- Email: [email protected]
Experimental investigation on a shield and magnetic assisted EDM of EN24 steel
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Experimental investigation on a shield and magnetic assisted EDM of EN24 steel Nitin S. Chityal ⇑, Amar Bhandare, U.A. Dabade Walchand College of Engineering, Sangli 416415, India
a r t i c l e
i n f o
Article history: Received 11 July 2019 Accepted 3 August 2019 Available online xxxx Keywords: MRR (Material Removal Rate) EWR (Electrode Wear Rate) POT (Pulse On Time) Shield Bottom clearance
a b s t r a c t Electric discharge machining is a non-traditional method of machining and also it is an electro-thermal machining process where an electric spark is generated by electrical energy. In the EDM process, workpiece material needs to be electrically conductive. In EDM machining any type of workpiece material which is conductive can be machined also can be cut into any profile. An electrode which is generally used as a tool must be a good conductor of electricity. Both the electrode and workpiece material are immersed in a dielectric medium and connected to the DC power source. An electric field is generated within the gap between the electrode and the workpiece is retained based on the potential difference applied. There will be a big amount of electrons flowing from the tool to the job and ions from the job to the tool such electron and ion movement can be seen visually as a spark. The electrical energy is thus dissipated as the spark’s heat energy. But in the above process, there is a problem associated with the energy utilization produced in the spark. As just a little extent of the energy created in the spark is utilized for melting and evaporating of the workpiece material, the rest of the energy is dispersed in the dielectric liquid. In this present work, an attempt has been made to restrict the energy dissipation in the dielectric fluid and for this purpose, an enclosure is attached around the cathode with the plan to make a back pressure in this manner confining the development of the plasma in the EDM procedure. This the enclosure is also called as a shield and again to remove debris from the workpiece, the magnetic field generated by the magnets is used around the machining region. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 1st International Conference on Manufacturing, Material Science and Engineering.
1. Introduction EDM is a regulated metal removal method used by electrical spark erosion to remove metal. In this phase, an electrical spark is used to cut (erode) the workpiece to create the completed portion to the required form as the cutting tool. The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the workpiece. A small proportion of the energy produced in the spark is used for melting and evaporation of the workpiece material, the remaining energy is dissipated in the dielectric fluid in the form of convection and radiation. As per the above literature review [1] the researcher had used shield attached to the workpiece. In this case, there is a problem with the evacuation of the machining gap debris [1]. Generally, it is recommended that during pulse off time dielectric fluid should evacuate machining gap debris, but in the ⇑ Corresponding author. E-mail address: [email protected] (N.S. Chityal).
above case due to shield is mounted on the workpiece, it is forming an obstacle to remove debris. Accumulation of debris in gaps creates inactive pulses like short and open circuits and the abnormal electrical discharge, so the stability of the EDM process would be disturbed and for that reason, it adversely affects the material removal rate (MRR), surface roughness (SR) and electrode wear rate (EWR) [2]. By considering the above literature review [1] and the electrodischarge machining process it is defined to conduct the EDM under the influence of a shield which is mounted on the tool and also by using permanent magnets to remove debris. 2. Literature review Govindan and Joshi [1] conducted an experimental dry electrical discharge drilling assessment. It has been shown that it is possible to perform dry EDM by offering the sparking zone with an enclosure (shielding). In relation to the MRR and TWR research, this research disclosed multiple features of the dry EDM method by
https://doi.org/10.1016/j.matpr.2019.08.075 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 1st International Conference on Manufacturing, Material Science and Engineering.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
2
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx
measuring over size, examining machined surface morphology. Joshi et al. [2] suggested a fresh hybrid strategy using a pulsating magnetic field help to limit dry EDM plasma and enhance process efficiency. The magnetic field is shown to help a greater transfer of thermal energy to the workpiece owing to greater ionization and plasma containment and to help improvise the process of material removal and melting in dry EDM. Beravala and Pandey [3] indicated that comparative research was performed to assess EDM efficiency, helped by both the magnetic field and the dielectric liquidcum-gaseous. By experimentation, it is found that the MRR was increased by 21–41% and EWR was increased by 7–14% in Air Assisted EDM due to the enhancement in ionization process due to the incorporation of the magnetic field. Torres [4] researched the conduct of a copper electrode-positive polarity TiB2 ceramic EDM. To do so, in this sort of process, three of the most significant technological parameters have been discussed. The current intensity and duty cycle were the most influential parameters in the case of the MRR variable, to such an extent that an increase in both parameters resulted in higher MRR. Teimouri and Baseri [5] performed experiments to explore the combined impact of tool rotation and multiple internal magnetic field intensities on EDM processes by considering the primary variable reaction or output parameter as MRR and surface roughness (SR). Lin et al. [6] concentrated on optimizing the machining parameters in the Taguchi method-based magnetic force aided EDM. This work embraced a Taguchi-based L18 orthogonal array for conducting a sequence of tests and statistically assessed ANOVA’s experimental information. Wong et al. [7] performed studies to explore the impacts of flushing on the effectiveness and stability of EDM machining circumstances, including the impacts of the flushing setup on the wear of the instrument and the low profile of the workpiece on the impacts of flushing on the integrity of electro discharge surfaces machined.
