往复走丝电火花线切割高效低损耗切割研究

目前,高速往复走丝电火花线切割最高切割效率已突破200mm2/min,传统脉冲电源靠单纯提高脉冲能量来增加切割效率会导致钼丝损伤大、损耗加剧,短时间内就可能出现断丝。从脉冲电源的放电波形分析入手,分析了传统脉冲电源和高效低损耗脉冲电源的差异。研究认为,采用阶梯脉冲合理控制放电电流的前后沿,在加工中对非正常放电脉冲及时切断以减小对电极丝造成的损伤及损耗,采用等能量脉冲方式提高放电利用率等措施能大大提高切割效率,改善切割表面粗糙度,在切割效率190～200mm2/min条件下能实现长期稳定切割。     

An experimental investigation on machining parameters of AISI D2 steel using WEDM

The performance of the wire electrodischarge machining (WEDM) machining process largely depends upon the selection of the appropriate machining variables. Optimization is one of the techniques used in manufacturing sectors to arrive for the best manufacturing conditions, which are essential for industries toward manufacturing of quality products at lowest cost. As there are many process variables involved in the WEDM machining process, it is difficult to choose a proper combination of these process variables in order to maximize material removal rate and to minimize tool wear and surface roughness. The objective of the this work is to investigate the effects of process variables like pulse on time, pulse off time, peak current, servo voltage, and wire feed on material removal rate (MRR), surface roughness (SR), gap voltage, gap current, and cutting rate in the WEDM machining process. The experiment has been done using Taguchi’s orthogonal array L27 (3⁵). Each experiment was conducted under different conditions of input parameters and statistically evaluated the experimental data by analysis of variance (ANOVA) using MINITAB and Design Expert tools. The present work also aims to develop mathematical models for correlating the inter-relationships of various WEDM machining parameters and performance parameters of machining on AISI D2 steel material using response surface methodology (RSM).The significant machining parameters and the optimal combination levels of machining parameters associated with performance parameters were also drawn. The observed optimal process parameter settings based on composite desirability (61.4 %) are pulse on time 112.66 μs, pulse off time 45 μs, spark gap voltage 46.95 V, wire feed 2 mm/min, peak current of 99.99 A for achieving maximum MRR, gap current, gap voltage, cutting rate, and minimum SR; finally, the results were experimentally verified.     

复合运丝型电火花线切割加工参数分析与研究

提出了一种新型电火花线切割机床,即电极丝作往复直线运动的同时还绕自身轴线高速旋转的复合运丝型线切割机床。介绍了该类机床与其他线切割机床加工的基本工艺指标。通过与高速走丝电火花线切割机床比较实验,分析了脉冲宽度、脉冲间隔、脉冲峰值电流等电参数对加工工艺指标的影响,实验表明这种独特的复合运丝方式在降低表面粗糙度、提高加工精度等方面较传统运丝方式具有较大的优越性,且机床结构较为简单,对于各种工艺参数和电参数具有更加广泛的适用性,具有进一步研究和推广价值。     

On surface integrity of miniature spur gears manufactured by wire electrical discharge machining

This paper reports about investigations on some important aspects of surface integrity of the miniature spur gears manufactured by wire electrical discharge machining (WEDM) process. The investigations included study of variation of form errors (deviations in profile and lead) and surface roughness with discharge energy parameters, i.e., voltage and/or pulse-on time for the miniature gears. The effect of WEDM process on flank surface topography, bearing length parameters, microstructure, and microhardness for the best quality miniature gear were also studied. The manufactured miniature gears were of external spur type having 9.8 mm as outside diameter, 4.9-mm thickness, 0.7 mm as module, 12 teeth, and were made of brass. It was found that combination of low discharge energy parameters resulted in better form accuracy, surface finish, and microstructure ensuring enhanced service life and better functional characteristics of the WEDMed miniature gears. The best quality miniature gear had form errors (i.e., lead and profile deviations) as low as 5.4 μm, very little variation in the actual surface topography from the theoretical one, an average surface roughness of 1 μm, and maximum surface roughness within the entire evaluation length as 6.4 μm, showed consistent surface finish measured by other surface roughness parameters, good bearing area curve, and crack-free gear tooth surface without significant alteration in microhardness. Results of the present work demonstrate the superiority of the WEDM process over the conventional miniature gear manufacturing processes.     

