慢走丝线切割加工参数对表面粗糙度的影响

慢走丝电火花线切割加工精度是衡量加工性能的重要指标之一.在加工过程中,加工表面精度自然受到加工参数的影响,其中包括放电电流能量、电流脉冲宽度等的影响.通过在慢走丝线切割加工机床(日本SODICK机床)上进行多次加工实验观察,分析了不同加工参数对慢走丝线切割加工表面粗糙度的影响规律.     

基于圆台形热传导模型的慢走丝线切割仿真与试验

基于放电通道中等离子体的形成机理,根据慢走丝线切割在短脉冲放电加工时放电通道中电子流与离子流散射速度的差异,提出了圆台形热传导模型。采用基于圆台形热传导模型的有限单元法对航空材料Inconel 718的典型工况进行了仿真计算,系统地分析了放电能量对放电通道温度以及放电蚀坑深度的影响规律,并采用声发射检测技术在线监测慢走丝线切割的加工表面粗糙度。通过仿真结果与试验测得工件表面粗糙度Rt值的对比,再结合试验测得的声发射信号波形图特征及声发射信号均方根值发现：仿真计算得到的放电蚀坑深度与表面粗糙度Rt值吻合较好;声发射信号的强度随着放电能量的增加而增强,声发射信号强度随着放电温度变化速率的变小而减弱。最后回归分析得到材料表面粗糙度与声发射信号均方根值的数学预测模型,预测结果与测得的表面粗糙度误差仅为4.4%。     

电火花线切割加工工艺参数研究

电火花线切割加工的表面粗糙度是衡量加工质量的重要指标之一.在加工过程中,表面粗糙度会受到放电电流的影响,其中包括放电电流能量、电流脉冲宽度以及电流极性的影响.通过在快走丝线切割加工机床上进行多次加工实验,本文研究分析了放电电流对线切割加工表面粗糙度的影响规律.     

基于声发射信号的铣削加工表面粗糙度预测技术研究

使用声发射技术对铣削过程进行监测,通过对声发射信号进行频域分析,比较不同频段的能量比来在线预测加工后的表面粗糙度.     

深冷处理D2工具钢线切割加工数值分析

以深冷处理D2工具钢为研究对象,建立其在线切割加工过程中的能量比、单位时间去除材料体积、工件加工表面粗糙度数值计算模型,运用MATLAB软件进行分析,并用试验验证。仿真分析及试验验证的结果表明:随着加工电流和脉冲宽度的增加,能量比不断增加;随着加工电流的增加,单位时间去除材料体积逐渐增加,而随着脉冲宽度的增加,单位时间去除材料体积呈现逐渐减小的趋势;随着加工电流和脉冲宽度的增加,工件加工表面粗糙度呈现先减小后增加趋势;单位时间去除材料体积、工件加工表面粗糙度的仿真计算值与试验测量值最大相对误差分别为4.76%、4.75%,相对误差较小,验证数值分析的正确性,为工具钢线切割加工最佳工艺参数选择及工艺优化提供理论依据。     

基于声发射分析的磨料流光整加工在线检测试验研究

针对磨料流光整加工中孔类零件表面粗糙度在线检测困难的问题,将声发射检测技术应用到了磨料流加工中。通过研究磨料流加工过程中的声发射源与声发射特性,利用参数分析法得到了波形特征参数随加工时间的变化曲线,建立了声发射信号的能量及振铃计数与零件表面粗糙度之间的关系;根据幂率流体本构方程计算了壁滑速度,分析了壁滑速度对声发射信号能量的影响。研究结果表明:声发射信号能量和振铃计数随着表面粗糙度的增大而增大,且两者随表面粗糙度的变化规律基本相同;表面粗糙度是声发射信号发生变化的主要原因,随着表面粗糙度的减小,即使增大壁滑速度,声发射信号强度也会降低;声发射可用于磨料流加工孔类零件表面粗糙度的在线检测。     