tion. Therefore a large amount of heat energy is available for eroding the workpiece. Therefore we find better material removal in case shield attached EDM process. For the development of shield cylindrical shaped raw material is brought, then it is cut into the required dimension and shape on lathe machine according to electrode size it is drilled throughout the then boring operation is done up-to quarter length. A cross-nut is used for the electrode to be fit inside the shield very tightly. Bottom clearance of a shield is the diametric clearance between outer circle diameter (Db) and electrode diameter (Dt). Cb is taken as one of the parameters by using a shield. Cb is responsible for pressurized dielectric fluid to be swirled around the electrode. This Swirling action is responsible for the rate at which the heat to be withdrawn from an electrode. As Cb increases the rate at which heat drawn is slower because as Cb increases swirling velocity decreases. Fig. 1 shows the schematic and photograph of a shield. 3.1. Experimental details L18 array is selected for final experiments, for conventional magnetic field assisted EDM there are two factors of three levels and one factor of two levels whereas for Magnetic Field assisted EDM using shield one more factor is added in experiments which is nothing but clearance at the bottom between electrode and shield (Cb), so it becomes three factors of three levels one factor of two levels L18 design. The experiments are conducted on the S50 CNC EDM machine. After experimentation, the material removal rate (MRR) and electrode wear rate (EWR) are calculated. Photograph of EDM machining is shown in by using a shield is shown in Fig. 2.
3. Experimental work In this experimental work a shield which is made up of a nonconducting material known as ABS (Acrylonitrile Butadiene Styrene) polymer is being used to control heat dissipation rates away from machining region For the development of shield ABS polymer is being used since the process itself requires a non-conductive material which is also good resistant to heat. We know that the main purpose of developing the shield is that, to compare regular EDM process with shield attached EDM process because, in shield attachment, we can reduce heat losses by convection and radia-
Fig. 2. EDM machining by using a shield.
Fig. 1. (a) Schematic of a shield; (b) Photograph of a shield.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
3
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Experimental considerations. Considerations
Details
Workpiece Tool type Electrode dimension Shield material Design of Experiments
EN24 alloy Steel plate of 6 mm thick Electrode (Copper) Copper 8.00 mm diameter ABS polymer (Acrylonitrile Butadiene Styrene) Taguchi method
Table 2 Factors and their levels. Sr. no.
Parameters
Level 1
Level 2
Level 3
1 2 3 4
Current (I) [A] Pulse On Time (POT) [ls] Voltage (V) [V] Clearance at bottom (Cb) [mm]
20 100 40 4
25 200 50 6
30 – 60 8
Final experiments are performed by using copper electrode having an electrode diameter of 8.00 mm and workpiece with material EN24 alloy steel plate of 6 mm thickness as shown in Table 1. In the final experiments the levels of current, voltage and pulse on time and bottom clearance of a shield as shown in Table 2.
