Workpiece Removal Rate Research Articles

Machinability of B4C-reinforced Al2014 metal matrix composites in electric discharge machining

This study was conducted to clarify the effect of various variables such as the type of electric discharge machining, discharge current and reinforcement content of B4C-reinforced Al alloy metal matrix composite on workpiece removal rate, electrode wear rate and material removed per discharge pulse, which are not extensively explored in the literature. B4C-reinforced Al2014 matrix composite samples containing 5 and 10 vol.-% B4C particles, produced by vacuum infiltration method, were machined with electric discharge machining and powder mixed electric discharge machining at various discharge current settings. In both types of machining processes, the workpiece removal rate and electrode wear rates decreased and increased, respectively, when the reinforcement contents of the composites increased. However, powder-mixed electric discharge machining enhanced the machining stability, and a comparatively higher workpiece removal rate was observed with a decreased electrode wear rate. On the other hand, by increasing the discharge current, which was also verified as the most effective machining parameter in variance analysis, both workpiece removal rate and electrode wear rate values increased in both machining techniques. The experimentally calculated volumetric workpiece material removed by a discharge pulse was compared to that of a model in the literature, and they were also found to be consistent with each other.

Laser hybridizing with micro-milling for fabrication of high aspect ratio micro-groove on oxygen-free copper

High aspect ratio (HAR) micro-grooves are of great significance for vacuum electronic devices. However, the fabrication of HAR micro-groove on oxygen-free copper remains challenge since the high surface quality is hard to achieve. Aiming to improve the surface quality, a hybrid and successive method, obtained by combining nanosecond laser and micro-milling (NLMM), was presented. The nanosecond laser achieves the maximum workpiece removal rate, while the subsequent micro-milling provides the desired machining quality. Compared to one-way full slot micro-milling (FSMM), the presented manufacturing method (NLMM) could improve the surface quality, namely the top burr formation and the bottom and sidewall surface roughness. Furthermore, the NLMM displayed a lower tool wear rate compared to FSMM. Finally, a desired S-shaped groove with an aspect ratio of 2.5, a width of 0.2 mm, and the cycle number of 30 was successfully fabricated. The study offers a promising aspect for improving the HAR micro-groove fabrication quality.

Research on the embossment phenomenon of disc grinding by workpiece's removal rate

The disc grinding has become a widely used technology in the precision-manufacturing process for plate stainless steel. However, embossment phenomenon occurs on the ground workpiece's surface. Moreover, the workpiece's removal rate can be applied to measure the embossment. In most studies, the researches on the disc grinding technology mainly focus on the trajectory distributions, which might be not appropriate enough to capture the workpiece's removal rate. To this end, this paper has presented a multiple grits-discretized (MGD) model on the workpiece's removal rate to identify the formation mechanism of the embossment phenomenon. Meanwhile, the current model is established based on the grits’ distributions, the grits’ size and the kinematic multiple grits’ trajectory. The theoretical prediction for the distribution of workpiece's removal rate shows a reasonable agreement with the experimental validation. It shows that the removal rate is non-uniformly distributed on the workpiece's surface, which results in the workpiece's embossment. Furthermore, the workpiece's removal rate is greatly affected by the speed ratio. Therefore, the proposed model is not only anticipated to be meaningful for improving the uniformity of the machined workpiece by adjusting the speed ratio, but also expected to be useful for enhancing the understanding on the disc grinding enterprises.

Electromechanical Dynamics Model of Ultrasonic Transducer in Ultrasonic Machining Based on Equivalent Circuit Approach.

Ultrasonic transducer is a piezoelectric actuator that converts AC electrical energy into ultrasonic mechanical vibration to accelerate the material removal rate of workpiece in rotary ultrasonic machining (RUM). In this study, an impedance model of the ultrasonic transducer is established by the electromechanical equivalent approach. The impedance model not only facilitates the structure design of the ultrasonic transducer, but also predicts the effects of different mechanical structural dimensions on the impedance characteristics of the ultrasonic transducer. Moreover, the effects of extension length of the machining tool and the tightening torque of the clamping nut on the impedance characteristics of the ultrasonic transducer are investigated. Finally, through experimental analysis, the impedance transfer function with external force is established to analyze the dynamic characteristics of machining process.

