify the surface of the epoxy material and enhance the dissipation of surface charge to reduce the accumulation of surface charge. In the experiments, atmospheric-pressure air dielectric barrier discharge is driven by a microsecond pulse generator. Surface properties of epoxy before and after the plasma treatment are characterized by water contact angle, surface potential, and surface/volume conductivity measurements. Atomic force microscope and X-ray photoelectron spectroscopy are used to investigate the changes of the morphology and the chemical composition of the epoxy surface. Experimental results indicate that the surface of epoxy is etched by the plasma and the increase of the surface roughness enhances the surface insulation ability. The O radicals in plasma and the carbonyl groups formed on the surface make the surface charge trap shallower, change the epoxy surface composition then increase the surface conductivity and accelerate surface charge dissipation. When the epoxy is treated for an appropriate time, the epoxy surface insulation performance will be enhanced obviously and the surface charge dissipation will be accelerated.

3D-printing zirconia implants; a dream or a reality? An in-vitro study evaluating the dimensional accuracy, surface topography and mechanical properties of printed zirconia implant and discs

Abstract: Purpose The aim of this study was to evaluate the dimensional accuracy, surface topography of a custom designed, 3D-printed zirconia dental implant and the mechanical properties of printed zirconia discs. Materials and methods A custom designed implant was 3D-printed in zirconia using digital light processing technique (DLP). The dimensional accuracy was assessed using the digital-subtraction technique. The mechanical properties were evaluated using biaxial flexure strength test. Three different build angles were adopted to print the specimens for the mechanical test; 0°( V ertical), 45° ( O blique) and 90°(Horizontal) angles. The surface topography, crystallographic phase structure and surface roughness were evaluated using scanning electron microscopy analysis (SEM), X-ray diffractometer and confocal microscopy respectively. Results The printed implant was dimensionally accurate with a root mean square (RMSE) value of 0.1 mm. The Weibull analysis revealed a statistically significant higher characteristic strength (1006.6 MPa) of 0° printed specimens compared to the other two groups and no significant difference between 45° (892.2 MPa) and 90° (866.7 MPa) build angles. SEM analysis revealed cracks, micro-porosities and interconnected pores ranging in size from 196 nm to 3.3 µm. The mean Ra (arithmetic mean roughness) value of 1.59 µm (±0.41) and Rq (root mean squared roughness) value of 1.94 µm (±0.47) was found. A crystallographic phase of primarily tetragonal zirconia typical of sintered Yttria tetragonal stabilized zirconia (Y-TZP) was detected. Conclusions DLP prove to be efficient for printing customized zirconia dental implants with sufficient dimensional accuracy. The mechanical properties showed flexure strength close to those of conventionally produced ceramics. Optimization of the 3D-printing process parameters is still needed to improve the microstructure of the printed objects.

Optimization of surface roughness and cutting temperature in high-pressure coolant-assisted hard turning using Taguchi method

Abstract: In this article, the effects of material hardness and high-pressure coolant jet over dry machining are evaluated in respect of surface roughness and cutting temperature using Taguchi L36 orthogonal array. The experimental data was analyzed using empirical cumulative distribution function and box plot with respect to material hardness and machining environment. Afterward, optimization of the quality responses is performed using signal-to-noise ratio. As part of Taguchi optimization, the “smaller is better” was adopted as optimization principle; the design of experiment was used for parameters orientation, and the analysis of variance was used for determining the effects of control factors. For the present experimental studies, three types of hardened steels (40 HRC, 48 HRC, and 56 HRC) were turned by coated carbide insert at industrial speed–feed combinations under both dry and high-pressure coolant jet. Depth of cut, being a less significant parameter, was kept fixed. The high-pressure coolant jet was found successful in reducing cutting temperature, surface roughness, and tool wear. The statistical analysis showed that work material hardness is the most significant factor for both cutting temperature and surface roughness. However, for surface roughness, other variables exerted somewhat similar contribution, while in determining the cutting temperature, the environment demonstrated crucial role. The confirmation tests showed 15.85 and 0.28 % error in predicting surface roughness and cutting temperature, respectively.

