Removal Mode Research Articles

Fixed and Capture Level Reduction operating modes for carbon dioxide removal in a Natural Gas Combined Cycle power plant

The characteristics (flowrate, composition, CO2 partial pressure) of the flue gas exiting a Natural Gas Combined Cycle (NGCC) power plant are different from the ones of coal-fired units on which analyses in the literature are usually focusing, therefore for application of Carbon Capture and Storage (CCS) to the removal of CO2 from this type of stream a detailed study is needed. This work applies the method of flexible operation aimed at reducing the economic disadvantages of a CCS plant, and considers the Capture Level Reduction (CLR) mode for the carbon dioxide removal section of a NGCC power plant located in Italy, of which type the number of units is constantly increasing. The CLR mode consists in emitting part of the carbon dioxide at given times during the day by bypassing part of the rich solvent and thus reducing the energy requirements for regeneration of the solvent and compression of the removed CO2. For the study a proprietary code developed by the GASP group of Politecnico di Milano, based on real energy prices and demand and taking into account different values of possible carbon taxes, has been employed. The results show that the best load to the absorption section strongly depends on the value of the considered carbon tax, in addition to the time-dependent request and price of electricity. A carbon tax of 5 €/tonCO2 generally does not favor the operation of the CCS system, while higher values exert a more significant influence on the revenues. Carbon taxes of 115 €/tonCO2 for the winter period and of 145 €/tonCO2 for the summer period make the operation of the CCS section more economically advantageous than emitting carbon dioxide to the atmosphere. In any case, also when applied to CO2 removal in power plants fed by natural gas, the CLR mode results more advantageous than fixed operation, thus making power plants companies increasing their efforts in reducing greenhouse gas emissions.

Mixed dropwise-filmwise condensation heat transfer on biphilic surface

Condensation heat transfer on biphilic surface is investigated. The surface periodically populates hydrophobic stripes each having a coating layer thickness δp and a width WDWC, and hydrophilic stripes each having a width WFWC. The proposed model includes dropwise condensation on hydrophobic stripe, filmwise condensation on hydrophilic stripe, and droplet detachment radius rmax criterion for heat-mass coupling between the two wettabilities regions. The rmax is the minimum of detachment radii determined by droplet removal modes of double-sides-suction DSS, one-side-suction OSS and sliding, where DSS is a special case of OSS for droplet located at hydrophobic stripe centerline. Simulation results matched the measured heat transfer data well. Optimal width of hydrophobic stripe WDWCo is found to be dominated by δp and WFWC, but other parameters weakly influence WDWCo. Interfaced by a δp−WFWC transition curve, a heat transfer regime map is presented to contain Regime I for possible heat transfer enhancement and Regime II for heat transfer deterioration. Regime I enhances heat transfer if WDWC approaches WDWCo, but may deteriorate heat transfer if WDWC deviates WDWCo too much. The maximum heat transfer enhancement ratio is 1.67 compared with purely hydrophobic surface. Regime II always deteriorates heat transfer. Our work provides a general guideline to design biphilic surface for performance improvement.

Grindability of plasma sprayed thermal barrier coating using super abrasive wheel

ABSTRACTThermal Barrier Coatings (TBC) are commonly used on exhaust muffle of engines and gas turbine blades to protect the component from generated heat and increase the operational temperature. Machining of ceramic coatings is comparatively more challenging than sintered ceramics. In this study, a commonly used TBC coating, namely yttria stabilised zirconia coating was subjected to surface grinding using a mono layer nickel bonded diamond wheel. The grinding forces and specific grinding energy were studied experimentally. The normal force obtained experimentally was compared with a force model and the correlation was studied. The forces obtained were significantly low as compared to sintered YSZ and a close relationship was observed with the existing model. In addition, the specific grinding energy was also found to be minimum. This indicates that most of the energy is expended in ploughing, micro-brittle fracture and rubbing. This was ascertained through scanning electron images of the ground surface and the fragmented chips. X-Ray diffraction images of the ground sample and as-sprayed sample showed an insignificant change in material structure owing to the material removal mechanism. The surface roughness of the ground specimen was reduced significantly. The fracture toughness obtained using the Evans and Charles method was used to calculate the critical load for crack initiation and a significantly low value was observed for ductile to brittle transition. SEM images of ground chips of YSZ sample showed fragmented and broken chips indicating that the primary mode of material removal is owing to micro-brittle fracture.

