Now showing 1 - 9 of 9
  • 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.
      708
  • 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.
      303
  • Publication
    Dual mode control of the rotational grinding process
    The rotational grinding process enables the production of substrates to meet the submicron planarity specifications required for micro-fabrication of semiconductor integrated circuits. Improvements in process capability, with respect to both form and finish, have been generally realised by the development of machine tools and systems based on a principle of precise and predictable “position” control. An alternative principle for optimisation is demonstrated here comprising a dual mode control system where a “finishing mode” is based on local normal force control. Test results show significant relative improvements in levels of surface roughness and a reduction in the normal spatial variation.
      440Scopus© Citations 2
  • 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.
      893Scopus© Citations 7
  • Publication
    High Performance Cutting in the New Era of Digital Manufacturing - A Roadmap
    We are rapidly moving into the new era of digitisation, into an era of the Massive Internet of Things - towards the Gigabit Society and towards 5G Technology. The implications are truly far reaching. Rapid transformation through the implementation of INDUSTRY 4.0 is becoming visible in industries all over the world. Disruption to the more traditional industrial practices and processes is inevitable. High Performance Cutting is no exception. Developments in the Internet of Things (IoT) opens up new and extremely powerful capabilities to help us gain a significantly deeper understanding of the fundamentals of cutting processes and offers entirely new connectivity possibilities at all interfaces, some old and some new, 'between the Chip Root and the Cloud'. This supports us in our attempts since the foundation of CIRP in 1951 to remove technological roadblocks and can lead on a new journey towards new and unprecedented scientific/technological developments as well as new business models for companies involved in the various elements of the supply chain for cutting processes (DIN 8580). 'Performance' will take on a new and unanticipated meaning over what was originally meant when we established this CIRP-HPC Conference back in the early 2000’s. In this paper a critical review of a previous roadmap is undertaken for cutting processes presented in a CIRP Keynote Paper in 2003 by Byrne, Dornfeld and Denkena [1] and new thoughts and ideas are presented on a vision for a 2020 skeleton Roadmap for High Performance Cutting in the new age of Digitisation.
      401Scopus© Citations 24
  • 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.
      1121Scopus© Citations 18
  • 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.
      285Scopus© Citations 16
  • 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.
      381Scopus© Citations 16
  • 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.
      801Scopus© Citations 23