# Joining of Fibre-Reinforced Thermoplastic Polymer Composites by Friction Stir Welding--A Review
## 5 FSW of FRTP Composites
### Tilt Angle
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Authors [Ref.]** & **Material, Reinforcement, Thickness** & **Welding Parameters 1** & **Optimal Parameters** \\ \hline [PERSON] [45] & PP; 30 wt\% chopped GF; 10 mm & \(\omega\): 1200, 1500, 1800, 2100, & \(\omega\): 2100. \\  & 2400, 2700, 3000. & & \(\omega\): 630, \(\omega\): 8; \(\omega\): 2; **pin** \\ \hline [PERSON] et al. [46] & PP; 30 wt\% chopped GF; 5 mm & \(\omega\): 400, 500, 630, 1000; \(\
u\): 8; 12, 16, 20; & \(\omega\): 630, \(\
u\): 8; \(\omega\): 2; **pin** \\  & & \(\alpha\): 0, 1, 2; **pin geometry 2**. & **geometry**: tapered grooved. \\ \[PERSON] et al. [3] & PP; 20 wt\% chopped CF; 4 mm & \(\omega\): 1000; \(\
u\): 16, \(\alpha\): 1; & \(\omega\): 1000; \(\
u\): 16, \(\alpha\): 1; **pin geometry**: \\  & & **pin geometry 2**. & cylindrical conical threaded. \\ \[PERSON] et al. [47] & PP; 20 wt\% chopped GF; 4 mm & \(\omega\): 630, 800, 1000, 1250; \(\
u\): 12, 16, 20, & \(\omega\): 1000; \(\
u\): 20; \(\omega\): 1; **pin geometry**: \\  & & 25; \(\omega\): 0, 1.5, 2; **pin geometry 2**. & cylindrical conical threaded. \\ \[PERSON] et al. [49] & PP; 20 wt\% chopped CF; 4 mm & \(\omega\): 800, 1000, 1250; \(\
u\): 16, 20, 25; & \(\omega\): 1250, \(\
u\): 25; \(\omega\): 1. \\  & & \(\alpha\): 0, 1, 2. & \(\omega\): 1250, \(\
u\): 25; \(\omega\): 1. \\ \[PERSON] et al. [5] & PP; 30 wt\% chopped GF; 5 mm & \(\omega\): 1250, 1600, 2000, 2500; & \(\omega\): 2000; \(\
u\): 8; \(\omega\): 5. \\  & & \(\
u\): 8, 12, 16, 20; \(\alpha\): 3, 4, 5, 6. & \(\omega\): 2000; \(\
u\): 8; \(\omega\): 6. \\ \[PERSON] et al. [5] & PP; 30 wt\% chopped CF; 5 mm & \(\omega\): 2000; \(\
u\): 8; \(\omega\): 5; & \(\omega\): 2000; \(\
u\): 8; \(\omega\): 5; **pin geometry**: \\  & & **pin geometry 2**. & threaded tapered with a chamfer. \\ \[PERSON] et al. [50] & PA6; 30 wt\% chopped GF; 5 mm & \(\omega\): 400, 500, 600; \(\
u\): 12, 18, 24; & \(\omega\): 600; \(\
u\): 12; \(\alpha\): 2. \\  & & \(\alpha\): 0, 1, 2. & \(\omega\): 600; \(\
u\): 12; \(\alpha\): 2. \\ \[PERSON] et al. [51] & PA6; 30 wt\% chopped GF; 5.3 mm & \(\omega\): 2000; \(\
u\): 10, 25, 40, \(\omega\): 1, 2; & \(\omega\): 2000; \(\
u\): 25; \(\omega\): 2; \\  & & \(\mathbf{F}_{z}\): 1500, 2000. & \(\mathbf{F}_{z}\): 2000. \\ \[PERSON] et al. [54] & PC; 5, 10, 15 and 20\% of chopped GF; 4 mm & \(\omega\): 630, 800, 1000, 1250; & \(\omega\): 1250, \(\
u\): 12; **pin geometry**: \\  & & \(\upsilon\): 12, 16, 20, 25; **pin geometry** 2. & threaded tapered with a chamfer. \\ \[PERSON] et al. [52] & PA6; 30 wt\% chopped GF; 4 mm & \(\omega\): 2000, 2800; \(\
u\): 20, 40; & \(\omega\): 2800; \(\
u\): 40, \(\mathbf{F}_{z}\): 1000. \\  & & \(\mathbf{F}_{z}\): 800, 1000. & \\ \hline [PERSON] et al. [53] & PA6; 0, 15 and 30\% of chopped GF; 5 mm & \(\omega\): 300, 500, 700; & \(\omega\): 500; \(\
u\): 10. \\ \hline  & & \(\mathbf{}^{1}\) rotational speed-\(\omega\) (rpm), welding speed–\(\omega\) (mm/min), tilt angle–\(\alpha\) (\({}^{\circ}\)), and axial force–\(F_{z}\) (N). 2 pin geometries compared are listed in Table 2. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Welding parameters compared and optimal parameters found in the literature. concluded that a tilt angle of 2\({}^{\circ}\) was preferable. For higher values, these authors reported the loss of weld strength. On the other hand, [PERSON] et al. [5] observed that increasing the tilt angle up to 6\({}^{\circ}\) allowed successive higher values of tensile strength. Despite affecting the performance of welds, the tilt angle has a residual influence when compared to other parameters. [PERSON] et al. [47,49] and [PERSON] et al. [50] determined that the tilt angle has a percentage of contribution of between 5% and 8%, when compared to rotational speed and welding speed. The most recent FSW tools developed to weld polymeric-based material, such as FRTP composites, are designed with stationary shoulder, forcing the use of a zero-tilt angle.