An in-depth understanding of the liquid transport in roll-based printing systems is essential for... more An in-depth understanding of the liquid transport in roll-based printing systems is essential for advancing the roll-based printing technology and enhancing the performance of the printed products. In this study, phase-field simulations are performed to characterize the liquid transport in roll-based printing systems, and the phase-field method is shown to be an effective tool to simulate the liquid transport. In the phase-field simulations, the liquid transport through the ink transfer rollers is approximated as the stretching and splitting of liquid bridges with pinned or moving contact lines between vertically separating surfaces. First, the effect of the phase-field parameters and the mesh characteristics on the simulation results is examined. The simulation results show that a sharp interface limit is approached as the capillary width decreases while keeping the mobility proportional to the capillary width squared. Close to the sharp interface limit, the mobility changes over a...
Journal of Micromechanics and Microengineering, 2015
Micro/nano hot-embossing and injection molding are two promising manufacturing processes for the ... more Micro/nano hot-embossing and injection molding are two promising manufacturing processes for the mass production of workpieces bearing micro/nanoscale features. However, both the workpiece and micro/nano-mold are susceptive to structural damage due to high thermal stress, adhesion and friction, which occur at the interface between the workpiece and the mold during these processes. Hence, major constraints of micro/nano-molds are mainly attributed to improper replication and their inability to withstand a prolonged sliding surface contact because of high sidewall friction and/or high adhesion. Consequently, there is a need for proper surface coating as it can improve the surface properties of micro/nano-molds such as having a low friction coefficient, low adhesion and low wear rate. This review deals with the physical, mechanical and tribological properties of various surface coatings and their impact on the replication efficiency and lifetime of micro/nano-molds that are used in micro/nano hot-embossing and injection molding processes.
There is shift in trend towards the use of high quality polymers as the base material in manufact... more There is shift in trend towards the use of high quality polymers as the base material in manufacturing microfluidic chips. In this paper, an amorphous metallic alloy mold insert was used in a micro injection-molding process to fabricate microfluidic features onto cyclic-olefin-copolymer (COC) material. The insert and fabricated samples were compared in terms of the geometry and surface roughness attained. Findings indicate that replication, in general, was possible but the microfeatures formed had significant flashing and tearing at the edges. Singapore-MIT Alliance (SMA)
In this paper, a model for transverse web vibration in a roll-to-roll system is presented. Web ax... more In this paper, a model for transverse web vibration in a roll-to-roll system is presented. Web axial tension and web axial speed, decisive parameters in the equation of motion that describes web vibration, are rigorously obtained by considering the two rolls-web coupled system’s dynamics, coupled with the equation of motion. According to the present analysis, the idealized simply-supported boundary conditions, commonly used in studies on vibrations of axially moving structures are not needed. Instead, a mathematical model comprised of the governing equation of web transverse vibration and the roll angular velocity – web axial tension relationship is solved as a coupled system. A finite-difference based algorithm is used for solving the coupled system of differential equations. It is worth noting that the web axial speed and web-transmitted tension are not constants when a certain amount of the web material is transferred from the unwinding roll to the winding roll; they vary nonline...
Volume 14: Emerging Technologies; Safety Engineering and Risk Analysis; Materials: Genetics to Structures, 2015
Soft-lithography, or the printing of self-assembling molecular inks at micro or sub-micron scale ... more Soft-lithography, or the printing of self-assembling molecular inks at micro or sub-micron scale holds the promise of large-scale surface patterning for a variety of applications. One key to the ultimate utility of this concept is continuous roll-to-roll printing on lost-cost flexible substrates. Accordingly, this paper discusses the basic processes involved in roll-to-roll printing of octadecylphosphonic acid (ODPA) on aluminum-coated PET substrates using novel cylindrical stamps cast from PDMS. In addition to printing, visualization of the pattern is achieved through controlled condensation of water vapor and by a post-printing acid etch. By using a roll-to-roll configuration, along with continuous stamps and measurements that can permit real-time online quality monitoring, this method represents a significant step forward in making soft lithography a commercially viable process.
ABSTRACT In this paper, three metallic mould inserts for fabrication of polymer microfluidic devi... more ABSTRACT In this paper, three metallic mould inserts for fabrication of polymer microfluidic devices were produced using different methods. Firstly, metallic glass mould insert was cut by high speed micro-milling. Secondly, 316L stainless steel mould insert was made by micro metal injection moulding (μMIM) using D50 = 4 μm powder. Finally, 316L stainless steel powder with a smaller particle size of D50 = 2 μm was used to produce mould insert in order to improve surface quality of the mould insert. The geometry and surface roughness of micro-features on the three mould inserts are viewed and compared.
