5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT Guwahati, Assam, India
DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRODISCHARGE DIAMOND FACE GRINDING Sanjay Singh1, Vinod Yadava2, Ram Singar Yadav3* 1
MED, MNNIT Allahabad, Allahabad, India,
[email protected] 2 MED, MNNIT Allahabad, Allahabad, India,
[email protected] 3* MED, MNNIT Allahabad, Allahabad, India,
[email protected] Abstract
Electro-Discharge Diamond Face Grinding (EDDFG) is an advanced hybrid machining process for face grinding of wide variety of electrically conductive difficult-to-machine hard materials by suitable modification in Electro-Discharge Machining (EDM). In the present work, the EDDFG setup has been developed and tested for grinding difficult-to-machine materials and also attempted for fabrication of metal matrix composite of Aluminium (Al) reinforced by 10% Silicon Carbide (SiCp). To perform such hybrid machining process, the developed experimental setup was used for experimental study of EDDFG process on Al-SiCpMMCby considering the effect of gap current, pulse on time and wheel RPM on average surface roughness (Ra) and material removal rate (MRR). The metal bonded diamond abrasive grinding wheel is mainly responsible for higher value of MRR. It was also observed that MRR is higher at moderate value of wheel RPM and wheel rotation improves the flushing action. The average surface roughness (Ra) was observed better at low values of gap current, pulse on time and wheel RPM. The present developed EDDFG setup has proven to be successful for machining of difficult-to-machine materials. Texture of the machined surface has been studied using Scanning Electron Microscope (SEM). Keywords: Electro-Discharge Diamond Face Grinding (EDDFG),Al-SiCp MMC, MRR and Ra
1 Introduction The growth of superior ammunitions, fighting ships, aircraft and intercontinental ballistic missiles etc has resulted into the development of the tailored made advanced engineering materials, which are able to meet the stringent operational as well as environmental load requirements. Such advanced engineering materials are titanium alloys, metal matrix composites and superalloys etc. and are duly inherited with the characteristics of high strength at elevated temperature, resistance to chemical degradation, wear resistance and low thermal diffusivity etc. But at the same time, these materials do pose challenges to conventional as well as non-conventional machining processes and these materials are also referred as difficult-to-machine or advanced materials. The problem associated with conventional machining of advanced materials is the frequent failure of the cutting tool, whereas with nonconventional machining is lower production rate and in few cases not even viable. Koshy et al. (1996) have studied and suggested to overcome the difficulties of conventional as well as non -conventional machining processes, altogether a new trend in machining process known as hybrid machining processes (HMP), have been emerged and are in use at increasing rate. In HMPs, two or more machining processes are combined to achieve the aggregate
potential advantage of the constituent processes with impairing the inherent disadvantage of the constituent processes. In present case, HMP has been developed by combining the use of metal bonded abrasive grinding wheel with electrical discharge machining (EDM) and termed it as Electro-Discharge Diamond Grinding (EDDG). Grodzinskii (1979), Vitlin (1981) and Grodzinskii&Zubotava (1982) have suggested the concept of combination of EDM and diamond grinding, was made in late eighties (1980) in erstwhile USSR for machining of electrically conductive hard materials. In this process, the metal bonded diamond wheel removes the materials from work surface by simultaneous influence of diamond grains and continuous discrete electrical sparks, thereby causing the abrasion (microcutting) and electro-erosion action respectively as also shown in Figure 1.
