I’m trying to design a frame of sorts that has to morph into a certain shape and I’m looking for a polymer/solution that can be molded with different levels of flexibility. The attached image of the Knoll Generation chair depicts approximately the function I’m trying to achieve.
Think of a truss with rigid aluminum rods and rubber joints, but all molded in one plastic piece.
Hytrel by DuPont is quite close to what I’m looking for (used in backrest of chair), but I’m unsure if it’s possible to control the rigidity-flexibility gradient somehow. This is crucial to be able to control the shapes of the frame.
EDIT: Varying the frame profile (thick to thin) is also an option.
Varying thickness, support ribs, I-beams etc is you best bet. I don’t think you can vary hardness in a single part, unless you make it 2K.
I designed a single-part Hytrel hammerholder where it needed a hold the weight of a hammer (stiff), but also had a beltclip that needed to be flexible enough. Was achieved mostly with material thickness and different section profiles.
Depending on the design you could 2 shot a part with a harder and softer durometer material. The soft on soft overmold is tougher to control but not impossible.
You could potentially create a series of ribs in the hard material that get filled with the soft material and use varying wall thicknesses/cutout frequency to adjust the rate of spring you get out of it.
The concern of course is if it moves enough, the 2 materials will want to separate over time.
2K is not out of the question. Are there different durometer Hytrels available? Would it be possible to 2k with a softer and harder Hytrel?
Good idea with the ribs!
Different durometer are available. From soft-like-silicon to stiff-like-bone. Don’t know about hytrel-hytrel 2K, but can’t see why not, talk to your material supplier.