钛合金深小孔超声电火花加工工艺与实验研究

针对钛合金深小孔加工的技术难点,研制了具有四轴联动功能的微细超声电火花加工机床,在所研制的机床上,进行了钛合金深小孔超声电火花复合加工实验,就超声振动及削边电极在加工中的作用进行了系统和研究。     

INVESTIGATING THE EFFECTS OF EDM PARAMETERS ON SURFACE INTEGRITY,MRR AND TWR IN MACHINING OF Ti–6Al–4V

Ti–6Al–4V is a kind of difficult-to-cut material with poor machinability by traditional machining methods, while electrical discharge machining (EDM) is suitable for machining titanium alloys. In this paper, three input machining parameters including pulse current, pulse on time and open circuit voltage were changed during EDM tests. To investigate the output characteristics; material removal rate (MRR), tool wear ratio (TWR) and different aspects of surface integrity for Ti–6Al–4V samples such as topography of machined surface, crack formation, white layer (recast layer) thickness and microhardness were considered as performance criteria. The variations of MRR and TWR versus input machining parameters were investigated by means of main and interaction effect plots and also verified by ANOVA results. The effect of pulse energy based on pulse on time and pulse current variations against recast layer thickness and microhardness was studied. The possibility of forming different chemical elements and compounds on the work surface after EDM process was investigated by EDS and XRD analyses. The experimental results revealed that general aspects of surface integrity for machined samples are mostly affected by pulse current and pulse on time. The approximate density of cracks, micro holes and pits on the work surface is intensively dependent on pulse energy variations. Although increase of pulse energy improves the material removal efficiency but leads to increase of average thickness and microhardness of recast layer.     

超声振动辅助磨削脉冲放电复合加工工艺研究

利用超声振动、电火花脉冲放电的加工特点,将其同单一普通磨削优化组合,可以得到较好的加工效果。从加工表面粗糙度、表面微观形貌两个方面,比较了单一磨削、超声振动辅助磨削、磨削—电火花脉冲放电复合加工、超声振动辅助磨削—电火花脉冲放电复合加工的加工效果,得出了不同加工方法的优缺点。通过对几种加工方法的优化组合,设计了新的加工工艺。实验结果证明,新的加工工艺可以有效地提高加工表面质量,减少裂纹和热应力的产生。     

Error modeling and accuracy optimization of rotating ultrasonic vibration assisted EDM machine tool

Rotating ultrasonic vibration assisted EDM is a composite machining method that uses EDM to etch a metal surface and adds rotating and ultrasonic vibration     

Effect of ultrasonic vibration of tool on electrical discharge machining of cemented tungsten carbide (WC-Co)

This paper deals with the effect of copper tool vibration with ultrasonic (US) frequency on the electrical discharge machining (EDM) characteristics of cemented tungsten carbide (WC-Co). It was found that ultrasonic vibration of the tool (USVT) was more effective in attaining a high material removal rate (MRR) when working under low discharge currents and low pulse times (finishing regimes). In general, the surface roughness and the tool wear ratio (TWR) were increased when ultrasonic vibration was employed. It was observed that application of ultrasonic vibration significantly reduced arcing and open circuit pulses, and the stability of the process had a remarkable improvement. This study showed that, there were optimum conditions for ultrasonic assisted machining of cemented tungsten carbide, although the conditions may vary by giving other input parameters for those which had been set constant in the present work.     

超声振动辅助气体介质电火花加工实验机床的设计

提出了工具电极超声振动辅助气体介质电火花加工方法。设计了超声振动辅助气体介质电火花加工实验机床。实验结果表明,该机床能够满足超声振动辅助气体介质电火花加工的要求。     

Assessing the effects of different dielectrics on environmentally conscious powder-mixed EDM of difficult-to-machine material (WC-Co)

Electrical discharge machining (EDM) is a well-known nontraditional manufacturing process to machine the difficult-to-machine (DTM) materials which have unique hardness properties. Researchers have successfully performed hybridization to improve this process by incorporating powders into the EDM process known as powder-mixed EDM process. This process drastically improves process efficiency by increasing material removal rate, micro-hardness, as well as reducing the tool wear rate and surface roughness. EDM also has some input parameters, including pulse-on time, dielectric levels and its type, current setting, flushing pressure, and so on, which have a significant effect on EDM performance. However, despite their positive influence, investigating the effects of these parameters on environmental conditions is necessary. Most studies demonstrate the use of kerosene oil as dielectric fluid. Nevertheless, in this work, the authors highlight the findings with respect to three different dielectric fluids, including kerosene oil, EDM oil, and distilled water using one-variable-at-a-time approach for machining as well as environmental aspects. The hazard and operability analysis is employed to identify the inherent safety factors associated with powder-mixed EDM of WC-Co.     

