Bone and cartilage constructs are often plagued with mechanical failure, poor nutrient transport, poor tissue ingrowth, and necrosis of embedded cells. However, advances in computer aided design (CAD) and computational modeling enable the design of scaffolds with complex internal michroarchitectures and the a priori prediction of their transport and mechanical properties, such that the design of constructs satisfying the needs of the tissue environment can be optimized. The goal of this research is to investigate the capability of additive manufacturing technologies to create designed microarchitectured tissue engineering scaffolds for bone and cartilage regeneration. This goal will be achieved by pursuing the following two objectives: (1) the manufacture of bioresorbable thermoplastic scaffolds by selective laser sintering (SLS) (2) and the manufacture of hydrogel scaffolds by large area maskless photopolymerization (LAMP). SLS is a laser based additive manufacturing method in which an object is built layer-by-layer by fusing powdered material using a computer-controlled scanning laser. LAMP is a massively parallel ultraviolet curing-based process that can be used to create hydrogels from a photomonomer on a large-scale (558x558mm) while maintaining extremely high feature resolution (20µm). In this research, SLS is used to process polycaprolactone (PCL) and composites of PCL with hydroxyapatite (HA) for bone tissue engineering applications while LAMP is used to process polyethylene glycol diacrylate (PEGDA) which can be used for hard and soft tissue applications.

In current production systems, automation and handling of workpieces is often solved by use of vacuum technology. Most production systems use vacuum ejectors which generate vacuum from compressed air by means of the Venturi effect. However, producing vacuum with compressed air is significantly less efficient than using other principles. To minimize the energy costs of pneumatic vacuum generation or to make full use of the energy available, it is important that the inner contour of the nozzle is shaped precisely to suit the specific application - also the system\'s flow conduction needs to be optimal and the flow losses have to be minimized. This paper presents a method for optimally designing pneumatic vacuum generators and producing them economically even at very low lot sizes in order to keep the operation costs low and address other concerns (such as noise emissions) as well.

Scanning Laser Epitaxy (SLE) is a new laser-based layer-by-layer generative manufacturing technology being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. SLE allows creation of geometrically complex three-dimensional components with as-desired microstructure through controlled melting and solidification of stationary metal-alloy powder placed on top of like-chemistry substrates. The proposed research seeks to garner knowledge about the fundamental physics of SLE through simulation-based studies and apply this knowledge for hot section turbine component repair and ultimately extend the process capability to enable one-step manufacture of complex gas turbine components. Prior methods of repair specifically for hot-section Ni-base superalloys have shown limited success, failed to consistently maintain epitaxy in the repaired part and suffered from several mechanical and metallurgical defects. The use of a fine focused laser beam, close thermal control and overlapping raster scan pattern allows SLE to perform significantly better on a range of so-called “non-weldable” Ni-base superalloys. The process capability is expanded further through closed-loop feedback control of melt pool temperature using an infra-red thermal camera. The process produces dense, crack-free and epitaxial deposit for single-crystal (SX) (CMSX4), equiaxed (René-80, IN 100) and directionally solidified (DS) (René-142) Ni-based superalloys. However, to enable consistent and repeatable production of defect-free parts and future commercial implementation of the technology several concerns related to process capabilities and fundamental physics need to be addressed. To explore the process capability, the fabricated components are characterized in terms of several geometrical, mechanical and metallurgical parameters. An active-contour based image analysis technique has been developed to obtain several microstructural responses from the optical metallography of sample cross-sections and the process goes through continuous improvement through optimization of the process parameters through subsequent design of experiments. The simulation-based study is aimed at developing a multiphysics model that captures the fundamental physics of the fabrication process and allows the generation of constitutive equations for microstructural transitions and properties. For this purpose, a computational fluid dynamics (CFD) finite-volume solver is used to model the melting and solidification process. The development work also focuses on studying process response to different superalloy materials and implementing a multivariate statistical process control that allows efficient management and optimization of the design parameter space. In contrast to the prior work on single-bead laser scan, the model incorporates the raster scan pattern in SLE and the temperature dependent local property variations. The model is validated through thermal imaging data. The flow-thermal model is further tied to an empirical microstructural model through the active-contour based optical image analysis technique, which enables the identification of several microstructural transitions for laser beam describing a raster scan pattern. The CFD model can effectively be coupled with finite element solver to assess the stress and deformation and can be coupled with meso-scale models (Cellular Automata) to predict different microstructural evolutions. The research thus allows extending the SLE process to different superalloy materials, performs statistical monitoring of the process, and studies the fundamental physics of the process to enable formulation of constitutive relations for use in closed-loop feedback control; thus imparting ground breaking capability to SLE to fabricate superalloy components with as-desired microstructures.

ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / Functionally testing missiles in the All Up Round (AUR), a configuration that consists of a complete system packaged in its flight worthy state, requires the use of test sets along with constituent conformal equipment for interfacing. During developmental testing, telemetry (TM) sections are integrated within an AUR missile. These test sets monitor TM unit performance while maintaining form, fit, and function; therefore, resulting in complete data confidence. Initiating TM functional tests permit a capability in verifying that TM sections have been integrated properly. Safety being a priority, in order to attenuate RF radiation leakage while providing repeatable test capabilities in the near-field, antenna couplers are fabricated as a shielding interface between the user and radiating source and a coupling interface between an AUR missile and the test set. Generally, antenna couplers are composed of metallic bodies which require machine shop fabrication. The process of getting machined parts can take up to several months which can delay delivery schedules. With the availability of 3D printing capabilities and methods in metalizing various materials, a novel approach to fabricating antenna couplers has been explored. The use of modeling Software Packages (Computer Aided Design and Electromagnetic Solvers) and additive printing play key roles in reducing the development cycle time while saving costs, decreasing weight, and sustaining performance. This paper will detail the efforts using 3D printing capabilities in the development and fabrication of an antenna coupler with several examples cited herein.

The desktop publishing revolution of the 1980s is currently repeating itself in 3D, referred to as desktop manufacturing. Online services such as Shapeways have become available, making personalized manufacturing on cutting edge additive manufacturing (AM) technologies accessible to a broad audience. Affordable desktop printers will soon take over, enabling people to fabricate / Engineering and Applied Sciences

Titanium (Ti) alloys have been commonly used in the aerospace industry, not only because they have a high strength-to-weight ratio (comparing to the steels) but also their satisfactory corrosion resistance. Furthermore, they can be assembled with the carbon fibre composite parts. However, conventional manufacturing methods cause high material scrap rate and require lots of machining to obtain the final shape and size, which increases both the manufacturing time and cost. In order to improve the efficiency and reduce the cost of Ti parts, Additive Manufacturing (AM) has been developed. Rolled Wire and Arc Additive Manufacturing (rolled WAAM) is one of the AM processes. The main characteristics of this technology is the reduced β grain size to refine the alloy's microstructure. Both the ultimate tensile strength and yield strength of Ti alloy made by rolled WAAM are at least 10% higher than traditional wrought Ti. This project is to investigate the fatigue crack growth rates of the Ti-6Al-4V built by rolled WAAM process in both the longitudinal and transverse orientations to study the effect of rolling on fatigue crack growth rate of WAAM processed Ti. The project was carried out by testing the fatigue crack growth rates for 4 compact tension specimens. The test results of different orientations were compared with each other, and scatters in fatigue life and fatigue crack growth rate were found. Fatigue crack growth rate is lower in the longitudinal specimens. The results are also compared with those of the unrolled WAAM specimens tested in a previous project. It was found that rolling can significantly improve the fatigue crack growth behaviour in WAAM processed Ti, and can reduce the difference between the two orientations, i.e. achieving better isotropic material properties. Recorded scatters may be caused by the process induced residual stresses, error in measurement, and the test machine load range being much higher than the applied loads. More specimens can be tested to validate above observations further.

Inkjet printing (jetting) technology, due to its high speed of operation and accuracy, is utilised in Additive Manufacturing (AM) of three dimensional parts. Commercially available AM processes that use jetting technology include three dimensional printing (3DP by Z-Corporation), Polyjet (by Objet), Multi Jet Modelling (MJM by 3D Systems) and three dimensional printing by Solidscape. Apart from 3D Printing by Z-corporation, all the other jetting based processes require a support material to successfully build a part. The support material provides a base to facilitate the removal of the part from the build platform and it helps manufacturing of cavities, holes and overhanging features. These support materials present challenges in terms of their removability and reusability. This research is therefore, aimed towards finding a support material composition that can be used with jetting based AM processes. The support material should be easily removable either by melting or by dissolution and also, if possible, it should be reusable. AM processes often process materials with poor mechanical properties and therefore, the parts produced by these processes have limited functionality. In an attempt to obtain complex shaped, functional parts made of nylon (i.e. Polyamide 6), a new jetting based AM process is under research at Loughborough University. The process uses two different mixtures of caprolactam (i.e. the monomer used to produce polyamide). These mixtures are to be jetted using inkjet heads and subsequently polymerised into polyamide 6. Therefore, another aim of this research was to consider the support material s suitability for jetting of caprolactam. Two different polymers were researched which included Pluronic F-127 and methylcellulose (MC). Both these polymers are known for gel formation upon heating in aqueous solutions. Due to the inhibition of polymerisation of polyamide 6 by the presence of water, non-aqueous solvents such as ethylene glycol, propylene glycol and butylene glycol were studied. Since both F-127 and MC in the glycols mentioned above had not been studied before, all the compositions prepared and investigated in this report were novel. F-127 did not show gel formation in propylene and butylene glycol but formed a gel in ethylene glycol at a concentration of 25% (w/w) F-127. MC, on the other hand, showed gel formation upon cooling in all the three glycols at concentrations as low as 5% for ethylene glycol and 1% for both propylene and butylene glycol. These compositions were characterized using experimental techniques such as Fourier Transform Infrared (FTIR) spectroscopy, hot stage microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A mechanism of gelation for both F-127 and MC in glycols is presented based on the results of these characterisation techniques. Viscosity and surface tension measurements along with the texture analysis of selected compositions were also performed to evaluate their suitability for jetting. All these compositions, due to their water solubility and/or low melting temperatures (i.e. near 500C) present the advantage of ease of removal. Removal by melting at low temperatures can also provide reusability of these support materials and thus advantages such as reduction in build cost and environmental effect can be achieved.

