Scaffold-based techniques are a vital assistance tool to support main structure and enhance the resolution of target structure. In this study, a custom-made micro-extrusion bioprinting system was built and utilized to fabricate different scaffold structures such as log-pile scaffold and two-ring scaffold. This approach showed tremendous potential because of its ability to produce microscale channels with almost any shape. We were able to fabricate these scaffolds by using a custom-made 3D bioprinter to print hydrogel solution, mostly composed of Pluronic F-127, then wash away hydrogen by phosphate buffer saline (PBS) after crosslinking of main structure. We were able to achieve the desired scaffold structure by feeding G-codes data into user interface (Pronterface) and then translating that model into a program that utilizes a customized programming language, which instructs the microfabrication printer nozzles to dispense the hydrogel at specific locations. This fundamental study will be used to print increasingly viable and complex tissue shapes with living cells.
The EFAB process was first presented at the SFF Symposium in 1998, at a very early stage of its development. Currently, the technology is able to produce complex 3-D devices-including mechanisms built pre-assembled-in production volumes, using a three-step process of selective electrodeposition of one metal, blanket electrodeposition of another metal, and planarization. Layer thickness is as small as 4 μm, minimum feature size is down to 10 μm, and linear tolerances are ~2 μm. Metals are biocompatible materials with mechanical properties similar to stainless steel. The technology enables new instruments for minimally-invasive surgical and interventional procedures.
Mesoscopic additive/subtractive material processing (Meso A/SMP) is a solid freeform fabrication technique capable of producing engineering parts in mesoscopic (100 micron to several millimeters) scales. This process integrates silicon processing, electroplating, hot pressing, casting, and traditional machining methods to provide opportunities for 3D layer fabrication and parallel production, and opportunity to build small dimension parts. The proposed approach overcomes material constraints in MEMS fabrication and current layered manufacturing processes. In this paper, various manufacturing strategies are discussed for generating engineering parts with mesoscopic dimensions. In particular, processes to build components of magnetic field based micro motors and 3D thin airfoils are described.
Combining the advantages of layered manufacturing and material removal processes, additive/subtractive solid freeform fabrication (A/S SFF) can build parts with complex shapes without compromising precision requirements. However, preparing material removal operations requires special expertise, which has in fact become one of the bottlenecks of the A/S SFF manufacturing process. To achieve automated planning, a shaping process planner is being developed based on 3D solid representation and a surface classification scheme. This planner can generate numeric control (NC) codes for CNC milling in an automatic fashion on non-undercut features of arbitrary 3D input geometry. Planning approaches are also presented in order to shape parts accurately and efficiently. The proposed shaping planner thus delivers on the promise of fully automated process planning in A/S SFF.
The new additive/subtractive technology (Shape Deposition Manufacturing) enhances Solid Freeform Fabrication (SFF) capability in producing near net-shape surface finish. This technology also builds parts in fewer layers compared with conventional layered manufacturing technology. However, to decompose a part into freeform layers usually requires expensive geometric computation. Also, to plan build sequences often requires human intervention because of the complicated spatial relationships among the freeform layers. At present decomposition and build sequence planning are both performed by experienced designers/users. In this paper, a novel decomposition approach based on surface splitting is proposed to facilitate computation and planning of the additive/subtractive SFF processes. The results shown in this paper are from models with 3D planar geometry. Continuous effort is devoted into extending and implementing this new approach for models with 3D freeform geometry.
process called Rapid Freeze Prototyping. This process builds a three-dimensional ice part by depositing and rapidly freezing water according to its CAD model in a layer-by-layer manner. It provides a means to build a solid part with the potential of better performance than other rapid prototyping processes, including use of cheap and clean material, potential to build accurate ice parts with excellent surface finish, and ease of building color and transparent parts. An experimental system with a low-temperature building environment, a three-axis positioning mechanism, a water feeding and extruding subsystem, and control hardware and software has been built. Experiments conducted on this system demonstrate the feasibility of making three-dimensional ice parts. A heat transfer analysis helps understand the freezing process and provides useful information to the selection of building parameters.
Mold Shape Deposition Manufacturing (Mold SDM) is being developed in order to fabricate complex structural ceramic parts such as components for miniature turbine engines. For this application, the ceramic parts must not only be strong, but they also must have high dimensional accuracy and superior surface quality. This paper presents current progress with process development and characterizes fabricated silicon nitride (Si3N4) parts including their surface quality, part density, isotropic shrinkage and build rate. The microstructure of the sintered parts has been characterized. Mechanical testing gave flexural strength values ranging from 400 to 800 MPa. The isotropic linear shrinkage of 18±0.5% and best RMS surface roughness of 0.45 μm was observed. A number of process improvements that lead to better quality parts will also be described.
