Roughness of Hastelloy C22 Super Alloy in electrical discharge machining. Engin N a s S i t k i AKINCIOGLU2, Hasan GOKKAYA3, Gulsah AKINCIOGLU2.
1st International Conference o f Advanced Materials and Manufacturing Technologies (ICAMT’17) 25-27 October 2017, Safranbolu, Karabuk, Turkey
The Effect of Deep Cryogenic treatment on the Roughness of Hastelloy C22 Super Alloy in electrical discharge machining Engin N a s S i t k i AKINCIOGLU2, Hasan GOKKAYA3, Gulsah AKINCIOGLU2 University o f Duzce, Cumayeri Vocational School, Endustriel Molding, 81700, Duzce - TURKEY University o f Duzce, Gumu§ova Vocational School Machine design, 81850, Duzce - TURKEY enginnas@duzce. edu. tr
Abstract - In this study, Deep cryogenically treated (-145 °C) (HO) and untreated Hastelloy C22 Super Alloy (HI) were etched with a copper electrode on an electro erosion discharge. The parameters used in the experimental study were determined as three different durations (10, 20 and 30 ps), waiting time (5, 10 and 15 ps) and discharge currents (5, 10 and 15 amperes). As a result of the work done, the lowest surface roughness value was measured as 2.20 pm in 20 ps sweep time, 10 ps waiting time and 10 amperes current.
formed by electrical sparks are observed. It is important to optimize the dimensions of these craters in work pieces where surface sensitivity is important. In order to optimize the surface roughness in EDM process, it is necessary to optimize the pulse duration, waiting time and discharge current values. Higher throughput is achieved by using higher discharge current, lower discharge frequency, higher capacitance and minimum discharge voltage. However, the roughness of the surface is getting worse in fast processing. To achieve better surface roughness in the workpiece, low speed machining is required [5], Because there is no electrode contact with the workpiece, there are no disadvantages such as vibration and warming that occur in traditional methods [6], The chip removal process takes place when the workpiece is melted by electric energy. Therefore, it melts in the electrode together with the workpiece. [7], During processing, the dielectric fluid velocity is low, short circuit between the workpiece and the electrode, and arc-type pulses occur. This decreases the processing speed and increases the surface roughness [8], The improvement of surface roughness depends on the dielectric fluid application rate and the time between the two discharges [9],
Key Words - Electro-Erosion Processing, Surface Roughness, Machinability, Hastelloy C22
I.
INTRODUCTION
Nickel-based super alloys such as Hastelloy C-22 are used in chemically exposed environments such as strong oxidizers such as chlorine, acetic anhydride, sea water and saline solutions. Due to the high heat generated at the cutting edge of the tool during machining of these nickel alloyed materials with low thermal conductivity, their machinability properties are very low [1, 2], High temperatures during machining of super alloys destroy cutting tools, disrupt product quality and increase the amount of consumed cutting tool. The use of non traditional methods for processing such difficult-to-handle materials can increase product quality and reduce production costs.
The effects of cryogenic treatment on machining performance are examined extensively in traditional manufacturing methods such as turning, milling and drilling [1, 2], However, the effects of cryogenic treatment on non-traditional manufacturing methods have not been studied as widely as they are in conventional manufacturing methods. Positive developments in conventional manufacturing methods through cryogenic treatment -in particular, increased curing and cutting abrasion resistance of cutting tools - have been associated. In addition to properties such as hardness and abrasion resistance, the electrical and thermal properties of the materials can also be improved as a result of the cryogenic treatment. Reported in a study that increased electrode
Electrical Discharge Machining (EDM) is the thermal erosion of the workpiece with spark energy generated between two conducting materials. The ionization of the dielectric medium plays an important role in this process [3], The use of this machining method in mold, tooling, aerospace and automotive industry is expanding rapidly, especially since it can easily process rigid materials and parts with complex geometric shapes that are difficult or impossible to process with conventional manufacturing methods [4], When the surface of the workpiece is examined at the end of the EDM process, crater layers
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1st International Conference o f Advanced Materials and Manufacturing Technologies (ICAMT’17) 25-27 October 2017, Safranbolu, Karabuk, Turkey Fig. 1 Hastelloy C22 material 80 mm in diameter used in the experimental study
lifetime as a result of the cryogenic treatment [10], On the other hand, the application of cryogenic treatment to workpieces can give important results to the industry depending on performance and efficiency for serial production [10],
Experimental samples were subjected to deep cryogenic treatment to investigate the effect of the deep cryogenic treatment on the processing of Hastelloy C22 alloy with EDM. The samples were allowed to stand for 24 hours after being brought to -145 ° C for 6 horns in a nitrogen atmosphere in the cryogenic treatment unit. It was brought back slowly to room temperature for 6 hours. This process has been tried to prevent the formation of micro cracks in the material. Electrolytic copper 10 mm in diameter (Fig. 2) with a density of 8.9 gr / cm3 was used as the electrode. In the experimental work. King brand ZNC - K-3200 plunge erosion counter was used. The electro erosion discharge and the test setup are shown in Figure 2.
