Browsing by Author "Jin, T."

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    Burn threshold prediction for high efficiency deep grinding
    (2011-06-01T00:00:00Z) Bell, Andrew John; Jin, T.; Stephenson, David J.
    Burn threshold diagrams are useful for the prediction of thermally induced grinding damage and were originally developed to describe the conventional shallow cut grinding regime. With the development of new high stock removal grinding processes such as High Efficiency Deep Grinding (HEDG), the prevention of thermal damage to the workpiece is of particular concern. The principle of HEDG is based around the change in thermal characteristics of the grinding process at high Peclet numbers, whereby less heat is partitioned to the workpiece. Conventional burn threshold diagrams are valid for Peclet numbers below 50, well below the values expected in HEDG. This study presents a modified approach to the construction of burn threshold diagrams which takes account of the change in thermal partitioning with Peclet number. The approach has been validated through grinding trials over a range of specific material removal rates.
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    Burn threshold prediction for high efficiency deep grinding
    (Elsevier, 2006) Bell, Andrew; Jin, T.; Stephenson, David J.
    Burn threshold diagrams are useful for the prediction of thermally induced grinding damage and were originally developed to describe the conventional shallow cut grinding regime. With the development of new high stock removal grinding processes such as High Efficiency Deep Grinding (HEDG), the prevention of thermal damage to the workpiece is of particular concern. The principle of HEDG is based around the change in thermal characteristics of the grinding process at high Peclet numbers, whereby less heat is partitioned to the workpiece. Conventional burn threshold diagrams are valid for Peclet numbers below 50, well below the values expected in HEDG. This study presents a modified approach to the construction of burn threshold diagrams which takes account of the change in thermal partitioning with Peclet number. The approach has been validated through grinding trials over a range of specific material removal rates.
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    Electrolytic in-process dressing superfinishing of spherical bearings using metal-resin bond ultra-fine CBN wheels
    (Professional Engineering Publishing, 2011-01-01T00:00:00Z) Raffles, Mark H.; Stephenson, David J.; Shore, Paul; Jin, T.
    The use of electrolytic in-process dressing (ELID) superfinishing has been investigated with the aim of substantially improving surface finish on spherical bearing balls as well as reducing process times. Using ELID in a superfinishing configuration is substantially different from the more conventional precision grinding set-up. With this ELID superfinishing system, metal-resin bonded (MRB) wheels containing very small superabrasives (30 to 0.12 μm) were employed. Surface finishes of 2 nm Ra were achieved with a #12 000 wheel, an order of magnitude better than balls produced using the conventional production techniques of barrelling or polishing. Consistently sub-10 nm Ra finishes were achieved with a #2000 wheel. Different ways of using the ELID system, including ELID 1, ELID 2, and ELID 3, were studied to examine how the different types control the cutting condition at the wheel's surface. It is the ability to control easily the cutting condition of superabrasives of this size that allows mirror surface finishes to be efficiently produced. Monitoring of wheel spindle and ELID power usage was found to provide useful information in assessing the wheel c
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    Predictive grinding process optimisation and monitoring
    (2005-09-09) Leeson, David Christopher; Jin, T.; Stephenson, David J.
    Grinding is one of the oldest and most important metal removal processes, and is capable of high dimensional and surface finish tolerances. It is a complex and expensive process; industry has much to gain by increasing production rates to reduce cost. The major limitation to higher production rates is the risk of thermal damage of the workpiece. This is now being challenged by developments in “High Efficiency Deep Grinding” which has been proven to produce low grinding temperatures at extremely high material removal rates. In order to take advantage of these developments, whilst maintaining the integrity of the workpiece, it is necessary for production engineers to have tools available to them that allow the selection of optimal process parameters and monitor grinding conditions to sustain this optimum. A review of current research efforts in predictive and reactionary methods of optimising grinding process highlight a number of failings. This study leads to the development of a new system that employs analytical and empirically derived indicators of thermal damage to enable an operator to select optimal but safe grinding conditions. The system also provides a monitoring function that can warn of the onset of thermal damage and make recommendations to the machine operator. A demonstration of the systems possible benefits in an industrial context is presented. Validation via simulation is also performed. Predicted finished workpiece temperatures are compared against measurements taken using embedded thermocouple and the PVD coating melt depth method. The ability of the system to predict bum is also tested across a range of grinding conditions. The possibility of using the system as part of an adaptive controller is also reviewed and directions for further work are identified.
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    Reconfigurable micro-mould for the manufacture of truly 3D polymer microfluidic devices
    (Cranfield University, 2009-03-31) Marson, Silvia; Attia, Usama M.; Allen, David M.; Tipler, P.; Jin, T.; Hedge, J.; Alcock, Jeffrey R.; Rajkumar Roy; Essam Shehab
    This paper concerns the concept, the design and the manufacturing steps for the fabrication of a precision mould for micro-injection moulding of truly three dimensional microfluidic devices. The mould was designed using the concept of replaceable cavities to enable the flexible development of the complex microfluidic device and to reduce machining time and therefore costs during the prototyping, testing and subsequent production phase. The precision machining technique used for the cavity manufacture was micromilling.
