Statistical analysis on electrode wear in EDM of tool steel DIN 1.2714 used in forging dies

(BQ) Electrical discharge machining (EDM) is a widespread process which works very effectively in machining of difficult-to-cut materials and alloys in die and aerospace industries with high dimensional accuracies. However, this capability could be deteriorated due to electrode wear leading to decrease of process productivity. In this study, the effect of machining parameters of EDM process including on-time, current, voltage, the engaging time between workpiece and electrode, and pre-EDM roughing on electrode wear were experimentally investigated.
Nội dung trích xuất từ tài liệu:
Statistical analysis on electrode wear in EDM of tool steel DIN 1.2714 used in forging dies Journal of Materials Processing Technology 187–188 (2007) 711–714 Statistical analysis on electrode wear in EDM of tool steel DIN 1.2714 used in forging dies H. Zarepour a,∗ , A. Fadaei Tehrani b , D. Karimi c , S. Amini a a Department of Manufacturing Engineering, School of Engineering (2), Islamic Azad University, Najafabad Branch, Isfahan, Iran b Department of Mechanical Engineering, Isfahan University of Techology, Isfahan, Iran c Department of Mechanical Engineering, Tarbiat Modarres University, Tehran, Iran Abstract Electrical discharge machining (EDM) is a widespread process which works very effectively in machining of difficult-to-cut materials and alloys in die and aerospace industries with high dimensional accuracies. However, this capability could be deteriorated due to electrode wear leading to decrease of process productivity. In this study, the effect of machining parameters of EDM process including on-time, current, voltage, the engaging time between workpiece and electrode, and pre-EDM roughing on electrode wear were experimentally investigated. Main effects of factors and interactions were considered in this paper and regression equation was derived. A L50 (21 × 511 ) Taguchi’s standard orthogonal array was employed as experimental design. Copper was used as electrode to machine the hot work tool steel 1.2714, which is widely used to make forging dies and mandrels. © 2007 Elsevier B.V. All rights reserved. Keywords: EDM; Electrode wear; Orthogonal array; Statistical analyses 1. Introduction Among the non-traditional methods of material removal processes, electrical discharge machining (EDM) has drawn a great a deal of researchers’ attention because of its broad industrial applications. This process is well suited for machining of casting and forging dies, powder metallurgy and injection molds, and aerospace parts. The process is a spark erosion method, eroding the workpiece by high frequency spark discharges [1]. EDM has a high capability of machining the accurate cavities of dies and molds. Nevertheless, electrode wear occurs during EDM process leading to a lack of machining accuracy in the geometry of workpiece [2]. Furthermore, electrode wear imposes high costs on manufacturers to substitute the eroded complicated electrodes by new ones for die making. In order to increase the machining efficiency, erosion of the workpiece must be maximized and that of the electrode minimized in EDM process [1]. Therefore, ∗ Corresponding author. Tel.: +98 312 37 58930; fax: +98 312 37 56900. E-mail address: h-zare@iaun.ac.ir (H. Zarepour). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.11.202 studying the electrode wear and related significant factors would be effective to enhance the machining productivity and process reliability. A series of investigations have been conducted on electrode wear in EDM process. Soni and Chakraverti [3,4] studied the surface quality, material removal rate, wear ratio, and dimensional accuracy in EDM of alloy steels. Singh et al. investigated the effect of machining parameters on electrode wear in die-sinking EDM of En-31 tool steel with different electrode materials [5]. Also, Luis et al. have carried out a study on electrode wear in EDM of silicon carbide using the technique of design of experiments [6]. In this research, an experimental study is conducted to investigate on electrode wear in die-sinking EDM of DIN 1.2714 hot work tool steel. The selection of this material was made taking into account its wide range of applications in die and mold industries such as hammer and hydraulic forging dies. The aim of this study is to find out from which process parameters (factors) electrode wear is affected and to which factor interactions it is related. This is usually done by means of analysis of variance (ANOVA). Furthermore, regression analysis is used to establish the correlation between factors and response (tool wear). The appropriate degree of the polynomial regression equation is 712 H. Zarepour et al. / Journal of Materials Processing Technology 187–188 (2007) 711–714 found which is thought to be useful assessment of the predictive equation [7,8]. Finally, the optimal factor levels are obtained. 2. Experimentation 2.1. Experimental design During EDM experiments, the input parameters (factors) were on-time (pulse-on duration), peak current, pulsed voltage, engaging time, and pre-EDM roughing accuracy. The pulse-off duration was kept constant which could effectively control the flushing of the debris from the gap, giving machining stability. Therefore, the effect of the pulse-off duration on machining process was not considered in the present work. Table 1 shows factors and factor levels assessed in this study. The design of experiments was performed through Taguchi approach of experimental design. Accordingly, a L50 standard orthogonal array was employed. All the main effects of factors and two-order interactions were desired to be considered in this study. 2.2. Experimental equipment and setup Fifty DIN 1.2714 steel specimens were machined for 50 experimental runs in this work. The holes were created in the workpieces in five groups of dimensions as roughed cavities before EDM process. The allowances left for EDM die-sinking were considered equal to 0.25, 0.5, 0.75, 1, and 1.25 mm (preEDM rouging accuracy) for each group of dimensions. These dimensions are referred as 1, 2, 3, 4, and 5, respectively, in Table 1 and analyses. Hardness of the specimens was increased up to 48–50 HRC, nearly the same as the hardness of forging dies. Cylindrical copper rods with 99% purity and 8.98 g/cm3 density were machined with good surface finish and exact dimensions as tool electrodes. Fig. 1 illustrates a sample of copper electrodes. Both electrodes and workpieces were debu ...