Research on cutting temperature of work-piece in milling process based on WPSO

Wire electrical discharge machining (WEDM) is a commonly used process in manufacturing industries to machine electrically conductive materials with complex shapes and varying hardness. The performance of any machining process is based on right selection of input variables. The selection of optimal parameters in WEDM is a difficult task as it is a highly stochastic process in nature. The present work deals with the development of empirical relationships for the output responses of kerf (cutting width) and wire wear ratio considering pulse-on time, pulse-off time, wire tension, dielectric flow rate, and wire feed as the input variables. Response surface methodology is used to find the quantitative relations. Subsequently, the developed mathematical models are used for optimization. A recently developed global optimization technique, harmony search algorithm, is applied to find the optimal set of input control variables.     

Using wire electrical discharge machining for improved corner cutting accuracy of thin parts

The wire electrical discharge machining process (WEDM) allows one to achieved ruled surfaces along intricate contours in hard materials. When one intends to use such a machining process, one has to analyze both the magnitudes of the corners’ radii and the corner’s angles that are formed between adjoining surfaces. Some experimental research work carried out unveiled the systematic occurrence of machining errors when WEDM is used to obtain outside sharp corners, especially in small thickness workpieces. A permanent bending at the crest of sharp corners, which leads to a substantial deviation from the prescribed geometrical shape, was found. The deviation form depends on the magnetic properties of the workpiece material. The research was focused on establishing a means for characterizing this shape error. Moreover, the influence exerted by certain factors, such as the corner angle and the thickness of the workpiece on the above-mentioned machining error was quantified.     

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.     

Improving the surface quality in wire electrical discharge machined specimens by removing the recast layer using magnetic abrasive finishing method

This study explores the feasibility of removing the recast layer formed on aluminum alloy cylindrical specimens machined by wire electrical discharge machining (WEDM) by using magnetic abrasive finishing (MAF). The WEDM is a thermal machining process capable of accurately machining parts with high hardness or complex shapes. The sparks produced during the WEDM process melt the metal’s surface. The molten material undergoes ultra-rapid quenching and forms a layer on the surface defined as recast layer. The recast layer may be full of craters and microcracks which reduce service life of materials tremendously, especially under fatigue loads in corrosive environments. This investigation demonstrates that MAF process, can improve the quality of WEDM machined surfaces effectively by removing the recast layer. The present work studies the effect of some parameters, i.e., linear speed, working gap, abrasive particle size, and finishing time on surface roughness and recast layer thickness using full factorial analysis. Three-level full factorial technique is used as design of experiments for studying the selected factors. In order to indicate the significant factors, the analysis of variance has been used. In addition, an equation based on regression analysis is presented to indicate the relationship between surface roughness and recast layer thickness of cylindrical specimens and finishing parameters. Experimental results show the influence of MAF process on recast layer removal and surface roughness improvement.     

Selection of optimal process parameters in WEDM while machining Al7075/SiCp metal matrix composites

Aluminium metal matrix composites (MMCs) reinforced with silicon carbide particulate (SiCp) find several applications due to their improved mechanical properties over the conventional metals for a wide variety of aerospace and automotive applications. However, the presence of discontinuously distributed hard ceramic in the MMCs made them as difficult-to-cut materials for conventional machining methods. The wire electrical discharge machining (WEDM), as a widely adopted non-traditional machining method for difficult-to-cut precision components, found an appropriate metal removal process for MMCs to enhance quality of cut within the stipulated cost. While machining the advanced materials like MMCs, a clear understanding into the machining performance of the process for its control variables could make the process uncomplicated and economical. In light of the growing industrial need of making high performance-low cost components, the investigation aimed to explore the machining performance characteristics of SiCp reinforced Al7075 matrix composites (Al7075/SiCp) during WEDM. While conducting the machining experiments, surface roughness, metal removal rate, and wire wear ratio are considered the responses to evaluate the WEDM performance. Response surface methodology is used to develop the empirical models for these WEDM responses. SiC particulate size and volume percentages are considered the process variables along with pulse-on time, pulse-off time, and wire tension. Analysis of variance (ANOVA) is used to check the adequacy of the developed models. Since the machining responses are conflicting in nature, the problem is formulated as a multi-objective optimization problem and is solved using the Non-dominated Sorting Genetic Algorithm-II to obtain the set of Pareto-optimal solutions. The derived optimal process responses are confirmed by the experimental validation tests, and the results are analyzed by SEM.     

