Material Removal Volume Research Articles

An experimental study on the creep feed grinding of laser macro-structured alumina considering constant material removal volume

Engineering ceramics such as alumina have found special applications in aerospace, electronics, and automotive industries due to their superior mechanical and thermal properties. Among these properties, chemical stability at high temperatures, high strength to weight ratio, hardness, strength, wear, and corrosion resistance are of prime importance. Due to these superior properties, processing of these ceramics encounters some difficulties and requires special machining processes such as diamond grinding; in addition to high manufacturing costs, this technique suffers from noticeable challenges such as high grinding forces and temperatures which may lead to serious surface damages. To overcome these challenges, in recent years, laser-assisted grinding has been introduced; in this process, laser source is used to preheat or structuring the workpiece surface in order to reduce grinding forces and temperatures. In this research, first four different patterns were created on alumina using a pulsed laser. Then, these weakened structures were machined using creep feed grinding. In order to provide a better understanding from the effect of each pattern, the volume of the material that can be removed was kept constant in all four patterns. Finally, the effect of created patterns on grinding forces and surface roughness has been studied. Besides, scanning electron microscopy has been used to investigate possible surface damages. The results showed that the normal and tangential forces in the non-structured case were 2 and 2.7 times higher than the forces recorded in the best patterned samples. However, no significant effect of the created patterns on the surface roughness was observed. Furthermore, serious heat damage and cracks were not observed in the structured workpieces, but non-structured workpieces were crushed during operation. Among the created patterns, pattern with perpendicular grooves to the grinding direction was introduced as the best.

Wear characteristics of white corundum abrasive wheel in ultrasonic vibration-assisted grinding of AISI 9310 steel

Ultrasonic vibration-assisted grinding has been employed in machining difficult-to-cut materials (e.g. titanium alloys, superalloys, composites, hardened steels, etc.) aiming at improving wear-resistance abilities of abrasive wheels. In this paper, comparative experiments between the conventional grinding (CG) and ultrasonic vibration-assisted grinding (UVAG) were performed on AISI 9310 steel to study grain wear mechanisms. Results shows that UVAG achieves a significant reduction in grinding forces, force ratio and machined quality as material removal volumes raise. Moreover, the wear flat of grains and a sharp change in grinding forces occur. Then, the surface quality gradually deteriorates from the more severe chip clogging of wheels and increasing grinding forces during the CG process. Meanwhile, the steady wear stage of UVAG is longer by 23.07%, and the ground surface roughness in UVAG remain lower and more stably fluctuating than those in CG. Furthermore, UVAG possesses a small fluctuating height of worn grains according to the analysis of the protrusion height distribution at various wear stages, owing to the consistent micro-fractures of the grains under uniform alternating loads. In contrast, pull-out defects can be observed under high grinding forces on the tool–workpiece intersection during the CG process, affecting the ground surface quality.

An in vitro comparison of three nucleus pulposus removal techniques for partial intervertebral disc replacement: An ultra-high resolution MRI study.

Nuclectomy, also known as nucleotomy, is a percutaneous surgical procedure performed to remove nucleus material from the center of the disc. Multiple techniques have been considered to perform a nuclectomy, however, the advantages and disadvantages of each are not well understood. This in vitro biomechanical investigation on human cadaveric specimens aimed to quantitatively compare three nuclectomy techniques performed using an automated shaver, rongeurs, and laser. Comparisons were made in terms of mass, volume and location of material removal, changes in disc height, and stiffness. Fifteen vertebra-disc-vertebra lumbar specimens were acquired from six donors (40 ± 13 years) and split into three groups. Before and after nucleotomy axial mechanical tests were performed and T2-weighted 9.4T MRIs were acquired for each specimen. When using the automated shaver and rongeurs similar volumes of disc material were removed (2.51 ± 1.10% and 2.76 ± 1.39% of the total disc volume, respectively), while considerably less material was removed using the laser (0.12 ± 0.07%). Nuclectomy using the automated shaver and rongeurs significantly reduced the toe-region stiffness (p = 0.036), while the reduction in the linear region stiffness was significant only for the rongeurs group (p = 0.011). Post-nuclectomy, 60% of the rongeurs group specimens showed changes in the endplate profile while 40% from the laser group showed subchondral marrow changes. From the MRIs, homogeneous cavities were seen in the center of the disc when using the automated shaver. When using rongeurs, material was removed non-homogeneously both from the nucleus and annulus regions. Laser ablation formed small and localized cavities suggesting that the technique is not suitable to remove large volumes of material unless it is developed and optimized for this application. The results demonstrate that both rongeurs and automated shavers can be used to remove large volumes of NP material but the reduced risk of collateral damage to surrounding tissues suggests that the automated shaver may be more suitable.

