Yucan Fu

Optimization design of grinding wheel topography for high efficiency grinding

Abstract In view of the limitation of prior topography models of the grinding wheel, a new method for optimization design of grinding wheel topography is advanced. The optimization model can be used to optimize the topography in accordance with machining demands and grinding parameters as well as optimize grinding parameters in accordance with the topography and machining demands. Furthermore, a superabrasive slotted grinding wheel is designed as a practical application of the optimization model and a creep-feed deep grinding experiment is carried out to verify the optimization results.

Interfacial reaction between cubic boron nitride and Ti during active brazing

Thermodynamic and reaction process analyses were performed to understand the joining characteristic during high temperature brazing between cubic boron nitride (CBN) grit and a silver-base filler alloy containing Ti as an active element. Experimental information on the microstructure of the brazed joint, the composition of the interface, and the shape of the compounds formed on the surface of the grit was obtained by scanning electron microscopy, energy-dispersive x-ray, and x-ray diffraction. The results indicate that Ti in the molten filler alloy facilitated good wetting between the solid CBN crystals and braze filler alloy. The transition layer formed by the interaction of TiN and TiB2 was one of the key factors in joining the CBN and steel substrate.

Comparative investigation on wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains in high-speed grinding

High-speed grinding experiments were conducted on a nickel-based superalloy Inconel718 with the monolayer brazed wheel containing monocrystalline cubic boron nitride grains and polycrystalline cubic boron nitride grains. Comparative investigation on the wear behavior and self-sharpening phenomenon of polycrystalline cubic boron nitride and monocrystalline cubic boron nitride grains was carried out based on the fractal analysis. The results obtained indicate that the wear process of the monocrystalline cubic boron nitride grain cutting edges is, in order, attritious wear → large fracture → micro fracture → large fracture → attritious wear, while that of the polycrystalline cubic boron nitride grain cutting edges is micro fracture → attritious wear → micro fracture. Micro fracture of polycrystalline cubic boron nitride grain occurs easily in the particular zone where large impact load is formed due to the first contact between the grain cutting edges and the workpiece material. The fractal dimension of monocrystalline cubic boron nitride wheel is 2.040–2.047, while that of the polycrystalline cubic boron nitride wheel is 2.049–2.054, which indicates that the polycrystalline cubic boron nitride grain cutting edges are finer than that of the monocrystalline cubic boron nitride counterparts. Compared to monocrystalline cubic boron nitride grains, better performance, that is, smaller radial wheel wear, lower grinding force and forces ratio, is obtained for polycrystalline cubic boron nitride grains due to micro fracture behavior and self-sharpening phenomenon in high-speed grinding.

Chip formation of nickel-based superalloy in high speed grinding with single diamond grit

In order to understand chip formation mechanism during high speed grinding of nickel-based superalloy, grinding tests with single brazed diamond grit were performed with the wheel speed from 20 m/s to 150 m/s. The kinematic grit trace was geometrically optimised to meet the requirement of the real grinding process. The maximum undeformed chip thickness was kept at 1 μmm. Grooves and chips were observed and analysed by means of optical microscope and scanning electron microscope. The results obtained showed that, when the wheel speed was below 60 m/s, the serrated behaviour of the chips was not obvious. However, the typical serrated behaviour took place on the free surface in case of the wheel speed of above 60 m/s. The frequency of the chip segmentation was increased linearly with the increasing grinding speed from 60 m/s to 150 m/s.

Fabrication of Composite Blocks Containing Alumina Bubble Particles for Porous CBN Abrasive Wheels

Alumina (Al2O3) bubble particles were added into the mixture of CBN abrasive grains, Cu-Sn-Ti alloy and graphite particles to prepare the composite blocks for porous CBN abrasive wheels. The specimens were sintered at the temperature of 920°C for the dwell time of 30 min. The bending strength of the composite blocks was measured by the three-point bending tests. The fracture surface of the blocks was characterized. The results show that, the content of alumina bubble particles does not take significant effect on the mechanical strength of the composite blocks. Even the lowest strength of the composite blocks, 98 MPa, is higher than that of the vitrified CBN abra-sive wheels. Cu-Sn-Ti alloy has bonded firmly alumina particles and CBN grains by means of the chemical reaction and corresponding products. Finally, the chip space was formed through the re-moval of the ceramic wall of the alumina bubble particles within the CBN abrasive wheel during dressing.

