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  • 标题:Experimental investigations into electrochemical machining of high carbon high chromium die steel.
  • 作者:Sekar, T. ; Marappan, R.
  • 期刊名称:International Journal of Applied Engineering Research
  • 印刷版ISSN:0973-4562
  • 出版年度:2008
  • 期号:February
  • 语种:English
  • 出版社:Research India Publications
  • 摘要:Electrochemical machining (ECM) has tremendous potential because of its versatile applications and it is expected that it would be a promising, successful, and commercially viable machining process in the modern manufacturing industries. ECM is a non-traditional process used mainly to cut hard or difficult to cut metals, where the application of a more traditional process is not convenient. Different from the other machining processes, in ECM there is no contact between tool and workpiece. ECM was developed initially to machine the hard alloys, although any metal can so be machined [1]. Electro chemical reactions are responsible for the chip removal mechanism [2]. The difficulties to cut poor machinable materials like high carbon high chromium die steel by conventional process have been largely responsible for the development of the ECM process. The main components of ECM system are a low voltage and high current power supply and an electrolyte circulation system. The electrolyte is normally solutions of inorganic salts, like sodium chloride (NaCl) or sodium nitrate (NaN[O.sub.3]) [3]. Machining performance of ECM mainly depends on feed rate of the tool, applied voltage, electrolyte discharge rate, current density and inter electrode gap [4]. The objective of this work is to attempt an experimental study of the influencing variables that affect the performance of electrochemical machining of high carbon high chromium die steel with the hardness of 63 HRC. The material removal rate and surface roughness were studied. Three parameters were changed during the experiments: feed rate, applied voltage and electrolyte discharge rate. The inter electrode gap of 0.1 mm was maintained as constant throughout the experimentation. Twenty seven experiments were conducted out in the ECM equipment. The sodium chloride (NaCl) electrolytic aqua solution was used. The electrochemical machining of high carbon high chromium die steel with the sodium chloride electrolytic aqua solution presented better results of material removal rate and surface roughness.
  • 关键词:Chromium;Chromium (Metal);Hardness;Hardness (Materials);Machining;Steel

Experimental investigations into electrochemical machining of high carbon high chromium die steel.


Sekar, T. ; Marappan, R.


Introduction

Electrochemical machining (ECM) has tremendous potential because of its versatile applications and it is expected that it would be a promising, successful, and commercially viable machining process in the modern manufacturing industries. ECM is a non-traditional process used mainly to cut hard or difficult to cut metals, where the application of a more traditional process is not convenient. Different from the other machining processes, in ECM there is no contact between tool and workpiece. ECM was developed initially to machine the hard alloys, although any metal can so be machined [1]. Electro chemical reactions are responsible for the chip removal mechanism [2]. The difficulties to cut poor machinable materials like high carbon high chromium die steel by conventional process have been largely responsible for the development of the ECM process. The main components of ECM system are a low voltage and high current power supply and an electrolyte circulation system. The electrolyte is normally solutions of inorganic salts, like sodium chloride (NaCl) or sodium nitrate (NaN[O.sub.3]) [3]. Machining performance of ECM mainly depends on feed rate of the tool, applied voltage, electrolyte discharge rate, current density and inter electrode gap [4]. The objective of this work is to attempt an experimental study of the influencing variables that affect the performance of electrochemical machining of high carbon high chromium die steel with the hardness of 63 HRC. The material removal rate and surface roughness were studied. Three parameters were changed during the experiments: feed rate, applied voltage and electrolyte discharge rate. The inter electrode gap of 0.1 mm was maintained as constant throughout the experimentation. Twenty seven experiments were conducted out in the ECM equipment. The sodium chloride (NaCl) electrolytic aqua solution was used. The electrochemical machining of high carbon high chromium die steel with the sodium chloride electrolytic aqua solution presented better results of material removal rate and surface roughness.

Experimentation

The workpiece material was high carbon high chromium die steel with hardness of 63 HRC and the chemical composition is shown in table 1.