Peridynamic simulations of damage in indentation and scratching of 3C-SiC

The cubic silicon carbide (3C-SiC) has broad application prospects due to its excellent properties. The modeling of damage in 3C-SiC due to contact loads is important yet challenging. In this paper, simulations based on peridynamics theory are proposed to model damage of 3C-SiC in indentation and scratching. In indentation, the pop-in phenomenon of load-depth curve and initiation and propagation of cracks are observed. During scratching, the specific cutting energy (energy consumed per unit volume of material removed) increases nonlinearly with the decrease of scratching depth. Initiation and propagation of radical cracks on both sides of the groove are found. In addition, for scratching with double indenters, the volume of material removal is more than twice that of scratching with an indenter when indenter interval is less than the threshold. This paper demonstrates that peridynamics is a powerful tool to investigate damage in indentation and scratching of brittle materials.Graphical abstract

Experimental and numerical investigation into material removal mechanism of fast ED-milling

Fast electrical discharge milling (fast ED-milling) has become a promising technology in the manufacturing industry for machining complex structures such as diffuser-shaped film cooling holes. However, the mechanism of the efficient removal of materials in this technology is not yet fully understood. To gain a further insight into this matter, an experimental investigation on the morphology of discharge craters including the absolute material removal volume per discharge, material residual volume per discharge, and directionality, is firstly carried out. The obtained results imply that a high-pressure inner flushing can significantly promote the expelling of molten material from a molten pool and is a fundamental reason why fast ED-milling can be of higher machining efficiency than regular ED-milling. To explore the mechanism behind, a novel thermal-fluid coupling model is developed to simulate the evolution process of the molten material under the effect of a flow field. The results of numerical simulation show that during a discharging, the molten material moves along the workpiece surface towards the outlet of a gap channel and solidifies at the side of a crater that is away from the electrode center. Another interesting finding is that an inappropriately high flushing pressure can result in a low machining efficiency because the severe heat convection will consume a large part of the heat generated by a discharge. This well explains the phenomenon that occurred during the experimental investigation.

Development of morphable polishing tools with labyrinth and dimple textures

Inspired by the physical nature and functionality of morphable surfaces, this paper develops the polishing tools with such surface characteristics. The surface textures of morphable polishing tools can be tuned and adapted according to the stage and requirements of the targeted surface finish and material removal rate. To investigate the performance of morphable surfaces in polishing, morphable polishing tools with labyrinth, dimple and hybrid textures were fabricated by curing silicone materials with different Young’s moduli. The morphable polishing tools can be produced with fast responsiveness and reversibility by controlling the air pressure in the tool cavity. Fixed-spot polishing experiments with the developed morphable tools were performed on a copper surface, and the surface morphology, surface roughness and removed volume of polished copper were measured with a laser confocal microscope. Furthermore, static and dynamic polishing forces, polishing pressure distribution and interfacial friction coefficient between the tool and workpiece were obtained and benchmarked in polishing experiments regarding the labyrinth, dimple and hybrid tools. The results show that under the investigated polishing parameters, the roughness of polished surface is the smallest with the dimple tool, higher with the hybrid tool and the labyrinth tool. The material removal volume, static and dynamic polishing forces under different tool offsets are larger in the polishing processes with a dimple tool. In addition, the theoretical and experimental study indicates that the tool surface texture significantly affects the polishing pressure distribution. Labyrinth tools show denser pressure distribution owing to the finer textures of a smaller characteristic length, while dimple tools show sparsely distributed pressure owing to the coarser surface texture.

