Total Material Removal Research Articles

Effect of atomization amounts on electrical discharge ablation machining and electrochemical machining

ABSTRACT This study investigated the impact of varying atomization amounts on composite machining involving both atomized electrical discharge ablation machining and electrochemical machining (EDAM-ECM). Additionally, this study examined the effects of different atomization amounts on the material removal rate, relative electrode wear rate, processing waveforms, surface roughness, surface morphology and elements, and the EDAM-to-ECM ratio. Moreover, a theoretical model for describing the material removal process in composite processing was developed. Furthermore, the effect of the ECM ratio on the processing results was quantitatively analyzed through the integration of statistical circuits with a formula for calculating recast layer thickness. The model was used to predict and select the optimal atomization amounts required to achieve recast layer removal during processing. The results revealed that at an atomization amount of 200 mL/min, 16.7% of the total material removal was attributable to ECM, indicating the successful removal of the recast layer. At this atomization amount, the fabricated sample maintained a machining precision of 0.02 mm.

Study on the dynamic influence of the distribution of cutting depth on the ground surface quality in a precision grinding process

Focusing on the excitation mechanisms of self-excited vibration and forced vibration, a time-delay differential model of the radial cutting depth of a single active abrasive grit is presented. Based on the principle of the layered superposition characteristics of each component of radial cutting depth, a full discrete simulation technology is used to analyze the dynamic mechanisms of different vibration excitations on the grinding characteristics. The reliability of the dynamic mechanisms is verified by the corresponding grinding experiments. The verification results demonstrate that static and dynamic components in the grinding dynamics, including radial cutting depth, grinding force, surface roughness and surface morphology of workpiece are greatly influenced by total material removal rate, followed by speed ratio and grinding directions. With the increase of cutting depth, the variation amplitude of grinding process influenced by forced-vibration mechanism are nearly twice larger than those influenced by self-excited vibration mechanism. When speed ratio reduces to a half, surface roughness of workpiece improves by nearly 33 %. The stability of machining process and finish surface of workpiece during up-grinding are better than those during down-grinding, where force reduction by up to 10 % and surface finish improvement by 37 %.

Study on the influence of milling tool inclination angle on surface quality and optimal selection in the ultra-precision diamond milling of curved surfaces

During the milling of a curved surface, the shape of the curved surface changes continuously along the milling path, and the direction of the angle between the axis of the milling tool and the normal vector of the machined surface also changes. In turn, these changes greatly affect the quality of the machined surface. Therefore, to improve the surface quality of machined workpieces, the milling tool inclination angle should be optimized. In the present study, a three-dimensional model of the milling tool path and the workpiece surface was created. The three-dimensional surface model of the workpiece at each machining moment was iteratively built based on the Z-map method. From the macroscopic perspective, the influences of different milling tool inclination angles on surface roughness were analyzed. The difference in surface roughness generated by different inclination angles under the same feed rate and pitch was obtained. When cutting with the top of the milling tool, the roughness was larger compared to other inclination angles, and there was a roughness deviation of about 8% when other inclination angles were selected. Moreover, from the microscopic perspective, the material removal rate from a single feed cycle and the optimal inclination angle range for milling stability were explored. An optimal inclination range of 15–30% was obtained, considering both the total material removal volume and unit-angle material removal volume. Finally, a spherical machining verification experiment was conducted on an ultra-precision machining tool, and the experimental findings agreed well with the simulation results, demonstrating the reliability of the proposed model. The theoretical model of this study can provide a basis for optimal cutting tool inclination angle selection during complex surface milling.

Tribocorrosion Behavior of γ′-Fe4N Nitride Layer Formed on Mild Steel by Plasma Nitriding in Chloride-Containing Solution