A new rapid tooling technique ElectroChemical Liquid Deposition Based Solid Freeform Fabrication (ECLD-SFF) was introduced in this paper. In the ECLD-SFF a substrate made of or coated with conductive materials is connected to a DC power supply, and the substrate is put into a plating bath. A very thin metal pin is connected to the DC power as a positive electrode. Between the substrate and the tip of the pin there is a thin layer of metal powder. Under the effects of electric field, metal ions from electrode moving to chemical liquid will deposit onto the powder particle and growing so that the metal particles can be bound by the deposited materials to form freeform solid. By controlling the pin's movement and electrified time, a desired 3-D shape will be built through layer by layer scanning. ECLD-SFF distinguishes itself from other SFF techniques with advantages of products: high build rate, high accuracy, high density, low shrinkage and controllable microstructures. It has been found that the electrochemical deposition among metal particles during ECLD-SFF is a fractal growth process. The fractal dimension and the width of the deposited metal band are all related to electric field density, composition of electroplating liquid and processing time. Several models on the fractal growth between electrodes or metal particles were developed in order to explain these fractal growth phenomena and obtain desired process parameters and conditions for the ECLD-SFF process.
Processing of non-random porous ceramic structures via fused deposition process is discussed. These structures are characterized experimentally and statistically based on their compressive strength. Finite element modeling is used to understand the effect of stress concentration leading to the strength degradation of these brittle elastic solids.
Layered Manufacturing processes accumulate residual stresses during material build-up. These stresses may cause part warping and layer delamination. This paper presents work done on investigating residual stress accumulation and part distortion of Layered Manufactured ar-tifacts. A simple analytical model was developed and used to determine how the number of layers and the layer thickness influences part warping. Results show that thin layers produce lower part deflection as compared with depositing fewer and thicker layers. In addition to the analytical work, a finite element model was developed and used to investigate the deposition pattern's influence on the part deflection. Finite element model and corresponding experimental analysis showed that the geometry of the deposition pattern significantly affects the resulting part distortion. This finite element model was also used to investigate an inter-layer surface defect, known as the Christmas Tree Step, that is associated with Shape Deposition Manufacturing. Results indicate that the features of this defect are influenced only by the material deposited close to the part surface and the particular material deposited. The step is not affected by the deposition pattern.
This paper presents the recent redesign of a tangent-cutting machine for CAM-LEM (Computer-Aided Manufacturing of Laminated Engineering Materials). Our former 5-axis, serial-joint, open-chain mechanism for laser cutting has been reduced to two parallel, 2-axis kinematic chains and articulated optics. The redesign results in lower inertias, higher stiffnesses, and less calibration sensitivity to homing and misalignment of axes. As a result, the system has higher acceleration capability, higher tracking bandwidth (translating into faster laser cutting) and greater precision, enabling improved build rates. The new design is presented, along with experimental evaluation of the performance improvements. Performance improvements are quantified in terms of calibration sensitivity, tracking bandwidth, and resonant frequencies.
The Fused Deposition of Metals (FDMet) technique has been developed to directly fabricate complex functional components. The goals of this study are to successfully fabricate reasonably long filament which could be used to successfully fabricate parts using FDMet, and to optimize the build parameters in the fused deposition technology specifically for metals. In this research, two types of stainless steel powders (spherical and irregular) were investigated. The issues related to filament fabrication and FDMet were investigated. A number of parts have been successfully fabricated (FDMet) using about a foot long filament. The parts are currently being characterized and evaluated.
Muscle-like actuators have been made from bilayers of crosslinked polyacrylamide and polyacrylic acid hydrogels sandwiched between electrodes. The polyacrylic acid responds to applied positive polarity field by contracting and expelling water which is taken up by the polyacrylamide layers. Previous studies have shown that the effective swelling modulus of polyacrylamide is much lower than polyacrylic acid. Hence the polyacrylamide acts as a sponge. As the polyacrylic acid layer contracts in the x, y and z directions the polyacrylamide is also pulled in on x and y, so that the whole stack becomes narrower and expands along the z- axis. Reversing the field reverses this effect with a time constant of about 1 minute for 1 mm thick layers with a thickness change of about 10%. Linear changes up to 50% have been obtained. Other gel actuators either transfer water across a sheet and so bend, or contract by expelling water. This new system shows a linear contraction and expansion without a volume change and so can be run (sealed) in a dry environment.
