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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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    Development of a novel moulding technique to produce a unique gummy confectionery product : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Mechatronics, Massey University, Albany, New Zealand
    (Massey University, 2020) Smith, David J.
    ZURU Toys, one of the fastest growing toy companies in the world, identified an opportunity to capitalise on a unique opportunity within the growing confectionery industry by creating a product to merge a surprise toy egg with a unique gummy confectionery experience. The concept was to have a plastic surprise toy capsule shaped as an egg, which was to be encapsulated by gummy laid out in a spiral of eight distinctive colour strips. The gummy strips were to be peeled off the surface of the egg capsule and consumed to reveal the capsule housing the surprise toy. ZURU partnered with Massey University’s Engineering and Food Technology departments to explore the product opportunity further. The project was given to the Engineering Department, as there was no clear method for creating the product with existing manufacturing techniques. The client commissioned the project with virtually no constraints attached with the intention that the department would have complete freedom to explore all possible methods of manufacturing the product concept on a mass scale. The purpose of this thesis is to explore appropriate manufacturing techniques which can be used to mass manufacture the desired gummy confectionery product. To address the complexity of the client’s desired confectionery product, a feasibility analysis of injection moulding techniques is investigated. To gather the necessary understandings for developing a solution to this concept, the two industries relevant to this study, Gummy Confectionery Production and Mass Manufacturing of Polymers, are explored in a literature review. Early stage material testing was done to understand how the material behaves. This process included fabricating the first aluminium mould concept to explore the behaviours of gummy moulding in aluminium. This testing led to the development of the first mould concept. Following several mould iterations and subsequent testing, a clear understanding of how the egg could be produced at a mass scale was documented. The final mould concept was a two-part egg-shaped aluminium mould with seven spiral ribs sectioning off the eight cavities, with the toy capsule acting as a centre core. At the correct volumes, different coloured gummy could be injected into each cavity to encase the egg capsule with a spiral effect of eight distinctive strips of gummy. By following the ideal test conditions of injecting gummy at 60°C and cooling the mould for four minutes in water at 3°C it was possible to manufacture a gummy egg of the described characteristics at the scale described by the client. The mould designs and requirements for manufacturing the product on a mass scale was subsequently delivered to the client which has since filed for patent protection on the method in select countries and implemented the solution on an automation line in a food safe factory in China in preparation for launch.