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Abstract: This paper aims to reveal the material removal mechanisms and the mechanics behind the vibration-assisted cutting (VAC) of unidirectional fibre reinforced polymer (FRP) composites. Through a comprehensive analysis by integrating the core factors of the VAC, including fibre orientation and deformation, fibre–matrix interface, tool–fibre contact and tool–workpiece contact, a reliable mechanics model was successfully developed for predicting the cutting forces of the process. Relevant experiments conducted showed that the model has captured the mechanics and the major deformation mechanisms in cutting FRP composites, and that the application of ultrasonic vibration in either the cutting or normal direction can significantly decrease cutting forces, minimise fibre deformation, facilitate favourable fibre fracture at the cutting interface, and largely improve the quality of a machined surface. When the vibrations are applied to both the cutting and normal directions, the elliptic vibration trajectory of the tool tip can bring about an optimal cutting process. There exists a critical depth of cut, beyond which the fibre–matrix debonding depth is no longer influenced by the vibration applied on the tool tip. [Copyright &y& Elsevier]

Abstract: This paper investigates the feasibility to achieve grinding-hardening in a plunge cylindrical grinding process. To understand the mechanisms, a temperature-dependent finite element heat transfer model incorporating a triangular moving heat source was developed to describe the temperature field, thus to predict the thickness of the grinding-hardened layer. The analysis carried out included the variation effect of depth of cut caused by the change in wheel–workpiece engagement. The model was applied on quenchable steel 1045 and the analysis was verified experimentally. It was shown that the heating cycle in plunge cylindrical grinding is the result of consecutive heating and cooling processes, varying from location to location in a workpiece. The ratio of the workpiece speed to the infeed rate plays an important role in the heat treatment cycle. [Copyright &y& Elsevier]

Abstract: This paper investigates the grinding–hardening both theoretically and experimentally with a plunge surface-grinding process. Theoretically, the paper presents a temperature-dependent finite element heat transfer model, incorporating a triangular moving heat source and various cooling conditions, to investigate the phase transformation kinetics, thus to predict the thickness of a layer hardened. The temperature variation and thickness of the hardened layer were also investigated experimentally on quenchable steel 1045 using dry air and liquid nitrogen as the cooling media. The predictions were in good agreement with the experimental results. It was found that the phase transformation follows the martensitic kinetics. The application of liquid nitrogen enhances the transformation of retained austenite to martensite and results in a refinement of the martensitic structure. [ABSTRACT FROM AUTHOR]

Abstract: Through a systematic experimental investigation into the polishing of polycrystalline diamond composites by the dynamic friction technique, this paper identified three major regimes of polishing conditions: the regime capable of a low material removal, that enabling a safe, high removal processing, and that of an unsafe but ultra-high material removal. The study concluded that a higher polishing pressure–speed combination results in a high material removal rate, but with a greater risk of workpiece cracking. At a too low-pressure–speed combination, on the other hand, material removal may not take place. Based on the systematic experimental measurements, the paper established a polishing map to characterise the polishing conditions. It was found that using the polishing parameters determined by this polishing map, a quality surface finish can be obtained efficiently in duration about 10 times shorter than that of the abrasive polishing process currently used in industry. [Copyright &y& Elsevier]

Abstract: This paper investigates the mechanical and thermal effectiveness of a new segmented grinding wheel system with controlled radial coolant supply. The applicability of the system was examined in terms of grinding forces, specific energy and ground surface integrity in plunge grinding of AISI 4140 steel. It was found that compared with a standard grinding wheel, the new system enhanced the grindability with a lower specific energy and less application of coolant. It was also found that the new grinding system could effectively maintain the sharpness of active cutting edges, evidenced by the minimisation of ploughing and rubbing deformation in ground workpieces. The cleaning capacity of the wheel was improved and chip loading on wheel surfaces was avoided. Meanwhile, the new wheel system generated better surface integrity without tensile residual stresses. [Copyright &y& Elsevier]

Abstract: Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes. [Copyright &y& Elsevier]