Ductile-brittle transition detection in scratching of single crystal silicon using charged particle emissions

During machining of single-crystal silicon, material removal involves two modes ductile shear-based removal and brittle fracture-based removal. Ductile shear-based chip removal occurs when fracture is suppressed due to local stress conditions along with reduced chances of defect involvement and is desirable for achieving better surface integrity of the machined silicon wafer. In this work, we use charged particle emissions to identify mode of material removal (ductile or brittle) during scratching of a silicon wafer. Scratching tests were performed using a pin-on-disc tribometer setup with a conical diamond tip indenter, in which the wafer was held at an inclined position to achieve a varying-depth tapered scratch. The varying-depth scratch test was performed in such a manner that both ductile-to-brittle and brittle-to-ductile modes occur in a single scratch test. The charged particles emitted during the material deformation were collected using a Faraday plate mounted in the vicinity of the indenter and the intensity of the charged particles were measured using a sensitive femto/picoammeter. The scratch depth was measured using a 3D surface profiler and the mode of fracture was identified by examining crack density per unit length in a scanning electron microscope. These results were then correlated with the emission intensity signals. From the experimental results, a positive current intensity was observed for ductile mode of scratching and highly varying current intensity signal is observed during brittle mode of scratching. The results obtained were consistent over time and exhibited good repeatability. The present work indicates suitability of employing charge emission signals to detect mode of material removal during scratching of silicon. This work can be field-tested by conducting diamond turning experiments of silicon in real-time machining environment further testing the scope of use of charged particle emission to monitor real-time machining process.

Particle removal is explored by the motion of individual particles based on laser-induced plasma shock wave

Removing particles from the device is a challenging in the micro-field. The traditional method is easy to often result in device damage. Therefore, developing an alternative method to resolve the shortcomings is necessary for micro-contamination removal. In this study, a non-contact method is presented, which is based on the shock wave for removal of particles from substrate surface. A series of experiments of particle removal and simulation mode of shock wave characteristics was performed to investigate the removal mechanisms, particle removal modes, and the influence of relevant parameters (laser energy, particle properties, and gap distance d) on particle removal. By analyzing the experimental and simulation results, the particle removal mechanism is dominated by the shock wave ejection mechanism, which is owned to its strong pressure. The particle removal velocity is closely related to the gap distance d and the laser energy, and the maximum velocity was approximately 0.0138Mach for gap distance d is ∼1.45 mm at the energy of 9.32 mJ. Moreover, it is considered that the detachment will be obtained by the combination of lifting, rolling and sliding modes. Our basic research contributes to a better understanding of the particle removal.

Theoretical and experimental analysis of material removal and surface generation in novel fixed abrasive lapping of optical surface

Abstract Fixed abrasive machining, which overcomes the lack of determinacy and efficiency of current loose abrasive polishing or lapping processes, is an alternative technology for fabricating large-aperture aspheric surfaces with high finishing efficiency and high-quality surface finish. A novel fixed abrasive lapping (NFAL) tool, which combines computer-controlled optical surfacing and conventional fixed abrasive lapping process, is introduced in this study to produce off-axis aspheric surfaces efficiently while surface state is controlled and subsurface damage (SSD) is avoided. The removal mechanism analysis shows that fused quartz glass is primarily removed in ductile regime and the SSD depth is 14.7 μm when the tool load is 25 N. The material removal volume is linear with the machining time under the ductile removal mode. The material removal and surface generation models are developed on the basis of the calculation of the spatial distribution of abrasive particles, the pad–particle–workpiece interactions, the single-particle abrasion mechanism, and the linearly cumulative removal of surface generation in the NFAL process. The models are verified through a series of spot and surface lapping experiments. Results show that the theoretical model can be successfully used to predict and optimize the NFAL process. The spot lapping experiments indicate that the material removal volume is linear with the rotation speed, and the maximum depth is limited to the specific value that depends on the stiffness of lapping tool. The surface roughness Ra and Rz values of the measured and simulated surface data decrease with the increase in feed rate and increase with the increase in raster spacing. The power spectral density analysis indicates that high feed rate can distinctly improve the high-frequency errors, and the selection of the raster spacing can principally affect the low-frequency and middle-spatial frequency errors.