Optimization of wire electrical discharge machining (WEDM) process parameters using Taguchi method

Wire electrical discharge machining (WEDM) is extensively used in machining of conductive materials when precision is of prime importance. Rough cutting operation in WEDM is treated as a challenging one because improvement of more than one machining performance measures viz. metal removal rate (MRR), surface finish (SF) and cutting width (kerf) are sought to obtain a precision work. Using Taguchi’s parameter design, significant machining parameters affecting the performance measures are identified as discharge current, pulse duration, pulse frequency, wire speed, wire tension, and dielectric flow. It has been observed that a combination of factors for optimization of each performance measure is different. In this study, the relationship between control factors and responses like MRR, SF and kerf are established by means of nonlinear regression analysis, resulting in a valid mathematical model. Finally, genetic algorithm, a popular evolutionary approach, is employed to optimize the wire electrical discharge machining process with multiple objectives. The study demonstrates that the WEDM process parameters can be adjusted to achieve better metal removal rate, surface finish and cutting width simultaneously.     

Surface crack density and recast layer thickness analysis in WEDM process through response surface methodology

In this work, quantitative assessment of surface damage in terms of parameters like surface crack density and recast layer thickness in wire electrical discharge machining (WEDM) process has been undertaken. The effect of processing conditions on crack formation is studied using scanning electron microscope. Surface crack density and recast layer thickness analysis in terms of machining parameters such as pulse on time, pulse off time, peak current, spark gap voltage significantly deteriorate the microstructure of machined samples, which produces the deeper, wider overlapping craters, pock marks, globules of debris and micro cracks. The microstructure analysis of WEDM surface was based upon the theory of electrical discharge phase and metallurgical physics. It is found that the pulse on time, pulse off time and peak current are the most dominating parameters for both surface crack density and recast layer thickness.     

新型节能电火花加工脉冲电源的脉冲发生器

循环叠加斩波式节能电火花加工脉冲电源的主要特点是不含有传统脉冲电源的限流电阻和多数节能脉冲电源使用的储能电感，采用功率开关管不完全导通的方法，通过对每只功率开关管的斩波电流进行循环叠加来产生电火花加工脉冲。对功率开关管进行循环叠加斩波控制时，根据各档延迟时间是最小延迟时间整数倍的特点。对脉冲发生器的逻辑进行巧妙的优化设计，可以大大节省PLD内部的资源。在该电源所选电路规格的情况下大约只占用了优化前常规方法所占资源的1／8，避免了硬件资源的浪费,降低了成本。     

基于PWM技术节能型线切割脉冲电源的研制

分析了线切割脉冲电源电能的利用现状，简要介绍了目前节能型电火花脉冲电源的研究情况。研制了一种新型的节能型线切割加工脉冲电源。并对其原理进行了探讨。     

Experimental investigation of the real-time micro-control of the WEDM process

The wire electrical discharge machining (WEDM) process has inherent instability due to its high complexity and stochastic characteristics. For more stable and efficient machining, the process must be actively controlled in real time while precisely determining the state of the instantaneous machining process. Feedback information when used in conjunction with an unstable discharge pulse ratio and instantaneous discharge energy can be applied to this micro-control system. This study presents the design and implementation of a system that fulfills these demands. Experimental results demonstrate that the proposed system is capable of simultaneously enhancing the machining stability, machining efficiency, and machining performance. For fine machining, the surface quality was enhanced by approximately 10 % without a loss of machining efficiency. Overall, both the feedrate and the surface roughness could be improved concurrently by more than 5 %.     

Influence of machining parameters on surface roughness in finish cut of WEDM

Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.     

Multiple process parameter optimization of wire electrical discharge machining on Inconel 825 using Taguchi grey relational analysis

In this paper, an effective approach, Taguchi grey relational analysis, has been applied to experimental results of wire cut electrical discharge machining (WEDM) on Inconel 825 with consideration of multiple response measures. The approach combines the orthogonal array design of experiment with grey relational analysis. The main objective of this study is to obtain improved material removal rate, surface roughness, and spark gap. Grey relational theory is adopted to determine the best process parameters that optimize the response measures. The experiment has been done by using Taguchi’s orthogonal array L36 (2¹?×?3⁷). Each experiment was conducted under different conditions of input parameters. The response table and the grey relational grade for each level of the machining parameters have been established. From 36 experiments, the best combination of parameters was found. The experimental results confirm that the proposed method in this study effectively improves the machining performance of WEDM process.     