4. Results and discussion Discharge energy is the most important aspect of EDM but the effectiveness of shield also plays a very important role to achieve
optimum machining characteristics. The ANOVA results of MRR and EWR with a shield as indicated in Table 3 are also represents the same fashion of influence of various process parameters on response variables. Under the influence of shield, POT is the most significant factor and the peak current is the second highest influencing factor whereas voltage is less significant factors as compared to others as represented by Table 3. As compared to other factors like current, POT and voltage Cb has less influence on the MRR and EWR even though within this range of Cb as the Cb increases the MRR and EWR also increased as represented by Figs. 3 and 4 and this is because as the Cb increases there is a decrease in swirling action because of decrease in swirling velocity due to which heat dissipation is lowered. As heat dissipation is lowered from the machining region, accumulation of heat rises around the machining region hence this will result into increase in MRR and EWR. As per the selected factors and their levels L18 orthogonal array is selected for experimentation and material removal rate (MRR) and electrode wear rate (EWR) calculated. MRR and EWR calculated by Eq. (1). MbMa
MRR=EWR ¼
q
1000 t
mm3 =min
ð1Þ
Where t = machining time (min), q = Density of the material. Density of EN24 alloy steel = 7840 kg/m3 and Density of Cu material = 8960 kg/m3. Ma and Mb are the mass of electrode or workpiece after and before machining.
Table 3 ANOVA results of MRR and EWR. Source
DF
MRR (mm3/min)
EWR (mm3/min)
F
P
F
P
POT [ls] Current (I) Voltage (V) Cb (mm) Error
1 2 2 2 10
30.11 10.75 0.58 1.15 R-Sq = 67.80% R-Sq (adj) = 54.39%
0.000 0.003 0.576 0.354
95.76 12.07 0.28 0.22 R-Sq = 97.86% R-Sq (adj) = 96.97%
0.000 0.002 0.782 0.809
Fig. 3. Main Effects plot of MRR.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
4
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 4. Main Effects plot of EWR.
5. Conclusion Table 4 Optimum parameter combination for minimum EWR. Parameters
Optimum levels
Current Pulse on Time Voltage Cb
: : : :
20A 100 (ms) 40 V 4 mm
As shown in Fig. 3 current increases, the value of MRR increases. As heat generation is directly proportional to the square of the current (I) melting and evaporation rate of the material is dependent on the amount of heat generation. As pulse on time increases (POT), there is continuous heat generation rate in the spark for a large duration of time rises due to which higher rates of melting are possible and voltage forms the correct combination so that, a large amount of heat is available for an increase in MRR. In case of the shield, as Cb increases from 4 mm to 6 mm MRR decreases, initially there is less swirling velocity is found around electrode this is due to less stabilized swirling action of the EDM oil around the electrode but swirling velocity increases from 4 mm to 6 mm Cb. As Cb increases from 6 mm to 8 mm swirling velocity again decreases due to which heat dissipation rate also decreases, therefore, MRR increases. There are melting and evaporation of an electrode similar to the workpiece, but the erosion rate is very less compared to the workpiece. As shown in Fig. 4, as current increases, the value of EWR increases. As heat generation is directly proportional to the square of the current (I), melting and evaporation rate of the material is dependent on the amount of heat generation. As pulse on time increases (POT) increases there is continuous heat generation in the spark for a large duration of time due to which higher rates of melting are possible and voltage forms the correct combination so that, a large amount of heat is available for an increase in EWR. In this case, it is preferred fewer values of above parameters because it is finally aimed to minimize electrode erosion rate. As electrode surrounded by the shield there is a direct effect of Cb EWR rate. As Cb increases, EWR rate also increases similar to MRR. Table 4 represents the optimum parameter and their level combination to decrease EWR.
In this research paper, an attachment called ABS Shield which is mounted on the electrode to restrict the amount of heat dissipation away from the machining region and to understand the effect of the shield on EDM. Machining of EN24 steel is performed by conventional EDM and EDM using a shield and also the effect of various process parameters viz. peak current, pulse on time, voltage and bottom clearance on the response variables (MRR and EWR) of EDM are investigated and the following conclusions are drawn. EDM with a shield has a positive effect on the EDM which improves the machining characteristic of EDM. Pulse on time (POT) is the most influencing parameter followed by the current for MRR and EWR which has F value 30.11 and 95.76 respectively by EDM using a shield. Even though the selected levels of bottom clearance of a shield (Cb) is not majorly influencing the response variable as compared to other parameters (I and POT) but the presence of shield helps to control the rate of heat dissipation away from the machining region which has an impact on MRR and EWR. As shown in Fig. 3 the optimum parameter combination for maximum MRR has been found for I, POT, V, and Cb is 30 A, 200 ms, 60 V and 8 mm respectively. As shown in Fig. 4 the optimum parameter combination for minimum EWR has been found for I, POT, V, and Cb is 20 A, 100 ms, 40 V and 4 mm respectively.