Impact Analysis of Electrolyte Pressure on Shape Accuracy of Micro Holes in ECM with Hollow Electrodes

In electrochemical machining (ECM) of micro holes with high aspect ratio, hollow electrodes are commonly utilized to remove electrolytic products from the inter-electrode gap. In this paper, the effect of electrolyte pressure through hollow electrode on shape accuracy is studied by both numerical simulations and experimental tests. The multi-physics models consisting of electric current field, electrolyte flow, gas diffusion and heat transfer are established by using COMSOL Multiphysics software. With the inlet pressure range of 0.25-1.15MPa employed, the material removal rate of workpiece is predicted. At different machining depths, the material removal rate of micro-hole bottom is in an increasing trend with the pressure increasing, which has a positive effect on machining stability. With the pressure increasing, the material removal rate of side wall is fluctuating. And the area of vortex zone in the machining gap increases. Consequently, the shape accuracy is deteriorated. From experimental results of reverse tapered holes, at a small machining depth, the shape accuracy is deteriorated (straightness error > 20μm) with excessive electrolyte pressure. When the hole is deep, the shape accuracy is deteriorated with low pressure because of electrolytic products blocking. The shape accuracy can be improved by changing the electrolyte pressure in optimal rules obtained from the simulated results. The proposed simulation model can be used as a predictive tool to provide optimal parameters for better shape accuracy in micro ECM. On 1.0mm thick 18CrNi8 workpiece, a reverse tapered hole with diameter of 175μm and taper angle of 1.12° is machined. The deviation between designed shape and experimental results is 4.2μm.

Lubricating property of MQL grinding of Al2O3/SiC mixed nanofluid with different particle sizes and microtopography analysis by cross-correlation

With the increased requirements for environmental protection, energy conservation, and low consumption, nanofluid minimal quantity lubrication (MQL) grinding, which is an environment-friendly machining method, has been paid increasing attention. Improving the lubricating property of nanofluids effectively is currently a main research trend. Meanwhile, optimizing mixed nanoparticle (NP) size ratio is an effective way for enhancing the lubricating property of MQL grinding. In the experiment, different sizes (30, 50, and 70nm) of Al2O3 and SiC NPs were mixed, and nanofluids were prepared at 2% (volume fraction) mixed NPs and base oil. The prepared nanofluids were then used in MQL grinding on a hard Ni-based alloy (inconel 718). The experiment was then evaluated by specific grinding force, removal rate of workpiece, surface roughness, morphology of grinding debris, and contact angle. The effect of the sizes of the Al2O3/SiC mixed NPs on MQL grinding performance was discussed in accordance with the period and amplitude, as well as cross-correlation coefficient, of the workpiece surface cross-correlation function curve profile. Experimental results suggest that different Al2O3/SiC mixed NP sizes affect the nanofluid MQL grinding performance variably. The highest removal rate of the workpiece [189.05mm3/(sN)] and the lowest RSm (0.0381mm) were achieved when the Al2O3/SiC mixed NP size ratio was 70:30. The lowest Ra (0.298μm) was obtained at 50:30. Meanwhile, the highest length ratio of the profile support (90%), the best morphology of abrasive dusts, and the largest wetting area of liquid drops were acquired at 30:70. Furthermore, a cross-correlation analysis of the workpiece surface profile curve under three size ratios (30:70, 50:30, and 70:30) was carried out. The cross-correlation function curve of the workpiece surface profile under 30:70 attained the shortest period, the largest amplitude, and the largest cross-correlation coefficient (0.67), thereby indicating good workpiece surface quality. Therefore, 30:70 was the best size ratio of the Al2O3/SiC mixed nanofluid.

Mechanical and Machining Properties Analysis of Al6061-Cu-Reinforced SiC<sub>P</sub> Metal Matrix Composite