A cutting force prediction model for rotary ultrasonic side grinding of CFRP composites considering coexistence of brittleness and ductility

Cutting force has a great effect on the machining surface/subsurface damage. The prediction model of cutting force is necessary to optimize input variables. During rotary ultrasonic side grinding (RUSG), the indentation depth of a single abrasive grain increases (up milling) from 0 to maximum or decreases (down milling) from maximum to 0 with the motion of abrasive grains. Therefore, the ductile removal mode and brittle fracture removal mode coexist. In this research, a mechanistic cutting force model in RUSG of carbon fiber–reinforced polymer (CFRP) composites, considering both brittleness and ductility, has been developed for the first time. The ductile-brittle ratio K has been put forward and obtained through experiments. The cutting force perpendicular to feed direction has been calculated by integration method from the point of force analysis. The results showed that K increases with the rise of spindle speed or the decrease of feed rate and cutting width. The cutting force behaves oppositely with respect to K. Finally, orthogonal experiments have been conducted to verify the cutting force model and the results show good consistency between theoretical cutting force and measured cutting force. The developed model is capable to predict the cutting force in RUSG of CFRP composites and provides a support for optimizing the process.

Experiment and theoretical prediction for surface roughness of PV polycrystalline silicon wafer in electroplated diamond wire sawing

The electroplated diamond wire sawing technology is the mainstream processing method of cutting PV polycrystalline silicon ingots. Surface roughness is one of the most significant evaluation indexes for wafers surface quality, and has an important influence on subsequent processes such as surface texturization, screen printing, subsurface damage layer prediction and so on. In this paper, a mathematical model, considering the random distribution characteristic of abrasive parameters and its location on saw wire surface, was developed. The influence of brittle and ductile material removal modes on the wafers surface morphology was taken into account, the model can obtain the cutting depths of abrasives by discretizing the cutting groove and wire profile during the sawing process, and then the material removal modes of abrasives are judged by cutting depth. According to the calculation nodes closest to the sawn surface, the wafer surface profile and roughness along the feed speed direction were calculated. The correctness and reasonability of the model were verified by experiments. Then, the model was used to predict the variation trend of surface roughness under different process parameters. The results showed that the relationships between surface roughness and feed speed Vf, wire speed Vs and their ratio Vf /Vs satisfied power functions. Finally, the calculation result of surface roughness was used to generate a 3D surface morphology of wafer.

Effects of pressure and slurry on removal mechanism during the chemical mechanical polishing of quartz glass using ReaxFF MD

Reactive force field molecular dynamics (ReaxFF MD) simulation was employed to study the interfacial interaction during the Chemical mechanical polishing (CMP) process of quartz glass. Results indicated that dissociation and adsorption of H2O occurred on the quartz glass surface in pure H2O, and the dissociation of H2O could hydroxylate quartz glass surface to form SiOH bonds. In addition, it was found that the surface hydroxylation degree is higher in aqueous H2O2. The formation of SiOSi bonds plays a key role in the CMP process. Dehydrogenation and dehydroxylation are two ways to form interface bridge bonds. The interface bridge bonds between abrasive and substrate could transmit mechanical force with the movement of abrasive. Interface pressure affects the number and forms of atoms removed. With the increment of pressure, the removal form gradually changes from single removal mode to chain removal mode. The effect of aqueous H2O2 on the removal process was also studied by adding different amount of OH group on the quartz glass surface. This work helps us reveal the removal mechanism in the CMP process of quartz glass from an atomic perspective.

