The portable pneumatic system was installed to power the aluminum friction stir welding tool. The tool was installed in the rotary pilot. The Schneider Super Master 400-10-60 W compressor was used to develop and control the rotation speed and generate friction heat for joining the polymer plates. This experiment made it possible to use à speed margin of between 800 and 1400 rpm thanks to the specifications of the compressor used and a welding speed (advance) between 25 and 30mm/min by the machine table in the case of linear welding and a holding time margin of 15 and 35 sec for the case of spot welding. The FSW tool (in AA7075 aluminium) has a 14 mm diameter shoulder, a 3 mm diameter pin and a 3.75 mm length, while the opposite end of the tool has an 8 mm diameter neck which can be firmly fixed in the chuck (as shown in Figure 1). Total tool length is 65mm.
A holder for the pneumatic rotary actuator was used in this process. Important operations such as the rotation speed of the tool are selected using a stroboscope, while the crossing speed and penetration duration are set on the machine in the case of linear and spot welding, respectively.
resulting assembly after welding of the two polymers HDPE and PP by the friction stir welding process in linear mode and point mode.
Friction stir welding (FSW) and spot welding (FSSW) were studied to improve the welding temperature of copolymer (HDPE-PP). Weld zone temperatures were measured via an infrared thermometer for real-time monitoring. The optional maximum temperatures of the copolymer welding zone for each experiment for FSW and FSSW are shown in Table 4.
Table .1. Measured temperature for Bi-polymer welding zone during FSW and FSSW prices
|
|
FSW
|
|
|
FSSW
|
|
#
|
Rotational speed (rpm)
|
Traversig velocity (mm/mi)
|
Temperature (°C)
|
Rotational speed (rpm)
|
Dwell time (sec)
|
Tempe rature (°C)
|
01
|
800
|
15
|
99
|
800
|
30
|
83
|
02
|
800
|
25
|
103
|
800
|
35
|
84
|
03
|
800
|
30
|
106
|
800
|
40
|
92
|
04
|
1000
|
15
|
102
|
1000
|
30
|
94
|
05
|
1000
|
25
|
107
|
1000
|
35
|
105
|
06
|
1000
|
30
|
110
|
1000
|
40
|
106
|
07
|
1250
|
15
|
105
|
1250
|
30
|
100
|
08
|
1250
|
25
|
109
|
1250
|
35
|
104
|
09
|
1250
|
30
|
111
|
1250
|
40
|
108
|
2.1. Response Surface Methodology (Rsm)
Response surface methodology (RSM) [9-10] is a simple and effective method in industrial processes, because it allows finding the optimal solution. This method uses statistical techniques and mathematics to design a solution that optimizes the outcome based on the factors that make up the phenomenon.
The expected response is Y, a is a constant, and ai, aii, and Iij are the linear, quadratic, and intercept coefficients. Indeed, the Iij is the interaction between the factors and the term ei is the difference between the experimental value and that given by the polynomial. After performing nine experiments, a matrix can be developed as shown below:
The coefficients are found by the Eq. 3.
Since this work studies two modes of linear and spot friction welding, we apply Formula (3) to table (1) to extract parameter coefficients in order to formulate polynomials describing FSW and FSSW.
Table .2. estimated values of the coefficients for FSW weld.
Coef
|
a0
|
a1
|
a2
|
I12
|
a11
|
a22
|
value
|
106.01
|
2.90
|
3.42
|
-0.42
|
-1.16
|
0.37
|
The polynomial of FSW can be written as follow :
Table .3. estimated values of the coefficients for FSSW weld.
Coef.
|
a0
|
a1
|
a2
|
I12
|
a11
|
a22
|
value
|
87.89
|
9.61
|
10.98
|
-0.47
|
-7.57
|
-1.12
|
The polynomial of FSSW can be written as follow:
2.2. Influence of factors in FSW
The influence diagrams of the main factors in FSW were presented in the fig.5. The graphs show that increasing the rotation speed leads to an increase in the temperature generated between the aluminum tool and the dissimilar polymer welded parts, which means that pneumatic energy maintains the same welding pattern as mechanical energy.
The curves in fig.5 (a, b) show that within the specified range of tool rotation speed per minute and tool feed speed per minute, the temperature gradually increases until it reaches its optimum value 112 °C, to welding PEHD withe PP at 1250 rpm and 30 mm/min.
The curves in Figure 6 confirm that the individual effect of the two main factors is the same as their combined effect. The optimal welding temperatures for these two types of polymers are when the tool rotation speed is limited to between 1100 and 1250 rpm and the welding speed is between 28 and 30 mm/min.
2.3. Influence of factors in FSSW
In the case of spot welding, the rotational speed continues to remain the FSSW parameter, and the welding velocity is replaced by the dwelling time of the tool on the plates.
Rotational speed remains the most influential factor on temperature during spot welding, as the heat generated reaches 100 degrees Celsius at a rotational speed of 1100 rpm. The temperature begins to decrease if the rotational speed exceeds this value. Regarding the residence time of the tool, its relationship with temperature is a relative relationship. As the residence time increases, the temperature increases, taking into account the melting point.
In the case of spot welding, the effect of the interaction between the rotation speed of the tool and the penetration time of the tool into the material (welding time) shows that the temperature required for welding HDPE with the pp is ensured at a rotation speed equal to 1100 rpm and a residence time within the range of 25 to 30 seconds.