Study on the generative design method and error budget of a novel desktop multi-axis laser machine for micro tool fabrications

Micro end mills made of hard or ultra-hard materials are mainly fabricated by grinding or by wire electrical discharge machining (WEDM). However, with the advances of new tool materials from ultra-hard to super-hard together with lower or no electrical conductivity such as the material of nano-polycrystalline diamond, the grinding or the WEDM method cannot be used for machining due to their ultra-low process efficiencies for such materials. Laser machining has been tested an effective method. Accordingly, multi-axis laser machines need to be designed for micro tool fabrications. In the paper, a typical micro ball end mill with relatively complex features has been analyzed by the generative design method to generate the number and properties of needed motion axes. Based on the analysis, a novel five-axis laser machine has been designed. Aiming at high-quality micro tool fabrications, the kinematics model has been derived for this five-axis laser machine and error budge has been studied for the subsequently optimum selection of key motion components.     

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.     

空间曲面电火花线切割CAD/CAM系统

为解决高速走丝电火花线切割机床加工空间曲面的难题,实现大锥度空间复杂曲面零件的加工,以空间曲面数学模型和数控模型为基础,开发了一种计算机辅助设计/计算机辅助制造(Computer aided design/computer aided manufacturing,CAD/CAM)系统.其硬件系统以研制的数控转摆摆工作台为核心装置,并与现有高速走丝电火花线切割机床结合,组成空间曲面线切割加工系统.其软件系统可以根据上下导线的参数方程进行分析计算,建立空间曲面的三维模型,自动生成NC加工代码,进行加工仿真和空间曲面零件的加工.利用本系统进行典型空间复杂曲面零件的加工试验,结果表明加工结果与仿真结果基本相似.此外,还分析数控模型以及回摆间隙角对加工误差的影响.这些工作为解决高速走丝电火花线切割加工空间曲面的难题打下基础.     

线切割中加工不良原因分析与排除

线切割中加工不良现象很多,高加工精度和效率是追求的最终目标,斜度加工是加工中的难点。本文针对加工精度不良现象,从工艺方案、加工材料、加工参数、电极丝、工作液和走丝系统6个方面进行了分析,从高速走丝和低速走丝2种不同机床对线切割速度不良进行了阐述,从机床、工件材质和电极丝3个方面的原因对斜度加工不良进行了研究。详细地介绍了产生这些不良现象的原因,并提出了有效的克服办法,以期对从事线切割加工领域的相关人员起到借鉴作用。     

A Study on an Open Architecture CNC System with a NURBS Interpolator for WEDM

This paper deals with the design and implementation of an open architecture CNC system for wire electrical discharge machining (WEDM) with a consideration of the differences between WEDM and NC cutting machines. Work using open architecture controllers (OACs) has focused mainly on metal cutting machines. WEDM has many aspects similar to milling machines. However, there are differences in the machining processes and control strategies. To close the gap between previous general work on OAC and the WEDM specific needs, an open architecture NC model for WEDM comprised of a synchronisation kernel and an NC functional module is proposed. The proposed CNC system is applied to an existing commercial WEDM system by a retrofitting method. A precise NURBS interpolation function is implemented and sample runs are conducted with a NURBS interpolator that is added to the proposed system.     

