PSI - Issue 35

Enes Günay et al. / Procedia Structural Integrity 35 (2022) 42–50 Gu¨nay et al. / Structural Integrity Procedia 00 (2021) 000–000

47

6

(Avg: 75%) TEMP

(Avg: 75%) TEMP

25 25 26 26 27 27 27 28 28 29 29 30 30

25 29 33 38 42 46 50 54 58 63 67 71 75

(a) deformation heating

(b) friction heating

Deforma�on Hea�ng

14.9

Fric�on Hea�ng

14.4

13.9

13.4

Internal Heat Energy [kJ]

12.9

0

0.5

1

1.5

2

2.5

3

Process time [s]

(c) comparison of internal heat energy

Fig. 5: Thermal analysis results for two types of heat generation

conductance. In such cases, temperature increase may become too quick and the heat would become trapped in the material. Fig. 7 shows the temperature distributions, obtained from three di ff erent flow forming FE simulations after rollers have moved 13.75mm. The important observations are presented in Table 1. The di ff erence between the cases are the axial and tangential speeds of the rollers. Interestingly, lower heating is observed when roller RPM is increased. Strain analysis reveals that the preform experiences slightly less strain under faster rotating rollers. It was previously shown that frictional heating constitutes a small portion of total heat generation. Therefore, even though there is more frictional heat generated with larger roller RPM around the mandrel, the fact that there is slightly less deformation reduces overall generated heat. This is not beneficial, since increased roller rotational speed is often not desired due to its contribution to diametric growth. More importantly, increasing the axial speed of rollers has a significant e ff ect on temperature rise. A 50% increase in velocity resulted in approximately 25% more total heat energy generated in the simulations. Fig. 8 shows the temperature on an element close to the edge in this case. Here, it can be seen that temperature can reach up to 400 °C before starting to decrease, even if it is for a few seconds, much higher than what is seen in the other cases. This suggests that changing the axial speed of rollers plays an important role on thermo mechanical characteristics, likely to bring softening e ff ects on certain materials. Additionally, even at lower axial feed