Hole Overcut Research Articles

Sonication of tool electrode for utilizing high discharge energy during ECDM

ABSTRACTThe use of high applied voltage during the electrochemical discharge machining (ECDM) process forms a thick gas film and generates high discharge energy on film breakdown. This results in polarization and evaporation of electrolyte at the tooltip. Consequently, the ECDM process results in a low depth of penetration (DOP) with a large hole overcut (HOC). The present investigation is an attempt for utilizing high discharge energy during the ECDM process using sonication of tool electrode. The experimental results reveal that sonication regulates the gas bubble departure radius and thereby controls the gas film thickness. Besides, an increase in the electrolyte concentration reduces the gas film thickness and results in the generation of high-intensity and high-frequency electric discharges. Sonication results in improved electrolyte replenishment and sludge removal. A mathematical model is developed to understand the effect of process parameters on the gas bubble departure radius. Also, the present investigation compares ultrasonic-assisted electrochemical discharge machining (UAECDM) and the general ECDM process. Sonication of tool electrode during UAECDM process exhibit improvement in material removal rate (MRR) by 11.13%, DOP by 27.17% and reduction in HOC by 23.10% over the ECDM process.

Analysis, predictive modelling and multi-response optimization in electrical discharge machining of Al-22%SiC metal matrix composite for minimization of surface roughness and hole overcut

Due to the widespread engineering applications of metal matrix composites especially in automotive, aerospace, military, and electricity industries; the achievement of desired shape and contour of the machined end product with intricate geometry and dimensions that are very challenging task. This experimental investigation deals with electrical discharge machining of newly engineered metal matrix composite of aluminum reinforced with 22 wt.% of silicon carbide particles (Al-22%SiC MMC) using a brass electrode to analyze the machined part quality concerning surface roughness and overcut. Forty-six sets of experimental trials are conducted by considering five machining parameters (discharge current, gap voltage, pulse-on-time, pulse-off-time and flushing pressure) based on Box-Behnken's design of experiments (BBDOEs). This article demonstrates the methodology for predictive modeling and multi-response optimization of machining accuracy and surface quality to enhance the hole quality in Al-SiC based MMC, employing response surface methodology (RSM) and desirability function approach (DFA). Finally, a novel approach has been proposed for economic analysis which estimated the total machining cost per part of rupees 211.08 during EDM of Al-SiC MMC under optimum machining conditions. Thereafter, under the influence of discharge current several observations are performed on machined surface morphology and hole characteristics by scanning electron microscope to establish the process. The result shows that discharge current has the significant contribution (38.16% for Ra, 37.12% in case of OC) in degradation of surface finish as well as the dimensional deviation of hole diameter, especially overcut. The machining data generated for the Al-SiC MMC will be useful for the industry.

Performance enhancement of rotary tool near-dry EDM of HSS by supplying oxygen gas in the dielectric medium

ABSTRACTThe present investigation was carried out with an objective to enhance the performance of the rotary tool near-dry EDM (RT-ND-EDM) process by adding oxygen gas in addition to the dielectric medium. The effects of the amount of oxygen, rotational speed of the tool, current, pulse on time, and liquid flow rate were investigated on the performance characteristics of RT-ND-EDM process using high-speed steel as work material. The material removal rate (MRR), hole overcut (HOC), and surface quality were chosen as performance characteristics to represent the viability of the process. Surface quality was measured and analyzed in terms of debris deposition, micro-globules on the surface, porosity, micro-cracks, blowholes, and flow marks. The analysis of experimental results of RT-ND-EDM process, when oxygen gas was used along with dielectric medium, revealed that the MRR was 203%, 110%, and 85% higher than that of MRR obtained by the dry EDM using air, dry-EDM using air-oxygen, and RT-ND-EDM process without oxygen, respectively. This can be attributed to the fact that the addition of oxygen in the water-air dielectric medium helped in more amount of melting due to the rapid oxidation of work material. The debris formed during the oxygen mixed RT-ND-EDM process, cross-sectional analysis of the machined surface and analysis of tool wear were also investigated.