散热翅片刀具斜坡加工线切割轨迹求解

建立线切割轨迹的几何模型,并推导渐开线齿轮形刀具斜坡加工线切割轨迹的求解过程,为线切割轨迹的产生提供理论依据。根据轨迹的求解过程,运用VB编制通用计算程序。利用Pro/E建立轨迹的三维模型,以三维模型为基础,提取其中的数据求出轨迹上若干点的坐标值,其结果与求解结果相吻合。计算结果表明,求解方法适合于产生线切割轨迹。试验验证了求解方法的有效性。     

Surface integrity study of WEDM with various wire electrodes: experiments and analysis

Abstract

Wire electrical discharge machining (WEDM) is always significant for its high-precision machining. However, due to the generation of high discharge energy during machining, machined surfaces are often got distorted. These might be upgraded by choosing the correct tool with proper machining condition. The effects of the electrode materials and process parameters on different responses of WEDM like average surface roughness, recast layer thickness, and surface morphology are systematically examined here to enhance the knowledge of WEDM and its correlation with electrode property. The experiments have been carried out on one of the expensive steel namely Maraging steel 300 due to its applicability in tooling and aerospace industries. Plain brass wire, zinc-coated brass wire (ZCB), and silver-coated brass (SCB) wires are used as a tool electrode for analysis. Comparative experimental studies prove that among BW, ZCB, and SCB, the overall performance of SCB is commendable owing to the high-quality surface considering control parameters in low discharge energy level. However, the second-best performance is shown by ZCB.     

Experimental investigation and parameter optimization of near-dry wire-cut electrical discharge machining using multi-objective evolutionary algorithm

The near-dry wire-cut electrical discharge machining (WEDM) process is an environment-friendly manufacturing process, in which there is no harmful effect to the operators. The authors focus on the non-polluting ways to cut the materials and to meet the technical requirements like high material removal rate (MRR) and low surface roughness (Ra). In the near-dry WEDM, the finite discrete periodic series sparks between the wire electrode and conducting work material separated by minimum quantity of deionized water mixed with compressed air (air-mist) as a dielectric medium. In the present research, parametric analysis of the process has been performed with the molybdenum wire tool and high speed steel (HSS-M2) work piece. Experiments have been performed using air-mist as the dielectric medium to study the impact of gap voltage, pulse-on time, pulse-off time, air-mist pressure and discharge current on the MRR and Ra using the mixed orthogonal (L₁₈) array-Taguchi method. Taguchi based analysis of variance test was performed to identify the significant parameters. The gap voltage, pulse-on time, discharge current and air-mist pressure were found to have momentous effects on MRR and Ra. The best regression models for MRR and Ra have been developed by regression analysis. The optimal rough and finish cutting parameters have been predicted by Pareto-front using the multi-objective evolutionary algorithm (MOEA).     

Determining cutting parameters in wire EDM based on workpiece surface temperature distribution

The material removal process in wire electrical discharge machining (WEDM) may result in work-piece surface damage due to the material thermal properties and the cutting parameters such as varying on-time pulses, open circuit voltage, machine cutting speed, and dielectric fluid pressure. A finite element method (FEM) program was developed to model temperature distribution in the workpiece under the conditions of different cutting parameters. The thermal parameters of low carbon steel (AISI4340) were selected to conduct this simulation. The thickness of the temperature affected layers for different cutting parameters was computed based on a critical temperature value. Through minimizing the thickness of the temperature affected layers and satisfying a certain cutting speed, a set of the cutting process parameters were determined for workpiece manufacture. On the other hand, the experimental investigation of the effects of cutting parameters on the thickness of the AISI4340 workpiece surface layers in WEDM was used to validate the simulation results. This study is helpful for developing advanced control strategies to enhance the complex contouring capabilities and machining rate while avoiding harmful surface damage.     

