TPI April 2011

Results Figure 9 shows the situation during the corrugation process. At this point a steady state is reached and a periodic annular corrugation is achieved on the tube. Steady state is reached when the tube gets in contact with the outlet bearing. Before the outlet bearing is in contact with the tube, wrinkling occurs, which can be seen at the front end of the tube in Figure 9. Model validation Validation of the simulation results is done by comparing the actual geometry of the corrugated tube with the simulation results. For this purpose a corrugated tube is sliced axially and the wave period, the amplitude and the profile length (l, u and s in Figure 10) as well as the inner and outer diameter of the actual geometry produced with a feed rate of 6.4m/min are compared with the computed values (see Table 1). The values in Table 1 represent an average over nine waves and show a good agreement between the measured and computed values for the outer diameter. The inner diameter and the wave period as well as the amplitude show a small deviation between the experiment and the related simulation (Simul 1). Considering necessary simplifications in the numerical model the agreement between the computed and measured values is sufficient. Influence of the feed rate on the tube geometry To investigate the influence of the feed rate on the results of the corrugation process the feed rate is increased from 6.4m/ min to 7m/min. This leads to increased axial pressure in the forming zone and to a change in the resulting tube geometry. Table 1 summarises the main geometric results for this simulation (Simul 2).

Figure 9 : Geometry of the tube and corrugation disk during the corrugation process

Figure 10 : Wave period l, amplitude u and profile length s

Experiment

Simul 1

Simul 2

Feed rate

6.4m/min

6.4 m/min

7m/min

Inner Diameter Outer Diameter Wave period l

19.5mm 19.3mm 18.5mm 21.3mm 21.3mm 21.3mm 4.71mm 4.59mm 4.87mm

Amplitude u

0.7mm

0.8mm

1.2mm

Profile length s 4.65mm 4.6mm 4.84mm Table 1 : Comparison between the actual geometry produced with a feed rate of 6.4m/min and the computed geometry with a feed rate of 6.4m/min and 7m/min, respectively – average for nine waves

Figure 8 : Overview of the entire model to simulate the corrugation process

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April 2011 Tube Products International