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

Real Time Video Microscopy for the Fused Deposition Method

Fused deposition is a layered manufacturing technology, which is being investigated for fabrication of functional parts. Defects and voids in the build process affect the quality andlevel of accuracy of components. These occur due to several factors, such as the.toolpath contours in a layer, material(s) deposited, and the environmental/conditions. For a functional part to be constructed, a perfect green part is critical. To further understand this process, a visualization of the deposition is needed. Therefore, we have developed a real-time. video microscopy system. The hardware has been constructed and mounted on theexistingliquifier.·Real time deposition·of layered manufacturing is being recorded. Three materials being investigated are: PZT, silicon nitride, and wax. The contrast in wax layering is not as strong, which·makes•• visual observation extremely hard. However, interaction between the roads of PZT and silicone nitride parts has been successfully quantified. Using the current set. up and software, the raod width and height have been quantified.Mechanical Engineerin

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

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

Evaluation of Pseudo-Haptic Interactions with Soft Objects in Virtual Environments

This paper proposes a pseudo-haptic feedback method conveying simulated soft surface stiffness information through a visual interface. The method exploits a combination of two feedback techniques, namely visual feedback of soft surface deformation and control of the indenter avatar speed, to convey stiffness information of a simulated surface of a soft object in virtual environments. The proposed method was effective in distinguishing different sizes of virtual hard nodules integrated into the simulated soft bodies. To further improve the interactive experience, the approach was extended creating a multi-point pseudo-haptic feedback system. A comparison with regards to (a) nodule detection sensitivity and (b) elapsed time as performance indicators in hard nodule detection experiments to a tablet computer incorporating vibration feedback was conducted. The multi-point pseudo-haptic interaction is shown to be more time-efficient than the single-point pseudo-haptic interaction. It is noted that multi-point pseudo-haptic feedback performs similarly well when compared to a vibration-based feedback method based on both performance measures elapsed time and nodule detection sensitivity. This proves that the proposed method can be used to convey detailed haptic information for virtual environmental tasks, even subtle ones, using either a computer mouse or a pressure sensitive device as an input device. This pseudo-haptic feedback method provides an opportunity for low-cost simulation of objects with soft surfaces and hard inclusions, as, for example, occurring in ever more realistic video games with increasing emphasis on interaction with the physical environment and minimally invasive surgery in the form of soft tissue organs with embedded cancer nodules. Hence, the method can be used in many low-budget applications where haptic sensation is required, such as surgeon training or video games, either using desktop computers or portable devices, showing reasonably high fidelity in conveying stiffness perception to the user

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

Fused Deposition of Ceramics: Progress Towards a Robust and Controlled Process for Commercialization

The feasibility of using the Fused Deposition ofCeramics (FDC) process to rapidly fabricate functional quality advanced ceramic components has been demonstratedl - 5 . This direct manufacturing technique, by eliminating the need for costly tooling, dramatically reduces functional prototype development time. This makes it suitable for small quantity production runs and complex parts. The move from 'feasibility" to a robust, reliable commercial fabrication tool requires that every aspect ofthe manufacturing be understood and brought under control. An overview ofthe five basic process steps in FDC: batch compounding, filament fabrication, fused deposition, binder burnout and sintering will be presented in light ofthis drive toward a robust process. Tools such as Statistical Process Control and Experimental Design techniques are being used to monitor, improve, and stabilize each step and sub-process. Hardware and software modifications have been made to the FD machine to effect the required changes. This paper will identify the remaining technical barriers to commercialization and our progress in addressing these issues.Mechanical Engineerin

MOLECULAR MODELING AS A VISUALIZATION TOOL IN DESIGN OF DNA CROSSLINKED POLYACRYLAMIDE

ABSTRACT Polymers such as polyacrylamide form a diverse class of biomaterials in use today. The experimental research performed by our group has demonstrated how a critical concentration of crosslinking DNA strands can lead to gel formation in the polyacrylamide. The removal or addition of DNA strands can reverse or significantly increase the stiffness and strength of the gel. DNA is a versatile material for the exploration of nanoscale structures because its hybridization chemistry is very specific. DNA crosslinked gels use end-modified DNA oligonucleotides in the gels. The ability to choose the base sequence in the DNA crosslinks offers an opportunity to engineer the nanoscale structure of this material. However, it is extremely difficult to visualize the sequence of events that occurs when DNA is crosslinked with polyacrylamide. Computer modeling is a tool that enables the researchers to study the structural aspects of the newly engineered DNA crosslinkers. In this study, polyacrylamide gel crosslinked with DNA has been assayed with respect to energy and size using AMBER 7.0 software [1]. Since DNA-crosslinked gels are likely to find a range of applications it is important to know how to tailor the gel composition for a particular application. It is also of interest to know what the composition is that would induce the greatest change in stiffness. The molecular models generated in AMBER survey the mechanical properties of the gel as a function of crosslinker density, polyacrylamide density, and crosslinker length. The structure of an equilibrium state is computed using an explicitly solvated model. Visual inspection of the model determines other mechanical properties of the gel and helps predict chemical interactions. A long-term goal of this work is to use computer assisted modeling techniques to guide the experiments, to predict linker stiffness, and to examine other mechanical properties of the DNA crosslinker

Fused Deposition of Ceramics (FDC) for Structural Silicon Nitride Components

Fused Deposition of Ceramics is aI! SFF tec~que based on comm~rcial FDMTM ~echno.logy, f?r fabrication of structural and functIonal cerannc components. ThIS study descnbes, ill detail, process improvements made in pre-FDC, FDC, and post-FDC fabrication steps to achieve functional properties in commercial GS-44 silicon nitride ?omponents. . Microstructural characterization of sintered FDC parts reveals microstructures simllar to convennonally processed silicon nitride material. Mechanical properties of FDC processed silicon nitride bend bars and toughness samples were evaluated. These property evaluation studies demonstrate that mechanical properties similar to commercial GS-44 silicon nitride materials can be achieved using FDC. The study also describes results achieved on fabrication of complex components from silicon nitride using FDC.Mechanical Engineerin