Porous ceramic aerostatic bearings enable precise and smooth motion and improved stiffness compared with widely used orifice restrictor bearings. However, the processing techniques so far used are too complex or rely in lowering the sintering temperature to increase fluid flow.Preferred combinations of fine-grade alumina powders and starch granules were used to produce quality porous structures using fixed processing parameters. Component shrinkage, permeability, pore size and elastic properties were comprehensively characterised as a function of porosity.The new porous ceramic structures exhibited controllable and reproducible permeability and modulus, within the range required for ultra-precision porous aerostatic applications.(c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The cooling efficiency of grinding fluids in deep grinding, at different material removal rates and grinding speeds, has been investigated. Two ‘inverse’ methods have been proposed to determine the level of convective heat transfer coefficients of grinding fluids, by matching the theoretical and experimental grinding fluid burn-out thresholds or matching the theoretical and measured grinding temperatures. Instead of using a constant chip melting temperature to estimate the energy partition to the grinding chips, the chip temperature and chip energy were calculated using the newly developed approach considering the variation of chip size, deformation and heat transfer at the abrasive/work interface. The variation of grinding heat taken away by the process fluids and grinding chips under different process parameters has been calculated, which shows the importance of cooling effects by the grinding fluids and the transition of thermal characteristics of deep grinding from cooling dominant to ‘dry’ grinding regime, where a large percentage of grinding heat is taken away by the grinding chips.

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 condition.

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.

The aim of this work is to identify relationships between the input variables and the process response and to develop predictive models that can be used in the design of new friction surfacing applications. Moreover to investigate the use of standard CNC machines for friction surfacing. The experimental design techniques and response surface methodology were used to investigate and select the combination of factor levels that produced the optimal response. The main effect of the velocity ratio obtained by dividing the feed rate of mechtrode with traverse rate of substrate was observed to be the most significant factor on the process response. Based on the results of optimisation it was observed that the lower to intermediate levels of rotational speed and intermediate to higher levels of velocity ratio produced good coating quality.

The performance of a porous-ceramic hydrostatic journal bearing manufactured by the starch consolidation (SC) technique has been examined using a highly instrumented test rig. The results have been compared with those of a 5-recess hydrostatic bearing of the same size and comparable design, under the same testing conditions. The SC porous-ceramic bearing showed an improved performance over the conventional hydrostatic bearing. Static and rotational stiffness were 95 per cent and over 150 per cent higher, respectively. In addition, the porous ceramic bearing exhibited a more economic performance with a 64 per cent lower flowrate and pumping power than the hydrostatic bearing. In terms of heat generation, the porous ceramic bearing showed 50 per cent lower temperature rise.

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 high efficiency deep grinding (HEDG), creep feed and finish grinding.

The development of high performance grinding machines together with the latest superabrasive technology has the potential to impact significantly on existing process chains. Abrasive machining is one material removal process that has the potential to span several orders of magnitude in terms of stock removal. This ranges from high efficiency deep grinding (HEDG) which can now compete with conventional cutting processes and provides the potential for improved surface integrity, surface finish and form accuracy, through to superfinished surfaces with roughness values as low as 10nm Ra. Thus, using a single machine tool and a single set-up, exceptionally high stock removal rates are achievable in a roughing cycle followed by superfinishing to generate the required surface characteristics and profile, providing higher precision and reduced manufacturing costs.

In order to investigate the surface and subsurface integrity of diamond-ground optical glasses, a Tetraform ‘C’ machine tool featuring high close-loop stiffness was used to conduct the ultra-precision machining of fused silica and fused quartz assisted with electrolytic in-process dressing (ELID). An acoustic emission (AE) sensor and a piezoelectric dynamometer were used to monitor the grinding process to correlate the processing characteristics with the generated surface and subsurface integrities, which were characterized by atomic force microscope (AFM), scanning electronic microscope (SEM), and nano-indentation technique. Experimental results showed that for optical glasses the fracture toughness value can be used to predict the machinability while its bigger value always means a better surface and subsurface integrity. During the grinding process of optical glasses, the smaller amplitude and RMS values of AE signal, as well as the smaller grinding forces and the ratio of normal force to tangential force, correspond to a better surface and subsurface integrity. With selected machining parameters and a 6–12 μm grain-sized diamond-grinding wheel, nanometric quality surfaces (Ra<5 nm) with minimal subsurface damage depth (< 0.5 μm) can be generated for fused quartz on Tetraform ‘C’.