The influence of surface texture and wettability on initial bacterial adhesion on titanium and zirconium oxide dental implants

Abstract: This study aims to investigate bacterial adhesion on different titanium and ceramic implant surfaces, to correlate these findings with surface roughness and surface hydrophobicity, and to define the predominant factor for bacterial adhesion for each material. Zirconia and titanium specimens with different surface textures and wettability (5.0 mm in diameter, 1.0 mm in height) were prepared. Surface roughness was measured by perthometer (R a ) and atomic force microscopy, and hydrophobicity according to contact angles by computerized image analysis. Bacterial suspensions of Streptococcus sanguinis and Staphylococcus epidermidis were incubated for 2 h at 37 °C with ten test specimens for each material group and quantified with fluorescence dye CytoX-Violet and an automated multi-detection reader. Variations in surface roughness (R a ) did not lead to any differences in adhering S. epidermidis, but higher R a resulted in increased S. sanguinis adhesion. In contrast, higher bacterial adhesion was observed on hydrophobic surfaces than on hydrophilic surfaces for S. epidermidis but not for S. sanguinis. The potential to adhere S. sanguinis was significantly higher on ceramic surfaces than on titanium surfaces; no such preference could be found for S. epidermidis. Both surface roughness and wettability may influence the adhesion properties of bacteria on biomaterials; in this context, the predominant factor is dependent on the bacterial species. Wettability was the predominant factor for S. epidermidis and surface texture for S. sanguinis. Zirconia did not show any lower bacterial colonization potential than titanium. Arithmetical mean roughness values R a (measured by stylus profilometer) are inadequate for describing surface roughness with regard to its potential influence on microbial adhesion.

Grinding performance of textured monolayer CBN wheels: Undeformed chip thickness nonuniformity modeling and ground surface topography prediction

Abstract: The ground surface roughness and topography are commonly used to characterize the surface finishing. In the application of textured monolayer CBN wheels, the nonuniformity of wheel topology will render a nonuniform undeformed chip thickness which greatly affects the ground surface. In order to predict the ground surface topography more accurately and efficiently, grinding experiment has been conducted in the current study, with measured grinding wheel topology. The measured surface topology of textured monolayer CBN wheels has been reconstructed by using the Johnson transformation and its inverse transformation. The influence of wheel topology evolution on the undeformed chip thickness nonuniformity has been determined with an improved model. It has been found the ground surface roughness is improved with a continuous reducing undeformed chip thickness nonuniformity. The percentage of active grains, the mean value and standard deviation of undeformed chip thickness have been found the main factors in determining the surface roughness. The reconstructed wheel surface topology has been used to predict the workpiece topography in different stages of the grinding process.

Experimental investigation on densification behavior and surface roughness of AlSi10Mg powders produced by selective laser melting

Abstract: Effects of laser energy density (LED) on densities and surface roughness of AlSi10Mg samples processed by selective laser melting were studied. The densification behaviors of the SLM manufactured AlSi10Mg samples at different LEDs were characterized by a solid densitometer, an industrial X-ray and CT detection system. A field emission scanning electron microscope, an automatic optical measuring system, and a surface profiler were used for measurements of surface roughness. The results show that relatively high density can be obtained with the point distance of 80–105 μm and the exposure time of 140–160 μs. The LED has an important influence on the surface morphology of the forming part, too high LED may lead to balling effect, while too low LED tends to produce defects, such as porosity and microcrack, and then affect surface roughness and porosities of the parts finally.

