A New Feature in an Extrusion Based LM Process – Adaptive Roadwidth 399

For extrusion based LM processes, a computational based adaptive roadwidth algorithm have been developed which further reduces (if not eliminate) all voids and defects. Toolpath equations are written in terms of roadwidth, vector path offset, subperimeter offset, and vector angles. The program computes all contours and vector paths to fill a layer, the location and size of all voids/defects, and makes comparison with the acceptable void limits. Based on this information, the adaptive roadwidth for the vector paths are then created to minimize the voids and defects. This new feature is added to the existing in-house multi-material LM CAD software.Mechanical Engineerin

Virtual Simulation for Multi-material LM Process

In an ONR funded MURI program, to improve quality of multi-material parts, we've been developing an advanced computer simulation for the multi-material layered manufacturing (LM) process. The CAD models and their .stLfiles are created using. the commercially available software such as I-DEAS and ProE. Using this information, one tool path file per material is generated. Our file preparation algorithm, systematically, layer by layer, integrates all tool path files into one multi-material tool path file. The results of the multi-material tool path are graphically visualized using the simulation algorithm (written in c++ & SGI OpenGL). From a virtual simulation, we can check the LM process, and make the best selection of tool path parameters afterwards. After several trials from design to simulation, if the simulation result is acceptable, the real manufacturing can be started. And the part's quality should be better than a part manufactured without running simulation in advance. This paper will represent .•. new studies on using real toadshapes to get more realistic simulation results. Many parts have been successfully simulated using our method.Mechanical Engineerin

Development of DNA Based Active Macro–Materials for Biology and Medicine: A Review

DNA was first discovered as the carrier of genetic information for the majority of the known living organisms, encoding the secret of life. Its delicate design based upon double helical structure and base pairing offers a stable and reliable media for storing hereditary codes, laying the foundation for the central dogma (Watson et al. 2003). The impact of this molecule is far reaching into scientific community and our society, as manifested in many fields, for instance, forensics (Budowle et al. 2003), besides medicine. To date, a great deal of research effort has been directed towards understandin

High Quality, Fully Dense Ceramic Components Manufactured Using Fused Deposition of Ceramics (FDC)

Solid Freeform Fabrication (SFF) is a technology that produces physical solid components or parts from computer design models. This technology has the potential of reducing functional ceramic product development cycle time in terms of reducing design iteration and production time, minimizing extra post processing, and therefore reducing cost. A commercially available Fused Deposition Modeling (FDM™) 3D Modeler was altered for use with ceramics. This newly developed method referred to as Fused Deposition of Ceramics (FDC) is capable of fabricating complex shape, functional ceramic components. We have investigated issues related to hardware, software, feed material, and build strategy which are required to achieve high quality, fully dense green ceramic parts. In this paper, we report recent improvements made in the FDC process, including hardware modifications, software improvements, feed material standardization, as well as build strategy/condition control. We also report the current FDC status for making complex functional parts. Our goal is to optimize the FDC condition to ensure its robustness for producing defect free green ceramic parts consistently and without interruption.Mechanical Engineerin

A System Approach in Extrusion-Based Multi-Material CAD

For extrusion based multi-material Layered Manufacturing (LM) processes, a CAD system has been developed for the Fused Deposition of Multiple Ceramics (FDMC) hardware. This closed loop CAD system includes solid model design & multi-material slicing, multi-material toolpath generation and virtual simulation modules. Intelligent features and an adaptive roadwidth optimum toolpath generation algorithm compute void sizes & their location and generate a void free toolpath [1][2]. The present study focuses on a comprehensive approach, which includes a format that contains the information on the geometry of the multi-material components, the build materials and the necessary fabrication process information. Multi-CAD utilizes computer graphics techniques to visualize the fabricated part. The slicing algorithm is utilized to create multi-material contours, which then are integrated into our previously developed intelligent toolpath system.Mechanical Engineerin

Simultaneous Determination of Young\u27s Modulus, Shear Modulus, and Poisson\u27s Ratio of Soft Hydrogels

Besides biological and chemical cues, cellular behavior has been found to be affected by mechanical cues such as traction forces, surface topology, and in particular the mechanical properties of the substrate. The present study focuses on completely characterizing the bulk linear mechanical properties of such soft substrates, a good example of which are hydrogels. The complete characterization involves the measurement of Young\u27s modulus, shear modulus, and Poisson\u27s ratio of these hydrogels, which is achieved by manipulating nonspherical magnetic microneedles embedded inside them. Translating and rotating these microneedles under the influence of a known force or torque, respectively, allows us to determine the local mechanical properties of the hydrogels. Two specific hydrogels, namely bis-cross-linked polyacrylamide gels and DNA cross-linked polyacrylamide gels were used, and their properties were measured as a function of gel concentration. The bis-cross-linked gels were found to have a Poisson\u27s ratio that varied between 0.38 and 0.49, while for the DNA-cross-linked gels, Poisson\u27s ratio varied between 0.36 and 0.49. The local shear moduli, measured on the 10 μm scale, of these gels were in good agreement with the global shear modulus obtained from a rheology study. Also the local Young\u27s modulus of the hydrogels was compared with the global modulus obtained using bead experiments, and it was observed that the inhomogeneities in the hydrogel increases with increasing cross-linker concentration. This study helps us fully characterize the properties of the substrate, which helps us to better understand the behavior of cells on these substrates