Study on influence of grinding depth and grain shape on grinding damage of K9 glass by SPH simulation

This work use the SPH method to study the relationship between grinding depth and grinding force of K9 glass in ultra-precision grinding, and the effect of grain shape on material removal. The relationship between the force and the depth in the stable scratching stage is FR = 0.55078ap1.15356, which provides a basis for controlling the grinding depth by force. The material removal modes at different grinding depths were obtained, that is, plastic removal occurs below 0.2 μm, brittle transition occurs between 0.2 and 0.4 μm, and brittle removal occurs at more than 0.5 μm. It is found that the cutting resultant force of sharp grains is smaller and the normal force is smaller than the tangential force. By analyzing the plastic deformation depth and residual stress depth, it is found that the material removal mode with small deformation and little removal has the lowest cutting force fluctuation and the highest grinding quality. It provides a reference for the choosing of grain shape in rough grinding and ultra-precision grinding. The correctness and reliability of the simulation results were verified by the comparison of the simulation findings with the results obtained from varied-depth scratching experiments and the multi-shape indenter scratch experiments.

Study on the three-dimensional topography of the machined surface in laser-assisted machining of Si3N4 ceramics under different material removal modes

The surface topography directly impacts the component performance. However, the two-dimensional (2D) surface roughness parameters in the previous studies have been inefficient and inadequate to describe a surface. In this study, with the help of a confocal laser scanning microscope and a scanning electron microscope, the three-dimensional (3D) topography of a machined Si3N4 surface using laser assisted machining (LAM) under different material removal modes was comprehensively characterised and compared using the standard ISO 25178–2:2012 surface texture parameters. The relationship between the 3D topography parameters and service properties was analysed. LAM is effective for machining ceramics with a high hardness and high brittleness. Different material removal modes were obtained by changing the power of the laser and were inferred by comprehensively analysing the macroscopic and microscopic topography of the chips, tool wear, and machined surface. In ductile material removal mode, the surfaces are anisotropic and cutting marks are clearly visible. Decreasing the power of the laser increases the value of the height and functions parameters. Decreasing the power of the laser also decreases the value of the hybrid and feature parameters.

Ductility-oriented high-speed grinding of silicon carbide and process design for quality and damage control with higher efficiency

Grinding of brittle materials is always a removal process of coexisting ductile and brittle removal modes. Ductility-oriented grinding has been regarded as a precision machining pursuit for grinding quality and efficiency. This paper is devoted to investigating ductility-oriented grinding mechanism and process design for quality promotion with a higher efficiency in high-speed grinding of silicon carbide ceramics. The Rayleigh chip thickness model and critical chip thickness model are given to quantitatively calculate the ductile removal proportion. Moreover, the grinding forces and specific removal energy are discussed to reflect the high-speed grinding removal mode. The results show that the increase of wheel speed or decrease of maximum chip thickness could enhance the percentage to a more ductile-oriented removal mode, which will cause a smaller surface roughness with fewer fracture cracks and more plastic removal stripes. Finally, the grinding process conditions for surface roughness below 0.2 μm and ductile removal area higher than 50% are suggested to obtain better surface quality at higher ductile removal and material removal rates.

Mechanism of Unstable Material Removal Modes in Micro Cutting of Silicon Carbide.

This study conducts large-scale molecular dynamics (MD) simulations of micro cutting of single crystal 6H silicon carbide (SiC) with up to 19 million atoms to investigate the mechanism of unstable material removal modes within the transitional range of undeformed chip thickness in which either brittle or ductile mode of cutting might occur. Under this transitional range, cracks are always formed in the cutting zone, but the stress states cannot guarantee their propagation. The cutting mode is brittle when the cracks can propagate and otherwise ductile mode cutting happens. Plunge cutting experiment is conducted to produce a taper groove on a 6H SiC wafer. There is a transitional zone between the brittle-cut and ductile-cut regions, which has a mostly smooth surface with a few brittle craters on it. This study contributes to the understanding of the detailed process of brittle-ductile cutting mode transition (BDCMT) as it shows that a transitional range can occur even for single crystals without internal defects and provides guidance for the determination of tcritical from taper grooves made by various techniques, e.g., to adopt larger tcritical around the end of the transitional range to increase machining efficiency for grinding or turning as long as the cracks do not extend below the machined surface.

