Brian K. Paul

Effect of Layer Thickness and Orientation Angle on Surface Roughness in Laminated Object Manufacturing

Abstract The laminated object manufacturing (LOM) process is a freeform fabrication process used to produce wood-like prototypes and patterns for manufacturing processes such as sand casting. Therefore, surface roughness is an important factor in the utility of LOM prototypes. This study investigated the source of surface roughness in the LOM process to offer insight into the in-process control of surface roughness. A full-factorial experiment was performed to investigate the effect of layer thickness and orientation angle on the centerline average surface roughness of LOM prototypes. Results show orientation angle and paper thickness to be statistically significant. Further, the nature of surface roughness in LOM was found to be different than the nature of surface roughness in other freeform fabrication processes such as stereolithography. Overall, this study indicates that the inprocess control of prototype surface roughness may be possible in LOM by gaining greater control of the working distance during processing.

Comparison of two passive microvalve designs for microlamination architectures

Two passive, one-way microvalves have been created for use in microlamination architectures. The microlamination procedures involve the forming, alignment and bonding of thin metal laminae. A prerequisite to the creation of the flapper valve was the capability for selective bonding so as not to bond the flapper mechanism to the valve seat. A microprojection welding process was developed to meet this requirement. Projections as small as 125 µm in height were used to fabricate the microflapper valve. A microfloat valve, which consists of a small disk that floats up and down within a valve cylinder, was also fabricated. A capacitive dissociation process was developed to separate the small disk from within the valve body. Pressure drop tests were performed across each valve in order to evaluate the theoretical orifice size and the ratio of forward to backward flow over a wide range of mass flow rates. Forward flow was detected in all valves at pressures as small as 20 Pa. The results indicate that the best performing valve was the microfloat valve, with a theoretical orifice size of 629 µm and an average ratio of forward to backward flow of 12.76. Reasons given for these results include the ability for floats to reorient themselves to seal against surface asperities along the valve seat.

Nanostructured ZnO as Biomimetic Anti-reflective Coatings on Textured Silicon Using a Continuous Solution Process

A novel table-top, microreactor-assisted nanomaterial deposition (MAND™) process, which combines the merits of microreaction technology with solution-phase nanomaterial synthesis and film deposition, was used to grow a nanostructured ZnO anti-reflective coating on a textured silicon substrate from aqueous solution. The subwavelength, anti-reflective nanostructures mimicked the structure and performance of the surface of the eye from a night-flying moth. Solution-processed Ag nanoparticles were applied as a seed layer on the textured silicon surface leading to preferred heterogeneous nucleation and good area coverage. Preferential growth of the nanostructured ZnO was controlled by changing residence time, reaction temperature, and concentration of precursor solution without the use of a buffer reagent (e.g. HMTA). Well-aligned ZnO nanorod arrays were fabricated by MAND at a very high deposition rate (i.e. 125 nm min−1) compared to batch hydrothermal method. The surface reflection of the polished silicon was suppressed from an average of 30.8% between wavelengths of 400 and 900 nm to 10.6% after micro-scale pyramidal surface texturing to 3.4% after application of the ZnO nanostructure on the textured silicon. The results provide a potential economical path to broadband anti-reflection (AR) for silicon wafers and solar cell substrates.

High-rate synthesis of phosphine-stabilized undecagold nanoclusters using a multilayered micromixer

Growth in the potential applications of nanomaterials has led to a focus on the development of new manufacturing approaches for these materials. In particular, an increased demand due to the unique properties of nanomaterials requires a substantial yield of high-performance materials and a simultaneous reduction in the environmental impact of these processes. In this paper, a high-rate production of phosphine-stabilized undecagold nanoclusters was achieved using a layer-up strategy which involves the use of microlamination architectures; the patterning and bonding of thin layers of material (laminae) to create a multilayered micromixer in the range of 25-250 µm thick was used to step up the production of phosphine-stabilized undecagold nanoclusters. The continuous production of highly monodispersed phosphine-stabilized undecagold nanoclusters at a rate of about 11.8 (mg s(-1)) was achieved using a microreactor with a size of 1.687 cm(3). This result is about 500 times over conventional batch syntheses based on the production rate per reactor volume.

Understanding Limits on Fin Aspect Ratios in Counterflow Microchannel Arrays Produced by Diffusion Bonding

This paper investigates the manufacturability limits of fin aspect ratios within two-fluid counter-flow microchannel arrays based on the stress state between laminae during diffusion bonding. In prior papers, it has been shown that the diffusion bonding of two-fluid systems by microlamination can result in regions of the device that do not directly transmit bonding pressure and, consequently, result in unbonded regions leading to device leakage. A finite element model is used to analyze the stress state between laminae during diffusion bonding. The stress state is used to determine the critical stress necessary for diffusion bonding to occur in areas not receiving direct bonding pressure. Model results are compared with experimental results over a wide range of counter-flow geometries. It has been found generally that a compressive stress state must exist in every part of the geometry in order to produce leak-free bonds. Implications of this finding on the design of two-fluid microchannel arrays are discussed. DOI: 10.1115/1.2280672

