Effect of machining fluid on the process performance of electric discharge milling of insulating Al2O3 ceramic

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical techniques for the production of tools and parts from conducting ceramic blanks. However, the manufacturing of insulating ceramic blanks with these processes is a long and costly process. This paper presents a new process of machining insulating ceramics using electrical discharge (ED) milling. ED milling uses a thin copper sheet fed to the tool electrode along the surface of the workpiece as the assisting electrode and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on insulating ceramics. Machining fluid is a primary factor that affects the material removal rate and surface quality of the ED milling. The effects of emulsion concentration, NaNO₃ concentration, polyvinyl alcohol concentration and flow velocity of the machining fluid on the process performance have been investigated.     

An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts

Inconel 718 is a difficult-to-cut nickel-based superalloy commonly used in aerospace industry. This paper presents an experimental study of the tool wear propagation and cutting force variations in the end milling of Inconel 718 with coated carbide inserts. The experimental results showed that significant flank wear was the predominant failure mode affecting the tool life. The tool flank wear propagation in the up milling operations was more rapid than that in the down milling operations. The cutting force variation along with the tool wear propagation was also analysed. While the thermal effects could be a significant cause for the peak force variation within a single cutting pass, the tool wear propagation was believed to be responsible for the gradual increase of the mean peak force in successive cutting passes.     

Investigation of the spark cycle on material removal rate in wire electrical discharge machining of advanced materials

The development of new, advanced engineering materials and the need for precise and flexible prototypes and low-volume production have made the wire electrical discharge machining (EDM) an important manufacturing process to meet such demands. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon–carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits are identified. An envelope of feasible EDM process parameters is generated for each work-material. Applications of such a process envelope to select process parameters for maximum MRR and for machining of micro features are discussed. Results of Scanning Electron Microscopy (SEM) analysis of surface integrity are presented.     

Damage-free machining of monocrystalline silicon carbide

Cutting tests of monocrystalline SiC, on the surface of which an amorphous layer was preformed by ion implantation, were performed. Ductile-mode machining was observed at a depth of cut smaller than 60 nm. At a depth of cut larger than 60 nm, cracks were observed on the work surface. However, transmission electron micrographs show that crack propagation was obstructed at the interface between the amorphous and crystalline layers even under brittle-mode machining, and no subsurface damage extended into the crystalline layer. The results suggest that the damage-free machining of monocrystalline SiC is possible by surface modification to an amorphous structure.     

Influence of silicon powder-mixed dielectric on conventional electrical discharge machining

Electrical discharge machining (EDM) is a technological process with a large industrial implementation. Its use is particularly intense when very complex shapes on hard materials with a high geometrical and dimensional accuracy are required. However, the technological capability of the process has limited its application when the specification of the part surface quality imposes polished and mirror-like characteristics. The addition of powder particles in suspension in the dielectric modifies some process variables and creates the conditions to achieve a high surface quality in large areas. This paper presents a new research work aiming to study the performance improvement of conventional EDM when used with a powder-mixed dielectric. A silicon powder was used and the improvement is assessed through quality surface indicators and process time measurements, over a set of different processing areas. The results show the positive influence of the silicon powder in the reduction of the operating time, required to achieve a specific surface quality, and in the decrease of the surface roughness, allowing the generation of mirror-like surfaces.     

Machining of micro rotational parts by wire electrical discharge grinding

Micro rotational parts are used in several industrial sectors. Well-known applications are micro shafts of gears, ejector pins in forming tools, pin electrodes for micro electrical discharge drilling or micro stamping dies. Depending on the geometrical complexity of micro rotational parts different process variants of micro electrical discharge machining characterized by a rotating work piece can be used: wire electrical discharge grinding (WEDG) with fine wire electrodes, electrical discharge turning (EDT) with micro structured tool electrode, cylindrical electrical discharge grinding (CEDG) with micro profiled disk electrode. Characteristic to these process variants is the superimposed relative motion between the rotating electrodes and the feed. This relative motion can be varied in a wide circumferential velocity range to improve the material removal process. The paper gives an overview of kinematic and technological restrictions and requirements of the WEDG process influencing the process behavior with respect to the technological requirements of micromachining.     