Experimental investigations, empirical modeling and multi objective optimization of performance characteristics for ECDD with pressurized feeding method

Electrochemical discharge drilling (ECDD) is a hybrid micromachining process that can be used to drill micro holes on all kind of materials, irrespective of their mechanical and electrical properties. In ECDD, the continual penetration of tool electrode having electrochemical discharge (ECD) energy along the work material generates the holes. The relative movements between tool electrode and work material controls the energy penetration rate, and subsequently effects the performance characteristics. Therefore, the effect of process parameters associated with feeding motion and ECD energy are important to investigate simultaneously with respect to the performance characteristics. In the current study, a Buckingham’s dimensional method was used to determine the relation between input process parameters (that includes simultaneous interaction of ECD energy based parameters and feeding motion based parameters) and performance characteristics. The material removal rate (MRR) and hole overcut (HOC) were considered as the performance characteristics. MRR and HOC symbolize the productivity and accuracy of the process, respectively. During predictive modeling, the constant terms and coefficients were estimated from the non-linear experimental data. The outcomes manifested by the predictive models are in good agreement with the experimental results. The underlying process mechanism for ECDD with the pressurized feeding system has been explored by considering the simulation results as an evidences. Microscopic images of machined holes and discharge characteristics were used to develop the fundamental background of ECDD process mechanism with pressurized feeding method. Additionally, genetic algorithm (GA) was used to perform the multi objective optimization of ECDD process.

Micro-ultrasonic drilling of monocrystalline silicon: An experimental investigation on machined surface topography and optimization using User's preference rating based TOPSIS

In the current scenario, silicon is extensively used as raw material in microelectromechanical systems and microelectronic devices. But, it has low fracture toughness that renders it difficult to process by conventional machining techniques. Thus, to overcome the barriers of conventional machining, rotary tool micro-ultrasonic drilling (RT-MUSD) process has been attempted for machining of silicon in this research endeavour. Taguchi's L9 orthogonal array was adopted as experimental design. The influence of variable parameters viz. rotation speed, power rating and abrasive size were analysed on performance characteristics (i.e. hole overcut (HOC), taper angle (TA) and material removal rate (MRR)) of RT-MUSD process. Analysis of variance (ANOVA) was applied to determine the significant parameters affecting the RT-MUSD process. Subsequently, optimal parametric setting for minimum HOC and TA and maximum MRR was obtained through user's preference rating based technique for order preference by similarity to ideal solution method. The ANOVA results showed that rotation speed was the most influencing parameter affecting the HOC, TA and MRR. The optimal parametric combination resulted in an average improvement of 26% in the performance of RT-MUSD process. The machined surface topography revealed that two types of material removal mode (i.e. pure brittle fracture and ductile + brittle fracture) occurred during RT-MUSD of silicon.

Effect of tool rotation in near-dry EDM process on machining characteristics of HSS

ABSTRACTRotary tool near-dry electrical discharge machining (RT-ND-EDM) is a process variant of EDM, which utilizes two phase dielectric medium instead of a conventional liquid or gaseous dielectric medium. The present work, RT-ND-EDM was investigated while machining of high speed steel (AISI M2 grade) using glycerin-air dielectric medium. The effect of various input process parameters was investigated on material removal rate (MRR), surface roughness (SR), and hole overcut (HOC). The input parameters considered were tool rotation speed, current, pulse on time, liquid flow rate, and gas pressure. Experiments were designed and conducted using response surface methodology. Regression models were also developed. The results revealed that the tool rotation speed has a significant effect on MRR, SR, and HOC. FE-SEM micrographs showed that the machined surfaces obtained by RT-ND-EDM have relatively lower micro-cracks, debris accumulation and craters. Also, deep through holes were successfully drilled in 24 mm plate using RT-ND-EDM process.

On machining of hard and brittle materials using rotary tool micro-ultrasonic drilling process

ABSTRACTThe present paper reports on a recently developed rotary tool micro-ultrasonic drilling (RT-MUSD) process. The RT-MUSD process was utilized for machining of micro-holes in zirconia, silicon and glasswork materials. The effects of work material properties on the performance characteristics (material removal rate (MRR), depth of hole and hole overcut) of RT-MUSD process were investigated by varying the power rating, rotation speed, abrasive size and slurry concentration. Additionally, machined micro-holes and tool surface were analyzed considering microscopic images. The experimental results revealed that the MRR and depth of hole increased by increasing the power rating. An increase in rotation speed up to 300 rpm, abrasive size up to #1200 mesh and concentration up to 20% increased the MRR, depth of hole and decreased hole overcut. The maximum machining rate and hole overcut were observed during machining of silicon followed by glass and zirconia. The fracture toughness and hardness of the work material affected the MRR and tool wear, respectively. Pure brittle fracture mode of material removal was observed in all the work materials during RT-MUSD process. Eventually, the RT-MUSD process was optimized using desirability approach and a micro-hole of depth 4355 µm was achieved using optimal parameter settings.

