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    An investigation into non-destructive testing strategies and in-situ surface finish improvement for direct metal printing with SS 17-4 PH : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Albany, New Zealand
    (Massey University, 2022) Pereira, Tanisha Mary
    Additive Manufacturing (AM) technologies have the potential to create complex geometric parts that can be used in high-end product industries, aerospace, automotive, medical etc. However, the surface finish, part-to-part reliability, and machine-to-machine reliability has made it difficult to qualify the process for load dependent structures. The improvement of surface finish on metal printed parts, is a widely sought solution by these high-end industries and non-destructively characterizing the mechanical aptitude of metal printed parts, would pave the way for quality assessment strategies used to certify additively manufactured parts. This thesis examines the capability of laser polishing and non-destructive testing technologies and methods to address these difficulties. This research study presents an investigation into quality management strategies for Direct Metal Printing (DMP) with powdered Stainless Steel 17-4 PH. The research aim is split into two key categories: to improve the surface finish of metal additive manufactured parts and to non-destructively characterize the impact of defects (metallurgical anomalies) on the mechanical properties of the printed part. To improve surface finish of a printed part, a novel methodology was tested to laser polish the Laser-Powder Bed Fusion (L-PBF) parts during print with the built-in laser. Numerous technologies for non-destructive testing techniques already exist, and in the duration of this doctoral study various technologies were explored. However, the final solution focuses on layer-wise capture with a versatile low-cost imaging system, retrofitted within the DMP machine, to capture each layer following the lasering process. In addition, the study also focuses on progressing the characterization of data (images), using a combination of image processing, 3D modelling and Finite-Element-Analysis to create a novel strategy for replicating the as-built specimen as a computer-aided design model and performing simulated fatigue failure analysis on the part. This thesis begins with a broadened justification of the research need for the solutions described, followed by a review of literature defining existing techniques and methods pertaining to the solutions, with validation of the research gap identified to provide novel contribution to the metal additive manufacturing space. This is followed by the methodologies developed, to firstly, control the laser parameters within the DMP and examine the influence of these parameters using surface profilometry, scanning electron microscopy and mechanical hardness testing. The control variables in this methodology combines laser parameters (laser power, scan speed and polishing iterations) and print orientation (polished surface angled at 0º, 20º, 40º, 60º, 80º and 90º degree increments from the laser), using several Taguchi designs of experiments and statistical analysis to characterize the experimental results. The second methodology describes the retrofitted imaging system, image processing techniques and analysis methods used to reconstruct the 3D model of a standard square shaped part and one with synthesized defects. The method explores various 2D to 3D extrusion-based techniques using a combination of code-based image processing (Python 3, OpenCV and MATLAB image processing toolbox) and ready-made software tools (Solidworks, InkTrace, ImageJ and more). Finally, the new research findings are presented, including the results of the laser polishing study demonstrating the successful improvement of surface finish. The discussion surrounding these results, highlights the most effective part orientation for laser polishing the outline of an AM part and the most effective laser parameter combination resulting in the most significant improvement to surface finish (roughness and profile height variation). Summarily, the best improvement in surface roughness was achieved with the <80 angled surface with the laser speed, laser power and polishing iterations set to 500mm/s, 30W, 3 respectively. The sample set total average measured a 16.7% decrease in Ra. NDT digital imaging, thermal imaging and acoustic technologies were considered for defect capture in metal AM parts. The solution presented is primarily focused on the expansion of research to process digital images of each part layer and examine strategies to move the research from a data capture stage to a data processing strategy with quantitative measurement (FEA analysis) of the printed part’s mechanical properties. In addition, the results discuss a method to create feedback to the DMP to selectively melt problematic areas, by re-creating the sliced part layers but removing the well-melted areas from the laser scanning pattern. The methods and technological solutions developed in this research study, have presented novel data to further research these methods in the pursuit of quality assurance for AM parts. The work done has paved the way for more the research opportunities and alternative methods to be explored that complement the methods detailed here. For example, using a combination of in-situ laser polishing, followed by post-processing the AM specimens in an acid-based chemical bath. Alternatively, further exploring acoustic NDT techniques to create an in-built acoustic-based imaging device within the AM machine. Finally, this thesis cross-examines the work done to answer the research questions established at the start of the thesis and verify the hypotheses stated in the methods chapter.