Improvement of wire electrical discharge machining efficiency in machining polycrystalline silicon with auxiliary-pulse voltage supply

This study proposes a novel pulse voltage configuration, auxiliary-pulse voltage, for wire electrical discharge machining (WEDM) of polycrystalline silicon (polysilicon) used in solar cell production. It is developed with the objectives of reducing material waste due to the large kerf loss as well as achieving greater efficiency and better quality compared with conventional machining approaches. Experimental results show that compared with conventional-pulse voltage supply, the auxiliary-pulse voltage mode can avoid delay in electrical discharge during pulse-on time. Enhanced frequency of effective discharge for machining would increase machining speed, which would in turn reduce machining groove width, and obtain better surface roughness. In addition, parameters of significant influence on machining characteristics were examined with the Taguchi method, and the optimal combination levels of machining parameters were determined. In sum, our findings reveal that WEDM with auxiliary-pulse voltage supply is an effective approach to machining polysilicon with good quality and high efficiency achieved.     

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.     

Optimization of multi machining characteristics in WEDM of WC-5.3%Co composite using integrated approach of Taguchi,GRA and entropy method

Wire electrical discharge machining (WEDM) is a well known process for generating intricate and complex geometries in hard metal alloys and metal matrix composites with high precision. In present work, intricate machining of WC-5.3%Co composite on WEDM has been reported. Taguchi’s design of experiment has been utilised to investigate the process parameters for four machining characteristics namely material removal rate, surface roughness, angular error and radial overcut. In order to optimize the four machining characteristics simultaneously, grey relational analysis (GRA) coupled with entropy measurement method has been employed. Through GRA, grey relational grade has been computed as a performance index for predicting the optimal parameters setting for multi machining characteristics. Using Analysis of Variance (ANOVA) on grey relational grade, significant parameters affecting the multi-machining characteristics has been determined. Confirmatory results prove the potential of present approach.     

端面正弦直纹曲面零件的线切割加工技术

为解决端面正弦直纹曲面的加工难题,提出了利用国产高速走丝电火花线切割机床进行加工的一种方法。依据正弦直纹曲面的形成原理,分析线切割加工的运动方式。通过数控回转台与线切割机床相结合,形成实现加工所需的运动,进行了样件的实验加工,实验结果表明,设计的加工方法合理有效。     

Theoretical and experimental analysis of machining errors on small arced corners during WEDM finishing stages

Abstract

Accurate machining in small-radius paths is a challenge associated with Wire Electrical Discharge Machining (WEDM). This article experimentally and theoretically analyzes the machining errors of the arced paths through successive machining stages. The machining errors of a three-stage WEDM on both straight and arced paths are first experimentally analyzed. Mathematical expressions are derived to relate new theoretical concepts, including spark angle and spark density, for each finishing stage on both straight and arced paths. Then, the effects of these concepts on machining errors of the finishing stages are determined. The causes of the machining errors of the first and second finishing stages on male and female arced paths are theoretically analyzed, and a novel mathematical methodology for the prediction of these errors is developed. The experimental machining errors of the first and second finishing stages on the different arced paths are compared and evaluated with related theoretical ones. Results reveal that the mathematical methodology predicts and compensates the machining errors of the first finishing stage with the accuracy of 78% and of the second finishing stage with the accuracy of 83%. There is a good improvement which can be employed in WEDM applications and to increase the wire electrical discharge (WED) machine capability.     

Study of machining parameters optimization for different materials in WEDM

In process planning of wire electrical discharge machining (WEDM), determination of appropriate machining conditions is likely to face problems in many ways. In addition to the construction of the relationship between machining parameters and machining characteristics, optimization search technique, a large number of experiments must be conducted repeatedly to renew parameters for different workpiece materials. The concept of specific discharge energy (SDE) was employed in this paper to represent the WEDM property of workpiece materials as one of the machining parameters. Two kinds of materials with distinctive SDE values, i.e., higher and lower, respectively, were selected for our experiments. The experimental data obtained were used, and a neural network that can accurately predict the relationship between machining parameters and machining characteristics was constructed. It was found that the predicted error was less than 7 %. The optimization technique of genetic algorithms was employed, and the optimal combination of machining parameters that meet the required machining characteristics for different workpiece materials was obtained. The system proposed in this study is both user-friendly and practical. It can save considerable time and cost during the construction of the database for the expert system of process planning.