Now showing 1 - 10 of 63
  • 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
    Protein adhesion on water stable atmospheric plasma deposited acrylic acid coatings
    (Elsevier, 2013-11-15) ;
    There is considerable interest in the application of plasma polymerised acrylic acid (ppAAc) coatings due to their ability to enhance the adhesion of cells and proteins. An issue with this coating however is its stability in water and previous studies carried out using low pressure plasmas have demonstrated that high plasma powers are required to achieve water stable coatings. In this paper the use of both helium and air atmospheric plasmas is compared for the deposition of ppAAc coatings. The deposition studies were carried out on silicon wafer substrates using the PlasmaStream™ and PlasmaTreat™ plasma jet deposition systems respectively. The coatings were characterised using contact angle, FTIR, SEM, XPS, ellipsometry and optical profilometry. While both the helium and air plasmas were successful in the deposition of ppAAc coatings, the nm thick films deposited using the PlasmaTreat system exhibited significantly higher levels of water stability, probably due to a higher level of coating cross-linking. Ellipsometry measurements demonstrated only a 0.2 nm reduction in the thickness of an 18 nm thick ppAAc coating, when immersed in an aqueous buffer solution for one hour. Protein attachment studies were carried out using a flow cell system, which was monitored using a spectroscopic ellipsometer. This study was carried out with Bovine Serum Albumin (BSA), Immunoglobulin G (IgG) and Fibrinogen (Fg) proteins. In all three cases increased levels of protein adhesion were observed for the ppAAc coating, compared to that obtained on the uncoated silicon wafer substrates.
      983Scopus© Citations 29
  • Publication
    Comparison between the properties of polyamide 12 and glass bead filled polyamide 12 using the multi jet fusion printing process
    This study investigates the material and mechanical properties of both polyamide 12 (PA12) and reinforced glass bead PA12 composites, fabricated using a production scale additive manufacturing (AM) process. The printing studies were carried out using the production scale, Multi Jet Fusion powder bed fusion process. The study demonstrated that the chemical functionality and the thermal properties of the printed PA 12 parts and the glass bead composite, were similar. Almost identical infrared spectra were obtained demonstrating the same chemical functionality. Based on DSC measurements, the melting temperature was 184°C and 186°C and the associated cooling cycle temperature was 150°C and 146°C for the composite and the PA12 respectively. The percentage crystallinity of the glass bead composite was 24 %, compared with the 31% obtained for the PA12 only parts. Based on mechanical tests, the addition of glass beads increased the tensile and flexural modulus by 85% and 36% and lowered the tensile and flexural strength by 39% and 15% respectively. The effect of print orientation during the MJF process was evaluated based on porosity and mechanical performance. Using X-ray micro computed tomography, it was demonstrated that the porosity of the PA12 and composite parts were less than 1%. Polymer and composite parts printed in the ZYX orientation were found to exhibit both the lowest porosity and highest mechanical strengths
      1269Scopus© Citations 63
  • Publication
    Low‐pressure additive manufacturing of continuous fiber‐reinforced polymer composites
    Continuous fibre reinforced polymer composites have found a wide range of applications in the automotive and aerospace industry, due to their lightweight properties. Recently the use of additive manufacturing (AM) has been developed for the fabrication of these composites. This study investigates the use of both atmospheric and for the first time, low-pressure (1 Pa) processing conditions, for the AM of continuous carbon, glass and Kevlar fibre reinforced nylon composites. DSC was used to compare the thermal properties of the three types of fibre reinforced filament, prior to printing. It was found that the melting peak was dependent on filament type, which can be related to the polymer processing conditions used during their fabrication. Based on computed tomography measurements, it was found that the use of low-pressure printing conditions yielded a reduction in porosity for the carbon, glass and Kevlar printed composites of 5.7, 1.0 and 1.7 % respectively. The mechanical properties of the composites were compared, using a short beam shear test, which assisted in the measurement of interlaminar properties. An increase in interlaminar shear strength of 33, 22 and 12% was obtained for the carbon, glass and Kevlar fibre reinforced polymer composites respectively, when printed under low-pressure, compared with that obtained at atmospheric pressure.
      569Scopus© Citations 59
  • 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.
      92Scopus© Citations 19
  • Publication
    Evaluation of the microstructure, mechanical and tribological properties of nickel-diamond nanocomposite coatings
    This study investigates the feasibility of a two-step process for the deposition of wear resistant, nickel-diamond nanocomposite coatings onto steel substrates. The steps involve the spray deposition onto stainless steel substrates, of nickel nanoparticles (40 - 60 nm diameter) and nanodiamonds (approx. 100 nm diameter). This is followed by the sintering of the nanoparticle coating using a microwave plasma. The 0.2 - 2 µm thick nanocomposite coatings exhibited very good adhesion on the steel substrates, based on Rockwell C indentation tests. The morphology and roughness of the coatings was found to be significantly influenced by the sintering temperature, which was investigated in the range 711 to 885 ᵒC. The effect of nanodiamond concentration and spray duration were also investigated. Of the parameters studied, the concentration of nanodiamond in the composite was the dominant factor controlling the wear performance of the coatings, when assessed based on pin-on-disc wear tests. Compared to the nickel coating and the steel substrate, the nickel-diamond nanocomposite coatings exhibited a 126 and 55-fold enhancement respectively, in wear performance.