Micro-fracture behavior of a single-aggregated cBN grain and its relation to material removal in high-speed grinding of Ti–6Al–4V alloys

Aggregated cubic boron nitride (cBN) abrasive grains were developed using high-temperature liquid phase sintering processes and then the single-grain scratching trial was conducted to study the grain wear behavior and material removal characteristics. Characterizations of grain wear evolutions and related surface scratches grinded by aggregated and monocrystalline cBN grains are performed, respectively. The evaluations of wear-resistance and self-sharpening abilities of both abrasive grains are carried out based on the proposed indicators of volumetric pile-up ratio, volumetric groove removal rate, and grain grinding ratio. Compared to the monocrystalline cBN grain, the as-developed aggregated cBN grain exhibits the more stable grinding process, excellent self-sharpening ability as well as a higher material removal volume provided by the dynamic balance between microfracture and partial macrofracture of multi-layer micro cBN particles.

Machinability investigation and sustainability analysis of high-pressure coolant assisted turning of the nickel-based superalloy Inconel 718

In recent years, issues related to eco-friendly machining have received more and more attention, leading to the development of new cooling/lubrication techniques. Herein, the paper investigates the effect of high-pressure coolant (HPC) supply on machining performance of Inconel 718 and compare with conventional flood cooling. Significant improvement in tool life, tool wear, tool-chip contact length, material removal volume, and cutting forces have been observed from the outcomes of HPC cooling condition. Moreover, in order to study the environmental impact of machining Inconel 718, a carbon emissions model was established and analyzed for high-pressure and flood cooling conditions, taking into account the carbon emissions from energy, material, cutting tool, and cooling/lubrication fluid. HPC assisted machining was revealed to be better as it makes possible a reduction in overall carbon emissions at higher cutting speeds. In addition, economic analysis for both cutting environments was also carried out. Significant improvement in reduction of the overall machining cost was observed under HPC conditions, especially at higher cutting speeds. In a nutshell, the findings revealed better performance of HPC assisted machining, with regard to machinability, environmental, and economic issues.

Material Removal Optimization Strategy of 3D Block Cutting Based on Geometric Computation Method

During the material removal stage in stone rough processing, milling type has been widely explored, which, however, may cause time and material consumption, as well as substantial stress for the environment. To improve the material removal rate and waste reuse rate in the rough processing stage for three-dimensional stone products with a special shape, in this paper, circular saw disc cutting is explored to cut a convex polyhedron out of a blank box, which approaches a target product. Unlike milling optimization, this problem cannot be well solved by mathematical methods, which have to be solved by geometrical methods instead. An automatic block cutting strategy is proposed intuitively by considering a series of geometrical optimization approaches for the first time. To obtain a big removal block, constructing cutting planes based on convex vertices is uniquely proposed. Specifically, the removal vertices (the maximum thickness of material removal) are searched based on the octree algorithm, and the cutting plane is constructed based on this thickness to guarantee a relatively big removal block. Moreover, to minimize the cutting time, the geometrical characteristics of the intersecting convex polygon of the cutting plane with the convex polyhedron are analyzed, accompanied by the constraints of the guillotine cutting mode. The optimization algorithm determining the cutting path is presented with a feed direction accompanied by the shortest cutting stroke, which confirms the shortest cutting time. From the big removal block and shortest cutting time, the suboptimal solution of the average material removal rate (the ratio of material removal volume to cutting time) is generated. Finally, the simulation is carried out on a blank box to approach a bounding sphere both on MATLAB and the Vericut platform. In this case study, for the removal of 85% of material with 19 cuts, the proposed cutting strategy achieves five times higher the average material removal rate than that of one higher milling capacity case.

