Tip Wear Research Articles

Monitoring tip-based nanomachining process by time series analysis using support vector machine

In this paper, time-series data analysis and pattern recognition using a multi-class support vector machine (SVM) were studied to monitor the state changes of the AFM tip-based nanomachining process with respect to the machining performance and tip wear. Time series data (i.e. machining force from the process), which has transient, nonlinear, and non-stationary characteristics, was collected by a data acquisition system. Three status detection features including the maximum force, peak-to-peak force value, and the variance of the collected lateral machining force, were extracted to classify the state of the nanomachining process. Directed Acyclic Graph Support Vector Machines (DAGSVM) with a Gaussian Radial Basis Kernel Function (RBF Kernel) was constructed to identify the different process states. Using this multi-class SVM, the machining process and the tip wear can be classified into three regions, which are effective machining with a sharp tip, transition region and bad/no machining with severe tip wear. The experimental data showed that the accuracy of the SVM was over 94.73% in both binary and ternary classifications, which confirmed that the SVM-based pattern recognition technology via time series data could successfully monitor the tip wear and process performance for tip-based nanomachining process.

Effect of Pin Speed on Cerchar Abrasion Test Results

Abstract Abrasive properties of rocks affect tool selection and design of rock excavation machines as well as their productivity and operational costs. The Cerchar test is a simple and commonly used method of measuring rock abrasion. The current article focuses on the effect of pin sliding speed on the Cerchar abrasion index. For this study, Cerchar tests were conducted on seven mono-mineral rock samples with different pin speeds. The results showed that the variation of pin speed could affect the wear of the pin tip. However, the effect is not uniform and depends on the hardness of rocks and pins. The changes in the pin speed can change the pin penetration into the sample surface as well. Harder pins penetrate deeper into the sample surface. However, the difference between harder and softer pins decreases with an increase in pin speed. Pin tip penetration into the sample surface is not changed by its sliding speed in hard samples such as quartz. Accordingly, a new parameter was introduced: the ratio of the volume of rock removed by scratch to the volume of pin tip wear. This ratio is called scratch volume to wear ratio (SVWR) and is used to determine the optimum pin motion speed in various conditions. The optimum pin speed could also be used as a guide to determine the optimum speed of cutting tools on rock surfaces in practical conditions. A new abrasion classification system was introduced based on SVWR and showed that it could be used regardless of pin hardness.

Surface Study of Ge2Sb2Te5-Based Electrical Probe Memory for Educational Archival Storage

Surface roughness that is an inherent character of deposited films determines contact resistance at layer interfaces and thus may play a critical role in write and readout operations of phase-change electrical probe memory comprising multiple stacked layers. The surface roughness of different layered components was therefore simulated and their impact on resulting temperature, write/read current, and bit size was evaluated. It was revealed that using capping layer with larger root-mean-square and denser roughness significantly decreases the temperature and write/read current, and therefore forms a written bit embedded inside the active layer, while surface roughness of active layer, bottom electrode, and substrate have a negligible effect on electro-thermal characteristic and phase-transformation extent of the probe memory. To trigger optimum readout current and exempt from tip wear, probe tip was suggested to penetrate into the capping layer by 0.2 nm for the densest roughness of 3 nm root-mean-square.

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Development of cutting fluid from spent engine oil

The suitability of cutting fluids formulated from spent engine oil has been considered. In the formulation, recycled Spent Engine Oil was used as a base oil, liquid washing soap as emulsifier, phenol was applied as disinfectant while sulphur served as extreme pressure agent. Analysis and comparative assessment of the physical-chemical properties of samples of cutting fluid was conducted. From the performance analysis, the optimal sample has values such as flash point, 205.92 o C; pour point, -13.04 o C. Viscosity, at 40 o C gave an average value of 96.06cst. At 100 o C, have average value of 7.57cst. The sample has average pH value of 9.03. In corrosion grading, it rated non-corrosive. Furthermore, the effectiveness of the developed products was measured, among other parameters, through tool tip temperature, material removal rate and tool tip wear. Sample VII presented the least mean temperature of 32.5 o C. Sample III presented the minimum mean value of tool tip wear. Sample VII gave the best material removal rate of 5.68g/min. From the results obtained from the analysis, the developed spent engine oil based cutting fluid samples compared favourably with the conventional cutting oil, thus making them acceptable for machining application and can also be an economical choice for use in machining processes. Keywords: Spent engine oil, Cutting Fluid, Turning, Regeneration process, Comparative assessment

Graphene used as a lateral force microscopy calibration material in the low-load non-linear regime.