An investigation of ultrasonic-assisted electrical discharge machining in gas

This study focuses on using ultrasonic to improve the efficiency in electrical discharge machining (EDM) in gas medium. The new method is referred to as ultrasonic-assisted electrical discharge machining (UEDM). In the process of UEDM in gas, the tool electrode is a thin-walled pipe, the high-pressure gas medium is applied from inside, and the ultrasonic actuation is applied onto the workpiece. In our experiment, the workpiece material is AISI 1045 steel and the electrode material is copper. The experiment results indicate that (a) the Material Removal Rate (MRR) is increased with respect to the increase of the open voltage, the pulse duration, the amplitude of ultrasonic actuation, the discharge current, and the decrease of the wall thickness of electrode pipe; and (b) the surface roughness is increased with respect to the increase of the open voltage, the pulse duration, and the discharge current. Based on experimental results, a theoretical model to estimate the MRR and the surface roughness is developed.     

Experimental study of surface roughness in slot end milling AL2014-T6

The aim of this work was to analyze the influence of cutting condition and tool geometry on surface roughness when slot end milling AL2014-T6. The parameters considered were the cutting speed, feed, depth of cut, concavity and axial relief angles of the end cutting edge of the end mill. Surface roughness models for both dry cutting and coolant conditions were built using the response surface methodology (RSM) and the experimental results. The results showed that the dry-cut roughness was reduced by applying cutting fluid. The significant factors affecting the dry-cut model were the cutting speed, feed, concavity and axial relief angles; while for the coolant model, they were the feed and concavity angle. Surface roughness generally increases with the increase of feed, concavity and axial relief angles, while concavity angle is more than 2.5°.     

A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling

A new high efficiency method of synthesis of ultrafine vanadium carbide (VC) at a low carburization temperature has been developed. Firstly, a mixture of V₂O₅ and graphite powders is milled using dielectric barrier discharge plasma assisted milling (denoted as DBDP milling) for 4 h, and then the milled powders are carburized at 1200 °C, causing the V₂O₅ to react completely with graphite to form ultrafine VC. The formation temperature of VC is much lower than that needed in the conventional milling and heating process. This is because of the greatly enhanced reaction between V₂O₅ and graphite arising from the unique lump-like morphology and large number of clean surface contacts and greater surface area induced by DBDP milling.     

An in-process surface recognition system based on neural networks in end milling cutting operations

An in-process based surface recognition system to predict the surface roughness of machined parts in the end milling process was developed in this research to assure product quality and increase production rate by predicting the surface finish parameters in real time. In this system, an accelerometer and a proximity sensor are employed as in-process surface recognition sensors during cutting to collect the vibration and rotation data, respectively. Using spindle speed, feed rate, depth of cut, and the vibration average per revolution (VAPR) as four input neurons, an artificial neural networks (ANN) model based on backpropagation was developed to predict the output neuron-surface roughness R_a values. The experimental results show that the proposed ANN surface recognition model has a high accuracy rate (96–99%) for predicting surface roughness under a variety of combinations of cutting conditions. This system is also economical, efficient, and able to be implemented to achieve the goal of in-process surface recognition by retrieving the weightings (which were generated from training and testing by the artificial neural networks), predicting the surface roughness R_a values while the part is being machined, and giving feedback to the operators when the necessary action has to be taken.     

放电加工用金属结合剂碳化硅工具的研究

本文利用热压烧结工艺制备了含有20vol％～50vol％SiC的放电加工用金属结合剂工具电极。采用非均相沉淀包裹法制得Cu包SiC复合粉体。并对试样的气孔率、电阻率、抗弯强度进行了研究,结果表明,随着SiC含量的增加,试样气孔率和电阻率提高,而抗弯强度下降;在20vol％-50vol％SiC含量范围内,采用直接混合法和包裹法制备的试样具有大致相同的气孔率、电阻率,但包裹法的强度却大大提高。用X—ray衍射、扫描电镜（SEM）、能谱分析（EDAX）等测试手段对试样进行了成分和微观形貌分析。研究结果表明,包裹法制得的Cu结合SiC试样,SiC分散更均匀,并通过形成Cu2O—SiO2共熔物（玻璃相）来提高SiC和Cu的界面结合强度。     

Simulation and experimental investigation of the end milling process considering the cutter flexibility

In this paper, a new type of model for the end milling process is presented considering cutter flexibility, which includes not only the static but also the dynamic deflection of the cutter. According to the basic assumption for a linear elastic body, the force acting on the cutter and its deflection in the milling process are both divided into two parts: the static and the dynamic. By considering the regenerative feedback in the practical milling process, the dynamic milling force acting on a unit length of the cutter is derived. Furthermore, a new kind of dynamic deflection model of the cutter is established. Based on this model, a new set of efficient numerical simulation algorithms are presented. In the mean time, the static deflection of the cutter is also formulated. Finally, the simulation and measurement of the milled surface topography for the end milling process show the feasibility of this model.     