The high carbon high chromium die steel was chosen because of its high hardness and low machinablility in conventional processes with high tool wear. A Design of Experiment (DOE) is used for determining the relationship between tool feed rate, applied voltage and electrolyte discharge rate affecting a process and the material removal rate and surface roughness of that process. Three factors and three level full factorial (27) experiments were conducted using sodium chloride aqua solution [5] as electrolyte. The material removal rate and surface roughness obtained were studied. The actual ECM setup is shown in figure 1. The tool was made of electrolytic copper [6] with 2.45 cm as outer diameter. The experiments were conducted for three minutes and the results were recorded. Sartorius electronic weighing machine with 1mg accuracy and Mitutoyo surface tester with a range of 0-150[micro]m were used for measuring material removal rate and surface roughness (Ra) respectively.

[FIGURE 1 OMITTED]

The complete working environment of the experiment is shown in table 2.

Results and Discussion

The material removal rate and surface roughness of the electrochemical machining process is primarily influenced by the controlled variables like feed rate, applied voltage and electrolyte discharge rate in high carbon high chromium die steel. The effects of the above influencing parameters have been studied through the experiments.

The intervening Parametrics on the Material removal rate

The results obtained in the experiments reveal that the effects of the influencing parameters on material removal rate. This facilitates analyze of the suitable parametric combinations that can be made for achieving better material removal rate. Figures. 2-4 show the effect of feed rate, applied voltage and electrolyte discharge rate on the material removal rate. From figure. 2, it can be observed that the feed rate has a significant effect on material removal rate at different voltages. It is observed that material removal rate increases with the increase of feed rate for all voltage conditions. The material removal rate is found to reach a maximum value of 405 [mm.sup.3]/min at a feed rate of 0.54 mm/min and the applied voltage of 18V conditions.

[FIGURE 2 OMITTED]

Variation of material removal rate with varying voltages is plotted in figure. 3 for different feed rate conditions. The experimental results show that the material removal rate increases with the increase in the applied voltage.

[FIGURE 3 OMITTED]

This obviously indicates that a fixed inter electrode gap, the increase in the applied voltage causes a greater machining current to be available in the machining gap causing the enhancement of the material removal rate. The result of the experiments reveal that the effect of the applied voltage with higher feed rate condition gives better material removal rate as compared to that achieved with lower feed rate condition. Figure. 4 shows the influence of electrolyte discharge rate for a preset inter electrode gap under various voltage conditions on material removal rate. The figure demonstrates that the electrolyte discharge rate increases result decrease in the material removal rate, the pattern remaining the same for all voltage conditions. The material removal rate decreases with electrolyte discharge rate because there is less mobility of the ions from the metal to the solution decreasing the speed of the chemical reactions.

[FIGURE 4 OMITTED]

The Intervening Parametrics on the Surface Roughness

Fig.5 shows the pattern of results for all the three voltage conditions. When sodium chloride aqua solution was used, the machined surface showed a general trend that the surface roughness starts decreasing with increasing feed rate for all voltage conditions. A feed rate ranges from 0.32 mm/min to 0.54 mm/min seems to give better surface roughness as compared to that achieved with lower feed rate condition. This is because the increase in feed rate at a particular applied voltage condition causes greater electrolyzing current to be available in the machining gap, as well as causing a greater current intensity. At low feed rates, the process of material removal may be instable resulting in poor surface roughness. The roughness can be affected, if machining gap is not maintained at the specified value which implies that the shape of the tool will not be accurately duplicated in the workpiece.

[FIGURE 5 OMITTED]

Figure. 6 indicates that the significant effect of the applied voltage on surface roughness is pronounced at the highest applied voltage.

