Creating Metal Molds for Directional Gecko-Inspired Adhesives

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Capella Kerst ◽  
Srinivasan A. Suresh ◽  
Mark R. Cutkosky
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Surface Finish ◽  
High Aspect Ratio ◽  
Smooth Surface ◽  
Metal Mold ◽  
Dry Adhesives ◽  
Single Use

Abstract We describe a process for creating durable metal molds for the fabrication of directional, gecko-inspired dry adhesives. The adhesives require microscopic inclined features with a challenging combination of tapered geometry, high aspect ratio, and smooth surface finish. Wedge-shaped features produced by the new metal mold exhibit the same geometry and surface finish as those cast from single-use wax molds and epoxy molds in previous fabrication methods. They also produce the same levels of adhesion and shear stress. The metal molds, and the adhesives cast from them, show no degradation after repeated molding cycles.

Active Scalable Elastomer Mold to Ease Demolding of High Aspect Ratio Micro Features

2012 ◽  
Vol 591-593 ◽  
pp. 880-883
Author(s):  
Yan Xu ◽  
Kai Leung Yung ◽  
Hang Liu
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Experimental Results ◽  
Metal Mold ◽  
Micro Features ◽  
New System

To fabricate high aspect ratio micro/nano features, demolding is more challenging than filling of melt into micro mold as solidified micro features can be easily peeled off when demolding resistance is high. Besides using anti-stick agent, using deformable mold is a new solution proposed by the authors. This paper presents a setup for testing the deformable active mold. Experimental results on micro thermal molding with the developed mold deforming system prove that the new system can successfully demold high aspect ratio micro features that can not be produced with traditional metal mold.

High Aspect Ratio Polymer Micro/Nano-Structure Manufacturing Using Nanoembossing, Nanomolding and Directed Self-Assembly

2003 ◽  
Author(s):  
Metin Sitti
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Self Assembly ◽  
Scanning Tunneling ◽  
Nano Structure ◽  
Liquid Polymer ◽  
Dry Adhesives ◽  
Liquid Polymers ◽  
Assembly Technique ◽  
Dc Electric Field

This paper proposes three methods to fabricate synthetic gecko foot-hair high aspect ratio polymer micro/nanostructures. In the first method, nano-robotically indented templates are molded with liquid polymers, and the cured polymer is peeled off or etched away. Atomic force microscope and scanning tunneling microscope probe tips are used to emboss/indent flat wax surfaces, and silicone rubber micro/nano-bump structures are demonstrated. The second one uses a self-organized polycarbonate nano-pore membrane as the molding template. PDMS is molded into these micro/nano-pores under vacuum, and 1:2 and 1:9 aspect ratio pillar structures with 5 micron and 0.6 micron diameters are manufactured successfully. Finally, a directed self-assembly technique is proposed to grow regularly spaced and oriented micro/nano-pillars. Here, instability of a liquid polymer thinfilm under a DC electric field is used to grow nano-pillars, and stretching and shearing of the grown hairs enable high aspect ratio and oriented hair structures. These hair structures will be utilized as novel biomimetic dry adhesives in future miniature space and surgical robot feet.

High Aspect Ratio Micro-EDM Drilling with Nano Surface Finish

2016 ◽  
pp. 157-164
Author(s):  
Mohammad Yeakub Ali ◽  
Mohamed Abd Rahman ◽  
Asfana Banu ◽  
Shakira Adnan ◽  
Fatin Nadia
Keyword(s):  
Aspect Ratio ◽  
Surface Finish ◽  
High Aspect Ratio ◽  
Micro Edm ◽  
Edm Drilling

Machining of High Aspect Ratio Micro-Holes on Titanium Alloy Using Silver Nano Powder Mixed Micro EDM Drilling