Reliability of electrode wear compensation based on material removal per discharge in micro EDM milling

This paper investigates the reliability of workpiece material removal per discharge (MRD) estimation for application in electrode wear compensation based on workpiece material removal. An experimental investigation involving discharge counting and automatic on the machine measurement of removed material volume was carried out in a range of process parameters settings from fine finishing to roughing. MRD showed a decreasing trend with the progress of the machining operation, reaching stabilization after a number of machined layers. Using the information on MRD and discharge counting, a material removal simulation tool was developed and validated.     

Detection of chatter vibration in end milling applying disturbance observer

Suppression of chatter vibration is required to improve the machined surface quality and enhance tool life. For monitoring the chatter vibrations, additional sensors such as acceleration sensors are generally used, which results in high costs and low reliability of the machine tools. In this study, a novel in-process method to detect chatter vibrations in end milling is developed on the basis of a disturbance observer theory. The developed system does not require any external sensors because it uses only the servo information of the spindle control system. Self-excited and forced chatter vibrations are successfully detected.     

Geometric modeling of the linear motor driven electrical discharge machining (EDM) die-sinking process

Based on Z-map method, in this paper the development of a geometric model for the linear motor equipped EDM die-sinking process is described. Firstly discussed are the advantages and benefits of the introduction of the linear motor into EDM die-sinker. The current model has been employed to calculate the minimum gap distance for sparks to occur and to analyze the possibility of spark generation between the workpiece and electrode surfaces. Also calculated is the crater formed by a single spark. The final machined surface topography is predicted. The influence of peak current and discharge duration on the average surface roughness is simulated. The experiment has been conducted to study the effects of machining conditions as well as to verify the effectiveness of the developed geometric model.     

Feasibility study of electrical discharge machining for W/Cu composite

This study investigates the feasibility and optimization of electrical discharge machining for inspecting the machinability of W/Cu composites using the Taguchi method. W/Cu composites are a type of cooling material highly resistant to heat corrosion produced through powder metallurgy. As W/Cu composites are highly brittle, they are not suited to be machined of traditional machine manufacturing. This paper utilizes electrical discharge machining, which is thermal processing workpieces and not affected by mechanical properties of materials. This experiment utilizes the Taguchi method and L₁₈ orthogonal table to obtain the polarity, peak current, pulse duration, duty factor, rotary electrode rotational speed, and gap-load voltage in order to explore the material removal rate, electrode wear rate, and surface roughness. The influence of each variable and optimal processing parameter will be obtained through ANOVA analysis and verified through experimentation to improve the process. The final step is to study the surface integrities of W/Cu composite, such as surface profile and heat-affected zone, the energy distribution transferring phenomenon of W/Cu composite, and the discharge phenomenon of tungsten and copper elements with electrical discharge machining.     

Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.

In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si₃N₄ ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine.     

Analytical prediction of chatter stability in ball end milling with tool inclination

The paper presents an analytical method to predict chatter stability in ball end milling with tool inclination. The chatter stability limits in ball end milling without the tool inclination have been predicted in the previous study by deriving directional milling force coefficients and then solving a simple quadratic equation. However, the tool is generally inclined and not perpendicular to the cut surface in practice. Therefore, a new method is developed to compute the directional milling force coefficients considering the tool inclination. It is confirmed that the chatter stability predicted by the proposed method agrees well with the experiments.     

Performance of electrical discharge textured cutting tools

Tool face friction adversely affects chip formation and consumes about 25% of the total cutting energy. Friction in cutting can be controlled by introducing a lubricant into the tool-chip interface, the effectiveness of which may be enhanced by surface texturing the tool. This paper details the innovative application of electrical discharge machining for generating an isotropic texture on the tool rake face, with a view to facilitating lubricant penetration and retention. A significant reduction in feed and cutting forces that ensues from said texturing is demonstrated, followed by a presentation of the features and application areas of the technology.