Now showing 1 - 10 of 62
  • Publication
    Tool Wear in Milling of Medical Grade Cobalt Chromium Alloy - Requirements for Advanced Process Monitoring and Data Analytics
    (Machine Tool Technologies Research Foundation, 2016-07-07) ; ; ; ;
    Computer Aided Design (CAD), Computer Aided Manufacturing (CAM) and Computer Numerical Control (CNC) are platform technologies in high end manufacturing. However, the machining process on the CNC Machine Tool is generally the main source of loss of component accuracy, precision and extraneous effects on surface finish and integrity. Moreover these 'losses', and therefore costs, only increase in cutting processes due to the inherent modes and mechanisms of progressive and catastrophic tool wear. In high end manufacturing sectors, these losses are also exacerbated by the use of 'difficult-to-cut (DTC)' materials while more stringent specifications apply and higher levels of process capability are demanded. The use of Cobalt Chromium (Co-Cr-Mo) alloys in the Medical Device sector is indicative of the many challenges. However, notwithstanding the importance of the application, there are few publications on the fundamental mechanisms in cutting this alloy, other than by the present authors. This paper builds on our research to date by reporting some preliminary results on tool wear progression in CNC milling of the Co-Cr-Mo alloy conforming to ASTM F75. It also assesses the feasibility of real time tool wear monitoring on a Mori Seiki NMV1500 CNC Machining Centre using the MTConnect communication standard. The results obtained through MTConnect are provided by embedded sensors within the machine tool and are correlated with a laboratory piezoelectric dynamometer. The results from both methods, obtained at two cutting speeds, are also related to observed tool wear progression and the cumulative volume of material removed. The results are discussed in terms of the potential and limitations of using of MTConnect and the machine tools embedded sensors, for monitoring of the process and the onset of tool wear.
  • Publication
    Deposition of nano and micron thick aligned fiber plasma polymerised coatings using an atmospheric plasma jet technique
    (International Symposium on Plasma Chemistry, 2011-07) ;
    This paper reports on the deposition of siloxane coatings exhibiting ‘aligned’ and ‘non-aligned’ fibrous structures using an atmospheric plasma jet system called PlasmaStreamTM. The coatings were deposited from both liquid HMDSO and TCFS (tetramethyl cyclotetrasiloxane / fluorosiloxane) precursors. These precursors were nebulized into a helium / nitrogen plasma and the coatings were deposited onto silicon wafer substrates. By controlling the deposition conditions superhydrophobic coatings exhibiting a needle-like coating morphology was obtained from both precursors. Initial fibre lengths were in the nm range but after longer deposition time’s coatings with micron long fibre lengths were obtained. In the case of the HMDSO precursor individual aligned fibres with diameters of up to 300 nm and lengths of up to 12 μm were observed. The TCFS coatings were structurally different as they exhibited a non-aligned, more densely packed, fibrous structures. For the same deposition time as used with HMDSO, the TCFS coatings exhibited fibre lengths of up to 10 microns. Coating morphology, water contact angle and functional chemistry were examined using optical profilometry, contact angle and FTIR techniques respectively. The micron thick fibrous coatings both exhibited superhydrophobic properties with contact angles of over 150°.
  • Publication
    Enhancing the mechanical performance of 3D‐printedbasalt fiber‐reinforced composites using in‐line atmospheric plasma pretreatments
    The objective of this study is to investigate the use of an air atmospheric plasma jet for the treatment of sized basalt fibres, used in the fabrication of continuous fibre reinforced polypropylene filaments. The plasma treatments were carried out both at a laboratory scale, as well as in-line during the production of fibre reinforced filaments. The latter was carried out at a fibre processing speeds of approx. 15 metres/second, just immediately prior to the polymer coating of the fibre by extrusion. After the air plasma treatment, the water contact angle of the sized basalt fibre decreased from 86° to < 10°. XPS analysis demonstrated that the treatment yielded enhanced levels of oxygen functionality on the fibre surface. After coating with polypropylene, it was observed that there was consistently more homogeneous polymer layer deposited onto the plasma activated fibre, compared with that on the unactivated control fibre. The resulting polymer filament with embedded basalt fibre was used to fabricate mechanical test specimens by 3D printing (fused filament fabrication method). Both three-point bending tests and short beam strength tests were performed. A comparison study was carried out between test specimens fabricated using sized basalt fibre, with and without the plasma pre-treatment. The flexural modulus and maximum shear stress were found to increase by 12% and 13% respectively, for composite's fabricated using the plasma pre-treated basalt fibres. This increased mechanical strength is likely to be due to an increase in interfacial bond strength between the polymer and fibre, with an associated reduction in the level of air incorporation around the basalt filaments as demonstrated using CT analysis.