Spark IEG
Figure 1 Schematic representation of use of diamond abrasives in rotating tool electrode in EDM
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Ramesh and Sagar (1999) have discussedfabrication of metal matrix composite automotive parts for the mixtures of four different compositions (15, 20, 25 and 30% by weight) of SiC which is prepared by the Powder Metallurgy technique, and fabricated by placing these powder mixtures in layers in a die. Choudhury et al. (1999) have studied the effect of current on MRR and grinding forces for different voltage, pulse on-time and duty factor during EDDG process on HSS. It has been observed that tangential grinding force decreases with increase in voltage and duty factor for a particular value of gap current. They have also reported the effect of process parameters on the MRR andtestedthe feasibility of EDDG process experimentally in cut-off grinding configurations. Mohan et al. (2002) studied the effect of SiC and rotation of electrode on electric discharge machining of Al-SiC composite. The MRR was more with positive polarity and increased with increase in current. MRR was found more with Brass electrode in comparison with Copper electrode. The increase of volume percentage of SiC resulted in less MRR. The increase of pulse duration resulted in less MRR and it was more with increase in RPM. Yadav et al. (2008) have observed for Electro-Discharge Diamond Grinding (EDDG) process, developed new experimental setup to increase the material removal rate of the hard materials and studied the influence of various factors on the performance characteristics, such as current, wheel speed, pulse-on time and duty factor on MRR.It was found that MRR is increases with increasing current, wheel speed, and pulse on time and decreases with the high surface finish mode of EDM on High Speed Steel (HSS) workpiece. Singh et al. (2010) have used Diamond abrasive in bronze bonding material for grinding wheel and WC-Co Composite workpiece for Electro-Discharge Diamond Face Grinding (EDDFG) and found Improvement in MRR by 86.49%, reduction in WWR by 21.70% but deterioration in ASR by 14.86% have been found at the optimum parameter setting compared to ElectroDischarge Face Grinding (EDFG). Abothula et al. (2010) have discussed the rotation of non-abrasive disc shape tool electrode about vertical axis and find improves material removal rate (MRR) and average surface roughness (ASR) because of effective flushing of working gap. The effect of input process parameters of EDFG processsuch as gap current, pulse on-time, pulse off-time and wheel speed on MRR and ASR during machining of High Carbon Steel and High Speed Steel workpieces, are investigated and also compared the results with those of stationary electrodes. Singh et al. (2011) have studied the process synergic interactive effect of abrasion action and electrodischarge action. A face grinding setup for Electro-
Discharge Diamond Grinding (EDDG) process is developed and the effect of wheel RPM, gap current, pulse on-time and duty factor on material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (Ra) are investigated while machining High Speed Steel (HSS) workpiece. Velmurugan et al. (2011) have experimentally investigated the machining characteristics of Al6061 based hybrid metal matrix composite processed by electro-discharge machining and observed effectson material removal rate (MRR), tool wear rate (TWR) and surface roughness with variation in current, pulse ontime, flushing pressure of dielectric fluid and voltage. Therefore no work have been reported on influence ofinput process parameters such as wheel speed, gap current and pulse on-timeon material removal rate (MRR) and average surface roughness (Ra) for the process of Electro-Discharge Diamond Face Grinding (EDDFG) mode on Al-SiCpmetal matrix composite. In this paper, The authors have made an attempt for fabrication of metal matrix composite of Aluminium (Al) reinforced by 10% silicon carbide (SiCp) particles with grain size 600 mesh number and also developed an experimental setup for grinding wheel rotation attached with EDM machine. Experiments were conducted to investigate the effect of gap current, pulse on time and wheel RPM on material removal rate (MRR)and average surface roughness (Ra).
2 Development of Experimental Setup The EDDFG attachment has been designed and fabricated with consideration of all fundamental mechanism of the EDDFG process and basic functional requirement of different parts with special consideration of weight and vibration. The designed attachment has been fitted on the ram of Smart ZNC Sinker EDM machine (ZNC 320 Ecoline) by replacing actual tool holder of die-sinking EDM and also tested successfully. The preliminary experiments were conducted to find the range of input process parameters applicable for successful machining characteristics of EDDG process. The EDDFG setup consist of perpendicularly mounted (buttJoint) at one side of Al-alloy base plate of thickness 12 mm, electrical permanent magnet direct current (PMDC) motor of 0.25 hpRotomag (India) make with 1500 rpm, electrically conductive tool electrode, rotating spindle cum tool electrode holder mechanism, mounted on the ram of EDM machine. The housing assembly of rotating spindle has one side pulleyand another side for holding of tool electrode. The spindle housing is mounted on lower side of horizontal plate and the horizontal plate has a hole through which assemblyof rotating spindle passes. The driven pulley is mounted on the top of the spindle.
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT Guwahati, Assam, India
The power transmitted from electrical motor to spind spindle through driver pulley mounted on motor shaft and driven pulley by ‘V’ belt of trapezoidal section. Table 1 Specifications of different parts S. No. 1. 2. 3. 4.