The metal matrix composite (MMC), despite of its high stiffness, strength, corrosion resistance, wear resistance, non-react with chemicals and so many other tailored qualities which are never obtained in alloy of metals, has limited utilization due to the high cost of fabrication. In this study, a modest attempt has been made to find out the process parameters at which best mechanical properties of Al6061, 4% Cu and reinforced 5% SiCP ceramic MMC can be obtained. The addition of 4% Cu in Al6061 is more or less comparable to the composition duralumin, which are widely used in aerospace applications. SiCP is hard and has linear thermal expansion at high temperature. With reinforcement of SiCP in Al6061-Cu alloy, it can be postulated that hardness of MMC retains at high temperature applications. An analysis of Variance (ANOVA) and linear regression was used for analysis of data with the help of SPSS (Version-17.0). Independent parameters are five levels of pouring rates (1.5 cm/s, 2.0 cm/s, 2.5 cm/s, 3.0 cm/s and 3.5 cm/s), and material type (Al6061 + 4% Cu alloy and Al6061 + 4% Cu, reinforced 5% SiCp MMC processed using stir casting technique) and dependent parameters are hardness and impact strength material removal rates of workpiece. It is found that at different pouring rates material hardness and impact strength of workpiece are highly significant but the material removal rate of workpiece is having no significance value. At pouring rate of 2.5 cm/s and 700℃ ± 5℃ pouring temperature, optimum values of hardness and impact strength are observed as compared to other values of pouring rates (1.5 cm/s, 2.0 cm/s, 3.0 cm/s and 3.5 cm/s). Material Removal rate for work pieces of Al6061 + 4% Cu alloy is less as compared to MMC. So it can be concluded that MMC has better machining ability compared to Al6061 + 4% Cu alloy. Material removal rate of Al6061 + 4% Cu, reinforced 5% SiCP MMC has maximum values at 1.5 cm/s pouring rate compared to 2.0 cm/s, 2.5 cm/s, 3.0 cm/s and 3.5 cm/s pouring rates. With reinforcement of 5% SiC trend of mechanical properties is same, but the hardness and impact strength of MMCs are increased by 25% and 20% respectively. Also it is observed from scanning electron microscopy (SEM) that at pouring rate 2.5 cm/s a better homogeneity can be obtained.

Study on Fixed Abrasive Lapping Hard and Brittle Materials with Brazed Micro Powder Diamond Disk

In this study, two different arrangement lapping disks fixed with brazed diamond pellets were used to lap silicon wafer and alumina ceramic. The effects of the surface morphology, roughness, and removal rate of workpiece caused by lapping pressure, lapping time, workpiece velocity, and disc arrangement were operated with serials experiments. The results of the researches provided guidance for fixed abrasive lapping of hard and brittle materials with the brazed micro powder diamond disk.

Parametric optimization of ultrasonic machining of co-based super alloy using the Taguchi multi-objective approach

Stellite 6 is the most generally useful cobalt alloy, having excellent resistance to many forms of mechanical and chemical degradation over a wide temperature range. Therefore, in particular, their use in aerospace projects world wide has provided confidence leading to acceptance as prime material for aerospace vehicles in recent years. This paper outlines the effectiveness of the ultrasonic machining of stellite 6 in terms of tool wear rate of the tool used and the material removal rate of work piece produced. The optimum combination of various input factors as type of abrasive slurry, their size and concentration, nature of tool material and power rating of the machine for the ductile chip formation in the machining of stellite 6 has been determined by applying the Taguchi multi-objective optimization technique and F-test. The analysis of results has been done using the statistica 7.0 software and results obtained are validated by conducting the confirmation experiments. The study shows the considerable improvement in multiple S/N ratio as compared to initial cutting conditions.

EDM performance of electroformed Cu‐ZrB2 shell electrodes

PurposeCu‐ZrB2 shell electrodes were fabricated by composite electroforming to improve the spark‐resistance of the electrical discharge machining (EDM) electrodes made by rapid tooling.Design/methodology/approachCu‐ZrB2 shell electrodes were fabricated using composite electroforming, separating and backing. EDM performance evaluation of the Cu‐ZrB2 shell electrodes is performed using tool steel as the cathode workpiece and the Cu‐ZrB2 composite as the anode tool. The effects of ZrB2 content on the electrode and workpiece removal rate, wear ratio of the electrode to workpiece, and surface quality of workpiece and electrode were studied.FindingsCompared with the conventional electroformed copper tools, Cu‐ZrB2 shell electrodes yield higher workpiece removal rate and lower tool wear ratio. Scanning electron microscopy (SEM) and electron microprobe analysis reveal that, due to the large difference between the melting point of ZrB2 and copper, the heat generated by the sparks is conducted mainly through the copper matrix, reducing the erosion of ZrB2 particles. The refractory ZrB2 particles then act as barriers to the flowing and outburst of melted copper and enhance the resistance to erosion of the electrodes.Originality/valueThe use of Cu‐ZrB2 shell electrodes improves the anti‐erosion properties of the EDM electrodes made by rapid tooling, especially in finish machining conditions. Such electrodes will not only reduce the failure of the EDM electrodes but also improve the machining precision due to the less dimension loss of the electrodes during machining.

