Gregory Hayes

Fabrication and Design of a Nanoparticulate Enabled Micro Forceps

A novel fabrication process and design optimization method for a micro forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments. The micro forceps is a monolithic compliant mechanism that due to its two-dimensional design can be manufactured using the new fabrication process. The process begins with fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol wipe. Finally, the photoresist molds are removed with a reactive ion etch (RIE) step, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with a large aspect ratio (≥40:1), sharp edges (∼ 1 μm), and a resolution of 2 μm. Two optimization problems are formulated to determine the effect of dimensional parameters and material strength on the performance of the compliant micro forceps. First, performance is sensitive to small changes in the geometry, indicating that dimensions and shrinkage rates must be carefully controlled during processing. Second, performance can also be improved by using very large aspect ratios and/or improvements in material strength. A sample part manufactured using the new process is presented.Copyright

Design of contact-aided compliant cellular mechanisms with curved walls

Contact-aided compliant cellular mechanisms are cellular structures designed with contact mechanisms integrated into each cell to provide stress relief. This article addresses compliant cellular structures having curved walls and internal contact mechanisms. The use of curved walls in cellular structures tends to improve their performance in terms of global strain capability and is beneficial for fabrication. In some cells, the addition of contact mechanisms results in stress relief, allowing the cells to be stretched farther than they could without contact. The cellular structures with curved walls are modeled, and finite element analysis is used to calculate the maximum global strains for comparable noncontact and contact-aided cells. An optimization procedure is performed to find the cell geometries that result in the highest global strains. Strains of up to 32.4% and 19.7% are predicted for the optimized curved noncontact and contact-aided cells, respectively. Additionally, a comparison of curved and noncurved, noncontact and contact-aided cells shows that the addition of curved walls results in a significantly greater improvement in global strains than that gained by adding a contact mechanism. Mesoscale contact-aided compliant cellular mechanism designs are fabricated via the lost mold–rapid infiltration forming process and are tested using a custom-designed test rig.

Robust parameter design for multiple-stage nanomanufacturing

Process reproducibility is a major concern for scientists and engineers, especially when new processes or new products are transitioned from laboratory-scale to full-scale manufacturing. Robust Parameter Design (RPD) is often used to mitigate this problem. However, in multiple-stage manufacturing process environments, it is difficult to employ the RPD concept because experiments cannot strictly follow the principle of complete randomization. Furthermore, the stages can be located at different sites, leading to multiple sets of noise factors. In the existing literature, only a single set of noise factors is considered. Therefore, in this research, the foundation of using the RPD concept with multistage experiments is developed and discussed. Some optimal design catalogs are provided based on a modified minimum aberration criterion. The context for this work is the development of a medical device made of nanoscale composites using a multiple-stage manufacturing process.

Yield improvement for lost mould rapid infiltration forming process by a multistage fractional factorial split plot design.

Statistical design of experiments is widely used among scientists and engineers to understand influential factors in a laboratory or manufacturing process. One of the underlying principles of using the statistical design of experiments method is randomisation, each run of experimental settings will be determined completely unsystematically. In practice, especially in a complicated process that consists of multiple stages, randomisation may pose too high a burden on time and cost.In this study, the multistage fraction factorial split plot design is proposed for green yield improvement in a lost mould rapid infiltration process that has been developed to fabricate zirconia ceramic parts. This design allows a relaxation of the randomisation principle so that certain experimental runs can be carried out in convenient groups. The results indicate that the type of immersion chemical and mould coating play a role in improving process yield. Additionally, the results suggest that a mould infiltration machine should be used to improve the reproducibility of the process.

Design, fabrication, and testing of contact-aided compliant cellular mechanisms with curved walls

Contact-Aided Compliant Cellular Mechanisms (C3M) are compliant cellular structures with integrated contact mechanisms. The focus of the paper is on the design, fabrication, and testing of C3M with curved walls for high strain applications. It is shown that global strains were increased by replacing straight walls with curved walls in the traditional honeycomb structure, while the addition of contact mechanisms increased cell performance via stress relief in some cases. Furthermore, curved walls are beneficial for fabrication at the meso-scale. The basic curved honeycomb cell geometry is defined by a set of variables. These variables were optimized using Matlab and finite element analysis to find the best non-contact and contact-aided curved cell geometries as well as the cell geometry that provides the greatest stress relief. Currently, the most effective contact-aided curved honeycomb cell can withstand global strains approximately 160% greater than the most effective contact-aided, non-curved cell. Four different designs were fabricated via the Lost Mold-Rapid Infiltration Forming (LM-RIF) process. An array of the contact-aided optimized curved cell was then mechanically tested using a custom designed test rig, and the results were found to have a higher modulus of elasticity and lower global strain than the predictions. Despite these discrepancies, a high-strength highstrain cellular structure was developed, for potential use in morphing aircraft applications.

Fabrication and Strength-Based Design of a Meso Forceps

A novel fabrication process and design optimization method for a mesoscale forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments using an iterative fabrication-design technique. The current paper focuses on the fabrication of thick (∼hundreds of microns) two dimensional parts with large aspect ratios (length/width > 20). The paper also describes an optimization method that accounts for manufacturing requirements and material strength. The process begins with the fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol bath. Finally, the photoresist molds are removed via pyrolysis, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with large aspect ratios, sharp edges (∼ 1 μm), and a resolution of 2 μm. An optimization algorithm, using ANSYS optimization module, is formulated to determine the effect of dimensional parameters and material strength on the optimal design and predicted performance of the compliant meso forceps. Three ultimate strength values are separately implemented as a stress constraint in our optimization problem. Results conclude that our manufacturing process is capable of producing meso scale forceps considering the anticipated ultimate strength at this scale.Copyright