某型产品摩擦片加工工装设计

某型产品摩擦片零件材料为NCu-30-4-2-1,零件尺寸要求如图1所示,其中R=17mm、17.5mm、18mm,该零件是首次加工,任务要求紧。在加工中零件外形由慢走丝线切割加工完成,很好地保证了零件内表面粗糙度值Ra=0.8μm;     

孔光整加工表面粗糙度在线测量实验研究

针对液体磁性磨具光整加工孔时,无法对孔内壁表面质量进行在线检测的现状,提出利用声发射技术检测加工过程中摩擦声发射信号并进而在线预测孔壁粗糙度的方法。通过实验和分析验证了声发射(Acoustic Emission,简称AE)信号与试件表面粗糙度值有良好的对应关系,获取了与孔壁粗糙度值相对应的AE信号特征值,研究了某零件光整加工时AE信号的均方根值与表面粗糙度值变化情况的对应规律,为利用声发射技术进行孔表面光整加工的在线检测和相关设备的自动化控制提供了有益的参考。     

基于正交设计的GH4169高温合金电火花线切割加工研究

GH4169合金是一种典型的难加工材料,具有高强度,切削加工时切削力大等特征,采用普通方法加工时刀具磨损严重,表面质量和精度难以保证。针对上述现象,采用正交实验对镍基高温合金GH4169进行线切割加工研究。研究了不同的加工参数(脉冲宽度、间隙、管数、加工限速)对中走丝线切割加工GH4169合金的表面粗糙度和切割速度的影响。并对实验结果进行了主效应分析以及方差分析。结果表明:表面粗糙度随着加工限速的增大而增大,切割速度随着管数的增大而增大。加工参数在脉宽为60μs,间隙为4ns,管数为8,加工限速150步/s时获得最快的切割速度;加工参数在脉宽为40μs,间隙为10ns,管数为2,加工限速50步/s时获得较小表面粗糙度值。     

薄镍板上Meso尺度结构的电火花线切割

研究了利用常规电火花线切割技术加工薄镍板微小结构的方法.利用慢走丝电火花线切割加工机床对厚度为0.6 mm镍板上的Meso尺度结构进行了加工试验.以机床现有的工艺条件对零件进行试切割,对试切割后的尺寸精度和表面质量进行测量分析,在此基础上通过对放电能量、冲液压力、切割速度等机床参数的调整改进加工工艺.探讨了在200 μm缝宽范围内进行多次切割的方法,并对切割次数进行合理优化、合并.试验结果表明:慢走丝线切割加工对小于机床设定厚度的薄板Meso尺度结构仍可进行稳定加工;通过多次切割的方法可提高表面质量.在200μm窄缝范围内进行5次常规切割,加工后的表面粗糙度值Ra为0.54 μm;在保证表面质量的前提下,将5次切割合并为3次切割,加工后的表面粗糙度值Ra为0.62 μm,加工时间缩短了30％左右.该技术可为电火花线切割加工其他材料薄板微小零件提供支持与参考.     

Investigation of Damage Processes of Mortar in Different Aggregate Size by Acoustic Emission Characteristics

In order to study acoustic emission (AE) characteristics of damage process of mortar in different aggregate size, mortar specimens were tested under axial compression in the experiment, the whole damage evolution processes were monitored by full-digital AE acquisition system. The effects of mortar in different aggregate size on damage processes and failure mode were conducted by cumulative AE energy, amplitude, peak frequency and the ratio N/E (hits/energy) respectively. The ratio of cumulative AE hits of each frequency band and amplitude band to the whole cumulative AE hits in different stress level were counted, and the difference and evolution process of microcracks of mortar in different aggregate size in the failure process were revealed. The results show that cumulative AE energy increase with the increase of aggregate size in mortar. Distribution of cumulative AE hits of each amplitude band versus the stress in different aggregate size are the same, and AE hits of each amplitude band increase sharply suggests that the specimen will be destroyed. Besides, AE hits focus on low-frequency band at low stress level, while all peak frequency bands are active at high stress level, and the aggregate size of mortar have significant influence on cumulative hits of each peak frequency band. The ratio N/E decreased with the increase of aggregate size, and which increased linearly with the increase of the stress.     

