Honghua Su

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 study on cutting behavior of vitrified cubic boron nitride wheel and electroplated cubic boron nitride wheel in high-speed grinding of (TiCp + TiBw)/Ti-6Al-4V composites

High-speed grinding experiments of particle reinforcing titanium matrix composites ((TiCp + TiBw)/Ti-6Al-4V) were carried out with vitrified cubic boron nitride wheel and electroplated cubic boron nitride wheel, at the wheel speed ranged from 80 to 140 m/s. The cutting behavior, that is, grinding force, grinding temperature, specific grinding energy, and ground surface morphology, and grinding chips are analyzed. The results indicate that compared to the workpiece speed and the depth of cut, the wheel speed has a more significant influence on the grinding forces. The grinding temperature and specific grinding energy obtained with the vitrified cubic boron nitride wheel are always larger than those with the electroplated cubic boron nitride wheel. Based on the comprehensive consideration in terms of grinding force, grinding temperature, and specific grinding energy, the electroplated cubic boron nitride wheel is more suitable than vitrified cubic boron nitride wheel for high-speed grinding particle reinforcing titanium matrix composites. The removal of the reinforcements of particle reinforcing titanium matrix composites is mainly by means of pullout, fracture or crushing, micro-cracks, voids, and smearing. The segment chips containing the reinforcements are formed during high-speed grinding of particle reinforcing titanium matrix composites.

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.

Comparative Investigation on Brazing Behavior, Compressive Strength, and Wear Properties of Multicrystalline CBN Abrasive Grains

In order to fabricate the abrasive wheels with good grain self-sharpening capacity, two types of multicrystalline CBN grains, that is, polycrystalline CBN (PCBN) and binderless CBN (BCBN), were brazed using Cu-Sn-Ti alloy, respectively. Comparative investigation on the brazing interface, compressive strength, and wear properties of the different grains was carried out. Results obtained show that the PCBN grains have more intricate reaction, more complicated resultants, and thicker reaction layer than the BCBN counterparts under the identical brazing conditions. Though the average compressive strength of the PCBN grains is similar to that of BCBN ones, stronger self-sharpening action by virtue of the microfracture behavior takes place with BCBN grains during grinding. As a consequence, compared to the brazed PCBN wheels and the conventional monocrystalline CBN (MCBN) ones, longer service life is obtained for the brazed BCBN wheels.

Simulation on Grind-Hardening Residual Stress Field of 48MnV Steel

By using ANSYS, the temperature distribution in workpiece of steel 48MnV under the actions of a moving thermal source, is first carried out by FEM for non-linear transient temperature field. On this basis, the residual stress distribution in the workpiece under the action of temperature variation and moving grinding loads is determined by FEM for thermo elastic-plasticity. The result shows that the existent residual stress on surface of grinding hardening is press. The reason of this is discussed. The difference between the simulated value and measured value of grind-hardening stress is acceptable.

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.

Removal Mechanism of Titanium Alloy Ti6Al4V Based on Single-Grain High Speed Grinding Test

Single-grain grinding test plays an important part in studying the high speed grinding mechanism of materials. In this paper, a new method and experiment system for high speed grinding test with single CBN grain are presented. In order to study the high speed grinding mechanism of TC4 alloy, the chips and grooves were obtained under different wheel speed and corresponding maximum undeformed chip thickness. Results showed that the effects of wheel speed and chip thickness on chip formation become obvious. The chips were characterized by crack and segment band feature like the cutting segmented chips of titanium alloy Ti6Al4V.

Predicting the grinding force of titanium matrix composites using the genetic algorithm optimizing back-propagation neural network model:

A back-propagation neural network BP model and a genetic algorithm optimizing back-propagation neural network (GA-BP) model are proposed to predict the grinding forces produced during the creep-feed deep grinding of titanium matrix composites. These models consider quantitative and non-quantitative grinding parameters (e.g. up-grinding mode and down-grinding mode) as inputs. Comparative results show that the GA-BP model has better prediction accuracy (e.g. up to 95%) than the conventional regression model and the BP model. Specific grinding energy was calculated against the grinding parameters and grinding modes based on the grinding forces predicted by the GA-BP model.

Preparation and Characterization of Self-Lubrication CBN Grinding Wheel Containing Graphite as Lubricant

Self-lubrication CBN abrasive composite blocks and corresponding grinding wheels were made through the sintering process of CBN grains, graphite particles and Cu-Sn-Ti alloy at 920° for 30 min. The mechanical strength of the composite blocks was measured by means of the three-point bending experiments. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) were employed to characterize the fracture morphology and the interfacial microstructure of the composite blocks. Dressing experiments were carried out and the graphite film on the CBN grain surface was observed. The results obtained show that the bending strength of the composite blocks with 5 wt.% graphite particles reached 116 MPa, which met the mechanical requirements of the working layer of the grinding wheels. Chemical joining has taken place at the interface of CBN/Cu-Sn-Ti and graphite/Cu-Sn-Ti during the sintering process. Graphite film has been formed and spread to the grain surface after dressing.