Nitriding has long been used to engineer the surfaces of engineering steels to improve their surface and subsurface properties. The role of the surface compound layer (γ′-Fe4N and/or ε-Fe2-3N) in improving the tribological and corrosion-resistant properties of nitrided steels has been established. However, there have been very few studies on the response of the compound layer to tribocorrosion in corrosive environments. In this work, the tribocorrosion behavior of a 5 μm thick γ′-Fe4N nitride layer produced on mild steel (MS) by plasma nitriding has been studied in a NaCl-containing solution under various electrochemical conditions. The results show that at a cathodic potential of −700 mV (saturated calomel electrode, SCE), where mechanical wear is predominant, the total material removal (TMR) from the γ′-Fe4N layer is 37% smaller than that from the untreated MS, and at open circuit potential, TMR from the layer is 34% smaller than that from the untreated MS, while at an anodic potential of −200 (SCE), the γ′-Fe4N layer can reduce TMR from mild steel by 87%. The beneficial effect of the γ′-Fe4N nitride layer in improving the tribocorrosion behavior of mild steel is derived from its high hardness and good corrosion resistance in the test solution and its ability to resist both mechanical wear and corrosion and to reduce wear–corrosion synergism.

Study on heterogeneous Fenton reaction parameters for polishing single-crystal SiC using magnetorheological elastomers polishing pads

Magnetorheological elastomers (MRE) are intelligent controllable materials used as polishing pads in chemical mechanical polishing (CMP), and the magnetic particles in the MRE polishing pad are used as solid-phase catalysts for heterogeneous Fenton reactions for oxidizing single-crystal SiC surfaces, thereby helping reduce the processing difficulty and obtain high-quality surfaces. The influence of the solid-phase catalyst (Fe3O4 mass fraction, particle size) and polishing solution environment (H2O2 concentration, pH value) on the CMP heterogeneous Fenton reaction polishing single-crystal SiC were investigated. The material removal behavior of the MRE polishing pad was investigated. The results demonstrated that the solid-phase catalyst, Fe3O4, has a better superior effect than the carbonyl iron powder (CIP). The polishing material removal rate (MRR) increased and the surface roughness (Ra ) decreased with an increase in the Fe3O4 mass fraction. Superior polishing results were obtained at a particle size of 0.3 μm. The higher the H2O2 concentration in the polishing solution, the greater the MRR, with lower Ra at 10% concentration. The highest MRR and lowest Ra were achieved at pH = 3 in acidic environments. During polishing, the heterogeneous Fenton reaction can significantly enhance the removal ability of polishing materials. The MRR increased by 33.4% with the heterogeneous Fenton reaction compared with those without the heterogeneous Fenton reaction, and the contribution of the heterogeneous Fenton reaction to total material removal was 25.03%. The analysis of the SiC–Abrasive–MRE polishing pad contact state revealed that the heterogeneous Fenton reaction can oxidize the SiC surface and reduce the surface hardness, increasing the indentation depth δwa of the abrasive grain into the SiC surface and exhibiting greater material removal.

Polishing trajectory planning method for optimal removal of full surface

Optical free-form surface elements have better optical characteristics than traditional optical elements, but their more complex curved structure also increases the difficulty of optical processing. Aiming at the problem of insufficient equal overlap ratio spirals, this paper proposes a polishing trajectory planning method for the optimal removal of the full surface. Based on the overlap length model of the curvature change, the polishing area, track residence time and total material removal model are established, and the processing efficiency is determined. The projection method is used to map the spatial polishing trajectory to the plane, and the mathematical relationship between the material removal amount and the trajectory spacing of the circular polishing and the projection trajectory spacing is established. This paper analyzes the influence of contact area change, geodesic radius of curvature and polishing posture on the material removal of the curved surface, as well as the change trend of the material removal contour and the contour of the overlapping part. Finally, taking the rotationally symmetrical aspherical workpiece made of K9 glass as an example, the corresponding polishing plan is formulated to verify the effectiveness of the proposed method.

Treatment of female recurrent or not stress urinary incontinence with intrinsic sphincter deficiency: Sub-urethral retropubic adjustable sling (Remeex)