Investigation of EDM characteristics of nickel-based heat resistant alloy

The EDM processing characteristics of one of the nickel-based heat resistant alloys, Hast-elloy-X, were investigated under the various EDM conditions and analyzed in terms of surface integrity. This alloy is commonly used as a material for the hot gas path component of gas turbines and it is difficult to machine by conventional machining methods. The primary EDM parameter which was varied in this study were the pulse-on time. Since the pulse-on time is one of the main factors that determines the intensity of the electrical discharge energy, it was expected that the machining ratio and the surface integrity of the specimens would be proportionally dependent on the pulse-on duration. However, experimental results showed that MRR (material removal rate) and EWR (electrode wear rate) behaved nonlinearly with respect to the pulse duration, whereas the morphological and metallurgical features showed rather a constant trend of change by the pulse duration. In addition the heat treating process affected the recast layer and HAZ to be recrystallized but softening occurred in recast layer only. A metallurgical evaluation of the microstructure for the altered material zone was also conducted.     

Surface Improvement Using a Combination of Electrical Discharge Machining with Ball Burnish Machining Based on the Taguchi Method

This study investigates the feasibility of improving surface integrity via a novel combined process of electrical discharge machining (EDM) with ball burnish machining (BBM) using the Taguchi method. To provide burnishing immediately after the EDM process, ZrO₂ balls were attached to the tool electrode in the experiments. To verify the optimal process, three observed values, i.e. material removal rate, surface roughness, and improvement ratio of surface roughness were chosen. In addition, six independent parameters were adopted for evalu-ation by the Taguchi method. From the ANOVA and S/N ratio response graph, the significant parameters and the optimal combination level of machining parameters were obtained. Experimental results indicate that the combined process effectively improves the surface roughness and eliminates the micro pores and cracks caused by EDM. Therefore, the combination of EDM and BBM is a feasible process by which to obtain a fine-finishing surface and achieve surface modification.     

Experimental study of rotary magnetic field-assisted dry EDM with ultrasonic vibration of workpiece

Dry electrical discharge machining (EDM) is a green machining method which replaces the gas instead of liquid as dielectric medium. Due to the environmentally friendly nature of this method, recently, researchers focused on characterization of this process. In this work, effects of rotary magnetic field and also ultrasonic vibration of workpiece were studied on dry EDM process performance. Conducted experiments were divided in two main stages. At first stage, preliminary experiments were carried out to determine the best tool design in material and geometry points of view by considering the material removal rate (MRR). Also, effect of magnetic field was studied in the first stage. Results of the first stage of experiments indicated that the brass tool with two eccentric holes has the highest MRR rather than the other existing tool. In the second stage of experiments, parametric study on dry EDM process were implemented by using a brass tool with two eccentric holes and by applying rotary magnetic field for all experiments of the second stage. Influences of parameters such as pulse current, pulse on-time, pulse off-time, tool rotational speed, air injection inlet pressure, and especially power of ultrasonic table were studied on MRR, surface roughness (SR), electrode wear rate (EWR), and overcut (OC). Results showed that magnetic field has positive effects on MRR and SR. Also, by application of ultrasonic vibration achieving to superior MRR is feasible. At the end of the work, mathematical models were developed to correlate a relationship between process inputs and main outputs.     

微小型电火花加工装置连续自动送丝的研究

针对电极夹持、更换困难,辅助加工时间长等问题,提出了在微小型电火花加工装置中实现连续自动送丝的方案,采用该方案不仅可提高加工效率,同时可以消除电极重新定位所带来的误差。系统地分析了超声马达定子的驱动原理,推导出了马达的振动方程。进行了电极驱动性能的测试和实验加工,验证了连续自动送丝方案的可行性。     

Effect on crystalline structure of AISI M2 steel using tungsten–thorium electrode through MRR,EWR, and surface finish

To investigate on the crystalline structure of AISI M2 steel by using tungsten–thorium electrode in electrical discharge machining (EDM) process was studied. Furthermore, the investigation were carried out for finding the value of material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) of tool steel material depending upon three variable input process parameters. On the basis of weight loss, the value of MRR and EWR were calculated at optimized process parameter. Subsequently, surface topography of the processed material were examined through different characterization techniques like scanning electron microscopy (SEM), Optical surface profiler (OSP) and Atomic force microscopy (AFM), respectively. In XRD study, broadening of the peak was observed which confirmed the change in material properties due to the homogeneous dispersion of the particles inside the matrix. Lowest surface roughness and MRR of 0.001208 mg/min was obtained. Minimum surface roughness was obtained 1.12 μm and 2.18427 nm by OSP and AFM study, respectively. Also, minimum EWR was found as 0.013986 mg/min.     

