Now showing 1 - 5 of 5
  • Publication
    Prediction of tool-wear in turning of medical grade cobalt chromium molybdenum alloy (ASTM F75) using non-parametric Bayesian models
    We present a novel approach to estimating the effect of control parameters on tool wear rates and related changes in the three force components in turning of medical grade Co-Cr-Mo (ASTM F75) alloy. Co-Cr-Mo is known to be a difficult to cut material which, due to a combination of mechanical and physical properties, is used for the critical structural components of implantable medical prosthetics. We run a designed experiment which enables us to estimate tool wear from feed rate and cutting speed, and constrain them using a Bayesian hierarchical Gaussian Process model which enables prediction of tool wear rates for untried experimental settings. However, the predicted tool wear rates are non-linear and, using our models, we can identify experimental settings which optimise the life of the tool. This approach has potential in the future for realtime application of data analytics to machining processes.
      370Scopus© Citations 15
  • Publication
    Characterization of Chip Morphology in Orthogonal Cutting of Medical Grade Cobalt Chromium Alloy (ASTM F1537)
    Cobalt Chromium alloys (CoCr) are used in the manufacture of class 3 medical devices, notably knee and hip implants, due to singular mechanical properties such as wear resistance and biocompatibility. Notwithstanding the importance of the material, there has been limited research reported on the fundamental mechanism in machining of this alloy. This paper initially propounds on the properties that define a material as “difficult to cut” (DTC) in order to compare machining related properties of ASTM F1537 CoCr with other known DTC alloys. This is followed by a brief summary of literature specifically on the chip morphology produced in turning of ASTM F136 Ti-6Al-4V and Inconel 718. Orthogonal cutting tests are then undertaken to examine the chip morphology in cutting ASTM F1537 over a range of cutting speeds (Vc) and levels of undeformed chip thickness (hm). The findings of this research were compared with those found in literature. It is concluded that ASTM F1537 CoCr produced segmented chips under all tested conditions and chip segmentation frequency increases with the cutting speed but is independent of the undeformed chip thickness. Moreover, the ratio of the segment height to the maximum chip thickness was found to decrease with cutting speed.
      287
  • Publication
    An Investigation of Force Components in Orthogonal Cutting of Medical Grade Cobalt Chromium Alloy (ASTM F1537)
    An aging population, increased physical activity and obesity, are identified as life style changes contributing to growth in the use of in-vivo prosthetics for total hip and knee arthroplasty. Cobalt chromium alloys, due to mechanical properties and excellent biocompatibility, uniquely qualify as a class of materials that meet the stringent functional requirements for these devices. To cost effectively assure the required dimensional and geometric tolerances, manufacturers invariably rely on high precision machining. However, a comprehensive literature review has shown that there has been limited research into mechanical cutting of these materials. This paper delineates the physical and mechanical properties that determine the machinability of a material, and compares medical grade cobalt chromium alloy ASTM F1537 with titanium alloy, Ti-6Al-4V ASTM F136. The results of a full factorial orthogonal cutting experiment are reported where cutting and thrust force components were measured over a range of cutting speeds (Vc) and levels of undeformed chip thickness (hm). It was found that the forces generated in cutting of ASTM F1537 are significantly higher than for ASTM F136, depending primarily on undeformed chip thickness, but with some influence of the cutting speed. The effect of chip segmentation on component force variations is also reported.
      871Scopus© Citations 7
  • Publication
    Fundamental Mechanisms in Orthogonal Cutting of Medical Grade Cobalt Chromium Alloy (ASTM F75)
    (Elsevier, 2016-03-07) ;
    Cobalt chromium (Co-Cr-Mo) alloys are sui generis materials for orthopaedic implants mainly due to the unique properties of biocompatibility and wear resistance in the demanding in vivo environments. Notwithstanding the importance of the machining processes, a review of literature in the public domain has identified a niche for research into the fundamental mechanisms in cutting of Co-Cr-Mo alloys. This paper reports on initial research into cutting of the biomedical grade cobalt chrome molybdenum (Co-Cr-Mo) alloy, ASTM F75. Following an initial review of the known micro-structural, physical and mechanical properties of the class of Co-Cr-Mo alloys, the results of a full factorial, orthogonal cutting experiment are presented. This involved measurement of force components (Ff and Ft) as a function of the undeformed chip thickness (h) and cutting speed (vc) which were varied over ranges from 20 to 140 µm and 20 to 60 m/min respectively. The results demonstrated an expected linear increase in force components with h at speeds of 20 and 60 m/min. However, at the intermediate speed of 40 m/min, there was a transition between about 60 and 80 µm indicating a discontinuous rather than continuous effect of speed. The results enabled determination of the cutting force coefficients Ktc, Kte, Kf c and Kf e, for the ranges examined as well as the coefficients, ki1.0.1 and mi0.1, of the Kienzle equations. These relations will enable macro-mechanic modelling of more complex cutting operations, such as milling, in the future.
    Scopus© Citations 17  1060
  • Publication
    Prediction of tool-wear in turning of medical grade cobalt chromium molybdenum alloy (ASTM F75) using non-parametric Bayesian models
    We present a novel approach to estimating the effect of control parameters on tool wear rates and related changes in the three force components in turning of medical grade Co-Cr-Mo (ASTM F75) alloy. Co-Cr-Mo is known to be a difficult to cut material which, due to a combination of mechanical and physical properties,is used for the critical structural components of implantable medical prosthetics. We run a designed experiment which enables us to estimate tool wear from feed rate and cutting speed, and constrain them using a Bayesian hierarchical Gaussian Process model which enables prediction of tool wear rates for untried experimental settings. The predicted tool wear rates are non-linear and, using our models,we can identify experimental settings which optimise the life of the tool. This approach has potential in the future for real time application of data analytics to machining processes.
    Scopus© Citations 15  263