Sustainable solution to low-cost alternative abrasive from electric ceramic insulator waste for use in abrasive water jet machining

Increasing demand and resource overuse has prompted the exploration of spent secondary materials as a primary raw material for a variety of applications, leading to a more sustainable environment. Spent electric grid ceramic insulator, one of the waste materials of ceramic industry, has a good hardness and strength. It can be reused as value-added material in the Abrasive Water Jet Machining (AWJM) industry. The present work deals with the generation of cost-effective replacement material for abrasive water jet machining from electric insulator rejects (EIR). Mechanical crushing method is opted to generate the abrasive grit for the machining process. Grit generation pattern and the friability of the electric insulator rejects were determined experimentally. The results indicate that the friability of the processed electric insulator rejects is comparable with the commercially available garnet abrasive. Geometric parameters such as sphericity, elongation ratio, and shape factor for the processed electric insulator rejects were studied using scanning electron microscopy. The machining performance indicators for standard aluminium material such as volume of material removal, kerf angle, surface roughness, and cutting width were measured for electric insulator rejects and compared with existing garnet abrasive grain. The experimental results of the newly generated electric insulator reject abrasive were compared with the performance indicators of the garnet abrasive. The observed deviation was lower proving that it can be used as an alternative abrasive in the abrasive jet machining process. Cost analysis and recycling ability predict the economical usability of the newly generated abrasives.

Prediction and analysis of EDM performances considering random multiple-pulse discharges based on geometric optimization modeling

Continuous electrical discharge machining (EDM) is characterized by random discharge positions, uncertain discharge energy, extremely short discharge time, extremely narrow tool-workpiece gaps, etc. Theoretical research into the mechanisms leading to thermal erosion of material and the associated surface morphology has become urgent to allow the continued development and application of EDM technology. Firstly, multi-pulse theory and geometric optimization are utilized to derive an expression for the material removal rate and surface roughness in multi-pulse EDM. Secondly, based on the characteristics of multi-pulse discharge, a multi-pulse numerical simulation model was established to predict the material removal volume, surface roughness, and thickness of the recast layer. Finally, the results predicted by the geometric and numerical models are compared with the experimental results. Experimentally, 0.176 mg of material is removed in the multi-pulse EDM; the theoretical calculation and numerical simulation of the same produce errors of 5.11% and 11.36%, respectively. The analogous results for the surface roughness are 1.623 μm, 8.93%, and 1.23%. The experimentally determined thickness of the recast layer was 5.31 μm, which corresponds to an error in the simulation error of 7.53%.

Study on the cutting mechanism of randomly deflected truncated cone shape single abrasive grain

Based on the random distribution characteristic of abrasive grains for the grinding wheel circumferential surface during the manufacturing process, considering the grinding parameters and deflection parameters comprehensively, a randomly deflected truncated cone shape single abrasive grain cutting simulation model was established. Then, studying its cutting mechanism, i.e., the trajectory length value by numerical method and formula method was compared, the consequence indicates that the error is extremely small; this demonstrates the accuracy of the numerical method. The calculation and analysis of the workpiece cutting surface topography and the undeformed chip shape were carried out; it shows that the cutting surface topography and the undeformed chip shape are coincident. And the calculation results of the model were compared to verify. The influence laws of each grinding process parameter on the material removal volume (MRV) and material removal rate (MRR) were investigated; the results display that the grinding method affects the changing pattern of MRV and MRR; when the grinding method was up-grinding, a high wheel speed or a small wheel diameter is able to enhance the MRR; the MRV and MRR are increments with the increasing workpiece feed speed or abrasive grain cutting depth; and the MRV and MRR decrease with the raising of the absolute value of single abrasive grain deflection angle. The situation is a similar or opposite trend in down grinding. This work can provide a theoretical reference for the selection and optimization of parameters and further lay a foundation for the research in the grinding mechanism of the grinding wheel.

Surface form error measurement for rough surfaces using an infrared lateral shearing interferometry

The fabrication of a large monolithic mirror or a segmented mirror requires a high throughput that satisfies the time-cost requirement. Particularly, the rough surface properties of grinding pose a challenge for accurate measurement of the surface figure error (SFE). If the SFE during grinding is as small as possible, the material removal volume in the figuring process gets reduced, and the total required time of the fabrication is greatly minimized. In this paper, we propose a new metrology tool called intermediate surface figure error measurement (ISFEM) that can be applied to measurement of SFE for rough surfaces. It consists of a CO2 laser of wavelength 10.6 µm as a light source, a lateral shearing interferometer as a wavefront sensor, and several optical components for beam shaping and imaging. The ISFEM demonstrated its ability to measure the microns to sub-micron rms SFE of the ground surface by testing the samples with a 0.59 µm -1.56 µm rms of surface roughness and a large SFE of about 3 µm rms. The system was applied to the fabrication of an off-axis parabolic mirror of diameter 1.1 m, where it successfully performed as an intermediate metrology between laser tracker measurement for the rough surface and interferometric measurement for the polished surface. The ISFEM obtained measurements from 3.88 µm rms SFE during the fine grinding process and down to 0.38 µm rms during the polishing process. Therefore, we confirmed that the ISFEM provides a unique solution for high throughput for the fabrication of large or multiple segmented mirrors.