Additive Manufacturing (AM) refers to the use of a group of technologies capable of combining material layer-by-layer to manufacture geometrically complex products in a single digitally controlled process step, entirely without moulds, dies or other tooling. AM is a parallel manufacturing approach, allowing the contemporaneous production of multiple, potentially unrelated, components or products. This thesis contributes to the understanding of the economic aspects of additive technology usage through an analysis of the effect of AM s parallel nature on economic and environmental performance measurement. Further, this work assesses AM s ability to efficiently create complex components or products. To do so, this thesis applies a methodology for the quantitative analysis of the shape complexity of AM output. Moreover, this thesis develops and applies a methodology for the combined estimation of build time, process energy flows and financial costs. A key challenge met by this estimation technique is that results are derived on the basis of technically efficient AM operation. Results indicate that, at least for the technology variant Electron Beam Melting, shape complexity may be realised at zero marginal energy consumption and cost. Further, the combined estimator of build time, energy consumption and cost suggests t AM process efficiency is independent of production volume. Rather, this thesis argues that the key to efficient AM operation lies in the user s ability to exhaust the available build space.

This research introduces a method to aid the design of products or parts to be made using Additive Manufacturing (AM), particularly the laser sintering (LS) system. The research began with a literature review that encompassed the subjects of design and AM and through this the need for an assistive design approach for AM was identified. Undertaking the literature review also confirmed that little has been done in the area of supporting the design of AM parts or products. Preliminary investigations were conducted to identify the design factors to consider for AM. Two preliminary investigations were conducted, the first investigation was conducted to identify the reasons for designing for AM, the need for a design support tool for AM and current challenges of student industrial designers designing parts or products for AM, and also to identify the type of design support they required. Further investigation were conducted to examine how AM products are developed by professional industrial designers and to understand their design processes and procedures. The study has identified specific AM enabled design features that the designers have been able to create within their case study products. Detailed observation of the case study products and parts reveals a number of features that are only economical or possible to produce with AM. A taxonomy of AM enabled design features was developed as a precursor for the development of a computer based design tool. The AM enabled design features was defined as a features that would be uneconomical or very expensive to be produced with conventional methods. The taxonomy has four top-level taxons based on four main reasons for using AM, namely user fit requirements, improved product functionality requirements, parts consolidation requirements and improvement of aesthetics or form requirements. Each of these requirements was expanded further into thirteen sub categories of applications that contained 106 examples of design features that are only possible to manufacture using AM technology. The collected and grouped design features were presented in a form of a database as a method to aid product design of parts or products for AM. A series of user trials were conducted that showed the database enabled industrial designers to visualise and gather design feature information that could be incorporated into their own design work. Finally, conclusions are drawn and suggestions for future work are listed. In summary, it can be concluded that this research project has been a success, having addressed all of the objectives that were identified at its outset. From the user trial results, it is clear to see that the proposed tool would be an effective tool to support product design for AM, particularly from an educational perspective. The tool was found to be beneficial to student designers to take advantage of the design freedom offered by AM in order to produce improved product design. As AM becomes more widely used, it is anticipated that new design features will emerge that could be included in future versions of the database so that it will remain a rich source of inspirational information for tomorrow s industrial designers.

The aim of this master thesis project was to statistically correlate various powder characteristics to the quality of additively manufactured parts. An additional goal of this project was to find a potential second source supplier of powder for GKN Aerospace Sweden in Trollhättan. Five Inconel® alloy 718 powders from four individual powder suppliers have been analyzed in this project regarding powder characteristics such as: morphology, porosity, size distribution, flowability and bulk properties. One powder out of the five, Powder C, is currently used in production at GKN and functions as a reference. The five powders were additively manufactured by the process of laser metal deposition according to a pre-programmed model utilized at GKN Aerospace Sweden in Trollhättan. Five plates were produced per powder and each cut to obtain three area sections to analyze, giving a total of fifteen area sections per powder. The quality of deposited parts was assessed by means of their porosity content, powder efficiency, geometry and microstructure. The final step was to statistically evaluate the results through the analysis methods of Analysis of Variance (ANOVA) and simple linear regression with the software Minitab. The method of ANOVA found a statistical significant difference between the five powders regarding their experimental results. This made it possible to compare the five powders against each other. Statistical correlations by simple linear regression analysis were found between various powder characteristics and quality of deposited part. This led to the conclusion that GKN should consider additions to current powder material specification by powder characteristics such as: particle morphology, powder porosity and flowability measurements by a rheometer. One powder was found to have the potential of becoming a second source supplier to GKN, namely Powder A. Powder A had overall good powder properties such as smooth and spherical particles, high particle density at 99,94% and good flowability. The deposited parts with Powder A also showed the lowest amount of pores compared to Powder C, a total of 78 in all five plates, and sufficient powder efficiency at 81,6%.