Mechanism of material removal by fixed abrasive lapping of fused quartz glass

In this paper, a novel fixed-abrasive lapping process to finish off-axis aspheric surfaces efficiently is proposed. The lapping mechanism of fused quartz glass was evaluated using the novel fixed-abrasive pad tool. The applied load and not the rotation speed and feed rate is the key factor affecting the material removal mode of fused quartz glass in the fixed-abrasive lapping process. Analysis of surface characteristic and subsurface damage indicates that lower applied load produces more ductile mode removal and that the removal on fused quartz glass can be changed from brittle fracture to ductile regime if the applied load is less than 25 N. The material removal rate (MMR) increases as the applied load is increased, which further increases the surface roughness. In addition, the MMR increases and the surface roughness decreases as the rotation speed is increased or the feed rate is deceased. A theoretical model for predicting the maximum SSD depth of the specimens during lapping was developed. The model can predict well that the maximum SSD depth increases with increasing applied load.

Characterization of electroplated diamond wires and the resulting workpiece quality in silicon sawing

Abstract The aim of this research is to introduce a fast characterization method for diamond wires and the resultant silicon workpiece surface quality at high wire cutting speeds. The work is presented in two parts. Initially, four electroplated diamond wires with varying properties are characterized with the proprietary wire analysis algorithm and experimentally investigated at wire speeds up to 75 m/s. Following, the proprietary surface analysis algorithm which evaluates the brittle and ductile material removal characteristics of silicon workpiece surfaces is introduced and experimentally validated. Influence of the wire speed and feed rate on the material removal regime, surface roughness and process forces are studied on the Wire Wrapped Grinding Wheel setup, a novel-design experiment test rig designed to emulate the wire sawing process. The aspects and kinematics of the experiment setup are discussed in detail. Primary findings show that (1) better surface finish is achievable at higher wire speeds with ductile material removal as the dominant material removal mode (2) for wires of different grain sizes, at the cutting speed threshold of around 30 m/s, cutting force behavior changes and the difference between normal forces starts diminishing over this limit.

Mechanisms of ductile mode machining for AlON ceramics

This paper aims to reveal the mechanisms of ductile mode machining for AlON ceramics. The removal characteristics during machining were studied through ultra-precision grinding experiments. The machined surface consists of fractured and smooth areas, which were generated by brittle and ductile removal, respectively, of the individual AlON grains. The material removal mode has a determining effect on the surface/subsurface quality. The proportion of the fractured areas on the ground surface decreased gradually with a decrease in the depth of cut. The crystal indices of the grains most prone to brittle removal on the workpiece surface were determined using micro-area X-ray diffraction (μXRD) analysis performed using a beam with 50 μm diameter. The results showed that the ductile removal of the {111} planes is critical for the ductile mode machining of AlON. Nanoindentation tests based on electron back-scattered diffraction (EBSD) indicated that AlON shows strong anisotropy in its mechanical properties and machinability. The (111) plane has the highest hardness and lowest fracture toughness, at 22.91 GPa and 1.8 MPa m1/2, respectively. The material removal mechanism during the grinding of AlON was discussed in detail. The minimum and maximum dc(hkl) values must be known for classifying whether the removal mode of the workpiece is brittle or ductile. A damage-free surface could be obtained during ductile mode grinding by controlling hmax to be less than dc(111). The subsurface deformation mechanism during ductile mode grinding was analysed. An amorphous layer was observed close to the ground surface. Further, dense dislocations with no particular orientation were present beneath this amorphous layer. As the crystal structure became clearer with an increase in the depth, the plastic deformation shifted to stacking faults parallel to the {111} planes.

