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Metal-bonded aggregated cubic boron nitride (cBN) grinding wheels were developed by employing open-pore structures in abrasive layers, aiming to solve the problems, such as severe tool wear, low machining efficiency, and poor quality stability with conventional abrasive grinding wheels. Comparative grinding performances, including grinding forces and force ratio, grinding temperature, specific grinding energy, ground surface roughness were performed between vitrified monocrystalline cBN wheels and porous aggregated cBN wheels. Characterisation of morphologies, such as pore structures and tool wear features were also conducted. Results show that the as-sintered porous aggregated cBN wheels possess the lower grinding forces (reduced by 35.9%–43.3% for F n ′ ; 3.9%–18.8% for F t ′), a smaller grinding temperature (decreased by 10.4%–71.8%), and a stable grinding force ratio of 2.5 in comparison of vitrified monocrystalline cBN wheels. In addition, the ground surface roughness of porous aggregated cBN wheels ranges from 0.76 to 1.19 μm, whilst the other one possesses over 1.65 μm. Furthermore, the worse ground surface quality is obtained, resulting from the smaller chip storage space and poor self-sharpening ability of vitrified monocrystalline cBN wheels compare to porous aggregated cBN wheels. [ABSTRACT FROM AUTHOR]

Aggregated cubic boron nitride (AcBN) grains were developed by sintering monocrystalline cBN (McBN) grains and inter-abrasive metallic phase. The sintering parameters, including sintering temperature and dwelling time, and volumetric proportions of McBN grains are optimized and correlated with the fracture strength of AcBN grains. Quantitative characterization of the grain and scratches were tracked based on the 3D reconstruction technique to study the grain wear characteristics and material removal ability of AcBN grains. The grinding performance for different AcBN grain types, including grinding force, force ratio, volumetric pile-up ratio and volumetric groove removal rate were investigated. Experimental results indicate that the optimized sintering parameters are 800 °C with a dwelling time of 10 min. The AcBN grains with 90% volumetric proportion of McBN grains possess the more stable grinding force ratio and grain wear rate, better self-sharpening ability, and higher grinding ratio. In addition, the material removal efficiency tends to decline and then increase due to the self-sharpening characteristics through the analysis of the volumetric pile-up ratio regardless of AcBN grain types. [ABSTRACT FROM AUTHOR]

Thin-wall diamond trepanning bits are extensively used for processing hard and brittle materials such as engineering ceramics. However, it is difficult to achieve high-efficiency processing of engineering ceramics at a constant feed speed, because of high dynamic compressive strength, high hardness, and low density of engineering ceramics. In this study, a novel composite diamond bit combining sintering and brazing has been designed, along with the low-frequency axial vibration technology, to realize the continuous hole processing of engineering ceramics. Drilling experiments have been conducted on Al 2 O 3 and SiC engineering ceramics with a constant feed speed. The variation of axial force, micromorphology of hole wall surface drilled, as well as the method of removing nesting during the drilling process were analyzed. According to the results, the novel composite diamond bit fabricated by combining sintering and brazing, can achieve the continuous hole processing of engineering ceramics at a constant feed speed, including Al 2 O 3 and SiC. Compared to the conventional drilling (CD), the low-frequency axial vibration drilling (LFVD) can significantly reduce the axial force, and produce fewer plastic scratches on the hole wall surface drilled. In particular, the automatic blanking ratio approaches to 100% by LFVD, and only about 73.58% by CD. It can be concluded that LFVD technology can be used to realize continuous hole processing of engineering ceramics. The research results achieved in this study show that the drilling machinability of engineering ceramics by LFVD and novel composite diamond bit is good. Accordingly, this study provides a useful reference for continuous processing or batch production of engineering ceramics at a constant feed speed. [ABSTRACT FROM AUTHOR]

Abstract High purity engineering ceramics have been increasingly used for constituting novel lightweight ceramic composite armors along with various FRP materials. In the assembly process of ceramic composite armors, a large number of hole processing is required. Usually, diamond trepanning drills are preferentially adopted for machining relatively large holes of engineering ceramics. However, during drilling high purity armor engineering ceramics, the diamond tools are usually worn considerably due to their high dynamic compression strength and high hardness. In this study, taking the high purity alumina armor ceramics (99 wt% Al 2 O 3) as machining object, the comprehensive wear features of the sintered diamond trepanning drill have been intensively studied through SEM examinations, including the microscopic wear morphologies of diamond grains and matrix binding agent, the diamond abrasion mechanism, the wear disfigurations of the drill labial surface and the drill slipping mechanism. According to the discussed results, the wear process of the diamond grains at the matrix labial surface can be divided into three stages: intact crystal, slight wear and severe wear stages. The quicksand phenomenon occurrence around the diamond grains is the typical feature of the matrix binding agent wear. The normal grinding of the drill can be interrupted by the severe inner-trumpet-shape wear and the cutting-groove wear of the drill labial surface. In most situations, only the slight inner-trumpet-shape wear occurs for the drill, which does not affect the normal drilling operation. The drill slipping is mainly attributed to the fact that most exposed diamond grains at the drill labial surface have been rubbed down into a polished planar shape and totally blunted. The results achieved in this study can provide helpful references for the performance improvement design of the sintered diamond trepanning drill. [ABSTRACT FROM AUTHOR]

In this paper the influence of copper film on the stress distribution, damage evolution and failure mechanism of glass-fiber reinforced laminates was investigated. The specimens were tested at the in situ three-point bending tester. Simultaneously, a microscope and acoustic emission (AE) system were applied to in situ characterize the damage evolution of surface and inside of specimens, respectively. Moreover, a finite element analysis (FEA) model was constructed to simulate the stress distribution on the different types of specimens during the three-point bending. The result of the finite element simulation was in agreement with that of the experiment. The bending stress distribution on the specimen of glass-fiber reinforced laminates (no copper film) and double-sided copper-clad laminates was different from that of the single-sided copper-clad laminates, which made the failure mechanism of single-sided copper-clad laminates was not the same as the glass-fiber reinforced laminates and double-sided copper-clad laminates. It is obviously that the copper film can effectively improve the mechanical properties of glass-fiber reinforced laminates. The in situ images revealed the damage evolution of glass-fiber reinforced laminates and single-sided and double-sided copper-clad laminates was not the same. Furthermore, the glass-fiber fracture, the glass-fiber stripping from the substrate and matrix cracking were characterized by the amplitude, count, rise time, duration time, energy of AE signals during the three-point bending. [ABSTRACT FROM AUTHOR]