A Nickel Aluminide Microchannel Array Heat Exchanger for High-Temperature Applications

The miniaturization of microtechnology-based energy and chemical systems (MECS) is made possible by the manifold improvement in the heat and mass transfer performance of the system due to the high surface area to volume ratios of the microchannel arrays within the devices. It is desirable to perform many exothermic and endothermic chemical reactions above 650°C (e.g., gasoline steam reforming). At these temperatures, conventional engineering materials, such as stainless steel, are not functional. As a result, alternate microchannel materials are being investigated. Because of the high melting temperature and chemical inertness of nickel aluminide (NiAl), this paper introduces a fabrication procedure for NiAl microchannel arrays, including novel methods for material synthesis, NiAl machining, and NiAl bonding. NiAl microchannel arrays fabricated using this approach were tested for leakage and pressure drop. The research outcome indicated the viability of the proposed method in fabricating NiAl MECS devices.

Cost Drivers in Microlamination Based on a High-Volume Production System Design

The purpose of this research is to develop a cost estimation model in an attempt to begin exploring the current cost drivers for microlamination. To do this without actual cost information, a production system design is proposed for the high-volume production of MECS devices. Constraints on this facility are that it produces microlaminated structures from stainless steel diffusion bonding. Also, a cost estimation model is developed based on the known cycle time and capital equipment costs from the production system design. Finally, a sensitivity analysis is performed to determine the cost drivers under different market and product scenarios. Results from the sensitivity analysis indicated that device size and production rate do have an effect on the overall manufacturing cost of microlamination devices. Therefore, it is concluded that the emphasis of future research in metallic microlamination should focus on bonding larger laminae and in reducing both cycle time and warpage.Copyright

Application of Nickel Nanoparticles in Diffusion Bonding of Stainless Steel Surfaces

In this study, the effect of nickel nanoparticles (NiNPs) interlayer application to transient liquid-phase diffusion brazing was investigated. The primary focus was to bond stainless steel 316L laminae in a stack using a Nickel nanoparticles interlayer and to compare the bond line of the sample with the conventionally bonded and nickel-phosphorous interlayer (NiP) brazed samples for microstructure evolution and bond strength. The bonding was carried out in a vacuum hot press and the bonding parameters were kept same for all the samples: bonding temperatures 1000°C, bonding pressure 1000 psi, heating rate 10°C/min and dwell time of 2 hrs. The cross sections of the bonded samples were investigated for microstructure evolution using optical microscopy and scanning electron microscopy (SEM). The inter-diffusion of the diffusing species across the bond line (interface) was evaluated by wavelength dispersive spectroscopy (WDS). X-ray diffraction technique (XRD) is proposed to determine the formation of any brittle intermetallic phases along the bond line and transmission electron microscopy (TEM) to confirm the same. Bond strength will be measured with the help of samples bonded according to ASTM standards.Copyright

APPLICATION OF CONTROLLED THERMAL EXPANSION IN MICROLAMINATION FOR THE ECONOMICAL PRODUCTION OF BULK MICROCHANNEL SYSTEMS

Diffusion bonding has been widely used within microlamination architectures for the fabrication of micro energy and chemical systems (MECS). MECS are microsystems with the ability to process bulk amounts of fluid within highly parallel microchannel arrays capable of accelerated heat and mass transfer. Thus far, diffusion bonding of microchannel arrays is commonly done in a vacuum hot press system. The use of the hot press greatly restricts the production rate due to vacuum pump-down time and heating-up and cool-down periods. Furthermore, larger substrates are gaining interest in the system design of MECS devices, and it is not apparent that uniaxial pressing within a hydraulic vacuum hot press will provide the bonding pressure uniformity necessary for large substrate bonding. This article presents a novel fabrication approach for high-volume thermal bonding of MECS devices with the use of controlled thermal expansion. A thermal bonding fixture based on the principle of differential thermal expansion was developed with a focus on controlling the bonding pressure magnitude, the pressure timing, and its sensitivity. The application of such a fixture within a conveyorized furnace system could be the key to a continuous thermal bonding approach for the mass production of MECS devices.

Manufacturing of Smart Goods: Current State, Future Potential and Research Recommendations

Smart goods are everyday products with wireless connection to cloud computing enabling cost-effective strategies for embedded computation, memory and sensing. A 2015 workshop sponsored by the National Science Foundation and the Oregon Nanoscience and Microtechnologies Institute brought industry and academic leaders together in the Pacific Northwest to help identify future manufacturing research needs in this emerging industry. Workshop findings show that the impetus exists to drive the costs of smart goods lower and several technological challenges stand in the way. This paper summarizes the outcomes of the workshop including the current state of practice, future potential, technological gaps, and research recommendations to realize lower cost routes to manufacture smart goods. [DOI: 10.1115/1.4033968]