Surfaces are the primary place of contact between a biomaterial and its host organism. Typically, prostheses have to fulfil demanding structural and mechanical requirements, yet the material best for those functions may be bio-incompatible. Surface treatment or coating provides a means to overcome that problem, which means both integration within the host physiology and stabilization with respect to corrosion and wear. The adsorption of biomacromolecules is pivotal for biocompatibility. The impossibility of keeping proteins away from most implants means that very careful consideration has to be given to this aspect, and both prevention (for bloodstream implants) and promotion (for bone replacement and repair) occur with equal importance. This paper also considers the metrology of relevant physical and chemical aspects of surfaces.

Based on the concept of the interaction between a magnetic and electric field, a magnetic field was suppressed on the Electrochemical Machining (ECM) setup to improve the copying accuracy of ECM. Mathematical modeling and finite element modeling of the magnetic field was also developed using ANSYS to study the influence of permanent magnet design on the ECM process. The results indicate that by introducing the magnetic field the threshold of electrochemical reaction is decreased and the tracks of ions become complicated which makes the chemical reaction more extensive and more uniform in the inter-electrode gap. The distribution of magnetic field in the gap helps to improve the machining accuracy and the process efficiency, when the permanent magnet is at the end of the electrodes. Experiments have been carried out to validate the results of finite element analysis and the effect of a magnetic field on the ECM process is discussed.

Developments in measuring surface temperatures during grinding at high specific material removal rates using PVD low melting point coatings are reported. This paper considers the use of this type of coating to determine the finished surface temperature and the thermal gradient below the workpiece surface under aggressive grinding conditions. Theoretical surface temperatures derived from mathematical modelling are compared to those measured by the PVD coating technique. Theoretical temperatures showed good correlation to the measured temperatures. Metallographic examination including Vickers microhardness testing was used to validate the measured thermal gradients and depth of phase transformations. The effect of the heating rate due to the grinding conditions was shown to have a significant influence on the A3 austenitic transition temperature. The technique of using low melting point PVD coatings is shown to offer a robust measurement technique for the determination of the finished surface temperature of a ground component, within aggressive environments and at high specific material removal rates.

By using experimental data including the monitored temperature and power signals, combined with detailed theoretical analysis, the relationship between the undeformed grinding chip thickness and specific grinding energy has been studied and used to derive the heat flux distribution along the wheel-work contact zone. The relationship between the grinding chip thickness and specific grinding energy (SGE) has been shown to follow an exponential trend over a wide range of material removal rates. The distribution of the total grinding heat flux, qt, along the grinding zone does not follow a simple linear form. It increases at the trailing edge with sharp gradients and then varies nearly linearly for the remainder of the contact length. The heat flux entering into the workpiece, qw, is estimated by matching the measured and theoretical grinding temperatures, and it has been found that the square law heat flux distribution seems to give the best match, although the triangular heat flux is good enough for most cases to generate accurate temperature predictions. With the known heat flux distributions of qt and qw, the heat flux to the grinding fluid can then be estimated once the heat partitioning to the grinding wheel is determined by the Hahn model for a grain sliding on a workpiece. The convective heat transfer coefficient of the grinding fluid has been shown to vary along the grinding zone. An understanding of this variation is important in order to optimise the grinding fluid supply strategy, especially under deep grinding conditions when contact lengths are large. It has been demonstrated that the down grinding mode can provide a beneficial fluid supply condition, in which the fluid enters the grinding zone at the position of highest material removal where a high convective cooling function is needed.