Name of parts
Specification
PMDC Motor Variac V-belt Diameter of driving & driven pulleys Bearing housing
0.25hp,, 1500 RPM 0.5 hp DC drive M 6x500 x500 60 mm
5. Bearing
6.
Shaft
7.
Thickness of Alalloy base plate Electrode holder
8. 9.
Outer diameter 50 mm and inner diameter 45 mm, mild steel Antifriction ball bearing 13 mm diameter, mild steel 12 mm
Figure 3 EDDFG attachment fitted on EDM Machine achine
3 Fabrication of MMC Aluminium ingots are melted in a graphite crucible of a tilting oil-fired fired furnace at a temperature of about 800oC. Diesel was used as the fuel in oil-fired oil furnace.
8.5 mm diameter
The rotating spindle is supported on four antifriction ball bearings in housing, so that axial thrust load is taken care of and to avoid the axial movement ofrotating spindle.The The selection of these four antifriction ball bearings is done based on the expected load, motor power, motor RPM and endurance run. DC Motor
Spindle Driven pulley
Driving pulley Al base plate
Bearing housing
V V- belt
Grinding wheel
Figure 2 Schematic diagram of EDDFG attachment Dimensional specification of ‘V’ belt is M6 M6x500. The tension is provided in V-belt to avoid slippage. The motor is mounted on vertical Al-alloy alloy plate fitted on horizontal Al-alloy base plate. Portable digital tachometer Electronic Automation Private Ltd (EAPL), India make model: DT 200 1B (01rpm-99999rpm) 99999rpm) is used to calibrate the rotation of the tool electrode RPM on speed controller (variac).
Figure 4 Melting of Aluminium luminium alloy The melting of the Al6061 6061 alloy at the th preset temperature and is being kept for more than 2 hrs 45 min. A controlled atmosphere has been maintained inside the furnace to prevent oxidation of the molten metal by using cap of oil-fired fired furnace. At the same time the reinforcing SiC particulate (600 (6 mesh number) 10% by weight fraction was pre-heated pre for approximately 45 minute to remove surface impurities and assist in the adsorption of gases. The preheated SiC particles continuously entered in to the molten metal via a long handle spoon with small amount at a time along with continuously stirring manually with a mild steel rod about 20 to 30 min. The flame intensity of oil-fired oil furnace was regulated accordingly to the requirement via blower. The composite mixture has been collected from the crucible le to a ladle and then is poured in the sand mould. It passes through the runner system and enters into the cavity and settles down. The composite
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DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF ELECTRO-DISCHARGE DIAMOND FACE GRINDING
mixture was allowed to solidify for approximately 1hr and finally the mould is broken to get the desired casting component.
Figure 5 Manual stirring view of oil-fired furnace at the time of fabrication of MMC Al/SiCp The casted metal matrix composite was machined to get the cylindrical shape. The pictorial views manufactured metal matrix composite are shown in figure given below.
IEG depends upon breakdown strength of dielectric fluid. Both wheel electrode and workpiece are submerged in dielectric fluid. The variac was connected in-line with PMDC motor used to control wheel RPM. Workpeicespecimens wereheld in vice and leveled horizontal with help of spirit level. After an exhaustive pilot experimentationinput process parameter ranges are determined. The input process parameters are gap current, pulse on-time, duty factor, wheel RPM. On the basis of pilot experimentation it was decided to conduct the experiments in reverse polarity withconstant pulse off time of 40 µs. The variation in Ra and MRR were observed by varyingone input process parameter at a time, keeping other parameters constant.The Ra value was measured using a Surface Roughness Tester with accuracy of 0.01µm (SURTRONIC-25 model, Taylor Hobson Ltd.) and for evaluation of MRR, the loss in weight of the machined specimen was measured on a weighing digital microbalance (accuracy 10 µg, CAS India Private Limited)
5 Results and Discussion Influences of wheel rotation, gap current and pulse on-time on the material removal rate (MRR) and average surface roughness (Ra) are investigated.
5.1 Effect of wheel RPM
(a) (b) Figure 6(a) MMC workpieces of disc shape (b) EDDFG wheel
The effect of wheel speed on Ra is shown in fig. 7, for different values of gap current keepingconstant pulse on-time at 40 µs and pulse off-time at 40µs. Ra value slightly increases on increasing wheel RPM due to corresponding increase in flushing action and diamond abrasive grinding.