A lateral force microscopy (LFM) calibration technique utilizing a random low-profile surface is proposed that is successfully employed in the low-load non-linear frictional regime using a single layer of graphene on a supporting oxide substrate. This calibration at low loads and on low friction surfaces like graphene has the benefit of helping to limit the wear of the LFM tip during the calibration procedure. Moreover, the low-profiles of the calibration surface characteristic of these layered 2D materials, on standard polished oxide substrates, result in a nearly constant frictional, adhesive, and elastic response as the tip slides over the surface, making the determination of the calibration coefficient robust. Through a detailed calibration analysis that takes into account non-linear frictional response, it is found that the adhesion is best described by a nearly constant vertical orientation, rather than the more commonly encountered normally directed adhesion, as the single asperity passes over the low-profile graphene-coated oxide surface.

Fabrication of Sub-Micrometer-Sized MoS2 Thin-Film Transistor by Phase Mode AFM Lithography.

The phase mode atomic force microscopy (AFM) lithography and monolayer lift-off process are combined to fabricate electronics based on 2D materials (2DMs), which remove the need for pre-fabricating markers and increase the accuracy of the overlay and alignment. The promising phase mode of AFM lithography eliminates the drawbacks of the conventional force mode such as the over-cut, under-cut, debris effect, and severe tip wear. The planar size of MoS2 thin-film transistors is shrunken down to sub-micrometer by the proposed method, and the fabricated devices demonstrate n-type characteristics. It offers a more flexible and easier way to fabricate prototypes of sub-micrometer-sized 2DMs based devices, and gives the opportunity to explore the size effect on the performance of 2DMs devices.

Influence of chisel edge thinning on helical point micro-drilling performance

Chisel edge thinning can effectively improve the drilling performance of austenitic stainless steel. Four kinds of helical point micro-drills, each with a thinned chisel edge of a distinct length, are fabricated based on the mathematics models of the micro-drill by using a six-axis computer numerical control tool grinder. Micro-drilling experiments on 304 stainless steel are conducted. Drilling performance is evaluated according to the measured and observed micro-hole machining quality, chip morphology, thrust force, and tool wear of the micro-drill tip. With a decrease in the chisel edge length, the micro-holes drilled using thinned micro-drills have small entrance burrs, roundness errors, and regular shapes, which are attributed to an increase in self-centering capability. Owing to increased equivalent chip thickness and different directions of chip flow, micro-drills with thinned chisel edge can generate more small-size chips and improve chip breaking. In addition, the inner cutting edge with a positive rake angle replaces the chisel edge with a negative rake angle to cut the workpiece, significantly reducing the chip curl, thrust force, and tool wear of micro-drills. However, helical point micro-drills with critical chisel edge lengths by thinning exhibit less thrust force and tool wear than do helical point micro-drills with no chisel edge because of the increase in the uncut chip width of the micro-drill. Thus, with the selected parameter range, the optimal helical point micro-drill is the micro-drill with a specific chisel edge length by thinning to improve drilling performance.

Effects of AFM tip wear on frictional images of laser-patterned diamond-like nanocomposite films

Contact-mode atomic force microscopy (AFM) techniques (lateral force microscopy, force-distance curves) are applied to study the effects of femtosecond-laser ablation and micropatterning of diamond-like nanocomposite (DLN) films (a-C:H:Si:O films) on the friction behavior at the nano and microscale. A femtosecond laser (wavelength 515 nm, pulse duration 320 fs, pulse repetition rate 101 kHz) is used to fabricate line-like micropatterns (microgrooves) on the DLN films under ablation conditions with a scanning beam. Lateral force microscopy (LFM) studies of the laser-ablated microgrooves have revealed wearing-tip-induced nanofriction changes during AFM imaging with Si tip, characterized by much lower friction forces inside and around the microgrooves compared to the original surface (due to strong influence of the capillary forces on friction forces with increasing radius of the worn tip). Using wear-resistant diamond-coated tips, the friction contrast is found to reverse to higher friction in the laser-modified regions. The increased nanoscale roughness of the ablated DLN surface and redeposited surface layers is considered responsible for the observed nanofriction behavior of both the Si and diamond-coated tips.

Metrological large range magnetic force microscopy.