Modeling and analysis of the effects of machining parameters on the performance characteristics in the EDM process of Al2O3+TiC mixed ceramic

Electric discharge machining (EDM) has achieved remarkable success in the manufacture of conductive ceramic materials for the modern metal industry. Mathematical models are proposed for the modeling and analysis of the effects of machining parameters on the performance characteristics in the EDM process of Al₂O₃+TiC mixed ceramic which are developed using the response surface methodology (RSM) to explain the influences of four machining parameters (the discharge current, pulse on time, duty factor and open discharge voltage) on the performance characteristics of the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR). The experiment plan adopts the centered central composite design (CCD). The separable influence of individual machining parameters and the interaction between these parameters are also investigated by using analysis of variance (ANOVA). This study highlights the development of mathematical models for investigating the influences of machining parameters on performance characteristics and the proposed mathematical models in this study have proven to fit and predict values of performance characteristics close to those readings recorded experimentally with a 95% confidence interval. Results show that the main two significant factors on the value of the material removal rate (MRR) are the discharge current and the duty factor. The discharge current and the pulse on time also have statistical significance on both the value of the electrode wear ratio (EWR) and the surface roughness (SR).     

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.     

Analysis of acoustic emission in precision and high-efficiency grinding technology

Current demands of machining hard and brittle materials at very small tolerances have predicated the need for precision and high-efficiency grinding. In situ monitoring systems based on acoustic emission (AE) provide a new way to control the surface damage and integrality of the components. However, a high degree of confidence and reliability in characterizing the manufacturing process is required for AE to be utilized as a monitoring tool. The authors established AE based online monitoring system and studied technique parameters versus the waveforms of AE under different working conditions. The results show that there are obvious mapping relations between the technique parameters of grinding and the effective values of the AE signals. Grinding along different directions would result in different strength of AE signal. Comparing with grinding along first longitude, fewer AE signal is released when grinding along latitude and better surface quality is generated. Similar variation tendency is observed no matter between AE root mean square (RMS) and linear speed or between surface roughness and linear speed which justify some kind of correlation may exist between AE RMS and surface roughness. The distance between the AE transducer and the AE source should be less than 80 mm while monitoring the process of grinding composite ceramics.     

Soft computing models based prediction of cutting speed and surface roughness in wire electro-discharge machining of tungsten carbide cobalt composite

This paper reports on an experimental investigation of small deep hole drilling of Inconel 718 using the EDM process. The parameters such as peak current, pulse on-time, duty factor and electrode speed were chosen to study the machining characteristics. An electrolytic copper tube of 3 mm diameter was selected as a tool electrode. The experiments were planned using central composite design (CCD) procedure. The output responses measured were material removal rate (MRR) and depth averaged surface roughness (DASR). Mathematical models were derived for the above responses using response surface methodology (RSM). The results revealed that MRR is more influenced by peak current, duty factor and electrode rotation, whereas DASR is strongly influenced by peak current and pulse on-time. Finally, the parameters were optimized for maximum MRR with the desired surface roughness value using desirability function approach.     

Optimization of the EDM parameters on machining Ti–6Al–4V with multiple quality characteristics

In this paper, parameter optimization of the electrical discharge machining process to Ti–6Al–4V alloy considering multiple performance characteristics using the Taguchi method and grey relational analysis is reported. Performance characteristics including the electrode wear ratio, material removal rate and surface roughness are chosen to evaluate the machining effects. The process parameters selected in this study are discharge current, open voltage, pulse duration and duty factor. Experiments based on the appropriate orthogonal array are conducted first. The normalised experimental results of the performance characteristics are then introduced to calculate the coefficient and grades according to grey relational analysis. The optimised process parameters simultaneously leading to a lower electrode wear ratio, higher material removal rate and better surface roughness are then verified through a confirmation experiment. The validation experiments show an improved electrode wear ratio of 15%, material removal rate of 12% and surface roughness of 19% when the Taguchi method and grey relational analysis are used.     