Table 2 Specifications of grinding wheel Diamond 75 % 80/100 M (Medium) Bronze 10 mm 30 mm 40 mm 8.3 mm
4 Experimentation EDDFG process is performed on the workpiece specimens in reverse polarity on Smart ZNC EDM machine. During EDDFG process, rotating wheel electrode moves downwardsunder servo control mechanism and maintains inter electrode gap (IEG).
4A
7.26
6A 6.55 Surface Roughness (Ra)
Abrasive Concentration Grit number Grade Bonding Material Depth of abrasive Wheel diameter Holding length Holding diameter
Effect of rotating grinding wheel on Average Roughness for different current at on time 40 µs % 8 7.97
8A
5.84
5.13
4.42
3.71
3 500
600
700
800
900 Wheel RPM
1000
1100
1200
1300
Figure 7 Effect of wheel RPM on Raat different current values (pulse on-time 40µs & off-time 40µs) The effect of wheel RPM on MRR is shown in fig. 8, for different values of gap current keepingconstant pulse on-time at 140 µs and pulse off-time at 40µs. MRR increases on increasing wheel RPM because of corresponding increase in flushing action and abrasion action by diamond abrasives.
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT Guwahati, Assam, India 0.04 0.0386
5.3 Effect of Pulse on-time
4A 0.0338
6A 8A
MRR (gm/min)
0.029
The effect of pulse on-time on Ra is shown in fig. 11, for different values of pulse on-timekeeping constant gap current at 4A and pulse off-time at 40 µs.Ra value increases on increasing pulse on-time because of corresponding increase in duration of heat addition resultingincreased spark energy. Increased spark energy causes increase recast layers at machined surface and gives poor surface finish.
0.0242
0.0194
0.0146
0.0098
0.005 500
600
700
800
900 Wheel RPM
1000
1100
1200
1300 Effect of duty factor on Average Roughness for different rpm at 4 A 6
Figure 8 Effect of wheel RPM on MRR at different current values (Pulse on-time 140µs & off-time 40µs)
The effect of gap current on Ra and MRR are shown in fig. 9 and fig. 10, for different values of pulse on-timekeepingconstant wheel RPMand pulse off-time at 40µs.
Surface roughness (Ra)
5.2 Effect of Gap current
600 RPM 5.55
4.63
4.17
3.71
8 7.97
3.25
40 µs 7.26
Surface Roughness (Ra)
5.84
5.13
4.42
3.71
3 3.5
4
4.5
40
5
5.5 6 6.5 Gap current (A)
7
7.5
8
8.5
140
600 RPM
0.0378 0.036
900 RPM 1200 RPM
0.0343 0.0325
0.0383
40 µs
MRR (gm/min)
0.0308
90 µs 140µs
0.0272 MRR (gm/min)
120
0.04 0.0395
0.04
0.0309
80 100 Pulse on-time (µs)
More heat addition in each spark makes ease of material removal by electro erosion and abrasion action result corresponding increase in MRR as shown in fig. 12. MRR increases with increasing pulse on-time at different wheel RPM keeping constant gap current at 8A and pulse off-time at 40µs.
Figure 9 Effect of gap current on Ra at different pulse on-time (wheel RPM 600 and off-time 40µs)
0.0346
60
Figure 11 Effect of pulse on-time on Ra at different wheel RPM (gap current 4 A and off-time 40µs)
90 µs 140µs
6.55
900 RPM 1200 RPM
5.09
0.029 0.0273 0.0255 0.0238 0.022
0.0235
0.0203 0.0198
0.0185 0.0168
0.0161
0.015 0.0124 0.0087 0.005 3.5
4
4.5
5
5.5 6 6.5 Gap current (A)
7
7.5
8
8.5
Figure 10 Effect of gap current on MRR at different pulse on-time (wheel RPM 1200 and off-time 40µs) On increasing gap current results increase in spark energy which increases melting and evaporation of work material causes larger crater depth subsequently results an increase in Ra and MRR. Larger crater depth is responsible for increase in Ra and increase in spark energy results rise of MRR.