A new metrological large range magnetic force microscope (Met. LR-MFM) has been developed. In its design, the scanner motion is measured by using three laser interferometers along the x, y, and z axes. Thus, the scanner position and the lift height of the MFM can be accurately and traceably determined with subnanometer accuracy, allowing accurate and traceable MFM measurements. The Met. LR-MFM has a measurement range of 25 mm × 25 mm × 5 mm, larger than conventional MFMs by almost three orders of magnitude. It is capable of measuring samples from the nanoscale to the macroscale, and thus, it has the potential to bridge different magnetic field measurement tools having different spatially resolved scales. Three different measurement strategies referred to as Topo&MFM, MFMXY, and MFMZ have been developed. The Topo&MFM is designed for measuring topography and MFM phase images, similar to conventional MFMs. The MFMXY differs from the Topo&MFM as it does not measure the topography profile of surfaces at the second and successive lines, thus reducing tip wear and saving measurement time. The MFMZ allows the imaging of the stray field in the xz- or yz-planes. A number of measurement examples on a multilayered thin film reference sample made of [Co(0.4 nm)/Pt(0.9 nm)]100 and on a patterned magnetic multilayer [Co(0.4 nm)/Pt(0.9 nm)]10 with stripes with a 9.9 μm line width and 20 μm periodicity are demonstrated, indicating excellent measurement performance.

Molecular dynamics and experimental study on comparison between static and dynamic ploughing lithography of single crystal copper

Dynamic ploughing lithography based on atomic force microscope (AFM) is a promising technique for fabrication of nano structures and devices. This study investigates the material removal mechanism and surface generation in dynamic ploughing of single crystal copper by molecular dynamics (MD) simulations in addition to the experimental tests, and compares it with that of static ploughing lithography. It is found that the material removal in dynamic ploughing is mainly due to downwards and sidewards slipping of workpiece material on the {1 1 1} slip planes and the subsequent elastic recovery, whereas forwards and sidewards slipping account for the material removal in static ploughing. As a result, there is little chip formation in dynamic ploughing, while significant chip formation is observed for static ploughing in both simulations and experiments. In addition, this results in smaller groove depth and width for dynamic ploughing, allowing fabrication of nanostructures with smaller features. The slipping processes in both static and dynamic ploughing can be corresponded with the periodical variations of machining forces. The average machining force in dynamic ploughing is significantly smaller than that in static ploughing. This indicates the possibility of reducing the wear of AFM tip by employing dynamic ploughing lithography, since the tip wear is greatly influenced by the magnitude of machining force. These results reveal the mechanism of material removal and surface generation in dynamic ploughing lithography, which can be of useful reference for its practical application in nanomanufacturing.

Experimental studies on helical milling process to improve hole quality for the Superalloy (MSRR7197)

Conventional drilling is widely adopted to manufacture holes in difficult-to-cut materials such as superalloys. However, as a newer hole processing technology, helical milling possesses several advantages including low cutting forces, reduced tool wear, and improved hole quality. In this study, different hole-making processes like conventional drilling and helical milling were conducted on the superalloy (MSRR7197). Combining the deformation mechanism of the hole wall material, the influence of both hole-making processes on the processing quality of the MSRR7197 were investigated. The experimental results demonstrate that the axial force for the helical milling is about 1/10 of that for the drilling. Compared with drilling, the flank wear, rake wear, and wear of tool tip for the helical milling are smaller. The hole wall quality such as surface morphology and roughness of helical milling is better than that of the drilling. Last but not least, the helical milling can get a higher machining accuracy such as circularity and aperture. Hence, helical milling remains the favorable and alternative to conventional drilling.

A position-controllable external stage for critical dimension measurements via low-noise atomic force microscopy

An independent external stage for low noise atomic force microscope has been developed for mid-range movements so that it aids in measurements of critical dimensions through the low-noise atomic force microscope. The maximum travel length of the external four-axes stage is 10 mm. For image scanning of the specific target region, the sample needs to be moved through two steps: coarse positioning with the external stage and fine positioning with PI XY piezo scanner. Prior to the CD measurements, we confirmed that the position errors caused by the external stage and tip stage were negligible through the reproducibility experiments. In this study, custom-designed software stored the initial position of the probe and then moved it precisely to the sample location to be measured. Subsequently, the sidewalls of an improved vertical parallel structure were measured and the repeatability and reproducibility of the CD measurements were estimated using a CDR30-EBD tip. Finally, we confirmed that tip wear could be minimized by measuring TGX1 samples with undercut structures.

