Review on Additive Manufacturing of Multi-Material Parts:Progress and Challenges

Additive manufacturing has already been established as a highly versatile manufacturing technique with demonstrated potential to completely transform conventional manufacturing in the future. The objective of this paper is to review the latest progress and challenges associated with the fabrication of multi-material parts using additive manufacturing technologies. Various manufacturing processes and materials used to produce functional components were investigated and summarized. The latest applications of multi-material additive manufacturing (MMAM) in the automotive, aerospace, biomedical and dentistry fields were demonstrated. An investigation on the current challenges was also carried out to predict the future direction of MMAM processes. It was concluded that further research and development is needed in the design of multi-material interfaces, manufacturing processes and the material compatibility of MMAM parts

Validation of an in vivo model for monitoring trabecular bone quality changes using finite element analysis.

A combination of three techniques – high resolution micro computed tomography (micro CT) scanning, Archimedes-based volume fraction measurement and serial sectioning or milling – were used to determine the volume fraction, trabecular thickness, trabecular separation, trabecular number and micro finite element analysis combined with mechanical testing was used to determine the apparent stiffness and tissue modulus to quantify bone quality in rabbit distal femur trabecular bone. The objectives of this dissertation were two-fold. First, to develop the capabilities of micro CT scanning and micro CT image segmentation based on a slice-by-slice global thresholding technique to investigate trabecular microstructural changes in vivo and in vitro; and second, to develop the capability of translating micro CT scans into three dimensional finite element models based on direct voxel conversion technique. These results were validated within the in vivo and in vitro scans at the same time, and validated with the Archimedes-based volume fraction measurements and serial sectioning or milling experiments. The micro FE models were executed as linear analyses and the same bone cubes of the models were mechanically tested (compressive testing) to determine the correct tissue modulus of the bone specimens. The apparent stiffness of these micro FE models was recalculated using the average tissue modulus. A total of six six-month-old New Zealand white rabbits were utilized in this study. Three rabbits were scanned twice in vivo seven days apart (T1 and T7) and three rabbits were only scanned once in vivo. All of the femurs were scanned in vitro. All micro CT images were obtained at 28 um (in vivo) or 14 um (in vitro) nominal resolutions. Specimens from six left and right rabbit distal femurs (medial and lateral) were measured based on Archimedes\u27 principle and serial milling. The volume fraction for lateral condyles between two in vivo scans T1 (0.401+0.015) and T7 (0.397+0.021), between in vitro micro CT (0.352+0.035) and Archimedes (0.365+0.031) and between in vitro micro (0.352+0.035) and serial milling (0.369+0.031) were not significantly different. The medial condyles were also not significantly different: T1 (0.513+0.010), T7 (0.515+0.011), in vitro micro CT (0.454+0.049), Archimedes (0.460+0.060) and serial milling (0.467+0.505). Specimens from another six left and right distal femurs (medial and lateral) were mechanically tested along the anterior-posterior directions. The tissue modulus of each specimen was determined by making the calculated apparent stiffness values from FEA to be equal to mechanical compressive testing (MTS). Based on a new constant tissue modulus, the recalculated FEA apparent stiffness (1.77E9+6.45E8) and MTS apparent stiffness (1.76E9+7.37E8) were linearly correlated (r-value = 0.8721). These findings suggest that the capabilities of slice-by-slice global thresholding and direct voxel conversion are sensitive, reliable and consistent for the study of trabecular bone microstructural changes in vivo utilizing high resolution (\u3c 28 um) micro CT scanning and micro FEA

Hybrid additive manufacturing platform for the production of composite wind turbine blade moulds

This dissertation discusses the application of additive manufacturing technologies for production of a large-scale rapid prototyping machine, which will be used to produce moulds for prototype composite turbine blades for the emerging renewables energy industry within the Eastern Cape region in South Africa. The conceptualization and design of three complete printer builds resulted in the amalgamation of a final system, following stringent theoretical design, simulation, and feasibility analysis. Following the initial product design cycle stage, construction and performance testing of a large-scale additive manufacturing platform were performed. In-depth statistical analysis of the mechatronic system was undertaken, particularly related to print-head locational accuracy, repeatability, and effects of parameter variation on printer performance. The machine was analysed to assess feasibility for use in the mould-making industry with accuracy and repeatability metrics of 0.121 mm and 0.156 mm rivalling those produced by some of the more accurate fused deposition modellers commercially available. The research data gathered serves to confirm that rapid prototyping is a good alternative manufacturing method for wind turbine blade plug and mould production

An advanced prototyping process for highly accurate models in biomedical applications