Acknowledgment The authors wish to sincerely acknowledge for financial support through Research Promotion Scheme for the project title Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, under which the procurement of equipment and experimental work is performed at Walchand College of Engineering, Sangli References [1] P. Govindan, S. Joshi, Experimental characterization of material removal in dry electrical discharge drilling, Int. J. Mach. Tools Manuf. 50 (2010) 431–443.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx [2] S. Joshi, P. Govindan, A. Malshe, K. Rajurkar, Experimental characterization of dry EDM performed in a pulsating magnetic field, CIRP Annal. Manuf. Technol. 50 (2010) 431–443. [3] H. Beravala, P. Pandey, Experimental investigations to evaluate the effect of magnetic field on the performance of air and argon gas assisted EDM processes, J. Manuf. Process. 34 (2018) 356–373. [4] A. Torres, C. Luis, I. Puertas, EDM machinability and surface roughness analysis of TiB2 using copper electrodes, J. Alloy. Compd. 16 (2016).
5
[5] R. Teimouri, H. Baseri, Effects of magnetic field and rotary tool on EDM performance, J. Manuf. Process. 14 (2012) 316–322. [6] Yan-Cherng Lin, Yuan-Feng Chen, Der-An Wang, Ho-Shiun Lee, Optimization of machining parameters in magnetic force assisted EDM based on Taguchi method, J. Mater. Process. Technol. 209 (2009) 3374–3383. [7] Y.S. Wong, L.C. Lim, L.C. Lee, Effects of flushing on electro-discharge machined Surfaces, J. Mater. Process. Technol. 48 (1995) PP.299-305.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Experimental investigation on a shield and magnetic assisted EDM of EN24 steel Nitin S. Chityal ⇑, Amar Bhandare, U.A. Dabade Walchand College of Engineering, Sangli 416415, India
a r t i c l e
i n f o
Article history: Received 11 July 2019 Accepted 3 August 2019 Available online xxxx Keywords: MRR (Material Removal Rate) EWR (Electrode Wear Rate) POT (Pulse On Time) Shield Bottom clearance
a b s t r a c t Electric discharge machining is a non-traditional method of machining and also it is an electro-thermal machining process where an electric spark is generated by electrical energy. In the EDM process, workpiece material needs to be electrically conductive. In EDM machining any type of workpiece material which is conductive can be machined also can be cut into any profile. An electrode which is generally used as a tool must be a good conductor of electricity. Both the electrode and workpiece material are immersed in a dielectric medium and connected to the DC power source. An electric field is generated within the gap between the electrode and the workpiece is retained based on the potential difference applied. There will be a big amount of electrons flowing from the tool to the job and ions from the job to the tool such electron and ion movement can be seen visually as a spark. The electrical energy is thus dissipated as the spark’s heat energy. But in the above process, there is a problem associated with the energy utilization produced in the spark. As just a little extent of the energy created in the spark is utilized for melting and evaporating of the workpiece material, the rest of the energy is dispersed in the dielectric liquid. In this present work, an attempt has been made to restrict the energy dissipation in the dielectric fluid and for this purpose, an enclosure is attached around the cathode with the plan to make a back pressure in this manner confining the development of the plasma in the EDM procedure. This the enclosure is also called as a shield and again to remove debris from the workpiece, the magnetic field generated by the magnets is used around the machining region. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 1st International Conference on Manufacturing, Material Science and Engineering.