An in-depth understanding of the liquid transport in roll-based printing systems is essential for... more An in-depth understanding of the liquid transport in roll-based printing systems is essential for advancing the roll-based printing technology and enhancing the performance of the printed products. In this study, phase-field simulations are performed to characterize the liquid transport in roll-based printing systems, and the phase-field method is shown to be an effective tool to simulate the liquid transport. In the phase-field simulations, the liquid transport through the ink transfer rollers is approximated as the stretching and splitting of liquid bridges with pinned or moving contact lines between vertically separating surfaces. First, the effect of the phase-field parameters and the mesh characteristics on the simulation results is examined. The simulation results show that a sharp interface limit is approached as the capillary width decreases while keeping the mobility proportional to the capillary width squared. Close to the sharp interface limit, the mobility changes over a...
Journal of Micromechanics and Microengineering, 2015
Micro/nano hot-embossing and injection molding are two promising manufacturing processes for the ... more Micro/nano hot-embossing and injection molding are two promising manufacturing processes for the mass production of workpieces bearing micro/nanoscale features. However, both the workpiece and micro/nano-mold are susceptive to structural damage due to high thermal stress, adhesion and friction, which occur at the interface between the workpiece and the mold during these processes. Hence, major constraints of micro/nano-molds are mainly attributed to improper replication and their inability to withstand a prolonged sliding surface contact because of high sidewall friction and/or high adhesion. Consequently, there is a need for proper surface coating as it can improve the surface properties of micro/nano-molds such as having a low friction coefficient, low adhesion and low wear rate. This review deals with the physical, mechanical and tribological properties of various surface coatings and their impact on the replication efficiency and lifetime of micro/nano-molds that are used in micro/nano hot-embossing and injection molding processes.
There is shift in trend towards the use of high quality polymers as the base material in manufact... more There is shift in trend towards the use of high quality polymers as the base material in manufacturing microfluidic chips. In this paper, an amorphous metallic alloy mold insert was used in a micro injection-molding process to fabricate microfluidic features onto cyclic-olefin-copolymer (COC) material. The insert and fabricated samples were compared in terms of the geometry and surface roughness attained. Findings indicate that replication, in general, was possible but the microfeatures formed had significant flashing and tearing at the edges. Singapore-MIT Alliance (SMA)
In this paper, a model for transverse web vibration in a roll-to-roll system is presented. Web ax... more In this paper, a model for transverse web vibration in a roll-to-roll system is presented. Web axial tension and web axial speed, decisive parameters in the equation of motion that describes web vibration, are rigorously obtained by considering the two rolls-web coupled system’s dynamics, coupled with the equation of motion. According to the present analysis, the idealized simply-supported boundary conditions, commonly used in studies on vibrations of axially moving structures are not needed. Instead, a mathematical model comprised of the governing equation of web transverse vibration and the roll angular velocity – web axial tension relationship is solved as a coupled system. A finite-difference based algorithm is used for solving the coupled system of differential equations. It is worth noting that the web axial speed and web-transmitted tension are not constants when a certain amount of the web material is transferred from the unwinding roll to the winding roll; they vary nonline...
Volume 14: Emerging Technologies; Safety Engineering and Risk Analysis; Materials: Genetics to Structures, 2015
Soft-lithography, or the printing of self-assembling molecular inks at micro or sub-micron scale ... more Soft-lithography, or the printing of self-assembling molecular inks at micro or sub-micron scale holds the promise of large-scale surface patterning for a variety of applications. One key to the ultimate utility of this concept is continuous roll-to-roll printing on lost-cost flexible substrates. Accordingly, this paper discusses the basic processes involved in roll-to-roll printing of octadecylphosphonic acid (ODPA) on aluminum-coated PET substrates using novel cylindrical stamps cast from PDMS. In addition to printing, visualization of the pattern is achieved through controlled condensation of water vapor and by a post-printing acid etch. By using a roll-to-roll configuration, along with continuous stamps and measurements that can permit real-time online quality monitoring, this method represents a significant step forward in making soft lithography a commercially viable process.
ABSTRACT In this paper, three metallic mould inserts for fabrication of polymer microfluidic devi... more ABSTRACT In this paper, three metallic mould inserts for fabrication of polymer microfluidic devices were produced using different methods. Firstly, metallic glass mould insert was cut by high speed micro-milling. Secondly, 316L stainless steel mould insert was made by micro metal injection moulding (μMIM) using D50 = 4 μm powder. Finally, 316L stainless steel powder with a smaller particle size of D50 = 2 μm was used to produce mould insert in order to improve surface quality of the mould insert. The geometry and surface roughness of micro-features on the three mould inserts are viewed and compared.
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Papers by David Hardt