Another feature for "flexing" an elastomeric (rubber) part is the deform feature (option: curve to curve). I just discovered this feature recently, and the flex feature does not provide the option to flex around a target curve, so the flex feature can be a challenge to control accurately.
The deform feature (curve to curve) allows a part to be bent along a spine (curve). It is similar to Pro-E's spinal bend, and require an initial & target curve. Try the deform feature and let us know if it works for your situation.
Here is a post in the SolidWorks forum comparing deform to flex:
https://forum.solidworks.com/message/71444#71444
Chris
To Create a Spinal Bend (Pro-E)
The Spinal
Bend option bends a solid or quilt about a curved spine by
continuously repositioning cross-sections along a curve. Planar cross-sections
perpendicular to an axis are repositioned perpendicular to the trajectory with
no distortion. All compression or distortion is done longitudinally along the
trajectory.
1.
Click Feature > Create > Solid > Tweak > Spinal
Bend, or Insert
> Advanced > Spinal Bend.
Deform - Curve to Curve (SW)
Curve to curve deform is a more precise method for altering complex
shapes. You deform objects by mapping geometry from initial curves, which can
be sets of curves, edges, section curves, sketch curves, and so on, to a set of
target curves.
Edited by: c_thompson_68