Friction force microscopy of tribochemistry and interfacial ageing for the SiO x /Si/Au system.

Friction force microscopy was performed with oxidized or gold-coated silicon tips sliding on Au(111) or oxidized Si(100) surfaces in ultrahigh vacuum. We measured very low friction forces compared to adhesion forces and found a modulation of lateral forces reflecting the atomic structure of the surfaces. Holding the force-microscopy tip stationary for some time did not lead to an increase in static friction, i.e., no contact ageing was observed for these pairs of tip and surface. Passivating layers from tip or surface were removed in order to allow for contact ageing through the development of chemical bonds in the static contact. After removal of the passivating layers, tribochemical reactions resulted in strong friction forces and tip wear. Friction, wear, and the re-passivation by oxides are discussed based on results for the temporal development of friction forces, on images of the scanned area after friction force microscopy experiments, and on electron microscopy of the tips.

Modelling and experimental study of nanoscratching process on PMMA thin-film using AFM tip-based nanomachining approach

This paper proposes a nanogroove machined depth prediction model for the atomic force microscopy (AFM) tip-based scratching method on the polymer thin-film. This model is used to predict the normal load required to just cut through the polymer thin-film without contacting the silicon substrate excessively to reduce the tip wear. In this proposed theoretical model, the AFM tip is assumed as a rectangular pyramid with a spherical apex. The elastic recovery, material pile-up, adhesive friction coefficient and mounted angle of the tip on the AFM head are considered in the developed model. Nanogrooves are scratched on a poly(methyl methacrylate) (PMMA) thin film by a silicon AFM tip. Results show that the bulk volume of the material pile–up can be enlarged after scratching with a relatively sharp tip. The equivalent height value of the material pile-up is thus introduced into the theoretical model, and the relationship between the equivalent height values of the material pile-up and the radius of the tip is analyzed in detail. Based on the proposed model and the experimental results, the effect of the radius of the AFM tip on the flow stress and adhesive friction coefficient is studied. Finally, several nanogrooves when the tip just cutting through the polymer thin-film are achieved on the polymer thin-films with different thicknesses using the tips with various radii.

On-line Tool Wear Detection on DCMT070204 Carbide Tool Tip Based on Noise Cutting Audio Signal using Artificial Neural Network

This study develops an on-line detection system to predict the wear of DCMT070204 tool tip during the cutting process of the workpiece. The machine used in this research is CNC ProTurn 9000 to cut ST42 steel cylinder. The audio signal has been captured using the microphone placed in the tool post and recorded in Matlab. The signal is recorded at the sampling rate of 44.1 kHz, and the sampling size of 1024. The recorded signal is 110 data derived from the audio signal while cutting using a normal chisel and a worn chisel. And then perform signal feature extraction in the frequency domain using Fast Fourier Transform. Feature selection is done based on correlation analysis. And tool wear classification was performed using artificial neural networks with 33 input features selected. This artificial neural network is trained with back propagation method. Classification performance testing yields an accuracy of 74%.

Surface Machining after Deposition of Wear Resistant Hard Coats by High Velocity Oxygen Fuel Technology

The article deals with some aspects related to the machining of surfaces that have been deposited by wear-resistant hard coats using HVOF (high velocity oxygen fuel) technology. HVOF coating is a thermal spray process used to improve a component's surface properties, thus extending equipment life by significantly increasing errosion and wear resistance, along with corrosion protection. For a purpose of this research, the chromium-cobalt alloy - Stellite 6 was used as a sprayed material. Considering that the parts made of stellites are widely used in various industries and very popular in specific applications, it is a big drawback that adequate machining processes for stellites have not yet been developed other than the costly and time-consuming technique of grinding. However, in this research, an attempt has been made to reveal the optimal machining parameters for a lower value of surface roughness for the purpose of successful machining of Stellite 6 using inserts with various radii of cutting edge. Authors have evaluated the quality of machined surface not only by means of Abbott curve, but they have also observed the dependency of arithmetical mean roughness value on both cutting-edge radius and feed. The analyses of cutting tips wear at changeable inserts have shown that typical wear appears in the form of a notch.

Suppressing Nanoscale Wear by Graphene/Graphene Interfacial Contact Architecture: A Molecular Dynamics Study.