An integrated prototyping process for the derivation of complex medical models is introduced. The use of medical models can support today’s medicine by improving diagnosis and surgical planning, teaching and patient information. To withstand the challenges of time and accuracy, a process for generating accurate virtual and physical medical models is needed. The introduced process offers the possibility to derive virtual and physical models for biomedical engineering applications. Reviewing the current situation of medical virtual prototyping and rapid prototyping applications, limitations were found related to the influential variables of data acquisition, data processing, virtual reality use, and rapid prototyping manufacturing. An integrated prototyping concept (MPP) is introduced for embedding virtual prototyping and rapid prototyping in biomedical applications. Data processing and 3D modeling of complex anatomical structures from computerized image data were investigated and discussed in detail. Finally, parameter analyses were evaluated to derive optimal parameters needed for preparing 3D models for virtual prototyping and rapid prototyping processing in medicine. Summarizing from the accuracy analysis, the present investigation is the first to examine tomographic scanning as decisive factor for inaccuracy of medical prototyping models. The human nose is an example of a complex anatomical geometry, which has been an object of scientific research interest for several years. One of the applications introduced here uses the developed MPP concept as basis for a procedure that generates animated medical models in a virtual reality environment. Although, attempts are being made to reconstruct the human nose as an experimental rapid prototyping model, a process for accurate reconstruction as a transparent rapid prototyping model is still missing. The MPP concept allows fabricating individual models of the human nose with a high level of accuracy and transparency. Finally, temporal analysis revealed major time improvements in modeling complex anatomical models compared to approaches without optimized process sequences and approved parameters. The prototyping of the human hip was the second example used. The results of this particular example emphasized the strengths of the medial prototyping process in preparing hip models for presurgery planning. Here, accuracy was enhanced considerably. Rapid prototyping hip models can provide assistance as a surgical planning tool in complex cases, especially in improving surgical results and implant stability. Thus, the accuracy and time of model generation is improved, thereby establishing a defined process for medical model generation. Considering the novel findings of broad improvements in accuracy and time, a new field of research is emerging, serving both virtual surgery applications and physical implant generation. The MPP developed in this work can be viewed as an initial approach for launching international standards of prototyping technologies in medicine

Economic aspects of additive manufacturing: benefits, costs and energy consumption

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 that 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

Smart machining system platform for CNC milling with the integration of a power sensor and cutting model

Novel techniques and strategies are investigated for dynamically measuring the process capability of machine tools and using this information for Smart Machine System (SMS) research. Several aspects of the system are explored including system integration, data acquisition, force and power model calibration, feedrate scheduling and tool condition monitoring. A key aspect of a SMS is its ability to provide synchronization between process measurements and model estimates. It permits real time feedback regarding the current machine tool process. This information can be used to accurately determine and keep track of model coefficients for the actual tooling and materials in use, providing both a continued improvement in model accuracy as well as a way to monitor the health of the machine and the machining process. A cutting power model is applied based on a linear tangential force model with edge effect. The robustness of the model is verified through experiments with a wide variety of cutting conditions. Results show good agreement between measured and estimated power. A test platform has been implemented for performing research on Smart Machine Systems. It uses a commercially available OAC from MDSI, geometric modeling software from Predator along with a number of modules developed at UNH. Test cases illustrate how models and sensors can be combined to select machining conditions that will produce a good part on the first try. On-line calibration allows the SMS to fine tune model coefficients, which can then be used to improve production efficiency as the machine learns its own capabilities. With force measurements, the force model can be calibrated and resultant force predictions can be performed. A feedrate selection planner has been created to choose the fastest possible feedrates subject to constraints which are related to part quality, tool health and machine tool capabilities. Monitoring tangential model coefficients is shown to be more useful than monitoring power ratio for tool condition monitoring. As the model coefficients are independent of the cutting geometry, their changes are more promising, in that KTC will increase with edge chipping and breakage, while KTE will increase as the flank wearland expands

Marginal fit of CAD/CAM restorations on the basis of CBCT and their optical behavior

The use of CBCT data obtained from dental impressions might be indicated to serve as a basis to manufacture lithium disilicate crowns with a marginal fit in the range of clinical acceptance. Furthermore, the results of the present study suggest that new technologies associated with software improvements might enhance the quality of the data obtained from CBCT. Monolithic materials present different transmittances for visible and blue light, thus they should be indicated according to their esthetic and required luting procedures. The dental team should acquire knowledge on the technology and materials, working synergistically with digital technology resources to provide more accurate and predictable treatments for the patient

From 3D Models to 3D Prints: an Overview of the Processing Pipeline

Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step, in particular along the Process Planning pipeline, can now count on dozens of methods that prepare the 3D model for fabrication, while analysing and optimizing geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and Innovation action; Grant agreement N. 68044

Fabricate

Bringing together pioneers in design and making within architecture, construction, engineering, manufacturing, materials technology and computation, Fabricate is a triennial international conference, now in its third year (ICD, University of Stuttgart, April 2017). Each year it produces a supporting publication, to date the only one of its kind specialising in Digital Fabrication. The 2017 edition features 32 illustrated articles on built projects and works in progress from academia and practice, including contributions from leading practices such as Foster + Partners, Zaha Hadid Architects, Arup, and Ron Arad, and from world-renowned institutions including ICD Stuttgart, Harvard, Yale, MIT, Princeton University, The Bartlett School of Architecture (UCL) and the Architectural Association