J．W．Lee studied the forming limit of a structural aluminum tube in rubber pad bending． However, there are still some key problems，such as the relation between the roller stroke and the curvature radius and the effect of
hyperelastic pad properties which all need to be investigated
comprehensively．
In this study，flexible bending of typical aluminum profiles with hyperelastic pad was carried out． The effects of roller stroke，shape of cross．section，relative thickness，material properties of hyperelastic pad on bending were investigated by experimental work．Typical failures and other quality problems met in the experiments and their countermeasures were also analyzed and discussed．
1 Experiment
1.1 Flexible Bending Device
Fig．1 shown the bending divice used． As shown in Fig．1，the profile is laid on a hyperelastic pad and will be pushed into it by the roller．The pressure between the roller and the profile and the hyperelastic pad results in a distributed moment upon the profile．The curvature radius of final bent profile will be determined by controlling the roller stroke and the horizontal displacement of the workpiece．If the roller stroke can be changed when moving the profiles horizontally，complex contours and different curvature radius can be realized along the length of the profile．
1.2 Materials
Trough--shaped and H--shaped aluminum profiles with different thickness are chosen to investigate the shape of cross—section and relative thickness． Fig．2 shows the shape and dimension of each profile． The material of the two profiles is 606 1 aluminum alloy with thick nesses 2 mm and 1.5 mm，respectively．The hyperelastic pads used are polyurethane with hardness of 93 Shore A and rubber with hardness of 75 Shore A．The thickness and width of the hyperelastic pads are 40mm and 150mm．
1.3 Experimental Procedure
For a trough—shaped profile，there are three possible bending layouts as shown in Fig．3， which are called normal bending．reverse bending and side bending respectively． Because torsion will happen if a single profile is bent in side bending，pair bending shown in Fig．3 f c)will be used．The diameter of the roller is 40 mm．
As for H—shaped profile．Fig．4 shows two possible bending layouts．Considering its relative small thickness with respect to the cross—section，straight roller in Fig．3 cannot be used because early wrinkle will occur during bending．A special designed wheel inserted hyperelastic bar and side baffle as shown in Fig．4 were used together to increase the stiffness of shoulders．In practice, both rigid wheel and PUR wheel were used．The diameter of the wheel and its two shoulders are 110mm and 80mm．In Fig．4(b)，the inserted hyperelastic bar will be bent together with the profile，which will affect the bending of profile．Therefore，only the layout in Fig．4(a)will be studied．