Recommendations for the treatment of stress urinary incontinence (SUI) due to intrinsic sphincteric deficiency (ISD) or recurrent, are complex. They accept the use of sub-urethral slings (BSU), if unsuccessful the artificial urinary sphincter. The objective was to report the results in terms of continence and morbidity of the Remeex® Adjustable BSU in the treatment of SUI by ISD recurrent or non-recurrent. Monocentric retrospective study of 70 patients with a mean age of 67.7 years (±12) operated of Remeex sling, between 2015 and 2019, was conducted. Preoperative and postoperative characteristics were analyzed from medical records. Two groups were analyzed: Group A (n=28) with no history of incontinence surgery and Group B (n=42) with history (recurrent). Patients who were totally continent (0 protection) and those who were socially continent (1 safety protection) were considered successful. Postoperative success rate was similar between groups B (90%) and A (92%) with respectively: 64% versus 71% of totally continent patients, 26% versus 21% wearing safety protection. The postoperative complications were mainly Clavien II (28%) such as urinary tract infections (6%), transient urinary retention (3%) and de novo bladder overactivity (20%) with no significant statistical difference between the groups. Six patients were reoperated (Clavien III): BSU detension (1%), vaginal exposure (4%) (including one total material removal for infection), varitensor explantation (1%) or scar disunion (1%). The Remeex® BSUA seems to lead to satisfactory perioperative results in patients with SUI with ISD recurrent or non-recurrent.

Material removal energy in ultraprecision machining of micro-lens arrays on single crystal silicon by slow tool servo

An accurate evaluation of the energy consumption in machining provides useful instruction for energy saving. In this paper, the material removal energy in ultraprecision machining of micro-lens arrays on single crystal silicon by slow tool servo was investigated. Theoretical models were firstly proposed to illustrate the evolution of the material removal energy, material removal rate (MRR), specific cutting energy (SCE) and stresses. Experiments were then conducted with different cutting parameters, and surface morphologies as well as cutting forces were also analyzed. Results show that the total material removal energy decreases with the increasing of feedrate, but the maximum material removal energy increases by about 90.67% and 6.25% when the feedrate increases from 1 μm/rev to 2 μm/rev and from 2 μm/rev to 3 μm/rev, respectively. The SCE at the feedrate of 3 μm/rev is much smaller than that of 1 μm/rev and 2 μm/rev, which is induced by the formation of cleavage fracture. Furthermore, the required removal energy to overcome deformation in the right region of the lens is higher than that of in the left region even at the same MRR. The formation mechanism of the cleavage fracture and its effects on the cutting were also discussed with respect to crystalline orientations and surface energy.

Dynamic grinding force model for carbide insert peripheral grinding based on grain element method

Peripheral grinding force influences the accuracy of carbide inserts to a considerable extent, thereby making the study of grinding force crucial to improve the process of peripheral grinding. To predict the peripheral grinding force in the grinding process, a dynamic grinding force model based on the grain element method is proposed in this paper. The proposed model divides a grain into several grain elements and the cross-section of each element is assumed to be a rectangle. The actual cutting depth, including the influence of the other grain paths of each element, is calculated to simulate the actual cross-section cutting area and the wear flat area. Thus, the interference region between grain paths is included in this model. By combining the single grain grinding force model, the cross-section cutting area and the wear flat area, the peripheral grinding force can be simulated. Because the grinding force is simulated using the grinding wheel topography and the grinding kinematic directly, the influence of the workpiece residual is included. Therefore, the simulated grinding force is more accurate than the force predicted with the total material removal rate.

Combined rough and finish machining of Ti–6Al–4V alloy by electrochemical mill-grinding

This study proposes a combined method for the electrochemical mill-grinding of Ti–6Al–4V alloy to achieve a high material removal rate, high machining accuracy and good surface quality based on rough and finish machining. In the rough machining stage, a maximum feed rate of 2.7 mm min−1 and a material removal rate of 248.3 mm3 min−1 were achieved experimentally at a 10 mm cut depth using an abrasive tool with five rows of tool-sidewall outlet holes. In the finish machining stage, there were almost no overcuts or stray corrosions produced. The sidewall surface roughness and sidewall flatness were Ra = 1.06 and 76.8 μm after the finishing stage, which represent a 68% and 79.2% improvement compared with the rough machining stage, respectively. Finally, we fabricated a 1-mm-thick thin-walled structure using the combined machining operations, in which approximately 96% of the total material removal volume was performed at the rough machining stage.