40
60
80 100 Pulse on-time (µs)
120
140
Figure12 Effect of pulse on-time on MRR at different wheel RPM (gap current 8A & off-time 40µs)
6 Analyses of SEM Micrographs Irregular surface texture is rectified upto some extent as shown in figure 13 (b)but presence of recast layers on machined surface as a result of higher pulse on-time andthe scratches due to diamond abrasives are notappeared on machined surface as a result of larger spark size.
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Steel, Machining Science and Technology, Vol. 3(1), pp.91-105. Grodzinskii E. Ya. (1979), Grinding with Electrical Activation of the Wheel Surface, Machines Tooling, Vol. 50, pp.10-13.
Figure 13 (a) before machining (b) after machining Diamond abrasives assisted quick removal of SiC particles results minimized cavity due to electro erosion for removal SiCp particle.
7 Conclusions 1.
2.
3.
4.
5.
6.
Metal matrix composite of Aluminium Silicon Carbide (Al-SiCp) improves the material properties like strength to weight ratio, heat resistance, wear resistance, hardness etc. and can be easily machined on EDM machine with better productivity. Machining of Al-SiCpmetal matrix composite with the combination of Electro-Discharge Grinding and Diamond Grinding improves the grinding performance more than the sum of individual machining performance. Electro-Discharge Diamond Face Grinding process experimented on Al-SiCpcomposite, indicates MRR increases with increase in wheel speed for all values of current within the specified range. The average surface roughness (Ra) increase with increase of wheel speed for all values of gap current. The effect of wheel speed on MRR is more significant than that for Ra value. MRR increases on increasing wheel RPM because of corresponding increase in flushing action and diamond abrasive grinding. Presence of recast layers on machined surface as a result of higher pulse on-time and the scratches due to the diamond abrasives are not appeared as result of larger spark size. Diamond abrasives assisted quick removal of SiC particles results minimized cavity due to electro erosion for removal of SiC particles.
References Abothula B. C., Yadava V. and Singh G. K. (2010), Development and Experimental Study of ElectroDischarge Face Grinding, Materials and Manufacturing Processes, Vol. 25, pp.1-6. Choudhary S. K., Jain V. K. and Gupta M. (1999), Electric-Discharge of Diamond Grinding of High Speed
GrodzinskiiEYa. andZubotava L. S. (1982), Electrochemical and electrical-discharge abrasive machining, Soy. Engng Res., Vol. 2, (3), pp.90. Koshy P., Jain V. K. and Lal. G. K. (1996), Mechanism of Material Removal in Electrical Discharge Diamond Grinding, International Journal of Machine Tools and Manufacture, Vol. 36(10), pp.1173-1185. Mohan B., Rajadurai A. and Satyaanarayana K. G. (2002), Effect of SiC and rotation of electrode on electric discharge machining of Al-SiC composite, Journal of Material Processing Technology Vol. 124, pp.297-304. Ramesh K. C. and Sagar R. (1999), Fabrication of Metal Matrix Composite Automotive Parts, International Journal of Advanced Manufacturing Technology, Vol. 15, pp.114–118. Singh G. K., Yadava Vinod and Kumar R. (2010), Diamond face grinding of WC-Co composite with spark assistance: Experimental study and parameter optimization, International Journal of Precision Engineering and Manufacturing, Vol. 11 (4), pp. 509518. Singh G. K., Yadava Vinod and Kumar R. (2011), Experimental study and parameter optimization of electro-discharge diamond face grinding, International Journal of Abrasive Technology, Vol. 4, No. 1. Velmurugan C., Subramanian R., Thirugnanam S. and Ananadavel B. (2011), Experimental Investigation on Machining Characteristics of Al6061 Hybrid Metal Matrix Composites Processed by Electrical Discharge Machining, International Journal of Engineering Science and Technology, Vol. 3 (8), pp.87-101. Vitlin V. B. (1981), Model of the Electro-ContactAbrasive Cutting Process, Soviet Engineering Research, Vol. 1, pp.88-91. YadavSanjeev Kumar Singh, Yadava Vinod&Narayana V. Lakshmi (2008), Experimental Study and Parameter Design of Electro-Discharge Diamond Grinding, International Journal of Advanced Manufacturing Technology, Vol. 36, pp.34–42.
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