Investigation on the Edge Chipping in Ultrasonic Assisted Sawing of Monocrystalline Silicon

Monocrystalline silicon is an important semiconductor material and occupies a large part of the market demand. However, as a hard-brittle material, monocrystalline silicon is extremely prone to happen edge chipping during sawing processing. The edge chipping seriously affects the quality and performance of silicon wafers. In this paper, both conventional and ultrasonicassisted sawing tests were carried out on monocrystalline silicon to study the formation mechanism of edge chipping. The shape and size of edge chipping after sawing process were observed and measured. The experimental results demonstrated that different sawing processes present different material removal modes and edge quality. The mode of crack propagation was continuous cracks in conventional sawing process, while the expansion mode in ultrasonic assisted sawing was blasting microcracks. This results in the cutting force of ultrasonic assisted sawing becomes much smaller than that of conventional sawing process, which can reduce the size of edge chipping and improve the quality of machined surface.

Modeling and evaluation in grinding of SiCp/Al composites with single diamond grain

In this paper, the theoretical model of grinding force and the finite element simulation model of single diamond grain grinding SiCp/Al aluminum matrix composites were established, and the material removal mechanism was studied, including grinding force, stress distribution and material removal behavior of SiC reinforced particles. The validity of the theoretical model and the finite element model are proved by experiments. The results show that the maximum stress displays smoothly during the removal process of the aluminum matrix, while during the removal process of SiC particles, it fluctuates greatly. Material removal is divided into four stages: plastic removal of aluminum matrix, crack initiation of SiC particles, crack growth of SiC particles, and brittle fracture of SiC particles. The surface defects of grinding SiCp/Al with single diamond grain mainly include voids, microcracks and aluminum matrix delamination. According to the current experimental results, compared to the grinding wheel speed, the undeformed chip thickness (UCT) has more significant influence on the machined surface/subsurface quality. In addition, the removal modes of the SiC particle can be divided into ductile removal, ductile-brittle removal and brittle removal.

AlNiCrFeMn Equiatomic High Entropy Alloy: A Further Insight in Its Microstructural Evolution, Mechanical and Surface Degradation Response

The microstructure and properties of an equiatomic AlCrFeMnNi high entropy alloy (HEA) in the as-cast condition are presented. The microstructure consists of two phases (NiAl-rich B2 and FeCr-rich A2) featuring various eutectic morphologies, ranging from regular to anomalous development. Solidification phenomena (undercooling and recalescense) are used in order to assess the various morphological features along with theories of anomalous eutectic growth. Sliding wear testing shows an oxidation-delamination mode of material removal along with some partial abrasive mode character. Modulus of elasticity and yield point are significantly high and elongation presents at a satisfying level, whereas fracture surface examination reveals the characteristics of a brittle fracture mode. High temperature oxidation tests show multiple oxidation phenomena of different kinetics, formed oxide phases and material deterioration phenomena.

On the interpretation of drilling CFRP/Ti6Al4V stacks using the orthogonal cutting method: Chip removal mode and subsurface damage formation

The present paper aims to utilize the orthogonal cutting method to offer an enhanced interpretation of the drilling process on CFRP/Ti6Al4V stacks. It contributes to relating the chip separation modes of the orthogonal cutting of multilayer CFRP/Ti6Al4V stacks with their drilling characteristics. A particular focus was made to identify the effect of different cutting sequence strategies on the 3D topographies and defects formation of cut CFRP/Ti6Al4V stacks as well as the mechanisms controlling the drilling of the stack interface. Three configurations of orthogonal cutting operations considering both the impact of varying cutting sequence strategies and the combined interface machining were implemented and the in-situ chip removal characteristics were documented. Mechanical drilling of CFRP/Ti6Al4V stacks was performed subjected to varying cutting sequences and process parameters. Aspects involving the cutting forces, drilling-induced damage as well as the machined hole morphologies were carefully addressed with respect to the used cutting conditions. The obtained orthogonal cutting results were utilized to facilitate the stack drilling comprehension. The results discussed in this paper highlight the vital role of the cutting sequence strategy in the stack machinability and permit an enhanced interpretation of drilling this multilayer material.