Abstract: This paper investigates the mechanisms of material removal in dynamic friction polishing of polycrystalline diamond composites through the analysis of polishing-produced debris. The specimens used were PCD compacts composed of diamond and silicon carbide. In order to uncover the debris’ structure, high-resolution transmission electron microscopy (HRTEM), electron diffraction and electron energy loss spectroscopy (EELS) were used. Additionally, the density and the sp2 to sp3 ratio in the hybridized carbon materials of the debris were estimated from the EELS spectra. It was found that the debris were mainly of amorphous structure and consisted of different forms of carbon, silicon oxide/carbide, iron oxides, etc. The results show that during polishing, the diamond has transformed to non-diamond carbon, and silicon carbide to amorphous silicon carbide/oxide. [Copyright &y& Elsevier]

Abstract: This paper investigates the material removal mechanisms of PCD using the dynamic friction polishing technique. Scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and Raman spectroscopy were used to identify the mechanisms by analyzing the specimen surfaces and debris produced by polishing. It was found that the material removal occurred in a rather complex way, which can be a chemo-mechanical process, diffusion, oxidization and evaporation, or their combinations. [Copyright &y& Elsevier]

Abstract: An analytical or experimental method is often unable to explore the behavior of a metal matrix composite (MMC) during machining due to the complex deformation and interactions among particles, tool and matrix. This paper investigates the matrix deformation and tool–particle interactions during machining using the finite element method. Based on the geometrical orientations, the interaction between tool and particle reinforcements was categorized into three scenarios: particles along, above and below the cutting path. The development of stress and strain fields in the MMC was analyzed and physical phenomena such as tool wear, particle debonding, displacements and inhomogeneous deformation of matrix material were explored. It was found that tool–particle interaction and stress/strain distributions in the particles/matrix are responsible for particle debonding, surface damage and tool wear during machining of MMC. [Copyright &y& Elsevier]

Abstract: This paper presents a mechanics model for predicting the forces of cutting aluminum-based SiC/Al2O3 particle reinforced MMCs. The force generation mechanism was considered to be due to three factors: (a) the chip formation force, (b) the ploughing force, and (c) the particle fracture force. The chip formation force was obtained by using Merchant''s analysis but those due to matrix ploughing deformation and particle fracture were formulated, respectively, with the aid of the slip line field theory of plasticity and the Griffith theory of fracture. A comparison of the model predictions with the authors’ experimental results and those published in the literature showed that the theoretical model developed has captured the major material removal/deformation mechanisms in MMCs and describes very well the experimental measurements. [Copyright &y& Elsevier]

Abstract: This paper investigates the interface temperature rise in polishing a polycrystalline diamond (PCD) surface. First, the Greenwood–Williamson''s statistical asperity model is applied to characterise the surface roughness of a PCD specimen. The result is then used to estimate the contact area and total number of contact asperities under an applied polishing load. The heat generated is taken as the product of the friction force and the relative sliding velocity between the PCD asperities and the metal disk surface. The Jaeger''s moving heat source analysis is then applied to determine the fractions of heat flux flowing into the PCD asperities and their counterpart in contact sliding and to give rise to the average temperature rise. A comparison with the observations made in the authors'' experiments and those reported in the literature showed that the model predicts very well the temperature rise at the polishing interface. [Copyright &y& Elsevier]

Abstract: The wear mechanisms of cutting tools made of tungsten-carbide (WC), PCBN and PCD were investigated using the tool life and temperature results available in the literature. For tool/work combinations WC/steel and PCBN/hardened-steel, under practical conditions, tool wear was found to be greatly influenced by the temperature. It was concluded that the most likely dominant tool wear mechanism for WC is diffusion and that for PCBN is chemical wear. For PCD, more experimental results and hence further research is required to determine the dominant wear mechanism. [Copyright &y& Elsevier]

Abstract: This paper develops a quantitative model to predict the power of coolant penetration into the grinding zone of a segmented wheel. The model accounts for the coolant properties and system design characteristics governing the penetration mechanism revealed by the theory established in Part 1 of this series study. By coupling with the author''s previous mist formation analysis, the model offers a quantitative control guideline for the optimal use of grinding coolants. [Copyright &y& Elsevier]