ИССЛЕДОВАНИЕ МНОГОФАКТОРНОЙ ЗАВИСИМОСТИ РАЗБИВКИ ОТВЕРСТИЙ ПРИ ЭЛЕКТРОЭРОЗИОННОЙ ПРОШИВКЕ МИКРООТВЕРСТИЙ

The PURPOSE of the paper is to determine the actual dependence of hole overcut at the EDM drilling of microholes on the main process parameters. METHODS. An experimental and calculation research methods are used to study the multifactorial dependence of the hole overcut. Mathematical modeling of the three-factorial dependence of the hole overcut is performed. RESULTS. Mathematical models of the hole overcut dependence on main process parameters have been received. CONCLUSIONS. The pulse energy has been determined to be the most significant parameter influencing the hole overcut at EDM drilling. The obtained mathematical models allow to select the optimum diameter of an electrode-tool and to specify the optimum electric modes at the EDM drilling of microholes.

Minimization of the hole overcut and cylindricity errors during rotary ultrasonic drilling of Ti-6Al-4V

Titanium and its alloys e.g. Ti6Al4V have widespread applications in aerospace, automotive and medical industry. At the same time titanium and its alloys are regarded as difficult to machine materials due to their high strength and low thermal conductivity. Significant efforts have been dispensed to improve the accuracy of the machining processes for Ti6Al4V. The current study present the use of the rotary ultrasonic drilling (RUD) process for machining high quality holes in Ti6Al4V. The study takes into account the effects of the main RUD input parameters including spindle speed, ultrasonic power, feed rate and tool diameter on the key output responses related to the accuracy of the drilled holes including cylindricity and overcut errors. Analysis of variance (ANOVA) was employed to study the influence of the input parameters on cylindricity and overcut error. Later, regression models were developed to find the optimal set of input parameters to minimize the cylindricity and overcut errors.

Optimization of size and form characteristics using multi-objective grey analysis in abrasive water jet drilling of Inconel 617

Inconel 617, a group D category of Superalloys, is the prime material for ultra-supercritical power plant components. Nontraditional machining methods are explored for machining Inconel 617 as the traditional processes are limited. Abrasive water jet machining is very promising in processing hard-to-machine materials and machining of superalloys using abrasive water jet machining needs attention. This paper focuses on establishing hole characteristics in abrasive water jet drilling using multi-objective grey analysis. The form and orientation characteristics of the hole are defined using entry and exit hole overcut, entry and exit hole circularity, taper angle of hole and depth averaged radial overcut apart from drill rate and surface roughness. The process parameters are water jet pressure, standoff distance, and abrasive mass flow rate. Analysis of variance of the individual responses is used to identify the pattern in which each parameter affects the performance of the process. Interaction effects of the various factors have been elaborated using plots. Analysis of means was conducted to obtain the mean effects plot. The results from analysis of variance and analysis of means were compared and good correlation was obtained. The parameter levels for obtaining optimal individual responses were identified and reported. Grey relational analysis combines the attributes of each of the responses into a single grey grade. The grey grade represents the overall hole characteristic of the drilled hole. Analysis of means of the grey grade gives the optimal parameter setting. The adjudged optimal parameters are tested experimentally and reported.

Experimental investigation on drilling of borosilicate glass using micro-USM with and without tool rotation: a comparative study

The application of microproducts is increasing rapidly in various fields such as automobiles, electronics, microfluidics, bio-MEMS, etc. These microproducts are generally made of hard and brittle materials, e.g., glass, quartz, ceramics and silicon, etc. The machining of these materials in micro-domain is a difficult task. Micro-ultrasonic machining (micro-USM) is a preferred process for machining of hard and brittle materials. But high tool wear and low aspect ratios limits its industrial use. This investigation compares the effect of tool rotation on material removal rate and hole overcut. Additionally, aspect ratio was measured. The variable process parameters for the investigation were power rating, static load, slurry concentration and abrasive size. Imaging was used for qualitative analysis of tool wear. The experimental results reveal that micro-USM with tool rotation resulted in higher material removal rate, lesser hole overcut, high aspect ratios and lesser tool wear in compared with micro-USM without tool rotation.

Experimental investigation and multiphysics simulation on the influence of micro tools with various end profiles on diametrical overcut of holes machined using electrochemical micromachining for a predetermined optimum combination of process parameters

Electrochemical micromachining (EMM) process is generally applied to shaping of electrically conductive materials which has been gaining popularity in the production of biomedical, MEMS, aerospace and nuclear components. The dimensional accuracy is affected by various process parameters of EMM and by the end profile of the cathode (tool) used to machine the feature. In this study, it is proposed to investigate the EMM process to know the influence of various process parameters on the diametrical overcut of the machined hole and the optimum combination of process parameters to produce holes with minimum diametrical over cut. A bare electrode with flat end is used for this purpose. Later, insulated electrode with flat end and bare electrodes with various end profiles are used to drill holes at the optimum combination of process parameters on Titanium grade II sheet to identify the most suitable micro tool to produce holes with minimum diametrical overcut and minimum stray machined zone. The EMM process of drilling holes using insulated electrode with flat end and bare electrodes with various end profiles are simulated at the optimum combination of process parameters using COMSOL Multiphysics V4.2a software. Results justified the use of multiphysics simulation to understand the process before conducting experiments so that costly trial and error experiments can be reduced to a minimum.