Model of workpiece erosion for electrical discharge machining process

The previously published step-wise model (SWM) of cold electrodes erosion of electric arc heaters (EAHs) was modified for the calculation of workpiece removal rate (WRR) in electrical discharge machining (EDM) process. Modified model applies both relations the step-wise erosion model and the point heat source erosion model and takes into account the discharge current, the discharge pulse/pause time and thermophysical properties of machined material. The results of calculations show a reasonable agreement with data obtained experimentally by different authors about different materials and conditions.

An experimental investigation on the effect of powder mixed dielectric on machining performance in electric discharge machining

In this study, the variations of machining performance outputs, namely workpiece surface roughness, surface profile power spectral density, workpiece removal rate, electrode wear rate, relative wear, workpiece surface hardness, and workpiece surface microstructure were experimentally investigated with the varying machining parameters for metal powder mixed dielectric liquid in electrical discharge machining (EDM). The machining tests were conducted by using a prismatic steel workpiece and copper electrodes with graphite and boric acid powders (H3BO3) mixed kerosene dielectric at different powder concentrations and pulse time settings. The experiments have shown that the type and concentration of the powders mixed into the dielectric and the pulse time were effective on machining performance outputs in EDM.

An experimental investigation of tool wear in electric discharge machining

In this study, the variations of geometrical tool wear characteristics – namely, edge and front wear – and machining performance outputs – namely, workpiece removal rate, tool wear rate, relative wear and workpiece surface roughness – were investigated with varying machining parameters. Experiments were conducted using steel workpieces and round copper tools with a kerosene dielectric under different dielectric flushing conditions (injection, suction and static), discharge currents and pulse durations. The experiments have shown that machining parameters and dielectric flushing conditions had a large effect on geometric tool wear characteristics and machining performance outputs. Additionally, published research on tool wear is presented in detail in this study.

The effect of machining parameters on tool electrode edge wear and machining performance in Electric Discharge Machining (EDM)

The main purpose of this study is to investigate the variation of tool electrode edge wear and machining performance outputs, namely, the machining rate (workpiece removal rate), tool wear rate and the relative wear, with the varying machining parameters (pulse time, discharge current and dielectric flushing pressure) in EDM die sinking. The edge wear profiles obtained are modeled by using the circular arcs, exponential and power functions. The variation of radii of the circular arcs with machining parameters is given. It is observed that the exponential function models the edge wear profiles of the electrodes very accurately. The variation of exponential model parameters with machining parameters is presented.

ＥＬＩＤ研削と放電加工の複合化に関する基礎的研究 直流パルス電流を用いた複合加工の試み

A new combination machining method of ELID-grinding & EDM was lately proposed by the authors. As the results, grinding forces were successfully diminished in comparison with the conventional ELID-grinding. The finished surface, however, severely deteriorated due to EDM using a DC power-source, and a loss of electrodes could not be ignored. In this paper, the DC power-source is replaced by a DC-pulse power-source in order to improve the surface roughness. As the results, both the surface roughness and the loss of the electrodes are successfully reduced. The maximum downfeed, in which a stable combination machining can be performed, increases with the applied voltage for EDM. Workpiece removal rate shows the peak value at a certain table speed under the constant combination machining condition. The finishing process through the combination machining to ELID-grinding is also discussed, and the most efficient process is proposed.

Rapid tooling of EDM electrodes by means of selective laser sintering

Besides using the selective laser sintering of metal powder for tooling of, e.g., moulding dies, the sintering of EDM-electrodes is one modern development in the field of the Rapid Tooling. The electrodes are built up layer by layer using the 3-D CAD data. So far, a bronze–nickel powder mixture has been used. The made optimization of the sintering process parameters showed that the speed and the sintering strategy have the biggest impact onto the quality of the sintered electrodes, besides the laser power and the hatch distance. Slower scan speed leads to a higher particle density by a lower roughness. A 90° rotation of the scan direction at every other layer (gitter scanning) leads to an increase in strength and a decrease in porosity compared to the alternate scanning (no rotation). The minimum porosity achieved was 20% by using the bronze–nickel powder. The behavior of sintered electrodes has been investigated in relative electrode wear and workpiece removal rate during EDM-experiments. It could be proved that they are useable as electrode wear compared to massive copper electrodes. The wear behavior leads to an unacceptable change of the shape of the electrodes and furthermore, of the workpiece. The so-far made investigations showed that a decrease in porosity of the electrodes leads to a decrease electrode wear and increased workpiece removal. An improvement is possible during the EDM-process by shortening the pulse duration ( t i<10 μs) and the pulse interval ( t 0<5 μs) as long as the flushing of the frontal gap is guaranteed to prevent a process failure. A specific after-treatment of the electrodes by infiltration with silver-containing solder results in an almost fully dense tool body and a decrease in relative electrode wear by 30–50% in contrast to an infiltration with tin-containing solder that worsen the erosion behavior. The investigation of the impact of the workpiece material onto the relative wear of the selective laser sintered electrodes showed a decrease in tool wear when the pulse duration is set to t i=10–70 μs by spark erosion of X210Cr12 and C45 steel. The reason for that lies in the high content of chrome in the steel that leads to a lower workpiece removal rate due to the higher melting point of the material. Even by a low pulse energy, an arc may occur. Future research projects will concentrate especially on the future optimization of the process parameters of the EDM as well as on variations of the metal powder for the laser sintered electrodes. The aim is to decrease the porosity and the roughness of the sintered tools. By improving the laser beam absorption ability by the metal powder, the strength of the tool can be increased.

