PSI - Issue 28

Shayan Eslami et al. / Procedia Structural Integrity 28 (2020) 659–666 Shayan Eslami/ Structural Int grity Procedia 00 (2019) 000–000

663

5

(a)

(b)

(c)

(d)

Figure 1- a) conventional welding tool, b) stationary shoulder welding tool; surface quality of the produced welds c) using a conventional tool, and d) using the PEEK stationary shoulder tool.

The experimental results obtained from the Taguchi design of experiment regarding the ultimate tensile strength is presented in Table 3. The constant parameters for these experimental tests are: 40 seconds dwell time, 5mm probe diameter, and 4mm probe length. As presented in Table 3, the S4 parameter combination produced the strongest welds, with maximum joint efficiency of 43%, when compared to the base material. From the obtained results, it is clear that the strength of the produced welds are increasing as the tool is advancing, due to increase of the welding temperature, as shown in Figure 2a. In this study, no temperature or force sensors were used to have a closed-loop control system to guarantee the consistency of the welds. Figure 2b shows the effect of the welding parameters on the weld strength. All the welding parameters have statistically significant effect on the weld quality (p-value lower than 0.05). The most significant welding parameters and their contributions are: rotational speed (57%), welding speed (12%) and axial force (7%). This tool design showed promising results, however, lack of heat generation and consistency were the main issues using the PEEK welding tool. The capacity of this tool (Figure 1b) was limited to amount of the generated frictional heat and capacity of the CNC machine for maximum rotational speed. In order to improve the weld quality by increasing the welding temperature, a new welding tool was designed and tested.

Table 3. Ultimate tensile strength of welded specimens.

Tensile Strength [MPa]

Experiment Rotation Speed (rpm)

Welding Speed (mm/min)

Axial Force (N)

#1

#2

#3

#4

#5

S1 S2 S3 S4

2000 2000 2800 2800

20 40 20 40

800

32.0 58.0 44.0 59.5

43.2 58.5 54.2 61.7

43.7 63.2 54.6 60.3

44.6 63.7 56.1 64.1

50.5 58.2 57.9 63.4

1000 1000

800