Selection of dry drilling parameters for minimal burr size and desired drilling quality

The drilling of metals produces undesired raised material which is defined as burr. It is important to minimize the burr size by modifying the drill geometry or selection of drilling parameters. Although, selection of optimal drilling parameters can be minimize the burr size, but it may be increases the overcut or decreases the material removal rate (MRR). In this paper, drilling parameters have been selected for minimal burr size and desired overcut and MRR. Four adaptive neuro fuzzy inference system (ANFIS) models have been designed based on experimental observation in drilling of copper. Outputs of ANFIS models are burr height, burr thickness, burr type and overcut of hole; While input parameters of drilling process are cutting speed, tool diameter and ratio of feed rate to diameter. Then the particle swarm optimization method has been used to select the optimum condition of input parameters to minimize the burr size in desired value of overcut and MRR. Results showed that the proposed models can be predict the outputs well and they can be used as adequate predictors and optimizer for achieving the drilling parameters which gives a type of burr with low value of burr height and burr thickness with desirable overcut and MRR.

Effect of Electrolytes on Quality Characteristics of Glass during ECDM

Electrochemical discharge machining (ECDM) is an ideal process for machining of nonconductive materials in micro-domain. The material removal takes place due to combined action of localised sparks and electrolysis in an electrolytic chamber. The electrolyte is most important process parameter for ECDM as it governs spark action as well as electrolysis. This article presents a comparison of three preferred electrolytes used in ECDM viz. NaCl, KOH and NaOH on drilling of glass workpiece material. The quality characteristics measured are material removal rate (MRR) and hole overcut. Results reveal that NaOH provides 9.7 and 3.8 times higher MRR than NaCl and KOH respectively. MRR and hole overcut are found significantly affected by spark characteristics.

Experimental investigation on the influence of electrochemical micro-drilling by short pulsed voltage

In this work, a tungsten carbide (WC) pin 50 μm in diameter was used to drill throughout nickel plates of 200 μm in thickness by electrochemical micro-machining. A novel pulsed power generator was used to support pulses of nanosecond duration in drilling. The influences of working parameters, such as pulsed duration, applied voltage, pulse frequency, electrolyte concentration, tool feed rates, and hole depth, on the hole overcut and conicity are investigated. A high-quality micro-hole with 11.1-μm overcut was drilled on a nickel plate of 200 μm in thickness.

Electrochemical Micro-Drilling with Ultra-Short Pulses

Electrochemical micro-machining (EMM) has a high removal rate, leaves no residual stress on the surfaces of machined products, and generates a low level of roughness on the surface of machined products. In this work, a novel pulsed power generator is used to support tens of nanosecond duration to drilling. The influences of working parameters, such as pulsed duration, applied voltage, electrolyte concentration, pulse frequency, tool feed rates, and hole depth, on the hole over-cut and conicity in electrochemical micro-drilling are investigated. A high-quality micro hole with a 13.75 μm overcut is drilled into a nickel plate 300 μm thick.

Electrochemical micro-drilling of deep holes by rotational cathode tools

In numerous non-conventional micro-machining, electrochemical micro-machining has merits such as high removal rate, leaving no residual stress and lower roughness on surfaces of machined products. It has been considered as a highly promising technology in micro-machining. Little research has been done on the deep-hole micro-drilling by electrochemical methods. This work utilizes a rotational system to extract insoluble sludge from a deep hole and reduce the difficulty of filling deep hole with electrolyte. As well as a rotational tool cathode, a pulsed power generator is used to support the intermittence machining to increase the precision of the workpiece. The influence of working parameters, such as pulsed on-times, applied voltages, electrolyte concentrations, pulsed frequencies, tool feeding rates, tool diameters, tool rotational rates, and hole depth, on the hole overcut and conicity in a electrochemical micro-drilling is investigated. A high quality micro-hole with a 33.35-µm overcut is drilled by a tungsten carbide pin of diameter 50 µm on a 304 stainless steel plate of thickness 1,000 µm. The hole aspect ratio (depth/diameter) reaches 8.6. It shows that a rotational tool can be utilized in the deep-hole electrochemical micro-drilling.