Abstract: This paper aims to study the mechanism of coolant penetration into a wheel-work contact zone when a segmented or conventional wheel is used in surface grinding. Based on the principles of fluid motion and considerations of spin-off and splash, analytical models for both conventional and segmented wheels were developed for predicting the power of pumping coolant into the contact zone. It was revealed that the pumping power of a segmented wheel increases with the increment of wheel speed, but that of a conventional wheel decreases. It was shown that coolant minimisation in surface grinding is possible when using a segmented wheel, although its efficiency depends on the wheel speed and methods of coolant supply. The model predictions were in good agreement with experimental observations. [Copyright &y& Elsevier]

It has been found that using a segmented grinding wheel with a fluid chamber can significantly minimise the quantity of coolant while improving the ground surface integrity. The present investigation aims to explore the fluid flow mechanism in such a wheel system. To this end, the Weber theory for Newtonian jet instability was applied to quantitatively determine the contribution of coolant flow rate to mist and ligament modes. A semi-analytical model was then developed to predict the mist flow rate by taking into account both the grinding parameters and fluid properties. It was shown that the model prediction was in good agreement with experimental measurements. Because of the comprehensive integration of variables in the formulation, the model provides a good fundamental understanding of the mist formation and offers a practical guideline for the selection and use coolant in minimising the mist flow rate. [Copyright &y& Elsevier]

Existing analytical thermal models for predicting surface burns due to grinding have limited use because of their reliance on parameters that are not readily obtainable in practice. This paper presents a practical and consistent fuzzy rule-based model for estimating the grinding conditions at which “burn limits” occur. The model consists of 37 absolute and eight relative rules. It has a wide range of applications over many types of steels, Alundum wheels, and grinding conditions. It is also simple to implement, from a rule-chart mode to an intelligent on-line adaptive control mode. [Copyright &y& Elsevier]

This paper aims to understand the machinability of epoxy composites reinforced by unidirectional carbon fibres when subjected to orthogonal cutting. It was found that the subsurface damage and its mechanisms of a machined component are greatly influenced by fibre orientation. The material’s bouncing back is a characteristic phenomenon associated with the cutting of a fibre-reinforced composite. Three distinct deformation zones appear, i.e., chipping, pressing and bouncing when the fibre orientation is <90°. Otherwise, fibre-bending during cutting will become more significant and subsurface damage caused by fibre-matrix debonding will be severer. As a result, surface roughness, subsurface damage and cutting forces all change dramatically with the fibre orientation. It was also found that the curing conditions of making the composites do not have an obvious effect on the machinability, though the mechanical properties of the materials vary. [Copyright &y& Elsevier]

This paper revisited some wheel–workpiece interaction problems in surface grinding including the profile of heat flux and the variation of the wheel’s elastic modulus. A method of using an optical microscope and a CCD camera was applied to capture the depth and width of the heated zone, the details of the temperature field and the stability of the heat flux. It was found that the heat flux in up-grinding can be modeled as a triangle with its apex at the inlet of the wheel–workpiece contact arc. The elastic modulus of the grinding wheel decreases significantly when the grinding temperature is beyond a critical value and can be described by a power law. It was also found that the depth of cut has almost no effect on the partition of the grinding energy. [Copyright &y& Elsevier]

Abstract: This investigation aims to develop a quantitative model to estimate the material removal of polycrystalline diamond composites (PCDCs) by dynamic friction polishing. The model accounts for the contributions from the constitutive characteristics and thermal properties of the materials and the key polishing parameters. It was found that the material removal was dominated by six dimensionless variable groups involving chemical reaction, diffusion and mechanical wear. A comparison with the experimental measurement showed that the model predicts quantitatively and can be used conveniently for process planning and equipment design. [Copyright &y& Elsevier]

Abstract: This paper studies an innovative development of a steel grinding–hardening technology using an inert cryogen—liquid nitrogen. It was found that phase transformations took place during grinding with the application of liquid nitrogen and resulted in hardened surface layer in a ground component. The layer had a fine laths martensite structure which gave rise to a remarkably high hardness. It was also shown that the treatment can produce superior surface integrity, with compressive surface residual stresses and without surface oxidation. Due to the inert nature of the liquid nitrogen, the grinding process becomes environmentally conscious. [Copyright &y& Elsevier]