Use of zirconium diboride-copper as an electrode in plasma applications

Frequent replacement of electrodes, due to their high wear rate, is an undesired feature of most thermal plasma processes. Hence, the discovery of a high spark-resistive tool, ZrB2-Cu, is of interest. Performance evaluation of this metal matrix ceramic (MMC) employed electrical discharge machining (EDM), where steel is used as the cathode workpiece and the MMC is used as the anode tool. Compared with the performance of copper and graphite tools, ZrB2-Cu yields the highest workpiece removal rate,; and the lowest tool wear rate at high plasma heat flux conditions, resulting in an extremely low wear ratio. Energy dispersive spectroscopy shows deposition of workpiece materials (Fe, Cr, Ni and S) on the ZrB2-Cu surface after EDM. This is due to the difference between the surface temperature of the tool and the workpiece. Scanning electron microscopy and elemental mapping analysis reveal that the composite electrode erodes by a combination of dominant evaporation and melting of the metal phase, negligible melting and thermal spalling in the ceramic phase, quick refreezing of the metal phase back to the surface, and deposition of the workpiece (steel) on the tool surface. Most of the heat is conducted through the Cu phase, reducing thermal stress in the ceramic phase. This causes lower surface temperatures for the molten ZrB2 matrix; hence, the Cu tends to refreeze quickly near the surrounding ceramic matrix.

Electrical Discharge Machining of ZrB2-Based Ceramics

Abstract The objective of this study is to investigate the possibility of fabricating ZrB2-based materials using wire-cutting and die-sinking electrical discharge machines. Compared to diamond saw machining, which machined ZrB2-based materials at a relatively low rate, electrical discharge machining is very attractive. Based on the experimental results under different machining conditions, the higher the energy input, the higher will be the material removal rate. ZrB2-Cu is difficult to machine due to partial surface oxidation, which was confirmed by x-ray diffraction and microprobe analysis. The extremely low workpiece removal rate makes ZrB2-Cu appealing for machine tool use.

電界付加バイオマシニングに関する研究

This paper deals with the possibility of electric field assisted biomachining using chemolithotrophic bacteria Thiobachillus ferrooxidans that usually lives in waste fluid of mine. It is pointed out that the removal rate of anode workpiece increases steeply in this method when stainless steel bar is used as a cathode tool electrode. The etch factor for copper in this method is approximately 2, which indicates that there is an anisotropic characteristic in the removal amount. The grain boundary of workpiece is likely to remove preferentially for copper and iron. After all, it was made clear that the removal rate of workpiece was controlled by the machining time and the applied voltage between workpiece and tool electrode. It is considered that some genetic technology will be needed in the future for controlling the activity of individual bacteria.

Improvement of Machining Characteristics with Polarity-Changed Pulse in EDM Processes.

In this paper, a new type of discharge current waveform, named polarity-changed pulse, is proposed in order to improve the machining characteristics in the EDM process. The principle of the method is to alter the polarity so that a greater instantaneous removal rate of the workpiece can be obtained, since the removal rates of the anode and cathode change with the development of the plasma arc. The polarity of the workpiece is set to positive when the discharge takes place, and then the polarity is changed to negative at a certain time after the discharge ignition. At first the removal amount of the workpiece and the tool wear ratio with respect to the polarity-changed pulse were calculated on the basis of the experimental results obtained with the conventional pulse. The removal rate and tool wear ratio were then investigated when the polarity-changed pulse was used. It is found from both experimental and calculated results that the use of polarity-changed pulse can decrease the tool wear ratio and increase the workpiece removal rate.