Joseph E. Petrzelka

Static load-displacement behavior of PDMS microfeatures for soft lithography

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.

Advanced Process Planning for Subtractive Rapid Prototyping

Purpose – Subtractive rapid prototyping (SRP) uses layer‐based removal from a plurality of orientations in order to create geometry in a highly automated manner. However, unlike additive means, the method can be inefficient due to redundant cutting operations on previously machined regions. The purpose of this paper is to present process planning methods for SRP, specifically dealing with stock material management in multiple setup operations.Design/methodology/approach – Analysis of remaining stock material was performed by considering slices of respective stereolithography (STL) models. Further, an initial approximation was made of accessibility to enable iterative visibility analysis. The combination of these approaches led to efficient and fast algorithms. After analysis, the slices could be converted back to useful STL models through polyhedral reconstruction.Findings – This method of approximation yields results similar to exact geometry. Using remaining stock data from this approach leads to a sign...

Conventional machining methods for rapid prototyping and direct manufacturing

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.

Laser direct write system for fabricating seamless roll-to-roll lithography tools

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.

Emergent Structure Detection for Multi-Axis Machining

This paper examines the phenomenon of emergent structures that occur in the transient stock material during multi-axis rough machining from a plurality of fixed orientations. Taking the form of thin webs and strings, emergent structures are stock material conditions that can lead to catastrophic failure during machining, even when tool path verification is successful. We begin by discussing the motivation for use of fixed orientations in multi-axis machining using multiple automated setups via rotary axes, which enables fast processing and ‘first part correct’ machining. Next, we demonstrate how unintended emergent structures occur in this paradigm of machining and can lead to catastrophic failure of the tool or work piece. Our original work focuses on the problem of geometric detection of these structures during process planning and prior to tool path planning, to the end of altogether avoiding emergent structure formation. To quickly simulate the machining process, we present an object-space method for determining the transient state of stock material based on the inverse tool offset. To identify emergent structures within this transient stock state, we propose a metric based on the medial axis transformation. Finally, we present our implementation of these methods and demonstrate realtime computation appropriate for an optimization scheme to eliminate emergent structures. Our methods provide consistent and logical results, as demonstrated with several freeform component examples. This work enables the development of robust algorithms for autonomous tool path planning and machining in multi-axis environments.Copyright