1. Introduction EDM is a regulated metal removal method used by electrical spark erosion to remove metal. In this phase, an electrical spark is used to cut (erode) the workpiece to create the completed portion to the required form as the cutting tool. The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the workpiece. A small proportion of the energy produced in the spark is used for melting and evaporation of the workpiece material, the remaining energy is dissipated in the dielectric fluid in the form of convection and radiation. As per the above literature review [1] the researcher had used shield attached to the workpiece. In this case, there is a problem with the evacuation of the machining gap debris [1]. Generally, it is recommended that during pulse off time dielectric fluid should evacuate machining gap debris, but in the ⇑ Corresponding author. E-mail address: [email protected] (N.S. Chityal).
above case due to shield is mounted on the workpiece, it is forming an obstacle to remove debris. Accumulation of debris in gaps creates inactive pulses like short and open circuits and the abnormal electrical discharge, so the stability of the EDM process would be disturbed and for that reason, it adversely affects the material removal rate (MRR), surface roughness (SR) and electrode wear rate (EWR) [2]. By considering the above literature review [1] and the electrodischarge machining process it is defined to conduct the EDM under the influence of a shield which is mounted on the tool and also by using permanent magnets to remove debris. 2. Literature review Govindan and Joshi [1] conducted an experimental dry electrical discharge drilling assessment. It has been shown that it is possible to perform dry EDM by offering the sparking zone with an enclosure (shielding). In relation to the MRR and TWR research, this research disclosed multiple features of the dry EDM method by
https://doi.org/10.1016/j.matpr.2019.08.075 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 1st International Conference on Manufacturing, Material Science and Engineering.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
2
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx
measuring over size, examining machined surface morphology. Joshi et al. [2] suggested a fresh hybrid strategy using a pulsating magnetic field help to limit dry EDM plasma and enhance process efficiency. The magnetic field is shown to help a greater transfer of thermal energy to the workpiece owing to greater ionization and plasma containment and to help improvise the process of material removal and melting in dry EDM. Beravala and Pandey [3] indicated that comparative research was performed to assess EDM efficiency, helped by both the magnetic field and the dielectric liquidcum-gaseous. By experimentation, it is found that the MRR was increased by 21–41% and EWR was increased by 7–14% in Air Assisted EDM due to the enhancement in ionization process due to the incorporation of the magnetic field. Torres [4] researched the conduct of a copper electrode-positive polarity TiB2 ceramic EDM. To do so, in this sort of process, three of the most significant technological parameters have been discussed. The current intensity and duty cycle were the most influential parameters in the case of the MRR variable, to such an extent that an increase in both parameters resulted in higher MRR. Teimouri and Baseri [5] performed experiments to explore the combined impact of tool rotation and multiple internal magnetic field intensities on EDM processes by considering the primary variable reaction or output parameter as MRR and surface roughness (SR). Lin et al. [6] concentrated on optimizing the machining parameters in the Taguchi method-based magnetic force aided EDM. This work embraced a Taguchi-based L18 orthogonal array for conducting a sequence of tests and statistically assessed ANOVA’s experimental information. Wong et al. [7] performed studies to explore the impacts of flushing on the effectiveness and stability of EDM machining circumstances, including the impacts of the flushing setup on the wear of the instrument and the low profile of the workpiece on the impacts of flushing on the integrity of electro discharge surfaces machined.
tion. Therefore a large amount of heat energy is available for eroding the workpiece. Therefore we find better material removal in case shield attached EDM process. For the development of shield cylindrical shaped raw material is brought, then it is cut into the required dimension and shape on lathe machine according to electrode size it is drilled throughout the then boring operation is done up-to quarter length. A cross-nut is used for the electrode to be fit inside the shield very tightly. Bottom clearance of a shield is the diametric clearance between outer circle diameter (Db) and electrode diameter (Dt). Cb is taken as one of the parameters by using a shield. Cb is responsible for pressurized dielectric fluid to be swirled around the electrode. This Swirling action is responsible for the rate at which the heat to be withdrawn from an electrode. As Cb increases the rate at which heat drawn is slower because as Cb increases swirling velocity decreases. Fig. 1 shows the schematic and photograph of a shield. 3.1. Experimental details L18 array is selected for final experiments, for conventional magnetic field assisted EDM there are two factors of three levels and one factor of two levels whereas for Magnetic Field assisted EDM using shield one more factor is added in experiments which is nothing but clearance at the bottom between electrode and shield (Cb), so it becomes three factors of three levels one factor of two levels L18 design. The experiments are conducted on the S50 CNC EDM machine. After experimentation, the material removal rate (MRR) and electrode wear rate (EWR) are calculated. Photograph of EDM machining is shown in by using a shield is shown in Fig. 2.