High Speed Grinding of Nickel-Based Superalloy with Single Diamond Grit

Nickel-based superalloy plays an extremely important role in gas turbine engines in aerospace industry. To understand the high and super high speed grinding mechanism of nickel-based superalloy, the single-grit grinding mechanism is needed to be investigated. Previous studies on single grit were all carried out by mean of cutting or scratching. In this work, a novel experimental set-up of single-grit grinding had been developed to meet the reality of the complex kinematic grinding process. Grooves and collected chips were investigated in grinding of a typical nickel-based alloy GH4169 with wheel speed up to 150 m/s. The groove integrity is improved by increasing the grinding speed even though the chip thickness is kept constant. The typical serrated chips were observed and the frequency of chip segmentation increases linearly with the increasing of the grinding speed. Under high and super high grinding, the thermal softening due to the high temperature in adiabatic shear zone contributes to accelerate the chip formation and leads to decrease the grinding force.

Experimental study on the cooling effects of cryogenic pneumatic mist jet impinging cooling method

Grinding, characterised by its high specific energy consumption, may generate high grinding zone temperature. These can cause thermal damage to the ground surface and poor surface integrity, especially in the grinding of difficult-to-machine materials. Conventional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. Here a new high efficiency cooling technology – Cryogenic Pneumatic Mist Jet Impinging (CPMJI) cooling technology is offered. It utilises the high penetrative power of fast cryogenic air jet combined with a little quantity of water of 0°C to greatly improve heat transfer effects in the machining zone. Experimental results, including heat transfer experiments and grinding experiments, indicate that CPMJI has strong cooling ability and can offer better cooling effects compared to cold air jet and traditional flood cooling method in the grinding of titanium alloy.

Study on coolant-induced hydrodynamic pressure in contact zone while deep grinding with CBN wheels

ABSTRACT The use of coolant has been considered an effective way to avoid workpiece burn in the grinding process. Hydrodynamic pressure induced by coolant in the contact zone is always measured to characterize the coolant condition in the contact zone. In this study, grinding experiments with a cubic boron nitride wheel were first performed to determine the evolution of hydrodynamic pressure during the grinding process. The experimental results showed that when burn happened, hydrodynamic pressure was at a low level and decreased gradually while the temperature and power signals fluctuated sharply. A theoretical calculation model and a 3D air–liquid two-phase numerical simulation model were subsequently constructed to predict the hydrodynamic pressure. Both theoretical calculation and numerical simulation results showed that the hydrodynamic pressure in such a case is in inverse proportion to the gap distance between the wheel and the workpiece. The theoretical calculation results are higher than the numerical simulation results. Furthermore, the experimental results correspond to the results of the 3D air–liquid two-phase simulation, which confirms the validity of this simulation. This article presents an accurate approach to predict hydrodynamic pressure, which provides an effective analytical method of studying and avoiding workpiece burn.

Performance of micro-crystalline ceramic alumina wheels during creep feed grinding nickel-based superalloy

The dramatical reduction of abrasive crystallite size is an efficient way to improve grinding performance of wheels. In the present investigation, the performance of micro-crystalline ceramic alumina wheels in creep feed grinding Inconel 718 is investigated extensively. Grinding forces and temperature were measured and analysed to characterise the grinding process. Surface roughness was used to describe the quality of ground surfaces. Meanwhile, the wheel surface topography was also observed and studied. It was found that grinding forces of 5SG wheel were lower than that of SG wheel. Better surface quality and lower grinding forces and temperature were achieved by TG wheel when compared to SG wheel. Additionally, less adhesion was observed on 5SG wheel surface while dressing with higher feedrate. The results show that, grinding forces decrease when SG abrasives are blended with regular fused abrasives. High aspect ratio of TG abrasives reduces adhesion on the wheel surface. Furthermore, dressing with high feedrate enlarges chip storage space for grinding wheel.

Microstructure and performance of self-lubrication CBN grinding wheels

Cu-Sn-Ti alloy, CBN grains and graphite particles were mixed, moulded and sintered to prepare the self-lubrication CBN abrasive composite blocks and grinding wheels. The mechanical strength of the composite blocks was measured. The fracture morphology and the interfacial microstructure of blocks were characterised. Dressing experiments were conducted. The graphite film was observed on the working surface. Finally, the grinding temperature of self-lubrication CBN grinding wheel was compared with that of the vitrified counterpart. The obtained results show that the bending strength of the composite blocks reaches 116 MPa in case of 5 wt.% graphite particles. Chemical joining has happened within the interface of CBN/Cu-Sn-Ti and graphite/Cu-Sn-Ti. Graphite film has been formed successfully and spread to the working layer surface after dressing. The grinding temperature of the self-lubrication CBN wheel is lower than that of the vitrified counterparts. All this indicates the potential of the graphite self-lubrication CBN grinding wheels in machining difficult-to-cut materials.