Investigated iterative convergences of neural network for prediction turning tool wear

This study investigates the iterative convergences of neural network for prediction turning tool wear. For the smart manufacturing, the intelligent prediction systems have been gradually developing for processing of CNC machine tools. Recently, many artificial intelligent algorithms of machine learning have been widely applied for forecasting and decision making in intelligent manufacturing. In general, the cutting tool wear in manufacturing of CNC machine tool plays a major role for a high quality and an efficient operation, but it is very difficult to diagnose and prognoses the tool wear for tool life due to many cutting parameters. Therefore, the study investigates the iterative gradient convergences of backpropagation neural network (BNN) algorithm for prediction tool life with analytics of its convergence and stability. The estimative methods of iterative convergences include stochastic gradient descent (SGD), momentum, adaptive gradient (Adagrad), adaptive delta (Adadelta), and adaptive moment (ADAM) algorithms. In BNN prediction model, the data inputs are the cutting speed, feed rate, and total material removal volume and data output is tool wear measured from the microscope. Results showed that the tool wear curves at different cutting conditions can be predicted and trained using BNN model for intelligent manufacturing. In addition, the convergence of ADAM gradient for the tool wear in all cases is the best prediction for the BNN model. However, it is worth to notice that the momentum gradient is faster training speed to converge to a constant error at fewer iteration numbers.

Precision processing of ceramics by the raster machine

Ceramic materials processing techniques have been briefly presented in the article. The process of grinding, lapping as well as the stages of technical ceramics processing have been reported. Up to 80% of the material to be removed at the first stage, where a rough tool was utilized for machining at high speed. At stage second, the fine grain instrument was employed for the grinding process. Thus, the volume of the grinded material is reduced. At the third stage, lapping is performed by diamond abrasive flour grains and pastes of the necessary granularity. After the stage of lapping the polishing of the surface is done to achieved high accuracy and elegant finish. The investigation of abrasive lapping of the parts made of VSH-75 oxide ceramics material. It has been found that the efficiency of the diamond flour grains is 15-30 times greater than the efficiency of Al2O3 and SiC flour grains. With the increasing of granularity, the volume of the total material removal and surface finish enhances. In order to obtain the highly finished surface (Rz=0.8 µm), it is recommended to use ASM20 synthetic diamond flour grain. The influence of the part’s contact pressure (range 25-150 KPa)on the lap has also been investigated. The volume of the total removal is distinctly increased with the increase of contact pressure from 25 to 50 KPa, while the diamond discharge intensity and the processed surface finish reduces. Further, the contact pressure increases up to 150 KPa exhibited deep scratches and machining marks on the tool surface which seriously impairing the tool. The optimal contact pressure for the superior ceramics lapping on the cast- iron lap SCH-28 should be in between 50-100 KPa

Surface quality and material removal in magnetic abrasive finishing of selective laser melted 316L stainless steel

As one of the most important additive manufacturing (AM) techniques, selective laser melting (SLM) shows great potential in directly producing functional tooling and complex structural parts through layer-by-layer fabrication. However, some critical issues such as poor surface finish, insufficient dimensional accuracy and inadequate fatigue life need to be addressed systematically before SLM could be widely applied in industries. Though the capabilities of some conventional finishing techniques such as machining, abrasive finishing and electrochemical polishing on surface finish of components generated by SLM have been explored by some researchers, there is still a great research gap on finishing AM-ed surfaces uniformly due to their high complexity. In this paper, the effect of slope angle on surface finish of the samples fabricated by SLM is characterized by scanning electron microscope and profilometer. Magnetic abrasive finishing (MAF), as a flexible polishing technique, has been developed to polish the samples generated by SLM with different slope angles. Surface roughness and material removal rate are recorded and evaluated during MAF process. To reveal the underlying mechanism, an analytical model of material removal rate is devised by correlating initial surface roughness of workpiece generated by SLM with abrasive indentation depth, which eventually determines the total material removal volume in MAF process.

Research on the fabrication and grinding performance of 3-dimensional controllable abrasive arrangement wheels