Development of surface roughness optimisation and prediction for the process of wire electro-discharge grinding

This paper investigates the technological capabilities of a hybrid micro machining process for performing wire electro-discharge grinding (WEDG). In particular, micro wire electrical discharge machining (μWEDM) is employed in combination with a rotating submergible spindle to perform WEDG. In this research, first a machining strategy for workpiece preparation is presented. Then, the effects of different machining setup parameters on the achievable surface finish after WEDG are investigated. In particular, an experimental study was conducted to identify the most statistically significant setup parameters for performing the main cut that affect the resulting surface quality. A signal-to-noise (S/N) ratio analysis was conducted to optimise the technological parameters for performing WEDG. By modifying the discharge energy for main cuts when performing WEDG surface finish comparable to that of μWEDM can be achieved. In addition, a simple and cost-effective method for on-the-machine estimation of resulting surface roughness is proposed. Especially, by applying inductive learning a surface roughness prediction model for WEDG can be generate based on data acquired by monitoring on-line the process.     

Pulsed Nd:YAG laser treatment of monocrystalline silicon substrate

To minimize reflection and increase the opportunity for photovoltaic (PV) devices to absorb incident light, we produced rough-textured surfaces using a pulsed Nd:YAG laser. We investigated the effect of various operating parameters on surface features and optical performance. The parameters investigated were pulse repetition frequency, pulse energy, and textured surface exposure time. Following laser surface treatment, no chemical solution etching or anti-reflective coatings were necessary. Reflectance values were measured by spectrophotometer. Structural properties including surface morphology and surface roughness of the textured surfaces were analyzed by a three-dimensional confocal laser scanning microscope. The resulting surface reflection curves indicated that, of the different laser machining paths, the vertical and circular paths produced identical optical properties in the samples. Surface reflection values decrease as the pulse energy and exposure times increase. By contrast, surface roughness increases with exposure time. An increase in pulse frequency reduces surface roughness, although the extent of the reduction depends upon the pulse energy. Following surface texturing of the monocrystalline silicon samples, the total reflection was reduced from 40% to approximately 10% of incident light. Our experimental results indicate that the rougher surfaces attained by laser surface treatment provide better light-trapping properties for PV devices.     

EXPERIMENTAL INVESTIGATIONS INTO THE INFLUENCE OF MAJOR OPERATING PARAMETERS DURING MICRO-ELECTRO DISCHARGE DRILLING OF CEMENTED CARBIDE

Present study investigates the influence of major operating parameters on the performance of micro-EDM drilling of cemented carbide (WC-10wt%Co) and identifies the ideal values for improved performance. The operating parameters studied were electrode polarity, gap voltage, resistance, peak current, pulse duration, pulse interval, duty ratio, electrode rotational speed and EDM speed. The performance of micro-EDM drilling process was evaluated by machining time, material removal rate (MRR), relative electrode wear ratio (RWR), spark gap, surface finish and dimensional accuracy of micro-holes. It has been found that there are two major conflicting issues in the micro-EDM of carbide. If the primary objective is to obtain better surface finish, it can be obtained by the sacrifice of high machining time, low MRR and high RWR. However, for faster micro-EDM, the surface roughness is higher and electrode wear is again much higher. It is concluded that negative electrode polarity, gap voltage of 120 V, resistance of 33 Ω, peak current of 8 A, pulse duration of 21 μs, pulse interval of 30 μs, duty cycle of 0.47, electrode rotational speed of 700 rpm and EDM speed of 10 μm/s can be considered as ideal parameters to provide improved performances during the micro-EDM of WC-Co.