A Physical Surface Roughness Model and Its Applications

Abstract: This paper covers the essential aspects of modeling surface roughness for microwave applications based on underlying physics After a short summary of the relevant field theoretical fundamentals, surface roughness metrology and commonly used roughness parameters are described Existing models and their limitations are discussed before the recently proposed Gradient Model is introduced To this purpose, the modeling approach, the derivation from Maxwell’s equations, model predictions, and their experimental verification are shown Reasonable choices for effective material parameters reflecting the electromagnetic effects of surface roughness as well as a corresponding surface impedance concept are derived Both concepts allow for easy application of the Gradient Model with 3-D field solvers or analytical models The obtained simulation results illustrate roughness impact on loss and phase delay in typical transmission lines Comparison to measurement results up to 100 GHz shows that the Gradient Model accurately predicts these quantities for rough conductor surfaces As it is not limited to transmission lines only, it significantly improves the design process for arbitrary microwave applications with 3-D field solvers for this frequency range

Nanoengineering of Core–Shell Magnetic Mesoporous Microspheres with Tunable Surface Roughness

Abstract: Functional core–shell mesoporous microspheres with integrated functions, controlled structure, and surface properties and morphologies have received increasing attention due to their excellent physicochemical properties. Herein, core–shell magnetic mesoporous materials with cauliflower-like morphology and tunable surface roughness have been synthesized through a kinetics-controlled interface co-assembly and deposition of mesostructured nanocomposites on Fe3O4@RF microspheres (RF refers to resorcinol formaldehyde resin). The obtained microspheres, synthesized via this interface nanoengineering method, possess well-defined sandwich structure with a tunable rough morphology, uniform size (560–1000 nm), perpendicularly aligned mesopores (∼5.7 nm) in the outer shell, RF-protected magnetic responsive core, high surface area up to 382 m2/g, and large pore volume of 0.66 cm3/g. As a result of the unique surface features and magnetic properties, these microspheres exhibit excellent performance in stabilizing and o...

Ductile machining of single-crystal silicon for microlens arrays by ultraprecision diamond turning using a slow tool servo

Abstract: Microlens arrays of single-crystal silicon are required increasingly in advanced IR optics. In this study, we attempted to machine spherical concave microlens arrays on a single-crystal silicon wafer by slow tool servo diamond turning. The form error, surface topography, material phase transformation, and cutting force characteristics were investigated experimentally. It was found that brittle fracture occurred preferentially at one side (the exit side of tool feed) of the lens dimples when cutting direction is along and tool feed rate is high. Amorphous silicon phase was generated significantly at one side (the exit side of tool feed) of the dimples as tool feed rate increased. The peak values and the direction angles of cutting forces changed with tool feed rate, crystal orientation, and the cutting direction. Two kinds of tool wear, namely, micro chippings and flank wear were observed in different regions of the tool edge where undeformed chip thickness is different. Spherical microlens arrays with a form error of ~300 nmPV and surface roughness of ~6 nmSa were successfully fabricated.

Thermal analysis during turning of AZ31 magnesium alloy under dry and cryogenic conditions

Abstract: In this study, the effect of both cryogenic and dry machining of AZ31 magnesium alloy on temperature and surface roughness was examined. Cryogenic machining experiments were conducted by applying liquid nitrogen at the cutting zone. The cutting parameters (cutting speed, depth of cut, and feed rate) were varied, and their effect on the results was identified. It was found that the cryogenic machining was able to reduce the maximum temperature at the machined surface to about 60% as compared with dry machining. A finite element model was developed to predict the temperature distribution at the machined surface. The simulated results showed good agreement with the experimental data. After analyzing the temperature distribution, the model also suggested that the cryogenic-assisted machining removes heat at a faster rate as to that of the dry machining. An arithmetic model using the response surface method was also developed to predict the maximum temperature at the surface during cryogenic and dry machining. The analysis pointed out that the maximum temperature was greatly affected by the cutting speed followed by feed rate and depth of cut. Cryogenic machining leads to better surface finish with up to 56% reduction in surface roughness compared with dry machining.

Chemical vapor treatment of ABS parts built by FDM: Analysis of surface finish and mechanical strength

Abstract: The present study investigates the simultaneous effect of part building orientation (along the X, Y, and Z axis) and raster angle (0°, 30°, 60°, and 90°) on surface roughness, tensile strength, flexural strength, consumption of model, support material, and building time of acrylonitrile butadiene styrene (ABS) test specimens fabricated by fused deposition modeling (FDM) process. Mechanical properties and surface roughness show a strong anisotropic behavior for the parts. For parts built with the X or Y orientations and 30° or 60° raster angle, pulling of fiber and a small amount of necking along with tearing are observed, which are responsible for higher strength. Post-built treatment of the parts with cold vapors of dimethyl ketone resulted in an immense improvement in surface finish. Exposing the parts in cold vapors turns the surfaces to a soft/mushy-like state due to the weakening of the secondary bonds, and the minor flow of polymer layers fills the cavity region between the adjacent layers and helps in improving the surface finish after the treatment.

