This paper develops a general model for the load-displacement behavior of polymer microfeatures, such as those encountered in polydimethylsiloxane (PDMS) stamps for soft lithography. Soft lithography is an attractive low-cost method of patterning surfaces via selective mechanical contact, often by printing a molecular monolayer or depositing thin films. The fidelity of the transferred pattern is dependent on successful mechanical contact, however, the soft elastomers used for stamps can often collapse or buckle under moderate pressures. This work seeks to complement the existing understanding of collapse pressure with an understanding of the complete load-displacement behavior of the stamp features. A model is developed for feature stiffness by examining an analytical solution in the limits of very large or very small feature aspect ratios and computing intermediate behavior through a large set of finite element simulations. This model is subsequently validated with experimental load-displacement data. Analytical models are used to predict particular modes of collapse, showing excellent agreement with experimental observations.
This paper presents process planning methods for Subtractive Rapid Prototyping, which deals with multiple setup operations and the related issues of stock material management. Subtractive Rapid Prototyping (SRP) borrows from additive rapid prototyping technologies by using 2½D layer based toolpath processing; however, it is limited by tool accessibility. To counter the accessibility problem, SRP systems (such as desktop milling machines) employ a rotary fourth axis to provide more complete surface coverage. However, layer-based removal processing from different rotary positions can be inefficient due to double-coverage of certain volumes. This paper presents a method that employs STL models of the in-process stock material generated from slices of the part along the rotation axis. The developed algorithms intend to improve the efficiency and reliability of these multiple layer-based removal steps for rapid manufacturing. IntroductionSubtractive Rapid Prototyping (SRP) is a considerably lesser known and utilized form of rapid prototyping technology, mainly due to continued challenges in the pre-process engineering and setup planning required. Subtractive operations in general afford excellent accuracy and repeatability, which is why it is more often utilized as an additional function of a hybrid-type rapid prototyping system that includes both additive and subtractive operations. Since the early days of RP technology, with systems such as Laminated Object Manufacturing (LOM), subtractive means have been employed as part of a solution alongside the conventional additive layer-based approaches. Although perhaps not purely subtractive, in LOM, a laser was used to cut the profile and surrounding support structures of each layer, after the layer of paper is added. In this manner, the additive approach enabled improved geometric capability while the laser cutting offered reasonable shaping accuracy. Later, the Sanders Modelmaker system, now used heavily in jewelry and dental manufacturing, utilized a machining process to accurately mill each deposited layer to a precise thickness. In a research project, Shape Deposition Manufacturing (SDM) used 5-axis machining in conjunction with a variety of deposition approaches to create both parts and molds. More recently, systems such as LAMP and Ultrasonic Consolidation (UC) continue to use subtractive means in an iterative manner to improve accuracy and surface finish. Desktop milling machines suitable for rapid prototyping have been marketed for lower-end materials in single or multisided machining operations, while lower-end, but more user-friendly SRP software systems such as Millit and Deskproto have attempted to facilitate the NC programming for these applications. To date, subtractive processes continue to be utilized in a few RP systems, while SRP-only systems have had limited success. The overwhelming success of RP technologies to date can be attributed almost solely to the additive-only machines; however, there are niche applications where an SRP system would b...
Scaling contact lithography (microcontact printing, microflexography, and nanoimprint lithography) to large roll-to-roll platforms will enable high speed, low cost lithographic patterning of surfaces. However, many details of robust implementations at the roll-to-roll scale remain an engineering challenge, including precise regulation of printing pressures and the stamp-substrate interaction. This paper introduces a method for precise control of contact pressure that can accommodate large dimensional variations, i.e. varying stamp and substrate thicknesses. This control algorithm is implemented on a simply supported roll positioning stage. Experimental results for microcontact printing and microflexography are shown both with in situ contact measurements on a pseudo substrate and with 5 um silver nanoparticle prints. Ultimately, this approach enables robust printing despite sensitive stamp patterns and large dimensional variations (> 10 μm) in substrates, stamps, and roll equipment.
Implementations of roll to roll contact lithography require new approaches towards manufacturing tooling, including stamps for roll to roll nanoimprint lithography (NIL) and soft lithography. Suitable roll based tools must have seamless micro-or nano-scale patterns and must be scalable to roll widths of one meter. The authors have developed a new centrifugal stamp casting process that can produce uniform cylindrical polymer stamps in a scalable manner. The pattern on the resulting polymer tool is replicated against a corresponding master pattern on the inner diameter of a centrifuge drum. This master pattern is created in photoresist using a UV laser direct write system. This paper discusses the design and implementation of a laser direct write system targeting the internal diameter of a rotating drum. The design uses flying optics to focus a laser beam along the axis of the centrifuge drum and to redirect the beam towards the drum surface. Experimental patterning results show uniform coatings of negative photoresist in the centrifuge drum that are effectively patterned with a 405 nm laser diode. Seamless patterns are shown to be replicated in a 50 mm diameter, 60 mm long cylindrical stamp made from polydimethylsiloxane (PDMS). Direct write results show gratings with line widths of 10 microns in negative photoresist. Using an FPGA, the laser can be accurately timed against the centrifuge encoder to create complex patterns.
The material and product accuracy limitations of rapid prototyped products can often prevent the use of rapid prototyping (RP) processes for production of final end-use products. Conventional machining processes are well-developed technologies with the capability of employing a wide range of materials in the creation of highly accurate components. This paper presents an overview of how conventional machining processes can be used for RP and direct manufacturing processes. The methodologies of computer numerical control machining for rapid prototyping (CNC-RP) and wire electronic discharge machining for rapid prototyping (WEDM-RP) are presented in this paper. A general discussion of selection criteria and cost comparisons among both current additive RP and conventional machining approaches to rapid manufacturing are also presented.
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