The base plate is chosen in such a way that the plate is able to withstand the heat. Aluminium 6061 alloy is used as base plate for the fabrication. This base plate has a thickness of 16 mm. The base plate material contains 97.9% of Aluminium (Al), 1% of Magnesium (Mg), 0.60% of Silicon (Si), 0.28% of Copper (Cu) and 0.20% of Chromium (Cr). It has a density of 2.7 g/cm and a melting point of 588°C. The aluminium wire Al5356 used for welding has a thickness of 1.2mm. The alloy consists of 93-95% of Aluminium(Al), 4-5% of Magnesium(Mg), 0.10% of Copper(Cu), 0.05-0.20% of Manganese(Mn), 0.10% of Zinc(Zn), 0.05-0.20% of Chromium(Cr), 0.06-0.20% of Titanium(Ti), 0.25% of Silicon(Si) and 0.40% of Iron(Fe).
The current, voltage and holding time can be set. Holding time is the cooling time between deposition of consecutive layers. There is a difference in unit input between the first two layers and the rest of the layers in order to set a stable and adequate base layer. The first two layers have high voltage, current and wire feed speed. The feeding torch is set. When the input for movement is provided, the torch starts to run through the way while the molten metal is getting deposited on the base plate and stops at the end till the holding time is over. During the holding time, the temperature of the layer comes down and the layer is cleaned after formation. After the holding time it again starts the cycle from where it stops and this processes until requirement. The dimensions are measured in between the formation of each layer.
A. SAMPLE FABRICATED USING PULSE WELDING
Pulse or Pulse MIG welding is a method of WAAM in which a solid wire is heated and fed onto the base plate from a welding torch, to form a wall by depositing layer upon layer by pulsing the current. A 5-minute cooldown time should be given after deposition of each and every layer to avoid overheating and disintegration of the component. 12 layers are deposited one upon another to obtain a height of 30 mm and the length of the wall remains the same which is 140 mm. The thickness of the wall changes in each and every layer and height of the component differ in different parts. Voltage = 20 V, Current = 126A, Wire feed speed =8m/min. The change in thickness and height of the consecutive layers is shown in the figures. (Fig. 4 - 14).
After deposition of every layer, the wall thickness, height of the welded layer at both the ends and middle are observed and noted as below (TABLE 1)
Graphs are plotted between layers and their respective heights (Fig. 11) and between layers and respective widths (Fig. 12) in pulse welding.
TABLE 1
THICKNESS AND HEIGHT LAYER BY LAYER - PULSE
Layer
|
Wall Thickness
(mm)
|
Height at Point A (mm)
|
Height in The Middle (mm)
|
Height at The Other End (mm)
|
Layer 1
|
8.16
|
5.08
|
4.50
|
4.37
|
Layer 2
|
10.39
|
7.75
|
6.83
|
6.59
|
Layer 3
|
12.36
|
9.92
|
9.32
|
8.83
|
Layer 4
|
12.75
|
12.07
|
11.26
|
10.54
|
Layer 5
|
13.66
|
15.25
|
12.76
|
12.63
|
Layer 6
|
14.14
|
18.30
|
15.81
|
14.78
|
Layer 7
|
14.34
|
21.36
|
18.28
|
17.18
|
Layer 8
|
14.45
|
23.58
|
19.92
|
19.16
|
Layer 9
|
14.81
|
26.41
|
22.78
|
21.13
|
Layer 10
|
14.53
|
28.88
|
24.57
|
22.90
|
Layer 11
|
14.43
|
31.24
|
27.00
|
25.50
|
Layer 12
|
14.98
|
33.30
|
29.52
|
25.80
|
TABLE 2
CURRENT AND VOLTAGE FOR EACH LAYER - PULSE
Layer
|
Current (A)
|
Voltage (V)
|
Layer 1
|
128
|
19.7
|
Layer 2
|
128
|
19.7
|
Layer 3
|
127
|
20.0
|
Layer 4
|
128
|
19.7
|
Layer 5
|
130
|
19.5
|
Layer 6
|
125
|
20.3
|
Layer 7
|
125
|
20.4
|
Layer 8
|
127
|
20.1
|
Layer 9
|
126
|
20.1
|
Layer 10
|
130
|
19.5
|
Layer 11
|
126
|
20.2
|
Layer 12
|
127
|
19.9
|
Graphs are plotted between layers and their respective input current in ampere in pulse welding (Fig. 13) and between layers and their respective input voltage in volt in pulse welding (Fig. 14).
