-- MicheleLanzetta? - 20 Aug 2007

Layered Manufacturing of hierarchical structures

Related work

See also

• StickyBot
• MicrohairIntegration -- MarkCutkosky 10 Oct 2005 - 16:52 - r1.8
• HierarchicalFabrication (private)
• HierarchicalTransverse (private)
• MicrohairIntegration (private)

Recommendations

As soon as we consolidate the information, we keep adding on top of this list

• only the smallest hair will provide adhesion, the rest of the structure is just for compliance over a continuous range of different roughnesses
• this method will create a positive, directly the hierarchical structure, stacks of 0.1-0.2 mm in SU-8; a wafer will contain enough stackable parts for a patch of a square cm to be tested (DanielSoto) or 0.2-0.5 mm in wax
• to keep the structure directional, the front surface can have a bumped shape: ideal contact area just points with high curvature. FEM can be used to evaluate the size producing the minimum contact surface for a given elastic modulus
• inserts to have flat surface
• saw shape for faster deposition
• taper stalk for reduced stiffness
• we want a thin tip, to "activate" adhesion
• magic number 1:2 (to 2.5 conservative) produces same gecko stiffness defined as F/d
• FEM modeling of adhesion is difficult because we need a complete material characterization also in the non-elastic regime
• FEM (Ansys) can roughly model (NoeEsparza) the behavior of the hierarchy to understand the role of each for the compliance, working in the elastic regime
• possibility to have a different material for each hierarchical stack (instead of layer to avoid confusion, change nomenclature)
• during casting, pour below the top to avoid film creation and demolding problems
• thickness of each stack does not matter, but the surface needs to be flat for good stacking, by glue or curing
• angles 25 for flat surface and 20 for stalks (gecko angles, source: DanielSoto)
• coat the inside of the mold with some fluid (e.g. demolding spray, SangbaeKim? ) to prevent clumping (the inserts inserted in the mold after spraying will not affect the flat surface)

Open issues

• hierarchy ratio: constant or proportional (FEM by NoeEsparza)
• demolding?

Current work

We are setting up a task force to test the new approach (HierarchicalTransverse)

There are three phases

• design MicheleLanzetta? , consulting DanielSoto (gecko info and SU-8 issues), SangbaeKim? (wax manufacturing) and AlanAsbeck (integration with the Zman project)
• simulation by FEM, starting with simpler shape and assessing the compliance on a range of different surface roughness, NoeEsparza
• test with the wax material on higher scale of three levels and extrapolation the the fourth smallest layer will work the same way (ManuelDonnay? and JacobiG? )
• building with SU-8 to add the smallest layer with fine features down to .001 mm (DanielSoto). Current work on microhair will help understand the shape of the smallest stack
• engineering for mass production ???

Zman project

This approach is of interest to the Zman project because layered manufacturing will allow to build an integrated part with spines and adhesion patch. They should be designed so that the duration of both is the same and needs to be replaced together (AlanAsbeck). Current building practice is already layered so the experience for assembly can be used.