Validation of different tungsten carbide-cobalt grades as tool electrode material for sinking EDM

In sinking electrical discharge machining (EDM), tool electrode wear is crucial for an economical production. The tool electrode wear affects the process efficiency and determines the number of required tool electrodes for a specific machining process. Therefore, the relative tool wear, describing the relation of removed material volume between tool and workpiece electrode, needs to be minimised. The tool wear characteristics in sinking EDM depend strongly on EDM processing parameters and the applied electrode materials. Especially in micro-EDM, a significant increase of relative tool wear is representative. Because of its thermophysical properties tungsten carbide-cobalt (WC-Co) is a suitable material for the application as sinking EDM tool electrode. The economical production of WC-Co form electrodes for EDM sinking is enabled by recent advancements in precision milling of hard materials.Due to non-existent research on which composition of WC-Co is most advantageous for the application as sinking EDM tool electrode material, previous investigations have been intensified to describe correlations between material properties, EDM processing parameters and EDM processing results concerning material removal rate and relative tool wear. Therefore, various WC-Co grades with differing grain size and cobalt content were analysed in sinking EDM experimental studies. It was observed that the factor grain size showed an ambiguous effect concerning the process results. An increasing cobalt content led to a reduction of relative tool wear, which can be explained by the microstructure of the cobalt binder phase with its higher electrical conductivity. The WC-Co grades with beneficial EDM processing results have been further investigated in EDM parameter studies with differing tool electrode geometries. The experimental results concerning relative tool wear, with a minimum of 3 % for macro- and 5 % for micro-sized geometries, proved the suitability of specific WC-Co compositions as tool electrode material for sinking EDM.

Electrochemical machining of microrods using a self-drilled hole

In the electrochemical machining (ECM) of microrods using a tool electrode, block or wire tool electrodes are usually employed. However, high-accuracy alignment of the tool electrode and workpiece is time-consuming, especially when an ultrasmall-diameter microrod is to be fabricated. A microrod fabrication method by ECM using a self-drilled hole was therefore proposed in the present study. In the first step of the method, a rod workpiece was used as the tool electrode and a microhole was drilled in a sheet by ECM. The sheet with the drilled hole functioned as the tool electrode in the next step of fabricating the workpiece into a microrod by ECM. The workpiece and drilled hole were easily aligned with their axes being coincident. As a result, a straight stainless-steel microrod 2.5 µm in diameter was successfully fabricated using a 5-µm-thick stainless-steel sheet. This is the smallest-diameter straight microrod fabricated by ECM, to the best of our knowledge. Furthermore, machining parameter sets suitable for realizing both a reasonable material removal volume and high machining accuracy were experimentally determined.

Research Part Surface Position Influence on Metal Removal and Steady-State Roughness During Vibro-Abrasive Processing

The paper is devoted to the study of part surface position and its influence on metal removal and steady-state rougness during vibro-abrasive processing. The article raises the differences between vibro-abrasive processing of external and internal part surfaces. Theoretical dependencies analysis for determination on part material removal and surface steady-state roughness is carried out. It is known that available theoretical dependencies do not take into account part surface position for material removal and the steady-state roughness calculation. Experimental researches to determine internal surface material removal with external surface isolation were carried out. The influence of part surface position on the steady-state roughness is investigated. Based on obtained experimental results, the dependence graphs of material removal and roughness on the processing time are constructed. The comparative analysis of the part surface position influence on material removal and the steady-state roughness during vibro-abrasive processing is carried out. The results showed that material removal volume from the internal surface more than from the external for short part length, however material removal volume from the external surfaces grows significantly in case of part length increasing, while from the internal surfaces is not significant. It is established that the internal surface steady-state roughness is ∼1.55 times higher than external surface steady-state roughness after processing in triangular prism 15×15, grit 16.

