Cutting to the Point: Directly Machined Metal Molds for Directional Gecko-Inspired Adhesives

Fabrication techniques for gecko-inspired adhesives generally target mold durability, adhesive performance, and process efficiency and simplicity. With these goals in mind, we present a micromachining process for creating reusable aluminum molds used to fabricate directional dry adhesives. The molds require deep, narrow and overhanging grooves to create sharp and angled adhesive features. This geometry precludes most traditional machining and lithographic material removal processes. The presented process is a hybrid of indenting and orthogonal machining, using a diamond-coated microtome blade as the tool. An finite element analysis reveals the local extent of work hardening as each groove is created, and helps to define a trajectory that reduces the effects of tool deflection and chip build up. The results of a series of experiments agree with predictions from the analysis and reveal a range of blade approach angles and a lower bound on groove spacing to achieve the desired geometry. This range is narrower than for molds machined from wax in previous work. Nonetheless, adhesive samples cast from the new metal molds achieve comparable performance to those previously cast from wax.