Fabrication and Design of a Nanoparticulate Enabled Micro Forceps

Journal of the American Ceramic Society

Kirkpatrick

et al. 2009

Free-standing mesoscale (340 lm Â 30 lm Â 20 lm) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter (B400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal process. The colloid and interfacial chemistry of the nanoscale zirconia particulates has been modeled and used to prepare highly concentrated suspensions. Engineering solutions to challenges in mold fabrication and casting have yielded free-standing, crack-free parts. Molds are fabricated using high-aspect-ratio photoresist on ceramic substrates. Green parts are formed using a rapid infiltration method that exploits the shear thinning behavior of the highly concentrated ceramic suspension in combination with gelcasting. The mold is thermally decomposed and the parts are sintered in place on the ceramic substrate. Chemically aided attrition milling disperses and concentrates the as-received 3Y-TZP powder to produce a dense, fine-grained sintered microstructure. Initial three-point bend strength data are comparable to that of conventional zirconia; however, geometric irregularities (e.g., trapezoidal cross sections) are present in this first generation and are discussed with respect to the distribution of bend strength.

Section: Introductionmentioning

confidence: 99%

Lost Mold Rapid Infiltration Forming of Mesoscale Ceramics: Part 1, Fabrication

Antolino

Journal of the American Ceramic Society

Kirkpatrick

et al. 2009

“…A deflection of 1.5% is tolerable in the mesoscale bend bars, which have an aspect ratio of 19:1, meaning the bars have an average maximum height difference of 5 μm. Although the deflection is small in Gen3 bend bars, it will not be acceptable for higher aspect ratio parts5 for which the manufacturing process is ultimately intended. Efforts to further reduce the warping and accompanying drying cracks in the higher aspect ratio parts will be addressed in a later report.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, free-standing mesoscale components are being codeveloped for the next generation of surgical instruments 5,6. Ceramics, particularly yttria-tetragonal zirconia polycrystals (Y-TZP), have the high fracture strength and elastic modulus required for mesoscale surgical instruments 5.…”

Section: Introductionmentioning

confidence: 99%

“…In the current study, the mesoscale Y-TZP bend bars provide an excellent model for iterative process improvements to eliminate the strength-limiting geometric flaws that specifically occur in mesoscale ceramics. In addition, the mechanical strength determined for the mesoscale bend bars is used in the finite-element design for mesoscale applications such as surgical instruments 5. Although there are numerous forming processes for micro or mesoscale ceramics,4 the metrology of the parts produced is often left uncharacterized.…”

Section: Introductionmentioning

confidence: 99%

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Lost Mold‐Rapid Infiltration Forming of Mesoscale Ceramics: Part 2, Geometry and Strength Improvements

Antolino

Journal of the American Ceramic Society

Kirkpatrick

et al. 2009

Iterative process improvements have been used to eliminate strength-limiting geometric flaws in mesoscale bend bars composed of yttria-tetragonal zirconia polycrystals (Y-TZP). These improvements led to large quantities of high bend strength material. The metrology of Y-TZP mesoscale bend bars produced using a novel lost mold-rapid infiltration-forming process (LM-RIF) is characterized over several process improvements. These improvements eliminate trapezoidal cross sections in the parts, reduce concave upper surfaces in cross section, and minimize warping along the long axis of 332 × 26 × 17 μm mesoscale bend bars. The trapezoidal cross sections of earlier, first-generation parts were due to the absorption of high-energy ultraviolet (UV) light during the photolithographic mold-forming process, which produced nonvertical mold walls that the parts mirrored. The concave upper surfaces in cross section were eliminated by implementing a RIFbuffing process. Warping during sintering was attributed to impurities in the substrate, which creates localized grain growth and warping as the tetragonal phase becomes destabilized. Precision in the part dimensions is demonstrated using optical profilometry on bend bars and a triangular test component. The bend bar dimensions have a 95% confidence interval of < ±1 μm, and the tip radius of the triangular test component is 3 μm, consistent with the UV-photolithographic process used to form the mold cavities. The average bend strength of the mesoscale Y-TZP bend exceeds 2 GPa with a Weibull modulus equal to 6.3.

“…Aspect ratios of 17:1 are standard for ASTM (2002), three point bend bars, however, surgical instrument designs require larger aspect ratios to withstand the deformation and force used in surgery. Aguirre et al (2008) show that 400 micron thick parts with an aspect ratio of 35:1 are feasible dimensions for surgical instruments. Therefore, it is necessary to improve the process to fabricate such parts for surgical instruments by increasing the dimensions.…”

Section: Lm-rif Processmentioning

confidence: 98%

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

Yuangyai

Nembhard

et al. 2009

IJNM

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.