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    Modular mechatronics technology for fibre-based manufacturing and biofabrication research : this dissertation is presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering conducted at Massey University, Albany, New Zealand
    (Massey University, 2019) Schutte, Juan
    There exists an opportunity within manufacturing for the development of technology capable of creating complex fibre-based structures. Additive Manufacturing (AM) has become increasingly relevant due to its ability to generate parts of a higher complexity relative to other traditional techniques. 3D Printing (3DP) technology is a form of AM through which much of this type of complex manufacturing is conducted. Currently this technology allows for the processing of many materials through a range of mechanisms. Whilst 3DP development has predominantly focussed on synthetic polymer and metal production, there is opportunity for this technique within Tissue Engineering (TE). This field is motivated by the shortage of donor organ tissues such as the cornea. AM is a potential methodology for the controlled manipulation of biomaterial/biopolymer as a form of production within TE. It is however critically limited in its ability to process submicron and nanofiber to generate fibre-based constructs such as those found within the cornea (stroma). This limitation yields restrictions in not only bio-printing based applications but also within attempts to innovate in traditional fibre-reinforcement based industry. There is a manufacturing based opportunity for the research and development of a technology capable of overcoming these limitations. The current restrictions within this field were evaluated through an analysis of relative literature. This led to the identification of electrospinning as a viable technology for both synthetic and biopolymer submicron and nanofiber production. The limitations of this technology were evaluated, leading to the potential for overcoming these utilising traditional methods of 3DP. Further evaluating current literature led to a hypothesized manufacturing technique. Additionally this literature indicated the need for development of a novel technology capable of performing research and development related work within this field. This resulted in much experimentation related to the generation of technology/componentry/mechanisms related to both the testing of the hypothesis as well as capable of facilitating future research. Work related to an increase in electrospinning productivity via electric field related manipulation was conducted as an attempt to reduce system complexity. This work did not circumvent the requirement for environmental control; as such, a method for the implementation of this to aid in productivity was required. Development of mechanisms yielded a strong requirement for a modular system allowing these components to be varied in accordance with the processing requirements. This ability to manipulate the system was achieved through the creation of both a function based coding strategy as well as the derivation of a potential modular electronics (PCB-stacking) technique. The derived novel technology’s success was demonstrated through a range of experimentation related to implemented forms of technology within the final machine. Regarding the forming of electrospun material, the direct method of electrospinning-based deposition of material upon molds did not achieve generation of the desired objects as such a method of fibre acquisition was implemented. Regarding collagen electrospinning, no dramatic variation on fibre distribution (alignment) could be derived in comparing the parallel or rotating mandrel-inspired approaches. Functionalisation strategies utilising ultrasonically generated vapour demonstrated promising capability in the bonding of synthetic polymers whilst acting to disrupt the more sensitive biopolymer. The use of corona discharge plasma for crosslinking yielded promising results for synthetic polymer ultimate tensile strength however, the proximity analysis/optimisation of this requires further research if this is to be applied to electrospinning-based AM. Finally, the ability to utilise the developed technology to generate both an automated manufacturing technique for fibre-based additive manufacturing and the creation of associated 3D forms was demonstrated as viable, thus validating this research project.
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    Hybrid deposition additive manufacturing: novel volume distribution, thermo-mechanical characterization, and image analysis
    (The Brazilian Society of Mechanical Sciences and Engineering, 25/08/2022) Harris M; Mohsin H; Potgieter J-G; Arif K; Anwar S; AlFaify A; Farooq MU
    The structural integrity of additive manufacturing structures is a pronounced challenge considering the voids and weak layer-to-layer adhesion. One of the potential ways is hybrid deposition manufacturing (HDM) that includes fused filament fabrication (FFF) with the conventional filling process, also known as “HDM composites". HDM is a potential technique for improving structural stability by replacing the thermoplastic void structure with a voidless epoxy. However, the literature lacks investigation of FFF/epoxy HDM-based composites regarding optimal volume distribution, effects of brittle and ductile FFF materials, and fractographic analysis. This research presents the effects of range of volume distributions (10–90%) between FFF and epoxy system for tensile, flexure, and compressive characterization. Volume distribution in tensile and flexure samples is achieved using printable wall thickness, slot width, and maximum width. For compression, the printable wall thickness, slot diameter, and external diameter are considered. Polylactic acid and acrylonitrile butadiene styrene are used to analyze the brittle and ductile FFF structures. The research reports novel application of image analysis during mechanical characterization using high-quality camera and fractographic analysis using scanning electron microscopy (SEM). The results present surprising high tensile strain (0.038 mm/mm) and compressive strength (64.5 MPa) for lower FDM-percentages (10%, 20%) that are explained using in situ image analysis, SEM, stress–strain simulations, and dynamic mechanical analysis (DMA). In this regard, the proposed work holds novelty to apply DMA for HDM. The optimal volume distributions of 70% and 80% alongside fractographic mechanisms for lower percentages (10%, 20%) can potentially contribute to structural applications and future material-based innovations for HDM.