2019 ◽  
Author(s):  
Chong Liu ◽  
Asif Rashid ◽  
Muhammad P. Jahan ◽  
Jianfeng Ma
Keyword(s):  
Titanium Alloy ◽  
Aspect Ratio ◽  
Surface Finish ◽  
High Aspect Ratio ◽  
Electrical Discharge Machining ◽  
Turbine Blades ◽  
Weight Ratio ◽  
Recast Layer ◽  
Micro Edm ◽  
Micro Holes

Abstract Titanium alloy Ti-6Al-4V is used extensively in aerospace engines because of its high strength-to-weight ratio and corrosion resistance. Machining of cooling holes in turbine blades for aerospace engines is one of the major challenges faced in aerospace industries. Ti-6Al-4V is known as a difficult to be machined material by conventional machining processes, and machining of micro-through-holes with diameter less than 100 microns is even more challenging. Therefore, the objective of this study is to investigate the feasibility of machining high aspect ratio micro-through holes in Ti-6Al-4V using micro electrical discharge machining (micro-EDM) with the silver (Ag) nanopowder mixed dielectric. The machining time, overcut, recast layer, crater size, aspect ratio and surface finish of the micro-holes were evaluated. In order to minimize the positional inaccuracy and spindle runout, the microelectrodes were fabricated in-situ using block micro-EDM process. In this study, as received electrode of 300 microns diameter tungsten wire was reduced to about 50 microns diameter rod by micro block EDM using a tungsten carbide block. The effect of powder concentration, gap voltage, capacitance and electrode rotational speed was studied. It is found that high quality micro-holes of about 50 microns diameter can be achieved successfully and repeatedly using powder mixed micro-EDM (PM-μEDM). The micro-holes generated by PM-μEDM provides comparatively smoother surface finish and minimal recast layer around the rim of the micro-holes. In addition, PM-μEDM process improves machining stability, thus allowing to minimize the hole size and quality, thus enhancing the aspect ratio of micro-holes.

scholarly journals Debinding and Presintering of High Aspect Ratio Microbi-Lumen Tubes Produced by Extrusion of 17-4PH Feedstock

2020 ◽  
Vol 8 (2) ◽  
Author(s):  
Sandeep Kuriakose ◽  
Salvatore Cataldo ◽  
Paolo Parenti ◽  
Massimiliano Annoni
Keyword(s):  
Aspect Ratio ◽  
Structural Properties ◽  
Surface Finish ◽  
High Aspect Ratio ◽  
Three Dimensional ◽  
Processing Technologies ◽  
Green State ◽  
Aspect Ratios ◽  
Recent Developments ◽  
Thermal Debinding

Abstract Recent developments have showcased that micro-extrusion of feedstock can be used for manufacturing metallic microbi-lumen tubes with very high length-to-diameter aspect ratios, which are not viable by conventional metal extrusion or commonly used feedstock processing technologies like injection molding or hot pressing. The extrusion of high aspect ratio microcomponents faces the challenge of maintaining the geometrical accuracy, surface finish, and structural properties since the micro-extrusion in green state is followed by debinding and sintering operations, which result in shrinkage and variations in surface finish and structure. The stages of the process chain such as solvent/thermal debinding (TD), to remove the polymeric binder, and presintering (PS), to achieve a mild structural rigidity before the sintering, are of critical importance to achieve the surface and structural properties of high aspect ratio microparts and have not been yet studied in case of micro-extrusion of feedstock. In this study, the effect of debinding and PS on surface and structural properties of bi-lumen tubes processed at different extrusion conditions is discussed. Surface roughness of the tubes is analyzed using three-dimensional microscopy, and structural properties are studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The debinding and PS experiments on extruded microbi-lumen tubes retained very good surfaces integrity without any cracks or defects. The study shows that the interactions of extrusion temperature and extrusion velocity influence the surface finish of the extruded tubes the most. The sintered bi-lumen samples showed a good areal surface finish, Sa of 2.21 μm, which is near to the green state value confirming the suitability of the applied debinding and PS parameters.