In this study, Hastelloy C22 superalloy with deep cryogenic treatment and untreated copper electrode was used in electro erosion discharge with different processing parameters (three different pulse durations (10, 20 and 30 ps), waiting times (5, 10 and 15 ps) and discharge current (5, 10 and 15 amperes)), parameters affecting surface rouglmess were investigated. The effect of the deep cryogenic treatment on the surface rouglmess was investigated when Hastelloy C22 superalloy was treated with EDM. II. METHOD In the experimental study Hastelloy C22 superalloy material with a diameter of 80 lmn (Fig. 1) was used. Hastelloy C22 superalloy lias superior tingling and corrosion resistance in acidic and salt water environments [2], The chemical composition of Hastelloy C22 superalloy material is shown in Table 1. TABLE I CHEMICAL COMPOSITION OF HASTELLOY C22 USED IN EXPERIMENTAL WORK Ni
Cr
Mo
Fe
W
Other
58.2
21.28
12.94
4
2.87
0.71
Fig. 2 Electro erosion discharge and test setup
The parameters used in the processing of the Hastelloy C22 material were three periods (10, 20 and 30 ps), duration of Toff (5, 10 and 15 ps) and a discharge current (5, 10 and 15 ps) and 27 experiments were carried out. The obtained results were plotted and the effects of the used parameters on surface rouglmess were investigated. III. RESULTS The average surface rouglmess values obtained after the experimental work are given in Table 2.
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1st International Conference o f Advanced Materials and Manufacturing Technologies (ICAMT’17) 25-27 October 2017, Safranbolu, Karabuk, Turkey TABLE II SURFACE ROUGHNESS MEASUREMENTS ACCORDING TO THE PARAMETERS USED IN THE EXPERIMENTS.
Exp. No
Vault duration Ton 0b )
Waiting time Toff (ps)
Current Amper (A)
Untreated Hastelloy C22 (HO) Avg. surface roughness Ra (pm)
Deep Cryogenically treated Hastelloy (HI) Avg. surface roughness Ra (pm)
1
10
5
5
2.93
5.29
2
10
5
10
3.13
4.05
3
10
5
15
3.40
4.27
4
10
10
5
2.93
3.63
5
10
10
10
3.47
3.49
6
10
10
15
4.07
3.66
7
10
15
5
3.27
2.80
8
10
15
10
3.07
2.48
9
10
15
15
3.20
2.58
10
20
5
5
2.93
2.47
11
20
5
10
3.60
2.56
12
20
5
15
3.63
2.63
13
20
10
5
2.86
3.21
14
20
10
10
3.83
2.20
15
20
10
15
3.92
3.19
16
20
15
5
3.45
2.65
17
20
15
10
3.49
2.82
18
20
15
15
3.95
3.78
19
30
5
5
2.97
3.09
20
30
5
10
3.44
5.68
21
30
5
15
3.59
7.01
22
30
10
5
3.47
3.95
23
30
10
10
3.70
5.32
24
30
10
15
3.84
5.52
25
30
15
5
3.21
4.96
26
30
15
10
3.57
6.18
27
30
15
15
3.60
7.63
The mean surface rouglmess values given in Table 2 were plotted according to the values of the waiting time (Toff), the duration (Ton) and the amperage values. It was observed that surface rouglmess values generally increased with increasing current in experiments with 10, 20 and 30 ps pulses and 5, 10 and 15 ps waiting times. The highest surface rouglmess value was achieved at 7.63 pm, at a 15 ps waiting time at 15 Amperes current and 30 ps pulse duration. The lowest surface rouglmess value was 2.20 pm and this value was realized at 20 ps, 10 ps pulse durations and 10 amperes current. In general, it has been detennined that the surface rouglmess values increase with the increase
of the current value, and the surface rouglmess value decreases with the current decrease [8], When the results were evaluated according to the stand-by times (5, 10 and 15 ps) (Fig. 3), the highest surface rouglmess values at all the waiting times were found to be 7.01, 5.52 and 7.63 pm, respectively. The lowest surface rouglmess value according to the waiting times is 2.63 pm at 20 ps waiting time in 5 ps waiting time, 2.20 pm at 20 ps in 10 ps waiting time at 10 ps waiting time, 2.48 pm at 10 ps in 10 ps waiting time at 15 ps waiting time.
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1st International Conference o f Advanced Materials and Manufacturing Technologies (ICAMT’17) 25-27 October 2017, Safranbolu, Karabuk, Turkey W a itin g tim e .
Tbff: 5|is
Pulse duration (us)
W a itin g tim e .
Toff. 10ns
Pulse duration (p s)
W a itin g tim e .