Nanoscale wear is one of the key factors hindering the performance and lifetime of micro- and nanosystems, such as the scanning tip wear in atomic force microscopy (AFM), the head-disk interface in magnetic storage system, and the moving components in micro- or nanoelectromechanical systems (MEMS/NEMS). Here, we propose to construct the graphene/graphene interfacial architecture to suppress the nanoscale wear. Molecular dynamics simulations show that the atomic roughness of the sliding surfaces with either stepped or amorphous structure can lead to strong inhomogeneity of the local contact pressure distribution. By coating graphene on both sides of the frictional surfaces, the local contact pressure fluctuations due to the atomic roughness are suppressed. Moreover, this trend is more evident with the increasing layer number of the graphene coating. Furthermore, the nanoscratching simulation suggests that the rupture of graphene is driven by the inhomogeneous pressure distribution-induced lateral atomic interlocking between the rough tip and substrate and the consequent in-plane lattice deformation and C-C bond breaking during sliding. By coating graphene on the rough amorphous carbon tip, the critical normal load for wear failure of graphene is significantly increased, due to the weakening effect of the atomic interlocking by improving the contact conditions with atomically smooth graphene/graphene sliding interface. This investigation reveals a strategy for reducing nanowear by suppressing the local contact pressure fluctuations via graphene/graphene sliding interface architecture, which provides a theoretical guidance for designing wear-resistant coatings for the longevity of AFM probes and MEMS/NEMS systems.

Tribochemical Wear of Diamond-Like Carbon-Coated Atomic Force Microscope Tips.

Nanoscale wear is a critical issue that limits the performance of tip-based nanomanufacturing and nanometrology processes based on atomic force microscopy (AFM). Yet, a full scientific understanding of nanoscale wear processes remains in its infancy. It is therefore important to quantitatively understand the wear behavior of AFM tips. Tip wear is complex to understand due to adhesive forces and contact stresses that change substantially as the contact geometry evolves due to wear. Here, we present systematic characterization of the wear of commercial Si AFM tips coated with thin diamond-like carbon (DLC) coatings. Wear of DLC was measured as a function of external loading and sliding distance. Transmission electron microscopy imaging, AFM-based adhesion measurements, and tip geometry estimation via inverse imaging were used to assess nanoscale wear and the contact conditions over the course of the wear tests. Gradual wear of DLC with sliding was observed in the experiments, and the tips evolved from initial paraboloidal shapes to flattened geometries. The wear rate is observed to increase with the average contact stress, but does not follow the classical wear law of Archard. A wear model based on the transition state theory, which gives an Arrhenius relationship between wear rate and normal stress, fits the experimental data well for low mean contact stresses (<0.3 GPa), yet it fails to describe the wear at higher stresses. The wear behavior over the full range of stresses is well described by a recently proposed multibond wear model that exhibits a change from Archard-like behavior at high stresses to a transition state theory description at lower stresses.

Contact atomic force microscopy using piezoresistive cantilevers in load force modulation mode

Scanning probe microscopy (SPM) encompasses several techniques for imaging of the physical and chemical material properties at nanoscale. The scanning process is based on the detection of the deflection of the cantilever, which is caused by near field interactions, while the tip runs over the sample's surface. The variety of deflection detection methods including optical, piezoresistive, piezoelectric technologies has been developed and applied depending on the measurement mode and measurement environment. There are many advantages (compactness, vacuum compatibility, etc.) of the piezoresistive detection method, which makes it very attractive for almost all SPM experiments. Due to the technological limitations the stiffness of the piezoresistive beams is usually higher than the stiffness of the cantilever detected using optical methods. This is the basic constraint for the application of the piezoresistive beams in contact mode (CM) atomic force microscopy (AFM) investigations performed at low load forces (usually less than 20 nN). Drift of the deflection signal, which is related to thermal fluctuations of the measurement setup, causes that the microscope controller compensates the fluctuations instead of compensating the strength of tip-surface interactions. Therefore, it is quite difficult to keep near field interaction precisely at the setpoint level during the whole scanning process. This can lead to either damage of the cantilever's tip and material surface or loosing the contact with the investigated sample and making the measurement unreliable.For these reasons, load force modulation (LoFM) scanning mode, in which the interaction at the tip is precisely controlled at every point of the sample surface, is proposed to enable precise AFM surface investigations using the piezoresistive cantilevers. In this article we describe the developed measurement algorithm as well as proposed and introduced hardware and software solutions. The results of the experiments confirm strong reduction of the AFM entire setup drift. The results demonstrating contactless tip lateral movements are presented. It is common knowledge that such a scanning reduces tip wear.