As the spatial position of abrasive particles in the grinding wheel has a major impact on the uniform abrasion of the grinding wheel and the grinding quality of the workpiece, the design and fabrication of 3-dimensional (3D) controllable abrasive arrangement wheels are of great importance. In this paper, the simulation of grinding process with 3D controllable abrasive placement grinding wheel is presented by using MATLAB software. The influence of the abrasive spatial distribution on the uniformity of the grinding trajectories was theoretically studied. Based on the additive manufacturing technology, a stereolithography apparatus equipment was developed to produce the resin-bonded grinding wheel with 3D controllable abrasive arrangement. Some light-cured resin grinding wheels with different spatial arrangement of abrasive particles were prepared for the verification grinding experiments. The variation coefficient of standard deviation (VCSD) value and the non-uniformity coefficient (NUC) of the ground surface roughness were used to evaluate the uniformity of the grinding trajectories, that is, the machining quality of the workpiece surface. It can be obtained from the simulation results and the experiment results that the abrasive distribution had a significant influence on the uniformity of workpiece surface quality. Comparing with traditional random arrangement abrasives grinding wheel, the grinding experiment results indicated that the 3D controllable abrasive arrangement wheel had a longer effective grinding time and greater total material removal amount. Both the simulation results and experimental results indicated that the uniformity of the grinding trajectories could be optimized with the controllable abrasive arrangement.

Modeling and experimentation of dynamic material removal characteristics in dual-axis wheel polishing

CCOS (computer-controlled optical surfacing) approach is widely used in different optical polishing processes for making ultra-precision components with high surface form accuracy requirements. Under the polishing mode using complex tool motions, middle-spatial-frequency errors (MSF, i.e., residual ripples) tend to be generated on the workpiece surface, which would deteriorate the functional performance of the parts. In this paper, a dynamical removal model (DRM) based on the spatial kinematic analysis and polishing material removal theory is proposed, to investigate the actual material removal characteristics in dual-axis wheel polishing (DAWP). The model is developed to calculate the overall material removal profile (low-spatial-frequency error, LSF) and the middle-spatial-frequency errors, simultaneously. The shape and the stability of the tool influence function (TIF) are firstly investigated. A series of straight line path polishing tests on BK7 glass are carried out to investigate the effects of process parameters on the generated MSF errors and also check the validity of the proposed DRM. Uniform polishing tests on 50 × 50 mm BK7 samples are conducted, under different polishing parameters, the power spectral density (PSD) characteristics of the surface are also analyzed. The results show that the proposed model can effectively predict the material removal profile and especially the ripple characteristics generated on the surface, which are not reflected when using the conventional convolution algorithm typically used in a CCOS process. When increasing the ratio of feed velocity to co-rotating speed, the wavelength and amplitude of the residual ripples increase, and the ratio of ripple amplitude to total material removal depth also increases. The level of residual ripples can be effectively restrained by the appropriate setting of the speed ratio (reducing the feed velocity or increasing the co-rotating speed).

Computer simulation and experimental benchmarking of ultrashort pulse laser ablation of metallic targets

AbstractIntegrated simulation results of femtosecond laser ablation of copper were compared with new experimental data. The numerical analysis was performed using our newly developed FEMTO-2D computer package based on the solution of the two-temperature model. Thermal dependence of target optical and thermodynamic processes was carefully considered. The experimental work was conducted with our 40 fs 800 nm Ti:sapphire laser in the energy range from 0.14 mJ to 0.77 mJ. Comparison of measured ablation profiles with simulation predictions based on phase explosion criterion has demonstrated that more than one ablation mechanisms contribute to the total material removal even in the laser intensity range where explosive boiling is dominating. Good correlation between experimental and simulation results was observed for skin depth and hot electron diffusion depth – two parameters commonly considered to identify two ablation regimes in metal. Analysis of the development dynamics for electron–lattice coupling and electron thermal conduction allowed explaining different ablation regimes because of the interplay of the two parameters.

Study of Machining Characteristics of Micro EDM in Nitrogen Plasma Jet

Micro electrical discharge machining (EDM) has been used to drill micro-holes and to generate micro-features for applications in automotive, aerospace and biomedical industries. The tool electrode wear ratio in micro-EDM usually is larger than that in conventional EDM process. It has been reported that the electrode wear ratio is almost zero in gas. However, its narrow discharge gap leads to frequent occurrence of abnormal discharges. In order to enlarge the discharge gap in micro-EDM, Nitrogen plasma jet (NPJ) has been used as the working media for micro-EDM in this study. NPJ is generated by using a needle-cylinder type corona discharge with an AC power supply in pure nitrogen gas. A RC-type pulse generator is used to realize micro electrical discharges in this investigation. It is expected that the electrons and ions in NPJ increase the electrical conductivity in the discharge gap. Thus, a large discharge gap can be obtained.To investigate the machining characteristics of micro-EDM in NPJ, series of experiments in NPJ, nitrogen jet (NJ) and deionized water (DIW) have been carried out. The discharge distance, machining time, electrode wear and surface roughness under different conditions have been recorded. The measured data has been analyzed together with the discharge signals. It was found that the discharge distance in NPJ is larger than that in NJ. The machining process in NPJ is much more stable than in NJ. The observed volumetric difference of electrode wear is very small, probably due to the small total material removal. The machining efficiency in DIW is the highest. However, the surface roughness in DIW is worse than that in NPJ.