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    A study of the convection heat transfer coefficients of grinding fluids
    (Technische Rundschau, Hallwag Publishers; 1999, 2008-05-09T00:00:00Z) Jin, T.; Stephenson, David J.
    By using hydrodynamic and thermal modelling, the variation of the convection heat transfer coefficient (CHTC) of the process fluids within the grinding zone has been investigated. Experimental measurements of CHTC for different grinding fluids have been undertaken and show that the CHTC depends on the grinding wheel speed and the fluid film thickness within the contact zone. The film thickness is determined by grinding wheel speed, porosity, grain size, fluid type, flow rate and nozzle size. The CHTC values are compared for a wide range of grinding regimes, including HEDG, creep feed and finish grinding.
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    Temperatures in high efficiency deep grinding
    (Cranfield University, 2009-02) Bell, Andrew John; Stephenson, Tom; Jin, T.
    This research considers the temperatures generated in the workpiece during profile and cylindrical traverse grinding in the High Efficiency Deep Grinding (HEDG) regime. The HEDG regime takes large depths of cut at high wheel and workpiece speeds to create a highly efficient material removal process. This aggressive processing generates high temperatures in the contact zone between the wheel and workpiece. However, the beneficial contact angle and the rapid removal of the heated wheel – workpiece contact zone results in low temperatures in the finished surface. Temperatures in the ground surface can be predicted with knowledge of the specific grinding energy and the grinding parameters used. Specific grinding energies recorded at high specific material removal rates demonstrated a constant value of specific grinding energy dependent on cutting and contact conditions, improving accuracy of the predictive model. This was combined with a new approach to burn threshold modelling, which demonstrated an improved division of damaged and undamaged surfaces. Cutting and contact conditions in the grinding profile vary dependent on their position. This thesis shows how temperatures vary with location and estimates the partitioning of the heat flux to the regions of the grinding profile. This suggested a constant partitioning of energy to each of the three surfaces considered independently of specific material removal rates. Further a potential link was shown between the surface and the sidewall of the grinding profile, which allows temperatures in a secondary surface to be predicted given knowledge of that in the primary. Finally, the work has demonstrated the feasibility of the Superabrasive Turning process. Using small values of feed per turn and high workpiece feedrates promoted high values of removal rate with low depths of thermal penetration in the as ground surface. Thus the process has become viable for high speed cylindrical traverse grinding.
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    Thermal characteristics of grinding fluids
    (Cranfield University, 2008) Massam, Mark; Stephenson, David J.; Jin, T.
    High Efficiency Deep Grinding (HEDG) combines high depths of cut, high grinding wheel speeds with high work piece feed rates to deliver a very high stock removal process that can produce components free of surface damage. High contact temperatures are a characteristic of the process and this produces a mass of hot grinding sparks being ejected from the grinding zone. Neat oil cutting fluids are typically used in HEDG due to their excellent lubricity, but the high grinding wheel speeds employed leads to high levels of highly volatile cutting fluid mist in the machine canopy. This mist can mix with the hot grinding sparks being ejected from the grinding zone to create a potential fire hazard. The project aim was to produce a cutting fluid application strategy for the HEDG regime, focusing on establishing the thermal characteristics of cutting fluids in order to determine the optimum cutting fluid for the HEDG process. The cutting fluid application strategy also involved investigating the optimum means by which to apply the cutting fluid, based on minimising amount of cutting fluid used in the process and in reducing the potential fire hazard. The characteristics that have a thermal impact on the grinding process are the cooling, lubrication, ignition and misting properties of the fluid. A series of tests were established to investigate these properties and therefore allow different fluids to be compared and contrasted for their suitability for the HEDG regime based. Once an optimal cutting fluid had been established, the project then investigated the optimal method of applying this fluid, with particular reference to the type and design of the nozzle used to apply the fluid to the grinding zone. As part of these trials, a series of benchmark tests were also conducted using long established cutting fluid application techniques to enable the benefits of the new strategy to be evaluated. The project concluded that high viscosity neat oil ester based cutting fluids were the best fluids to be used in the HEDG regime due to they excellent lubricity and low misting properties coupled to their relatively high resistance to ignition when compared to neat mineral oils. The studies also found that using a high viscosity ester based fluid and then applying it using a coherent jet nozzle, significant reductions in the grinding powder and specific grinding energy could be achieved whilst significantly lowering the amount of mist in the machine, thus reducing the potential fire hazard and the volume of cutting fluid used by the process.