Adhesion and abrasive wear resistance of TiN deposited on electrical discharge machined WC–Co cemented carbides

Electrical discharge machining (EDM) is a non-traditional machining method extensively used to manufacture complex geometries of hard and brittle materials such as WC–Co cemented carbides (CC). Although the thermal action of the EDM process is known to yield a relatively poor surface integrity in these materials, it may be minimized through the implementation of multi-step sequential EDM and post-EDM surface treatments. Particularly, hard coating application has been demonstrated to be effective for decreasing the EDM-induced mechanical degradation. However, additional studies are required on such coating–EDMed substrate systems to determine other crucial properties in terms of applications, e.g. adhesion and micro-scale wear behaviour. In this work the adhesion strength and the microabrasive wear resistance of TiN deposited on EDMed substrates have been evaluated by means of scratch and crater grinder testing, respectively. The results indicate that both critical load for decohesion of the coating from the substrate and coating specific wear rate increase with finer-executed EDM, reaching values close to those measured for a TiN coating deposited on a ground and polished substrate.     

Optimization of cryogenic cooled EDM process parameters using grey relational analysis

This paper presents an experimental investigation on cryogenic cooling of liquid nitrogen (LN₂) copper electrode in the electrical discharge machining (EDM) process. The optimization of the EDM process parameters, such as the electrode environment (conventional electrode and cryogenically cooled electrode in EDM), discharge current, pulse on time, gap voltage on material removal rate, electrode wear, and surface roughness on machining of AlSiCp metal matrix composite using multiple performance characteristics on grey relational analysis was investigated. The L₁₈ orthogonal array was utilized to examine the process parameters, and the optimal levels of the process parameters were identified through grey relational analysis. Experimental data were analyzed through analysis of variance. Scanning electron microscopy analysis was conducted to study the characteristics of the machined surface.     

A review on the use of dielectric fluids and their effects in electrical discharge machining characteristics

Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. In electrical discharge machining (EDM), a process utilizing the removal phenomenon of electrical discharge in dielectric, the working fluid plays an important role affecting the material removal rate and the properties of the machined surface. Choosing the right dielectric fluid is critical for successful operations. This paper presents a literature survey on the use of dielectric fluids and also their effects in electrical discharge machining characteristics.     

Experimental Investigation on Electrical Discharge Drilling of Ti-6Al-4V Alloy

This article describes the experimental investigation related to creation of holes in aerospace titanium alloy workpiece using static electrode machining and electrical discharge drilling (EDD) process. Special attachment for holding and rotating the tool electrode was developed and installed on electrical discharge machining (EDM) machine by replacing the original conventional tool holder provided on die sinking EDM. The effect of input parameters such as gap current, pulse on-time, duty factor and RPM of tool electrode on output parameters for average hole circularity (C_a) and average surface roughness (R_a) have been studied. It is observed that the effect of rotating electrode machining has considerable influence on the output parameters over stationary electrode machining. The micro-graphs and photographs of few selected samples were taken by SEM and metallurgical microscope, which also commensurate with the findings of the study.     

Surface modification using semi-sintered electrodes on electrical discharge machining

This study investigates how machining characteristics and surface modifications affect low-carbon steel (S15C) during electrical discharge machining (EDM) processes with semi-sintered electrodes. Among the machining characteristics determined, the material removal rate (MRR), surface deposit rate (SDR), and electrode wear rate (EWR) are included. Additionally, exactly how semi-sintered electrodes affect the surface modifications is also evaluated by electron probe microanalyzer (EPMA), micro hardness, and corrosion resistance tests. The experimental results confirmed that the composition of the semi-sintered electrodes is transferred onto the machined surface efficiently and effectively during the EDM process, and that the process is feasible and can easily form a modified layer on the machined surface.     

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.     

Investigation of electro-discharge micro-machining of titanium super alloy

Being a difficult-to-cut material, titanium alloy suffers poor machinability for most cutting processes, especially the drilling of micro-holes using traditional machining methods. Although electrical discharge machining (EDM) is suitable for machining titanium alloys, selection of machining parameters for higher machining rate and accuracy is a challenging task in machining micro-holes. The present research attempts to optimize micro-EDM process parameters for machining Ti-6Al-4V super alloy. To verify the optimal micro-EDM process parameters settings, metal removal rate (MRR), tool-wear rate (TWR), over cut (OC) and taper were chosen as observed performance criteria. In addition, four independent parameters such as peak current, pulse-on time, flushing pressure, and duty ratio were adopted for evaluation by the Taguchi method. From the ANOVA and S/N ratio graph, the significant process parameters and the optimal combination level of machining parameters were obtained. It is seen that machining performances are affected mostly by the peak current and pulse-on time during micro-electro-discharge machining of titanium alloy. Mathematical models have been developed to establish the relationship between various significant process parameters and micro-EDM performance criteria. In-depth studies have also been made to examine the influence of various process parameters on the white layer and surface topography through SEM micrographs of machined micro-hole.     

超声振动辅助磨削-脉冲放电加工表面粗糙度研究

通过多因素方差分析法分析了超声振动辅助磨削一脉冲放电复合加工参数（脉冲宽度、脉冲间隔、参考电压、超声振幅）对加工表面粗糙度的影响程度,建立了表面粗糙度的二次模型,并用响应曲面法预测一定切削参数范围内任意切削条件下的表面粗糙度值,方差分析结果和响应曲面法预测结果基本一致。研究结果对实际生产过程中加工参数的优化具有一定的指导作用。