3. Experimental work In this experimental work a shield which is made up of a nonconducting material known as ABS (Acrylonitrile Butadiene Styrene) polymer is being used to control heat dissipation rates away from machining region For the development of shield ABS polymer is being used since the process itself requires a non-conductive material which is also good resistant to heat. We know that the main purpose of developing the shield is that, to compare regular EDM process with shield attached EDM process because, in shield attachment, we can reduce heat losses by convection and radia-
Fig. 2. EDM machining by using a shield.
Fig. 1. (a) Schematic of a shield; (b) Photograph of a shield.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
3
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Experimental considerations. Considerations
Details
Workpiece Tool type Electrode dimension Shield material Design of Experiments
EN24 alloy Steel plate of 6 mm thick Electrode (Copper) Copper 8.00 mm diameter ABS polymer (Acrylonitrile Butadiene Styrene) Taguchi method
Table 2 Factors and their levels. Sr. no.
Parameters
Level 1
Level 2
Level 3
1 2 3 4
Current (I) [A] Pulse On Time (POT) [ls] Voltage (V) [V] Clearance at bottom (Cb) [mm]
20 100 40 4
25 200 50 6
30 – 60 8
Final experiments are performed by using copper electrode having an electrode diameter of 8.00 mm and workpiece with material EN24 alloy steel plate of 6 mm thickness as shown in Table 1. In the final experiments the levels of current, voltage and pulse on time and bottom clearance of a shield as shown in Table 2.
4. Results and discussion Discharge energy is the most important aspect of EDM but the effectiveness of shield also plays a very important role to achieve
optimum machining characteristics. The ANOVA results of MRR and EWR with a shield as indicated in Table 3 are also represents the same fashion of influence of various process parameters on response variables. Under the influence of shield, POT is the most significant factor and the peak current is the second highest influencing factor whereas voltage is less significant factors as compared to others as represented by Table 3. As compared to other factors like current, POT and voltage Cb has less influence on the MRR and EWR even though within this range of Cb as the Cb increases the MRR and EWR also increased as represented by Figs. 3 and 4 and this is because as the Cb increases there is a decrease in swirling action because of decrease in swirling velocity due to which heat dissipation is lowered. As heat dissipation is lowered from the machining region, accumulation of heat rises around the machining region hence this will result into increase in MRR and EWR. As per the selected factors and their levels L18 orthogonal array is selected for experimentation and material removal rate (MRR) and electrode wear rate (EWR) calculated. MRR and EWR calculated by Eq. (1). MbMa
MRR=EWR ¼
q
1000 t
mm3 =min
ð1Þ
Where t = machining time (min), q = Density of the material. Density of EN24 alloy steel = 7840 kg/m3 and Density of Cu material = 8960 kg/m3. Ma and Mb are the mass of electrode or workpiece after and before machining.
Table 3 ANOVA results of MRR and EWR. Source
DF
MRR (mm3/min)
EWR (mm3/min)
F
P
F
P
POT [ls] Current (I) Voltage (V) Cb (mm) Error
1 2 2 2 10
30.11 10.75 0.58 1.15 R-Sq = 67.80% R-Sq (adj) = 54.39%
0.000 0.003 0.576 0.354
95.76 12.07 0.28 0.22 R-Sq = 97.86% R-Sq (adj) = 96.97%
0.000 0.002 0.782 0.809
Fig. 3. Main Effects plot of MRR.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
4
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 4. Main Effects plot of EWR.