      68Scopus© Citations 5
  • Publication
    Three Dimensional Coupled Fluid-Droplet Model For Atmospheric Pressure Plasmas
    A three-dimensional coupled fluid-droplet model is developed specifically to characterize the significance of droplet-plasma interaction at atmospheric pressure. The liquid droplet introduces a perturbation in atmospheric pressure plasma (APP) and under many conditions, the behavior of this perturbation is not clear during transport in PlasmaStream system. In this study, we identify the importance of ionization mechanism in two-phase flow. The affect and spatial expansion of vaporization in discharge plasma depend on the flow rate of liquid precursors. Penning ionization is recognized as the leading process along the pulse of evaporating droplets as compared to other ionization processes that explain the relevance of small nitrogen impurities in an APP. The influence of different precursors, such as Hexamethyldisiloxane, Tetraethyl orthosilicate and water is described by contrasting the implication of the evaporation process along the pulse of droplets in the APP. Finally, we validate the numerical simulation by comparison with the experimental observations of droplet size distributions using a laser diffraction particle size analysis technique as a part of atmospheric pressure plasma jet deposition system.
  • Publication
    In-situ XRD Study on the Effects of Stress Relaxation and Phase Transformation Heat Treatments on Mechanical and Microstructural Behaviour of Additively Manufactured Ti-6Al-4V
    Additively Manufactured (AM) titanium (Ti) components are routinely post-thermal heat treated (HT), to reduce internal stresses, as well as to obtain more desirable microstructural features, yielding improved mechanical performance. Currently, there is no consensus on the optimum HT method for AM Ti-6Al-4V, as the mechanism for the main phase transformation (α′ (martensite) → α + β (equilibrium)) is still ambiguous. In this study, stress relaxation and phase transformation in the alloy are investigated in detail, via isothermal heat treatments and in situ high temperature X-ray Diffraction (XRD). The latter was carried out at heating rates of 5 and 200 °C/min. The relationship between crystallographic evolution during isothermal treatments and mechanical behaviour was determined. Isothermal holding at 400 °C resulted in an increase in ultimate tensile strength (UTS) and yield strength (YS) by 3.4% and 2.1%, respectively, due to the relief of tensile microstrain. It was found that isothermal treatment conducted between 550 and 700 °C promotes martensitic decomposition, resulting in the formation of a transitional - αtr phase, which has an asymmetrical hexagonal crystal lattice. The formation of this αtr phase was determined to be the main factor contributing to a major decrease in ductility.
      35Scopus© Citations 9
  • Publication
    Antifouling coatings made with Cold Spray onto polymers: Process characterization
    Cold Spray (CS) of copper particles onto polymers has been validated as an effective tool for maintaining surface integrity in bioenvironments. CS requires limited heat input, can be applied locally or in large areas. The key parameters are particle penetration depth and copper surface coverage. However, the process parameters that can optimize the coating performance with deposition have not been comprehensively explored. In this paper, copper particles were deposited onto two polymers used in marine applications. A detailed analysis was carried out to correlate the key surface properties to the process so as to determine the optimum conditions.
      610Scopus© Citations 17
  • Publication
    Characterisation of titanium oxide layers using Raman spectroscopy and optical profilometry: Influence of oxide properties
    This study evaluates the use of a combination of Raman spectroscopy and optical profilometry as a surface characterisation technique for the examination of oxide layers grown on titanium metal substrates. The titanium oxide layers with thickness of up to 8 µm, were obtained using a low-pressure oxygen microwave plasma treatment of the titanium metal substrate. The effect of the microwave plasma processing conditions (input power, pressure and treatment time) on the Raman bandwidth, intensity and peak position was evaluated. Also, the effect of these processing conditions on the surface roughness parameters (Sa, Sdq, Ssk and Sku) of the oxide layers was investigated. Analysis of the peak positions of Eg and A1g modes indicated that the effects of input power and chamber pressure was to induce a shift towards the lower frequency with increasing input power and pressure (1–2 kPa). The intensity of the Raman bands was found to be dependent on the morphology and surface chemistry of the oxide layer. The intensity of Raman band (A1g), was found to be particularly influenced by the average surface roughness (Sa) and the crystallite size. Exponential and polynomial relations were found to correlate with these properties. A two-latent variable Partial Least Squares Regression model developed on Raman spectral data could predict surface roughness with a coefficient of determination (R2) of approx. 0.87 when applied to the testing of an independent set of titanium oxide test coatings.