      259Scopus© Citations 14
  • Publication
    Influence of coating properties on the adhesion of proteins to atmospheric plasma modified surfaces
    Protein adhesion is of key importance for the biocompatibility of medical devices. This study investigates the adsorption of protein, bovine serum albumin (BSA), onto both uncoated silicon wafers and nanometre thick fluorosiloxane coated wafers. A plasma polymerised coating was deposited from a mixture of tetramethylcyclotetrasiloxane (TC) and perfluorooctyltriethoxysilane (FS) (1:1 by vol. ratio). The liquid precursor mixture was nebulised into an atmospheric plasma jet formed using the PlasmaStreamTM system. The adsorption of protein on the plasma polymerised coatings was evaluated under dynamic flow conditions using a spectroscopic ellipsometry technique. The rate of protein adsorption onto coated and uncoated silicon wafer substrates was monitored over time after the BSA solution was introduced into a flow cell. These measurements indicated the adsorption of a 2 nm thick BSA protein layer on the uncoated silicon wafers. The ellipsometry thickness measurements of adsorbed protein on silicon wafer were confirmed using quartz crystal microbalance measurements (QCM). The BSA adsorption studies were then repeated with a fluorosiloxane coating. These coatings exhibited a highly textured surface morphology with low surface energy and a high water contact angle of 156 . The ellipsometry flow cell tests with BSA indicated almost no adsorption of protein onto the superhydrophobic fluorosiloxane coating. This study demonstrated the ability of ellipsometry to measure protein adsorption under dynamic flow 2 conditions and the influence of surface properties on protein adsorption.
  • Publication
    Comparison between the SBF response of hydroxyapatite coatings deposited using both a plasma-spray and a novel co-incident micro-blasting technique
    (Trans Tech Publications, 2011-10) ;
    This paper reports on the response of hydroxyapatite (HA) coatings, fabricated using two deposition technologies, to immersion in simulated body fluid (SBF). The deposition methods used were: plasma spray, a commercial standard, and CoBlast, a novel low temperature microblast technique. In the case of the latter, HA coatings are deposited by simultaneous blasting HA and abrasive powders concentrically at a metallic substrate, resulting in a thin layer of HA (approx. 2.5 μm thick). Groups of the CoBlast and plasma spray HA coatings were immersed in 7 ml of SBF solution for 1, 2, 4, 7, 14 and 28 days, and were subsequently removed and examined for any alterations caused by the SBF solution. It was noted from this study that the CoBlast HA coatings appeared to undergo a two step calcium phosphate recrystallisation process; initial homogenous nucleation and subsequent heterogeneous nucleation. Conversely recrystallisation on the plasma spray coatings appeared to proceed largely through a heterogeneous nucleation process. Two factors that may influence the differences in HA recrystallisation is the presence of amorphous HA resulting in rapid dissolution, and/or the significantly lower surface area (roughness) offered to the SBF solution by the CoBlast coatings. The interpretation of recrystallisation mechanisms from this preliminary study is limited however by the differences in coating morphology and thickness (27 versus 2 μm) for the plasma spray and CoBlast HA coatings respectively.
      1239Scopus© Citations 10
  • Publication
    Application of in situ process monitoring to optimise laser parameters during laser powder bed fusion printing of Ti-6Al-4V parts with overhang structures
    (Springer Science and Business Media LLC, 2023-12-15) ; ; ; ;
    Enhanced levels of alloy print defects such as porosity are associated with the printing of overhang structures by laser powder bed fusion (L-PBF). This study compared the microstructure and porosity of Ti-6Al-4V overhang structures, with that observed for the bulk alloy. It was observed in the region around the overhang structure that the microstructure exhibited larger grain sizes and was less homogenous, compared to the that obtained within the bulk alloy. An increased level of porosity of up to 0.08% was also observed in the overhang print alloy, compared with the corresponding < 0.02% in the alloy bulk. It is hypothesised that these microstructural changes are associated with the excess heat generated in the overhang region, due to the decreased thermal conductivity of the powder immediately below the print layers, compared with solid alloy. During L-PBF alloy printing, in situ process monitoring of the melt pool emissions was obtained in the near-infrared range and correlated with the properties of the printed parts. This in-process data was used to assist in selecting optimal laser processing conditions, in order to help prevent melt pool overheating at the overhang. By systematically controlling the laser energy during the printing of the first fifteen layers over the overhang structure, the level of porosity was reduced, to the < 0.02% level of the bulk alloy. There was also an associated reduction in the roughness (Ra) of the overhang itself, with its Ra decreasing from 62.4 ± 7.3 to 7.5 ± 1.9 µm.
  • Publication
    Can attenuated total internal reflection-fourier transform infrared be used to understand the interaction between polymers and water? A hyperspectral imaging study
    This study investigates the potential use of attenuated total internal reflection-Fourier transform infrared (ATR-FT-IR) imaging, a hyperspectral imaging modality, to investigate molecular level trends in the interaction of water with polymeric surfaces of varying hydrophobicity. The hydrophobicity of two categories of polymeric biomaterials is characterised using contact angle (CA) measurements and their relationship with the band area of the OH stretching v S vibration of water over time is presented. This is supported with correlations between CA data and single wavenum-ber intensity values (univariate analysis). Multivariate analysis of the spectra captured at the OH stretch for all polymers is carried out using principal component analysis to study the spatial variation in the interaction between the polymeric surfaces and water. Finally, a comparison between the univariate and multivariate strategies is presented to understand the interaction between polymeric biomaterials and water.
      185Scopus© Citations 6