B. SAMPLE FABRICATED USING DOUBLE PULSE WELDING
Double pulse welding is a method of WAAM in which a solid wire heated and fed onto the base plate from a welding torch, to form a wall by depositing layer upon layer, by pulsing the current in two separate levels which are controlled independently. The deposition of layers is done from alternative ends for every layer. A 5-minute cooldown time should be given after deposition of each and every layer to avoid overheating and disintegration of the component. 14 layers are deposited one upon another to obtain a height of 30 mm and the length of the wall remains the same which is 140 mm. The thickness of the wall changes in each and every layer and height of the component differ in different parts. The increase in thickness and height can be observed in the (Fig. 15- 21). Voltage = 19.2 V, Current = 112 A, Wire Feed Speed = 8m /min
TABLE 3
THICKNESS AND HEIGHT LAYER BY LAYER FOR DOUBLE PULSE
Layer
|
Wall Thickness (mm)
|
Height at
The One End (mm)
|
Height in
The Middle (mm)
|
Height at
The Other End (mm)
|
Layer 1
|
8.05
|
5.30
|
4.42
|
4.07
|
Layer 2
|
9.42
|
6.50
|
6.54
|
7.33
|
Layer 3
|
11.75
|
9.11
|
8.35
|
8.79
|
Layer 4
|
12.02
|
10.70
|
10.20
|
12.12
|
Layer 5
|
12.71
|
13.10
|
12.27
|
13.13
|
Layer 6
|
13.57
|
15.53
|
14.56
|
16.07
|
Layer 7
|
13.32
|
16.55
|
16.57
|
17.57
|
Layer 8
|
14.19
|
18.18
|
19.21
|
20.06
|
Layer 9
|
14.63
|
20.45
|
21.37
|
21.51
|
Layer 10
|
15.31
|
22.76
|
23.02
|
23.16
|
Layer 11
|
15.36
|
24.87
|
23.68
|
26.05
|
Layer 12
|
15.81
|
27.05
|
27.57
|
27.59
|
Layer 13
|
15.28
|
30.75
|
30.20
|
30.01
|
Layer 14
|
14.42
|
32.52
|
32.09
|
32.13
|
After deposition of every layer, the wall thickness, height of the welded layer at both the ends and middle are observed and noted as below (TABLE 3) Graphs are plotted between layers and their respective heights (Fig. 22) and between layers and respective widths (Fig. 23) in pulse welding. Increase and decrease in width is observed because of the bulge on the top most layer.
TABLE 4
CURRENT AND VOLTAGE FOR EACH LAYER - DOUBLE PULSE
Layer
|
Current (A)
|
Voltage (V)
|
Layer 1
|
119
|
19.3
|
Layer 2
|
121
|
18.8
|
Layer 3
|
118
|
19.5
|
Layer 4
|
121
|
19.0
|
Layer 5
|
119
|
19.9
|
Layer 6
|
119
|
19.7
|
Layer 7
|
117
|
19.5
|
Layer 8
|
117
|
19.8
|
Layer 9
|
116
|
19.3
|
Layer 10
|
114
|
20.0
|
Layer 11
|
115
|
19.2
|
Layer 12
|
113
|
19.7
|
Layer 13
|
117
|
19.6
|
Layer 14
|
115
|
20.3
|
Fluctuation in current is more in double pulse when compared pulse as the current is pulsed twice.