Modeling of material removal in ultrasonic assisted magnetic abrasive finishing process

Ultrasonic assisted magnetic abrasive finishing (UAMAF) integrates ultrasonic vibrations with magnetic abrasive finishing (MAF) process to finish the workpiece surface more efficiently as compared to MAF. In this work, mechanism of material removal has been discussed. A kinematic analysis of an abrasive particle and an analysis of material removal during UAMAF is presented. The total material removal during finishing is attributed to two simultaneous and independent phenomena — a steady state material removal and a transient material removal. The steady state removal mainly depends on the finishing condition and remains constant throughout the finishing time, while transient removal is primarily associated with the surface roughness of the workpiece. A finite‒element analysis of electromagnet was performed to calculate magnetic‒flux density in the finishing region to evaluate the normal force acting on the active abrasive particles. The steady state material removal was modeled as a function of velocity and normal force using the process physics. The transient material removal was modeled as a function of the volume of instantaneous irregularities available on the workpiece surface. The developed model predicted the material removal rate (MRR) in UAMAF as a function of supply voltage, working gap, angular speed of the electromagnet, amplitude and frequency of ultrasonic vibration, hardness and initial surface roughness of the workpiece. The model brought out that there was an exponential relationship between MRR and finishing time.

A theoretical model incorporating both the nano-scale material removal and wafer global uniformity during planarization process

In the ultra large-scale integration process, as chemical mechanical polishing (CMP) is developing to higher precision, nano level planarity and sub-nano level roughness of wafer surfaces become key problems to be overcome. In this work, a theoretical model for local and total material removal was proposed based on the particle sliding trajectories and chemical-mechanical synergy, and the material removal distribution on wafer surface were analyzed. Furthermore, the chemical-mechanical mechanism was studied and synergy maps constructed. It is found that the passivation-wear and additive-synergistic effects dominate the material removal during CMP. This study establishes a correlation mechanism between the nano material removal and global uniformity of wafer surfaces, which provides theoretical and experimental framework for optimizing the slurry and the process parameters.

Modelling the particles impingement angle to produce maximum erosion

A semi-mechanistic, semi-empirical erosion model was developed and validated by experimental data. The novelty of the developed model is by accurately predicting the impingement angle that produce maximum erosion and relating it to measurable mechanical properties such as hardness and fracture toughness. The ratio of the target material fracture toughness (R) to its hardness (H) is the parameter which governs the erosion mechanism and consequently the angle for maximum erosion. It was noticed that for material with high R/H, i.e. ductile materials, the preferred mode is ploughing, a process analogous to rubbing in which the penetrating particle squeeze the target material out of the indentation to preform ridges, which are knocked off at subsequent impacts. The lower the ratio R/H is, a tendency to fracture mechanism occurs. The fracture mechanism is a process very similar to brittle chipping during metal cutting, where the applied force propagates cracks parallel to the surface. A simplified model, defining the horizontal force which is applied on the particle in its movement through the material, was introduced. This simplified model takes into account the relative effect of each of the ploughing and fracture mechanism on the total material removal. The material parameter which governs the relative effect of the mechanisms is R/H. Particle angularity also contributes to decreasing of the fracture mechanism, hence a governing non-dimensional number was received, R/H·deff, where deff is the effective diameter of the penetrating particle tip. Incorporating this parameter in the erosion model yielded good agreement with experimental data and was able to explain the phenomenon of different maximum erosion angle and velocity exponent for different target materials. The relation between the developed model empirical coefficients to target material mechanical properties was studied for eight different materials, ranging from soft metals to hardened stainless steel. Correlations between model coefficients to R/H were developed and exhibited good agreement with mechanistic analysis.