Optical surface finish below Ra 10nm can be achieved on a 'Tetraform C' grinder of ultra-high stiffness, when grinding a low alloy steel with or without the help of ELID (electrolytic in process dressing). Surface roughness generation modelling has been carried out to predict the possible surface roughness values. Efforts have been made to transfer the process knowledge to different grinding mode using a rigid 5-axis Edgetek CNC grinder. The effects of material removal rate and grit size and also that of spark out passes on the surface roughness generated have been investigated.

A new approach is introduced to refine the analysis for the chip energy in the high-efficiency deep grinding process, by considering the heat partitioning at the chip formation area. The analysis for the chip-work subsystem has been combined with the whole thermal system to derive the grinding temperature on the workpiece surface. The variation of chip temperature with material removal rate under different grinding conditions was investigated, and the relationship between the chip temperature and workpiece contact temperature was derived. The grinding temperatures obtained using different approaches were compared with 'measured temperatures', estimated from the depth of thermal damage observed on ground samples.

In the last decade the relevance of modeling and simulation of grinding processes has significantly risen which is caused by industrial needs and is indicated by the number of publications and research activities in this area. This keynote paper results from a collaborative work within the STC G and gives an overview of the current state of the art in modeling and simulation of grinding processes: Physical process models (analytical and numerical models) and empirical process models (regression analysis, artificial neural net models) as well as heuristic process models (rule based models) are taken into account, and outlined with respect to their achievements in this paper. The models are characterized by the process parameters such as grinding force, grinding temperature, etc. as well as work results including surface topography and surface integrity. Furthermore, the capabilities and the limitations of the presented model types and simulation approaches will be exemplified.

In this paper the application of high efficiency deep grinding to cylindrical plunge grinding is demonstrated and thermal modelling used to optimise the grinding cycle for an automotive steel and cast iron. The benefits associated with the high work speed achievable in cylindrical grinding are highlighted and both thermal modelling and experimental measurements have established that low workpiece temperatures are possible even when specific material removal rates of 2000 mm3/mm.s are achieved. Surface integrity studies based on microstructural analysis and Barkhausen noise have also demonstrated the effectiveness of the process.

ELID grinding of BK7 glass and Zerodur was investigated using acoustic emission. Experiments showed that the contacting area between the wheel and workpiece in a grinding process was critical to influence wheel loading for a fine grit size resin-bonded cup wheel. ELID can be used for efficient material removal when the wheel/workpiece contacting area is large. Correlations were observed between the dressing intensity on the ELID wheel and the detected AE signals. Aggressive ELID dressing parameters for grinding with finer grit size wheels corresponded to a lower AE level. With an increase in the processing time of an ELID wheel, low and stable AE amplitudes became large with fluctuations due to the deterioration of the grinding wheel. Results indicate that the AE sensing technique has the potential to be adopted as an effective method for monitoring an ultra precision grinding process, identifying the condition of the grinding wheel and investigating the mechanism of ELID grinding.

Conventional grinding of BK7 glass will normally result in brittle fracture at the surface, generating severe sub-surface damage and poor surface finish. The precision grinding of BK7 glass in parallel and cross grinding modes has been investigated. Grinding process, maximum chip thickness, ductile/brittle regime, surface roughness and sub-surface damage have been addressed. Special attention has been given to the condition for generating a ductile mode response on the ground surface. A polishing–etching method has been used to obtain the depth of sub-surface damage. Experiments reveal that the level of surface roughness and depth of sub-surface damage vary differently for different grinding modes. This study gives an indication of the strategy to follow to achieve high quality ground surfaces on brittle materials.

The current application of fluids in grinding processes is discussed, the issues related to the use of both mineral oil and water based fluids and the desire to move towards minimum quantity lubrication (MQL) or even dry grinding. The impact of fluid application strategy on workpiece quality is considered. In particular the importance of reliable thermal modelling and knowledge of the thermal partitioning of heat is essential if robust fluid application strategies are to be developed. Examples are given showing how an understanding of the thermal characteristics of the process can be used to develop different and successful fluid application strategies for various grinding regimes from creep feed through to high efficiency deep grinding (HEDG). The possibility of using solid lubricants is also discussed for particular grinding regimes.