Fast Freeform Fabrication (FFF) is widely used in the casting industry, for tooling in sand casting, investment casting and die casting to save time and to take advantage of the variety of build materials, e.g. polymer, paper, ABS plastics, powder, wax and so on. A FFF process chosen to make patterns or cores depends on the nature of the casting processes, the availability and capability of the FFF machines among other requirements, e.g. production volume, accuracy, time, cost, and durability. This paper investigates applications of FFF in foundry processes. Issues discussed include the application of FFF models and the limitations and frontiers of those applications.
The significant cycle-time improvements and geometrical capabilities of solid freeform fabrication systems have led to applications in sand casting industry for design verification and tooling. The time and cost effective deployment of rapid tooling processes using rapid prototyping technology has thus becoming an emerging area to be studied. To make full use of the advantages of rapid prototyping processes, the factors influencing the tooling approach must be identified and understood. This understanding is then used to develop a decision-making structure for RP process selection for rapid tooling in sand casting. In this manuscript we review our work in evaluating and building a framework for tooling process selection for sand casting.
The Sand-Painter project addresses the problem ofpointwise deposition ofmulti-material powders in layered manufacturing. This approach is key to the development of selective aggregation processes capable ofproducing functional prototypes with internal sub-structures not achievable by any of the extant layered manufacturing processes. The solution adopted for this project is an automated version of the ancient Native American art of sand painting. Preliminary results pertaining to powder flow and deposition characterization are presented. A proof of concept multi-material deposition process was demonstrated.
This paper introduces some results of a research work carried out on the automation of digitization process of complex parts using a precision 3D-laser sensor.It will be presented st new way to scan automatically a complex 3-D part in order to measure and to compare the acquired data with the reference CAD model. Due to the fact that rapid prototyping processes do not allow the direct manufacturing of high precision parts, it is very often necessary to measure a first part in order to modify the process parameters.After introducing the digitization means, based on a CMM machine and a plane laser sensor, the simulation environment will be presented as adapted for simulation and validation of 3D-laser scanning paths. The CAPP (Computer Aided Process Planning) system used for the automatic generation of the laser scanning process will also be introduced.
This paper introduces a knowledge-based system for the choice of rapid product development processes.Rapid product development processes are not limited to layer-manufacturing machines, but they also integrate CAD, reverse engineering, indirect methods for metallic and plastic part manufacturing, etc...Due to short delays, people have no time to test and compare different solutions of rapid product development processes. Even if people have no time, tests are time and money consuming. It is also very difficult for somebody to know all about industrial technologies, and to be able to evaluate a multi-criteria choice in a short time.The aim of the proposed knowledge-based system is to generate, from the specification of parts or tools, different alternatives of rapid product development processes, which can be discriminated and optimized when considering a combination of the different specification criteria (cost, quality, delay, etc...).
Two techniques were studied in an effort to direct write diamond-like carbon (DLC) films. The first process employed a pulsed YAG laser to decompose a frozen precursor and deposit thin films directly on SiC and 304 stainless steel. After the initial film is deposited, additional layers may be subsequently condensed and deposited onto the substrate. A second approach is considered, whereby, the pulsed YAG is used to ablate the frozen precursor target and deposit a film on a nearby SiO(2) substrate that was locally heated by a CO(2) laser in an effort to augment the surface reaction rates.
Silicon carbide has long been recognized as an ideal material for applications where superior attributes such as stiffness and hardness, strength atelevatedtemperatures, high thermal conductivity, low coefficient of thermal expansion and resistance to. corrosion, oxidation, wear and abrasion are of primary value. Silicon carbide or its composites for structural applications are usually fabricated using hot pressing (HP), sintering, reaction sintering, pressureless sintering, or hot isostatic pressing (IDPing). All these belong to powder metallurgy approach. To reduce processing temperature and/or processing time, the second phase is almost widely strategically used in above techniques. In •other words, the "impurity" materials, at least two phases, act to compromise the true performance of the silicon carbide. For example, some reaction bonded SiC contains as much as 40% second phase. This, of course, is not a case in the electronic applications of SiC where high purity SiC is required. It is also obvious that using powder metallurgy is difficult to produce SiC parts with a complex shape because of its high hardness and low toughness. Selective area laser deposition (SALD) is a unique technique for fabricating complex ceramic shapes, tailoring functionally graded structures and embedding in-situ sensors into ceramic parts. In general, high deposition rate is desired. For the case of fabricating in-situ sensors, the chemical composition must also be controlled. Proper shapes and deposition rate using tetramethylsilane (TMS) precursor to deposit SiC has been demonstrated in previous studies 1-3. However, carbon contamination has been found •• to ·be a potential obstacle for the further application of this precursor in sensor-related fabrication. It has been suggested using the thermodynamic calculation that hydrogen has significant effect on the composition of SiC deposits 4. In this study, therefore, the effect of hydrogen on the SALD SiC will be experimentally evaluated.