[FIGURE 6 OMITTED]

This result is due to the higher applied voltage values causing a greater current intensity during higher feed motion of tool, which leads to decrease the spike formation on the machined surface. At 18 V condition, the value of surface roughness decreases with the ratio of 27 % that compared to 15V and 0.54 mm/min conditions. The best surface roughness has been achieved as Ra. 2.19[micro] under the conditions of 18 V and 0.54 mm/min. Figure 7 shows the influence of electrolyte discharge rate on surface roughness under varying voltage conditions. The experimental results reveal that the electrolyte discharge rate increases here also cause decreases in surface roughness and the pattern remaining the same for all voltage conditions. Higher order electrolyte discharge rate minimizes dissolution rate and flushes out the residues in the machining gap and hence lower surface roughness is obtained.

[FIGURE 7 OMITTED]

Conclusions

Based on the results obtained in this experiment, the following conclusions are drawn.

The material removal rate increases with the increase of the feed rate and the applied voltage and decreases with the increase in the electrolyte discharge rate.

The full factorial experiments used in the present work has proved its adequacy to be an effective tool for the analysis of the ECM process.

Machining of High carbon high chromium die steel by using sodium chloride aqua solution at the tool feed rate of 0.54 mm/min, the applied voltage of 18 V and the electrolyte discharge rate of 8 lpm gives the maximum MRR of about 410 [mm.sup.3]/min.

Surface roughness decreases with the increase of the applied voltage, feed rate and electrolyte discharge rate.

The lowest value of surface roughness Ra 2.19 [micro]m has been achieved at the feed rate of 0.54 mm/min, the applied voltage of 18V and the electrolyte discharge rate of 12 lpm.

The NaCl aqua electrolyte solution presented better results of material removal rate and surface roughness in the machining of high carbon high chromium die steel in ECM.

References

[1] McGeough, J.A., 1974, Principles of electrochemical machining, Chapman and Hall, London.

[2] Hewidy, M.S., 2005, "Controlling of metal removal thickness in ECM process," J. Mat. Process. Tech, pp. 348-353.

[3] El-Dardiry, M.A., Asfoor, M.A., and Osman, H.M., 1984, "Experimental investigation into the performance of electrochemical machining processes," Part-II Proc.5th International Conference on Production Engineering, Tokyo, pp. 382-388.

[4] Joao Cirilo da Silva Neto., Evaldo Malaquias da Silva and Marcio Bacci da Silva., 2006, "Intervening variables in electrochemical machining," J. Mat. Process. Tech., pp. 92-96.

[5] Mohan Sen and H.S Shan., 2005, "A review of electrochemical macro to micro hole drilling processes," Int. Jr. Mach Tools & Manufact, pp.137-152.

[6] Pandey, P.C., and Shan, H.S., 1980, Modern Machining Processes, Tata McGraw Hill, New Delhi.

T. Sekar

Faculty of Mechanical Engineering, Advanced Manufacturing Laboratory Government College of Engineering, Salem - 636011. India. [email protected]

R. Marappan

Director (Academic), Paavai Institutions, Pachal Namakkal, India.
Table 1: Chemical composition of High carbon high chromium die steel

Element   C       Cr      Ni      Si      Mn

Wt %      1.8     12.23   0.416   0.492   0.205

Element   Co      V       Mg      Mo      S       P       Fe

Wt %      0.192   0.042   0.01    0.01    0.047   0.038   84.42

Table 2: Complete working conditions

Voltage (V)                         12,15 &18
Current (A)                         0 - 280
Current density (A/[cm.sup.2])      0-25
Inter electrode gap (mm)            0.1
Feed rate (mm/min)                  0.1,0.32 & 0.54
Power supply--DC                    Continuous
Electrolyte discharge rate (lpm)    8, 10 & 12
Electrolyte type                    NaCl--aqua solution
Electrolyte concentration           150 g/l
Tool material                       Copper
Tool outer diameter                 2.45 cm
Electrolyte temperature             20-30[degrees]C
Work piece                          High carbon high chromium die steel
Workpiece hardness                  63 HRC
Machining time (min)                3
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