Toft’ 15|is
pulse duration (ps)
Fig. 3 Average surface rouglmess value change graph based on waiting time, pulse duration and ampere. It is observed that as the discharge current value increases, the average surface rouglmess values increase. It is emphasized that as the discharge current value increases, the increase in surface rouglmess is related to the growth of the crater size [4],
waiting time for the 30 ps pulses. In the experiment with 15 amperes current, the lowest surface rouglmess value was found to be 2.58 pm in 15 ps waiting time in 10 ps pulses and the maximum surface rouglmess value was found to be 7.63 pm in 15 ps waiting time in 30 ps pulses. In general, when the literature studies are examined, when the duration of the fault is increased (Figure 3), a large part of the surface is affected by the electrical erosion and therefore the changes in the surface are important [11, 12],
When the surface rouglmess results are evaluated according to the pulse durations (Figure 3); the lowest surface rouglmess value was achieved in HI material and 20 tonnes of pulp. The highest surface rouglmess values were measured in cryogenic HI material when the duration of the vortex was 30 tons. The lowest surface rouglmess value in the 10 ps pulse duration was obtained as 2.48 pm in 10 amps current at 15 ps waiting time respectively. The surface rouglmess values were measured as 2.20 pm at 10 amps current in the 10 ps standby period and 3.09 pm at the 5 amps current in the 30 ps pulses during 20 ps pulses. The lowest surface rouglmess values were measured as 3.78 pm at a current of 15 ps at a current of 15 ps in a 20 ps pulse. The highest surface roughness value was measured at 15 ps in the 30 ps pulse duration and 7.63 pm at the 15 amperes current. The increase in the duration of the pulse causes the spark to emit more energy into the area where it touches the workpiece surface and increase the diameter and depth of the crater that is formed [5],
Compared to untreated Hastelloy C22 and deep cryogenic treated materials obtained in the treatment with the EDM surface rouglmess values of the surface rouglmess in the low current value it was observed in both materials generally have improved. The lowest surface rouglmess value is measured in the cryogenic treated material, which is why the tempering process applied after the cryogenic treatment causes some loss of hardness, ft is also known that the cryogenic treatment increases the secondary carbide precipitation along with the decrease in hardness, which in turn decreases the stresses. Reduced stresses and hardness in the material; it also reduces the risk of brittleness and cracking on the surface. As a result, it is known that the surface of the material improves the rouglmess value [13], The first reason for obtaining the highest surface rouglmess value in cryogenic treated material is that the surface hardness is slightly reduced and the surface is further damaged due to increased current, ft is also considered that the surface rouglmess value is increased because of the increase of the current due to the chemical structure of the C22 super alloy and the high temperature chip removal during machining affects negatively.
According to the graph in Fig. 3, the minimum surface rouglmess value was measured as 2.47 pm in the 5 ps waiting time for the 20 ps pulse duration in the experiment with the pulse duration and the waiting times in the 5 amp current. The highest surface rouglmess value was obtained as 5.29 pm at 5 ps waiting times for 10 ps pulses. In the experiment with 10 amperes current, the lowest surface rouglmess value was found to be 2.20 pm in the 10 ps waiting time for 20 ps pulses and the highest surface rouglmess value was found to be 6.18 pm in the 15 ps
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1st International Conference o f Advanced Materials and Manufacturing Technologies (ICAMT’17) 25-27 October 2017, Safranbolu, Karabuk, Turkey IV. CONCLUSION AND DISCUSSION [9] Cogun, C., Keeping electric discharge machining under control. Mach. Des., 1990. 62(8): p. 105-108.
As a result of the work done;
[10] Sundaram, M.M., Yildiz Y., and Rajurkar K.P., Experimental
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Study o f the Effect o f Cryogenic Treatment on the Performance o f Electro Discharge Machining. 2009(43628): p. 215-222.
It has been observed that surface rouglmess values generally increase with increasing current in the experiments. Surface rouglmess values were also found to increase with the increase of the duration of the pulsation. At 15 ps Toff and 15 Amps current, the surface rouglmess values increased with the increase of the pulse duration. The highest surface rouglmess value was found to be 7.63 pm at 15 ps waiting time, 15 amperes current and 30 ps pulse duration. The lowest surface rouglmess value of 2.20 pm was obtained at 20, 10 ps pulse durations and 10 amperes currents. During the test it was determined that when the pressurized water was not held between the material and the electrode, the abraded material and electrode parts caused a short circuit in the worktop and caused the head to move upwards. The deep cryogenic treatment ensures that the surface rouglmess of the Hastelloy C22 material is healed at low flow rates.
[11] Kahng, C. and Rajurkar K.. Surface Characteristics BehaviorDue To Rough And Fine Cutting By EDM. in Unknown conference. 1977. Tech Rundsch. [12] Gurhan, H., et ah, Effect O f Cryogenic Processes On Hie Mechanical Properties O f SAE 4140 Steel. Journal of SelcukTechnic. 2014.13(2): p. 25-37. [13] Demir E, Tokta§ L, AISI D2 (feligine Uygulanan Farkh
Bekletrne Siirelerindeki Derin Kriyojenik ifcrnin Yiizey Puruzlulugune Etkisinin Incelenmesi, in ISITES2014. 2014: Karabuk - TURKEY, p. 2038-2042.
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