      321Scopus© Citations 60
  • Publication
    Electrochemical characterization of NiO electrodes deposited via a scalable powder microblasting technique
    In this contribution a novel powder coating processing technique (microblasting) for the fabrication of nickel oxide (NiOx) coatings is reported. ~1.2 μm thick NiOx coatings are deposited at 20 mm2 s−1 by the bombardment of the NiOx powder onto a Ni sheet using an air jet at a speed of more than 180 m s−1. Microblast deposited NiOx coatings can be prepared at a high processing rate, do not need further thermal treatment. Therefore, this scalable method is time and energy efficient. The mechano-chemical bonding between the powder particles and substrate results in the formation of strongly adherent NiOx coatings. Microstructural analyses were carried out using SEM, the chemical composition and coatings orientation were determined by XPS and XRD, respectively. The electroactivity of the microblast deposited NiOx coatings was compared with that of NiOx coatings obtained by sintering NiOx nanoparticles previously sprayed onto Ni sheets. In the absence of a redox mediator in the electrolyte, the reduction current of microblast deposited NiOx coatings, when analyzed in anhydrous environment, was two times larger than that produced by higher porosity NiOx nanoparticles coatings of the same thickness obtained through spray coating followed by sintering. Under analogous experimental conditions thin layers of NiOx obtained by using the sol–gel method, ultrasonic spray- and electro-deposition show generally lower current density with respect to microblast samples of the same thickness. The electrochemical reduction of NiOx coatings is controlled by the bulk characteristics of the oxide and the relatively ordered structure of microblast NiOx coatings with respect to sintered NiOx nanoparticles here considered, is expected to increase the electron mobility and ionic charge diffusion lengths in the microblast samples. Finally, the increased level of adhesion of the microblast film on the metallic substrate affords a good electrical contact at the metal/metal oxide interface, and constitutes another reason in support of the choice of microblast as low-cost and scalable deposition method for oxide layers to be employed in electrochemical applications.
      670Scopus© Citations 29
  • Publication
    The Study on Microstructural Evolution During Post-processing of Additively Manufactured Ti64
    The effect of furnace heat treatments to 850 °C, on the evolution of microstructure in Ti–6Al–4V alloy produced via selective laser melting (SLM), was studied using optical microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Columnar prior-β grains in the build direction with lamellar α-martensite laths contained within the prior-β grains were determined. α-martensite laths present in the as-built microstructure had thicknesses around 236 nm while the heat-treated microstructure showed an α-lath thickness values of around 1.8 μm. Based on XRD analysis, upon heat treatment the formation of β-phase was determined with associated peaks around 41° and 58°, corresponding to (110) and (200) planes, respectively.
      39Scopus© Citations 1
  • Publication
    3D Printing of Fibre-Reinforced Thermoplastic Composites Using Fused Filament Fabrication—A Review
    Three-dimensional (3D) printing has been successfully applied for the fabrication of polymer components ranging from prototypes to final products. An issue, however, is that the resulting 3D printed parts exhibit inferior mechanical performance to parts fabricated using conventional polymer processing technologies, such as compression moulding. The addition of fibres and other materials into the polymer matrix to form a composite can yield a significant enhancement in the structural strength of printed polymer parts. This review focuses on the enhanced mechanical performance obtained through the printing of fibre-reinforced polymer composites, using the fused filament fabrication (FFF) 3D printing technique. The uses of both short and continuous fibre-reinforced polymer composites are reviewed. Finally, examples of some applications of FFF printed polymer composites using robotic processes are highlighted.
      59Scopus© Citations 60