2 Part Design

A conical tube should be used as a part which has a large expan-sion ratio between both end sides when used in the hydroform-ing process. In the present study, the conical tube was designed for the hydroforming of an IP-beam representative part for using a conical tube. The corresponding manufacturing process and the die were developed within this study. Figure 1 shows the

 i 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Figure 8. U-forming process.

 shape of the IP-beam part for the conical tube. As shown in Fig. 1 the section difference and the expansion ratio was about 100%. For this part, the tube diameters were 37.8 mm and 70 mm as the small end and the large end, respectively.

After laser cutting of the sheet, the conical tube was formed in a U-O forming type. In order to design the appropriate die shape and the forming process, a computer aided engineering (CAE) analysis was performed. Figs. 2 and 3 show the simulation model

of the U-forming and O-forming analysis and Figs. 4 and 5 show the simulation results of minor strain distribution after U-form-ing and plastic strain distribution after O-forming, respectively. The straight section was finished in the large diameter region and the compressive stress arose in the starting point of the con-ical section (transition region) in the large diameter region, Fig. 4. Since this could result in some weak wrinkles in this region, the gap between the upper die and lower die was deter-

 i 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Mat.-wiss. u. Werkstofftech. 2013, 44, No. 5 Conical tube hydro-forming design of automotive instrument panel beams 357

Figure 12. IP-beam fabricated by conventional assembly method.www.chuibin.com

Figure 10. U-formed tube.

mined as material thickness plus 0.1 mm. The overall deforma-tion degree after tube forming was small except for the transition region for the starting point of the conical section.

Figs. 6 and 7 show the side view of the U-forming and O-form-ing die, respectively.

Figs. 8 and 9 show the tube forming process and Figs. 10 and 11 show the tube after U and O-forming.

The formed tube was laser welded by using a designated jig which was fabricated for the conical tube shape. However, the fol-lowing problem occurred: the out-of-roundness was deviated in the welding zone, from this, a crack in the welding zone occurred after hydroforming. Namely, when the pressure was generated in the inner tube, the sheet was flattened along the die and when expanded, a first crack occurred in the weld zone. In order to compensate this problem, the management of the out-of-round-ness of the formed tube in the welding zone was most important. In addition, an edge preparation was necessary in the weld seam region in order to remove the V-type grove.

The IP-beam component is a skeleton role in the inner dash panel of a vehicle. It has a large diameter at the driver side and a

Figure 13. Analyses of cross sections of IP-beam along the part, (unit: mm).

small diameter in passenger side. Therefore, the IP-beam was composed of four numbers of parts and conventionally assembled by welding of two numbers of welded tubes in the central position, Fig. 12. However, when using hydroforming, only one piece of the conical tube was formed and the integration forming effect could be considerable.

Figure 13 shows the analyses results of the cross section perim-eter along the IP-beam. From these results the maximum and minimum perimeters were 242.8 mm and 117.6 mm, respec-tively.

The forming process for the fabrication of IP-beam was designed as 2 steps of preforming using press bending prior to the hydroforming. Figs. 14 and 15 show the analysis model for preforming and hydroforming simulation.