Bipolar high-repetition-rate high-voltage nanosecond pulser

The pulser designed is mainly used for producing corona plasma in waste water treatment system. Also its application in study of dielectric electrical properties will be discussed. The pulser consists of a variable dc power source for high-voltage supply, two graded capacitors for energy storage, and the rotating spark gap switch. The key part is the multielectrode rotating spark gap switch (MER-SGS), which can ensure wider range modulation of pulse repetition rate, longer pulse width, shorter pulse rise time, remarkable electrical field distortion, and greatly favors recovery of the gap insulation strength, insulation design, the life of the switch, etc. The voltage of the output pulses switched by the MER-SGS is in the order of 3-50 kV with pulse rise time of less than 10 ns and pulse repetition rate of 1-3 kHz. An energy of 1.25-125 J per pulse and an average power of up to 10-50 kW are attainable. The highest pulse repetition rate is determined by the driver motor revolution and the electrode number of MER-SGS. Even higher voltage and energy can be switched by adjusting the gas pressure or employing N(2) as the insulation gas or enlarging the size of MER-SGS to guarantee enough insulation level.     

Electrical discharge precision machining parameters optimization investigation on S-03 special stainless steel

S-03 is a novel special stainless steel, which is widely used in precision aerospace parts and electrical discharge machining technology has the merit of high-accuracy machining. This paper aims to combine gray relational analysis and orthogonal experimental to optimize electrical discharge high-accuracy machining parameters. The four process parameters of gap voltage, peak discharge current, pulse width, and pulse interval are required to optimize in the fewest experiment times. The material removal rate and surface roughness are the objective parameters. The experiment were carried out based on Taguchi L9 orthogonal array, then we carried out the gray relational analysis to optimize the multi-objective machining parameter, finally, we verified the results through a confirmation experiment. The sequence of machining parameters from primary to secondary are as follows: discharge current 7A, pulse interval 100 μs, pulse width 50 μs, and gap voltage 70 V. Using the above machining parameters, we can obtain good surface roughness Ra1.7 μm, and material removal rate 13.3 mm³/min. The machined work piece almost has no surface modification layer. The results show that combining orthogonal experiment and gray relational analysis can further optimize machining parameters, the material removal rate increased by 23.8 %, and the surface roughness almost has no change.     

Effect of process parameters in nanosecond pulsed laser micromachining of PMMA-based microchannels at near-infrared and ultraviolet wavelengths

This paper presents investigations on the effects of nanosecond laser processing parameters on depth and width of microchannels fabricated from polymethylmethacrylate (PMMA) polymer. A neodymium-doped yttrium aluminium garnet pulsed laser with a fundamental wavelength of 1,064 nm and a third harmonic wavelength of 355 nm with pulse duration of 5 ns is utilized. Hence, experiments are conducted at near-infrared (NIR) and ultraviolet (UV) wavelengths. The laser processing parameters of pulse energy (402–415 mJ at NIR and 35–73 mJ at UV wavelengths), pulse frequency (8–11 Hz), focal spot size (140–190 μm at NIR and 75 μm at UV wavelengths) and scanning rate (400–800 pulse/mm at NIR and 101–263 pulse/mm at UV wavelengths) are varied to obtain a wide range of fluence and processing rate. Microchannel width and depth profile are measured, and main effects plots are obtained to identify the effects of process parameters on channel geometry (width and depth) and material removal rate. The relationship between process variables (width and depth of laser-ablated microchannels) and process parameters is investigated. It is observed that channel width (140–430 μm at NIR and 100–150 μm at UV wavelengths) and depth (30–120 μm at NIR and 35–75 μm at UV wavelengths) decreased linearly with increasing fluence and increased non-linearly with increasing scanning rate. It is also observed that laser processing at UV wavelength provided more consistent channel profiles at lower fluences due to higher laser absorption of PMMA at this wavelength. Mathematical modeling for predicting microchannel profile was developed and validated with experimental results obtained with pulsed laser micromachining at NIR and UV wavelengths.     