scholarly journals Effect of Feedstock Properties on Extrusion of High Aspect Ratio Microbi-Lumen Tubes

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Sandeep Kuriakose ◽  
Paolo Parenti ◽  
Massimiliano Annoni
Keyword(s):  
Aspect Ratio ◽  
Structural Properties ◽  
Surface Finish ◽  
High Aspect Ratio ◽  
Research Work ◽  
Three Dimensional ◽  
Extrusion Process ◽  
Powder Size ◽  
Scanning Calorimetry ◽  
Processing Technologies

Abstract The micro-extrusion of feedstock is a promising and emerging technology for manufacturing very high length to thickness aspect ratio metallic microcomponents which are not feasible for conventional metal processing methodologies or commonly used feedstock processing technologies. Extrusion of high aspect ratio microcomponents using metallic feedstock confronts the challenges of achieving a continuous extrusion without any breakage, the geometrical accuracy, surface finish and structural properties for the component which are required for the micro-application, during micro-extrusion process. The type of metallic powder, powder size, type of binder, and binder properties are very decisive in making the extrusion process feasible for the micro-application. The influence of feedstock properties on micro-extrusion of high aspect ratio microcomponents are still unknown in case of micro-extrusion of feedstock. In this research work, the effect of type of feedstock on micro-extrusion is studied by extruding microbi-lumen tubes using biocompatible steel feedstocks AISI316 L and 17-4PH at two different aging states (no aging and 1.5 years aging). The geometrical features of the extruded bi-lumen tubes, surface roughness and structural properties are analyzed using three-dimensional (3D) focus variation microscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The analysis showed that feedstock type affects the feasibility of extrusion and geometrical size to a great extent. An average Sa roughness deviation from 1.73 to 4.57 μm was observed for feedstocks 17-4PH and AISI316 L. The study also confirms that binder properties and aging of the feedstocks also have to be taken into account for maintaining the surface finish and structural properties in case of metallic feedstock extrusion of high aspect ratio bi-lumen tubes.

Stresses in Half-Elliptic Curved Beams Subjected to Transverse Tip Forces

2012 ◽  
Vol 80 (1) ◽  
Author(s):  
Eduardo Velazquez ◽  
J. B. Kosmatka
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Closed Form ◽  
High Aspect Ratio ◽  
Shear Stresses ◽  
Curved Beam ◽  
Curved Beams ◽  
Curvature Effects ◽  
Aspect Ratios ◽  
Peak Shear Stress

In-plane bending of curved beams produces substantial through-thickness normal and shear stresses that can result in structural failures. A half-elliptic curved beam, having a known prescribed variable radius of curvature, is studied as an extension of the previously published circular arc beam. The equations for the normal, tangential, and shear stresses are developed for a curved beam outlined by two confocal half ellipses loaded by a pair of concentrated perpendicular forces on its ends. Closed-form analytical solutions for the stresses are found using an elasticity approach, where the solution is found by using selected terms of the biharmonic equation in elliptic coordinates. For the case of an elliptic beam with an aspect ratio of very close to unity, the solution closely agrees with published circular beam solutions. For other elliptic beam aspect ratios, the calculated stresses display good correlation to detailed finite element model solutions for thickness to semi-axis ratios < 0.1. A parametric study revealed that the maximum normal stress is located at the midplane for high-aspect ratio (a/b ≥ 1) half-elliptic beams, but shifts toward the load tip for low aspect ratio (a/b < 1) beams due to local curvature effects. Moreover, the peak shear stress location moves toward the midplane and the magnitude greatly increases as the aspect ratio is increased. Thus, there are large normal and shear stress interactions occurring near the midplane for high-aspect ratio half-elliptic beams, which is not observed for circular beams. These stress interactions can produce unique failures in materials having low shear strength and through-thickness strength. The current closed-form solution is an improvement on previously published approximate solutions.

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