Elliptic vibration assisted cutting of metal matrix composite reinforced by silicon carbide: an investigation of machining mechanisms and surface integrity

This paper aims to investigate the deformation mechanisms and surface integrity of SiCp/Al composites machined by elliptic vibration assisted cutting (EVAC). Self-designed EVAC device was applied to generate the elliptical trajectory on tool tip, which is driven by three piezoelectric actuators along different directions with phase difference. A two-dimensional (2D) microstructure-based finite element (FE) model of SiCp/Al composites was also established to research the deformation mechanisms and surface integrity in the process of EVAC, including material removal mechanisms, cutting force, surface roughness and microstructure. Systematic orthogonal cutting experiments shown that the relative position of tool-particles are changed by the time-varying cutting thickness in EVAC, leading to more obvious particle fracture during SiC particles removal process. Particle fracture appears in the area of particle clusters affected by chip lifting of tool. The intermittent cutting effect not only reduces the average cutting force, but also eliminates the scratch on machined surface caused by SiC particles entering the flank face–workpiece interface, improving the machined surface quality. Limited by the volume of material removal, 2D FE model has a high prediction accuracy for the micro-removal process of composite materials. The application of elliptical vibration is able to create the special functional surfaces. In order to increase the hydrophobicity of machined surface, larger feed rate and smaller cutting depth should be selected as far as possible.

Effects of open pores on grinding performance of porous metal-bonded aggregated cBN wheels during grinding Ti–6Al–4V alloys

Porous metal-bonded wheels coupled with the aggregated cubic boron nitride (cBN) grains and water-soluble carbamide particles as pore-forming agents were fabricated, aiming to the improvement of grinding wheel performance and ground surface quality in grinding of Ti–6Al–4V alloys. Grinding forces and force ratio, ground surface roughness and microhardness were investigated to evaluate wheel performance. In addition, the wear evolutions of cBN grains and macropores were performed as the material removal volume increases during wheel wear tests. Findings show that the dynamic changing behavior of the coverage and exposure of open pores attributes to the improvement of grinding performance and ground surface quality of porous AcBN wheels. Meanwhile, the promising self-sharpening property of wheels can be guaranteed in basis of dynamic wear variations of multiple cBN abrasive grains layer by layer.

Mechanism of material removal through transient and selective laser absorption into excited electrons in fused silica

Transient and selective laser (TSL) processing is a method used for the rapid fabrication of transparent materials. In this method, electrons in glass are excited by an ultrashort-pulse laser. This electron-excited region selectively absorbs a long-pulse laser with low intensity, resulting in microfabrication. However, the mechanism of material removal during TSL processing is not completely understood. In this study, we measured the threshold of TSL processing in synthetic fused silica to investigate the details of the processing mechanism. The measurement revealed that the processing threshold was represented by the relationship between the intensity of the long-pulse laser and the electron density excited by the femtosecond laser. The calculations indicated that the absorption in synthetic fused silica was mainly due to linear absorption of the long-pulse laser into the excited electrons and that a simple threshold model can be used to explain the material removal volume. The revealed controlling factor from the identified threshold function will allow the shapes to be controlled during TSL processing.

Theoretical modeling and experimental research on the depth of radial material removal for flexible grinding

As a difficult-to-cut metallic material with excellent characteristics, titanium alloy has been widely used in the field of aero-engines. In this study, a series of grinding experiments of titanium alloy was carried out with the abrasive belt flap wheel. The effects of spindle speed n, feed speed Vw, workpiece curvature radius R2, and radial theoretical grinding depth ae on the material removal depth are investigated. Meanwhile, a noval approach to determine the depth of radial material removal was established based on the Hertz elastic contact theory, Preston equation, and the principle of equivalent material removal volume. The results obtained show that the radial material removal depth increases with the increase of the radial theoretical grinding depth and decreases with the increase of the workpiece curvature radius and the spindle speed, and the feed speed has almost no effect on it. Finally, the measured value is compared with the calculated value, and the absolute error is mostly less than 10%, which verifies the reliability and accuracy of the prediction model.