Influence of electrical conditions on performance of electrical discharge machining with powder suspended in working oil for titanium carbide deposition process

This paper describes the influence of the discharge current and the pulse duration on the titanium carbide (TiC) deposition process by electrical discharge machining (EDM) with titanium (Ti) powder suspended in working oil. Although the influence of the electrical conditions for removal EDM has been investigated, the criteria for deposition have not been discussed. In the experiments, a 1-mm copper rod was used for an electrode to prevent the flushing of working oil from the gap between the electrode and a workpiece. Ti powder reacted with the cracked carbon from the working oil, then depositing a TiC layer on a workpiece surface. A major criterion of the deposition or removal was the discharge energy over a pulse duration of 10 μs. A thickness of the TiC layer became the maximum at a certain discharge current and pulse duration. Larger discharge energy and power promoted the removal by heat and pressure caused by the discharge. The removal was classified further into two patterns; cracks were observed on the Ti-rich surface in removal pattern 1 and a workpiece was simply removed in removal pattern 2. The maximum hardness of the deposition was 2000 Hv. The workpiece about 10 μm beneath its surface was also hardened because of the dispersion of TiC. The machining conditions for the hardest deposition did not coincide with those for the highest one. Therefore, the discharge current and pulse duration should be optimized for the deposition.     

An experimental study on micro wire-EDM of polycrystalline diamond using a novel pulse generator

This paper presents a new pulse generator for cutting of polycrystalline diamond (PCD) by micro wire electrical discharge machining (micro wire-EDM). The pulse generator using anti-electrolysis circuitry and digital signal processor-based pulse control circuit was developed to suppress damages on the machined surface of PCD while achieving stable machining. A novel pulse control method was proposed to provide high-frequency pulse control signals with a period of off duty cycle for reionization of the dielectric in the spark gap so as to reduce the consecutive occurrence of short circuits. A series of experiments were carried out to investigate the effect of open voltage on machining performance in terms of material removal rate, slit width, thickness of the damaged layer on machined surface, and surface finish. An increase of open voltage increases peak current, thus producing greater discharge energy and, thereby, contributing to improvements in material removal rate, but leading to larger slit width and thickness of the damaged layer and worse surface finish. Experimental results not only demonstrate that the developed pulse generator could achieve satisfactory machining results but also have verified the applicability of this new technique in micro wire-EDM.     

Design and experimental study of a power supply for micro-wire EDM

This paper presents the development and application of a new power supply in micro-wire EDM. A transistor-controlled power supply composed of a low-energy discharge circuit and an iso-frequency pulse control circuit was designed to provide the functions of high frequency and lower energy pulse control. Pulse states are classified as open circuit, normal spark, arc discharge and short circuit by means of the level of gap voltage and associated discharge current. A power supply test revealed that a high current-limiting resistance results in a decrease of discharge current. Peak current decreases with an increase of pulse-control frequency. Experimental results not only demonstrate that the iso-frequency pulse generator can provide low-energy pulses with a frequency of 185 kHz and a discharge current of 0.7 A, they also verify the applicability of the developed power supply in micro-wire EDM.     

DK7732机床加工齿轮表面变质层分析

分析了线切割加工表面变质层的影响因素,在采用和真实加工相类似的边界条件下,用有限元软件ANSYS对线切割加工过程进行温度分布计算,模拟电参数(脉冲宽度)的变化对线切割加工齿轮工件表面变质层的影响,得出在实验条件下,按DK7732机床各档脉冲宽度加工齿轮时变质层的分布数据,以利于后续的工艺探究.同时提出了减少变质层的相应措施.     

利用ANSYS的模具线切割加工表面变质层分析

分析了线切割(WEDM)加工表面变质层的影响因素,根据DK7732机床在模具加工中的应用,用有限元软件AN-SYS对线切割加工过程进行温度分布计算,在采用与真实加工相类似的边界条件下,模拟电参数(脉冲宽度)的变化对线切割加工工件表面变质层的影响,得出在实验条件下,按DK7732机床各档脉冲宽度加工时变质层的分布数据,以及其高温层和低温层区域相对较宽、中温区域很窄的结论,有利于后续的工艺探究。同时提出了减少变质层的相应措施。     

Formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet

In this paper, the formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet at room temperature were investigated by the numerical simulation and experimental method. The numerical simulation for the magnetic pulse uniaxial tension of AZ31 sheet is performed by means of the ANSYS FEA software. The changes in velocity and strain rate were analyzed by simulation. The approximate rectangular flat spiral coil was employed to carry out the magnetic pulse uniaxial tensile experiments. The forming process was recorded by the high-speed camera, and the simulation result was consistent with it. The experimental results indicate that the total elongation of AZ31 sheet improves about 37 % compared with the quasi-static case. The major and minor principal strains at most increase by approximately 112 and 96 % under 5.12 kJ energy, respectively.