Effects of Defects, Surface Roughness and HIP on Fatigue Strength of Ti-6Al-4V manufactured by Additive Manufacturing

Abstract: The additive manufacturing (AM) is expected to be the promising manufacturing process for high strength or hard steels such as Ti-6Al-4V for the aerospace industry components having complex shapes. However, disadvantage or challenge of AM is presence of defects which are inevitably contained in the manufacturing process. This paper focuses on the effects of defects, surface roughness and Hot Isostatic Pressing (HIP) process on the fatigue strength of a Ti-6Al-4V manufactured by AM. The guide is presented for the fatigue design and development of high quality and high strength Ti-6Al-4V by AM processing based on the combination of the statistics of extremes on defects and the √area parameter model. Defects were mostly gas porosity and those made by lack of fusion. Many pores which were formed near surface were eliminated by HIP and eventually HIP improved fatigue strength drastically to the level of the ideal fatigue limit to be expected from the hardness. Surface roughness had strong detrimental influence on fatigue strength. The method for estimating the effective size √areaeffmax of irregularly shaped defects and interacting adjacent defects was proposed from the viewpoint of fracture mechanics. Although the statistics of extremes analysis is useful for the quality control of AM, the particular surface effect and interaction effect of adjacent defects must be carefully considered. The effective defect size for adjacent defects is much larger than a single defect. Since the orientations of defects in AM materials are random, a defect in contact with specimen surface has a higher influence (termed as the effective defect size √areaeff) than the real size of the defect from the viewpoint of fracture mechanics. Considering the volume and number of productions of components, the lower bound of the fatigue limit σwl based on √areaeffmax can be determined by the √area parameter model.

Influence of electrochemical oxidation of carbon fiber on the mechanical properties of carbon fiber/graphene oxide/epoxy composites

Abstract: In this paper, the results of the surface modification of carbon fiber (CF) by electrochemical oxidation coupled with the electrophoretic deposition technique are presented. Graphene oxide (GO) was deposited on the electrochemically oxidized CF surface to improve the mechanical performance of carbon fiber-reinforced epoxy composites. The surface roughness and wettability increased after the electrochemical oxidation treatment of CF by the electrophoretic deposition technique, which was shown to be a feasible method. The results showed that a uniform distribution of GO coating was constructed and that GO was firmly coated on the CF surface through covalent attachments. In addition, the results of the mechanical properties tests showed that the interlaminar shear strength and compressive strength of the composites increased by 59.4% and 12.8%, respectively. The presented continuous fabrication process, which did not involve long processing times or complex chemical reactions, offers a potential industry compatible method for preparing multiscale GO/CF reinforcements.

Universal emulsion stabilization from the arrested adsorption of rough particles at liquid-liquid interfaces.

Abstract: Surface heterogeneities, including roughness, significantly affect the adsorption, motion and interactions of particles at fluid interfaces. However, a systematic experimental study, linking surface roughness to particle wettability at a microscopic level, is currently missing. Here we synthesize a library of all-silica microparticles with uniform surface chemistry, but tuneable surface roughness and study their spontaneous adsorption at oil-water interfaces. We demonstrate that surface roughness strongly pins the particles' contact lines and arrests their adsorption in long-lived metastable positions, and we directly measure the roughness-induced interface deformations around isolated particles. Pinning imparts tremendous contact angle hysteresis, which can practically invert the particle wettability for sufficient roughness, irrespective of their chemical nature. As a unique consequence, the same rough particles stabilize both water-in-oil and oil-in-water emulsions depending on the phase they are initially dispersed in. These results both shed light on fundamental phenomena concerning particle adsorption at fluid interfaces and indicate future design rules for particle-based emulsifiers.