5. Conclusion Table 4 Optimum parameter combination for minimum EWR. Parameters
Optimum levels
Current Pulse on Time Voltage Cb
: : : :
20A 100 (ms) 40 V 4 mm
As shown in Fig. 3 current increases, the value of MRR increases. As heat generation is directly proportional to the square of the current (I) melting and evaporation rate of the material is dependent on the amount of heat generation. As pulse on time increases (POT), there is continuous heat generation rate in the spark for a large duration of time rises due to which higher rates of melting are possible and voltage forms the correct combination so that, a large amount of heat is available for an increase in MRR. In case of the shield, as Cb increases from 4 mm to 6 mm MRR decreases, initially there is less swirling velocity is found around electrode this is due to less stabilized swirling action of the EDM oil around the electrode but swirling velocity increases from 4 mm to 6 mm Cb. As Cb increases from 6 mm to 8 mm swirling velocity again decreases due to which heat dissipation rate also decreases, therefore, MRR increases. There are melting and evaporation of an electrode similar to the workpiece, but the erosion rate is very less compared to the workpiece. As shown in Fig. 4, as current increases, the value of EWR increases. As heat generation is directly proportional to the square of the current (I), melting and evaporation rate of the material is dependent on the amount of heat generation. As pulse on time increases (POT) increases there is continuous heat generation in the spark for a large duration of time due to which higher rates of melting are possible and voltage forms the correct combination so that, a large amount of heat is available for an increase in EWR. In this case, it is preferred fewer values of above parameters because it is finally aimed to minimize electrode erosion rate. As electrode surrounded by the shield there is a direct effect of Cb EWR rate. As Cb increases, EWR rate also increases similar to MRR. Table 4 represents the optimum parameter and their level combination to decrease EWR.
In this research paper, an attachment called ABS Shield which is mounted on the electrode to restrict the amount of heat dissipation away from the machining region and to understand the effect of the shield on EDM. Machining of EN24 steel is performed by conventional EDM and EDM using a shield and also the effect of various process parameters viz. peak current, pulse on time, voltage and bottom clearance on the response variables (MRR and EWR) of EDM are investigated and the following conclusions are drawn. EDM with a shield has a positive effect on the EDM which improves the machining characteristic of EDM. Pulse on time (POT) is the most influencing parameter followed by the current for MRR and EWR which has F value 30.11 and 95.76 respectively by EDM using a shield. Even though the selected levels of bottom clearance of a shield (Cb) is not majorly influencing the response variable as compared to other parameters (I and POT) but the presence of shield helps to control the rate of heat dissipation away from the machining region which has an impact on MRR and EWR. As shown in Fig. 3 the optimum parameter combination for maximum MRR has been found for I, POT, V, and Cb is 30 A, 200 ms, 60 V and 8 mm respectively. As shown in Fig. 4 the optimum parameter combination for minimum EWR has been found for I, POT, V, and Cb is 20 A, 100 ms, 40 V and 4 mm respectively.
Acknowledgment The authors wish to sincerely acknowledge for financial support through Research Promotion Scheme for the project title Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, under which the procurement of equipment and experimental work is performed at Walchand College of Engineering, Sangli References [1] P. Govindan, S. Joshi, Experimental characterization of material removal in dry electrical discharge drilling, Int. J. Mach. Tools Manuf. 50 (2010) 431–443.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075
N.S. Chityal et al. / Materials Today: Proceedings xxx (xxxx) xxx [2] S. Joshi, P. Govindan, A. Malshe, K. Rajurkar, Experimental characterization of dry EDM performed in a pulsating magnetic field, CIRP Annal. Manuf. Technol. 50 (2010) 431–443. [3] H. Beravala, P. Pandey, Experimental investigations to evaluate the effect of magnetic field on the performance of air and argon gas assisted EDM processes, J. Manuf. Process. 34 (2018) 356–373. [4] A. Torres, C. Luis, I. Puertas, EDM machinability and surface roughness analysis of TiB2 using copper electrodes, J. Alloy. Compd. 16 (2016).
5
[5] R. Teimouri, H. Baseri, Effects of magnetic field and rotary tool on EDM performance, J. Manuf. Process. 14 (2012) 316–322. [6] Yan-Cherng Lin, Yuan-Feng Chen, Der-An Wang, Ho-Shiun Lee, Optimization of machining parameters in magnetic force assisted EDM based on Taguchi method, J. Mater. Process. Technol. 209 (2009) 3374–3383. [7] Y.S. Wong, L.C. Lim, L.C. Lee, Effects of flushing on electro-discharge machined Surfaces, J. Mater. Process. Technol. 48 (1995) PP.299-305.
Please cite this article as: N. S. Chityal, A. Bhandare and U. A. Dabade, Experimental investigation on a shield and magnetic assisted EDM of EN24 steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.075